A VIBRATION DAMPER

Abstract: A vibration damper which is particularly suitable for vehicle seats. An inner cylinder (13) is divided by piston (23) into chambers (24) and (25) interconnected by passages (27) and (28) situated along the outer wall of the inner cylinder. Each passage has a one way valve (33), (36) to provide unidirectional fluid flow. A control valve (39), (40) controls the rate of oil flow and hence the damping rate. Body (12) interior (14) forms a reservoir around inner cylinder (13) into and out of which oil flows through relief valves (48, 50) to compensate for the volume of the chamber (24) occupied by piston rod (22).

Description: Title: "A VIBRATION DAMPER" BACKGROUND OF THE INVENTION (1) Field of the Invention This invention relates to a vibration damper adapted to control the vibration between two members. The invention is particularly suitable as, but not limited to, a vibration damper for vehicle seats or the like. (2) Brief Description of the Prior Art The vibrations transmitted to a vehicle operator via his seat are a major contributor to operator fatigue. This is particularly so in long distance transport vehicles, farm and earth-moving machinery, and power boats To combat this problem, such vehicles are now generally fitted with sprung seats, the seats having adjustable dampers to damp the vibrations. While these seats are an improvement, they are not totally satisfact¬ ory as the dampers cannot be "tuned" or accurately set to suit their particular applications and they generally require an external reservoir for the oil employed as the damping fluid or medium. SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to provide a vibration damper which does not require an external oil reservoir. It is a preferred object to provide a damper where the degree of damping in both directions can be independ¬ ently controlled. It is a further preferred object to provide a damper which can be readily adjusted by means of ' external controls It is a still further preferred object to provide a damper which can be easily assembled and maintained. Other preferred objects of the present invention will become apparent from the following description. in one aspect the present invention resides in a vibration damper including: a damper body, connectable to a first member; a closed cylinder in the body; a piston means, movable in the cylinder, dividing the cylinder into two variable volume chambers , and having a piston rod extending from the body, connectable to a second member; a pair of fluid passages interconnecting the two chambers and provided with respective one-way valve means to provide unidirectional flow, in opposite directions, of the damping fluid between the chambers; and independently controllable valve means in each passage to control the flow of the damping fluid through the passages and thereby control the degree of damping of the piston means in each direction. The body may be mounted on a fixed frame or support and the piston rod connected to a movable member, or vice versa, or the body and piston rod may be connected to a pair of relatively movable members. in one preferred embodiment, the body may include a closed outer cylinder enclosing the cylinder containing the piston means , the outer cylinder providing the reservoir for the damping fluid. In this embodiment, it is preferable that the fluid passages be provided in the outer cylinder and in communication therewith via bleed holes to compensate for the volume in one of the chambers occupied by the piston rod. The one-way valve may include relief valves which enable the damping fluid to flow through the respective passages between the chambers when the pressure difference between the chambers exceeds, or falls below, preset limits. Preferably the independently controllable valve means include valve members operable to vary the effective cross-sectional areas of the passages. The valve members may include valve blocks transversely movable in the fluid OMH_ r passages or eccentric plugs rotatably mounted in the passages . Preferably the valves are adjustable to allow 0% to 100% in each direction. BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS To enable the invention to be fully understood, a number of preferred embodiments will now be described with reference to the accompanying drawings, in which: FIG. 1 is a front view of a first embodiment of ' the damper, parts being broken away for clarity; FIG. 2 is a sectional plan view taken on line 2-2 in FIG. 1; FIG. 3 is a sectional side view of a second embodiment of the damper; and