# Vehicle transmission

Eight-speed automatic transmission from ZF Friedrichshafen , type 8HP70
A vehicle manual transmission of a truck; the shift forks and sleeves are easy to see

A vehicle transmission is the transmission in the drive train of a vehicle that translates the engine speed to the drive speed . The gearbox is designed as an adjustment or change gearbox; It is necessary in motor vehicles to bring the factor between the lowest and highest speed to coincide with the factor between the lowest and highest engine speed.

The vehicle transmission is a sub / special form of the general transmission, as the term is defined in mechanical engineering : In general, devices for any kinematically coupled conversion or conversion of movements are called “transmissions”.

## Need for a manual transmission

Vehicle transmissions allow the narrow speed ranges of internal combustion engines to be converted into the wheel speeds required for normal driving.

example

A car has a minimum speed of V min = 5 km / h (closed clutch) and a maximum speed V max = 250 km / h. This results in a factor = = 50 for the cardan shaft (the output of the vehicle transmission). The combustion engine has an idle speed of 600 / min and a maximum speed of 6000 / min, i.e. a factor of 10. Without a manual gearbox, the car could reach a maximum of 50 km / h if an engine speed of 600 / min led to 5 km / h. ${\ displaystyle \ textstyle {\ frac {V _ {\ text {max}}} {V _ {\ text {min}}}}}$

## Parameters and terms

• Gearboxes convert speed and torque and are therefore also classified as identification converters .
• Conventional vehicle transmissions translate into slow (coll. Also " reduce ") in vehicles in the lower gears - those for slow driving - and translate into high gear (coll. Also " translate ") in high gears, i. H. there the cardan shaft ( output ) then rotates faster than the crankshaft ( drive ).
• The spread of a gear indicates the ratio between the largest and smallest translation.
Example : A transmission with a gear ratio of 1: 4 to slow speed and 1: 0.8 in the highest gear has a spread of 5, since 4 / 0.8 = 5.
• When designing passenger cars, a distinction is made between “ optimal ”, “ too long ” and “ over-revving ” (“ too short ”) for individual gears as well as for the entire transmission .
• In the " optimal " configuration, the gear ratio is selected so that the vehicle in the highest gear (on level ground) at the nominal engine speed (maximum power) reaches the highest speed that is possible with this nominal power.
• If the design is (too) long , the engine will not reach its rated speed in the highest gear and therefore also not its maximum output; the vehicle's maximum speed will then often be reached in the next lower gear. The disadvantage of this gearbox design is that the gradations are coarser for the range that can be used, which leads to somewhat higher consumption at low speeds. The advantage is a lower speed of the motor at higher speeds; at higher speeds it runs more quietly and consumes less.
• In the case of over-revving ((too) short ) the highest gear is so low that the engine (in this gear) does not have to deliver its full power even at its maximum speed: the vehicle does not reach the (theoretical) maximum speed corresponding to the engine power , but the engine is already running in its speed limit beforehand.
This gradation enables good acceleration values ​​for sporty cars and good performance on inclines (trucks, tractors) for commercial vehicles.
• The gear gradation is often designed as geometrical or progressive in multi-step transmissions . With the geometrical gradation, two adjacent gears always have the same progressive ratio, for example an x% higher / lower ratio. With the progressive gradation, on the other hand, the increment decreases in the higher gears in order to better adapt the engine's range of power to the driving resistance (air resistance) and to achieve more comfortable shifting behavior. The increment is often chosen so that the difference between the top speeds in the upper gears remains the same.
Example: Progressive levels are used in fast vehicles because the air resistance increases quadratically at higher driving speed and has the predominant influence on the power requirement (the power requirement from air resistance is given by air resistance times speed and thus increases cubically).

## Manual actuation

### Manual transmission

Three-speed sliding gear with direct gear: The gears on the main shaft (above) are shifted for shifting with the selector forks in such a way that one gear engages in an opposite gear on the countershaft (below) or, in third gear, the main shaft via a claw coupling with the transmission input connects.

In a gearbox - also called a change gearbox - the speed ratios are formed by the gear pairs. The most common version of a manual transmission is that of the spur gear . The gearshift mechanism in the transmission is used to change gear. This mechanism in the transmission is in turn connected to a gearshift lever via a linkage or cable.

The torque is transmitted to the transmission input shaft from the clutch via a spline shaft. Either the gearwheels of the individual gear stages are mounted on the gearbox input shaft, which mesh with the gearbox output shaft, or the input shaft and output shaft of the gearbox are coaxial (aligned), but divided (jointly referred to as main shaft) with an axially parallel countershaft.

Manual transmissions can first be distinguished by the type of input and output:

• If the input and output shafts are coaxial (aligned), the gear unit also has a countershaft. This design is mainly found in longitudinally installed front engines with rear-wheel drive.
• The design with parallel offset input and output shaft is mostly used in vehicles with front-wheel drive with a transversely or longitudinally installed front engine or in vehicles with longitudinally / transversely installed rear-engine and rear-wheel drive (buses, sports cars and small cars).

Where engines are long due to many cylinders (luxury class, trucks), the coaxial gears dominate, as there is enough space in the vehicle for the long engines and a long gears with a small diameter.

Designs with coaxial shafts usually have several of the following characteristics:

• The main shaft , which consists of input and output, is divided, and the auxiliary group is located on the drive side.
• The upstream group at the transmission input transfers the power to the countershaft via one or one of several gear pairs.
• The countershaft (s) are in turn connected to several pairs of gears (transmission stages ) on the output side of the main shaft.
• The downstream group or range splitter is located on the extension of the main shaft at the transmission output.
• The direct gear connects the input and output shaft, but no power may be routed via the countershaft.
• If the gearbox is operated manually, there is a selector lever each for the front group, countershaft and downstream group.

The number of gears results as [number of gears upstream group] × [number of gears additional gear] × [number of gears downstream group].

The upstream group is used in vehicles that need many gear ratios, such as trucks. Planetary gears are available for the downstream group, which rotate as a block in normal operation (gear ratio 1: 1, no power loss) and are only engaged as a reduction when off-road.

Gearboxes with parallel-offset shafts lead the power from the drive shaft via gear stages to the output shaft; the countershaft is omitted. A 1: 1 gear ratio is only possible via a pair of gears, so the favorable efficiency of a direct gear is not possible. In the passenger car sector, only a few gears are generally required, so that the upstream group usually only consists of a gear set and a downstream group is not required.

