Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

1. PublisherThe Goodheart-Willcox Co., Inc.Tinley Park, Illinois PowerPoint for Modern Automotive Technology by Russell Krick

2. Chapter 69 Steering System Fundamentals

3. Contents • Functions of a steering system • Basic steering systems • Steering column assembly • Steering gear principles • Steering linkage (worm-type gearbox) • Manual rack-and-pinion steering (Continued)

4. Contents • Integral-piston power steering system (linkage type) • External cylinder power steering (linkage type) • Power rack-and-pinion steering • Electronic steering assist • Four-wheel steering systems

5. Functions of a Steering System • Provide precise control of the wheel direction • Maintain correct steering effort • Transmit road feel to the driver’s hands • Absorb most of the road shock going to the steering wheel • Allow for suspension action

6. Basic Steering Systems • Two basic kinds of steering systems are in use today: • linkage (worm gear) steering systems • rack-and-pinion steering systems • Each may be operated manually or with power assist

7. Steering Basic linkage steering Basic rack-and-pinion steering

8. Steering Column Assembly • Consists of the steering wheel, steering shaft, column, ignition key mechanism, and sometimes, a flexible coupling and universal joint • Bolts to the underside of the dash • Sticks through the firewall and fastens to the steering gear

9. Steering Column Components

10. Locking Steering Wheel • When the ignition is off, the steering wheel cannot be turned • A rack and sector slide a steel pin into mesh with a slotted disc that is splined to the steering shaft • The pin locks the steering shaft to the column, preventing the steering wheel from being turned

11. Locking Steering Wheel

12. Collapsible Steering Column • Helps prevent driver chest and face injury during an auto accident • The column will crumple or slide together when forced forward during a collision • Several types are used: • steel mesh (crushing) • tube-and-ball (sliding) • shear capsule (break and slide)

13. Collapsible Column Operation

14. Tilt Steering Columns • A flex joint, or U-joint, allows the top half of the column and the steering wheel to be positioned at different angles • Manual tilt column • uses a lever on the steering column to unlock the flex joint so the wheel can be moved up and down

15. Power Tilt Column • Uses a small electric motor, a control switch, and a gear mechanism to change the steering wheel angle or height • When the tilt switch is activated, current to the motor spins the small gears to move the steering column’s upper tube

16. Memory Tilt Wheels • Use a tilt control module to “remember” more than one steering wheel position • A steering column sensor provides feedback so the module knows where the wheel is located • When the driver selects a switch position, the control module energizes the power tilt motor until the wheel has moved to the preprogrammed position

17. Memory Tilt Wheel

18. Power Tilt Gear Mechanism

19. Steering Gear Principles • Two basic types of gear mechanisms are found in steering gearboxes: • worm gears • rack-and-pinion gears

20. Gear Mechanisms

21. Steering Gears Rack-and-pinion gear Worm steering gear

22. Recirculating-Ball Gearbox • Normally used with a linkage steering system • Small steel balls circulate between the gear members to reduce friction

23. Recirculating-Ball Gearbox

24. Gearbox Components • Worm shaft • the input gear connected to the steering shaft • Sector shaft • the output gear from the steering gearbox • Ball nut • rides on the ball bearings and the worm gear

25. Gearbox Components • Ball guides • route extra balls in and out from between the worm and ball nut • Adjusting nut • used to set worm shaft bearing preload • Adjusting screw • used to set the sector shaft clearance

26. Gearbox Components

27. Gearbox Ratio • Comparison between steering wheel rotation and sector shaft rotation • Ratios range from 15:1 to 24:1 • Variable-ratio gearbox • changes the internal gear ratio as the wheels are turned away from center • Constant-ratio gearbox • has the same gear reduction from full left to full right

28. Worm-and-Roller Steering Gearbox • Contains a roller that is mounted on the pinion shaft and meshes with the worm gear • The roller replaces the ball bearings and the ball nut used in the recirculating-ball gearbox

29. Steering Linkage (Worm-Type Gearbox) • Series of arms, rods, and ball sockets that connect the steering gearbox to the steering knuckles • Commonly called a parallelogram steering linkage

30. Steering Linkage

31. Steering Linkage • Pitman arm • transfers gearbox motion to the steering linkage • Center link (relay rod) • a steel bar that connects the right and left sides of the steering linkage

32. Steering Linkage • Idler arm • supports the end of the center link on the passenger side • Tie-rod assemblies • fasten the center link to the steering knuckles • ball sockets are used on both ends • a toe adjustment sleeve allows length change for alignment

33. Ball Sockets • Provide for motion in all directions between two connected parts • Some have a grease fitting, allowing lubrication • Others are sealed units • Used in pitman arms, idler arms, and tie-rods

34. Ball Sockets A. Idler arm B. Tie-rod end C. Tie-rod innerend D. Tie-rod (rack-and-pinion)

35. Manual Rack-and-Pinion Steering

36. Rack-and-Pinion Steering

37. Steering Gear • Consists of a pinion shaft, rack, thrust spring, bearings, seals, and a gear housing • Bolts to the frame or unibody structure • Rubber bushing mounts help absorb road shock

38. Steering Gear

39. Steering Gear • When the pinion shaft turns, the pinion gear acts on the rack gear • The rack slides sideways, moving the tie-rods and the front wheels

40. Tie-Rod Assemblies • Connect the ends of the rack with the steering knuckles • Rubber dust boots fit over the inner ball sockets to keep out road dirt and water

41. Power Steering Systems • Most systems use an engine-driven pump and a hydraulic system to assist steering action • An electric motor in the rack may be used to provide power assist

42. Basic Power Steering

43. Basic Operation • Pressure from the oil pump is used to operate a piston-and-cylinder assembly • When the control valve routes oil pressure into one end of the piston, the piston slides in its cylinder • Piston movement helps move steering system components

44. Types of Power Steering • There are three main types of power steering systems: • integral-piston linkage system • rack-and-pinion system • external cylinder power steering system

45. Integral-Piston Linkage

46. Rack-and-Pinion

47. External Cylinder

48. Power Rack-and-Pinion

49. Power Steering Pump • Engine-driven pump that produces the hydraulic pressure for steering system operation • Driven by a belt or directly off the back of the camshaft • The power steering fluid reservoir may be formed as part of the body or as a separate container

50. Pump and System