CLIAMS:No claims ,TagSPECI:FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005
PROVISIONAL SPECIFICATION
(SEE MEMBER 10 AND RULE 13)
TITLE OF THE INVENTION
“A SUSPENSION MECHANISM FOR ISOLATING LOW FREQUENCY EXCITATIONS IN VEHICLE SEATS”
APPLICANTS:
Name : Mahindra & Mahindra Ltd.
Nationality : Indian
Address : Mahindra Research Valley, Mahindra World
City Plot No. 41/1, Anjur P.O. Chengalpattu
Kancheepuram Dist, Tamilnadu.- 603204

The following specification describes the nature of the invention-
FIELD OF INVENTION
[001] This invention generally relates to suspension system for vehicle seats, and more particularly to a negative stiffness structure provided with vehicle seat to effectively isolate/reduce the effect of road shock and low frequency excitaions.

BACKGROUND OF INVENTION
[002] Experimental studies on the transmission and tolerance of vertical vibrations, caused by tractors, indicate that the tractor operator is exposed to low-frequency (0.5 to 20 Hz) and high-intensity vibrations, which are harmful to the body. These vibrations results in disorders of spine and supporting structures. The intensity of these "harmful" vibrations can’t be reduced by providing a standard-type suspension to the tractor seat. Explosure of a tractor occupant to high-intensity vibration levels in the range of 0.5Hz -20Hz (discomfort) for an extended period of time results in physical and mental disorders. A survey conducted by orthopaedic surgeons in the United States discloses that truck and tractor drivers suffer from a number of disorders of the spine and supporting structures. Osteoarthritis, traumatic fibrosis’s, herniated disks, coccygodynia, lumbosacral pain, abdominal pain, and intestinal disorders are more often noticed in the drivers who drive trucks, tractors, motorcycles, and other vehicles or machinery in which vibrations and jolts occur.
[003] Vibration intensity is characterized by the amplitude ratio, acceleration level, relative amplitude between the adjacent body parts and pitch, roll & yaw of the tractor. Any isolation of these vibrations by providing a suspension system should reduce all these characteristics. It is seen that the acceleration level in conventional tractor is about 0.5g to 1.5g and the frequency range is about 0.5Hz to 20 Hz, and standard seats (of different suspension parameters) give rise to amplitude ratios of 2.5 to 4.5. These vibration acceleration levels in the tractor are of much higher intensity than the one minute 'exposure limit' proposed by the International Standards Organization (ISO). Therefore, there exists a necessary to reduce the acceleration levels below the 'exposure limit' proposed by ISO by providing a new type of seat suspension and suitably selecting its parameters.
[004] It is been found that the conventional suspension system measures vibration only on the seat and does not consider low frequency excitations of the seat to which the human body parts are exposed. Thus causing the suspension systems to be ineffective. The vibration at low excitation frequencies ranging between (0.5–20 Hz) are the main risk factors for lumbago or backache & other body parts, which seriously affect to mental and physical health of drivers and reduce their working efficiency. In order to upgrade the safety and ride comfort of the drivers, these vibrations should be suppressed. Thus, currently vibration isolation approaches have been studied in great depth to suppress the tractor seat vibration.
[005] A model of spring & damper is often used to present vibration isolation. It consists of a linear stiffness spring in parallel to a damper. The vibration attenuation is obtained only for the input frequencies greater than root two times the natural frequency of an isolation system. The vibration level of the isolated equipment is actually increased compared with that of the base .Hence the system with normal spring damper can offer a good reduction in high excitation frequencies. To solve existing problem, many researchers have given solutions to expand the frequency region of isolation such as a thin strip bent such that the two ends are brought together and clamped to form a teardrop shape. It acts as a nonlinear spring for supporting the load and mitigating the transmissibility of a dynamic vertical excitation increasing the loop length, the loop becomes less stiff vertically. Thus resulting in low resonance frequency. However, the load bearing capacity of the system is reduced.
[006] Some researcher analyzed the vibration isolator having air spring and air damping. The result is to obtain vibration attenuation for low input frequencies and no linkage friction exists. But a disadvantage of the system is that the extra air volume is too large. In addition, developed is a tunable vibration absorbing isolator. In this system, a liquid inertia vibration eliminator, which employs hydraulic fluid as the vibration absorber mass, is incorporated in the isolator. The stiffness, absorber mass, port and reservoir geometry can be used to tune the absorber.But these isolator required additional power suppy,cost of the system & feasibility on vehicle like tractor , maintenance of the system
