Q.. Explain the construction of the rigid front axle.


Construction of the Rigid Front Axle

It is a reversed Elliot type. The king pin is secured in the eye of axle beam with the help of cotter bolt, the stub axle moves on king pin and the bronze bushes are used in the stub axle to reduce friction. For lubrication, a grease nipple is fitted on the stub axle which should be greased at each service. For lubrication of lower bush, sometimes a hole is drilled in king pin which takes oil from the housing to the lower bush so that this bush remains lubricated for ease of steering. As there is a lot of weight on the axle beam, the weight makes the stub axle tight on king pin. To releive this in some of the axles, the king pin is fitted to stub axle with the help of bottom thrust plate in between, so that stub axle does not rest on eye boss of axle beam and king pin is free in its bushes. To adjust, the play shims are added or removed over the thrust plate, so that king pin is free to rotate or move. In some vehicles, instead of thrust plate, thrust bearings are used. These are fitted under the lower bones of axle eye, a thrust bearing is used to take up the thrust due to load on the vehicle and ease of steering. In this type of axle, grease nipples are used for lubrication of bronze bushes fixed on the stub axle. On the left side stub axle, one steering arm is fitted and on the right side two, one of which is linked with left hand side stub axle with the help of tie rod. The other arm is linked with the
steering unit with the help of pull push rod. Due to this, on moving the steering wheel, both the stub axle move simultaneously. Brake back plate is bolted with the stub axle on which bake shoe assembly with wheel cylinder are mounted.


Q.. Explain the constructional details of a leaf spring with the help of a neat sketch.


Leaf Spring

It is a composite spring used in automobile suspensions, consisting of several layers of flexible metallic strips joined ta act as a single unit. It takes the form of a slender arc shaped length of spring steel of rectangular cross section. The centre of the arc provides location for the axle, while tie holes are provided at either end for attaching to the vehicle body. All the strips are bounded together by means of steel straps as shown in figure below. It is supported on the axle of the vehicle by means of U-bolt. One end of the spring is mounted on the frame with a simple pin and the other end is connected to a shackle in order to compensate for the deflection of spring when the wheels of the vehicle move up due to the projections on the load surface. It both the ends of the spring are fixed, then the spring will not be able to accommodate this change of length. Leaf spring car serve locating and to some extent damping as well as springing function. For heavy vehicles, they have the advantage of spreading the load more widely over the vehicle chassis.



Q.. What are helper springs?


Helper Springs

Helper springs are used in addition to the main spring to increase the life of the main springs for carrying heavy loads. It carries 6 to 7 leaves and is fixed to the main spring assembly at centre. The ends of the helper springs are kept loose so thatĀ  these ends could touch the special brackets fixed to the side member of the chassis frame under heavy loads. It is generally used in many commercial vehicles like buses and trucks. When the load on the vehicle is small, these springs do not come into operation. As the load increases, the main spring deflects so much that the ends of the helper spring touches the two brackets on the chassis frame making the helper springs to operate as to share some of the load of the main spring. By using helper springs, wide range of loadings can be handled successfully. Its arrangement is shown in figure below.



Q..Sketch and explain the construction and working of torsion bar.




Torsion bar is a straight solia bar made up of heat treated alloy spring steel. It has a circular or square cross section. OneĀ  end of it is connected to chassis frame and the other end is connected to the end of a wheel arm and is supported by bearing When vehicle moves on a rough road, then wheels vibrate up and down, thus exerting torque on torsion bar which then acts as a spring.

When vehicle moves over a rough road, wheels vibrate up and down which causes the wheel arm to move up and down, as a result of which bar will be twisted in torsion. The end of torsion bar or torsion spring attached to the frame is secured while the free end is supported by support bearing. Torsion bars are generally used in independent system. This bar is light in weight and occupies less space. The disadvantage of this bar is that, it cannot take braking or driving thrust and also there is no friction which controls the vibrations produced due to road shocks.


Q.. Explain the connecting of telescopic shock


Telescopic Type Shock Absorber

As shown in figure, it has upper eye and lower eye.
The upper eye is connected to the axle and lower eye is
connected to the frame. Basic parts of telescopic shock
absorber are,

(1) Two-way valve
(ii) Rod
(ii) Cylinder

A two-way valve is attached to the rod. Another two
way valve is attached to the lower end of the cylinder. The
fluid is filled above the top valve and below and also in the
annular space between the cylinder and the tube, which is
connected to the space below the bottom one-way valve. The
head has a gland. The fluid if any is scrapped off by the rod
and passes to the annular space through the vertical passage.

Consider, the vehicle comes across a bump. The bottom
or lower eye which is connected to the frame would move up.
It causes the fluid from the bottom side of the top valve to
move upper side. But, since the volume of space above the
top valve is less than the volume of the rod, causes the fluid
to exert the pressure on the bottom valve. The passing of the
fluid through valve opening provides damping force. When
the lower eye moves down the fluid passes from the upper
side of the top valve to the lower side and also from the lower
side of lower valve to its upper side.

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