Bendix Commercial Vehicle Systems COMPACT 500 9/87 User Manual

COMPACT 500 INTEGRAL HYDRAULIC POWER STEERING GEAR FOR FORD MOTOR CO. CARGO VEHICLES

SD-30-4250

I. DESCRIPTION

The Compact 500 Hydraulic Power Steering gear is designed for heavy duty vehicles with front axle weight ratings of up to 15,000 lbs. It is an integral power steering gear incorporating the mechanical and hydraulic actuation and control components in a single cast housing which serves as the power cylinder.

The vehicles steering column is coupled to the gear at the input shaft which transmits steering effort through a recirculating ball screw and piston nut. The piston nut is an integral part of the power assist piston and also acts as a steering damper. The direction and degree of power assist is controlled by a rotary hydraulic valve which is integral to the input shaft and supplied by an engine driven hydraulic pump.

This valve design assures light, responsive steering while maintaining a mechanical connection between the steering column and the ball screw.

II. OPERATION

GENERAL

The C-500 integral power steering gear is composed both of mechanical steering components and hydraulic power assist components. Actual steering is accomplished mechanically. Effort applied at the vehicles steering wheel results in mechanical movement within the steering gear which causes the vehicle to change its direction of travel. The hydraulic power assist components function solely to reduce the effort required to turn the vehicles steering wheel. Loss of hydraulic power will in no way prevent the vehicle from being maneuvered mechanically, however greater effort will be required to turn the steering wheel.

MECHANICAL OPERATION

The turning effort exerted by the driver on the steering wheel is transmitted to the input shaft which is part of the ball screw assembly. The ball screw and piston nut function like

TABLE OF CONTENTS

Page No.

I. DESCRIPTION 2

II. OPERATION 2-4

1. General 2

2. Mechanical Parts 2

3. Hydraulic Parts 2, 3

4. Power Steering Identification 4

III. TECHNICAL DATA 4

IV. PREVENTIVE MAINTENANCE 4-5

1. Power Steering Oil 4

2. Draining and Filling the System 4

3. Change Intervals 5

4. Output Shaft Sector Teeth Adjustment 5

5. Output Shaft Boot Seal 5

V. CAUTION NOTE 5

VI. REMOVAL 6

VII. SPECIAL TOOL REQUIREMENTS 6-7

VIII. DISASSEMBLY 9-16

1. General 9-11

2. Piston 11-13

3. Main housing 13

4. Side cover 13

5. Valve Body 14

6. Pressure Relief Valve 15

7. Output shaft 16

8. Cleaning 16

9. Inspection 16

IX. REASSEMBLY 16-23

1. Valve body 16-17

2. Spindle assembly 17-18

3. Piston 19-20

4. Main housing 21

5. Housing and valve body 21

6. Output shaft 21

7. Side cover 22

8. Housing and side cover 23

9. Adjustment of output shaft backlash 23

X. PRESSURE, FLOW & LEAKAGE TESTS 23-25

1. Relief Pressure Test - Power Steering Pump 24

2. Relief Pressure Test - Power Steering Gear 24-25

XI. TROUBLESHOOTING 25-27

LEFT TURN RIGHT TURN

BALL SCREW

PISTON NUT

RECIRCULATING

BALLS

PITMAN ARM

POWER CYLINDER

FIGURE 1 - MECHANICAL OPERATION

PISTON NUT

RECIRCULATING

a screw and nut through the action of the chain of recirculating balls that serve as an interface. Rotation of the ball screw causes axial movement of the piston within the power cylinder. Gear teeth cut directly into the piston mesh with corresponding sector gear teeth on the output shaft and as the piston moves, the output shaft and attached pitman arm are rotated.

HYDRAULIC OPERATION

The driven end of the ball screw rotates on a ball bearing contained in the valve body. Hydraulic pressure enters and exits the power steering gear through lines connected to threaded ports in the valve body. A pressure relief valve contained in the valve body prevents overpressurization of the power steering gear.

Hydraulic pressure in excess of the setting of the relief valve causes the valve to open a channel to the reservoir return side of the gear.

STEERING

WHEEL

SPINDLE

BALLS

PITMAN

ARM

The coarse splines form mechanical stops which limit the amount of relative rotation between the ball screw and input shaft. A torsion bar connects the input shaft to the ball screw. Six evenly distributed longitudinal grooves are machined into the outer surface of the input shaft and correspond to six grooves machined into the bore of the ball screw. Holes extend from the outside surface of the ball screw into the six grooves in the bore. These holes allow pressurized oil to enter and exit the two inner elements of the rotary control valve. The six grooves in the bore of the ball screw are connected alternately to each side of the piston through three pairs of the drilled holes. The other three holes admit pressurized oil directly to three of the six grooves in the input shaft. The other three grooves in the output shaft carry oil to the return line connection. The length of the six pairs of grooves cut into the ball screw and input shaft allows large pressure changes to be achieved with a small rotational displacement of the valve elements.

