A brief analysis of the technology of
wire-controlled steering system
The steering power system can be divided into: mechanical hydraulic power steering (HPS), electric hydraulic power steering (EHPS), and electric power steering (EPS).
HPS Hydraulic Power Steering
The specific working principle of HPS is: the hydraulic pump is driven by the engine. When the engine is started, the hydraulic pump can maintain operation. The rotation of the steering wheel will drive the opening and closing of the three-way control valve: when the steering wheel turns left, the left throttle valve opens, and the hydraulic oil flows through the throttle valve to the hydraulic cylinder to drive the wheel to turn left, and the same applies to right turn. When the steering wheel does not turn, the hydraulic oil flows back to the tank through the middle throttle valve.
It can be seen that HPS will continue to consume the engine's energy, increasing fuel consumption. The hydraulic pump's output power will change with the engine speed, so its steering power size is unstable.
EHPS Electro-Hydraulic Power Steering
The working mechanism of the electronic hydraulic steering EHPS is similar to the electronic hydraulic brake EHB mentioned above. It replaces the power source of the hydraulic pump from the engine to the electric motor and introduces a torque sensor and ECU to replace the mechanically controlled hydraulic valve. The torque sensor detects the torque transmitted from the steering wheel. After receiving the signal from the sensor, the ECU controls the opening and closing of the hydraulic valve and the start of the motor to complete the power steering.
Compared with HPS, the motor in EHPS does not need to work all the time, which weakens the engine power much less. The motor's output power is more stable. The hydraulic system can output a lot of force, so it is more used in commercial vehicles and heavy trucks.
EPS Electric Power Steering
The principle of the electric power steering EPS is somewhat similar to the electronic mechanical brake EMB mentioned above. After the torque sensor detects the torque data transmitted from the steering wheel, it transmits it to the ECU. The ECU controls the motor to output torque according to a certain algorithm logic, and acts on the steering column after deceleration through the gear mechanism to complete the steering assistance.
Of course, the motor and reducer can have different arrangements, and their power can drive the steering column or directly drive the steering screw, which does not affect our understanding of its principle.
Compared with the difficult birth of EMB, EPS is more popularized more rapidly. At present, almost all new mass-produced passenger cars use electric power steering. One of the important reasons is that the output power required by the steering system is relatively small compared to the braking system, and the motor is easier to drive. The steering motor power of a general passenger car is between 300~800W.
