UNIT 11
SUSPENSION
AND STEERING SYSTEMS
TEXT C
Wheel Alignment
PROFESSIONAL ENGLISH
TEXT A
Wheel Alignment
Alignment Measurement Values
Front Wheel Alignment Adjustments
Rear Wheel Alignment Adjustments
Alignment Equipment
本次课学习内容本次课学习目标
掌握车轮定位的英文专业词汇
训练快速阅读能力，提高阅读速度
NEW WORDS
wandering ['w?nd?ri?] n.漫游,神志恍惚,离题
provision [pr?'vin] n.预备,防备,设备，装置
misalign ['mis?lain] v.不重合,未对准，失准
setting ['seti?] n.调整位置，设定值，安置,安装
caster ['kɑ:st?] n.主销后倾（角）
camber ['k?mb?] n.车轮外倾
toe [t?u] n.前束
toe-out [t?uaut] n.(负 )前束
toe-in [t?uin] n.(正 )前束
offset ['?:fset] n,& v.偏移,抵销
scraping ['skreipi?] n.刮,擦
scrubbing [skr?bi?] n.洗擦,擦净
imaginary [i'min?ri] a.假想的,想象的,虚构的
deviation [?di:vi'ei∫?n] n.背离，偏离
chisel ['t∫izl] n.凿子； v.凿，雕
eccentric [ik'sentrik] n.偏心轮； a.偏心的
trammel ['tr?m?l] n.束缚物，量规
elaborate [i'l?b?r?t] a.精心制作的
necessitate [ni'sesiteit] v.成为必要
PHRASES AND EXPRESSIONS
wheel alignment 车轮定位
steering axis
inclination
转向轴线内倾角
toe-out on turns 转弯负前束
tipping effect 侧倾效应
thrust angle 推力角，推力线
wheel tracking （前轮与后轮）同辙行驶
dog tracking 蛇形行驶
eccentric cam 偏心凸轮
Wheel Alignment
4 Wheel alignment is the process of measuring and correcting the
various angles formed by the front and rear wheels,spindles,and
steering arms,Correct alignment is vital,Improper alignment can
cause hard steering,pulling to one side,wandering,noise,and
rapid tire wear.
Types of Wheel Alignment
11 Rear-wheel drive vehicles require a two-wheel alignment or
front-wheel alignment only,The rear wheels are attached to a solid
rear axle assembly which cannot be adjusted,and generally stays
in alignment throughout the life of the vehicle.
12 Today,most front-wheel drive vehicles have provisions for
adjusting the rear wheels,In addition,many rear-wheel drive
vehicles are equipped with independent rear suspensions,which
also must be adjusted,Also,modern solid rear axles and
suspension systems are lightweight and can become misaligned,
Therefore,the four-wheel alignment,in which the front and rear
wheel alignment angles are checked and adjusted,is commonly
performed.
159 Adjustable front wheel settings on most modern vehicles
are caster,camber,and toe,Nonadjustable settings are
steering axis inclination and toe-out on turns,Rear wheel
settings that can be made on many modern vehicles are
camber and toe,Modern practice is to check both front and
rear wheel alignment,Note that the various alignment angles
are all related,A change in one can alter the others,
Alignment Measurement Values
14 All alignment values,except for toe,are measured in
degrees,Toe is measured in fractions of an inch or millimeters.
Caster
15 Positive caster tends to force the wheels to travel in a
straight ahead position,It also assists in recovery (wheels
turning back to straight ahead position) after making a turn.
On late model cars,there is often little or no positive caster,
Positive caster makes it more difficult to turn the wheels from
the straight ahead position than when no caster angle is
present [1].
17 Another aspect of positive caster is a mild tipping effect
when cornering,When making a right turn,the right wheel will
cause the steering knuckle to raise slightly,while the left wheel
will allow the knuckle to lower,creating the tipping effect,If
the left side of the vehicle was allowed to rise during a right
turn,it would have an adverse effect on the vehicle's cornering
ability.
18 To ease turning,many cars employ a negative caster angle,
which angles the top of the steering knuckle to front of car,
This will ease steering while also causing the mild tipping effect
needed when cornering,
Camber
19 Camber is the tilting of the wheel centerline,viewed from
the front of the vehicle,away from a true vertical line,Camber
angles are usually small,usually no more than 1o positive or
negative from zero,An incorrect camber setting will cause
pulling and tire wear.
