How Power Steering Works
Text by Richie Setiawan
While you are driving a car, turning left or right is always something you will have to do. They cannot be left apart. This is because it is pretty impossible for you to reach your destination in one long straight road, at least most of the time. When you turn the steering wheel of your car left or right, you can tell that the wheels of your car turn as well.
It sounds simple, right? You turn the steering wheel and the car wheels turn. Yet, what actually takes place between the steering wheel and the car wheels themselves is not as plain as it seems to be. There is a certain mechanism otherwise you will have no ability to turn your car at all.
Types of power steering system
The very first power steering to exist seemed to be the DIRAVI power steering system. Citroen -- an automobile manufacturer originally from France, as you know -- was the first company to invent this power steering system. They managed to invent the DIRAVI back in the early year of the 1970s. At that time, American people knew the DIRAVI better as the Speedfeel system.
The DIRAVI power steering system turned out to be entirely comprised of hydraulic system. With that being said, it was impossible at all to find electrical components of any kind in the system.
The design of the DIRAVI was pretty simple. It followed the design pattern of the unassisted rack and pinion that had been in use ever since people managed to invent the very first motorcars.
At the rack centre, people would find a hydraulic ram that had a plate to divide a couple of pistons powered by fluid. These 2 pistons were always balanced in spite of one having half the mass of the other. This was possible because one of the pistons, the smaller one, was given a constant amount of hydraulic pressure while the other one was given varying pressure. This way, the rack was able to remain neutral. As a result, the centring pinion that the wheels were attached to were kept levelled as well. This made the car wheels point straight ahead.
The DIRAVI power steering made a connection between the steering wheel and a hydraulic control unit. This control unit came with a slide valve as well as a piston in the centre of it. When people turned their steering wheel, the slide valve raised or lowered the hydraulic pressure that existed behind the larger piston on the rack accordingly. This, in turn, resulted in the pinion shifting to one direction or the other accordingly. This was what turned the car wheels. Then, when people finally let go of their steering wheel, the centre piston would return to its neutral position thanks to the weight that came with it and the car wheels would go straight again.
Servotronic power steering system
A more modern power steering system is the servotronic system. It is partly electric yet it still maintains the hydraulic system. The servotronic power steering system makes use of a hydraulic servo that is attached to the car pinion.The servo normally looks like a piston. The servotronic power steering system works by retracting or extending the servo's piston. When it retracts it, the car wheels will turn to one direction and when it extends it, the wheels will go to the other direction.
Another important thing to notice about the servotronic power steering system is that between the power steering control system and the steering wheel itself, there is an electric linkage, a direct one.
Also, it is the power steering control system that determines the force that needs to be passed on to the servo in order to exert so that it will be able to turn the car wheels as desired in accordance with to which direction people turn their car steering wheel.
The speed of the car is another factor that plays an important role in this case. While the car is travelling with a lower speed, the force needed will be less compared to when the car is travelling at a higher speed.
Eventually, the power steering control system will attempt to send the servo an electrical impulse to engage the hydraulics so that it is possible for the car wheels to turn.
Electric power steering system
This is usually known as EPS for short as well. As you may have been able to guess based on how people call this power steering system, it is entirely dependent on electrical mechanisms.
The electric power steering system takes full advantage of a machinery that is powered electrically for the purpose of steering the wheels of the car in the same way that the servotronic power steering system uses to turn the wheels of the car.
However, the electric power steering system makes use of an electrical motor in place of a hydraulic servo. This electrical motor is attached to the car pinion. But both a hydraulic servo and an electrical motor does exactly just the same job.
As in the case of the servotronic power steering system, the steering wheel in the electric power steering system is also attached to the power steering control system. It is this system that will then relay a relative electrical energy amount that is considered necessary in order to be able to turn the wheels of the car to one direction or the other.
The power steering control system also takes into accounts the specified direction and angle of the motor. However, one quite unfortunate thing about the electric power steering system is that the entire mechanism is very dependent on the car battery. This, in turn, often results in the necessity to replace the car battery quite so often. Yet, this is not the case with 2 previous power steering systems mentioned earlier.
Wednesday, 6th April 2011
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