FIG. 4 is a sectional end view of one of the control valves taken on line 4-4 in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.l and 2, the damper has a rect¬ angular base plate 10 provided with mounting holes 11 adjacent each corner. A circular outer cylinder 12, forming the damper body, is mounted on the base plate 10 and welded thereto to close its lower end. A circular inner cylinder 13, of. reduced diameter, is similarly mounted on the base plate 10 and the annular space 14 formed between the two cylinders forms a reservoir for the oil used as the damping fluid. The upper end of the annular space is closed by an annular plate 15 sealably secured to the upper ends of the two cylinders 12, 13. A cover plate 16, has a central bush 17 and an annular flange 18, is secured to the annular plate 15 by studs 19. A central bore 20 is provided in the bush 17, and fitted with a pair of neo- prene seals 21 to sealably engage the piston rod 22 of a piston 23 slidably movable in the inner cylinder 13, dividing the latter into upper and lower variable volume cha bers 24, 25 respectively. A pair of neoprene piston rings 26 seal the piston 23 to the inner wall of the inner cylinder. A pair of fluid passages 27, 28 are provided adjacent the inner cylinder 13, being formed by square section tubes closed by the base plate 10 and annular plate 15. Fluid conduits 29, 30 connect the lower chamber 25 to the passages 27, 28 respectively, while conduits 31, 32 connect the upper chamber 24 to the passages. A one-way valve 33, having a spring loaded ball 34 and valve seat 35, allows the oil to pass from the lower chamber 25, through fluid passage 27, to the upper chamber 24 when the piston 23 moves down the inner cylinder. A similar valve 36, with ball 37 and valve seat 38, allows the oil to flow from the upper chamber 24 to the lower chamber 25 via passage 28, the valves 33, 36 preventing flow of the oil in the opposite direction. The flow of oil through the passages 27, 28 and thereby the damping applied to a body connected to the piston rod 22, is controlled by respective control valves 39, 40. Referring to the control valve 39, a rectangular hole is formed in the outer side wall of the passage 27 to slidably (and sealably) receive a valve block 41 which is movable transversely across the passage 27 to vary the effective cross-sectional area of the passage. The block 41 has a central bore which screwthreadably receives a threaded spindle 42. A seal block 43, with neoprene seals 44, is formed integrally with the spindle 42 and is seal¬ ably mounted in the seal housing 45 formed in the outer cylinder 12. The outer end of the spindle is of square cross section and engaged in a complementary hole formed in a control nut 46. By rotating the nut 46, the block 41 moves along the spindle 42 to open and close the passage. OMPI Control valve 40 is similar to the control valve 39, with a valve block 47 selectively varying the effective area of the passage 28. A bypass valve 48 is connected to the passage 27 via a hole 49 to enable oil under pressure to be bled to the reservoir 14, while an intake valve 50, connected to the passage 28 via a hole 51, allows the oil from the reservoir to enter the passage. The operation of the damper will now be described. The base plate 10 is secured to a frame e.g. a vehicle chassis and the piston rod 22 to a vehicle seat (not shown) . It will be assumed that the piston 23 is in the position shown in FIG. 1. When the piston 23 is forced downwardly (i.e. on its downstroke) , the volume of the lower chamber 25 is reduced, oil flows out of conduit 29 into the passage 27 ( the flow into passage 28 being prevented by the one-way valve 36) . The bypass valve 48 remains closed and the oil flows'.through the restriction in the passage formed by the valve block 41, through the one-way valve 33 and conduit 31 to the upper chamber 24. The piston rod 22 effectively reduces the volume of the upper chamber 24 and so the decrease in the volume of the lower chamber 25 is not matched by the increase in volume of the upper chamber 24. The pressure of the oil in the passage 27 increases, it unseats the bypass valve 48 and oil flows through the hole 49 to the reservoir 14. On the upstroke of the piston, valves 33 and 48 are closed but one-way valve 36 is opened to allow oil to flow from the upper chamber. 