The ball screw assembly is retained in the valve housing by a valve nut which forms the outermost element of the rotary control valve. The valve nut contains circular channels and radial passages which serve to direct hydraulic oil into and out of the rotary control valve. The ball screw assembly forms the rotary control and consists of three parts; the input shaft, torsion bar, and ball screw.

One end of the input shaft is finely splined for connection to the steering column while the other end has a coarse spline which fits loosely with a similar spline inside the worm screw.

The rotary control valve is an open center type which allows a continuous flow of oil (through the longitudinal grooves in the input shaft and bore of the ball screw) when held in the neutral position by the torsion bar. The large porting of the valve design allows neutral position operating pressure to remain in the 40-65 psi range which results in reduced hydraulic pump power consumption and lower oil temperatures.

When steering effort is applied, the input shaft and ball screw tend to turn in unison however the spring action of the torsion

CIRCULAR GROOVES

BY PASS

VALVE

INPUT

SHAFT

VALVE NUT

OIL IN

ROTARY

VALVE

SUPPLY

OUTPUT

SHAFT

PISTON

SEAL AND

GLIDE RINGS

FIGURE 2

bar results in the input shaft rotating slightly in advance of the ball screw. The six pairs of grooves that form the rotary control valve are displaced from their neutral flow position. As steering effort increases so does the amount of displacement. Depending on the direction steered, the groove displacement of the input shaft directs hydraulic oil through

OIL OUT

DELIVERY FROM

ROTARY VALVE

SPINDLE ASSEMBLY W/

ROTARY VALVE (BALL

SCREW ASSEMBLY)

OIL PASSAGE

DRAIN PLUG

the appropriate drilled passages in the ball screw to one side or the other of the piston. Hydraulic pressure acting upon the piston surface eliminates much of the pistons resistance to movement. Spring force exerted by the torsion bar causes the ball screw to rotate as piston resistance is removed. As the ball screw rotates, the relative groove

FIGURE 3

BY PASS

VALVE

OIL INLET

CONNECTING POLE

MECHANICAL

MOVEMENT PARTS

MECHANICAL-

HYDRAULIC PARTS

PARTS WITH NO

MOVEMENT

INPUT SHAFT

BEARING

OIL OUTLET

CIRCULAR GROOVES

LONGITUDINAL

GROOVES

TORSION BAR

BALL SCREW

STRAIGHT AHEAD RIGHT TURNLEFT TURN

FIGURE 4 - SCHEMATIC OF THE ROTARY VALVE OPERATION

RETURN

BY-PASS

VALVE

PUMP

displacement is eliminated and the rotary valve returns to a neutral position.

Moderate effort at the steering wheel produces smaller valve displacements and lower power assist, thus providing good steering feel. At increased displacements the pressure rises more rapidly giving increased power assistance and quicker response. Maximum pressure is developed after approximately 3' displacement giving a direct feel to the steering. Groove displacement is limited by the freeplay of the stop spline mesh between the input shaft and ball screw. The splines take up the steering movement while allowing the torsion bar to hold the groove displacement. The torsion bar and stop splines form two parallel means of transmitting the steering torque. When no steering torque is applied, the torsion bar returns the valve grooves to a neutral position allowing the pressurized oil to flow to the return line.

Power assisted movement of the piston nut within its bore is limited by poppet valves installed in both piston faces. When the piston approaches its extreme travel in either direction, the stem of the limiting poppet valve makes contact at the end of the piston bore. As piston travel continues, the limiting poppet is unseated and some hydraulic power assist is removed as pressurized oil is diverted to the return line. As more and more power assist is removed by the action of the limiting poppet valves, steering effort increases. The piston can travel to the extreme ends of its bore, however, the maximum steering assistance available is reduced to protect the steering components in the axle.

in operation. Oil displaced from one side of the piston is essentially transferred to the other side which prevents reservoir flooding and cavitation in the pressure line.

The pressure relief valve is located in the valve body and limits internal hydraulic pressure to a preset maximum. The pressure relief valve can be set to various pressures, however its setting is 150 p.s.i. lower than the power steering pump relief valve setting.

POWER STEERING GEAR IDENTIFICATION

A nameplate is installed adjacent to one of the mounting lugs of the unit which indicates part number, serial number and build date.

III. TECHNICAL DATA

- Steering ratio ........................................................... 21:1

- Number of turns of the steering wheel ..................... 5.25

- Turning angle on the output shaft .......................90° + 2°

- Output shaft torque obtained with an effective pressure of

1885 p.s.i. (132.5Kg/cm2) .......... 41,947 in.-Ibs (474 m/Kg)

- Hydraulic oil ............................................... Ford part no.