[007] Thus, there is a need for an improved suspension means in the vehicle seats which can effectively isolate/reduce the effects of road shock and low excitation frequencies.
OBJECT OF INVENTION
[008] The principal object of this invention is to provide a negative stiffness structure for vehicle seats which could isolate/reduce the effects of road shock and low excitation frequencies.
[009] Another object of the invention is to provide an improved suspension mechanism to vehicle seats, using inexpensive components.
[0010] These and other objects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[0011] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0012] Fig. 1 depicts a side view of a negative stiffness structure attached to a vehicle’s seat according to an embodiment of the present invention;
[0013] Fig. 2 depicts a perspective view of the negative stiffness structure attached to the vehicle’s seat according to an embodiment of the present invention;
[0014] Fig. 3 depicts a perspective view of the negative stiffness structure according to an embodiment of the present invention; and
[0015] Fig. 4 depicts a side view of the negative stiffness structure according to an embodiment of the present invention.
DESCRIPTION OF INVENTION
[0016] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. For example, it should be noted that while some embodiments are explained with respect to a negative stiffness structure (100) provided in a tractor’s seat (101), it should be noted that the negative stiffness structure (100) as disclosed in the present invention could also be used in several other vehicles by incorporating the subject matter of the invention with little or no modifications. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0017] The invention discussed herein achieves a suspension mechanism which includes a negative stiffness structure (100) assembled with the vehicle’s seat (101) to isolate/reduce the effects of road shock and low excitation frequencies to a vehicle driver. Further the negative stiffness structure (100) according to an embodiment of the present invention utilizes less or inexpensive components. In addition, the negative stiffness structure (100) according to an embodiment of the present invention reduces the cost of assembly when compared to the conventional system.
[0018] In one embodiment the present invention provides a suspension mechanism which comprises an isolation system, a seat frame (102) and a seat (101) as shown in Fig. 1. Further the isolation system includes at least one negative stiffness structure (100) provided in vertical direction, a plurality of dampers (110 and 111) and a load supporting spring (vertical spring) (109) as shown in Figs. 3 & 4. Each negative stiffness structure (100), which is con?gured by a horizontal spring (104), is connected to the vertical spring (109) in parallel direction. In one embodiment, one end of the horizontal spring (104) is ?xed to the wall of the frame (102) while the other end of the horizontal spring (104) is connected to a slide guide block (105). The slide guide block (105) is free to slide in horizontal plane within a horizontal cylindrical (103) enclosure. Another side of the slide guide block (105) is connected to a bar (107) through a first hinge joint (115). The joint between the bar (107) and the slide guide block (105) is formed by plurality of pins (106). The other end of the bar (107) is connected to the vertical spring (109) by a second hinge joint (116). The joint between the bar (107) and the vertical spring (109) is formed by plurality of pins (106). The bar (107) is free to rotate around the hinge joint.
[0019] In one embodiment, the horizontal springs (104) are guided within the horizontal cylindrical (103) enclosure for proper guidance. Each cylinder (103) is provided with a stopper (114) to restrict the movement of the horizontal springs (104) beyond the cylinder’s extreme end.
[0020] In another embodiment, the present invention includes a plurality of dampers (110 and 111) which are installed in the suspension mechanism (two in vertical & two in inclined directions) to reduce the vibration level in other directions. In one embodiment the damper connected to seat provides a firm support to the seat.

[0021] In one embodiment the present invention includes a cross bar mechanism called scissor mechanism which is connected between the seat and the frame. This mechanism provides support for the seat. The scissor mechanism provided in the suspension mechanism resists the lateral movement of the seat and facilitates free movement of seat in vertical direction. In another embodiment the scissor mechanism diverts the shock and vibration towards the spring and the damper.

