FORM 2
THE PATENT ACT 1970 &
The Patents Rules, 2005
PROVISIONAL / COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION "A SHOCK-ABSORBER WITH DISPLACEMENT DEPENDENT DAMPING COEFFICIENT "

(b) NATIONALITY: Indian Company registered under the provisions of the
Companies Act, 1956

2. APPLICANT(S) (a) NAME
(c) ADDRESS

GABRIEL INDIA LIMITED
29th Milestone, Pune-Nashik Highway,
Village Kuruli, Tal.. Khed,
PUNE-410 501. Maharashtra State, India

3. PREAMBLE TO THE DESCRIPTION
PROVISIONAL
The following specification describes the
invention. /

COMPLETE
The following specification particularly
describes the invention and the manner
in which it is to be performed.

4. DESCRIPTION (starts from next page)
5. CLAIMS : Given on separate page.
6. DATE AND SIGNATURE : Given at the end of last page of specification.
7. ABSTRACT OF THE INVENTION : Given on separate page.

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1 0 FEB 2005

The present invention relates to a shock-absorber with displacement dependent damping coefficient which provides variable damping force which depends on the relative speed between chassis and the wheel and also depends on the load of the vehicle.
As the natural frequency of vehicle depends on Suspension Stiffness and Total Vehicle mass (Empty vehicle mass+ Pay Load), so damping coefficient has to be different for different Loads to provide optimum damping (Near Critical Damping). This shock absorber provides optimum damping at all vehicle loads.
The conventional Twin Tube shock absorbers used in vehicles employ a simple design where in an Inner Tube , an outer Tube , Piston, Rod and valve discs are typically used. The conventional shock absorbers provide damping force which depends on the relative speed between chassis and the wheel.
These conventional shock absorbers do not provide optimum damping at different vehicle loads i.e. the ride comfort level varies with the number of passengers/ Pay-load in the vehicle. These shock-absorbers are designed for a particular Total Vehicle mass ( Empty vehicle + Fixed Payload). In real life situations , passengers and load in the vehicle varies greatly and thus these conventional shock-absorbers do not provide optimum damping for the entire Payload range.
The object of this invention is to provide optimum damping at all vehicle loads. As the natural frequency of vehicle depends on Suspension Stiffness and Total Vehicle mass (Empty vehicle mass+ Pay Load), so damping -coefficient has to be different for different Loads to provide optimum damping (Near Critical Damping). The invention aims at varying the Damping coefficient of shock absorber as Load on vehicle varies.
According to the present invention a twin tube shock absorber comprises of a piston with a rod, inner tube, outer tube, base valve and rod guide nut wherein the inner tube is a hollow pipe with a number of burr-free grooves of varying length on the inside surface of the inner tube, piston is connected to a rod on one end and the other end of rod
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is to be connected to a vehicle; the inner tube with grooves as stated above is clamped inside the outer tube which can be connected to the wheel of a vehicle with base valve, rod guide and nut.
Damping coefficient is the ratio of damping force to relative velocity between wheel and chassis / vehicle body. The damping coefficient required depends on the natural vibration frequency of the vehicle.
The natural vibration frequency of the vehicle depends on the vehicle + passengers mass and also on the stiffness of the suspension [springs' spring constant : which is force (Newtons) required to compress spring per unit deflection (mm)]. That means if the passengers mass changes (with increasing or decreasing number of passengers or dead weight) the natural frequency of the system (vehicle + passengers {payload}) also changes. Therefore, the damping coefficient of the shock absorber should change with the vehicle's load. The conventional shock absorber does not meet this expectation but the shock absorbers of the present invention meets the expectation.
The present invention is a Twin Tube shock absorber with Displacement Dependent damping coefficient. It provides a Recoil Damping force (Damping Force during Wheel moving away from the chassis) which depends on two factors:
8Relative Velocity between Chassis and Wheel
8Distance between Chassis and Wheel
The invention will now be described with the help of suitable drawings accompanying this specification wherein the salient features have been shown by suitable numerals and referred to appropriately in the following description :
Fig.l shows Oil flow path during Recoil stroke in a Conventional Twin Tube shock absorber. Recoil Stroke means that the Piston Rod is moving away from inner tube i.e Length of the Damper is increasing. Compression Stroke means Piston Rod is moving into the Cylinder i.e. Length of Damper is decreasing.
