Embed Size (px)
Citation preview
1
Steering Gear and Linkage
Steering Gear and Linkage
2
Steering Steering
• The steering system can be broken into two major components.– The steering column and shaft
• All the components located in the passenger compartment
– The steering gear and linkage• The steering gear and linkage converts the rotary
motion of the steering wheel into linear motion of the steering linkage
• A set of gears is needed to accomplish this• Linkage is needed to connect the steering knuckles to
the steering gear because the steering knuckles must move up and down with the suspension
• The steering system can be broken into two major components.– The steering column and shaft
• All the components located in the passenger compartment
– The steering gear and linkage• The steering gear and linkage converts the rotary
motion of the steering wheel into linear motion of the steering linkage
• A set of gears is needed to accomplish this• Linkage is needed to connect the steering knuckles to
the steering gear because the steering knuckles must move up and down with the suspension
3
Steering ratioSteering ratio
• The steering ratio is the number of turns of the steering wheel / number of turns of the steering knuckle.
• Most passenger cars have a steering ratio of around 16 to 1.
• 16 degrees of rotation of the steering wheel should produce 1 degree of rotation of the steering knuckle.
• The steering ratio is the number of turns of the steering wheel / number of turns of the steering knuckle.
• Most passenger cars have a steering ratio of around 16 to 1.
• 16 degrees of rotation of the steering wheel should produce 1 degree of rotation of the steering knuckle.
16o
1o 1o
4
Steering ratioSteering ratio
• If the engine stalls or the power steering belt breaks the vehicle must be capable of being steered safely to a stop.
• A lower steering ratio will have a quicker steering response but may make the vehicle nearly impossible to steer if the power assist fails.
• The heavier weight applied to the front tires of a trucks calls for a steering ratio of 20 to 1 or higher.
• If the engine stalls or the power steering belt breaks the vehicle must be capable of being steered safely to a stop.
• A lower steering ratio will have a quicker steering response but may make the vehicle nearly impossible to steer if the power assist fails.
• The heavier weight applied to the front tires of a trucks calls for a steering ratio of 20 to 1 or higher.
5
Turns lock-to-lockTurns lock-to-lock
• Most passenger cars have about 3 1/3 turns of steering lock-to-lock
• If you turn the wheels all the way to the left until the steering will no longer turn and then count the number of rotations of the steering wheel can turn to the right until it reaches the steering lock – that is the number of turns lock-to-lock.
• The average passenger car has about 3 and 1/3 turns.
• Trucks usually have a higher number of turns due to their higher steering ratio, typically 4 ½ or more.
• Most passenger cars have about 3 1/3 turns of steering lock-to-lock
• If you turn the wheels all the way to the left until the steering will no longer turn and then count the number of rotations of the steering wheel can turn to the right until it reaches the steering lock – that is the number of turns lock-to-lock.
• The average passenger car has about 3 and 1/3 turns.
• Trucks usually have a higher number of turns due to their higher steering ratio, typically 4 ½ or more.
6
Steering stopsSteering stops
• A steering stop is a mechanism in the steering linkage or steering gear that limits how far the steering knuckles can rotate.
• Without steering stops the sidewalls of the tires will contact the fenders, frame or control arms.
• On some suspension systems there are adjustable bolts on the control arms that contact a tab on the steering knuckle at full lock.
• A steering stop is a mechanism in the steering linkage or steering gear that limits how far the steering knuckles can rotate.
• Without steering stops the sidewalls of the tires will contact the fenders, frame or control arms.
• On some suspension systems there are adjustable bolts on the control arms that contact a tab on the steering knuckle at full lock.
7
Steering stopsSteering stops
• On most modern cars the steering stop is built into the steering gear.
• If the steering linkage is serviced improperly it may be possible for the steering to turn 35 degrees to the right and only 25 degrees to the left.
• If this was the case the tires may be damaged when making a hard turn as the steering angle exceeds the design limits.
• On most modern cars the steering stop is built into the steering gear.
• If the steering linkage is serviced improperly it may be possible for the steering to turn 35 degrees to the right and only 25 degrees to the left.
• If this was the case the tires may be damaged when making a hard turn as the steering angle exceeds the design limits.
