Acceleration Sensitive Damping for Automotive Dampers

The present invention relates generally to automotive dampers or shock absorbers which receive mechanical shock. More particularly, the present invention relates to automotive dampers or shock absorbers which are sensitive to accelerations imposed upon the damper or shock absorber to switch between a firm and a soft damping characteristic.

Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb unwanted vibrations, shock absorbers are generally connected between the sprung portion(body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and is connected to the sprung portion of the automobile through a piston rod. The piston divides the pressure tube into an upper working chamber and a lower working chamber. Because the piston is able, through valving, to limit the flow of damping fluid between the upper and lower working chambers when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the automobile. In a dual tube shock absorber, a fluid reservoir is defined between the pressure tube and the reservoir tube. A base valve is located between the lower working chamber and the reservoir to limit the flow of fluid between the lower working chamber and the reservoir to produce a damping force which also counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the automobile. The greater the degree to which the flow of fluid within the shock absorber is restricted by the piston valving or the base valve, the greater the damping forces which are generated by the shock absorber. Thus, a highly restricted flow of fluid would produce a firm ride while a less restricted flow of fluid would produce a soft ride.

In selecting the amount of damping that a shock absorber is to provide, at least three vehicle performance characteristics are considered. These three characteristics are ride comfort, vehicle handling and road holding ability. Ride comfort is often a function of the spring constant of the main springs of the vehicle as well as the spring constant of the seat, tires and the damping coefficient of the shock absorber. For optimum ride comfort, a relatively low damping force or a soft ride is preferred. Vehicle handling is related to the variation in the vehicle's attitude (i.e. roll, pitch and yaw). For optimum vehicle handling, relatively large damping forces or a firm ride are required to avoid excessively rapid variations in the vehicle's attitude during cornering, acceleration and deceleration. Road holding ability is generally a function of the amount of contact between the tires and the ground. To optimize road handling ability, large damping forces are required when driving on irregular surfaces to prevent loss of contact between the wheel and the ground for excessive periods of time.

Various methods for selectively changing the damping characteristics of a shock absorber in response to the operational characteristics of the vehicle have been developed. Continued development of shock absorbers have been directed towards simplified and low cost systems which effectively control the damping characteristics of the shock absorber in response to the varied operational characteristics of the vehicle.

The present invention provides the art with a dual or twin tube shock absorber which incorporates a compression valving system in the base valve of the shock absorber which is sensitive to accelerations imposed upon the shock absorber during movements of the unsprung mast. The compression valving system replaces the standard compression valving system in the base valve with a floating intake valving system sensitive to accelerations imposed upon the shock absorber.

Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.

In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

FIG. 1 is an illustration of an automobile using the automatically adjustable damping system in accordance with the present invention;

FIG. 2 is a side view, partially in cross section, of a shock absorber incorporating the automatically adjustable damping system in accordance with the present invention;

FIG. 3 is an enlarged side elevational view, partially in cross section, of the base valve portion of the shock absorber shown in FIG. 2 with the damping system providing a higher restriction to fluid flow and thus a firm ride; and

FIG. 4 is a view similar to FIG. 3 but with the damping system providing a lower restriction to fluid flow and thus a smooth ride.

Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a vehicle incorporating a suspension system having the automatically adjustable shock absorbers in accordance with the present invention which is designated generally by the reference numeral 10. Vehicle 10 includes a rear suspension 12, a front suspension 14 and a body 16. Rear suspension 12 has a transversely extending rear axle assembly (not shown) adapted to operatively support the vehicle's rear wheels 18. The rear axle assembly is operatively connected to body 16 by means of a pair of shock absorbers 20 and a pair of helical coil springs 22. Similarly, front suspension 14 includes a transversely extending front axle assembly (not shown) to operatively support the vehicle's front wheels 24. The front axle assembly is operatively connected to body 16 by means of a second pair of shock absorbers 26 and by a pair of helical coil springs 28. Shock absorbers 20 and 26 serve to dampen the relative motion of the unsprung portion (i.e. front and rear suspensions 12 and 14, respectively) and the sprung portion (i.e. body 16) of vehicle 10. While vehicle 10 has been depicted as a passenger car having front and rear axle assemblies, shock absorbers 20 and 26 may be used with other types of vehicles or in other types of applications such as vehicles incorporating independent front and/or independent rear suspension systems. Further, the term "shock absorber" as used herein is meant to refer to dampers in general and thus will include MacPherson struts.