(Ford Esp. M2C1 38-CJ) XT-2-QDX (Dextron II)

- Normal working temperature .................... 248°F(120°C)

- Normal peak temperature ........................ 302°F (150°C)

- Normal flow ......................... 4.2 + 2 G.P.M. (16 + 1 L/m)

- Maximum working pressure 1885 + 60 psi(130+4Kg/cm2)

- Maximum pressure drop in the return ducting .................

............................................................. 60 psi (3 Kg/cm2)

The bypass valve is located in the valve body and permits oil to flow from one side of the piston to the other when it is necessary to steer the vehicle without the hydraulic pump

IV. PREVENTIVE MAINTENANCE

POWER STEERING OIL

It is important that an approved oil be used to assure proper operation of the power steering unit. The vehicle manufacturers recommendations should be adhered to.

Once an oil type is in use, it should never be mixed with any other type. If it should become necessary to change types of oil, the entire system must be drained following the procedure below.

DRAINING AND FILLING THE SYSTEM

1. Lift the front axle sufficiently to raise the wheels clear of the ground.

2. Disconnect the return line at the valve body outlet port. The outlet port is identified by the arrow which flows out of the gear. Turn the steering wheel to the left as far as it will go. Run the engine for 10 seconds at the most until the oil is drained from the reservoir and pump. Switch off the engine and turn the steering wheel backwards and forwards from full lock to full lock until all the oil is drained out.

3. Clean the outside of the reservoir. Remove the old filter element. Oil the filter support and assemble with a new filter.

4. Fill reservoir full of oil.

5. Turn the engine over with the starter motor. (Must be done in a manner that the engine does not start.) Add oil as the level drops to avoid air being drawn into the system.

INPUT

SHAFT

VALVE

STOP

BALL BEARING

ROTARY VALVE

GLIDE RING (3)

VALVE NUT

LIMITING

POPPET

RECIRCULATING

BALLS

SPINDLE (BALL

SCREW)

HOUSING

SEAL & GLIDE

RINGS

PISTON

OUTPUT SHAFT

SECTOR GEAR

FIGURE 5

TORSION BAR

O-RING (3)

NEEDLE BEARING

BOOT

PITMAN

ARM NUT

OUTPUT

SHAFT

297676 297661

FIGURE 6 - REQUIRED TOOLS

297675 297660297674

V. IMPORTANT! PLEASE READ:

6. When the oil level reaches the full mark on the dipstick, start the engine and turn the steering wheel slowly from side to side until air bubbles cease to appear in the reservoir. Refill reservoir to full mark on the dipstick.

7. The oil level should be checked every 2,000 miles. The correct level is between the minimum and maximum level marks on the dipstick with the engine stopped.

CHANGE INTERVALS

It is recommended that the oil be changed at 40,000 mile intervals and at the time of rebuild. Beyond its function as the media for transmitting power, the oil also serves to lubricate and dissipate heat. Carefully clean, inspect, and replace if necessary all filter elements in the pump system including vents and breathers.

OUTPUT SHAFT SECTOR TEETH ADJUSTMENT

The gear lash between the piston teeth and sector gear should not require attention in normal service, however a provision for adjustment is provided.

Adjustment requires that the steering gear be drained and the pitman arm and input shaft disconnected from the vehicle. The adjustment procedure is described at the end of the assembly section of this manual.

OUTPUT SHAFT BOOT SEAL

When working on or around the Power Steering system and components, the following precautions, should be observed:

1. Always block vehicle wheels. Stop engine when working under a vehicle. Keep hands away from pinch points.

2. Never connect or disconnect a hose or line containing pressure. Never remove a component or pipe plug unless you are certain all system pressure has been depleted.

3. Never exceed recommended pressure and always wear safety glasses.

4. Never attempt to disassemble a component until you have read and understood recommended procedures. Use only the proper tools and observe all precautions pertaining to use of those tools.

5. Use only genuine Bendix replacement parts and components.

A. Only components, devices and mounting and

attaching hardware specifically designed for use in hydraulic systems should be used.

B. Replacement hardware, tubing, hose, fittings, etc.

should be of equivalent size, type and strength as the original equipment.

6. Devices with stripped threads or damaged parts should be replaced. Repairs requiring machining should not be attempted.

Inspect the integrity of the output shaft boot seal located between the pitman arm and housing. This component prevents contamination from entering the output shaft bearing and retains grease on the bearing and output shaft to prevent corrosion. If deterioration or leakage is detected, it should be replaced.

VI. REMOVING THE POWER STEERING GEAR

1. Mark or identify the inlet and return lines at the valve body ports.

2. Drain the system following the instructions presented under preventive maintenance. Remove both inlet and return lines.

