Steering

When steering is known to influence the direction of travel of vehicles of all kinds This article deals with the steering systems of land vehicles.

• 6.1 steering trapezoid
• 6.2 Self- steering
• 6.3 spread
• 6.4 restoring moment
• 6.5 scrub radius / steering roll radius

Generally

By steering device can be a non- rail-bound vehicle in a desired direction control. The wheels turn at each steering angle a defined by the suspension geometry position one another. The steering system allows for even under the influence of uneven ground, negative and positive accelerations, lateral forces and the weather a precise and safe handling. The angle between the wheel plane and straight position is referred to as the steering angle. The steering torque is opposite to the steering angle and is dependent on the speed of the torque on the steering column.

The following requirements are placed on the steering:

• Precise and rapid implementation of the steering movement
• Good provision in a straight-line stability
• Ease of use
• Good feedback to the driving condition
• Damping of shocks and noises
• Drive, braking and acceleration forces may have no influence
• Prevention of injury in a rear-end collision
• Low weight and low construction cost and small wear

In single-track vehicles (eg, motorcycle) is directed directly via the front suspension and the trailer vehicle by turning the whole axis. In track vehicles preferably Achsschenkellenkungen be installed. They offer high stability and good handling characteristics and have a little space.

Components of the steering system

• Steering column, steering gear and steering wheel in the car
• Steering head and handlebar with two-wheel- like vehicles
• Stem for bicycle
• Drawbar with towed vehicles
• Steering Damper
• Lenkbegrenzer
• Tie rods
• Axle beam
• Steering knuckle with bolts or ball joint

There are many different steering modes are used depending on the number of the wheels, axles, and the purpose of use. The best known and most frequently encountered is the front wheel steering. They can be found in cars, trucks, and motorcycles.

Schwenkachslenkung / turntable steering

When Schwenkachslenkung a rigid axis is tilted as a whole, most of the front axle. The shaft is connected to the vehicle via a pin ( king pin ) or a bogie (also turntable ) is rotatably connected. Before the invention of the threaded bolt is used Reibnägel. With the towed vehicle, the steering force is transmitted to the front axle a so-called pole.

Disadvantages of Schwenkachslenkung are primarily the rollover tendency of the vehicle at full lock as well as the retroactivity of wheel forces on the steering and the instability associated with it.

Classical representatives of Schwenkachslenkung are horse-drawn carriages and multi-axle trailers, but also the soapbox. On close-coupled trailer combinations several turntable (even turntable ) was used. In this case, the axis is moved to different vertical pivot points, thereby to prevent striking of the corners of the vehicle to the tractor. In rail vehicles with bogies, the position of the axles is controlled by the same principle, because with them the constant gauge is essential.

Articulated steering

In the articulated steering the vehicle is divided into two halves, each of which run on a fixed axis and connected to them are connected by a swivel joint. This form of steering provides more stability than the Schwenkachslenkung. But it is only suitable for vehicle types that can be functionally divided into two separate elements that must be connected only through the joint.

Articulated steering is used mainly in construction and machinery.

Skid steer

For tracked vehicles or motor vehicles, the type of construction have not steered axle, the skid steer is used. The steering movement resulting from different speeds of the two driven sides. In the simplest form, this is done by a steering brake with brake bands, but wear out quickly. Therefore, usually a complex Superimposed steering mechanism is used, which also minimizes power losses. The skid steer is used mainly for vehicles, excavators, dozers and compact or Hofladern.

Fork Steering

The fork steering is the simplest form of Einzelradlenkung and comes in single-track vehicles ( bikes, scooters ) or three wheels ( also some wheelchairs and forklifts ) are used, in which the run in a fork individual front or rear wheel is hinged directly. Their advantage consists in the lateral symmetry, the steering behavior is the same in both directions.

Ackermann steering

The double-pivot steering system in which each front wheel of an axle is rotated by itself, was invented in 1816 by the German Georg Lankensperger as Hofwagner in Munich and patented. He had them patented in England by the publisher and entrepreneur Rudolph Ackermann, why she was there under the term " A- Steering ". The theoretically correct angle of the front wheels is called Ackermann angle. The double-pivot steering was invented already in 1761 without patent of Dr. Erasmus Darwin. Later, independently in 1875 by Amédée Bollée ( fr. patent) and Carl Benz reinvented 1891.

It thus differs from the usual carriages rotary tiller with turntable bearing. The double-pivot steering was introduced there after the invention of the automobile soon.