Steering Axis Inclination
42 The steering knuckle ball joints are closer together at the
top than the bottom,The steering axis (view from the front of
the car) places the centerline of the steering ball joints closer
to the centerline of the wheel,This angle is known as steering
axis inclination,or SAI.
43 When the wheel centerline is to the outside of the center
line of the steering axis (where they intersect the road),the
wheels tend to toe-out,This is caused by the road-tire
resistance pushing back on the spindle,causing it to swivel
backward on the ball joints or toe-out,When the centerline of
the wheel intersects the road at a point inside of the steering
axis centerline intersection,the wheels tend to toe-in (tires are
closer together in the front than in the back).
Toe
45 Toe is the relative positions of the front and rear of a tire
in relation to the other tire on the axle,Note that distance at
the back of the tires is greater than distance in the front,Rear-
wheel drive vehicles are toed in to compensate for the natural
tendency of the road-to-tire friction to force the wheels apart.
46 On some front-wheel drive vehicles,the front tires are
toed out,This is done to offset the force created by the drive
axles,which tend to pull the tires inward during operation,The
toe setting compensates for this and allows the front tires to
run parallel to one another while rolling straight down the road.
47 Toe compensates for the wheel movement tendencies plus
any wear or play in the steering linkage,Proper toe will allow
the tires to move forward without a scrubbing,scraping action
between the tire and road,Excessive toe conditions will cause
a rapid tire wear condition called feathering,Toe can also be
adjusted on most vehicles to set the steering wheel in the
centered position when driving straight ahead.
Toe-Out on Turns
66 When a car turns a corner,the inner wheel must turn in a
shorter radius (smaller circle) than the outer wheel,To allow
the inner wheel to cut more sharply,both wheels must be able
to toe-out on turns automatically,This essential action is
accomplished by bending both steering arms so that they angle
slightly toward the center of the vehicle.
Thrust Angle
48 Aligning all four wheels makes it possible to set the thrust
angle to ensure perfect wheel tracking,The thrust angle is an
imaginary line at a right angle (90o) to the rear axle,Ideally,
the thrust angle should be parallel with the vehicle's centerline,
The vehicle should follow this line with no deviation when
driving straight ahead,This is known as wheel tracking,If the
rear wheels are not tracking correctly,the vehicle will not travel
in a straight line unless the front wheels are turned to
compensate for the misalignment,This misalignment is often
referred to as dog tracking.
49 Tracking is set by aligning the vehicle's thrust angle with
its geometric centerline to obtain perfect tracking,However,
factory tolerances,accident damage,and normal wear make
perfect tracking rare,Perfect thrust angle alignment is also
more difficult on vehicles with front-wheel drive,four-wheel
drive,and four-wheel steering,The thrust angle should be
aligned as close as possible to the vehicle's geometric
centerline,This will reduce tire wear,increase fuel economy,
and improve handling.
Front Wheel Alignment Adjustments
51 On some vehicles,caster is adjusted by moving the lower
strut rod in or out,Fig.11-5,The rod has a threaded section
and locknuts to make adjustment easier,Fig.11-6 illustrates
how caster is adjusted on some vehicles with MacPherson strut
suspensions by loosening the nuts holding the top of the strut
tower and sliding the tower forward or backward,The strut
tower mounting holes may be cut or filed out to allow enough
movement.
Fig.11-5 Adjusting caster by moving the lower strut rod in
and out by turning adjusting nuts
Fig.11-6 Adjusting front caster by moving the strut tower
Fig,11-7 Sliding strut tower in or out to change camber
52 Fig,11-7 shows one common way of changing the
camber and caster by loosening the nuts holding the top of
the strut tower and sliding the tower in or out,In this design,
the rivets holding the top of the strut tower to the body are
drilled out or chiseled off and the tower moved to the desired
position,Another method uses an egg-shaped washer,
sometimes called an eccentric,or eccentric cam,attached to
the lower control arm,Fig.11-8.
Fig.11-8 Adjusting camber and/or caster can be adjusted by
rotating the eccentrics on the lower control arm
Fig.11-9 Adjusting front
camber by loosing and
turning the eccentric
57 In Fig.11-9,the camber is adjusted
by moving an eccentric located on the
top or bottom bolt holding the strut
assembly to the spindle,On other
designs,camber is adjusted by
loosening the strut bolts and pushing or
pulling the wheel into position,The strut
bolts are then retightened,The strut rod
mounting slots may require filing or
cutting to allow enough movement to
reach the desired camber angle.
