Introduction To Automobile Steering System

In the automobile system, the power transmission system from the steering wheel to the wheel is called the steering system. As we all know, the vehicle steering system is a mechanism used to maintain or change the direction of the car; when the driver controls the front wheel angle by hand, it ensures that the vehicle changes its direction according to the driver's will. In addition, during the driving process of the vehicle, the "road feel" generated between the wheel and the road surface is transmitted to the driver through the steering system, so that the driver can perceive the current driving state of the vehicle.

According to the classification of the steering gear, the automobile steering system is roughly divided into mechanical and power types. The mechanical steering system relies on the driver's hand force to turn the steering wheel, while the power steering system can reduce the driver's hand force and relieve the driver's tension. This article will analyze the steering system and its dynamics:

1. Dynamic Analysis of Automobile Steering System

From the perspective of dynamics, when the car turns, all wheels should rotate around the instantaneous steering center and should not slip sideways, otherwise it will accelerate tire wear and reduce the driving stability of the car; after the car turns, the steering wheel should be able to automatically return to the straight driving position when the driver releases the steering wheel; the steering system should also ensure that the car has high maneuverability and has the ability to drive quickly and make small turns.

Mechanical steering gears are divided into rack and pinion type and recirculating ball type steering gears. The structure of the rack and pinion type steering gear is a pair of meshing gears and racks. The working principle is as follows: the steering shaft drives the pinion to rotate, and the rack moves in a straight line. The rack drives the tie rod to make the steering wheel turn. The recirculating ball steering gear consists of a two-stage transmission pair, a housing, a steel ball and a clearance adjustment device. The working principle is as follows: the first-stage transmission pair is a screw-nut transmission pair, and the second-stage is a rack-sector transmission pair. The steering screw is connected to the steering shaft, and the steering nut is both the first-stage transmission pair follower and the second-stage transmission pair active member.

2. Electric Power Steering System (EPS)

The steering booster device of the automobile power steering system can be divided into pneumatic, hydraulic and electric types. The following mainly introduces the electric power steering mechanism. In recent years, EPS has been widely used in passenger cars and also has some additional functions: such as anti-noise ability and overload protection ability. Compared with the mechanical transmission system, the electric power steering system also includes motors, batteries, sensors and control harnesses. The electric power steering mechanism can be divided into the following three categories:

Its working principle is as follows: When the driver applies torque to the steering wheel to try to turn it, the torque sensor converts the rotation angle displacement signal into an electrical signal and transmits it to the ECU. At the same time, the vehicle speed is also transmitted to the ECU. Based on the above signal input, the ECU calculates the output torque size and direction of the motor and outputs a signal. Finally, the output signal drives the motor through the current drive circuit.

3. Automobile Steering System Model

For current automobile experimental research, the steering system model is indispensable. Its function is to describe the relationship between the steering wheel angle, the front wheel angle and the steering wheel return torque. The steering system model is related to the simulation accuracy of automobile dynamics. This model should have the following characteristics, such as: ensuring the overall direction control of the car according to the input command and feedback of the steering wheel force response. The following introduces the analysis process of a linear two-degree-of-freedom automobile model.

Figure 7 Linear two-degree-of-freedom car model

Of course, the establishment of this model ignores many conditions, such as the role of the steering system and suspension, but it can still be used to establish the motion differential equations of the linear two-degree-of-freedom car. After decomposing the vehicle acceleration in the car coordinate system, the relationship between the external force, external torque and the car motion parameters can be obtained by listing the motion equilibrium equations. The parameters in the formula represent the structural parameters and motion parameters of the vehicle respectively.

By solving the equations to obtain certain performance indicators, it is possible to objectively analyze certain vehicle performance, such as handling stability. The stability factor K, an important parameter that characterizes the vehicle's steering characteristics, is obtained in this way: when the K value is 0, the vehicle has a neutral steering characteristic; when the K value is positive, the vehicle has an understeering characteristic; when the K value is negative, the vehicle has an oversteering characteristic.