In all vehicle transmissions, an attempt is made to place the output close to the center of the imaginary axis of the driven wheels in order to avoid the effects of drive shafts of different lengths and technical limitations in the steering angle. This is particularly difficult with front-wheel drives with transversely installed motors, only short gears are possible here, which may have a slightly larger diameter. The output to the differential is on the engine side. In order to make the transmission short and with a larger diameter, several output shafts are usually used, each of which is connected to a gear on the main output shaft via a gearwheel; each output shaft only carries part of the gears.

The gears of the main and countershaft or input and output shaft form pairs and mesh with one another. One gear wheel is firmly mounted on its shaft, the other freely rotating but axially fixed. In order to establish a frictional connection between the shaft and the freely rotating gear, these are fixed on the shaft with a claw coupling . A claw coupling is attached to the shaft so that it cannot rotate and is axially displaceable. There are tooth profiles on the flanks, the counterparts of which are found in the gear flank. For a shifting process, the dog clutch is pressed against a gear by the shift fork. If the tooth profiles engage, the gear is engaged. In order to make the shifting process more gentle, synchronizer rings are used on the sides of the dog clutches in vehicle transmissions . Synchronizer rings adjust the speed of the gear to the speed of the shaft before engaging. As a rule, the gear wheels are helically toothed; In order to keep the noise development low and to be able to transmit larger torques, several teeth are constantly in mesh. However, helical gearing creates axial forces that must be absorbed by the bearing, except for herringbone gears . There the opposing helical gears (in a gear) compensate for the axial forces. The direction of rotation must be reversed to drive backwards. This is achieved by another gear.

The power flow must be interrupted to change gears. This is done by a clutch. The driver operates the clutch lever, the clutch disengages and he can change a gear with the shift lever and the associated shift mechanism in the transmission (shifting process). The manual transmission is still the most common type of transmission in motor vehicles today.

### functionality

Coaxial five-speed gearbox:
The drive shaft (green) coming from the engine drives the countershaft (red). The wheels (blue) of gears 1, 2, 3 and 5 are freely rotating on the output shaft (turquoise). Shift sleeves (pink) connect these wheels to the output shaft if necessary. 4th gear is “direct” without using the countershaft. The reverse gear is coupled via a sliding wheel (orange) that reverses the direction of rotation.

The transmission of a vehicle with a front engine and rear-wheel drive serves as an example.

Two shafts run in the closed gear housing : the main shaft, which runs from the input on the motor flange to the drive shaft output and is interrupted after the first gear stage, and the countershaft , which runs parallel to the main shaft.

Starting from the front part of the main shaft, the countershaft is driven via the first gear pair. By switching the respective subsequent gear stages, the torque is transferred from the countershaft to the rear part of the main shaft and from there to the output. The individual gear pairs are constantly in mesh with the synchronized transmission. One gear is firmly connected to the shaft, while the other can be used to switch a positive connection to the shaft with a shift sleeve . As a rule, the shift sleeves are located on the main shaft, but they can also be located on the countershaft. By coupling the two parts of the main shaft, the output is driven directly (direct gear), in this case the countershaft runs with it, but without transmitting torque.

The gears are now shifted as follows:

When the transmission is in neutral, none of the gear wheels are connected to the drive shaft. The frictional connection is interrupted. All gears on the drive shaft and countershaft are constantly in mesh, but no power is transmitted.

In order to engage a gear, the frictional connection between the engine and transmission must be interrupted. The clutch is used for this.

A rotary slide mechanism now ensures that the shift claw is actuated by the movement of the gear lever, which pushes the shift shaft responsible for the selected gear with the shift sleeve between the gear wheel and the countershaft. To put it simply, a movement of the gear lever through the idle gate triggers a rotary movement of the shift rod in the transmission, which with the shift finger causes access to a shift shaft, which can be moved in two directions by the shift pawl. A shift sleeve that is moved by the claw on the shaft is responsible for two gears. One could say that a back and forth movement of the shift lever shifts the claw, and a right-left movement turns the shift rod and selects a different shift shaft. This results in the arrangement in the shift gate. Because the shift lever's path through the gears resembles a letter, they are referred to as an H or Z shift. With the H shift, first and second gears are opposite, with third and fourth next to them, with the Z shift, reverse and first gear, next with second and third. A four-speed transmission has three shift shafts - two H-shifts for the forward gears and one for the reverse gear. With Z shifts, the third shift shaft shifts into fourth gear.

By sliding the shift lever, also known as a gear stick, into the alley of the selected gear, a shift sleeve is pushed on the drive shaft between the gear wheel and the drive wheel. The gear wheel is firmly connected to the shaft and the frictional connection is established within the transmission.

Such shifts allow a free gear selection, at least theoretically: You can shift from any gear to any other, but of course this should not be done while in reverse gear.

#### Sequential transmission

Sequential transmissions cannot be shifted at will, you can only change to the next higher or next lower gear - the next in the sequence . It is not possible to skip one or more courses.

Such a transmission can be found, for example, in the Smart Fortwo and in motorcycles ; and dual-clutch transmission are always operated sequentially - they would have when skipping a gear, a traction interruption in purchase take or skip (without interruption) two courses.

Sequential gears that used to be widespread are draw key or bevel gear gears. With this type of gearbox, the shift claws are dispensed with. A cone is attached to a rod within the hollow countershaft; This pushes balls outwards through holes in the countershaft on the gear wheels, which ensure a form fit between the shaft and gear wheel. With draw key gears, a wedge is moved lengthways in a grooved shaft when changing gears and the respective gear is locked with positive locking. They were used, among other things, in Mokicks and small motorcycles from DKW , Simson and Zündapp , there also in two-stroke motorcycles up to 250 cc and in the small Janus ; also with the Goggomobil's Selectromat electromagnetic preselector gearbox, which is subject to a surcharge .

With claw-shifted sequential transmissions, the shift forks with matching pins engage in the partially coiled grooves of a shift drum. When the shift drum is rotated, the shift forks move the gears to or fro according to the groove shape, thus shifting gears. The shift drum is operated by the shift lever via a ratchet mechanism.

### synchronization

If the gear change is initiated in the case of a speed difference in a non- synchronized transmission, the difference must first be adjusted. If this condition is not met, there is a rattle that accompanies the shifting process in unsynchronized transmissions. The cause is the multi-toothed gearshift sleeve, which is pushed into the clutch body of the gear wheel, which runs at different speeds. It used to be a question of the skill of the driver how noisily the gear shift was carried out.

There are two techniques to prevent the noise: external and internal synchronization. With the internal synchronization, which is used in synchronized gearboxes, this is done by a synchronizer ring upstream of the shift sleeve . This usually consists of a base body made of brass, formed sheet steel or a steel-sintered material. It is provided with an additional special sintered friction layer or a molybdenum coating applied by plasma spraying. Carbon pads are also used. These friction layers act as a cone clutch and generate friction between the gear wheel and the countershaft. This adjusts the speed until the shift sleeve can finally slip in. A distinction is made between simple synchronization and forced synchronization (also locking synchronization), in which the shift sleeve only engages when the synchronization is correct.