58 On many vehicles,adjusting
caster will affect camber and vice versa,
For this reason,caster and camber are
usually adjusted and checked together,
Front toe is set by adjusting the tie rods,
Rear Wheel Alignment Adjustments
61 Since the rear wheels on most vehicles do not affect
steering,the most common effects of improper settings are tire
wear and noise,However,if the rear toe is off,it may be
difficult to center the steering wheel for straight ahead driving,
Note that there is no adjustment for caster on the rear wheels,
since this is an alignment angle that affects steering,and is not
needed on the rear.
Alignment Equipment
62 Wheel alignment equipment varies greatly,from simple
mechanical gauges to complex electronic devices,Simple
camber and caster checking devices,held by magnets to the
wheel hub,will allow fairly accurate checking,Toe can be
checked by using a trammel bar,or even a tape measure,
However,to do an accurate four-wheel alignment on a modern
vehicle,more elaborate equipment is needed.
63 The alignment machine itself should be able to
accurately measure all of the alignment angles,Modern
alignment machines must be capable of measuring the rear-
wheel alignment as well as front-wheel alignment,This
necessitates the use of rear wheel sensing devices,The wheel
mounted sensing devices used on modern alignment
machines are usually referred to as alignment heads.
65 Many alignment machines use wheel-mounted light
beam generators to measure the alignment angles,The latest
alignment machines use wheel mounted electronic sensors
and a self-contained computer to provide readouts on a
screen,Fig.11-10,There are many manufacturers of
alignment equipment,When checking and adjusting wheel
alignment,use quality equipment that is in good condition,
Wheel alignment is a precision operation; both equipment and
techniques must be perfect.
Fig.11-10 A computer wheel alignment display screen
小结
Wheel Alignment
Alignment Measurement Value
Front Wheel Alignment Adjustments
Rear Wheel Alignment Adjustments
Alignment Equipment
作业
熟记相关专业词汇
P259 EXERCIES Ⅰ &Ⅱ
SUSPENSION
AND STEERING SYSTEMS
TEXT C
Wheel Alignment
PROFESSIONAL ENGLISH
TEXT A
Wheel Alignment
Alignment Measurement Values
Front Wheel Alignment Adjustments
Rear Wheel Alignment Adjustments
Alignment Equipment
本次课学习内容本次课学习目标
掌握车轮定位的英文专业词汇
训练快速阅读能力，提高阅读速度
NEW WORDS
wandering ['w?nd?ri?] n.漫游,神志恍惚,离题
provision [pr?'vin] n.预备,防备,设备，装置
misalign ['mis?lain] v.不重合,未对准，失准
setting ['seti?] n.调整位置，设定值，安置,安装
caster ['kɑ:st?] n.主销后倾（角）
camber ['k?mb?] n.车轮外倾
toe [t?u] n.前束
toe-out [t?uaut] n.(负 )前束
toe-in [t?uin] n.(正 )前束
offset ['?:fset] n,& v.偏移,抵销
scraping ['skreipi?] n.刮,擦
scrubbing [skr?bi?] n.洗擦,擦净
imaginary [i'min?ri] a.假想的,想象的,虚构的
deviation [?di:vi'ei∫?n] n.背离，偏离
chisel ['t∫izl] n.凿子； v.凿，雕
eccentric [ik'sentrik] n.偏心轮； a.偏心的
trammel ['tr?m?l] n.束缚物，量规
elaborate [i'l?b?r?t] a.精心制作的
necessitate [ni'sesiteit] v.成为必要
PHRASES AND EXPRESSIONS
wheel alignment 车轮定位
steering axis
inclination
转向轴线内倾角
toe-out on turns 转弯负前束
tipping effect 侧倾效应
thrust angle 推力角，推力线
wheel tracking （前轮与后轮）同辙行驶
dog tracking 蛇形行驶
eccentric cam 偏心凸轮
Wheel Alignment
4 Wheel alignment is the process of measuring and correcting the
various angles formed by the front and rear wheels,spindles,and
steering arms,Correct alignment is vital,Improper alignment can
cause hard steering,pulling to one side,wandering,noise,and
rapid tire wear.
