UNIVERSITATEA TRANSILVANIA DIN BRASOV

FACULTATEA DE INGINERIE MECANICA

CATEDRA: AUTOMOBILE RUTIERE

DISCIPLINA: MECANISME

PROIECT SEMESTRUL II

SUSPENSIE DOUBLE WISHBONE

STUDENT: DAMIAN RADU-MIHAI

PROF. DORU TALABA

ANUL UNIVERSITAR 2013-2014

Double wishbone suspension

In automobiles, a double wishbone (or upper and lower A-arm) suspension is an independent suspension design using two (occasionally parallel) wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle.

The shock absorber and coil spring mount to the wishbones to control vertical movement. Double wishbone designs allow the engineer to carefully control the motion of the wheel throughout suspension travel, controlling such parameters as camber angle, caster angle, toe pattern, roll center height, scrub radius, scuff and more.

Two of the most popular suspensions systems for passenger cars today are the double wishbone suspension system and the MacPhersons strut suspension system. While it is more usual to see the double wishbone system at the rear end of the car, MacPhersons solution normally finds its place at the front end of the car. Both types of suspensions have their own sets of benefits and limitations, thus let us look at both the advantages and disadvantages of both systems, starting with the simpler of the two, the MacPherson struts.

MacPherson Struts The struts are designed with more simplicity, and thus takes up less space horizontally. As a result, passengers get more compartment place in the car. They also display low un-sprung weight, an advantage that reduces the overall weight of the vehicle as well as increases the cars acceleration. Lower un-sprung weight also makes your ride more comfortable. Another major advantage of this system is its ease of manufacturing as well as low cost of manufacture compared to other stand-alone suspension systems. Without an upper arm, the suspension system designers can directly block vibration from reaching the passenger compartment.

Choosing the tires is an important task. Fundamentally, brakes dont stop the car, the engine doesnt accelerate the car and the steering doesnt turn the car. All these tasks are achieved as a result reaction between the tyre contact patch and the ground. Slick tires are a type of tires that have a smooth tread used mostly in auto racing. By eliminating any grooves cut into the tread, this type of tires provide the largest possible contact patch to the road, and maximize traction for any given tire dimension. Slick racing tyres only work properly when they are hot, at their optimum working pressure. Slick tires are used only on dry circuits. For wet circuits wet tires(rain tires) are used. Rain tyres are cut with patterned grooves in them. This allows the tyre to quickly displace the water between the ground and the rubber on the tyre. If the water is not dispalced, the car will experience an effect called hydroplaning as the rubber will not be in contact with the ground. The first choice that must be made when choosing tyres is what size to use and this dictates the wheel size both diameter and width. By using 13 wheels rather than 10 the car has more grip, better handling and can have larger brakes. In my opinion, because of the size limits imposed by this project, I choose 205/55/R13 tires.

A: 2200 + 10k = 2300mm

E: 1200 + 2k = 1220mm

3DS Solidworks suspension computer aided design.

Position 1 : -10 degree angle inclinement

Position 2 : -5 degree angle inclinement

Position 3 0 degree inclinement

Position 4 - +5 degree inclinement

Position 5 : +10 degree inclinement

5. Write and solve the loop closure equation. Present numerical results for 5 positions

The input data are:

l1 = lower arml2 = linchpinl3 = upper arm

m = distance from point M to point A

p = hub length

n = distance from point N to A

r = wheel radius

a = steering rod length

E = track width

= initial pivot angle

, 0= caster angle

= chamber angle

01 = initial angle of lower arm

03 = initial angle of upper arm

01, 03 = position angles

0 = transversal inclination angle

Loop closure equation calculus

figure 3

Schematic of the suspension mechanism

The unit vectors of the elements of the two loops in the x, y, z using the reference systems from figure 3, are given by:

The dimensions l4 = M0N0 and the direction of the unit vector u4 are given:

The current angles of position of the pivot are obtained from the square loop M0MNN0M0 and are given by the following relations:

The angle 3 needed for the calculus of u3x,u3y,u3z, from the anterior relations, is also obtained from the loop M0MNN0M0 and is given by the following relations:

The induced steering angle a = a is given by the relation:

Variation of the chamber angle:

Track width variation related to the movement of the car:

Wheel base variation related to the movement of the car:

7. Conclusions, final dimensions and recommendations for the detailed design:

In conclusion, the Double Wishbone suspension mechanism is suitable for a car with the given dimensions. As shown in the measurements and the calculus, the final dimensions of the suspension mechanism, are:

Inferior arm of the suspension mechanism

234.39mm

Superior arm of the suspension mechanism

191.01mm

Linchpin

204mm

Distance between the fixed point of the inferior and superior arms

184.853mm

For this dimensions, the angle do not vary much, and the suspension can be built. I think that the double wishbone suspension mechanism is more suitable for this car than any other suspension, because of its simple and efficient design.