24 to the lower chamber 25 via the passage 28, the rate of flow (or degree of clamping) being controlled by the restriction in the passage formed by the valve block 47. As the increase in the volume of the lower chamber 25 is greater than the decrease of the upper chamber 24, . the -intake valve 49 opens to allow fluid to enter the passage 28 from the reservoir 14. As the flow of oil between the chambers follows different paths on the up - and down strokes, the adjust- ment of the control valves 39, 40 allows the damping on each stroke to be independently controlled, and the degree of damping on each stroke can be from 0% - 100%. The by¬ pass valve 48 and intake valve 49 allows the oil to flow between the reservoir and the inner cylinder, maintaining both chambers full of oil. In a modified form of this ' embodiment (not shown) , the valve blocks 41, 47 are rotatably, but non-axially, movable on the spindles and the nuts 46 of the control valves 39, 40 are screwthreadably mounted on the seal housings 45. As the nuts 46 are rotated, they move inward¬ ly or outwardly relative to the outer cylinder, respectively closing or opening the passages 27, 28. While circular cylinders 12, 13 have been shown in the drawings, these may be substantially square in plan, if preferred. In addition, the passages 27, 28 may be spaced from inner cylinder 13 and connected thereto by short tubes forming the conduits 29-32. The removable cover plate 16 enables the piston 23 to be withdrawn and the damper serviced. However, the cover plate 16 and annular plate 15 may be made in one piece and the damper sealed for life, the oil acting as a lubricant. Turning now to the second embodiment of FIGS. 3 and 4, the damper 60 has a damper body 61 formed by two body halves 62, 63 secured together by bolts 64 which pass through the length of the body. A central cylinder 65 is formed in the body 61 and is closed at each end by a respective stainless steel insert 66. Each insert has a peripheral flange 67 located in a recess at the respective ends of the cylinder. __ OMPI A bronze bearing or bush 68 is fitted in each insert 66 and aligned co-axial bores 69 are provided through the pairs of inserts 66 and bearings 68. A piston rod 70 is slidably journalled in the bronze bearings 68 and extends from each end of the body. A series of neoprene o-rings 71 are provided in the bearings 68 to provide a fluid-tight seal between the rod 70 and the bearings 68. A piston 72 is provided in the cylinder 65 and has its hub 73 fixed to the piston rod 70. A piston ring 74 around the periphery of the piston seals the piston to the inner wall of the cylinder 65. As shown, the pisto 72 divides the cylinder 65 into two variable volume chambers 75, 76. A pair of passages 77, 78 in the body 61 inter¬ connect the chambers 75, 76. Referring to passage 77, a ball 79 co-operates with a valve seat 80 to provide a one-way valve 81, the ball 79 being seated on the valve seat 80 when the oil seeks to flow from the chamber 76 to chamber 75 but being unseated to allow unrestricted flow from chamber 75 to chamber 76. A similar one-way valve 82 is provided in passage 78 to limit the flow of the oil in the direction of chamber 76 to chamber 75. The flow of oil through the passages, and thereby the damping of a body or member connected to the piston ro 70, is controlled by respective control valves 83, 84. Referring to control valve 83, this has a shaft 85 rotat- ably journalled in the body 61 and sealed thereto by an o-ring 86. A square head 87 on the outer end of the shaft 85 is adapted to receive an operating handle or leve (not shown) . Referring to FIG. 4, the shaft 85 has a reduced diameter portion, aligned with the passage 77, forming an eccentric metering plug 88. By rotating the shaft 85, the plug 88 selectively opens and closes. " he adjacent ports OMPI 89, 90 of the passage 77 to control the flow of oil through the passage. In FIG. 4, the plug 88 is shown intermediate its closed and open positions and so the degree of damping would be approximately 50% (the shaft 83 being rotatable through approximately 90 between its opened and closed positions) . A small clearance 91 is provided to ensure that some flow of oil is always possible through the passage 77 to prevent the travel of the piston 72. The operation of the damper will now be described. The body 61 may be mounted e.g. on a seat frame and one end of the piston rod 70 connected to one of the legs of a spring-loaded, scissor-type support frame. As the piston rod 70 moves the piston 72 to reduce the volume of oil in chamber 75, the flow of oil through passage 78 is prevented by the one-way valve 82 and so the oil can only flow to the chamber 76 via passage 77. The ball 79 of the one-way valve 81 is unseated and the oil flows through the control valve 83 