Types of Wheel Alignment
11 Rear-wheel drive vehicles require a two-wheel alignment or
front-wheel alignment only,The rear wheels are attached to a solid
rear axle assembly which cannot be adjusted,and generally stays
in alignment throughout the life of the vehicle.
12 Today,most front-wheel drive vehicles have provisions for
adjusting the rear wheels,In addition,many rear-wheel drive
vehicles are equipped with independent rear suspensions,which
also must be adjusted,Also,modern solid rear axles and
suspension systems are lightweight and can become misaligned,
Therefore,the four-wheel alignment,in which the front and rear
wheel alignment angles are checked and adjusted,is commonly
performed.
159 Adjustable front wheel settings on most modern vehicles
are caster,camber,and toe,Nonadjustable settings are
steering axis inclination and toe-out on turns,Rear wheel
settings that can be made on many modern vehicles are
camber and toe,Modern practice is to check both front and
rear wheel alignment,Note that the various alignment angles
are all related,A change in one can alter the others,
Alignment Measurement Values
14 All alignment values,except for toe,are measured in
degrees,Toe is measured in fractions of an inch or millimeters.
Caster
15 Positive caster tends to force the wheels to travel in a
straight ahead position,It also assists in recovery (wheels
turning back to straight ahead position) after making a turn.
On late model cars,there is often little or no positive caster,
Positive caster makes it more difficult to turn the wheels from
the straight ahead position than when no caster angle is
present [1].
17 Another aspect of positive caster is a mild tipping effect
when cornering,When making a right turn,the right wheel will
cause the steering knuckle to raise slightly,while the left wheel
will allow the knuckle to lower,creating the tipping effect,If
the left side of the vehicle was allowed to rise during a right
turn,it would have an adverse effect on the vehicle's cornering
ability.
18 To ease turning,many cars employ a negative caster angle,
which angles the top of the steering knuckle to front of car,
This will ease steering while also causing the mild tipping effect
needed when cornering,
Camber
19 Camber is the tilting of the wheel centerline,viewed from
the front of the vehicle,away from a true vertical line,Camber
angles are usually small,usually no more than 1o positive or
negative from zero,An incorrect camber setting will cause
pulling and tire wear.
Steering Axis Inclination
42 The steering knuckle ball joints are closer together at the
top than the bottom,The steering axis (view from the front of
the car) places the centerline of the steering ball joints closer
to the centerline of the wheel,This angle is known as steering
axis inclination,or SAI.
43 When the wheel centerline is to the outside of the center
line of the steering axis (where they intersect the road),the
wheels tend to toe-out,This is caused by the road-tire
resistance pushing back on the spindle,causing it to swivel
backward on the ball joints or toe-out,When the centerline of
the wheel intersects the road at a point inside of the steering
axis centerline intersection,the wheels tend to toe-in (tires are
closer together in the front than in the back).
Toe
45 Toe is the relative positions of the front and rear of a tire
in relation to the other tire on the axle,Note that distance at
the back of the tires is greater than distance in the front,Rear-
wheel drive vehicles are toed in to compensate for the natural
tendency of the road-to-tire friction to force the wheels apart.
46 On some front-wheel drive vehicles,the front tires are
toed out,This is done to offset the force created by the drive
axles,which tend to pull the tires inward during operation,The
toe setting compensates for this and allows the front tires to
run parallel to one another while rolling straight down the road.
47 Toe compensates for the wheel movement tendencies plus
any wear or play in the steering linkage,Proper toe will allow
the tires to move forward without a scrubbing,scraping action
between the tire and road,Excessive toe conditions will cause
a rapid tire wear condition called feathering,Toe can also be
adjusted on most vehicles to set the steering wheel in the
centered position when driving straight ahead.
Toe-Out on Turns
66 When a car turns a corner,the inner wheel must turn in a
shorter radius (smaller circle) than the outer wheel,To allow
the inner wheel to cut more sharply,both wheels must be able
to toe-out on turns automatically,This essential action is
accomplished by bending both steering arms so that they angle
slightly toward the center of the vehicle.
