FORM 2
THE PATENT ACT, 1970,
(39 OF 1970)
&
THE PATENTS RULE, 2003
COMPLETE SPECIFICATION
(SEE SECTION 10; RULE 13)
"MAGNETO-RHEOLOGICAL DAMPER FOR AUTOMOTIVE SUSPENSION SYSTEM"
MAHINDRA & MAHINDRA LIMITED
AN INDIAN COMPANY,
R&D CENTER, AUTOMOTIVE SECTOR,
89, M.I.D.C, SATPUR,
NASHIK-422 007,
MAHARASHTRA, INDIA.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES AND ASCERTAINS THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF INVENTION:
The present invention relates suspension system of an automotive vehicle. More particularly, the present invention relates to dampers used in suspension system of an automotive vehicle, for providing improved ride and handling.
BACKGROUND OF THE INVENTION:
The conventional dampers used in suspension system of automotive vehicles are hydraulic systems that employ oil as the dampening fluid. In this conventional system, the dampening effect or the damping ratio is primarily decided by the oil viscosity and shims or valves used in the dampers. The dampening effects are dependent on the linear vertical velocity of the wheel. The faster the vertical velocity of the wheel, the more is the damping force given by the damper. When the wheel moves with a particular vertical velocity, the oil inside the damper is forced to pass through small orifices in the piston and impinges on a set of shims, which are mounted on top of the piston. The high velocity jet of oil bends the shims, thus creating a resistive force or dampening effect. The number of shims mounted on the piston decides the reaction force or the dampening effect. But in these conventional systems the dampening force created is limited by the orifice size, number of shims and thickness of the shims. Hence, once the overall orifice and shim size are decided, the dampening force of the damper is also fixed. Therefore, there is limited flexibility of varying/changing the dampening force once the technical specifications are decided.
Variety of damping systems for automotive suspension system is available in public domain which has met with varying degrees of success.
European patent No. EP. 1013963 discloses magnetorheological fluid device in which dimensional relationships involved in the flow of magnetic flux are

related to an operational parametric ratio of magnetic flux density in the fluid to the flux density in the steel. A magnetic valve is utilized to change the flow parameters of the MR fluid and hence the operational characteristics of the damper. Baffle plates and toroidal magnetic segments interspersed with flow slots are utilized to increase contact between the fluid and the magnetic coil.
But such monotube designs with floating pistons are difficult to construct.
European patent No. 1245856 describes twin tube magnetorheological damper which includes an inner tube, a magnetorheological piston, and an outer tube. The magnetorheological piston is located within and slideably engages the inner tube. The outer tube surrounds the inner tube. The outer tube is in fluid communication with the inner tube.
American patent No. US.7234575 educates on magnetorheological damper system comprising a reservoir in communication with a damper. The damper comprises a damper cylinder defining a damper chamber, wherein the damper chamber contains a magnetorheological fluid and a movable damper piston. The damper piston comprises at least two coil windings on the outer surface of the damper piston, wherein the damper piston is capable of generating a magnetic field between the damper piston and a wall of the damper cylinder. The reservoir comprises a reservoir cylinder defining a passageway, wherein the reservoir includes a magnetorheological electromagnet capable of generating a magnetic field between the magnetorheological piston and a wall of the passageway. The combination of the MR reservoir and MR damper leads to a damping system capable of damping a wide range of extreme forces.
But these accumulator types of design with floating pistons are difficult to manufacture and assemble.
In all the above mentioned prior art concepts, a single coil controlling both rebound and compression forces does not have independent and finer

control over the forces; durability problems are more with piston and piston rods which carry wires inside them and moving wire leads are more prone to damage. Also the zero current damping is very difficult to alter and control.
OBJECTIVE OF THE PRESENT INVENTION:
The main object of the present invention is to provide a novel magneto-rheological damper for automotive suspension system.
Another object of the present invention is to provide magneto-rheological damper for automotive suspension system with permanent magnet and twin coil.
Still another object of the present invention is to provide magneto-rheological damper for automotive suspension system aimed at ease of manufacturability and assembly with the existing parts, without compromising on performance requirements.
Still another object of the present invention is to provide magneto-rheological damper for automotive suspension system in which twin coils allow independent control of rebound and compression with minimum coupling.
Further object of the present invention is to overcome the drawbacks of prior art dampers for automotive suspension system.
STATEMENT OF INVENTION:
Accordingly the invention provides a magneto-rheological damper comprises of an outer housing / outer tube(8) having an open end on the top, sealed by an oil seal mounted over a seal seat, and a closed end with an eye ring at the bottom, mounted therein a compression coil around a bobbin; the said outer tube (8) houses an inner tube (6); a piston rod, reciprocating in the said inner tube, having one end an eye ring and other end piston sub assembly consisting a rebound coil attached to a piston

