In , Francis Davis became the first person to successfully fit a hydraulic power steering unit into a automobile. Unfortunately, nobody really saw the potential and it was never commercialized. At least not until the when the second world war erupted. During the war, people started looking for ways to control their heavily armored war machine better, faster and easier.
In search for a competitive edge in the battle, the technology behind hydraulic power steering was quickly adopted into prominence.
By the time war ended in , 10, military vehicles have been fitted with a power steering unit. And so it happened. In , Chrysler is the first car manufacturer to make power steering unit commercially available. It was available to the public through their passenger car — the Chrysler Imperial. Soon after, many other cars manufacturers such as General Motors, Toyota and Honda quickly came up with their own variation of power steering and implemented them. And that brings us to where we are now.
In 21st century, virtually all cars are now equipped with power steering. If you really think about it, power steering is a piece of technology that is born out of difficult times and it blossomed into something that changed our life completely for the better.
This is because a regular non-power assisted steering rack works very similarly to a hydraulic power steering system. The only difference is that hydraulic power steering have a few additional parts to supply the extra power. Just like how we have a petrol tank for petrol, we have a steering fluid tank for steering fluid.
Whenever we are using fluid, we always have a container that holds them when we are not using them. There is nothing too fancy about this part here, and its purpose is quite self-explanatory too.
But, the journey of a hydraulic power steering begins here. When we fill the steering fluid, we put it into this reservoir. It holds the fluid, and supplies them to the steering pump through rubber hoses. We connect the steering pump to the engine through a belt-pulley mechanisms using an engine belt.
With that, the pump pulls the steering fluid from the steering fluid reservoir and pressurizes them. How exactly do they do that? For now, think of the steering pump as a black box.
We put low pressure steering fluid in, and high pressure steering fluid comes out of the other end. These high pressure steering fluid then leaves the steering pump, through the steering hoses and into the steering rack, specifically into the rotary valve. Inside the steering rack, we have what is known as the rotary valve.
A rotary valve is a highly sensitive metal casing with strategically placed holes that redirects the steering fluid either back to the steering pump or into the steering rack. Think of it as the traffic police at a busy road intersection.
It tells the steering fluid which way to go depending on where you turn your steering wheel. As the steering fluid from the rotary valve gets redirected into the hydraulic chamber, we start to get power assist!
In the hydraulic chamber, there is a hydraulic piston right down the middle. It separates the hydraulic chamber into two equal portions: the left side, and the right side. When there is more steering fluid on one side of the hydraulic chamber, it creates a pressure differential across the chamber.
The steering fluid then pushes the hydraulic piston towards the weaker side of the hydraulic chamber and the steering rack moves accordingly. Because of fluid dynamic. To give you a metaphor that helps you understand it, imagine two rooms of equal sizes with a movable wall that you can push in the middle.
One room is filled with 50 people while the other is filled with people. But hey, the other room want more space as well! It visualizes the turning effort required to stabilize the vehicle body on turns, and in winds, etc. Furthermore, to control a heavy vehicle with safety, particularly a loaded commercial vehicle, requires greater effort at the steering wheel.
It should also be able to tackle wide variations of road surfaces and bumps and bounces. The use of large-section, low-pressure tires have greater road contact. So, they further magnif y the steering efforts. Hence, manufacturers employ power-assisted steering on all types of vehicles i. Hydraulic power steering system consists of a steering gearbox, and an oil pump, a valve. It also includes a double-acting power cylinder, and a hydraulic oil reservoir.
The system becomes active when the exertion of pressure on the steering wheel exceeds a predetermined value. When the driver turns the steering wheel, it, in turn, operates a valve. This valve directs the fluid to either side of the piston inside a cylinder to turn the wheels in the required direction. The valve directs the fluid back to the cylinder to prevent the tendency of the wheels to deflect when they run into an obstruction.
Most designs provide a booster arrangement to turn the steering wheel shaft. This booster mechanism takes care of most of the work of the steering. Power steering employs compressed air, electrical mechanisms, and hydraulic pressure to run the steering shaft. However, most vehicles use a hydraulic pressure operated steering mechanism. The amount of flow provided by the pump depends on the car's engine speed. The pump must be designed to provide adequate flow when the engine is idling.
As a result, the pump moves much more fluid than necessary when the engine is running at faster speeds. The pump contains a pressure-relief valve to make sure that the pressure does not get too high, especially at high engine speeds when so much fluid is being pumped. A power-steering system should assist the driver only when he is exerting force on the steering wheel such as when starting a turn.
When the driver is not exerting force such as when driving in a straight line , the system shouldn't provide any assist. The device that senses the force on the steering wheel is called the rotary valve. The key to the rotary valve is a torsion bar. The torsion bar is a thin rod of metal that twists when torque is applied to it.
The top of the bar is connected to the steering wheel, and the bottom of the bar is connected to the pinion or worm gear which turns the wheels , so the amount of torque in the torsion bar is equal to the amount of torque the driver is using to turn the wheels.
The more torque the driver uses to turn the wheels, the more the bar twists. The input from the steering shaft forms the inner part of a spool-valve assembly. It also connects to the top end of the torsion bar.
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