Thrust Angle
48 Aligning all four wheels makes it possible to set the thrust
angle to ensure perfect wheel tracking,The thrust angle is an
imaginary line at a right angle (90o) to the rear axle,Ideally,
the thrust angle should be parallel with the vehicle's centerline,
The vehicle should follow this line with no deviation when
driving straight ahead,This is known as wheel tracking,If the
rear wheels are not tracking correctly,the vehicle will not travel
in a straight line unless the front wheels are turned to
compensate for the misalignment,This misalignment is often
referred to as dog tracking.
49 Tracking is set by aligning the vehicle's thrust angle with
its geometric centerline to obtain perfect tracking,However,
factory tolerances,accident damage,and normal wear make
perfect tracking rare,Perfect thrust angle alignment is also
more difficult on vehicles with front-wheel drive,four-wheel
drive,and four-wheel steering,The thrust angle should be
aligned as close as possible to the vehicle's geometric
centerline,This will reduce tire wear,increase fuel economy,
and improve handling.
Front Wheel Alignment Adjustments
51 On some vehicles,caster is adjusted by moving the lower
strut rod in or out,Fig.11-5,The rod has a threaded section
and locknuts to make adjustment easier,Fig.11-6 illustrates
how caster is adjusted on some vehicles with MacPherson strut
suspensions by loosening the nuts holding the top of the strut
tower and sliding the tower forward or backward,The strut
tower mounting holes may be cut or filed out to allow enough
movement.
Fig.11-5 Adjusting caster by moving the lower strut rod in
and out by turning adjusting nuts
Fig.11-6 Adjusting front caster by moving the strut tower
Fig,11-7 Sliding strut tower in or out to change camber
52 Fig,11-7 shows one common way of changing the
camber and caster by loosening the nuts holding the top of
the strut tower and sliding the tower in or out,In this design,
the rivets holding the top of the strut tower to the body are
drilled out or chiseled off and the tower moved to the desired
position,Another method uses an egg-shaped washer,
sometimes called an eccentric,or eccentric cam,attached to
the lower control arm,Fig.11-8.
Fig.11-8 Adjusting camber and/or caster can be adjusted by
rotating the eccentrics on the lower control arm
Fig.11-9 Adjusting front
camber by loosing and
turning the eccentric
57 In Fig.11-9,the camber is adjusted
by moving an eccentric located on the
top or bottom bolt holding the strut
assembly to the spindle,On other
designs,camber is adjusted by
loosening the strut bolts and pushing or
pulling the wheel into position,The strut
bolts are then retightened,The strut rod
mounting slots may require filing or
cutting to allow enough movement to
reach the desired camber angle.
58 On many vehicles,adjusting
caster will affect camber and vice versa,
For this reason,caster and camber are
usually adjusted and checked together,
Front toe is set by adjusting the tie rods,
Rear Wheel Alignment Adjustments
61 Since the rear wheels on most vehicles do not affect
steering,the most common effects of improper settings are tire
wear and noise,However,if the rear toe is off,it may be
difficult to center the steering wheel for straight ahead driving,
Note that there is no adjustment for caster on the rear wheels,
since this is an alignment angle that affects steering,and is not
needed on the rear.
Alignment Equipment
62 Wheel alignment equipment varies greatly,from simple
mechanical gauges to complex electronic devices,Simple
camber and caster checking devices,held by magnets to the
wheel hub,will allow fairly accurate checking,Toe can be
checked by using a trammel bar,or even a tape measure,
However,to do an accurate four-wheel alignment on a modern
vehicle,more elaborate equipment is needed.
63 The alignment machine itself should be able to
accurately measure all of the alignment angles,Modern
alignment machines must be capable of measuring the rear-
wheel alignment as well as front-wheel alignment,This
necessitates the use of rear wheel sensing devices,The wheel
mounted sensing devices used on modern alignment
machines are usually referred to as alignment heads.
65 Many alignment machines use wheel-mounted light
beam generators to measure the alignment angles,The latest
alignment machines use wheel mounted electronic sensors
and a self-contained computer to provide readouts on a
screen,Fig.11-10,There are many manufacturers of
alignment equipment,When checking and adjusting wheel
alignment,use quality equipment that is in good condition,
Wheel alignment is a precision operation; both equipment and
techniques must be perfect.
Fig.11-10 A computer wheel alignment display screen
小结
Wheel Alignment
Alignment Measurement Value
Front Wheel Alignment Adjustments
Rear Wheel Alignment Adjustments
Alignment Equipment
作业
熟记相关专业词汇
P259 EXERCIES Ⅰ &Ⅱ
