Contents: Rack and pinion steering with… ↧ Power steering with variable… ↧ Controller ↧ Rack and pinion steering with… ↧ Power steering pump ↧
Rack and pinion steering with hydraulic booster
A rack and pinion power steering system has a rotary control valve that directs hydraulic fluid from the hydraulic pump to one side or the other of the rack plunger. The integral rack plunger is connected to the rack. The rack plunger converts hydraulic pressure into a linear force that moves the rack left or right. This force is then transmitted through the tie rods to the steering knuckles, which turn the wheels.
If the power steering is not functioning, the rack and pinion steering mechanism is controlled mechanically, but in this case, greater efforts are required for steering. The rotation of the steering wheel is transmitted to the pinion. The rotational movement of the pinion is transmitted to the worm of the pinion, the threads of which are caught on the teeth of the rack, thus causing a linear movement of the rack.
A vane type hydraulic pump provides pressure for both steering systems.
Power steering with variable assistance depending on speed
The speed-sensitive power steering (SSPS) system varies the amount of effort required to turn the steering wheel as the vehicle speed changes. At low speeds, the system provides maximum assistance to make turns and parking maneuvers easier. At high speeds, the steering assistance is reduced to provide tighter steering and improve directional stability. The SSPS system accomplishes this by regulating the current (-3 ~ 3 A) supplied to the electromagnet coil of the electric power steering gear as the vehicle speed increases. When the vehicle is stationary, the SSPS system provides maximum assistance to the steering gear. As the vehicle speed increases, the steering assistance to the steering gear is reduced.
Controller
The SSPS controller processes vehicle speed information transmitted from the ABS controller to the solenoid coil located on the electric power steering assembly.
Rack and pinion steering with hydraulic booster
Except for the difference in valve processing, the design of the rack and pinion steering gear with SSPS is similar to that of the steering gear without SSPS. The rotation of the steering wheel is transmitted to the pinion via an intermediate shaft. The pinion moves the rack left or right by meshing the teeth of the pinion and the rack. This force is then transmitted through the tie rods and steering knuckles to the steered wheels.
The rack and pinion power steering system has a rotary control valve that directs hydraulic fluid from the hydraulic pump to one side or the other of the rack plunger. The plunger, which is connected to the rack, converts the hydraulic pressure into left or right movement of the rack. The rotary control valve adjusts the assistance based on driver torque.
If the hydraulic booster does not function, the mechanical steering works. However, in this case, more effort is required to steer.
Power steering pump
Standard vane type hydraulic pump that creates hydraulic pressure for the system.
System operation
The system operation starts with an input signal from the vehicle speed sensor through the ABS controller to the SSPS controller. The SSPS controller sends a signal to the SSPS actuator to change the level of reactive force produced by the solenoid coil.
Operation of the circuit
The SSPS system uses input signals from the ABS controller to the SSPS controller to determine the required amount of force applied by the electric power steering mechanism.
The SSPS controller continuously compares the current flowing through the SSPS actuator with its calculated value. The SSPS actuator has an electromagnet winding that can control the reactive force supplied to the steering torsion bar. The SSPS controller can vary the current flowing through the SSPS actuator by changing the output duty cycle.
The SSPS controller can detect faults in itself, the SSPS actuator, or circuits of such components. Any fault detected causes the steering assist to remain at its maximum level at all times, as the needle assumes its normally extended position at all speeds.
When the system is operating normally, the steering assist is reduced as the speed increases, giving the driver a better feel for the road and improving directional stability.
[Information taken from the official website: «ChevyMan»]