[0022] In one embodiment the cross bar mechanism consists of two bars (107) which are joined together at center by a pin (117). The extreme end of the cross bar (107) at back end side of the seat (101) is pivotably connected to the frame and underside of the seat. The cross bars (107) in front end side of the seat (101) are slidably connected to the frame (102) and underside of the seat. In another embodiment the cross bars (107) of the front end side are provided with a sliding bearing. These sliding bearings are configured to move within a guide rail provided in the frame and the underside of the seat to provide a smooth movement of the cross bars (107). A concentric bar is provided in the scissor mechanism to assist uniform horizontal movement and to avoid lateral movement of the cross bars (107). In another embodiment the cross bars (107) are provided on both the sides of the seat (101).
[0023] In one embodiment the present invention isolates/reduces the vibration in vertical direction as well as in horizontal direction (X-axis & Z-axis). For example, when a person is seated on the seat, the load of the person acts on the vertical spring. Due to road excitation, fluctuating energy created in the vehicle suspension system. The vertical spring (109) absorbes these fluctuating/vibrating energy by getting compressed i.e. the vertical spring (109) changes it length (deformation) in order to absorb the vibration energy. Here the applied force and the resulting displacement of vertical spring (109) are in same direction. This property is known as positive stiffness. After deformation, the vertical spring (109) tries to come back to its equilibrium position quickly. The plurality of damper (110 and 111) provided in the suspension mechanism resist this quick movement of the vertical spring (109). These dampers (110 and 111) absorb the energy from the vertical spring (109) in the form of shock and dissipate it in the form of heat.
[0024] In one embodiment the bars (107) connected to the vertical spring (109) of the seat (101) transfers the load of the vertical spring (109) to the horizontal springs (104). These horizontal springs (104) excerts a reverse force on the vertical spring (109) in opposite direction. Here the applied force and the resulting displacement are in opposite direction. This property is known as negative stiffness. Negative stiffness contributes to damping behavior because they tend to assist rather than resist the deformation as a result of internally stored energy. Negative stiffness offers more deformation to a system or a structure than a positive stiffness. For example a negative stiffness mechanism may include a mechanical system having bistable configuration and materials with negative moduli. Thus the horizontal springs (104) offers a negative stiffness which reduces the vibration to a larger extent.
[0025] In one embodiment two inclined damper (111) are connected between the frame (102) and the seat (101) at a predetermined location to reduce the vibration in horizontal direction. These inclinations in the dampers are formed with a predetermined angle to reduce the vibration.
[0026] In another embodiment the vertical spring (109) provided in the suspension mechanism takes the payload weight. The horizontal springs (104) connected to vertical spring reduce the load acting on the vertical spring (109) to a greater extent by changing stiffness as per user requirement.
[0027] In one embodiment a support bracket (108) is mounted on top of the verticle spring (109). Generally the support bracket (108) is of C-shaped. However, it is also within the scope of invention that the support bracket could be of any other shape without otherwise deterring the intended function of the support bracket as could be deduced from this description. In one embodiment bottom of the support bracket (108) is connected to the vertical spring (109) and the damper (110) while front and back side of the support bracket (108) are connected to the bars (107) of the cross bar mechanism.
[0028] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Referral numerals:
100 Negative stiffness structure
101 Seat
102 Frame
103 Horizontal cylinder
104 Horizontal spring
105 Slide guide block
106 Connecting pins
107 Bar
108 support bracket
109 Vertical spring
110 Vertical damper and guide
111 Inclined damper
112 Cross bars
113 Concentric bar
114 Stopper for horizontal slider
115 First hinge joint
116 Second hinge joint
117 Pin

ABSTRACT
A suspension mechanism having a negative stiffness structure (100) assembled with vehicle’s seat (101) is disclosed. The suspension mechanism isolates/reduces the effects of road shock and low excitation frequencies on a vehicle driver. The suspension mechanism comprises an isolation system, a seat frame (102) and a seat (101). Further the isolation system includes at least one negative stiffness structure (100) provided in vertical direction, a plurality of dampers (110 and 111) and a load supporting spring (vertical spring) (109).
Fig. 1

Date: 28th March 2013 Signature:
Vikram Pratap Singh Thakur