Referring now to FIG. 2, shock absorber 20 is shown in greater detail. While FIG. 2 shows only shock absorber 20, it is to be understood that shock absorber 26 also includes the piston and base valving described below for shock absorber 20. Shock absorber 26 only differs from shock absorber 20 in the way in which it is adapted to be connected to the sprung and unsprung portions of vehicle 10. Shock absorber 20 comprises a pressure tube 30, a piston 32, a piston rod 34, a reservoir tube 36 and a base valve assembly 40.

Pressure tube 30 defines a working chamber 42. Piston 32 is slidably disposed within pressure tube 30 and divides working chamber 42 into an upper working chamber 44 and a lower working chamber 46. A seal 48 is disposed between piston 32 and pressure tube 30 to permit sliding movement of piston 32 with respect to pressure tube 30 without generating undue frictional forces as well as sealing upper working chamber 44 from lower working chamber 46. Piston rod 34 is attached to piston 32 and extends through upper working chamber 44 and through an upper end cap 50 which closes the upper end of both pressure tube 30 and reservoir tube 36. A sealing system 52 seals the interface between upper end cap 50, reservoir tube 36 and piston rod 34. The end of piston rod 34 opposite to piston 32 is adapted to be secured to the sprung portion of vehicle 10. In the preferred embodiment, piston rod 34 is secured to body 16 or the sprung portion of vehicle 10. Valving within piston 32 controls the movement of fluid between upper working chamber 44 and lower working chamber 46 during movement of piston 32 within pressure tube 30. Because piston rod 34 extends only through upper working chamber 44 and not lower working chamber 46, movement of piston 32 with respect to pressure tube 30 causes a difference in the amount of fluid displaced in upper working chamber 44 than the amount of fluid displaced in lower working chamber 46. This difference in the amount of fluid displaced is known as the "rod volume" and it flows through base valve assembly 40.

Reservoir tube 36 surrounds pressure tube 30 to define a reservoir chamber 54 located between the tubes. The bottom end of reservoir tube 36 is closed by an end cap 56 which is adapted to be connected to the unsprung portions of vehicle 10. In the preferred embodiment, end cap 56 and reservoir tube 36 are attached to the unsprung portion of vehicle 10. The upper end of reservoir tube 36 is attached to upper end cap 50. Base valve assembly 40 is disposed between lower working chamber 46 and reservoir chamber 54 to control the flow of fluid between the two chambers. When shock absorber 20 extends in length, an additional volume of fluid is needed in lower working chamber 46 due to the "rod volume" concept. Thus, fluid will flow from reservoir chamber 54 to lower working chamber 46 through base valve assembly 40. When shock absorber 20 compresses in length, an excess of fluid must be removed from lower working chamber 46 due to the "rod volume" concept. Thus fluid will flow from lower working chamber 46 to reservoir chamber 54 through base valve assembly 40.

The present invention is directed to a unique base valve assembly 40 which automatically changes the restriction to fluid flow through base valve assembly 40 based upon the acceleration forces exerted on shock absorber 20 during a compression stroke of shock absorber 20. Base valve assembly 40 automatically switches between a restricted flow condition or firm ride as shown in FIG. 3 and a less restricted flow condition or soft ride as shown in FIG. 4.