seat holding therein a piston with piston rings tightened with a lock nut; a rebound coil bobbin(4) having rebound coil (5) attached to the said oil seal seat; a connector screw (21) fixed to the said outer tube extends external link of wire connection said rebound coil and said compression coil and holds the said rebound coil bobbin and seal seat to the said outer tube; the said compression coif and rebound coil are connected to a semi-active suspension controller or supplying activating current; and said outer tube and iiner tube is filled with magnetic rheological fluid.
BRIEF DESCRIPTION OF THE DRAWINGS:
The objects and features of the present invention will be more clearly understood from the following description of the invention taken in conjunction with the accompanying drawings, in which,
Figure 1 shows the cross sectional view of magneto-rheological damper with permanent magnet and twin coil in accordance with the present invention.
Figure 2 shows exploded view of rebound bobbin with electrical coil in accordance with the present invention.
Figure 3 shows exploded view of compression bobbin with electrical coil in accordance with the present invention.
Figure 4 shows exploded view of piston assembly with permanent magnet washer in accordance with the present invention.
Figure 5 shows the exploded view of connector screw of the present invention.
Figure 6 shows the block diagram of magneto-rheological damping system as per the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION:
For the purpose of this description, words such as 'upper', 'lower', 'right', left' and the like are applied in conjunction with the drawings for the purpose of clarity. As is well known, dampers may be oriented in substantially any direction, so these directional words should not be used to imply any particular absolute direction for a damper consistent with the invention.
Linearly acting magneto-rheological fluid damper as shown in Fig. 1 is a particular strut. The strut is designed for operation as a load bearing and shock absorbing device within a vehicle suspension system, and is connected between sprung and the un-sprung masses.
Referring to Fig. 1, the magneto-rheological damper comprises of a outer housing / outer tube (8), which houses the inner tube (6) and the piston subassembly components. The outer tube (8) has an open end on the top and a closed end at the bottom. The close end is held to the vehicle chassis by means of bottom eye ring (19), which is welded to the outer tube (8). The open end is sealed by means of an oil seal seat (2) and the oil seal (3), which prevent the magneto-rheological fluid from leakage. The damper assembly is mounted to the vehicle chassis by means of the top eyelet (20).
The oil seal seat (2), seats the oil / magneto-rheological fluid seal (3). The rebound coil bobbin (4) and the fluid seat (2) are connected together by means of the wire lead 'connector' screws (21). The connector screw (21) serve the dual purpose of fastening the bobbin and the fluid seal seat and also act as the connecting link to the wires inside the damper and to the external world. Having screw type connector (21) ensures that no fluid leaks through this passage, rather than when the passage is a hollow one, carrying the connecting wires directly. Moreover, the connector screws are made of non-conductive plastic material that carries wires inside them. This ensures that the wires do not make contact with the bobbin material.

The rebound coil (5) is wound around the rebound coil bobbin (4), which creates a cylindrical rebound shear passage way (22). The magnetic field created by the rebound coil (5), the width of the rebound shear passage way (22) and the rebound fluid 'bypass' (23), determine the strength of the rebound damping force. The rebound coil bobbin is composite material made of soft iron core and non-magnetic linings.
The compression coil (15) is wound around the compression coil bobbin (14). The compression coil connector holes (25) are used to pull the wire leads out of the compression coil bobbin (14), into the outer tube (8). The compression coil leads (26), are pulled along the length of the inner tube (6), and are finally brought outside through wire lead Connector screws (21).
The compression coil (15) is wound around the compression coil bobbin (14), which creates a cylindrical compression shear passageway (16). The magnetic field created by the compression oil (15), the width of the compression shear passage way (16) and the compression fluid 'bypass' (24) determine the strength of the compression damping force. The compression coil bobbin is again a composite material made of soft iron core and non-magnetic material linings.
Referring to Fig. 4, the piston sub-assembly consists of the piston seat (10), piston (11), piston ring (12), lock nut (13) and the rebound coil (9). The piston sub-assembly components are mounted 0n the piston rod (1) and fastened by the lock nut (13). The piston (11) is made of a non-magnetic material, so as to eliminate the crucial member becoming magnetic after several rounds of damper magnetization. It shall also eliminate the excess friction arising out of fluid hardening in the recess between piston (11) and the inner cylinder (6). The piston rod (1) is also made of a non-magnetic material, to avoid magnetization.
The MR damper piston sub-assembly consists of a small permanent magnetic washer (29), mounted on top of the piston (10). This permanent magnet piece enhances the off-state damping force and reduces the need