External synchronization is required for unsynchronized gearboxes. With old designs, it was the driver's responsibility to adjust the speeds of both ends of the power train. The adjustment was a matter of feeling and experience. Before upshifting, the clutch is briefly engaged in idle ( intermediate clutch ) in order to brake the drive or countershaft. This is necessary because the gears of the next gear have a slower peripheral speed. When downshifting is also engaged at idle, but it gave emotional gas ( declutching ). The gears on the drive shaft are adapted to the peripheral speed of the gears in the lower gear. If the speeds or circumferential speeds do not match, the gear cannot be engaged or can only be engaged with difficulty. Forcing the gear into gear leads to damage to the gears in sliding gearboxes and to the claws when shifting claws.

Even if intermediate coupling or double-declutching is not necessary in a gearbox with internal synchronization, it can lead to a faster and more gentle shifting process. The effect is hardly pronounced with small transmissions in the passenger car sector, but often noticeable with truck transmissions.

A gearbox with locking synchronization can also be switched without a clutch in an emergency. If the clutch is no longer functional, the engine is started with first gear engaged. The starter motor and vehicle battery must be powerful enough to accelerate the vehicle from standstill to walking speed while the engine is being started. Depending on the compression and ignition behavior of the engine as well as the play , elasticity and natural frequency of the drive train , the vehicle starts moving more or less hesitantly. If the driver wants to shift up, he accelerates and gives a slight pull in the direction of idling on the gearshift lever, which jumps into neutral when the accelerator is subsequently released . As the engine approaches idle speed, light pressure is applied to the gear lever toward the next gear. If the speed of the engine and drive train match, the gear slips into it. Is to downshift similar to the non-synchronized gear, intermediate gas given to the motor to the higher speed to bring the smaller gear. You should approach a red light as slowly as possible in order to avoid stopping as much as possible, as every restart puts a relatively high load on the starter, battery and drive train. Successfully coordinating these processes requires a certain amount of experience on the part of the driver.

One advantage of road vehicles is the lower level of noise. Slider gears almost always have straight toothed gears, where the initial meshing of the teeth causes a (howling) scratching. On the other hand, claw-shifted or synchronized gears allow the use of gears with helical teeth and smoother tooth engagement.

### Sliding gear

In sliding gearboxes , the gear wheels are almost always straight toothed and the hubs and gear shafts are provided with keyways , so they cannot be rotated on the countershaft. They are shifted on the shaft when shifting and are therefore not constantly engaged. Such transmission without synchromesh can only declutching downloaded and between domes upshift and the straight teeth is operative to produce a characteristic loud howling sound (like in modern cars or the reverse), but they have a higher efficiency. Slider gears were widespread before synchronization was introduced in the 1930s, and even after that, only the upper gears were synchronized from 2nd upwards for a long time. The last German car with a sliding gear was the Lloyd LP 300 . In the VW Beetle , the 1st and 2nd gear were initially designed as sliding wheels, the 3rd and 4th gear with low noise, helical teeth with claw shifting, the claws were designed as longitudinally movable round pins and matching semicircular grooves in shafts and gears.

Gearboxes for racing applications, also known as racing gearboxes for short, are still built today as sliding gearboxes. With the same dimensions, this enables a higher load capacity due to a higher maximum transferable torque, since shafts can be dimensioned more heavily. This is relevant for rally vehicles and vehicles of the Cup class, or due to the reduced weight of touring and racing cars.

The current development in racing is towards uninterrupted upshifting transmissions, due to the high air resistance and low weight, racing cars lose 2-3 km / h with a conventional gear change. For this purpose, two gears are engaged for a short time. There are several ways to avoid gearbox damage: One is to use one or more freewheels so that when there is an overlapping upshift, the faster rotating gear of the higher gear overtakes the slower rotating gear of the lower gear. The freewheel prevents the gear unit from being stressed.

The other variant is that two gears are engaged at the same time for a few milliseconds. To enable this without tension, a torsional backlash between the gear wheels and their shaft is required. If the previously engaged gear is not pulled out in time, the gearbox will be damaged. During the switching operations, there are very strong switching shocks, which is why such types are unsuitable for cars.

## Automated actuation

### history

At the end of the 1920s, the English Daimler Motor Company developed a gearshift aid that consisted of the combination of a gearbox with coupled planetary gear sets based on the concept of the Englishman Walter Gordon Wilson with a fluid coupling based on the ideas of the German Hermann Föttinger . In the case of the automatic preselector gears, mainly used as fluid flywheels in British double-decker buses from 1930 onwards, the gear position was preset with compressed air support on a small selector lever on the steering column and shifted with the left clutch pedal. This was much easier than the force required for usual domes, declutching -Provide and switching via a mechanical linkage. The Associated Equipment Company (AEC) used the pre-selection gearbox with fluid flywheel for the thousands of buses (e.g. AEC Regent III = RT) of the London Passenger Transport Board (LPTB) and its successor, the London Transport Executive (LTE).

### Operation

Automatic selector lever

A selector lever on the vehicle center tunnel with the adjustment options is common

P : Park, park position with mechanical locking of the gearbox against rolling away
R : reverse, reverse gear
N : neutral, idle
D : Drive, driving forward with automatic gear selection

In automatic transmissions, this sequence is usually adhered to, as there are legal requirements for this in the USA, for example.

Some transmissions offer further gear steps, and a manual mode is often possible:

z. B. M or S in conjunction with + and - : Device for manual switching of the automatic transmission in a second shift gate or with separate controls. The driver can make a manual preselection to intervene in the transmission control and select a higher or lower gear.

### Distribution in Western Europe

In an international comparison, the percentage of automobiles equipped with automatic transmissions in Western Europe is far below the percentage in countries such as the USA and Japan . This is due to some disadvantages compared to the manual gearbox, some of which no longer apply, including lower acceleration capacity (if there is no torque converter increase), lower top speed, higher consumption, delayed response at the beginning of an overtaking maneuver, surcharge compared to the manual gearbox (not common in all markets ), other traffic conditions and the sometimes unsporting image of the automatic, which is rarely found in motorsport in the classic form of the converter with planetary gear.

According to a Swedish study, the use of an automatic transmission reduces the number of driving errors in seniors, whereas there is no such correlation among middle-aged drivers.

