The device for influencing the direction of travel of vehicles of any kind is called steering . This article is primarily concerned with the steering technology on two-lane land vehicles , in particular with the kingpin steering.
In the case of rail-bound vehicles, the rails indicate the direction of travel.
Non-rail-bound land vehicles originally had swivel axle steering (or turntable steering). The front rigid axle body with its wheels mounted at both ends is usually pivoted horizontally around a bolt located in the middle. This type of steering is still often used on multi-axle trailer vehicles today .
In most motor vehicles with two front wheels, the kingpin steering was used almost from the beginning - also usually on the front axle . The two steering knuckles or wheel carriers on which the wheels are mounted are each mounted pivotably about their own, approximately vertical axis directly on the wheel. For coordinated pivoting, the steering knuckles are articulated to one another via the steering linkage.
After reaching the desired new direction of travel, the swiveling ( steering angle ) is canceled. Steering angle is the angle between the wheel plane and the straight-ahead driving position. Steering deflections are occasionally also necessary as steering corrections as a result of direction-changing disturbances such as uneven ground, acceleration or deceleration, differences in ground contact right and left and cross winds.
The term used for the steering technology of single-track vehicles (bicycles and motorcycles) is steering head steering . The front wheel is swiveled to the side with the front wheel fork that can be rotated in the steering head.
The steering behavior is determined by Ackermann models such. B. the single-track model described.
Components of the stub axle steering in automobiles
- Steering knuckle
- Kingpin or ball joints for connection via the wheel suspension to the axle beam
- Steering lever on the steering knuckle
- Tie rods (partly intermediate rod , intermediate lever and pitman arm )
- Steering gear ,
- Steering column ,
- steering wheel
Components of the steering head steering in single-track vehicles
- Wheel fork,
- Steering head (motorcycle) or headset (bicycle)
- Motorcycle handlebars or bicycle handlebars
Swivel axle steering / turntable steering
With the swivel axle steering, the rigid axle body with the wheels mounted at its ends is pivoted as a whole around a central bolt ( king bolt ). When the axle is swiveled, the contact area of the vehicle is reduced from a square to a triangle when swiveled through 90 °, which reduces the vehicle's stability against tipping.
The swivel axle steering is used in carriages and other horse-drawn carriages and generally in multi-axle trailers , since the drawbar for pulling the vehicle can also be used here in a simple manner to control the steered axle.
Only very simple self-propelled vehicles like soap boxes or early steam-powered road rollers were equipped with swivel-axle steering. This is because the vehicle either needs sufficient ground clearance to allow the wheels to swivel under the vehicle floor or the axle must be wide enough for the wheels to swivel outside the vehicle body. For the suspension of the axle, a turntable placed underneath is usually required, which further increases the center of gravity of the vehicle. Independent vehicles with steered front axles tend, due to their design, to tip over forwards when the front wheels are braked.
A plurality of pivot plate (to be close-coupled trailer combinations ring gears ) are used. The axle is moved around various vertical pivot points in order to prevent the vehicle corners from hitting the tractor.
Single wheel steering
If each steered wheel has its own axis of rotation, there is a single wheel steering . In two-lane vehicles, the steering knuckle is used with the steering knuckle lying outside the wheel plane; in single-lane vehicles, steering head steering with the axis of rotation in the wheel center plane is used.
Stub axle steering
The steering knuckle, in which each front wheel has its own pivot axis, was developed in 1761 by Dr. Erasmus Darwin invented. It was patented for the first time in 1816 by the Hofwagner Georg Lankensperger from Munich. This left it to the publisher and entrepreneur Rudolph Ackermann in England , which is why it became known there under the term "A-Steering". Ackermann is also reminiscent of the designation of the steering angle as Ackermann angle and the Ackermann function, which describes the steering angle difference, which depends on the wheelbase, track width and steering angle. Amédée Bollée received further patents in France in 1876 and Carl Benz in 1891. This type of design is almost exclusively used in today's multi-track vehicles, also in rear-axle-steered vehicles such as forklifts or harvesting machines. The wheel hub steering of some motorcycles can be understood as a stub axle steering. Yamaha used this single pivot steering on the Yamaha GTS 1000 motorcycle in the early 1990s.
