Variomatic

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Variomatic rear axle drive
Variomatic rear axle drive
principle
Animated representation of the principle

VARIOmatic is the name of the Dutch vehicle manufacturer DAF for a continuously stellbares fully automatic transmission, a construction of the CVT transmission (engl. C ontinuously v ariable t ransmission) as a belt transmission .

history

After developments at the beginning of the 20th century, van Doorne developed the Variomatic from 1950 and put it into series production in 1958. Features of this gearbox were:

  • V-belt made of rubber
  • Centrifugal force-operated weights for self-control of the transmission (variator discs) on the drive side of the Variomatic
  • Vacuum operated diaphragm
  • Springs on the variator discs on the output side
  • One V-belt per wheel, no differential gear

Since the centrifugal actuation only assigned one gear ratio to each driving speed, this was overridden by the vacuum membrane. When accelerating, it specified a shorter gear ratio for a higher engine speed and a longer gear ratio for a lower engine speed for longer, constant driving speeds.

The gearbox was designed twice so that each wheel had its own gearbox. The differential could be omitted because the belt slip already allowed the speed compensation between the wheels. The DAF 46 was equipped with only one V-belt and differential. Due to the rubber V-belt, this Variomatic was limited to a maximum torque of 100 Nm.

Between 1970 and 1975 van Doorne also developed a push link belt for the Variomatic, which went into series production from 1987.

Today, similar transmissions are widely used in mopeds and scooters and are also referred to as Variomatic.

construction

A flat, circumferentially closed belt runs between conical pairs of pulleys , the opposite, narrow flanks of which touch the conical surface of the pulleys. The torque is transmitted by frictional engagement . The necessary belt pretension can be generated, for example, by a spring force acting axially with respect to the belt pulleys. By simultaneously changing the distance between the conical pulleys in opposite directions, the contact radius of the belt flanks changes. The adjustment is speed-dependent, e.g. B. by centrifugal weights. This results in a stepless change in the transmission ratio. An additional control torque is the negative pressure from the intake tract, depending on the position of the accelerator pedal. The negative pressure is converted into a force via two very large, spring-loaded cans, which adjust the pulleys accordingly.

One advantage arises from the twistability: As can be seen in the picture, the V-belts allow a certain amount of twisting during compression; there is no need for constant velocity joints in the drive.

A differential gear was dispensed with in the DAF models 600 to 55. Each rear wheel was individually driven by a V- belt; the different wheel speeds in curves compensated for the slippage of the belts. A single wheel could not spin on a slippery road (as with a partial limited-slip differential ), which rally drivers in particular appreciated. Thanks to its technology, the DAF could drive forwards and backwards at the same speed. This has been adequately proven in some “spectacle races ” called AVRO-Achteruitrijden (German AVRO reversing) for the Dutch TV station AVRO with scrap-ripe DAF models. However, these attempts ended with the inevitable rollover after steering maneuvers. The caster of the steering axle, which automatically moves the wheels in the "straight ahead" direction when driving forwards, is reversed when driving backwards and leads to full lock of the wheels with corresponding consequences for driving stability, especially at higher speeds.

A De-Dion axle was installed in the DAF models 46, 66 , 77 and the Volvo models derived from them , as well as a synchronous reversing gear with reversed shifting pattern (“lever in front = backward”), a differential gear and cardan shafts. The limited slip differential effect was eliminated. With the weaker engine in the DAF 46, there was no need for a pulley group, which saved inert mass, friction and costs.

Belt variomatic gears are currently being used e.g. B. used in scooters , quads , ATVs , snowmobiles and pillar drills.

CVT transmissions with lamellar chains instead of V-belts work in a similar way . The force is not transmitted via V-belts, but via steel link belts (see picture) or chains. These gearboxes were developed and offered by various manufacturers, but have not yet been able to establish themselves on a larger scale. At Audi , this type of transmission is z. B. offered under the name Multitronic .

The A- (W169) and B-Class (W245) from Mercedes-Benz of the Daimler Group are equipped with a CVT automatic transmission with virtual gears (Autotronic), which can also be shifted manually.

Motorsport

In the then still young automobile sport rallycross , two DAF 555 Coupé 4WDs were used as the official CAMEL-DAF racing team by the DAF sports department in Eindhoven (under the direction of Rob Koch, later Fred Hagendoorn) in the early 1970s . The third 5 in the type designation stood for group 5 according to the FIA regulations. From 1971, the vehicles had a sports Variomatic - four-wheel drive , each with a belt for propeller shafts to the front and rear axle and self-locking differentials from the BMW 2002 . The Sportvariomatic used was originally developed for Formula 3 . The 147 kW (200 hp) Ford BDA engine was installed lengthways in the middle of the vehicle next to the driver, the Variomatic below him. There was a hump in the roof so the driver could sit upright. The car became known as "Het Bultje".

The vehicles were almost unbeatable across Europe among the two brothers and hauliers Jan de Rooy (who later also became famous as a DAF trucker at the Dakar Rally ) and Harry de Rooy, although they were usually only allowed to drive 5 seconds after the two-wheel drive vehicles ( 4WD penalty ). In 1973 all-wheel drive and continuously variable transmissions were banned in rallycross, so that other vehicles had a chance again.

Individual evidence

  1. a b c d Harald Naunheimer, Bernd Bertsche, Gisbert Lechner: Vehicle transmissions . Section 1, 2nd edition 2007, Springer, Berlin / Heidelberg, ISBN 978-3-540-30625-2 .
  2. https://drivetribe.com/p/double-dutch-1971-daf-555-4wd-variomatic-WAP0a8HAQpeGBKUuNlII1A?iid=YJJy7Gx7R8WcLztwNPcijg&sa=X&ved=2ahUKEwiX4bTmuIf-GQKhFj .KeggQHFj
  3. http://www.rallydaf.nl/Rallycr..html?sa=X&ved=2ahUKEwjwo7LIxIfnAhUPKewKHc-GAFcQFjALegQIAxAB