a simple macpherson strut suspension on the left front wheel of a rear

8/3/2019 A Simple MacPherson Strut Suspension on the Left Front Wheel of a Rear

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A simple MacPherson strut suspension on the left front wheel of a rear-wheel drive

vehicle. Front of the vehicle top right in image.

Red section: Steering knuckle or hub carrier

Blue section: Lowercontrol armor track control arm

Light blue section: Steering geartie rod

Lower purple section:Radius rod

Upper purple Section:Coil spring

Yellow section: Tubular housing containingshock absorberor damper

Inautomobiles, the tie rods are part of thesteeringmechanism. They differ from the

archetypical tie rod by both pushing and pulling (operating in both tension and

compression). In the UK, these items are generally referred to as track rods.
http://en.wikipedia.org/wiki/Control_armhttp://en.wikipedia.org/wiki/Control_armhttp://en.wikipedia.org/wiki/Control_armhttp://en.wikipedia.org/wiki/Tie_rodhttp://en.wikipedia.org/wiki/Tie_rodhttp://en.wikipedia.org/wiki/Tie_rodhttp://en.wikipedia.org/wiki/Radius_rodhttp://en.wikipedia.org/wiki/Radius_rodhttp://en.wikipedia.org/wiki/Radius_rodhttp://en.wikipedia.org/wiki/Coil_springhttp://en.wikipedia.org/wiki/Coil_springhttp://en.wikipedia.org/wiki/Coil_springhttp://en.wikipedia.org/wiki/Shock_absorberhttp://en.wikipedia.org/wiki/Shock_absorberhttp://en.wikipedia.org/wiki/Shock_absorberhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Shock_absorberhttp://en.wikipedia.org/wiki/Coil_springhttp://en.wikipedia.org/wiki/Radius_rodhttp://en.wikipedia.org/wiki/Tie_rodhttp://en.wikipedia.org/wiki/Control_arm


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The tie rod is part of the steering mechanism in a vehicle. A tie rod is a slenderstructural rod that is used as a tie and capable of carrying tensile loads only.

A tie rod consists of an inner and an outer end. The spokes on a bicycles wheels are

tie rods. As the ratio of its length to the radius of gyration of its cross section is

normally quite large, it would likely buckle under the action of compressive forces.

The tie rod transmits force from the steering center link or the rack gear to the steering

knuckle. This will cause the wheel to turn. The outer tie rod end connects with an

adjusting sleeve, which allows the length of the tie rod to be adjustable. This

adjustment is used to set a vehicles alignment angle.

The working strength of the tie rod is that of the product of the allowable working

stress and the minimum cross-sectional area. If the threads are cut into a cylindrical

rod, that minimum area can be found at the root of the thread. Rods are often made

thicker at the ends and this then means that the tie rod does not become weaker when

the threads are cut into it.

Tie rods are connected at the ends in various ways. But it is desirable that the strength

of the connection should be at least an equal strength to that of the rod. The ends can

be threaded and then passed through drilled holes or shackles (this is a U-shaped piece

of metal that is secured with a pin or bolt across the opening), and then retained by

nuts that are screwed on the ends.

If the ends are threaded right hand and left hand, the length between the points of

loading may be altered. This then brings a second method for prestressing the rod at

will by turning it in the buts so that the length will be charged.

A turnbuckle (a device that is used for adjusting the tension in tie rods) can

accomplish the same purpose. Another way of making any end connections is to forge

an eye or hook on the rod.

It is advisable that your vehicles steering and suspension systems are checkedregularly, at least once a year along with a complete wheel alignment. A worn tie rod

can cause wandering, erratic steering and also major tire wear.

If a tie rod is necessary then a wheel alignment will also be required because tie rod

replacement will disturb the alignment setting.

As the ratio of its length to the radius of gyration of its cross section is normally quite

large, it would likely buckle under the action of compressive forces.

The tie rod transmits force from the steering center link or the rack gear to the steering

knuckle. This will cause the wheel to turn. The outer tie rod end connects with an

adjusting sleeve, which allows the length of the tie rod to be adjustable. Thisadjustment is used to set a vehicles alignment angle.


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The working strength of the tie rod is that of the product of the allowable working

stress and the minimum cross-sectional area. If the threads are cut into a cylindrical

rod, that minimum area can be found at the root of the thread. Rods are often made

thicker at the ends and this then means that the tie rod does not become weaker when

the threads are cut into it.

Tie rods are connected at the ends in various ways. But it is desirable that the strength

of the connection should be at least an equal strength to that of the rod. The ends can

be threaded and then passed through drilled holes or shackles (this is a U-shaped piece

of metal that is secured with a pin or bolt across the opening), and then retained by

nuts that are screwed on the ends.

If the ends are threaded right hand and left hand, the length between the points of

loading may be altered. This then brings a second method for prestressing the rod at

will by turning it in the buts so that the length will be charged. A turnbuckle (a device

that is used for adjusting the tension in tie rods) can accomplish the same purpose.

Another way of making any end connections is to forge an eye or hook on the rod.

It is advisable that your vehicles steering and suspension systems are checked

regularly, at least once a year along with a complete wheel alignment. A worn tie rod

can cause wandering, erratic steering and also major tire wear. If a tie rod is necessarythen a wheel alignment will also be required because tie rod replacement will disturb

the alignment setting.

Reff

1. http://news.carjunky.com/how_stuff_works/what-is-a-tie-rod-abc170.shtml

Automotive Suspension Failures

by

Charles C. Roberts, Jr.

Automobile suspension systems are mechanical devices whose function

is to support the vehicle body and other components above the wheels.