8
Types of steering gearTypes of steering gear
• There are two types of steering gear used on modern cars:
– Rack and Pinion • Used on the majority of passenger cars
– Re-circulating Ball steering box• Used on mostly on trucks• Sometimes called linkage steering
• There are two types of steering gear used on modern cars:
– Rack and Pinion • Used on the majority of passenger cars
– Re-circulating Ball steering box• Used on mostly on trucks• Sometimes called linkage steering
9
Rack and pinion steeringRack and pinion steering
• Rack and pinion steering is very compact and simple and has relatively few moving parts.
• Steering arms can be extensions of the steering knuckle or separate parts that bolt to the steering knuckle.
• Rack and pinion steering is very compact and simple and has relatively few moving parts.
• Steering arms can be extensions of the steering knuckle or separate parts that bolt to the steering knuckle.
Sub-frame
Steering knuckle
Steering arm
Tie rod Tie rod
Steering coupler
Rack housing
10
Linkage type steeringLinkage type steering
• Linkage type steering is often called a parallelogram linkage because the angles formed by the links produces a parallelogram.
• With the steering straight ahead the linkage forms a rectangle.
• Linkage type steering is often called a parallelogram linkage because the angles formed by the links produces a parallelogram.
• With the steering straight ahead the linkage forms a rectangle.
Frame
Steering knuckle
Steering arm
Tie rod
Center linkTie rod
Pitman arm
Idler arm
Recirculating ball steering
box
11
Linkage [parallelogram] type steeringLinkage [parallelogram] type steering
• When the steering is turned to the left or right the shape formed by the idler arm, pitman arm and center link changes to a parallelogram.
• When the steering is turned to the left or right the shape formed by the idler arm, pitman arm and center link changes to a parallelogram.
Frame
Steering knuckle
Steering arm
Tie rodCenter link
Tie rod
Pitman arm
Idler arm
Recirculating ball steering
box
12
Rack and pinion vs. linkage steeringRack and pinion vs. linkage steering
• Rack and pinion steering is preferred by most drivers due to its positive feedback.
• Since the rack must be located within a foot of the front wheel axis centerline it is difficult to install in rear drive vehicles where the engine is placed between the front wheels.
• Some luxury car manufactures prefer to use recirculating ball steering because it isolates the driver from road shock transmitted through the steering.
• Rack and pinion steering is preferred by most drivers due to its positive feedback.
• Since the rack must be located within a foot of the front wheel axis centerline it is difficult to install in rear drive vehicles where the engine is placed between the front wheels.
• Some luxury car manufactures prefer to use recirculating ball steering because it isolates the driver from road shock transmitted through the steering.
13
Rack and Pinion locationRack and Pinion location
• Rack and pinion steering can be used on this sports car because the engine is located behind the front axle centerline.
• Rack and pinion steering can be used on this sports car because the engine is located behind the front axle centerline.
14
Rack and pinion steering
Rack and pinion steering
• On a front wheel drive car with the engine mounted transversely the steering rack can be mounted on the sub-frame directly behind the engine/transaxle.
• On a front wheel drive car with the engine mounted transversely the steering rack can be mounted on the sub-frame directly behind the engine/transaxle.
15
Rack and Pinion Steering
Rack and Pinion Steering
16
Rack and pinion Rack and pinion
• Rack and pinion steering is very simple and has few moving parts.
• When the pinion gear rotates the rack moves laterally.
• The pinion gear is connected to the steering wheel – the rack is connected to the steering knuckles.
• Rack and pinion steering is very simple and has few moving parts.
• When the pinion gear rotates the rack moves laterally.
• The pinion gear is connected to the steering wheel – the rack is connected to the steering knuckles.
Pinion gear
Rack
17
Rack and pinion steering linkageRack and pinion steering linkage
• The rack and pinion gears are mounted in an aluminum housing that usually sits on top of the front sub-frame.
• Tie rods connect the each end of the rack to the steering knuckles.
• The rack and inner tie rod ends are protected by rubber bellows.
• The rack and pinion gears are mounted in an aluminum housing that usually sits on top of the front sub-frame.
• Tie rods connect the each end of the rack to the steering knuckles.
• The rack and inner tie rod ends are protected by rubber bellows.
Bellows
Tie rod
Tie rod
Rack Housing
Pinion shaft
Mount bushings
18
Rack and pinion steeringRack and pinion steering
• The rack and pinion gears are located inside an aluminum housing that is bolted to the frame or firewall.
• The rack is free to slide laterally on bores machined into the housing.
• The pinion gear shaft is supported on ball bearings at the top and bottom.
