W-6-7-Ch-5-Tank Suspension system.pptx

Tank Suspension
System
1
CV Systems-Prof (Col) GC Mishra, Retd

Definitions
Sprung Mass/Weight
 In a vehicle with a suspension, sprung mass (or sprung weight) is the portion of
the vehicle's total mass that is supported above the suspension, including in
most applications approximately half of the weight of the suspension itself.
 The sprung weight typically includes the body, frame, the internal components,
passengers, and cargo.
 It does not include the mass of the components suspended below the
suspension components (including the wheels, wheel bearings, brake rotors,
calipers, and/or Continuous tracks (Also called caterpillar tracks), if any), which
are part of the vehicle's unsprung weight.
2

Unsprung Mass/Weight
 In a ground vehicle with a suspension, the unsprung weight (or the unsprung
mass) is the mass of the suspension, wheels or tracks (as applicable), and other
components directly connected to them, rather than supported by the
suspension.
 Unsprung weight includes the mass of components such as the wheel axles,
wheel bearings, wheel hubs, tires, and a portion of the weight of drive shafts,
springs, shock absorbers, and suspension links.
3

CV Systems-Prof (Col) GC Mishra, Retd 4
Wheel Travel
The travel of the wheel due to the weight of the tank.
Bump (& Rebound) Travel
It is additional to the above and is caused by the irregularities in
the ground causing a bump or, rebound.
Maximum Wheel Travel
It is the total of the above two.

Human Response to Vibrations
 The surfaces over which tanks move are generally uneven. In consequence they
give rise to vibrations which affect the crews and which can seriously degrade
or, restrict their performance.
 The severity of the vibrations depends in the first instance on the geometry and
hardness of the surfaces over which tanks move and on the speed of tanks.
 However, it also depends on the suspensions of tanks, which are intended to
minimise the displacements and the forces experienced by them.
 The nature of the surfaces which cause the vibrations varies considerably.
 Some are the rough surfaces of roads while others consist of the undulating
surfaces of soft soils but the most difficult, from the vibrations point of view,
are represented by broken, hard ground, which can severely restrict the speed
of tanks over it.
 Restrictions on speed can also be imposed by discrete terrain features, such as
ditches. 5

 When the wheels rise and fall over road surface irregularities, the springs of
suspension system momentarily act as energy storage devices and thereby
reduce greatly the magnitude of impact loading transmitted by the suspension
system to the car structure.
 The energy of impact loading is related to the product of the disturbing force
and the distance over which it is constrained to act by the spring medium.
 It thus follows that a soft or low-rate spring, which permits a generous
deflection for a moderate loading, will reduce to a minimum the impact or
disturbing forces transmitted to the vehicle occupants.
 The rate of the spring is equal to the load per unit of deflection.

The basic function of the suspension system is
1. To provide a flexible support for the vehicle, so that its
occupants ride comfortably isolated from the imperfections of
the road surface.
2. To stabilize the vehicle under all conditions of driver handling,
involving as it does cornering, braking and accelerating
maneuvers.
 These two basic requirements in respect of vehicle ride and
handling tend to conflict in actual practice, since ‘soft’ springing is
indicated on the one hand and relatively ‘hard’ springing on the
other.
 A successful design of suspension system is therefore one that
achieves an acceptable compromise between these two areas of
conflict.

Speed of a US M60 tank versus
surface roughness.
Speed of a US M60 tank corresponding to a
vertical acceleration of 2.5g versus height of
obstacles.
Speed versus Surface/Obstacle
A vertical acceleration of 2.5 g at the driver's seat has become fairly widely
accepted as a limit for the crossing of discrete obstacles 8

Definition of a Suspension System
It is defined as that complex of mechanical, pneumatic, hydraulic, and electrical
components that provides or, is associated with the
 provision of flexible support
between
 the ground and frame, or ground and hull, of the vehicle.
Suspension system also includes, in addition to the elastic or resilient members,
traction members and such members as are required to control the geometrical
relationship of the elastically constrained parts.
The suspension system is not considered part of the power train but its design is
greatly influenced by the vehicle’s power transmission and steering requirements.
9

Bogie
 A bogie is a wheeled wagon or trolley.
 In mechanics terms, a bogie is a chassis or framework carrying wheels,
attached to a vehicle.
 It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a
railway carriage/car or locomotive, or sprung as in the suspension of
a caterpillar tracked vehicle, or as an assembly in the landing gear of an
aircraft.
10

TYPES OF SUSPENSION
Dependent
Both wheels of a pair are mounted on a common axle that acts as a rigid beam,
which is then connected by springs to the vehicle structure.
Independent suspension
 Independent suspension is a broad term for any automobile suspension system
that allows each wheel on the same axle to move vertically (i.e. reacting to a
bump in the road) independently of each other.
 Note that “independent” refers to the motion or path of movement of the
wheels/suspension.
Active suspension
The active suspension/semi-active suspension are types of automotive
suspensions that controls the vertical movement of the wheels with an onboard
system, rather than in passive suspensions where the movement is being
determined entirely by the road surface. 11