There are a variety of designs including coil spring, longitudinal leaf,transverse leaf, torsion bar, MacPherson, Christy, and solid axle.
http://news.carjunky.com/how_stuff_works/what-is-a-tie-rod-abc170.shtmlhttp://news.carjunky.com/how_stuff_works/what-is-a-tie-rod-abc170.shtmlhttp://news.carjunky.com/how_stuff_works/what-is-a-tie-rod-abc170.shtml


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Figure 1 - MacPherson strut suspension

Figure 2 - Solid axle suspension


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Figure 3 - Control arm suspension with coil springs

Figures 1 through 3 are drawings of typical suspension systems found

on most vehicles on the road. Figure 1 is the classical MacPherson strut

suspension, which is common on many front drive vehicles. The strut,

which is also a shock damper, moves vertically while the control arm

limits transverse and longitudinal movement. The system is compact,

efficient and adapts easily to front and rear applications. Figure 2 is a

view of an earlier design: the solid axle suspension with king pin. The

solid axle beam is supported by springs and connects to a swiveling axlevia the king pin. This suspension is often used on heavier vehicles such

as trucks and on some older vehicles. Figure 3 depicts a control arm

suspension with coil springs. This independent suspension system is

used on many older and rear wheel drive vehicles. Automobile accident

investigation may focus on a vehicle's suspension system, being guided

by evidence of possible malfunction or statements from the insured

driver or witnesses. Automotive suspension failure can be caused by a

design defect, a manufacturing defect, poor maintenance or the

accident.


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Figure 4

Figure 4 is a view of a MacPherson front suspension on the right side of

a compact car. Evidence suggests that the lower ball joint (arrow)

failed, causing the vehicle to steer uncontrollably, which resulted in an

accident. Figure 5 is a top view of the ball joint showing wear patterns

from the drive shaft rotor just above the ball joint. The ball joint itself

was dry and badly worn with no evidence of lubrication. The vehicle

had over 100,000 miles on the odometer. The wear on the top of the ball

joint suggests that for a period of time, the joint had failed and had

moved vertically and rubbed against the axle rotor. The rotor was

acting as a retainer of the joint, preventing it from separating from the

suspension. This condition would result in excessive play in the steering,

plus a loud noise that should have acted as a warning to the insured

driver that a problem existed. The driver continued to operate the

vehicle until the accident occurred. The failure of the ball joint was

determined to be maintenance related with no evidence of a

manufacturing defect.


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Figure 5

Figure 6

Figure 6 is a view of a king pin assembly from a large road tractor.

Figure 7 is a close-up of a crack in the king pin housing. A truck driver

claimed loss of control while on a winding rural highway. Analysis of

the housing fracture surface indicated that environmentally assisted

cracking had caused the failure. What initiated the environmentally


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assisted cracking was severe wear from lack of lubrication, amaintenance related failure.

Figure 7


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Figure 8

Figure 8 is a view of a front control arm suspension with a fractured tie

rod end. Figure 9 is a close-up of the fracture surface. The driver

indicated that the tie rod end suddenly failed, and an accident resulted.

The lower arrow in Figure 9 points to a corrosion related crack that

had formed through the tubing wall. Despite the corrosion damage to

the tubing, the fracture surface (white area, upper arrow) is

characteristic of a sudden overload, indicating that a sudden failure

under normal conditions was unlikely. The likely cause would be animpact with a noncompliant object such as a curb or another vehicle.


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Figure 9

Figure 10

Figure 10 is a view of a rear control arm bolt in a late model front drive

automobile. The driver complained of loss of control, which resulted in


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a vehicle rollover and personal injury. The right end of the bolt hadfractured. A close-up of the fracture surface is shown in Figure 11.

Figure 11

Metallurgical analysis of the part revealed improper heat treating of the

bolt, which was the cause of the failure and was a manufacturing defect.

When the bolt failed, the right rear control arm parted from the

suspension, causing the right rear tire to point outward at an angle. The

ensuing yaw motion terminated with a vehicle rollover.


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Figure 12

Figure 12 depicts the right rear tire of a vehicle with a severe toe-in of

about 30 degrees. The body damage is characteristic of having struckanother vehicle. The control arm and tie rod end was badly bent, but

not fractured, suggesting that this condition was most likely a result of

the impact. Suspension systems are often blamed as a cause of an

accident. Driver error can explain many of the accidents, while the

remaining ones can be attributed to poor maintenance, design or

manufacturing defects. Obviously, insurers are interested in causes of

failure that suggest negligent behavior by some other party for

subrogation purposes. If legal action is contemplated, then potential

litigants should be placed on notice as to the existence of the evidence

and a joint protocol developed before any destructive testing isperformed.

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Design a slender, light table legs that will support the applied design load and will not

fracture if struck.

Function

Column, supporting compressive loads

Objective

Minimize mass and maximize slenderness

Constraints

Specified length, Must not buckle Must not fracture if struck

Free Variables

Diameter of the legs

Choice of materialsmass
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mass:

Maximum elastic buckling load:

Solving for r

Inverting equation (2) gives and equation for the thinnest legs which will not buckle:

to yield the second materials index (maximize):


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Set M1to be minimum of 5 and M2to be greater than 100 (an arbitrary choiceit canbe modified later if a wider choice of materials to be screened is desired). Candidate

materials include some ceramics, CFRP

engineering ceramics are not toughlegs are subjected to abuse and this makes them a

bad selection for this application

Selection = CFRP

must consult designer wrtcostexpensive


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a simple macpherson strut suspension on the left front wheel of a rear

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