• The rack and pinion gears are located inside an aluminum housing that is bolted to the frame or firewall.
• The rack is free to slide laterally on bores machined into the housing.
• The pinion gear shaft is supported on ball bearings at the top and bottom.
Pinion shaftPinion
bearings Rack bearing
19
Rack and pinion steeringRack and pinion steering
• The housing is filled with lubricating oil.• Seals on the ends of the housing and pinion
shaft keep the fluid from leaking out.• Rubber bellows protect the ends of the rack
and inner tie rod ends from dirt and moisture damage.
• The housing is filled with lubricating oil.• Seals on the ends of the housing and pinion
shaft keep the fluid from leaking out.• Rubber bellows protect the ends of the rack
and inner tie rod ends from dirt and moisture damage.
Pinion shaft seal
BellowsRack SealRack Seal
Inner tie rod end
Air pressure equalization passage
20
Rack and pinion steeringRack and pinion steering
• An air passage connects the left and right bellows.
• Without the air passage the bellows would collapse on one side and balloon on the other as the vehicle is steered
• An air passage connects the left and right bellows.
• Without the air passage the bellows would collapse on one side and balloon on the other as the vehicle is steered
Bellows
Air pressure equalization passage
21
Tie rodsTie rods
• Tie rods connect the steering gear to the steering knuckles.
• The length of tie rods must be adjustable so that the toe angle for each wheel can be adjusted.
• Tie rods connect the steering gear to the steering knuckles.
• The length of tie rods must be adjustable so that the toe angle for each wheel can be adjusted.
• Tie rod ends are ball and socket joints similar to ball joints.
• The tie rod ends must pivot with the steering and flex up and down with suspension movement.
• Tie rod ends are ball and socket joints similar to ball joints.
• The tie rod ends must pivot with the steering and flex up and down with suspension movement.
Nylon ball seat
Garter spring
22
Tie rods for rack and pinion steeringTie rods for rack and pinion steering
• The tie rod assembly for rack and pinion steering has 3 components:– Outer tie rod end– Inner tie rod end – Jamb nut [lock nut]
• The tie rod assembly for rack and pinion steering has 3 components:– Outer tie rod end– Inner tie rod end – Jamb nut [lock nut]
Jamb nutOuter tie rod end Inner tie rod end
23
Tie rod length adjustmentTie rod length adjustment
• When the inner toe rod is rotated the assembly gets shorter, when it is rotated in the opposite direction it gets longer.
• Most inner tie rods have machined flats to allow the tie rod to be turned using an open end wrench.
• When the inner toe rod is rotated the assembly gets shorter, when it is rotated in the opposite direction it gets longer.
• Most inner tie rods have machined flats to allow the tie rod to be turned using an open end wrench.
Jamb nut
Flats on tie rod
24
Linkage type steering
Linkage type steering
25
Recirculating ballRecirculating ball
• In the recirculating ball system the steering wheel is connected to a worm shaft.
• The worm shaft is a screw that moves a nut.• Ball bearings located between the threads
of the worm shaft and nut reduce friction to allow for a low steering effort by the driver.
• In the recirculating ball system the steering wheel is connected to a worm shaft.
• The worm shaft is a screw that moves a nut.• Ball bearings located between the threads
of the worm shaft and nut reduce friction to allow for a low steering effort by the driver.
Nut
Worm shaft
Ball bearings Return
tube
26
Recirculating ballRecirculating ball
• As the worm shaft turn the balls thread there way to the end of the shaft.
• A return tube transfers the balls back to the other end of the worm shaft.
• The ball nut is in mesh with a sector gear.
• As the worm shaft turn the balls thread there way to the end of the shaft.
• A return tube transfers the balls back to the other end of the worm shaft.
• The ball nut is in mesh with a sector gear.
Nut
Sector gear
Pitman arm
Return tube
27
Recirculating ballRecirculating ball
• The teeth on the ball nut forces the sector gear to rotate.
• The large end of the pitman arm is connected to the sector gear.
• The small end of the pitman arm is connected to the steering linkage.
• The teeth on the ball nut forces the sector gear to rotate.
• The large end of the pitman arm is connected to the sector gear.
• The small end of the pitman arm is connected to the steering linkage.
Return tube
28
Steering linkage Steering linkage
• Vehicle with independent front suspension have 5 links:
• Vehicle with independent front suspension have 5 links:
Pitman armIdler arm
Tie rod
Center link
Tie rod
29
What’s in the box.What’s in the box.
