What is Power Steering?
A power steering is a mechanical device equipped on a motor vehicle that helps drivers steer the vehicle by augmenting the steering effort needed to turn the steering wheel, making it easier for the vehicle to turn or maneuver at lower speeds.
Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver can provide less effort to turn the steered wheels when driving at typical speeds and reduce considerably the physical effort necessary to turn the wheels when a vehicle is stopped or moving slowly.
Power steering can also be engineered to provide some artificial feedback of forces acting on the steered wheels.
Hydraulic power steering systems for cars augment steering effort via an actuator, a hydraulic cylinder that is part of a servo system. These systems have a direct mechanical connection between the steering wheel and the linkage that steers the wheels.
This means that power-steering system failure (to augment effort) still permits the vehicle to be steered using manual effort alone.
Electric power steering systems use electric motors to provide assistance instead of hydraulic systems. As with hydraulic types, power to the actuator (motor, in this case) is controlled by the rest of the power steering system.
Other power steering systems have no direct mechanical connection to the steering linkage; they require electrical power. Systems of this kind, with no mechanical connection, are sometimes called “drive by wire” or “steer by wire”, by analogy with aviation’s “fly-by-wire”.
In this context, “wire” refers to electrical cables that carry power and data, not thin wire rope mechanical control cables.
History
The first power-steering system fitted to a production car debuted in the 1951 Chrysler Imperial, and the competition quickly followed suit.
Not only did power steering do the obvious allow the driver to steer a heavy vehicle with much less effort and greater comfort but it also allowed engineers to improve steering response, which is how quickly the car changes direction when the driver turns the wheel.
Before power assist became available, cars’ steering systems had been geared so that it took many turns of the wheel to negotiate tight turns or to park.
This slow gearing gave drivers more leverage against the high effort required to steer the front wheels. But the advent of power steering allowed engineers to quicken the steering ratio.
How much the steering wheel has to be turned relative to how much the angle of the front wheels changes because the additional steering effort could now be offset by the new system. In fact, it was more than just offset; steering a car became nearly effortless.
How Does Power Steering Work?
The power steering system uses intermediate electric or hydraulic devices to reduce the effort necessary to steer the front wheels of the vehicle side to side. It multiplies the force applied by the driver through the steering wheel to achieve a smooth and quick directional change of the vehicle.
The power steering system relies on several mechanical parts. Power steering systems function to provide easier maneuverability and a better degree of control over the vehicle, making driving all the more effort-free. It is sometimes referred to as the steering assist system or SAS. Without it, steering would be physically strenuous and challenging to perform.
Power steering systems can either be hydraulic, electric or a combination of the two. Steering a vehicle involves getting its front wheels to turn synchronously, either to the left or right. This is achieved with the help of different gear systems. The two main steering gear systems are the rack and pinion and the recirculating ball steering gear.
The power steering system uses intermediate electric or hydraulic devices to reduce the effort necessary to steer the front wheels of the vehicle side to side. It multiplies the force applied by the driver through the steering wheel to achieve a smooth and quick directional change of the vehicle.
Your car will respond immediately to even the smallest of adjustments you make, and it is easier to stay in your lane when you’re driving in traffic and carrying out complicated parking maneuvers.
How Does Hydraulic Power Steering Work?
Hydraulic power steering systems work by using a hydraulic system to multiply the force applied to the steering wheel inputs to the vehicle’s steered (usually front) road wheels. The hydraulic pressure typically comes from a generator or rotary vane pump driven by the vehicle’s engine.
A double-acting hydraulic cylinder applies a force to the steering gear, which in turn steers the roadwheels. The steering wheel operates valves to control flow to the cylinder.
The more torque the driver applies to the steering wheel and column, the more fluid the valves allow through to the cylinder, and so the more force is applied to steer the wheels.
How Does Electric Power Steering Work?
Electric power steering (EPS) or motor-driven power steering (MDPS) uses an electric motor rather than a hydraulic system to assist the driver of a vehicle.
Sensors detect the position and torque of the steering column, and a computer module applies assistive torque via the motor, which connects to either the steering gear or steering column. This allows varying amounts of assistance to be applied depending on driving conditions.
Engineers can therefore tailor the steering-gear response to variable-rate and variable-damping suspension systems, optimizing ride, handling, and steering for each vehicle.
On Fiat group cars the amount of assistance can be regulated using a button named “CITY” that switches between two different assist curves, while most other EPS systems have variable assist. These give more assistance as the vehicle slows down, and less at faster speeds.
Types of Power Steering
Following are the Types of Power Steering Systems:
- Hydraulic Power Steering.
- Electro-Hydraulic Power Steering.
- Electric Power Steering or Motor-Driven Power Steering.
All three power steering systems perform the same important function, but they execute it differently. A hydraulic system uses mechanically pumped high-pressure fluid, an electro-hydraulic system uses an electric motor to pressure fluid, and an electric system uses an electric motor and sensors.
The end result is the same: You can easily turn the steering wheel under all conditions. Fully electric power steering systems save about one mile per gallon, require less maintenance, and are more reliable than a hydraulic system.
1. Hydraulic Power Steering
This system uses pressurized power steering fluid, supplied by the power steering pump, to decrease steering effort. An engine-driven accessory drive or serpentine belt turns on the pump and directs high-pressure power steering fluid via the high-pressure hose to the input side of the power steering gear-control valve.
High pressure acting on the control valve assists the driver when turning the front wheels. Power steering fluid is stored in a reservoir. The proper fluid level in the reservoir is maintained when the fluid returns from the steering gear at much lower pressure.
Hydraulic power steering systems continuously pump fluid and are susceptible to engine speed high revolutions per minute equal high-pressure output, lower revolutions per minute equal low-pressure output. To maintain constant pressure, a power steering pump uses a bypass valve to maintain constant pressure no matter what the engine speed.
2. Electro-Hydraulic Power Steering
These systems employ a brushless electric motor to drive the hydraulic power steering pump instead of an engine-driven accessory drive or serpentine belt.
This system operates the same and provides the same feel as a conventional hydraulic power steering system.
3. Electric Power Steering or Motor-Driven Power Steering
This system eliminates hydraulics and pressurized fluid from the system. When the driver turns the steering wheel, a brushless bi-directional permanent magnet motor connected to the steering gear or steering column turns the front wheels. Sensors detect which way the steering wheel is turned to assist the movement of the steering gear in the correct direction.
No matter what kind of system you have, power steering only acts on the steering gear when the driver turns the wheel.
Advantages of Electric Power Steering
Hydraulic power steering systems are complex, heavy, require maintenance, and take up a lot of space. Electric power steering uses considerably fewer parts.
Using steering angle and steering torque sensors, plus sophisticated software, engineers can adjust the amount of assist, but also how the steering feels to the driver by reproducing different road feel characteristics for different driving conditions. And hydraulic power steering uses 90 percent more engine power than electric power steering.
Because an electric power steering system draws significantly less power from the engine, it greatly improves fuel economy and reduces tailpipe emissions. And removing a drive pulley and belt from the engine reduces wear and tear. This will prolong the engine’s life and help reduce costly repairs.
Advantages of Power Steering
Following are the advantages of power steering:
- It prevents the wheel from transferring the loading to the steering column.
- Power steering reduces driver fatigue.
- It lowers the input torque and continuous steering function.
- In power steering, the oil output is directly proportional to steer speed.
Disadvantages of Power Steering
Following are the disadvantages of power steering
- The design of the power steering is complicated.
- Power steering is costly than the manual steering
- It has a fluid leakage problem.