In the Ackermann steering but the two wheels must be different degrees taken. The wheels roll when cornering on a circular path. The circles all wheels must have a common center, to achieve a clean cornering. In Schwenkachslenkung with rigid axle, this is automatically the case. When Einzelradlenkung but the wheel outboard must be less severely hit, because it describes a larger arc than the inner. This is achieved by the so-called steering trapezoid of axle, tie rod and two steering arms at the wheels. The steering levers are easy hired usually inward, thereby resulting in them when turning the wheels of unequal length effective lever arms. This causes the extensions of all axles about the center of curvature intersect ( Ackerman principle ).

The position of the swiveling allows further improvements in the stability and steerability. By spreading, ie tilting the pivot axis to the inside, it approaches the center of the contact area of the wheel, the rolling radius is small, on the steering reduce steering effort and the reaction of the wheels (eg braking) up. The caster, ie the distance between the pivot axis and the center of the contact area in the direction of travel is greater when it is tilted backwards. This yields an automatic reset in the straight. By a slight toe-in, the wheels are not parallel, but close in the direction of travel, to improve straight-line stability.

The Ackermann steering avoids the disadvantages of Schwenkachslenkung like tendency to tilt and strong reaction of the wheels to the steering, you can able to carry out multi-axis drive vehicles.

Applications of Ackermann steering front axle arms are as passenger cars, trucks and tractors but also hinterachsgelenkte vehicles such as forklifts or harvesters. Even when motorcycle Yamaha GTS 1000 this guidance came in the early nineties for use. It has proven itself because of the higher torsional stiffness, because the distances and angles can be adjusted individually for motorcycle sidecars as a solution.

Steering trapezoid

The steering trapeze allows for different steering angle of the front wheels, with the inside wheel - depending on vehicle geometry and steering angle - between zero and a few degrees more steers ( thrust angle ). This decreases the " erasing" of the tire.

The steering Keystone enables easy adjustment of toe-out angle, but provides only for a maximum of two steering angle of the ideal geometric relationships; for all other steering angle, the steering trapezium only approximate the appropriate geometry.

To determine the steering trapezium in a first approximation, a rule of thumb that the pivot points of the steering levers should meet at the straight ahead in the center of the rear axle ( see figure above ). A method for the detailed calculation of steering trapezium with the help of a simple Excel program can be found in the web links.

Self- steering

There are many different steering modes are used depending on the number of the wheels, axles, and the purpose of use. The best known and most frequently encountered is the front wheel steering. They can be found in cars, trucks, and motorcycles.

The self- steering of a vehicle is described by a so-called self-steering coefficients. This coefficient describes the case of the integral discharge guidance route and the distance traveled of the wheel in relation to the Z -coordinate.

This coefficient is constant for various brand cars VW, different in others:

• VW Polo ( 9N2 ) 2.3 ...
• VW Golf (1K) .... 2.5
• VW Passat (3C ) .. 3.4

Spread

The steering pivot axis are located at each wheel to the vehicle's longitudinal axis relative to a normal to the road light ( about 5 to 8 degrees ) obliquely inwards. This reduces the scrub radius. The turning of the wheels effects the spreading, that the vehicle is front minimally elevated.

Restoring moment

Under restoring moment is defined as the provision of the wheels to the starting point, ie in a straight parallel position to the vehicle. The restoring moment must occur when the driver releases the steering wheel. This automation results from the design of the steering with the spread of the steering pivot axis. Due to the weight of the vehicle creates a torque which causes the autonomous provision of the wheels to the straight ahead. The steering is pressed into its starting position.

In addition to this static restoring moment which occurs even without the presence of tire lateral force, there is a further self-aligning torque, which results from the constructive as well as tracking the pneumatic trail as above. It produce the tire side forces whose center of distribution in the tire contact area has a distance to the intersection point of the steering axis by the road plane (overrun), a torque which tries to reduce the wheel steering angle. As the tire lateral force is proportional to the tire slip angle at low lateral accelerations, the restoring torque increases with the return of the wheels to the neutral position ( steering angle = 0) again, assuming the vehicle sideslip angle (angle between the vehicle longitudinal axis and current, the horizontal movement direction of the vehicle body ) is also zero.

Scrub radius / steering roll radius

Under a positive scrub radius ( steering roll radius ) is defined as the positive difference between the track width - Steering gauge ( see illustration ). That the distance between the points of intersection of the steering axis ( n ) by the road plane is smaller than the track width. In modern Vorderachskonstruktionen now also a negative scrub radius has been established, in which the track width is smaller than the steering gauge. The reasons for this lie in the improved vehicle stability at μ -split braking by a longitudinal force- induced steering torque and a resulting yaw torque build-up, which counteracts the longitudinal force difference Conditional yaw moment. When braking on so-called μ -split ratios (left / right different high friction μ ) occurs basically the problem that due to the different Längs-/Bremskräfte a yaw moment ( moment about the vertical axis ) is produced, which can make the car unstable and it rotates in the direction of high - μ - side. Due to the negative scrub radius steering torque is produced solely due to the different longitudinal forces, which in the opposite direction can turn (towards low- μ - side) the wheels. Thus, a counter-yaw moment to support the longitudinal force difference -induced yaw moment is generated and reduce the driver's burden with respect to counter-steering. In addition, the design of the vehicle dynamic control systems for this case can be further optimized in the direction of reduction in braking distance, since the trade-off between stability and braking distance by lenkungskonstruktiven this approach is weakened.