In Germany, automatic transmissions are particularly common in more expensive mid-range cars, but still only make up 28% of all new registrations (as of 2011). Manual transmissions for new car registrations are distributed as follows in Germany (January to July 2011, by vehicle class):

• Small car: 92%
• Compact SUV: 75%
• Compact class: 83%
• Minis: 77%
• Middle class: 61%
• Vans: 79%
• Total: 72%

### Automated manual transmission

Automated manual transmissions, also known as Automated Manual Transmission (AMT), enable the combination of increased driving comfort through a user-friendly transmission control with economy through reduced fuel consumption and reduced emissions due to specially coordinated drive programs of the transmission control. The main difference between the classic automated manual transmissions (ASG) and double clutch transmissions (DCT) discussed below is that the ASG only has one clutch. The disadvantage is the interruption of the tractive effort - the flow of force has to be briefly interrupted for shifting. The advantage is that the clutch is closed in the idle state and only needs energy to open, which is why the ASG is usually installed in particularly economical and light vehicles.

The DKG has two couplings. The advantage is that when one clutch is opened, the other can close at the same time and the pulling force is not interrupted. The disadvantage is that both clutches are open in the idle state and the clutch in the active power branch must be kept closed with energy expenditure.

#### Classic automated manual transmission (ASG)

An automated gearbox, also known as an automatic gearbox, is a conventional gearbox that has been expanded to include automated gearshift components. The fundamental difference to a manual transmission is that the gear change is not made by the driver, but by hydraulically operated cylinders and electric servomotors for the actuators . During the gear change, the activated clutch actuator separates the tractive effort, then the gear change calculated in the gearbox control unit is passed on to the gearshift actuators of the gearbox, and the gearbox shifts to the next higher or lower gear.

With the automated gearbox, the gear changes are carried out automatically by the gear shift program stored in the control unit, or the driver can use the selector lever in the center console or the tip switch on the steering wheel to set the next higher or next lower gear. The switching program prevents switching errors. As a rule, it is only possible to skip aisles to a limited extent. Such switching operations are only carried out by the electronics if the motor remains within a permissible speed range.

Since the mid-1980s, such automated transmissions have been used in trucks for long-distance transport, in which the driver preselects the gear and the electronic control of the transmission shifts the transmission via electro-pneumatic shift cylinders. With the classic EPS from Daimler-Benz, for example, the driver selects 6th gear / low and depresses the clutch pedal. This activates the control electronics and checks whether the switching process can also be carried out based on the engine speed. If this is the case, the control electronics switch to the selected gear via the pneumatic shift cylinder. If it refuses to change gears because the engine threatens to rev up, this is indicated to the driver by a warning tone. As a rule, the transmission then shifts to neutral.

Newer systems in trucks or coaches also switch fully automatically; a clutch pedal is missing or can be folded out for emergencies. Modern trucks are equipped with an eight-speed gearbox as standard. The basis of the truck gearbox is usually a four-speed manual gearbox that can be expanded with a front group and a range group, making 16 gear steps available.

The ASG shares most of the advantages with the manual gearbox:

• relatively simple mechanical structure
• good efficiency, because no circulating lubrication or splashing losses of the oil occur
• many identical parts with manual gearboxes, which means that the large number of items leads to low costs

• The design is compact because the actuators manage with low power and can be built simply and in a space-saving manner.
• The entire ASG actuator system is only active during the switching process and therefore only consumes energy in this situation.
• In addition, the usual advantages of automatic transmissions apply, such as security against stalling, shifting and over-revving the engine and strategies for optimal consumption, for particular sportiness or for engine-friendly operation during the cold running phase.

The ASG is used in some vehicles instead of a manual gearbox in order to comply with special approval regulations, as the switching program can be adapted to the official measurement cycles for consumption and exhaust gas measurement so that it delivers better measurement results than in the manual gearbox measurement cycle. The vehicle is then credited to the manufacturer with a lower fleet consumption, but it can lead to higher consumption or reduced acceleration capacity for the end customer, which is actually due to a reduction in the technical possibilities.

• Loss of tractive effort during the shifting process
• long shift duration (for an automatic transmission)

Against the disadvantages, newer ASGs use a second countershaft, on which the shifting process for the respective adjacent gear can be prepared, as with the DKG, so that the interruption of tractive power is reduced to the time for briefly releasing the clutch (50 ms with the Graziano ISR in the Lamborghini Aventador) becomes.

The first automated manual transmissions with hydraulic actuators used in mass-produced vehicles were the BMW M3 in 1997 , in which the existing classic manual transmission was upgraded to an automated transmission using hydraulics , and the Smart Fortwo in 1998 , which was the first vehicle to have an electric motor- operated, automated manual transmission. The special feature of the Smart was that its transmission was only offered automatically and the manually operated variant was only available as a program lock change in the software in the transmission control. A Smart that can initially only be switched manually can easily be automated by changing the software. Both transmissions were developed by the Getrag company.

##### distribution
In the Ford Fiesta with Durashift-EST , DC
electric motors set the gears of the manual transmission, the clutch is operated hydraulically
Hydraulic gear selector in the VW Lupo 3L
Hydraulic clutch slave cylinder of the Lupo 3L

Because of its favorable efficiency, the ASG is a popular equipment variant especially in small cars, for example in the Audi A2 1.2 TDI, Opel Corsa or Smart ; Only ASG were installed in the VW Lupo 3L . In the VW Group's three-liter car, however, the gearboxes with a relatively high proportion of damage and with very expensive replacement gearboxes attracted negative attention.

Automated manual transmissions are offered by various vehicle manufacturers with different brand names:

#### Double clutch

A variant of the automatic gearbox is the dual clutch gearbox . It consists of two sub-gears with associated clutches. One sub-transmission carries the even gears, the other the odd gears. The reverse gear can be assigned to both sub-transmissions. Before shifting, in the no-load branch the next higher gear is engaged when accelerating or the next lower gear when decelerating. Then the clutch of the no-load gear is closed and that of the other is opened at the same time. This means that you can shift without interrupting the tractive effort. The time it takes to change gears only depends on how quickly the clutches open and close.

It is also called “direct shift transmission”, also abbreviated as DSG, DKG, PDK, DCT, TCT.

The main advantages of the DKG are:

• Shifting without interruption of tractive effort, but only into adjacent gears (no gears can be skipped)
• very fast gear changes, also with manual actuation (suitable for use in racing)
• good efficiency compared to converter automatic transmissions without converter lockup
• Favorable space requirements for vehicles with engines installed across the front
• many identical parts with manual gearboxes, so that the large number leads to low costs
• the usual advantages of automatic transmissions, such as safety against stalling, shifting and over-revving the engine and strategies for optimum consumption, for particular sportiness or for engine-friendly operation during the cold-running phase

The disadvantage compared to the ASG is the often permanent energy requirement to keep the clutch in the power branch closed.

