Abstract:
A vehicle seat assembly includes an actuator controlled by a three-position spool valve which is connected by an adjustable two-link linkage to the seat. The valve is directly responsive to the geometry of the linkage to urge the seat, regardless of the load on the seat, to a ride position established by the linkage.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to adjustable-ride-position maintaining seat assemblies and more particularly to a simple seat assembly having a valve connected by a two-link linkage to the seat. 
     In the past, it was recognized that it would be desirable to have a vehicle seat which would absorb shocks and maintain a predetermined ride position across rough terrain regardless of the weight of the operator while featuring adjustment of the predetermined ride position to accommodate different size operators. 
     One of the first seats able to maintain an adjustable ride position is shown in the U.S. Pat. No. 3,210,019 granted to Elfes et al. on 16 Nov. 1965. The seat was made adjustable by having adjustment means for moving a platform relative to a base and placing a ride position maintaining device on the platform. The Elfes et al system was relatively complex in requiring separate means for adjustment and for maintaining the predetermined ride position. 
     Subsequently, a seat was developed such as that shown in the U.S. Pat. No. 3,638,897 granted to Harder, Jr., et al. on 1 Feb. 1972. The seat assembly moves substantially vetically by swinging on generally horizontal parallel linkages. To establish and adjust the ride position, a relatively complex three-link linkage is required to activate a valve which controls an actuator for raising and lowering the seat. To provide for large adjustments and to maintain the predetermined ride position, a specially fabricated flexible link is required between the seat and the valve. 
     SUMMARY OF THE INVENTION 
     The present invention provides for an adjustable-ride-position maintaining seat assembly which eliminates the drawbacks of past assemblies. 
     The assembly utilizes a hydraulic actuator activated by a valve whose spool is directly connected by a simple two-link linkage to the seat. Means are provided in the valve to change the response of an accumulator which is operatively connected to the actuator to cushion the ride and further means are provided in the valve to prevent change of the predetermined ride position adjustment when the fluid source is shut down. 
     The above and additional advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional elevation of the seat assembly incorporating the present invention in an operating position; and 
     FIG. 2 is a sectional elevation of the seat assembly incorporating the present invention in an inactive position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, therein is shown a seat assembly 8 having a seat 10 upon which an operator would be seated. Supporting the seat 10 is a rod 12 which is connected to a piston 14 which is slidably received within the body 15 of a single acting hydraulic cylinder 16. The cylinder body 15 has a relief port 18 in the rod end and a main port 20 in the piston end. The piston end of the cylinder 16 is secured to a structure generally designated by the number 22 which may be a part of a vehicle containing the seat assembly 8. The main port 20 is connected by a fluid passage 24 to an actuator chamber 26 in a valve body 28 of a height adjusting and maintaining assembly 29. The actutator chamber 26 is connected to an accumulator 30 by a fluid passage 32. Disposed in the actuator chamber 26 between the fluid passages 24 and 32 is conventional variable restrictor or accumulator dampening adjustment valve 34. Between the fluid passage 24 and the adjustment valve 34 is an actuator passage 36 which connects with a vertical bore 38 in the valve body 28. 
     The vertical bore 38 is open at the top end and connected to a reservoir passage 40 at the bottom end. The reservoir passage 40 is connected to a reservoir 42. Proximate the top end of the bore 38 is a retaining ring 44 and between the retaining ring 44 and the reservoir passage 40 is a source passage 46 which is supplied with pressurized fluid from a source or pump 48 which is fed from the reservoir 42. 
     Slidaly received within the bore 38 is a valve spool 50 which is limited in its upward travel by the retaining ring 44. The valve spool 50 contains an annular groove 52 located between top and bottom valve lands 53 and 55. Adjacent to and above the bottom valve land 55 is a metering land 51 of lesser diameter than the land 55 and adjacent to and below the land 55 is a metering land 57 which tapers toward the bottom. The valve spool 50 is provided with a longitudinal hole 54 therein open at the top and having an opening 56 therein fluidly connected to the bottom of the bore 38. Close to the opening 56 in the wall of the longitudinal hole 54 is a passage 58 which connects the longitudinal hole 54 to the surface of the metering 1 and 51 and thence to the annular groove 52. A ball 60 rests in the longitudinal hole 54 and blocks off the opening 56. The ball 60 is moveable to unblock the opening 56 by a pin 62 in the bottom of the bore 38 which protrudes through the opening 56 when the spool 50 bottoms in the bore 38. 
     A valve piston 66 is slidably positioned in the longitudinal hole 54 and is limited in its upward movement by a retaining ring 64 in the spool 50. The valve piston 66 is connected to the seat 10 by a rigid rod 68 which is pivotally secured to a rigid adjusting lever or link 70 which in turn is secured by a friction holding pivot 71. The adjusting link 70 has a manual adjustment knob 72 at the end opposite the rod 68 which is movable in the directions shown by the arrows in FIGS. 1 and 2. 