When cornering, both wheels should roll on a circular path with the same center point, the instantaneous center of movement. This is automatically the case with turntable steering. In the case of independent wheel steering, the inner wheel, which is closer to the center and runs ahead of the outer one, has to turn more strongly than the outer one. With stub axle steering, the wheels must be swiveled differently, the one on the outside less than the one on the inside. This is achieved with the formation of the so-called steering trapezoid from the axle beam , the two steering levers on the steering knuckles pointing slightly inwards and a tie rod that is shorter than the axle beam. This results in lever arms of unequal length when swiveling the wheels, so that the extensions of all wheel axles intersect roughly at the center of the curve ( Ackermann principle ). An indication of a correctly dimensioned steering trapezoid is the fact that the extended steering levers on the steering knuckles meet in the straight ahead position in the middle of the rear axle (see above in the figure above).
Toe (toe angle) and camber are determined by the position of the wheel axle (the stub axle ), spread and caster by the position of the steering axle
Toe-in means that the wheels are not exactly parallel when driving straight ahead , but rather form an acute angle in the direction of travel. This improves straight-line stability. The steering mechanism is kept under tension by the slightly "cross-eyed" adjustment of the wheels. This prevents the steering from fluttering due to bearing play . Ideally, the slight toe-in just compensates for the bearing play so that the wheels are parallel again during normal driving.
The toe-in can only be adjusted when the wheels are straight. When the steering is turned, the wheels get toe-out: the wheels form an angle that opens to the front so that the wheel on the inside of the curve can follow a smaller curve radius than the wheel on the outside of the curve.
The wheel axles or stub axles are not exactly horizontal, but point slightly downwards or upwards at the outer end. The first case is called a positive camber related to the vehicle . Here the wheels are pushed inwards and the play in the bearings is eliminated. A negative camber, on the other hand, compensates for the tendency to roll in curves and improves the grip of the tires in the curve.
The pivot axes of the wheels are inclined slightly inwards so that the extension of the pivot axis approaches the contact area of the wheel. This reduces the scrub radius . The steering force and the reaction of the wheels (for example, by braking on the right and left with non-slip surfaces) on the steering are reduced. If the steering scrub radius is positive, the spread causes the front part of the car to be lifted slightly when the vehicle is turned, which automatically returns to the straight line, even when standing ( return torque ).
Shock radius and disruptive force lever arm
In the rear view of the wheel, the expansion axis has the distances between the impact radius r σ and the disturbance force lever arm r St from the wheel center . Their distance parallel to the roadway is the impact radius, their smallest distance is the disturbance force lever arm. Both values are positive if the center of the wheel is further away from the center of the vehicle than the spread axis. They should be as small as possible so that no disruptive forces are generated in the steering.
The restoring torque acting on the steering wheel when cornering arises essentially from the tire restoring torque and the torque from the lateral force and the trailing distance of the wheels. This is caused by a slight inclination ( caster angle ) of the swivel axes (spread axes) of the wheels to the rear and the caster offset . The caster distance is defined as the distance between the point of intersection of the spreading axis on the roadway and the wheel contact point in a view from the side of the wheel.
Steering head steering in single-track vehicles
Another term is fork steering . One of its characteristics is the right-left symmetry , the steering behavior is the same in both directions.
Except for single -lane vehicles ( bicycles , scooters ), it is also used for three-lane vehicles. The individual front or rear wheel is swiveled, as is the case with classic three-wheelers and also with wheelchairs and rear-steered forklifts .
The Riedel Imme light motorcycle has no right-left symmetry; his designer Norbert Riedel gives two possibilities in a patent specification that are intended to reduce the disadvantages of asymmetry.