Due to their properties, DSG are in competition with conventional machines with converters and planetary gears.

##### distribution

Originally developed by Porsche for racing in the 1980s, Volkswagen and Audi were the pioneers in using this technology in large-scale production and were thus able to gain a technological edge on the market. A dual clutch transmission has been in series production in the Golf and Passat classes since 2002 (6-speed, the supplier for the wet clutch is BorgWarner ). The VW internal designation is DQ250 (for double clutch - transverse installation - 250 Nm, whereby it can transmit 320 Nm).

In the following years a 7-speed DSG with the internal designation DQ200 (Polo and small golf class) came out from VW. LuK supplies a dry double clutch for this.

In 2009, the first DSG specially developed for Audi, called DL501, came onto the market with the Audi Q5. A wet-running double clutch from BorgWarner is again used in this transmission . DL501 stands for double clutch - longitudinal installation - 500 Nm and is gradually being used in the A4, A5, A6 models.

The DQ500 (7-speed DCT) for the VW T5 bus followed in autumn 2009; it has also been available for the Tiguan since June 2010. The wet clutch is developed and manufactured by the VW plant in Kassel , which is the first time that a double clutch developed by VW is used.

All variants (DQ200, DQ250, DQ500 and DL501) are manufactured in the Volkswagen factory in Kassel.

Since July 2008, Porsche has been offering the 7-speed PDK from ZF for the new 911 . It is also available to order for the Boxster and Cayman . The PDK has also been available for the Panamera since September 2009 and for the Turbo since October 2009. A dual clutch transmission with seven forward gears has been available from Getrag for the BMW M3 since March 2008 . Ford , Mitsubishi , Ferrari , Mercedes-Benz and Volvo have also offered models with dual clutch transmissions from Getrag since 2008.

For the first time, a DKG has been installed in a series motorcycle since summer 2010 - a Honda ( VFR1200F ).

### Converter automatic transmission

6-speed automatic transmission ZF 6HP26 for outputs up to 320 kW, transmission input (engine side) is on the left of the converter (yellow)

A converter automatic transmission differs in structure from a manual transmission essentially in the following points:

The main advantages of the converter machine are:

• no interruption of traction
• virtually wear-free start-up
• the converter dampens vibrations in the drive train
• The torque provided by the engine is increased by the differential speed between the pump and turbine of the converter (up to two times the torque increase)
• the converter can be equipped with a converter clutch, with which the hydraulic circuit is bridged when no further converter boost is required (efficiency); the higher vibrations at lower engine speeds are reduced by a damper
• the gear changes are barely noticeable due to so-called overlapping gear changes
• high torque density and compact design thanks to planetary gear sets

• poorer efficiency and consumption disadvantage, this is largely compensated for in modern automatic transmissions
• Towing with a rolling drive axle is not possible with all models, and if so, then only over short distances, otherwise damage to the transmission due to lack of lubrication can occur, towing over long distances requires a second oil pump on the axle drive (older Mercedes vehicles)
• high costs, for example due to the production of tight tolerances in the hydraulic control box

In exceptional cases, planetary gear sets are not used in automatic transmissions, for example in the Hondamatic transmissions and in the automatic transmission of the Mercedes-Benz A-Class (W168). The structure of such transmissions is similar to that of a manual transmission. The main differentiating feature is that instead of synchronizers and shift sleeves, there is a separate multi-plate clutch for each gear stage of the automatic transmission.

The friction-locked connection of the individual planetary gear sets with the input and output shafts is made by multi-disc clutches. Driving operation is specified by a driving and switching program in the control unit. The transmission was controlled hydraulically until the end of the 1980s . At the present time (as of 2016) the control is electronic and the actuation of the clutches by means of electrically controlled hydraulic valves.

#### Function and control

In the torque converter, part of the engine power is transferred to the oil in the form of frictional heat due to the slip. In order to reduce the associated loss of efficiency, today's automatic converter transmissions are often equipped with a converter lock-up clutch, which enables direct mechanical frictional connection after starting up or changing gear.

Furthermore, energy is required to generate the hydraulic pressure by the oil pressure pump. The idle multi-plate clutches that are not required in the engaged stage cause additional drag losses because the clutches are open. Due to these drag losses, the fuel consumption is higher compared to a vehicle equipped with a manual transmission and otherwise the same. Modern automatic transmissions offer a torque converter lock-up clutch from first gear in order to reduce this additional fuel consumption. A further reduction in fuel consumption is made possible by stationary decoupling, which switches the transmission to neutral when the vehicle is stationary and the service brake is activated, thus preventing drag losses via the converter. The consumption disadvantages of the automatic system are usually hardly apparent in the case of standard consumption, in contrast to the consumption that occurs in normal road traffic, since the switching points are adapted to the standardized cycles.

A level change occurs by switching off a switching element and simultaneously switching on the switching element for the next higher or lower level. The second shift element thus takes over the torque from the first piece by piece until the entire torque is taken over by the second shift element at the end of the step change. The time span for this grinding process is in the two to three-digit millisecond range. Since the introduction of electronic transmission controls in the late 1980s, a "torque down request" has been sent to the engine control unit in order to protect the transmission from overload and / or to achieve better shift quality. Since the end of the 1990s, this has also been done via the Controller Area Network . This causes the engine management system to reduce the drive torque for the duration of the shift. Another means of increasing the shift quality is to open the converter clutch in certain shifting situations. The gear changes between the up to eight gear ratios are very smooth. The fact that the power flow is not completely interrupted due to the design also leads to the well-known "creeping" of vehicles with a coupled automatic transmission as long as it is not in idle. This creeping can be very helpful when maneuvering.

With the electronic control - for example with the EGS - other effects are achieved: At low gear it is now common to limit the torque of the engine. As a result, the clutches in the automatic transmission can be designed smaller and the rest of the drive train has to be designed for a lower torque, which makes it lighter and cheaper. If the brake and the accelerator pedal are pressed at the same time, the control system prevents the engine from tensioning the drive train, overloading it and overheating the converter. During the kick-down, the wheel slip is checked together with the ASR . When a wheel is spinning, it is controlled by braking. If all driven wheels spin, the engine output is limited.

The kickdown function ( excess throttle ) can already be found in early converter automatic transmissions with purely hydraulic control. In addition to full throttle , a signal is sent to the control of the automatic transmission by pressing the kickdown switch when the accelerator pedal is pressed . The automatic shifts to the gear with the best possible acceleration and brings the engine to high speeds. The use of the kickdown is particularly useful when overtaking.