Referring now to FIG. 3, base valve assembly 40 comprises an end cap 60, a finger spring 62, a sleeve 64, a valve body 66, a valve disk 68, a valve spool 70, a mass 72 and a valve retainer 74. End cap 60 is secured to the end of pressure tube 30 by being press fit into pressure tube 30 or by other means known well in the art. Valve retainer 74 is disposed between end cap 60 and pressure tube 30 such that the assembly of end cap 60 to pressure tube 30 also locates and secures valve retainer 74. End cap 60 defines a plurality of fluid passageways 76 which extend between lower working chamber 46 and reservoir chamber 54. Finger spring 62 is secure to end cap 60 and operates to bias valve body 66 against valve disk 68 and valve disk 68 against end cap 60. Sleeve 64 is secured to valve body 66 using an interference fit and extends through valve body 66, valve disk 68 and end cap 60 and defines an internal bore 78 and a radial bore 80. Sleeve 64 includes a radially extending flange 82 which abuts valve body 66. Valve body 66 is disposed between flange 82 of sleeve 64 and end cap 60. Valve body 66 defines a plurality of bores 84 through which hydraulic fluid flows during a compression stroke of shock absorber 20. Valve disk 68 is disposed between valve body 66 and end cap 60 and functions to restrict the flow of fluid between lower working chamber 46 and reservoir chamber 54 during a compression stroke of shock absorber 20. The stiffness of valve disk 68 is designed to provide a high resistance to fluid flow and thus a firm ride.

Spool 70 is slidingly disposed within internal bore 78 of sleeve 64. Spool 70 defines an internal bore 86, a radial bore 88 and an annular groove 90. Mass 72 is attached to the top of spool 70. Spool 70 and mass 72 are biased against valve retainer 74 by a valve spring 92 which is disposed within bore 78 of sleeve 64. Valve spring 92 reacts against an end plug 94 which is secured by a retainer 96 to bias spool 70 and mass 72 upward against valve retainer 74 to provide the desired response for base valve assembly 40.

During an extension stroke of shock absorber 20, fluid flows from reservoir chamber 54 through base valve assembly 40 into lower working chamber 46. Fluid within chamber 54 flows through fluid passageways 76 and causes fluid pressure to be exerted on the lower surface of valve disk 68. This fluid pressure builds to the point that valve disk 68 urges against valve body 66 which urges against finger spring 62 to cause movement of valve body 66 and valve disk 68 and the unseating of valve disk 68 from end cap 60 permitting fluid to flow to lower working chamber 46. The movement of valve body 66 also moves sleeve 64 which slides along spool 70 due to spool 70 and mass 72 being retained by valve retainer 74.

During normal operation of base valve assembly 40 during a compression stroke of shock absorber 20, a firm ride or restrictive fluid flow through base valve assembly 40 is provided. Spool 70 and mass 72 are located in a static position which allows for the firm damping. Fluid flows from lower working chamber 46 to reservoir chamber 54. Fluid flow occurs through valve retainer 74, through finger spring 62, through bores 84 of valve body 66 until sufficient pressure has been built up against valve disk 68 to unseat valve disk 68 from valve body 66. This allows fluid flow as shown by the arrows in FIG. 3 and provides a firm ride which is controlled by the stiffness of valve disk 68.

Referring now to FIG. 4, base valve assembly 40 is shown providing a less restrictive flow or a soft ride characteristic. When sufficient acceleration from road input is achieved which is greater than the calibrated acceleration level, mass 72 and the mass of spool 70 overcome the spring force of valve spring 92. The overcoming of the spring force of valve spring 92 causes spool 70 to slide within bore 78 of sleeve 64 to align annular groove 90 with radial bore 80 of sleeve 64. Fluid flows from lower working chamber 46 through bore 86 of spool 70, through radial bore 88 and into annular groove 90. Fluid flows from annular groove 90 through radial bore 80 of sleeve 64 through the fluid passageways 76 of end cap 60 into reservoir chamber 54. Fluid pressure will also build up against valve disk 68 to provide a second flow path identical to that described above for FIG. 3 or the firm damping flow path. These two flow paths as shown by the arrows in FIG. 4 provide a soft ride which is controlled by the stiffness of valve disk 68, the size of bores 86, 88, 80 and groove 90, and the size of mass 72.

Base valve assembly 40 thus provides firm damping for minimum road inputs on acceleration while switching to soft damping for large road inputs or accelerations. This system significantly reduces the ride harshness while providing proportional compression damping relative to wheel acceleration.

While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.