for excess magnetizing current, when the piston (10), moves closer to the rebound (7) and the compression bobbin (14) respectively.
The MR fluid (27) fills the inner tube (6) and outer tube (8). A dynamic equilibrium of MR fluid exists between both the tubes, and the rebound bypass (23) and compression bypass (24) aid in maintaining the balance. Pressurized nitrogen gas (28) is filled to account for volumetric changes caused due to piston rod movement.
The twin coil design provides independent control over the rebound and compression damping. Even though a coupling between the two can not be ruled out, a twin coil design provides lot of freedom to control the damping, independently, and in turn facilitates better ride comfort through easier tuning. The permanent magnet ensures higher off-state damping, apart from reducing current requirement.
The bobbin design is made in such way that minimal changes from existing passive damping systems, is all that is required.
While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will readily appear to those skilled in the art. For example although a twin tube cylindrical reserviour is depicted, applications consistent with the aspects of the invention may include a monotube cylindrical reservoir.
The magneto rheological dampers alter their damping forces based on the current applied to the coils. The current to be supplied to each coil is decided by the semi-active suspension controller as shown in Fig. 6. The Control algorithm based on the several vehicle sensor inputs decides / computes how much current is to be applied to each of the coils, for a particular road profile/ driving pattern. Once the current to be applied is

computed, a high current driver delivers the corresponding current to each of the coils. While the entire system is continuously working the system is monitored for over heating and over current, so as not to damage the coils.
The invention in its broader aspects is, thereof, not limited to specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit of scope of the general inventive concept.
ADVANTAGES OF THE PRESENT INVENTION:
1. The present invention employs a twin tube design which is easier to assemble and manufacture and is also more structurally rugged.
2. Gas forms an emulsion and does not require a floating piston to separate the oil and gas chambers.
3. Two independent non-moving coils are used to for independent and finer control over rebound and compression forces.
4. The coil wires are brought out through a rod guide bush and are not inside a moving member and hence, do not pose durability problems.
5. The strength of the permanent magnet decides the base damping force and hence there is flexibility to change the base / zero current damping forces. The piston shim stack also gives added flexibility to change base damping forces.
6. This design is built on standard twin tube dampers designs and hence requires minimum design changes.

WE CLAIM:
1. A magneto-rheological damper comprises of an outer housing / outer tube(8) having an open end on the top, sealed by an oil seal mounted over a seal seat, and a closed end with an eye ring at the bottom, mounted therein a compression coil around a bobbin; the said outer tube (8) houses an inner tube (6); a piston rod, reciprocating in the said inner tube, having one end an eye ring and other end piston sub assembly consisting a rebound coil attached to a piston seat holding therein a piston with piston rings tightened with a lock nut ; a rebound coil bobbin(4) having rebound coil (5) attached to the said oil seal seat; a connector screw (21) fixed to the said outer tube extends external link of wire connection said rebound coil and said compression coil and holds the said rebound coil bobbin and seal seat to the said outer tube; the said compression coil and rebound coil are connected to a semi-active suspension controller or supplying activating current; and said outer tube and iiner tube is filled with magnetic Theological fluid.
2. A damper as claimed in claim 1 where in the said piston rod is made of non magnetic material.
3. a damper as claimed in claims 1 to 2 wherein the said piston assembly consists a small permanent magnetic washer (29) mounted on top of the piston.
4. A damper as claimed in claims 1 to 4 wherein said pressurized nitrogen gas is filled in the said outer and inner tube for accounting volumetric changes due to piston rod movement.
5. A damper as claimed in claims 1 to 4 wherein the said rebound coil bobbin of composite material, made of soft iron core and non-magnetic linings.
6. A damper as claimed in claims 1 to 5 wherein the said compression coil bobbin is a composite material made of soft iron core and non-magnetic material linings.
7. A damper as claimed in claims i to 6 wherein the said semiactive suspension controller with algorithm based on several vehicle sensor

inputs decides/computes how much current is to be applied to each of the coilfor a particular road profile/driving pattern. 8. A damper as claimed in claims 1 to 7 wherein the said the connector screws are made of non-conductive plastic material that carries wires inside them