When shifting down, the principle of multiple downshifts is used in more complex automatic converter transmissions: The shifting process takes place by means of a snap shift. In this way, several gear steps can be skipped in order to call up the maximum acceleration. A switching program that can be selected in modern vehicles is usually overlaid by the kickdown signal. After the kickdown signal has ended, the drive switches to the energetically correct gear.

#### safety

Vehicles with converter automatic transmissions may only be towed over short distances or not at all if the driven axle is rolling, depending on the manufacturer. When the engine is not running, the oil pump is not driven in most gearboxes, so that sufficient lubrication is not ensured. An exception to this is automatic converter transmission with an additional secondary oil pump at the transmission output, for example older automatic converter transmissions from Mercedes-Benz.

In the 1980s, there were safety problems with alleged "self-running", that is, vehicles that unintentionally started moving. TV reports appeared in the USA claiming that vehicles - predominantly Audi models - unexpectedly started moving despite the brakes being applied. A final clarification was not reached, however, as a result, some security functions have become established:

• The ignition key can only be removed in the "P" position, which prevents the steering wheel lock from engaging when the vehicle is rolling.
• The engine can only be started in position "P" and / or "N". It is therefore not possible to roll when the engine starts.
• To leave the "P" position, the brake must be applied. For some manufacturers, this also applies to the "N" position (only when the vehicle is stationary). This forces the driver to press the correct pedal when starting. This is to avoid confusing the gas pedal with the brake.

With the spread of these precautions in new vehicles, the problem of self-selling has disappeared. In the meantime, other fuses have been introduced. With some automatic systems, the engine hardly increases its performance if the brake pedal is depressed at the same time. This prevents the drive train from becoming distorted and the converter overheating.

### Stepless transmission

• Continuously variable transmission (CVT) stands for transmissions with a continuously variable (limited) transmission range that corresponds to that of manual transmissions. After the DAF gearbox ( Variomatic ) there were trials by Fiat, Subaru, Ford, Mini and Mercedes-Benz (under the name Autotronic in the A-Class and B-Class ), today CVT gearboxes are made by Audi under the name Multitronic offered in the A4 and larger models, under the name Lineartronic from Subaru and simply as a CVT from Honda in the Jazz and Civic Hybrid . Suzuki uses Jatco CVTs ( Suzuki SX4 S-Cross). In addition, most scooters and, more recently, some motorcycles have CVT transmissions.
• Infinitely Variable Transmission (IVT) has an infinite translation range, i.e. H. with 1: ∞ the gearbox output shaft stands still, although the input shaft is connected to the running engine, so that with this type of construction no starting clutch is required.

A planetary gear as a summing gear or distribution gear is not continuously variable, but an input shaft can act in a pseudo-continuously variable manner, provided the second input shaft of the summing gear regulates the overall ratio. The second input can, for example, be hydrostatic ( tractors ), electrical ( Toyota Prius ) or also mechanical (CVT).

This gear design offers the following advantages:

• No switching stages, thereby
• improved comfort, as torque and speed changes are continuous and not in jumps
• no shift pauses as no gear change is carried out
• The transmission characteristic curve can be designed according to various criteria:
• Lower consumption, the engine always runs in the range of the most favorable instantaneous consumption and in drag operation the smallest drag torque can be selected by adapting the ratio
• Increased driving dynamics: if maximum acceleration is expected, the engine can always run at maximum power when accelerating, the driving speed is adjusted solely by the ratio of the CVT
• Noises: the engine is driven in the quietest operating range
• lower exhaust emissions: the engine is driven in the operating range with the lowest emissions

• very limited torque capacity for many types
• Increased technical effort, sometimes special types of oil required
• Efficiency lower than with gear drives
• limited customer acceptance

The torque capacity can be improved with a power split, for example. The continuously variable transmission is combined with a summing or splitting planetary gear. However, this either reduces the spread of the translation or the overall efficiency of the gear combination deteriorates.

With consumption-optimized characteristics, the disadvantage of the poor gearbox efficiency can be partially offset. Thanks to the consumption optimization of the engines and wider speed ranges for the best fuel consumption, the dual clutch transmissions are currently the strongest competitors of the consumption-optimized CVT.

In practice, one-sidedly optimized characteristics cannot be implemented due to a lack of customer acceptance, which means that the theoretical advantages are subject to certain restrictions.

Experience has shown that many drivers are not satisfied when the vehicle accelerates from zero to e.g. B. 100 km / h always drives with the same engine speed ("rubber band effect"). To avoid this, numerous CVTs offer a gearshift program in which they work with fixed gear ratios and thus imitate a normal automatic stepped automatic. However, this additional function is expressly not technically required; the above The dissatisfaction of some users is a purely psychological effect that can be traced back to decades of experience with conventional manual transmissions or multi-step automatic transmissions and their characteristics.

#### history

CVTs with friction wheels were used in series by various smaller manufacturers until the 1920s. From 1958, the Dutch manufacturer DAF started building V-belt drives with Variomatic . In this continuously variable transmission, a V-belt runs on belt pulleys with a variable width (see Continuously variable transmission ).

This principle according to Van Doorne has since been further developed with push chains made of metal links for higher torques. These transmissions were used in the Ford Fiesta , Fiat Uno and others. Audi came onto the market around 2000 with the new Multitronic transmission for powerful cars. A pulling cradle-joint chain works in it .

The Toyota Prius equipped with a hybrid drive has a pseudo-continuously variable automatic transmission; a planetary gear with power split superimposes the speeds and torques of the combustion engine and electric motor as well as the electric generator. The electronically controlled, variable distribution of the drive power between the electric motor and generator enables the ratio of internal combustion engine speed to output speed to be varied.

The Honda Civic Hybrid equipped with a hybrid drive has a continuously variable CVT transmission with a torque converter as a starting element.

Similar to the transmission of the Prius, hydrostatic transmissions work with power split, which are particularly common in tractors. The power is divided between a mechanical part and a stepless hydrostatic part. The overall ratio can be regulated by continuously adjusting the ratio in the hydrostatic part. In order to improve the overall spread of the transmission, some of these transmissions have additional gear steps. An example of such a design is the so-called "Vario transmission" from the tractor manufacturer Fendt , which works with hydraulic components coupled via a planetary gear.

### Semi-automatic gearbox and gearbox with converter clutch

A special form of manual transmission are semi-automatic transmissions, in which you do not need to clutch, but shift yourself. When the shift lever is touched, the clutch is automatically disengaged and, when the next gear is engaged, the clutch is engaged again. In principle, they are mechanical gears with an automatically operated single-disc clutch or magnetic particle clutch .