Nut
Worm shaft
Sector shaft AKA
Pitman shaft
Ball bearings
Housing
Control valve
30
Ball nut and sector gear
Ball nut and sector gear
• Notice the center tooth is longer than the other two teeth.
• Notice the center tooth is longer than the other two teeth.
• This produces a variable steering ratio.
• This produces a variable steering ratio.
31
Sector shaftSector shaft
• The spline at the bottom of the sector shaft is tapered to secure the pitman arm even if the nut loosens.
• The spline at the bottom of the sector shaft is tapered to secure the pitman arm even if the nut loosens.
• Master spline allows the pitman arm to be installed in only four positions.
• Master spline allows the pitman arm to be installed in only four positions.
Seal surface
Freeplay adjustment
screw
32
Sector [Pitman] shaft sealSector [Pitman] shaft seal
• The sector shaft seal is the most common problem with steering boxes.
• The sector shaft seal is the most common problem with steering boxes.
Master spline
33
Pitman armPitman arm• Some Pitman arms have an
integrated ball and socket joint that connects the Pitman arm to the center link.
• Some Pitman arms have an integrated ball and socket joint that connects the Pitman arm to the center link.
• When the Pitman arm doesn’t have a ball and socket joint the joint is integrated into the center link.
• When the Pitman arm doesn’t have a ball and socket joint the joint is integrated into the center link.
34
Steering box is attached to the frame railSteering box is attached to the frame rail
• If a steering box designed for forward mounting is installed a vehicle that requires a rear mounted box the steering will be backwards. [when you turn the steering wheel to the left the car will turn right]
• If a steering box designed for forward mounting is installed a vehicle that requires a rear mounted box the steering will be backwards. [when you turn the steering wheel to the left the car will turn right]
• A flange on the side of the steering box is used to bolt it to the frame rail.
• Steering boxes are designed to be mounted either ahead or behind the axle centerline.
• A flange on the side of the steering box is used to bolt it to the frame rail.
• Steering boxes are designed to be mounted either ahead or behind the axle centerline.
Freeplay adjustment
screw
Mounting flange
35
Idler armIdler arm
• The idle arm is attached to the passenger side frame rail and supports the center link.
• Some idlers are two piece assemblies where the support bearing can be replaced separately from the arm and ball and socket joint.
• The idle arm is attached to the passenger side frame rail and supports the center link.
• Some idlers are two piece assemblies where the support bearing can be replaced separately from the arm and ball and socket joint.
Bracket bolted to the
frame
Fixed pivot
Ball and socket joint
36
Center linkCenter link
• Center links come in two varieties:
– A solid steel bar with 4 holes• Rarely replaced because there’s nothing to wear out
– A steel bar with 2 ball and socket joints and two holes
• Center links come in two varieties:
– A solid steel bar with 4 holes• Rarely replaced because there’s nothing to wear out
– A steel bar with 2 ball and socket joints and two holes
37
Tie rods on linkage steering systemsTie rods on linkage steering systems
• The tie rods on linkage steering are 3 piece assemblies.– Inboard tie rod end with a ball and socket joint
• A left hand thread is used to connect it to the adjustment sleeve
– Outboard tie rod end with a ball and socket joint• A right hand thread is used to connect it to the
adjustment sleeve
– Adjustment sleeve forms the center of the assembly
• The sleeve is tapped with internal left hand threads on one end and right hand threads on the other end
• The tie rods on linkage steering are 3 piece assemblies.– Inboard tie rod end with a ball and socket joint
• A left hand thread is used to connect it to the adjustment sleeve
– Outboard tie rod end with a ball and socket joint• A right hand thread is used to connect it to the
adjustment sleeve
– Adjustment sleeve forms the center of the assembly
• The sleeve is tapped with internal left hand threads on one end and right hand threads on the other end
Inboard tie rod end
Outboard tie rod end
Adjustment sleeve
38
Steering linkage for solid axlesSteering linkage for solid axles
• A steering rod connects the pitman arm to the right side steering knuckle.
• A steering rod connects the pitman arm to the right side steering knuckle.
• Four wheel drive trucks with live front axles use single tie rod to connect the steering knuckles.
• Four wheel drive trucks with live front axles use single tie rod to connect the steering knuckles.