Other types of two-lane vehicles
With articulated steering , the vehicle consists of two parts, each with a mostly unsprung rigid axle . Both parts are connected to one another by a joint rotating around a vertical axis . The steering is done by pivoting the two vehicle parts against each other. In comparison with the swivel axle steering, which is also articulated, the contact area in the swiveled state and thus the stability is greater.
The articulated steering is primarily suitable for short and rather slow-moving vehicles. Masses in front of the front or behind the rear axle (such as shovels and other work equipment) have a stabilizing effect on vehicles with articulated steering. The articulated steering separates the vehicle into a front and a rear part, which support each other. The more evenly the respective axle load is divided between the area in front of and the area behind the relevant axle, the lower the risk of tipping over when the vehicle is steering.
The combination of articulated steering and stub axle steering is known as stereo steering .
The change in direction results from different speeds of the two driven sides, such as that of the chains of tanks and other tracked vehicles (such as crawler vehicles) and is also used in wheeled vehicles (e.g. compact and yard loaders ).
In its simplest form, this is done using a steering brake with brake bands , which, however, wear out quickly. For this reason, a superimposed steering gear is usually used, which also minimizes drive losses.
Steering brake, in addition to steering knuckle
With rear-wheel drive, the stub axle steering can be supported by temporarily braking one of the drive wheels. Due to the differential gear usually present on the rear axle, there is no loss of drive power. In vehicles with a low front axle load ( wheelchairs and some tractors ), the steering brake can change direction on its own.
Types of steering in relation to the vehicle axles
With regard to the vehicle and its axles, a distinction is made between:
- The two wheel steering is the most common form of steering in most road vehicles, in which the two wheels are steered the same axis.
- Rear-wheel steering is generally only used in slow-moving vehicles, since vehicles with rear-wheel steering tend to oversteer and this effect can increase dangerously if the bearing play increases with increasing wear. Rear-wheel steered forklifts benefit from increased maneuverability. On forklifts and combine harvesters, the rear-wheel steering simplifies the construction of the heavily loaded front axle.
- Front-wheel steering is the common steering on most motor vehicles . In 3-axle vehicles with unguided rear axles ( double axle or tandem axle ), the rear wheels are pushed at an angle to the direction of roll when cornering and rub against the ground. Due to the frictional resistance, they force the vehicle to understeer. The closer the two rear axles are together, the less the steering is hindered.
- The steered front axle must not be too far forward on vehicles with large payloads . If, due to a large load on the rear loading area of the vehicle, too little of the total vehicle weight acts on the front axle, the front wheels would otherwise lose their grip when steering.
- Double front- wheel steering is the name given to the steering of two front axles located in close succession. This steering is used to distribute a high front axle load on two axles. The alternative would be to enlarge the front tires, which, however, restricts the engine compartment with the engine in the front.
- Two articulated front axles are found in special vehicles such as large truck- mounted cranes . Construction vehicles such as bulk goods transporters ( dump trucks ) and self-propelled concrete mixers are also increasingly being equipped with them. The assumption of a higher load by the two front axles reduces tire wear by erasing the tires on the unguided rear axles when cornering. Occasionally, a second rear axle is dispensed with.
- The front-rear wheel steering is installed in 3-axle commercial vehicles with double rear axles. In addition to the front axle, one of the two rear axles also steers. Similar to proportional steering, the steering angle of the rear axle is reduced compared to the front axle.
- If the first rear axle is the steering axle, it steers in the same direction as the front axle. The second rear axle as a steering axle steers in the opposite direction to the front axle. Since the rear axles are not erased, the vehicle is easier to handle. The turning circle is reduced, especially when the rearmost axle is linked. Mainly used in heavy trucks that often have to be moved over narrow terrain (e.g. garbage trucks).
- A four-wheel steering allows a small turning radius of a wheel steering can be found among others in agricultural vehicles or heavy goods vehicles. A distinction is made between the following types:
- Proportional steering in which the rear wheels are turned in a certain ratio to the front wheels, for example the front wheel moves by 2 °, the rear wheel accordingly by 0.4 °.
