Purpose and steering device

8.1.1 Steering purpose

The steering is designed for changing the direction of movement of the car. The front axle wheels are usually steering, but this is mainly on cars. Sometimes, in order to improve the car's handling and maintain complete control over it, it is made fully steerable, i.e. not only the main front wheels are steerable - the rear wheels also have the ability to deviate by a certain angle.

The steering can be equipped with a booster or without it. It can be installed on a crossbeam of a body in an engine compartment or on a sub frame (practically on all modern cars).

8.1.2 Steering device

Figure 8.1 Example of steering gear.

1. Steering wheel;
2. Steering wheel mounting nut; 
3. Steering column upper cover; 
4. Steering gear assembly gear; 
5. Steering shaft flange; 
6. Steering shaft; 
7. Steering shaft tube; 
8. Steering column lower cover; 
9. Ball coupling; 
10. Track-rod end; 
11. Dust cap; 
12. Steering gear rail; 
13. Steering gear connection mounting bolt; 
14. Locking plate; 
15. Steering gear connection; 
16. A-post pivot rod.

8.1.3 Steering wheel

Steering wheel is the first thing you see when you get in the driver's seat. By turning it in one direction or another, you steer the car. There is nothing complicated in the steering wheel (or steering wheel…in case if it is, of course, the steering wheel of the simplest configuration. In modern cars the steering wheel is both a place for installation of an airbag, and the control panel of audio system together with phone. It is also the controller for control of the onboard computer. The steering wheel of a modern car is sometimes simply overloaded with all sorts of switches and buttons that have different purposes.

8.1.4 Steering column

The steering column consists, in fact, of two shafts (rarely one), that are interconnected by universal joints (similar to cardan shafts). It is designed for transmitting rotation from the steering wheel to the steering gear. Many current cars have adjustment of the angle of the steering wheel and the distance of steering column reach. In other words, you can, by moving the steering wheel up / down and towards/away from yourself, set the position, which is closest to ideal, according to your wishes.

Note
In order to ensure high passive safety, the design of the steering column is taken as seriously as, for example, the design of the seat. This is due to the fact that in case of a frontal collision the steering wheel should not move more than is permissible. Therefore, in case of a collision, the steering column must fold or break in certain places.

8.1.5 Steering gear

On modern cars two most widespread types of steering mechanisms are applied: worm and rack.

Interesting
The location of the steering mechanism on the sub frame relative to the imaginary axis of the steered wheels is of great importance. Thus, the installation of the steering gear behind the front axle or in front of it can eventually dramatically change the behavior of the vehicle on the road. Thus, the designers while designing a car consider this issue very seriously.

8.1.6 Worm gear steering

In case if the steering gear is of worm type, it consists of a Hindley worm and an angular sector on which the roller is mounted. A shaft is connected to the corner sector, and a tie-rod arm is attached to the shaft. The movement of the tie-rod arm is transmitted to the steering trapezoid, which consists of the steering rods. The rods, while moving, turn the wheels in one direction or another. The arrangement of the steering gear is shown in Figure 8.2. Nowadays cars with the worm-type steering gear meet less and less often.

Figure 8.2 Worm-type steering gear.

Worm-type gear is a type of gear in which there is a worm. This is a threaded part of the bolt, but only with many times increased turns, and a gear, which is engaged with this worm.

The Hindley worm is named so, because of its shape: its profile is concave, as shown in Figure 8.3.

Figure 8.3 Appearance of Hindley worm.

8.1.7 Rack and pinion steering gear

Now let’s describe a rack-and-pinion steering gear (figure 8.4). It consists of a gear and a rack/ The gear is connected to the steering column shaft, and the rail through the rods - with the rotary fists of the wheels.

Figure 8.4 Pack-and-pinion steering gear.

Interesting
Sometimes the teeth are made on the rack with a variable step (Figure 8.5). Designers do this in order to get the semblance of active steering for achieving the optimal combination of conflicting performance such as handling and comfort. Thus, for the sake of ease, it is desirable to reduce quantity of turns from a stop to a stop to one, and even to a half-turn. This is done so during parking the driver would not turn a steering wheel on 5 - 10 turns. But in case if there is only one turn from the right extreme position of the steering wheel to the left, the steering will be quite sensitive to each movement. This is dangerous while driving at high speeds, because it will be hard to perform all maneuvers, and this might have consequences. That’s why the designers came to such a fairly simple compromise solution: the step of the central teeth of the steering rack is small, and the gear ratio is slightly higher. Therefore, the sensitivity to the deviation of the steering wheel is small. But from the center the pitch of the teeth increases in order to reduce the gear ratio and the total speed of the steering wheel.

Figure 8.5 Example of steering gear toothed rack with variable teeth pitch.

Note
The pitch of the teeth is the distance between the centers of the vertices of the teeth.

Interesting
By the way, there may be a reverse situation when the pitch of the rack teeth decreases closer to the ends of the rack.

The rack-and-pinion steering gear replaced the worm-type gear and was firmly established as the most actual design. Its advantages speak for themselves: control of the car, which is even not equipped with the power steering, simple, small number of links of all steering mechanism, simplicity of installation on the car and reduction to a minimum of operations of service.

8.1.8 Steering drive

The steering gear connection is a set of rods and hinged joints that connect and transmit movements from the steering gear to the steering knuckles of the steered wheels.

If we return to the worm-type steering gear, then in the classic layout there are three rods - one central and two side. They are connected via hinged joints. The rods of the steering gear in this case is called the steering trapezoid. The design of the steering trapezoid in geometric terms is such that it provides rotation of the steered wheels at different angles (see the "Chassis" chapter).

In case of the installation of the rack-and-pinion steering gear, everything is a little easier Steering rods that transfer movement on steering knuckles of wheels are fastened on both sides to a steering rack. The advantages are obvious, because the fewer the various intermediate links, the more reliable and accurate the whole mechanism.

Note
In order to prevent dirt and dust from getting inside the rack-and-pinion steering gear housing, so-called dust caps (corrugated rubber covers) are installed on both sides.

8.1.9 Steering angles

While turning, the steering wheels of the car travel different distances. And in case if both wheels turn at the same angle, the car will shift from the set trajectory, thus tires of wheels will wear out much faster. 

Figure 8.6 Rotation of steering wheels at different angles.

In order to avoid this, the steering is designed to rotate the inner wheel at a greater angle to the outer.

Figure 8.7 Rotation of steering wheels at different angles.