DESCRIPTION
This vehicle is equipped with power steering as standard equipment. There are two different steering systems available, a standard and a special ACR/R/T system. The power steering system consists of these major components
- POWER STEERING PUMP
- POWER STEERING GEAR
- POWER STEERING FLUID RESERVOIR
- POWER STEERING FLUID PRESSURE HOSE
- POWER STEERING FLUID RETURN HOSE
- POWER STEERING FLUID COOLER
For information on the these components, refer to their respective sections within this article.
OPERATION
Turning of the steering wheel is converted into linear (side-to-side) travel through the meshing of the helical pinion teeth with the rack teeth within the steering gear. The lateral travel pushes and pulls the tie rods to change the direction of the vehicle's front wheels.
Power assist steering is provided by a belt driven rotary type pump. It directs fluid through power steering fluid hoses to the power steering gear where it is used to assist the driver's turning effort.
Manual steering control of the vehicle can be maintained if power steering assist is lost. However, under this condition, steering effort is significantly increased.
The power steering gear is mounted on the front suspension crossmember. (Scheme 6) The outer ends of the outer tie rods attach to the steering knuckles.
Scheme 6
There are two different type power steering gears used on this vehicle, a standard, and an optional which is used on the ACR and R/T vehicles. Externally the gears appear the same. Internally, the standard has a 16:1 turning ratio while the ACR/R/T gear has an 18:1 turning ratio. The gear used on ACR and R/T vehicles also has a restricted lateral (lock-to-lock) travel range to accommodate the R/T wheel and tire combination. Sport feel valve coding provides ACR/R/T vehicles with more firm feel steering to match the performance tire compounding and construction.
Note. The power steering gear should not be serviced or adjusted. If a malfunction or oil leak occurs with the steering gear, the complete steering gear needs to be replaced.
Turning of the steering wheel is converted into lateral (side-to side) travel through the meshing of the helical pinion teeth with the rack teeth located in the steering gear. This lateral travel pushes and pulls the tie rods to change the direction of the vehicle's front wheels.
Power assist is provided by a pump and is controlled by an open center, rotary type control valve. It directs fluid to either side of the gear's integral steering rack piston. Depending on the rotation of the steering wheel, more fluid pressure is directed to one side of the rack piston compared to the other.
Road feel is controlled by the diameter of a torsion bar which initially steers the vehicle. As steering effort increases, as in a turn, the torsion bar twists causing relative rotary motion between the rotary valve body and valve spool. This movement restricts fluid flow to one side of the integral rack piston and redirects fluid behind the other side of the integral rack piston, building up hydraulic pressure, thus assisting in the turning effort.
A power steering pressure switch is used to improve the vehicle's idle quality. The pressure switch improves vehicle idle quality by causing a readjustment of the engine idle speed as necessary when increased fluid pressure is sensed in the power steering system.
The pressure switch functions by signaling the powertrain control module that an increase in pressure of the power steering system is putting additional load on the engine. This type of condition exists when the front tires of the vehicle are turned while the vehicle is stationary and the engine is at idle speed. When the powertrain control module receives the signal from the power steering pressure switch, it directs the engine to increase its idle speed. This increase in engine idle speed compensates for the additional load, thus maintaining the required engine idle speed and idle quality.
The power steering pressure switch is mounted directly to the power steering gear. (Scheme 7)
Scheme 7
The switch provides an input to the PCM during periods of high pump load and low engine RPM; such as during parking maneuvers.
When power steering pump pressure exceeds 2758 kPa (400 psi), the switch is open. The PCM increases idle air flow through the IAC motor to prevent engine stalling. The PCM sends 12 volts through a resister to the sensor circuit to ground. When pump pressure is low, the switch is closed.
The hydraulic pressure for operation of the power steering gear is provided by a belt driven power steering pump manufactured by TTA. (Scheme 8) The constant flow rate and displacement vane-type power steering pump is located on the front corner of the engine.
Scheme 8
No repair procedures are to be done on the internal components of the power steering pump. The only serviceable components of the power steering pump are the power steering pump pulley and the pump itself. The power steering fluid reservoir is serviced with the pump.
Because of unique shaft bearings, flow control levels or pump displacements, power steering pumps may be used only on specific vehicle applications. Be sure that all power steering pumps are only replaced with a pump that is the correct replacement for that specific application.