3. Disconnect the steering column at the input shaft following the vehicle manufacturers instructions.

4. Disconnect the pitman arm from the vehicles steering linkage using the vehicle manufacturers instructions.

CAUTION: If it is necessary to remove the pitman before the steering gear can be removed from the vehicle, DO NOT USE HEAT OR POUND ON THE PITMAN ARM OR OUTPUT SHAFT as damage can result. Do not attempt repairs to these components. They must be replaced if damaged. Use a large gear puller to remove the pitman arm such as Snap-On puller #CG-283 or Ford part number T64P-3590-F.

5. Remove the steering gear from the vehicle.

VII. SPECIAL TOOL REQUIREMENTS

The following special tools are required to disassemble and

assemble the power steering gear.

297661 Spanner Wrench - Used to remove and replace the valve nut.

297676 Seating Tool - Used to assure seating and prevent damage to the teflon glide seal rings in the valve nut during reassembly.

297674 Piloted Seal Tool - Used to seat the seal and spacer in the body of the power steering gear.

297675 Piloted Seal Tool - Used to seat the seal in the end cover.

297660 Poppet Wrench - Used to remove and install limiting valve poppets.

The following special tools are available and are useful

but not required for routine disassembly/assembly of

the power steering gear unless replacement of the

bearing races is required.

297678 Holding Fixture - Used to hold the piston and

the valve assembly during disassembly and assembly. Note: Part No. 297678 includes the holding fixture and spanner wrench 297661.

297677 Piloted Bushing Tool - Used to seat the bearing race in the main housing.

297647 Piloted Bushing Tool - Used to drive bearing race out of the main housing. Also used to drive split bearing race into valve body.

VIII. DISASSEMBLY

GENERAL

A high level of cleanliness should be observed at all times when working on the power steering gear. Clean the exterior of all parts prior to disassembly.

The following disassembly and assembly procedure is presented for reference purposes and presupposes that a major rebuild of the power steering gear is being undertaken. Several replacement parts and maintenance kits are available which do not require full disassembly. The instructions provided with these parts and kits should be followed in lieu of the instructions presented here.

OUTPUT SHAFT REMOVAL

1. After removing the power steering unit from the vehicle and cleaning the outside, secure the power steering unit to the work bench for disassembly. A large vise with jaw protectors may be used. Clamp across the mounting bolt bosses. (Do not overtighten.)

2. Using a 17mm wrench, remove the drain plug from the housing and drain out all oil. (Fig. 8)

3. Loosen and remove the four bolts(1) from the valve body with a 22mm socket. (See Figures 7 & 9)

297677

FIGURE 6A - NON REQUIRED TOOLS

297678

297647

1. Valve Body Bolt

2. Washer

3. Pressure Relief Valve Plug

4. Sealing Washer

5. Adjusting Washer (Shim)

6. Pressure Relief Valve Spring

7. Spring Guide

8. Pressure Relief Valve

9. Pressure Relief Valve Seat

10. Sealing Washer

11. By-pass Ball Valve Spring

12. By-pass Ball Valve

13. Input Shaft Dust Seal

14. Snap Ring

15. Input Shaft Seal

16. Valve Body Housing

17. Valve Body O-Ring

18. Valve Body Seal Ring (Nylon)

19. Valve Body O-Ring

20. Pitman Arm Nut

21. Pitman Arm Nut Lock Washer

22. Pitman Arm

23. Output Shaft Boot

24. Boot Retainer

25. Snap Ring

26. Needle Bearing Assy

27. Output Shaft Seal

28. Valve Body & Spindle Ball Bearing

Outer Race (Split)

29. Ball

30. Ball Bearing Cage

31. Valve Nut O-Ring

32. Valve Nut Teflon Glide Ring

33. Valve Nut

34. Spindle Assy. (Valve & Ball Screw Assy.)

35. Output Shaft

36. Output Shaft Adjusting Screw

37. Output Shaft Adjusting Screw

Shim (Washer)

38. Snap Ring

39. Side Cover Output Shaft Seal

40. Side Cover O-Ring

41. Side Cover Assy. (includes Needle Bearing

Assy.)

42. Side Cover Bolt

43. Output Shaft Adjusting Screw Lock Nut

44. Housing Drain Plug

45. Housing

46. Piston Backup Ring

47. Piston O-Ring

48. Piston

49. Recirculating Ball Tube

50. Ball Tube Cover

51. Snap Ring

52. Piston Limiting Body Nut

53. Piston Limiting Body and Valve Seat

54. Piston Limiting Stem (Short)

55. Piston Limiting Stem (Long)

56. Limiting Body Stop Washer

57. Limiting Valve Spring

FIGURE 7

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