Tie rod
Steering rod
Frame
Pitman arm
39
Drag link steeringDrag link steering
• In a drag link system the pitman arm is located outboard of the frame rail.
• In a drag link system the pitman arm is located outboard of the frame rail.
• The drag link connects the pitman arm to the left side steering knuckle.
• The drag link connects the pitman arm to the left side steering knuckle.
Tie rod
Pitman arm
Drag link
40
Drag link steeringDrag link steering
• This antique pickup truck has kingpins instead of ball joints for its steering pivots.
• This antique pickup truck has kingpins instead of ball joints for its steering pivots.
Drag linkPitman arm Steering armTie rod
41
Toe angleToe angle
42
ToeToe
• Toe is an alignment angle established by the length of the tie rods.
• Toe is the difference in distance between the two front tires measured at the front [leading edge]and rear [trailing edge].
• Toe is normally expressed in inches but can also be expressed in millimeters or degrees.
• Toe is an alignment angle established by the length of the tie rods.
• Toe is the difference in distance between the two front tires measured at the front [leading edge]and rear [trailing edge].
• Toe is normally expressed in inches but can also be expressed in millimeters or degrees.
59 7/8”
60 1/8”
43
Toe-inToe-in
• When the tires are closer at the front the condition is called toe-in.
• Toe-in is normally displayed on an alignment machine precede by a negative sign [-].
• When the tires are closer at the front the condition is called toe-in.
• Toe-in is normally displayed on an alignment machine precede by a negative sign [-].
59 7/8”
60 1/8”
- ¼” toe-in
44
Toe-outToe-out
• When the tires are closer at the rear the condition is called toe-out.
• Toe-out is normally displayed on an alignment machine precede by a positive sign [+].
• When the tires are closer at the rear the condition is called toe-out.
• Toe-out is normally displayed on an alignment machine precede by a positive sign [+].
59 7/8”
60 1/8”
+ ¼” toe-out
45
Zero toeZero toe
• When the vehicle is driven straight ahead at highway speeds the tires should be at zero toe.
• Most cars and trucks are aligned for a small amount of toe-in to compensate for compliance in the control arm bushings.
• The forces caused by positive scrub radius causes the tire to want to toe-out as the vehicle comes up to speed.
• When the vehicle is driven straight ahead at highway speeds the tires should be at zero toe.
• Most cars and trucks are aligned for a small amount of toe-in to compensate for compliance in the control arm bushings.
• The forces caused by positive scrub radius causes the tire to want to toe-out as the vehicle comes up to speed.
60”
60”
46
Toe change during jounce/reboundToe change during jounce/rebound
• As the out board end of the tie rod moves up and down with the suspension it swings through an arc.
• As the tie rod swings up and down during jounce/rebound the tire is pulled toward toe-in if the steering arms are located in front of the axle centerline.
• As the out board end of the tie rod moves up and down with the suspension it swings through an arc.
• As the tie rod swings up and down during jounce/rebound the tire is pulled toward toe-in if the steering arms are located in front of the axle centerline.
47
Toe change during reboundToe change during rebound
• The location of the steering arm relative to the axle centerline determines whether the tire is pulled into toe-in or toe-out during jounce and rebound.
• If the tie rods attach to the steering knuckle behind the axle centerline the tires will toe-out during jounce and rebound.
• The location of the steering arm relative to the axle centerline determines whether the tire is pulled into toe-in or toe-out during jounce and rebound.
• If the tie rods attach to the steering knuckle behind the axle centerline the tires will toe-out during jounce and rebound.
48
Bump steerBump steer
• If both tie rods are the same length the toe change will be equal on both sides and the vehicle will not pull.
• If one tie rod is longer then the car will momentarily pull to the side with the shorter tie rod when ever the tires encounter a bump.
• If both tie rods are the same length the toe change will be equal on both sides and the vehicle will not pull.
• If one tie rod is longer then the car will momentarily pull to the side with the shorter tie rod when ever the tires encounter a bump.
10.5” 9.5”
¼” toe change ½ ” toe change
49
Bump SteerBump Steer
• The tie rods should be horizontal when the vehicle is at its static height.
• If one side of the center link is higher or lower than the other side the car will bump steer to that side.
• This condition is usually the result of an improperly installed idle arm.
• The tie rods should be horizontal when the vehicle is at its static height.
• If one side of the center link is higher or lower than the other side the car will bump steer to that side.
• This condition is usually the result of an improperly installed idle arm.
