The hydraulic steering is fairly common on passenger cars and trucks.
The Need for Hydraulic Steering
Ease of comfort for the driver has always been the idea of a good driving. The force required to turn wheels is directly proportional tot the weight of cars and also depends on whether your tires have been correctly pressurized. In case of tires not inflated to the require pressure, the effort is larger.
Hence the idea of power steering started to reduce the driver fatigue, the cause of many accidents.
Conventional Hydraulic Steering
Conventional hydraulic steering also known as power steering takes the power for hydraulics from the power train of engine through a system of belts and pulleys. The force required for steering comes from the pressurized oil from oil pump and a cylinder.
The steering column admits the oil into the a cylinder either on left hand or right hand side for a short time so that the wheels turn right or left. Once the steering wheel is brought back into the normal, the supply of oil to the cylinder is also stopped so that the car runs straight and vehicle goes on its course as desired by the driver. Since the hydraulic force can be increased many times, turning of wheels can be made possible with just a finger.
Electro Hydraulic Steering
The conventional hydraulic steering operates the hydraulic pump from the engine directly and therefore the speed of pump is directly proportional to the engine speed. When the engine is operating at its highest speed, the requirement for turning is minimal, but the pump continues consuming power at its maximum value, there by making the car less fuel efficient.
In order to reduce the fuel consumption, electro hydraulic steering was designed. In this design the pump is driven electrically and power requirement of pump are independent of engine speed thus the power required to drive the pump is reduced.. The steering linkages may be driven directly by the pump or through electrical drives.
The ease with which you can drive the car is the same in both cases and the engine becomes more efficient.
Both these suffer from the fact that it does not take into consideration the speed of the car at the moment of steering and can seriously affect the safety of car and the hydraulic steering is slowly being replaced by electronic steering
Electronic Power steering
The electronic power steering may employ hydraulic steering or employ just electrical signals for the supply of power to the wheel. The electronic power steering is a different steering mechanism in the sense that it takes signals from vehicle speed and steering, angular position and turning rate, wheel torque, and changes steering dynamics and driver effort.
Ultimate Driver Comfort
So you can see that the electronic power steering systems reduce the driver effort at the same time controlling the car in a better way. The turning effort required for steering the wheels during starting of the cars is more than when the car is cruising at a steady speed. The electronic steering takes care of this requirement. The hydraulics remain the same in each case.