Mechanical, hydraulic, electronic, what's the best steering system?

In the old days there was no power steering in cars, they were steered purely using a mechanical steering system, then we would need to exert more force to steer the car when we manoeuvre it, and we would feel very tired. Nowadays, the steering systems of the small cars we drive have power assisted steering, mainly to improve driving comfort and overcome the friction generated by the larger tyres in contact with the bottom surface.

Power steering can use external forces to reduce the owner's driving on the steering wheel to manoeuvre, according to the way of classification of the power-assisted, divided into two kinds: hydraulic and electronic, hydraulic is mainly the use of the hydraulic mechanism to provide power, the use of booster pumps to provide pressure to the hydraulic fluid, so that the fluid circulates to flow in the system. Electronic power using an electric motor for steering power, in some of the better models used in the electronic power.

1. Analysis of hydraulic power assist system

The structure of this type of booster system is shown in the figure below, mainly composed of return pipe, inlet pipe, outlet pipe, steering gear assembly (including steering control valve), booster fluid pot, steering booster pump and so on. The hydraulic power system is characterised by a small sound when working, a short response time to the hysteresis band, and a better absorption of road impacts from different road conditions. As shown in the figure below, when we hit the steering wheel, the steering control valve also follow the rotation, the internal structure of the steering gear control channel to open and close off, then the power cylinder in the steering gear will produce a different pressure difference between the left and right, at the same time to promote the power piston to move to the left or to the right, which produces the role of power assist. The power then transfers the torque to the wheels via the steering cross ties to create the correct steering relationship between the left and right wheels. The disadvantage of the hydraulic power type is that the steering fluid often needs to be added, and there will be oil leakage in the oil pipe, the leakage of the steering fluid will lead to insufficient oil pressure in the high-pressure and low-pressure lines resulting in bad power, then there will be a driving safety hazard and make a very loud noise when driving.

2.Analysis of electronic power type

Electronic power steering system is what we often call EPS, which is mainly composed of torque sensor, speed sensor, steering control unit, electric motor and electromagnetic clutch, as shown in the figure below. The system is mainly based on detecting the vehicle speed and steering angle and strength, and the electric motor is controlled by the electronic card in the unit as the power source to complete the power assist. When the steering wheel is operated, the torque sensor installed on the steering shaft will ‘feel’ the steering wheel rotating strength and how much angle has been turned, so as to detect the size of the torque on the steering shaft, and the signal is also provided to the ECU together with the speed sensor, which determines the current and steering of the power motor according to the signals and the torque of the motor is transmitted through the electromagnetic clutch through the deceleration mechanism to the electric motor as a power source. is then transmitted to the steering mechanism via an electromagnetic clutch via a reduction mechanism, producing a force appropriate to the engine and vehicle operation. Electronic power steering is more fuel efficient than hydraulic power steering because the power motor only needs to be switched on when the steering is being done, and is normally on standby. The power steering system also has a speed control function, that is, when the vehicle speed is higher than 40-50km/h, the control unit enables the electromagnetic clutch in the motor to disengage and steer according to the normal power-assisted method to ensure the stability of high-speed driving. We know that the steering wheel to the end is not good for the steering wheel, hydraulic power system will also be easy to damage the power pump, but in the electronic power system does not appear in this case, in the steering wheel to the limit position, at this time the motor is not running, the control unit will reduce the output voltage to the motor.

Through the above analysis of the two different types of power steering assist device, we can know that the electronic power steering system is a little better than the hydraulic power steering system, whether it is from the point of view of the operation and the cost of maintenance and use in the later stage, electronic power stability and more advantages.