Back in the day, cars had strictly mechanical steering. You turn the steering wheel which was connected to a steering shaft with a gear on it. That gear furthermore, meshes with another gear that moves the wheels in the direction you want. As long as you were moving, this worked well.
However, at low speeds, steering becomes heavy. Parking was a chore. Power steering provides a boost to ease the burden, particularly at low speeds. The power steering system may have a belt-driven hydraulic pump or an electric motor-driven pump. Some systems have an electric motor built into the steering column with no hydraulics at all.
Difference between Manual and Power Steering
Manual steering is the string system where steering is connected to a rod that turns the wheels to the steering direction. This is called Rack and pinion steering. Rack means rod and pinion means gear. A gear is attached to the steering rod.
Therefore, when the driver turns the steering wheel, it turns the gear in a circular motion and then moves the steering rod which can be seen behind the clutch, brake, and accelerator pedal. In this case, the rotational motion of steering wheels is converting into linear motion.
This linear motion turns the wheels. Hence, once the steering is heavy, the car is idle and as soon as the tires start moving, the kinetic energy reduces as well as the weight of the steering. In other words, the higher the speed, the lighter the steering. In power steering or hydraulic steering, a pump (motor) is attached to the steering column which uses oil to create hydraulic pressure to lighten the steering. To read more on power steering pumps, click here.
Once the engine is on the steering pump is on and the steering becomes light. This is also a rack and pinion system with a motor. Steering is super heavy when the engine is off.
Types of power steering systems
There are 3 main types of power steering systems, and they include:
- Hydraulic Power Steering
- Electric Power Steering
- Electro-hydraulic Power Steering
Hydraulic Power Steering
In earlier vehicle models, turning vehicle wheels was an incredible work that required incredible strength to achieve. As time went on, however, power steering was invented to aid in turning vehicles. Hydraulic power steering was the first to be developed.
The hydraulic power steering system is made up of an oil pump, a valve, and a steering gearbox. In addition, a reservoir and a double-acting power cylinder are also part of the setup. The system is idle until a pressure that exceeds a predetermined value on it is applied by the driver (to turn). Each time this pressure is exceeded the valve opens up and allows fluid to flow inside the gearbox.
The fluid then assists the piston inside a cylinder to turn the wheels in the desired direction. The fluid drains back into the reservoir to avoid possible shifting of the wheels when a disturbance is encountered.
Types of Hydraulic Power Steering System
There are different types of hydraulic power steering systems as developed by different manufacturers. They include:
- the Ross system
- Varmatic system
- Vicker’s system, and
- Marks-Bendix system
Of all of these hydraulic systems, the Varmatic is most widely used. All these systems use the same working principle and make use of pressurized fluid to perform. A booster is also part of the assembly in some car models. This also assists in steering the wheels. The SAE values for power steering oil are SAE 10W or SAE 5W in temperatures below 120 degrees. For hydraulic power steering systems two types of power steering gears could be employed.
The integral type or the linkage booster type. For the integral type, hydraulic pressure is used directly to work in the steering gearbox enclosure. But the linkage booster type uses a hydraulic cylinder and control valve with a conventional steering gearbox. Hydraulic power steering systems employ an oil pump that pressurizes the hydraulic fluid and is driven engine via a belt.
Furthermore, the control valve which controls the flow of pressurized fluid is actuated when the driver turns the wheels. Each time the control valve allows fluid to come in, it channels it to either side of the hydraulic cylinder. This pushes the piston to the other side. When this happens the pitman arm is forced to the steering linkage then to the wheel which turns either way.
Watch this to see how hydraulic power works
Electric Power Steering
Electric Power Steering or EPS uses an electric motor to assist the driver of a vehicle. This is unlike traditional systems that act on hydraulic pressure provided via a pump driven by the vehicle's engine. This pump is constantly running, whether the steering wheel is being turned or not. Its continuous operation continually places a load on the engine, adversely affecting the vehicle's fuel consumption.
How It Works
In ESP’s, an electric motor that is mounted on either the steering column or steering gear applies torque to the steering column. They, therefore, assist the driver in turning the steering wheel. There are sensors that detect the position of the steering wheel and any input from the driver. Any turn on the wheel to change the vehicle's direction is, therefore, picked up accurately.
A control module applies assistive torque via the electric motor. If the driver is holding the wheel steady, at the straight-ahead position, the system doesn't provide any assistance. Electric power steering does have some tricks up its sleeve. It offers the advantage of an improved fuel economy. Being electronic and computer-controlled the EPS system can be programmed for many different attributes.
Engineers can now program variable assistance for different modes. At parking speeds, for example, maximum assistance delivers easier maneuvering in and out of parking bays.
Also, at highway speeds, the steering assistance is reduced to enhance vehicle stability. There is a bit of resistance built into the steering at open-road speeds. This is to ensure the car doesn’t dart around due to the driver over-correcting.
Other Functions Performed by the ESP
There are also few other specialized functions that can be performed by the EPS. It could be programmed to support the vehicle's active safety systems, such as Lane Keep Assist. Different manufacturers have different naming conventions, however, it is basically where a camera or laser recognizes the road markings. This is so that when the vehicle drifts out of a lane the steering is activated to bring the vehicle back into the lane.