In transmissions with a converter clutch (WSK), a conventional manual transmission is combined with a torque converter , which is located between the engine and the clutch and enables comfortable, wear-free starting and maneuvering that is known from conventional automatic transmissions. In order to change gear, the driver has to operate the conventional clutch, as with a normal manual transmission, to interrupt the flow of power, and also to shift manually. The converter is often bypassed from a certain speed, so that the power flow is transmitted purely via the mechanical clutch from this point in time. This increases the efficiency of the transmission. Today this type of construction is mainly used in heavy-duty or all-terrain trucks such as the MAN gl .

In some vehicles, both concepts (semi-automatic transmission + WSK) were combined.

Examples of vehicles with semi-automatic transmissions are those in the Ford 17 M , the VW Beetle and Karmann Ghia , the DKW F 11/12 and the like. AU 1000 and Opel Rekord (Olymat) installed Saxomat , furthermore the Ferlec magnetic powder clutch available on request for Renault 4 CV and Dauphine , the WSK with an additional automated clutch for Mercedes-Benz 219/220 S / 220 SE (Hydrak), Porsche 911 (Sportomatic), NSU Ro 80 (standard), Citroën DS and Renault Frégate (Transfluide) or the C-Matic, which has recently been available in the Citroën CX . For the Trabant there was a semi-automatic transmission called the Hycomat .

Since the early 1990s, there have also been loss-free semi-automatic transmissions with an automatic clutch system in which manual shifting and the conventional disc clutch is operated electronically and hydraulically, for example in the Renault Twingo Easy, the Mercedes-Benz A-Class W168 with an automatic clutch system (AKS ), Saab and BMW with the SMG semi-automatic.

## Gearboxes in commercial vehicles

Many commercial vehicles also require a transmission that allows the speed range of the internal combustion engine to be expanded into a wheel speed range necessary for driving.

For example, the maneuvering speed of a heavy truck is around 3 km / h. This is achieved at an engine speed of approx. 550 rpm. When driving, the truck drives 89 km / h on the motorway. For reasons of consumption, one would like to achieve this speed (in long-distance traffic) at approx. 1100 rpm. With a speed spread of the internal combustion engine of 2 (550 / min to 1100 / min) one would like to represent a speed spread of 30. This means that the ratio of the lowest gear and the ratio of the highest gear differ by a factor of 15. The ratio of the ratio of the highest gear to the lowest gear is called the spread. In order to show the wide spread and still have closely spaced gears (good for fuel consumption), gearboxes with 12 or 16 gears are used in heavy trucks. Such transmissions are made up of several sub-transmissions, the so-called primary transmission (2 stages), the main transmission (3 or 4 stages) and the group transmission (2 stages). Since the stages of the partial transmissions can be combined in a multiplicative manner, 12 or 16 gears are obtained; However, since the translation factors of these can partially overlap, not all of them can be used sensibly.

The reverse gear functionality (reversal of direction of rotation) is implemented in the main transmission. As a result, the reverse gear is multiplied by the 2 stages of the primary gearbox and the 2 stages of the group transmission and you get (at least technically) four reverse gears. However, these are often blocked and cannot be selected.

Light trucks usually have 6 gears. The speed spread of the engine is greater in light trucks and the maneuvering speed is set a little higher so that 6 gears are sufficient (more similar to passenger cars).

### Primary gearbox

This gear is an extension of a conventional gear. An additional gear stage is attached to the input shaft. This has the effect that you can drive through each aisle in two stages. So there is a small and a large step for each gear. The individual aisle is divided up, "split up". This gives this gear the name “splitter” and the overall construction the name split gear. The term primary gearbox indicates that this gearbox is installed before the basic gearbox. More often, however, the upstream group is housed directly in the transmission.

Split transmissions are found in heavy trucks. They are usually operated using a switch on the gear lever. If only the splitter is actuated or if a gear is shifted from a high to the next lower gear, this is called "upshifting half a gear". If you switch from a low gear to the next lower high gear, you shift down "half a gear".

### Secondary gearbox

This gear is a two-stage planetary gear installed between the basic gear and the cardan shaft . This doubles the number of shiftable gears, in English 'Range' ([ reindʒ ]). For this reason, constructions that use such a rear-mounted gearbox are also called range gearboxes, see also overdrive .

You first shift the gears of the basic transmission and then operate the range group switch. This is done via a switch on the gear lever or via what is known as "overturning". In the former, the switch is switched to the upper (large) group before the shift, and then the gear lever is moved back into the first gear. However, this is then 5th gear in a 4-gear basic transmission or 4th gear in a 3-gear basic transmission. When rolling over, the driver has a split 8-speed backdrop in front of him, which is interrupted between the alleys of 3rd and 4th gear and 5th and 6th gear. Here you move the gear lever into neutral after driving through 4th gear and hit the lever to the right with the ball of your hand. This changes the range group and the lever no longer springs to the right in neutral, but to the left. From the driver's point of view, it is now in front of the 5th or 6th aisle. The lever is actually in front of the 1st or 2nd gear of the basic transmission, but the group change now turns it into 5th or 6th gear. This is also referred to as a “double H” circuit. Such transmissions can be found in heavy trucks.

Upstream and downstream gearboxes are often combined, which means that up to 16 gear steps are available in heavy trucks.

### Automated range splitter group transmission

Most modern trucks are equipped with automated transmissions as defined above. They offer low fuel consumption and ease of use.

#### history

These electronic gear shifting aids were developed for commercial vehicles at the beginning of the 1980s with the desire to save fuel, protect the drive components and also relieve the driver, which was, however, met with strong rejection from truck drivers at the beginning.

In 1984 Scania was the first manufacturer to introduce an electronic gearshift aid called CAG ( Computer Aided Gearshift ). The conventional gear lever has been replaced by a small joystick on the engine tunnel. Electronics that recorded various driving parameters such as speed and engine speed gave the driver a gearshift recommendation on a display on the instrument panel. If the driver accepted the suggested gear, he only needed to operate the clutch. If the gear selected was different, he switched to the desired gear using the joystick. In the event of a failure of the system, the box with the selector switch could be folded to the side and a conventional switch stick inserted, which was carried in the vehicle.

About a year later, Mercedes-Benz, as a manufacturer of its own commercial vehicle transmissions, and the Friedrichshafen-based supplier ZF followed suit with the production of its own shifting aids. At the 1985 IAA, Mercedes presented the electropneumatic gearshift (EPS) , which was offered as standard in the then most powerful model 1644. It was available for a surcharge for smaller models and for the O 303 coach . In contrast to the CAG from Scania and some models from ZF, the EPS did not give a gearshift recommendation, so the gear selection for upshifting or downshifting always had to be done by tapping the lever forwards or backwards. With the introduction of the Actros series, the "Telligent" gearshift ( suitcase word from telematics and intelligent) followed in 1996 , initially as a semi-automatic, later as a fully automatic gearshift.