OPERATION - POWER STEERING PUMP
Hydraulic pressure is provided for operation of the power steering gear by the belt driven, constant displacement, vane type power steering pump. The power steering pump is connected to the steering gear by a power steering fluid pressure hose and return hose.
Rectangular pumping vanes in the shaft driven rotor move power steering fluid from the intake to the cam ring pressure cavities of the power steering pump. As the rotor begins to turn, centrifugal force throws the vanes against the inside surface of the cam ring to pickup residual oil. This oil is then forced into the high pressure area. As more oil is picked up by the vanes, the additional oil is forced into the cavities of the thrust plate through two crossover holes in the cam ring and pressure plate. The crossover holes empty into the high pressure area between the pressure plate and the housing end cover.
As the high pressure area is filled, oil flows under the vanes in the rotor slots, forcing the vanes to follow the inside surface of the cam ring. As the vanes reach the restricted area of the cam ring, oil is forced out from between the vanes. When excess oil flow is generated during high-speed operation, a regulated amount of oil returns to the pump intake side through a flow control valve. The flow control valve reduces the power required to drive the pump and holds down temperature build-up.
When steering conditions exceed maximum pressure requirements, such as when the wheels are turned against the stops, the pressure built up in the steering gear exerts pressure on the spring end of the flow control valve. The high pressure lifts the relief valve ball from its seat and allows oil to flow through a trigger orifice located in the outlet fitting. This reduces pressure on the spring end of the flow control valve which then opens and allows the oil to return to the intake side of the pump. This action limits maximum pressure output of the pump to a safe level.
Under normal power steering pump operating conditions, pressure requirements of the pump are below maximum, causing the pressure relief valve to remain closed.
In the event of a power steering pump drive belt failure, manual steering control of the vehicle can still be maintained. However, under these conditions, steering effort will be significantly increased.
STANDARD PROCEDURE - POWER STEERING PUMP INITIAL OPERATION
| WARNING | Fluid level should be checked with the engine off to prevent injury from moving components. |
| CAUTION | Use only Mopar® ATF+4 Automatic Transmission Fluid (MS-9602). DO NOT overfill. |
Wipe the filler cap clean, then check the fluid level. The dipstick should indicate FULL (optimum level is at the FULL line) when the fluid is at normal temperature, approximately 21°C to 27°C (70°F to 80°F).
- Fill the power steering fluid reservoir to the proper level and let the fluid settle for at least two minutes.
- Start the engine and let run for a few seconds, then turn the engine off.
- Add fluid if necessary. Repeat the above procedure until the fluid level remains constant after running the engine.
- Raise the front wheels off the ground.
- Start the engine. Slowly turn the steering wheel right and left, lightly contacting the wheel stops.
- Add power steering fluid if necessary.
- Lower the vehicle and turn the steering wheel slowly from lock to lock.
- Stop the engine. Check the fluid level and refill as required.
- If the fluid is extremely foamy, allow the vehicle to stand a few minutes and repeat the above procedure.
All models of this vehicle are equipped with a cooler for the power steering system fluid. (Scheme 9) The purpose of the cooler is to keep the temperature of the power steering system fluid from rising to a level that would affect the performance of the power steering system.
Scheme 9
The power steering fluid cooler is located at the front of the front suspension crossmember. It is mounted to the crossmember top surface using 2 fasteners.
The cooler is placed in series with the power steering fluid return hose, between the steering gear fluid outlet port and the fluid return hose leading to the power steering fluid reservoir. The power steering gear has a steel fitting attached to its outlet port that a short hose leading to the cooler is pushed onto. This hose is secured to both the steering gear outlet fitting and the cooler using standard adjustable clamps. The cooler is secured to the power steering fluid return hose using a standard adjustable clamp.
The cooler used on this vehicle is referred to as a fluid-to-air type cooler. This means that the air flow across the tubes of the cooler is used to extract the heat from the cooler which it has absorbed from the power steering fluid flowing through it. Utilizing a small air dam mounted to its base to redirect air across its coils, the cooler lowers the temperature of the power steering fluid prior to it entering the power steering fluid reservoir where it is resupplied to the power steering pump.
Power steering fluid reservoir is mounted on the power steering pump. (Scheme 8) This power steering fluid reservoir is considered an integral part of the power steering pump and is not serviced separately.