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Fig. 2 shows the shock absorber of the present invention. Oil flow during Recoil stroke is explained. During Recoil stroke the Oil flow depends on the Displacement i.e Distance between Piston (A) and Base valve (B) , which depends on the Vehicle Load and Stiffness of the suspension (It could be Coil or Leaf spring suspension). As Stiffness of a vehicle suspension remains fairly constant , Displacement is directly related to vehicle load. In other words, the Oil flow depends on Vehicle load. (J) is a rod guide and its purpose is to guide the rod (L) nut (K) clamps inner cylinder (C), base valve (B) and rod guide (J) inside the outer tube (M).
When the vehicle is empty / partially loaded , Piston (A) moves in the grooved are of Inner tube (C). Oil passes through Piston Holes (D) & deflection valve (E), Base valve and also through the grooves (F) provided on the inner surface of Inner Tube. The extra Oil path generated by the grooves reduce the damping force which is desired for a partially loaded / empty vehicle. The grooves are burr free having controlled depth, width and length. The Oil flow path is highlighted with the help of arrows.
Fig. 3 shows, when the vehicle is fully loaded, piston moves down in the non-grooved area. Oil passes through Piston Holes & valves and Base valve. As the piston moves in the non-grooved area of Inner tube the extra oil leakage path is not available and hence Shock absorber offers a higher damping force, which is desired as the vehicle mass is higher.
In Fig. 4, Compression stroke is explained. During compression the oil flows through the Piston Bypass valve (G) and Base Valve Holes (H). The oil flows through the Base valve is restricted by holes, giving the desired Compression damping force. The same thing happens in Conventional Shock absorber also.
Fig. 5 shows the smooth transition from High Damping Force zone to Low damping force zone is achieved by providing a number of Grooves of different lengths on the inner surface of Inner tube .
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Fig.6 shows a typical suspension system used in some vehicles. Interconnection of various parts is also depicted. Piston (A) moves inside inner tube (C). Inner tube is clamped inside the outer tube (M). Piston (A) is clamped on Piston Rod (L) on one end with a rod guide (J). Piston rod's other end is connected to vehicle (V). Outer tube (M) is connected to wheel (W). Oil is filled in the inner tube and outer tube. The recoil damping force is the force required to pull piston rod out of the inner tube at a particular velocity. Ratio of the recoil damping force and pulling velocity is called the recoil damping coefficient at that velocity. The shock absorbers exhibit increasing damping force with increasing velocity.
ADVANTAGES
The present invention provides the advantage of uniform Ride comfort for the entire Payload range (i.e. the comfort level remains the same whether one or more persons are sitting in the vehicle ). With a higher weight / load on the vehicle, natural frequency of the vehicle decreases and it needs a higher damping coefficient from shock absorber to dampen the vibrations in the same time as in the case of vehicle with less load. The higher damping coefficient with higher load is provided by this invented shock absorber. Thus whether, a vehicle is partially loaded or fully loaded the invented shock absorber ensures same time to dampen vibration (i.e. uniform comfort level), unlike in vehicle with conventional shock absorber.
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We Claim:
A displacement dependent twin tube shock absorber comprising of a piston with a rod, inner tube, outer tube, base valve rod guide nut wherein the inner tube is a hollow pipe with a number of burr-free grooves of varying length on the inside surface of the inner tube, piston is connected to a rod on one end and the other end of rod is meant to be connected to a vehicle; the inner tube with grooves as stated above is clamped inside the outer tube which can be connected to a wheel of a vehicle with base valve, rod guide and nut.

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ABSTRACT
This invention relates to a twin tube shock absorber which comprises of a piston with a rod, inner tube, outer tube, base valve and rod guide nut. The inner tube is a hollow pipe with a number of burr-free grooves of varying length on the inside surface of the inner tube. The piston is connected to a rod at one end and the other end of this road is to be connected to a vehicle. The inner tube with burr-free grooves is clamped inside the outer tube which is to be connected to a wheel of a vehicle with base valve rod guide and nut.
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10 FEB 2005
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