Design Requirements of Suspension
1. Improve Mobility.
2. Support Vehicle body/hull at some selected height.
3. Provide lateral Stability.
4. Provide Longitudinal Stability.
5. Selective Distribution of Weight on Ground.
6. Adjust for Terrain Irregularities.
7. Comfort to Crew.
12

Design Requirements of Suspension………..
8. Protect from Shock and Vibration Damage.
9. Provide Traction Contact with Ground.
10. Transmit Driving and Braking Torque.
11. Obstacle Crossing Capability.
12. Provide means and stability for changing course.
13. Provide Stable Gun Platform.
13

Vertical Travel of the Road Wheels of Tanks
14

15
Types of Suspension Systems
1. Leaf spring
2. Coil spring
3. Volute spring
4. Rubber spring
5. Air spring
6. Bogie
7. Torsion Bar
8. Hydro-pneumatic or, Hydro-gas
 Modern tanks use either of the last three types only.

16
BOGEY SUSPENSION
 Bogie suspension usually has two or more road wheels and some type of
sprung suspension to smooth the ride across rough terrain.
 Bogie suspensions keep much of their components on the outside of the
vehicle, saving internal space.
 Although vulnerable to antitank fire, they can often be repaired or replaced in
the field.

17
BOGEY SUSPENSION
 Effective number of points of suspension to be two on each side
 A pair of wheels at either end of a pivoted beam
 Load carried at the pivot to be shared equally by them
 Besides improving ground contact also reduces the motion transmitted to
the hull

Advantages
1. Easy to change
2. Mounted externally therefore occupy less hull space.
3. Cheap
Disadvantages
1. Limited wheel travel
2. At high speed the inertia of linkage upsets the static balance & the loads
are no longer equalised.
 Suitable upto 40 km/ hr
18
BOGEY SUSPENSION

Torsion Bar
 A torsion bar is a flexible spring that can be moved about its axis
via twisting.
 Torsion bars are designed based on the following factors:-
1. Amount of torque used in the twisting of the spring,
2. The angle of the twist,
3. The overall dimensions of the torsion bar and,
4. Materials the torsion bar is made from.

Torsion Bar Suspension
 A torsion bar suspension, also known as a
torsion spring suspension or torsion beam
suspension, is a general term for any vehicle
suspension that uses a torsion bar as its main
weight bearing spring.
 One end of a long metal bar is attached firmly to
the vehicle chassis; the opposite end terminates
in a lever, the torsion key, mounted perpendicular
to the bar, that is attached to a suspension arm, a
spindle, or the axle.
 Vertical motion of the wheel causes the bar to
twist around its axis and is resisted by the bar's
torsion resistance.
 The effective spring rate of the bar is determined
by its length, cross section, shape and material.
Without load
With load

Torsion bar springing in principle

22
TORSION BAR
1. Torsion Bars are high quality steel rods of 50-70 mm diameter with splines at
either ends.

2. One end is joined to the bogey wheel hub & the other is enclosed in the
hull.
3. Length is equal to the width of the hull between the tracks.

4. The load on the wheel generates torque & creates a twist in the torsion
bar & brings the wheel back to pre bump condition.

1. Road wheel arm
2. Retainer
3. Shim
4. Rubber collars
5. Locking ring
6. Torsion bar (of LHS road
wheel arm)
7. Roller bearing
8. Support
9. Road wheel arm spindle
10. Felt oil seal
11. ---do—
12. Torsion bar (of RHS road
wheel arm)
13. Road wheel arm bracket
14. Bushing
15. Plug
16. Hole in support
17. Cover
18. Bumper
19. Mushroom shaped part of
bumper
20. Bumper rod
21. Stop
22. Capron bushing
23. Rubber plug
24. Cover
25. & 26 collar
Road wheel arm with torsion bar (Left side)- T-55

26
TORSION BAR
The wheel travel is directly proportional to the length of the
torsion bar and, is restricted by the width of the hull.
Earlier designs commonly permitted wheel travel of 130 mm.
To increase the wheel travel, double length hair pin bars were
used.
But this system suffered from stresses at the bend leading to
less life due to bending fatigue.
Maximum wheel travel of 385 mm has been achieved with the
following:-
1. Pre-stressing
2. ESR steer
3. Tube construction

Advantages of Torsion Bar Suspension
1. Light weight.
2. Simplicity of design
3. High levels of performance due to their ability to store more energy.
Disadvantages
1. It increases the height of the tank (about 100 mm in general).
2. Damaged torsion bars are difficult to replace when a hull is distorted by mine
blast.
3. Moreover, the fact that torsion bars store a large amount of energy in relation to
their weight means that their outside is highly stressed, which makes them
vulnerable to surface damage.