At the same time, as a manufacturer of truck transmissions, ZF offered semi-automatic shifting aids under the name AVS (automatic preselection), which could be operated using push buttons, gear shift knobs or a rocker switch on the steering wheel.

In terms of handling, however, all the initial systems are largely identical: the driver gives a switching impulse via a switch, which is implemented by the electronics and pneumatic actuating cylinders.

#### Current

Today we have moved on to relieve the driver of almost all switching work. Only idle and reverse gear are operated with all shifting aids using special buttons or key combinations. In some fully automated manual transmissions there is no longer a clutch pedal; in the Actros , for example, it is folded away in the footwell and can be used as an option. Since the electronics completely control all shifting and clutching processes, unsynchronized dog gears can also be used here, which are lighter and more compact in terms of their design and can be shifted faster in operation. However, these fully automatic shifting aids must not be confused with an automatic transmission with a torque converter .

The Actros offers transmission systems in which the next cheapest or manually operated gear can be selected by preselection. The gear is first checked for plausibility by the electronics and then engaged when the clutch pedal is pressed. Fully automatic systems, as they were first used in the Iveco - Stralis and the MAN-TGA, even do without the clutch pedal. Here, the engine speed of the drive train is adapted to the injection pump or the engine brake via electronic commands , which makes synchronization of the gearbox unnecessary. Hybrid systems such as the Opticruise from Scania only require the driver to actuate the clutch to start or stop the vehicle.

Newer commercial vehicles often only have twelve gears because modern engines do not need more than this.

Often only a display informs about the selected gear from 1–12, but the driver can actively intervene in the automatic system, for example by manually setting a higher or lower gear using the steering stick lever (MAN) or the gearshift console (Daimler) Gear selects. The automatic gearshift also takes changes to the accelerator pedal into account (e.g. kick-down).

Some automatic systems can skip aisles or offer special modes such as a free swing or maneuvering program.

### Transfer case

A transfer case is a transmission installed after the basic transmission. It can be used in vehicles that have multiple axles driven ( four-wheel drive vehicle ). The transmission distributes the drive power to several (in a 4 × 4 vehicle two) axles via one output per axle. Depending on the type, the individual axes can be switched on and off.

Reductions can also be integrated in the transfer case - this is often found in off-road vehicles (low-range). The function of the transfer case should not be confused with drive axles that have an integrated through drive, such as heavy trucks with 6 × 4 drive.

### Hydraulic transmission

Motors with a very high torque output, which require a transmission due to the narrow, optimally usable speed range, can be found in diesel locomotives, for example. Since conventional transmissions would place extremely high demands on a friction clutch when starting up, fluid transmissions or hydraulic power transmissions are often used in rail operations . In the gearboxes used, a torque converter is used for starting, the individual gears are shifted without interrupting the tractive effort by emptying one fluid coupling while another is being filled with oil at the same time. In some cases, lock-up clutches are also used to keep energy losses due to slippage low. One example of diesel-hydraulically powered locomotives is the German DB class 218 .

The more commonly used alternative, however, is electrical power transmission, which drives a generator that provides power for electric traction motors .

## Quiet corridors

In DIN 70020 “Motor vehicle construction; General terms, definition and explanation ”from April 1954 and December 1950 were defined as“ low-noise ”gears: gears running on low-noise gear pairs, ie not the direct gear . This determination was made in February 1957 in DIN 70020 Sheet 3 “General Terms in Motor Vehicle Construction; Performances, speeds, acceleration, miscellaneous ”.

## Gearboxes for other functions in motor vehicles

There are also gears in other places outside the drive train: the windshield wipers are moved by an electric motor via gears. The same applies to electric window regulators . The seat adjustment by means of turning wheels or servomotors to adjust the backrest angle is also carried out via a gearbox. Opening mechanisms of doors and hoods or the transmission of a pedal movement to a vehicle unit are also a vehicle transmission in the mechanical-kinematic sense: the pivoting movement of the pedal is converted into a linear movement or a rotary movement via a push rod, for example. The fluid-bound path of power transmission between the brake pedal and wheel brake cylinders is also represented by a hydraulic transmission.

## literature

• Eckhard Kirchner: Power transmission in vehicle transmissions. Basics of the design, development and validation of vehicle transmissions and their components. Springer Verlag, Berlin 2007, ISBN 978-3-540-35288-4 .
• Harald Naunheimer, Bernd Bertsche, Gisbert Lechner: Vehicle transmissions . 2nd edition, Springer Verlag, Berlin 2007, ISBN 978-3-540-30625-2 .
• Hans Jörg Leyhausen: The master's examination in the automotive trade part 1. 12 edition, Vogel Buchverlag, Würzburg 1991, ISBN 3-8023-0857-3 .
• Hans-Hermann Braess, Ulrich Seiffert: Vieweg manual automotive technology. 2nd edition, Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, Braunschweig / Wiesbaden 2001, ISBN 3-528-13114-4 .
• Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden 2003, ISBN 3-528-23876-3 .
• Gert Hack: make cars faster. 11th edition, Motorbuchverlag, Stuttgart 1980, ISBN 3-87943-374-7 .
• Hans Reichenbächer: Design of vehicle transmissions. (= Construction books, volume 15) Springer Verlag, Berlin 1955.
• NW Vorobjew: chain transmission. 2nd improved and supplemented edition, VEB Verlag Technik, Berlin 1953.

Commons : Vehicle Transmissions  - Collection of pictures, videos and audio files

## Individual evidence

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2. According to Harald Naunheimer, Bernd Bertsche, Gisbert Lechner: Vehicle transmissions - basics, selection, design and construction. Section 4.2.1 Gear ratio spread, 2nd edition, Springer, Berlin / Heidelberg / New York 2007, ISBN 978-3-540-30625-2 .
3. According to Harald Naunheimer, Bernd Bertsche, Gisbert Lechner: Vehicle transmissions - basics, selection, design and construction. Chapters 4.3.2 and 4.3.3, 2nd edition, Springer, Berlin / Heidelberg / New York 2007, ISBN 978-3-540-30625-2 .
4. Werner Klement: Vehicle transmission Hanser Verlag, Munich 2007, p. 74.
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11. a b Reif: Conventional drive train and hybrid drives. Vieweg and Teubner Verlag, 2010, p. 102.
12. ^ Eckhard Kirchner: Power transmission in vehicle transmissions. Springer, 2007, pp. 45/46.
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