Q.. Describe the construction and working of rotary vane type hydraulic shock absorber
Rotary Vane Type Shock Absorber
Rotary vane shock absorber consists of a cylindrical
hollow chamber filled with hydraulic oil. This chamber is fixed
to chassis, which contains a closely fitted rotor carrying a
vane mounted on a pin. The vane has a small orifice, through
which oil is allowed to pass through it. The other end of pin is
fixed to fulcrum as shown in figure. With the help of some
suitable linkages, the lever is connected to axle.
When the vehicle experiences a bounce due to road
shock, an upward force is exerted at the fulcrum. Due to this
force, the rotor rotates in clockwise direction as shown in
figure by arrows. When the force is exerted by the oil due to
road shock on the vane, the oil is restricted to flow through
the orifice. A pressure is created in the chamber when the oil
enters the other region. Due to this pressure, the movement
of fulcrum is restricted. In turn it resists the axle movement.
Similarly, for rebound, the oil is made to flow back from the
same orifice to the previous chamber. Thus, resisting the
movement of fulcrum. However, the resistance of this type of
shock absorber increases with the increase in speed of spring
deflection. Therefore it has become obsolete and very rarely
Q.. Describe the various types of Independent front suspension systems.
Types of independent front system are given below
I. Wishbone type or parallel link type
2. Macpherson strut type 3.Vertical slide type
4.Trailing link type
5.Swinging Half axle type.
1.Wishbone Type or Parallel Link Type
The essential parts of wishbone type suspension
(i) Smaller upper wishbone
(ii) Longer lower wishbone
(iii) Connecting arm
(iv) Coiled spring
(v) Frame cross-member.
In this popular type of independent system, coil
springs are mostly used. There are two suspension arms of
control on either sides. The shape of these suspension arms
is like a leg of chicken wishbone or the letter. These control
arms are connected to the frame at the open end. The upper
and lower wishbones are connected to the chassis frame. The
upper arm is shorter than the lower one. This keeps its wheel
The closed ends of both the arms are connected to the
steering knuckle support. Steering knuckle is attached to this
support by means of king pin. A coil spring is placed as shown
in between the lower suspension arm and the frame.
During motion, when the wheel encounters a bump,
the weight of the vehicle is transferred to the coil spring
through the connecting arm, upper wishbone and the cross
arm. This is then transmitted to lower wishbone which pushes
up the shock absorber. The wishbone arms are shaped as Y
profile in order to keep the wheels in correct position, to
resist forces produced due to acceleration, braking and
2. Mac pherson Strut Type
The up and down movement of wheels resulting into a
change in the wheel chamber is a big drawback of wishbone
Type suspension. Moreover, double wishbone arms make this
system a heavier one. These defects have been eliminated in
the Mac pherson strut type independent front suspension.
It consists of a lower wishbone only whereas the upper
Wishbone has been replaced by strut (a member under
compression). On one end, the lower wishbone is hinged to
the cross-member of vehicle frame while the other end is
listened to a channel shaped connector This connector is
centrally attached to the stub axle and also to the strut on its upper side.the strung ends are so shaped that they hold on the shock absorber and the coiled spring enclosing it.
Since, the space occupied by this arrangement is less,
therefore it is more favored suspension system on the front
wheel driven vehicles. It also allows more space for the engine.
The road safety and riding comforts forces are minimized due
to better wheel alignment. The up spring weights are also
reduced due to a lighter construction
3. Vertical Slide Type
During the up and down movement of the wheels,
the distance between wheels should not vary i.e., a constant
wheel track must be maintained. If constant wheel track is not
maintained, scuffing action occurs that results in quicker wear
of tyres. It can be avoided by employing a vertical slide
In this, the stub axle slides vertically on a long swivel
pin which carries the main spring as well as a small coiled
spring. The up and down motion of the road wheel due to a
bump causes up and down sliding of the swivel block which
either compresses the main spring or stretches it. The rebound
spring is used to exert rebounding pressure.
4. Trailing Link Type
This arrangement consists of a coiled spring placed in
horizontal position. One end of the spring is attached to frames
side member and the other end is fixed on one end of the
trailing arm. The trailing arm, at its other end is connected to
front wheel shaft which carries a wheel hub.
The mechanism of this type is explained as follows.
When a vehicle moves on a road bump. the wheels of the
vehicle experiences upward and downward movement and
this is transferred to the spring via trailing arm. Due to this,
vibrations are produced in the spring which are forcibly
damped by means of a multiplate type shock absorber
provided as shown in figure (4).
5. Swinging Half-axle Type
This uses only one transverse arm, which is known as
wishbone member and is held rigidly to the wheel stub-axle
through a king pin steering joint while pivoting on the body
sub-frame. The forks of the wishbone arm are spread widely
apart at the pivot joints to absorb any driving and braking
reaction torque slowly by the swinging arm member. The spring
installed between the body structure and the swinging arm,
supports only the vehicle’s weight. The swinging arm and the
supporting sub-frame pivot points completely absorb side
forces and reactions.