Let,
L = length of the effective part of the torsion bar.
T = Torque applied on the torsion bar, = W * l, Nm
W = Load acting on the lever arm of the bar causing the torque on the bar; m
l = length of the lever arm, m
d = diameter of the t. bar, m
θ = angular deflection of the t. bar, radians
τ = torsional/shear stress developed in the bar, Pa
G = modulus of rigidity = 73575 MPa for spring steel
J = Polar moment of inertia = π d4/32, m4
Design calculation for torsion bar

-(6)
-
-
-
-
-
-
-
-
-
2
.
.
get,
we
above
the
From
(5)
-
-
-
-
-
-
-
-
-
2
2
.
J
Tr
get
we
1
-
eq
in
this
using
;
have
we
4,
-
eq
From
(4)
-
-
-
-
-
-
-
JG
T
bar,
torsion
the
of
deflection
Angular
Now,
-(3)
-
-
-
-
-
-
-
T
16
d
by,
given
is
d
diameter,
Bar
-(2)
-
-
-
-
-
-
-
,
16
32
1
.
2
.
-(1)
-
-
-
-
-
-
-
J
Tr
bar,
torsion
in the
produced
stress
shear
Torsional/
max
max
3
max
max
3
4












d
G
l
l
Gd
Jl
d
JG
l
JG
T
l
Pa
d
T
d
d
T












OY-position of the arm in unloaded condition
OX-position of the arm under max. bump load
OZ-position of the arm under max. static load
α=upward inclination of arm with horizontal
= 0, when horizontal
θ=wind up angle or, angle of deflection;
β=wind up angle when arm is horizontal
If the arm is horizontal, the movement of the chasis/hull is equal to the movement
of the free end of the arm around the pivot.
But if the arm is inclined upwards considerably, increase in deflection is smaller with
increase in load.
x = linear deflection from the horizontal = l.Sinα
y = effective arm length (for application of load W) = l.Cosα
Therefore, Torque,
T = W.y = W. l.Cosα

Now, linear spring rate or, the Load rate of the Torsion bar, r is
bar
torsion
particular
a
for
constant
32
.
d
k
where,
N/m
;
4
2
2
l
G
x
l
Wx
k
dx
dW
r






 Value of r and x are +ve when the arm is inclined upwards.
 Values are negative if incline downwards

Exercise
A torsion bar suspension is to be designed
 To support a maximum static load of 3500 N at the end of a lever arm 250 mm
long.
 The deflection of the lever above the horizontal is to be 300 with a total angle of
deflection 900.
 Assume a safe allowable stress of 785 Mpa.
 Modulus of rigidity, G = 73575 Mpa.
Calculate:-
1. Diameter of the torsion bar.
2. The effective length of the tension bar.
3. The load rate (spring rate) of the bar.

Hydro-Pneumatic
Suspension

MBT-70 pitched forward by means of its adjustable
hydro-pneumatic suspension to gain additional
depression for its gun on a reverse slope.

 Compressibility of gases made use of as springing medium
 Fluid used for damping, controlling pitch and roll of vehicle
 100-140 bar pressure
 Soft rate at around static position
 Continuously rising rate from static to bump travel
 Bump travel of up to 500mm
 Better ride
 Does not occupy armour volume
mounted externally between bogey wheel & hull
First used on S-Tank. Also used on Challenger and Arjun.

Construction
These contain:
1. A volume of gas,
2. A floating piston, or a
diaphragm,
3. Hydraulic fluid
4. A second piston connected to
the road wheel arm.
 Springing action is provided
by the gas (N2).
 Fluid provides damping; as
also varying the height of the
tank.

Working
 Any bump experienced by
the road wheel is
transmitted to the
actuating piston through
the pivot, crank and the
connecting rod.
 The actuating piston
therefore applies pressure
on the oil.
 The oil moves forward and pushes the floating piston inside
thereby compressing the gas thus, providing springing action.
 After the removal of the bump, the gases expand and bring the
wheel to the original position. Returning oil provides damping.

Hydro-pneumatic spring unit of the type fitted
to the British Challenger tank.

Advantages of Hydro-pneumatic Suspension
1. Increased wheel travel.
2. Non-linear continuously rising spring rate.
3. Height and attitude control possible.
4. Leveling possible on slopes also.
5. Trunnion tilt avoided.

6. Being self-contained and normally bolted to the outside of hull side
plates, they do not add to the height of hulls, as torsion bars do, and
that they need not take up any space within the armour envelope.
7. Vehicle height exposed is less by lowering.
8. Variable ground clearance possible.
9. Hydraulic lock possible so that firing shocks are transmitted directly
to the ground.
10. Relatively compact and self-contained unit. Therefore easier to
install.

Disadvantages of Hydro-pneumatic Suspension
1. Complex design; therefore, it is costly and has low reliability.
2. Prone to leakage at high temperatures.
3. Additional recharging equipment need to be carried.
4. Sealing problems.
The End of chapter

W-6-7-Ch-5-Tank Suspension system.pptx

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