     When the pump 48 is shut off, the seat assembly 8 will be in the position shown in FIG. 2. The spool 50 will be at the bottom of the bore 38 with the ball 60 lifted off the bottom of the longitudinal hole 54 by the pin 62. The valve piston 66 will be positioned in the hole 54 in a position established by the position of the adjustment link 70. The piston 14 of the cylinder 16 will be bottomed out and the seat 10 will be in the lowermost position. 
     As the pump 48 starts to pump fluid, the fluid will pass into the valve body 28 through the source passage 46. The pressurized fluid will then circulate about the annular groove 52 and a portion of it will enter the longitudinal hole 54 through the passage 58 and be exhausted to the reservoir 42 past the ball 60 while the remainder will pass through the actuator passage 36 into the actuator chamber 26. The pressurized fluid in the actuator chamber 26 will pressurize the accumulator 30 and cause the cylinder 16 to extend to move the seat 10 upwardly. 
     As the cylinder 16 moves the seat upwardly, the adjustment link 70 and the rod 68 will be likewise moved up causing the valve piston 66 to move and abut the retaining ring 64. As the seat 10 continues to rise, the valve piston 66 will pull the valve spool 50 up until the pin 62 clears the opening 56 and the ball 60 seats to block the opening 56 and thus allow the longitudinal hole 54 to be pressurized. 
     As the spool 50 moves upwardly in the bore 38, it will reach a position where the land 55 will, due to the inherent overshoot, center over and block the actuator passage 36 from both the source and the reservoir passages 46 and 40 which prevents further extension of the cylinder 16. The seat height at which this occurs, which is referred to as the predetermined ride position, is dependent upon the geometry of the adjustment link 70 and the rod 68. 
     As is evident, the height of this predetermined ride position may be altered simply by moving the knob 72 to increase or decrease the distance between the pivot 71 and the valve spool 50. Due to the location of the pivot 71, raising the handle 72 will force the spool 50 downward to permit fluid communication between the source passage 46 and the actuator passage 36 to raise the seat 10 and lowering the knob 72 will cause the valve spool 50 to raise and permit fluid communication between the actuator passage 36 and the reservoir passage 40 to lower the seat 10. 
     When an operator sits down in the seat 10, the seat 10 will first lower from its predetermined ride position in proportion to the operator&#39;s weight as the accumulator 30 absorbs the weight loading. As the seat 10 lowers, the valve spool 50 will move downwardly to connect the source passage 46 with the actuator passage 36 to supply additional fluid to cause the cylinder 16 to raise the seat 10 to the position where the valve spool 50 will again block the actuator passage 36. Thus, regardless of operator size, the seat will always return to its predetermined ride position. 
     Once the vehicle is underway, minor road bumps and shocks are taken up by the accumulator 30 and do not result in the volume of pressurized fluid in the system being changed since the longitudinal length of the land 55 blocks the actuator port 36 from both the source passage 46 and the reservoir passage 40 for minor excursions in a predetermined range from the predetermined ride position. The operator has an additional control in the form of the accumulator dampening adjustment valve 34 which may be turned to adjust the rate at which fluid can flow to the accumulator 30 and thus change the system&#39;s equivalent spring stiffness to provide either a softer or stiffer ride. 
     For large excursions from the predetermined ride position due to major shocks, the accumulator 30 operates in conjunction with the assembly 29. The large excursions in the downward direction cause the spool valve 50 to move downwardly to connect the source passage 46 to the actuator port 36 and thence to the cylinder 16 to add pressurized fluid and substantially increase the system&#39;s stiffness. The large excursions in the upward direction cause the spool valve 50 to move upwardly to connect the actuator passage 36 to the reservoir passage 40 to relieve the pressurised fluid in the cylinder 16 and substantially reduce the sytem&#39;s stiffness. 
     Road bumps and shocks between the two extremes are accommodated by a metered addition or reduction of hydraulic fluid to the system around the metering lands 51 and 57, respectively, for predetermined distances above and below the bottom land 55. Thus, three modes of operation are provided to minimize the effects of different magnitudes of shock. 
     When the pump 48 is shut off, fluid seepage past the land 55 will allow the seat 10 to lower slowly. The position of the adjusting link 70 and the handle 72 will remain constant as the valve spool 50 is moved towards the bottom of the bore 38. As the valve spool 50 aproaches the bottom of the bore 38, the pin 62 will lift the ball 60 to allow pressure to be relieved in the longitudinal hole 54. With pressure relieved in the longitudinal hole 54, the piston 66 will slide downwardly into the valve spool 50 without requiring a change in the position of the adjusting link 70. 
     While the invention has been described in conjunction with a specific embodiment, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations which fall within the spirit and scope of the appended claims.