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

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 Sector shaft Ball nut
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 Adjusting nut Adjusting screw
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 Center link (relay rod)
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 Tie-rod assemblies
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 inner end
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

51. Pump Types

52. Slipper-Type Pump

53. Vane-Type Pump Operation

54. Pressure-Relief Valve
Used in a power steering system to control the maximum oil pressure
Prevents system damage by limiting pressure
A relief valve opens when the steering wheel is turned to the full-left or full-right position

55. Pressure-Relief Valve

56. Power Steering Hoses
High-pressure, hydraulic, rubber hoses that connect the power steering pump and the gearbox or power cylinder
One line serves as the pressure feed line
One line serves as a return line to the reservoir
Metal lines may be used where vibration or movement is not a problem

57. Integral-Piston Power Steering System (Linkage Type)
The hydraulic piston is mounted in the steering gearbox housing
System components:
power steering pump
hydraulic lines
integral power-assist gearbox

58. Integral Power Steering Gearbox
Contains a conventional worm-and-sector gear, a hydraulic piston, and a flow-direction valve
Two valve designs are commonly used:
spool valve
rotary valve

59. Spool Valve-Type Gear

60. Spool Valve Operation
When the steering wheel is turned, the pivot lever moves the spool valve so pressure enters a power chamber
Pressure forces the power piston left or right, helping to turn the sector shaft
As the power piston strokes, oil from the other power chamber is vented through the spool valve back to the reservoir

61. Rotary Valve Operation
Rotary valve-type steering boxes have a small torsion bar to detect steering wheel turning direction and turning effort
When the steering wheel is turned, the torsion bar twists and turns the rotary valve
Rotary valve directs pressure to the correct side of the power piston

62. Integral Gear Operation
Driving straight ahead

63. Integral Gear Operation
Right turn

64. Integral Gear Operation
Left turn

65. External Cylinder Power Steering (Linkage Type)
The power cylinder is commonly bolted to the frame and the center link
The control valve may be located in the gearbox or on the steering linkage

66. External Cylinder Power Steering

67. Power Rack-and-Pinion
Steering
Uses hydraulic pressure to assist the driver in moving the rack and the front wheels

68. Power Rack-and-Pinion Steering

69. Power Rack-and-Pinion Steering

70. Power Cylinder and Piston
precisely machined tube that accepts the power piston
Power piston
formed by attaching a hydraulic piston to the center of the rack
Routing oil pressure into either end of the power cylinder causes piston movement

71. Power Rack-and-Pinion (Rotary Control Valve)

72. Control Valves Rotary control valve Spool control valve
operated by a torsion shaft connected to the pinion gear
Spool control valve
operated by the thrust action of the pinion shaft that occurs when the pinion gear is rotated against the rack gear

73. Power Rack-and-Pinion (Spool Control Valve)

74. System Operation
When the steering wheel is turned, vehicle weight causes the front tires to resist turning, moving the control valve
Movement of the control valve aligns specific oil passages internally
Pump pressure forces oil through the control valve to the power cylinder
Pressure acts on the power piston, pushing the rack and the front wheels

75. Little valve movement, low power assist
High Speed Operation
Little valve movement, low power assist

76. More valve movement, high power assist
Low Speed Operation
More valve movement, high power assist

77. Electronic Steering Assist
Uses a small electric motor to help move the rack-and-pinion gearbox
The motor is mounted inside the rack housing and acts on the steering rack

78. Electronic Assist Rack-and-Pinion
Lighter and more compact than a hydraulic system

79. Electronic Assist Operation
A steering control module (computer) electronically reacts to steering pressure
The module operates the electric motor in the rack assembly to help the driver steer the wheels
The module can reverse motor rotation and alter motor speed as needed

80. Proportional Power Steering
Senses vehicle speed and steering load to ensure adequate road feel
Increases steering effort at higher speeds for more road feel
Lowers steering effort at lower speeds to ease maneuvering

81. Low Speed Operation
A computer-controlled electromagnet is used to alter the operation of the stub shaft, torsion bar, and rotary control valve
At low speeds, the computer sends current through the electromagnet in one direction to help attract and pull on the stub shaft and torsion bar, increasing valve output pressure

82. High Speed Operation
At high speeds, the computer reverses electrical flow through the electromagnet
The valve output pressure decreases, reducing assist, and increasing steering effort for better road feel

83. Proportional Steering
In this system, a computer, a vehicle speed sensor, and a solenoid control hydraulic pressure

84. Four-Wheel Steering Systems
In a four-wheel steering system, all four wheels change direction to improve handling, stability, feel, and maneuverability

85. Four-Wheel Steering System

86. In a gentle turn, the wheels pivot in the same direction
Four-Wheel Steering
In a gentle turn, the wheels pivot in the same direction

87. Four-Wheel Steering
In a sharp turn, the wheels pivot back and then turn in opposite directions

88. Mechanical System
Uses a special front rack-and-pinion gearbox with a transfer box
The transfer box operates a long shaft that extends back to the rear rack
When the front wheels are turned, the shaft rotates to turn the rear wheels

89. Hydraulic System
Uses a conventional power rack-and-pinion steering system up front
Hydraulic lines extend back to a rear power steering pump, which is driven by the differential
Depending on vehicle speed, the rear pump forces fluid under pressure into a control valve

90. Hydraulic System
When a specific road speed is reached, the control valve can then operate the rear steering system
The rear rack is connected by tie-rods to the rear suspension trailing arms
When activated, the rear rack shifts the trailing arms to steer the rear wheels

91. Electronic System An electronic system is speed-sensitive
An electric-motor-driven power rack (rear actuator) acts on the rear wheels using a recirculating-ball drive and mechanical links
The rear-wheel steering angles are computer controlled

92. Electronic System

93. Electronic System Operation
The computer analyzes signals from angle sensors in the front steering and signals from wheel speed sensors in the anti-lock brake system
The rear actuator is energized by the computer to move the rear wheels as needed

94. Rear Actuator