Types of Steering Systems
Some steering gears provide variable ratio steering. This allows the steering ratio to change, or vary, as the steering wheel is turned away from its straight-ahead position. A typical change might be from 16:1 to 13:1. For the first 40 degree of steering wheel movement in either direction, the steering ratio remains constant. This faster steering ratio offers more control for highway driving. As the steering wheel is turned beyond 40 degrees from the straight ahead position, the steering ratio decreases. This lower and slower steering ratio helps the driver in city driving when cornering or parking. The steering wheel doesn't have to be turned as far in order to pivot the wheels.
A small number of cars use a four-wheel steering system. In this type of system, the rear wheels turn as well as the front wheels. The purpose is to provide greater handling control and greater ability to make tight turns. The rear wheels of a four-wheel steering system can be controlled either mechanically or electronically. In order to provide more control at low speeds, the rear wheels may pivot in the opposite direction as the front wheels, allowing the rear of the car to pivot more. This can be useful in tight spaces or when parking. At higher speeds, the rear wheels will steer in the same direction as the front wheels, providing greater stability during cornering and high-speed lane changes.
- The manual steering system :
The manual steering system has four major components. First, the steering wheel and steering shaft are the "input" portion of the steering system. This allows the driver to input steering commands.
Then, the steering gear connection changes the rotary motion of the steering shaft into linear motion (left and right motion). The steering gear translates the input commands of the steering wheel and shaft into "output" commands.
Another component is the steering linkage, which connects the steering gear to the steering arms. Since the wheels are attached rigidly to the steering arm assemblies, the wheel turns whenever the steering arms move to the right or left. The steering motion that connects the steering gear to the wheels involves linkage that handles steering "output."
Finally, the steering arms are part of the wheel mounting assembly. Steering arms are basically extended lever arms that connect the wheel to the steering linkage.
- A power steering system :
A power steering system uses a device that assists the steering effort. This makes it easier for the driver to turn the steering wheel. A power-assist steering system multiplies the force that the driver applies at the steering wheel.
The most common type of power assist is the hydraulic type. This features a hydraulic pump (a power steering pump) that pressurizes hydraulic fluid to the steering gear system, helping the driver to move the gears. In some cases, a vehicle might be equipped with electronic power steering, where an electric motor provides the power assist.
- A hydraulic power steering systems :
All hydraulic power steering systems basically work in the same way. A hydraulic pump pressurizes the hydraulic fluid. Through hydraulic hoses and tubes that attach the power steering pump to the steering gear, this pressurized fluid is then made available to the steering gear when it's needed. When the steering wheel is turned, the control valve in the power steering gear opens and closes various fluid passages inside the gear housing. The pressurized fluid enters the gear housing, causing the piston to move, which places hydraulic force at the gears, helping them to move. This power assist reduces the amount of steering effort needed by the driver.
Many vehicles today use speed-sensitive power steering. This is a variable-assist system that uses an electronic control to decide how much power assist is needed at any given time. Additional parts in this type of system may include a special electronic control module (ECU) called a power steering control module, a steering angle sensor, vehicle speed sensor, and solenoid valve. Some cars will not use a steering angle sensor, and will only use the vehicle speed sensor signal to provide input to the ECU.
If a steering angle sensor is included, this sensor detects the rate of steering wheel movement, and the vehicle speed sensor detects vehicle road speed. These signals are inputs that go to the electronic controller. In turn, the controller decides how much steering assist is needed, and sends a signal to the solenoid valve. Cars equipped with a variable assist power steering system will feature a separate diagnostic connector at the steering ECU, allowing the technician to retrieve diagnostic codes for this system. Electronic variable power assist can be found on vehicles with either rack and pinion steering or recirculating ball steering.
- A mechanical four-wheel steering system :
A mechanical four-wheel steering system features a mechanical connection between the front steering gear and rear steering gear. This may be done with a long steering shaft that connects to a pinion output shaft at the front rack, and to a special rear steering gear. The rear steering gear is then connected to each rear wheel by a rear tie rod. During small input turns of the steering wheel, such as during highway driving, the rear wheels are steered by a small amount, in the same direction as the front wheels. When the steering wheel is turned more during low speed operation, the rear wheels will turn in the opposite direction as the front wheels.
- An electronic four-wheel steering system :
An electronic four-wheel steering system uses an additional power steering pump for the rear steering gear, and a separate rear control valve assembly for the rear. When the steering wheel is turned, the hydraulic pressure that is applied to the front steering gear acts on the rear steering system's control valve. This directs pressurized fluid to move from the rear power steering pump to the rear power cylinder. The power cylinder then forces the rear trailing arms to move right or left. In this type of system, the rear wheels always move in the same direction as the front wheels, up to a maximum of 1.5 degrees. The rear wheel steering angle changes in proportion to vehicle speed, wheel traction and steering wheel input. Some cars may use electromechanical four-wheel steering. This features a mechanical connection, using a steering shaft that connects the front steering gear to the rear steering gear. In addition, the ECU sends control signals to the rear steering gear. At low speeds, the rear wheels will turn in the opposite direction of the front wheels, and at high speeds, the rear wheels turn in the same direction as the front wheels.