Other functions are more subtle. These include camber control to hold the vehicle against the camber without the driver realizing it. This is because the steering wheel requires less effort to hold. It is also possible to dampen out vibrations caused by bumps and potholes that travel up the steering column. There will be minor changes to the steering effort required to hold the steering wheel straight because of this feature.
Electronic steering has been said by many to “lack feel” in comparison to hydraulic steering due to reduced feedback in the steering wheel as the motor holds the steering in a fixed position with metal gears, unlike the hydraulic fluid which has a small degree of flexibility (compression) allowing subtle details of the road to be felt through the steering wheel while driving.
Manufacturers are constantly striving to improve the perceived lack of feel and some progress has been made in this area. Watch this to see a detailed breakdown of how electric power steering systems work.
Electro-hydraulic Power Steering
Electro-hydraulic power is a combination of both electric and hydraulic power steering systems. The main difference, however, is how the hydraulic pump that supplies the pressure necessary for the power steering is driven. In an electro-hydraulic power steering, an electric motor drives the pump, which is controlled according to the required assisting steering force.
When the vehicle is at low speed or not moving at all, the delivery of the hydraulic pump is increased. This is to provide a large amount of steering power and reduced the effort of the driver. At high speeds, however, the pump rotational speed is reduced because assistance is not necessary.
Electro-Hydraulic Power Steering System[/caption]Electro-hydraulic power steering has an advantage over electric power steering due to improved comfort and feel. When maneuvering, steering is light to handle. But at high speeds, steering is firm. This enhances overall fuel economy, as the power uptake adjusts as required. To read more on types of power steering systems, click here
What is the difference between hydraulic steering and electric power steering?
A hydraulic power steering uses the laws of hydraulic to reduce the load on the driver. It has a pump that powers the hydraulic mechanism of the steering system. Electric power steering, on the other hand, uses sensors and a stepper motor to move the wheels in the direction of the steering. It is efficient, light, and uses much less power than the hydraulic system. image hydraulic vs electric power steering
Advantages of electric power steering over hydraulic power steering and vice versa
- Electronic power steering assistance has some advantages in that it is more on-demand and therefore efficient. Your level of assistance can be more easily tuned and varied based on factors like speed, turn-in angle, etc. Electronic assistance is also more compact overall. There is a motor mounted directly to the steering rack. No separate pump, hoses, cooler, reservoir, etc. This can help shrink the front profile of the engine to a degree by removing an accessory from the drive.
- Hydraulic power steering has the advantage of undergoing development over a long period of time. It is smooth, offers a high degree of “road-feel” and it is very well-proven.
- Electronic power steering has very low power consumption and a lower effort at low engine speed. It is also very reliable and accurate.
- Hydraulic power steering is cheap, a lot of people think it has a better steering feel.
Disadvantages of electric power steering over hydraulic power steering and vice versa
- Electronic power steering assistance has some disadvantages. One of them is the fact that the motor is connected to the rack mechanism via a toothed rubber belt making it not easily visible for inspection. Tuning the degree of assistance can be tricky. Another is a common complaint from drivers for a lack of “road-feel” through the steering. This system also demands the use of more sensors, control systems, feedback circuits, etc.
- Hydraulic systems have their disadvantages as well. The pump turns any time the engine is ON. This creates pumping losses as there is fluid circulating, whether there is demand or not. There are some losses, but it is infinitesimal. It also provides you with another fluid-filled system to maintain. Believe it or not, power steering fluid (be it ATF, engine oil, or actual PS Fluid) is a service item. Fluid breaks down. Hoses break down. Pumps wear. Steering gears or racks wear. Metal and rubber become suspended in the fluid accelerating wear.
As the technology enhances, a lot of the complaints about the electronic system are being addressed and will be addressed. For instance, there are currently sports cars that have the system and have excellent “road-feel”. Electrical systems are more efficient but place a higher technological demand on the vehicle. Hydraulic systems are less efficient, but are very basic and well understood.
Can a car still be steered even after the power steering has failed?
The answer is yes. A car can be steered when the power steering fails. If it is an electric power steering system, most of the steering ability would function normally. The effort required will be more than a similar car that uses hydraulic power steering.
Things could be worse if the system is a hydraulic power steering because the steering effort would be much higher. Most times you would also experience inconsistencies in steering. In some cases, the effort needed is more, while in other cases, it is less. These inconsistencies could cause loss of control and in worse cases result in accidents.
What do I do when my power steering fails?
What next? You should park your car and contact an auto mechanic. However, if you need to take the car to a nearby workshop without power steering, follow these precautions:
- Make sure you drive slower than normal speeds.
- Pay rapt attention to the road and avoid disturbances.
- Place both hands on the steering wheel. Also expect the chances of steering suddenly changing to left or right (Potholes, Irregularities in road)
- Increase the air pressure of front tires so that friction reduce making steering effortless.
- Both power steering systems are good.
- To have the best of both worlds go for electro-hydraulic Power Steering.
- Driving with a failed power steering system is bad.
- Try to fix a faulty power steering system as soon as possible.