- Synchronous steering , in which the front and rear wheels are rotated evenly, which means that the rear wheels run exactly in the track of the front wheels when cornering constantly.
- Delay steering, in which the rear wheels are only articulated when the front wheels have reached a certain steering angle.
- Crab steering is a type of steering that is mainly used in agriculture . The front wheels and the rear wheels are deflected in the same direction. This makes it possible to let the rear wheels run offset to the front wheels even when driving straight ahead. This reduces the formation of ruts and reduces the risk of tipping over on steep terrain.
- In cars, steering behavior is desired that cannot be achieved with proportionally turned wheels: small turning circle with wheels turning in opposite directions at low speed, increased driving stability at high speeds with wheels turning in the same direction. Honda implemented such a system from 1987 in the Prelude model. With a planetary gear steering gear on the rear axle, the wheels were turned in the same direction with a small steering angle and in opposite directions with a large steering angle. Modern systems work with computer-controlled electric servomotors. In this way, the steering angle of the rear wheels can be adjusted as a function of the driving speed and driving dynamics variables independently of the position of the front wheels in order to improve driving stability. Such systems can be part of a steering system that does not require a mechanical connection between the steering wheel and the wheels ( steer-by-wire ).
Steering of watercraft and missiles
The steering of watercraft and missiles is usually called control. It acts on the drive (for example, in helicopters or rowing boats ), for movable control surfaces to the medium flowing around (water or air - over height , side , ailerons in aircraft and control row for ships ), or the steering has its own power source ( for example as steering engines in rockets and bow thrusters in ships).
Self-steering and remote steering
Ground vehicles are usually self-steering, they are self-steering. The opposite, remote control or remote control, transmits the steering commands from outside to the vehicle, like a remote-controlled model car or a satellite .
- Erik Eckermann: The stub axle steering and other vehicle steering systems . Deutsches Museum, Munich 1998, ISBN 3-924183-51-1 . [online http://www.be-tech.bplaced.net/inhalt/02tew/techwerk/lenken/sachinformation/lenkungssysteme.pdf , accessed 2016-09-13]
- Anthony Bird, Edward Douglas-Scott Montagu of Beaulieu: Steam Cars, 1770-1970. Littlehampton Book Services, 1971, ISBN 0-304-93707-X . (English)
- Steering Equipment, regulation TRANS / WP.29 / GRRF / 2002/5 (PDF; 110 kB) of the Economic Commission for Europe
- ↑ Turntable steering, stub axle steering. In: hako-lehrmittel.de. Hako teaching materials, archived from the original on November 27, 2018 ; accessed on April 6, 2020 (pictorial comparison of the two types).
- ↑ Erik Eckermann gives an earlier attempt at single wheel steering in Kultur & Technik, 04/2003, p. 54 [online: http://www.deutsches-museum.de/fileadmin/Content/data/020_Dokumente/040_KuT_Artikel/2003/ 27-4-54.pdf , accessed 2016-09-13]
- ^ Bird, Montagu of Beaulieu: Steam Cars, 1770-1970 (1971), p. 52.
- ^ A century of automotive technology - commercial vehicles. VDI-Verlag, 1987, ISBN 3-18-400656-6 , pp. 164, 174, 175.
- ↑ A century of automotive technology - passenger cars. VDI Verlag, 1986, ISBN 3-18-400620-4 , p. 368.
- ^ Royal Society of London notices and records © 2002 The Royal Society
- ^ Konrad Reif, Karl-Heinz Dietschke: Kraftfahrtechnisches Taschenbuch . 27th edition. Vieweg & Sohn, 2011, ISBN 978-3-8348-1440-1 , p. 318 . : ( limited preview in Google Book search).
- ↑ Motorlexikon.de: The toe-in keeps the steering under tension [both wheels steer a little, which cancels out each other through lateral slip ] and thus reduces steering disturbances, also known as flutter. 
- ↑ Steering in the Universal Lexicon
- ↑ Self- steering in the Universal Lexicon