When zero scrub radius (Mercedes W116, W123 and W126 ), the extended steering axis meets the road in the exact center of the tire contact patch. The effect of braking forces on the steering is low.

Steering brake

Here it is, in principle, by directing a single-axle vehicle with rigid axle through various braking or driving forces on both wheels. Therefore, a motor-driven vehicle with steering brake mandatory requires a differential gear. In each case, one or all the wheels on one side of the vehicle to be braked, whereas the other spin unrestrained faster through the differential gear. This provides the advantage there is, among other things of a smaller turning circle.

Steering braking is applied in a wheelchair, tracked vehicle, with little tractor front axle load of tractors in addition to axle steering.

Steering modern motor vehicles

In today's multi-track motor vehicles is almost exclusively the steering mechanism, usually used in conjunction with an independent suspension. This accounts for a continuous axle body, a split handlebar replaced the tie rod and instead of the kingpin find a rotational axis of the shock absorber and support bearing ( top mount ). The steering force is transmitted from the steering wheel via the steering column to a steering gear unit, and from there to the steering rod of the steering levers to the steering knuckle. In order to apply ever greater steering forces with small steering movements and slight force due to getting heavier cars and always wider tire, is in most cases a steering booster, power steering, heavy-duty vehicles and the fully hydraulic steering, to train. More and more often also occur on vehicles with multiple steered axles, partly to increase the maneuverability as buses and trucks, but also in the context of stability programs for cars. The steering geometry is achieved by suitable steering gear or electronically. See also: dynamic steering, Active Steering

Normative guidelines for the steering equipment for motor vehicles and their trailers for road transport in Europe, the EC Directives 70/311/EEC and 75/321/EEC as well as the equivalent ECE rule ECE -R 79 The German Road Traffic Zulassungsverordung turn refers, in § 38 (2) " steering mechanism " and the related notes to this EC directive.

Steering modes

With respect to the entire vehicle, there are various steering modes:

• The two wheel steering is the most common form of steering in the most road vehicles, in which the two wheels of each axle are steered. Front axle is the usual steering in most motor vehicles.

• Proportional steering system in which the rear wheels are turned in a certain ratio to the front wheels, such as the front moves by 2 °, the rear wheel according to 0.4 ° ​​.
• Constant velocity steering system in which the front and rear wheels are rotated evenly, with the result that the rear wheels run after exactly in the tracks of the front wheels.
• Instantaneous steering system in which the rear wheels can be rotated only at a predetermined angle of the front wheels.
• Crab steering is a steering mainly used in agriculture. The front wheels and the rear wheels are turned in the same direction. This results in a straight-ahead, an offset to the front axle rear axle. Thus, the floor will be spared.
• Front-rear wheel steering is fitted with 3-axle trucks with double rear axle. In addition to her front axle steers with one of the two rear axles. If the first rear axle, the steering axis so directs this same direction as the front axle. The second rear axle, however, would give in the opposite direction to the front axle. As a grinding of the suspension is avoided, so that the vehicle is easier to handle and more maneuverable. Used mainly for heavy trucks that often have to be moved to confined areas (eg, garbage truck ).

Power transmission

To transmit the steering motion of the car or vehicle driver on the axle steering and wheels have vehicles a steering gear or actuator:

• The fork of the fork steering is connected to a handlebar or comprises an actuator
• The steering of a horse wagon done with reins and bridles
• The Ross steering is a variant of the worm and sector ( worm drive )
• The steering rack using a rack and pinion drive
• A hydraulic steering system alone can serve ( eg, in the articulated steering ), or as a steering aid
• The steering with electric drives can be done either with a separate actuator (for example, a remote-controlled vehicle ) or the unbalanced control of the electrical individual wheel of the wheels ( for example, when Segway Personal Transporter )

See also: List of topics of automotive engineering, Control of aircraft: flight control, steering of ships: Rowing

Manufacturer

The best-known manufacturers of such steering systems are:

• ZF Steering Systems
• TRW Automotive
• ThyssenKrupp Presta
• RBL braking and steering systems GmbH.
• LIM Automotive GmbH
• Jtekt
• Mando_ ( company )
• Tedrive steering
• Continental AG ( VDO)
• NSK