at a rate determin by the position of the plug 88 relative to the ports 89 or 90. When the piston 72 is moved in the opposite direction, the oil is transferred between the chambers 76 and 75 at a rate controlled by the control valve 84. While the control valves 83, 84 are shown on opposit sides of the body 61, it is preferred that they are provided on the same side with their control handles or levers adjacent each other. In a modified form of this embodiment (not shown) only one fluid passage may be provided where the inter¬ mediate portion of the passage is separated into two parallel branches, each having a one-way valve and contro valve to provide controlled unidirectional flow in each branch. it will be readily apparent to the skilled addressee that various other types of control or metering valves may be employed to control the degree of damping and one example is a needle valve. The damper can be used in a wide range of applicati where the vibration of a body relative to a datum, or between a pair of relatively movable bodies, is required to be damped. Various changes and modifications may be made to th embodiments described without departing from the scope of the appended claims. OMPI

Claims: CLAIMS 1. A vibration damper including: a damper body connectable to a first member; a closed cylinder in the body; a piston means, movable in the cylinder, dividing the cylinder into two variable volume chambers, and having a piston rod extending from the body and connectable to a second member; a pair of fluid passages interconnecting the two chambers and provided with respective one-way valve means to provide unidirectional flow, in opposite directions, of the damping fluid between- the chambers; and independently controllable valve means in each passage to control the flow of the damping fluid through the passages and thereby control the damping of the piston means in each direction. 2. A damper as claimed in Claim 1 wherein each control valve means includes: a shaft rotatably mounted in the body; and means to rotate the shaft; and a valve plug on the shaft aligned with the passage, the plug being of reduced diameter and eccentric to the shaft so arranged that as the shaft is rotated, the effective cross sectional area of the passage is selectively increased or decreased. 3. A damper as claimed in Claim 2 wherein: the passage has a pair of ports adjacent the control valve means; and the control valves provide substantially 100% damping when the valve is closed, the plug being adjacent one of the ports . 4. A damper as claimed in Claim 1 wherein each control valve means includes : a shaft rotatably mounted in the body extending transversely into the passage; means to rotate the shaft; and - 5HE i OMPI - -- a valve block screw-threadably mounted on the shaft and longitudinally movable along the shaft, so arranged that as the shaft is rotated, the valve block is movable transversely across the passage to selectively increase or decrease the effective cross-sectional area of the passage. 5. A damper as claimed in Claim 2 or Claim 3 wherein: the piston rod extends from both ends of the body, so arranged that as the piston moves in the cylinder, the decrease in volume of one of the chambers is substant¬ ially equal to the corresponding increase in volume of the other of the chambers . 6. A damper as claimed in Claim 4 wherein: the piston rod extends from one end of the body; the body includes an outer cylinder enclosing the cylinder and the annular space . forming between the two cylinders forms a reservoir for the damping fluid; and one-way relief valves provide communication between the passages and the annular space, so arranged that as the piston moves in the cylinder, the relief valves are selectively opened to enable transfer of the damping fluid between the annular space and the passages to compensate for the difference in the decrease, or increas in volume, in one of the chambers and the increase, or decrease in volume, in the other of the chambers due to the volume occupied by the piston rod in the one chamber. 7. A damper as claimed in Claim 1 wherein each one-way valve means includes: a valve seat in the passage; and a ball ' engageable with the valve seat to close the passage, the ball being urged into engagement with the valve seat by spring means or by the pressure of the damping fluid in the passage upstream of the ball.

Inventors: CULLEY DONALD MAXWELL, CULLEY, DONALD, MAXWELL
Applicants: CULLEY DONALD MAXWELL, CULLEY, DONALD, MAXWELL
Application year: 1983
Main classification: F16F9
IPC codes: B60N2, F16F9