VARIABLE RATE SHOCK ABSORBER

Abstract: A variable rate shock absorber having the interior of a working cylinder (10) divided by a piston (48) into an upper (44) and lower working chamber (56). The lower working chamber is connected to a reservoir (18) by a bi-directional valve member (16). A solenoid valve (62) housed in a hollow piston rod (24) has an actuated state connecting the upper working chamber to the reservoir. The output of the solenoid valve is connected to the reservoir by means of an axially disposed telescoping cylinder 6 passing through the piston and the bi-directional valve member.

Description: The present invention relates to a variable rate shock absorber and, more particularly, to electrically controlled variable rate shock absorbers for automotive vehicles. In order to deal with varying road conditions and different driving styles it is desirable to be able to change the rate of stiffness of a vehicle's shock absorbers which serve to provide hydraulic damping of the vehicle suspension. Various types of electrically controlled variable rate shock absorbers have been previously proposed. For example, US-A-2,507,276 describes a hydraulic damper using a solenoid valve to increase the stiffness of the suspension during application of the vehicle's brakes in order to reduce the phenomenon of the front end of the vehicle diving during sudden braking. US-A-3,039,566 discloses a hydraulic shock absorber in which a solenoid valve simultaneously vents the upper and lower working chambers of the shock absorber to a reservoir to thus selectively change the characteristics of the suspension. Similar variation of the shock absorber characteristics is provided in US-A-4,463,839 which describes a shock absorber having a solenoid actuated rotary valve which is operable to open and close piston by-pass passages connecting the upper and lower working chambers of the shock absorber. It is an object of the present invention to provide a variable rate shock absorber of simple construction, whose characteristics are easily controlled and in which the operational noise is minimised. A further example of variable rate shock absorber is disclosed in GB-A-2 159 604 on which the preamble of claim 1 is based. However the valve means of this document does not enable a smooth control of the degree of opening of the valve orifice. Another object of this invention is to provide a shock absorber not having this disadvantage. These objects and other advantages are achieved with the shock absorber according to the independent claim 1. The invention will now be described by way of example with reference to the accompanying drawings, in which : Figure 1 is a longitudinal section of a shock absorber according to a first embodiment of the present invention ; Figure 2 is an enlarged view of that part of Figure 1 indicated by reference arrow 2 ; Figures 3A and 3B are longitudinal sections of a shock absorber which corresponds to the invention claimed with the exception that the chamber is on the valve member and not on the core member. As shown in Figure 1. the variable rate shock absorber comprises a cylindrical outer shell 10 to which is secured a bracket 12 by means of which the shell 10 may be mounted on a support for one of a vehicle's wheels (not shown). An inner cylinder 14 is fixedly mounted inside the shell 10 and is closed at one end 15 by a two way pressure relief valve member 16 which connects the interior of the inner cylinder 14 with an annular reservoir 18 formed between the inner cylinder 14 and the outer shell 10. The other end 20 of the inner cylinder 14 is closed relative to the outer shell 10 by a closure member 22. The shock absorber further comprises a piston rod assembly 24 which is slideably received in the closure member 22 and extends within the inner cylinder 14, coaxially therewith. The piston rod assembly 24 comprises a tubular strut 26 in one end 28 of which is fitted a mounting member 30, the other end 32 of which being closed by a mounting bolt 34 whose free end is intended to be secured to the bodywork of the vehicle (not shown). The mounting member 30 also sealingly receives an end of a cylinder 36 and further receives, slidingly, a second cylindrical part 38 one end 40 of which is fixedly mounted in the valve member 16 and passes therethrough. The cylinder 36 and the cylindrical part 38 are free to slide in telescoping fashion one relative to the other. At least one aperture 42 is provided in the tubular strut 26 adjacent the mounting member 30 to provide fluid communication between the annular volume 44 defined within the inner cylinder 14 and the annular space 46 defined between the tubular strut 26 and the cylinder 36. The mounting member 30 supports a piston member 48 which is slideably received within the inner cylinder 14. The piston member 48 is secured on the mounting member 30 by a nut 50 and has a set of through passages 52 which are open at one end and closed at the opposite end by a spring loaded valve 54 which allows one-way fluid flow between the annular volume 44 and a working chamber 56 formed at an end of the inner cylinder 14. The piston member 48 has a second set of through passages 58 which are open to the working chamber 56 and closed at their opposite end by a second spring loaded valve 60 to provide unidirectional flow from the lower working chamber 56 to the annular volume 44. The valve member 16, mounted under pressure between the cylinder 14 and the outer shell 10, contains several passages 17 and 19 similar to those described in the piston, and which are closed by valves 21 and 23 under the effect of springs 25 and 27 respectively. The variable rate shock absorbing characteristic of the shock absorber is defined by the permanent passages 17 and 19, the passages 52 and 58 and the stiffness of the springs 54,60, 25 and 27. To be more precise, the shock absorbing characteristic is defined in the extension movements of the shock absorber by the permanent passages 52 and, their diameter and the resilience of the spring loaded valve 54 in the piston member 48 and the diameter of the passages 19 and the resilience of valve 23 in the valve member 16. In the compression movements of the shock absorber, the parts defining said characteristic and the permanent passages 12 and their diameter and, the resilience of the spring loaded valve 21 in the valve member 16, and the diameter of the passages 58 and the second spring loaded valve 60 in the piston member 48. Figure 2 shows details of an embodiment of solenoid valve 62. As shown, the solenoid valve 62 comprises a solenoid coil 64 which is selectively connectable by an electric cable 66 to a controlling power source (not shown). The solenoid coil 64 is formed around a core member 68 one end of which is fixedly mounted on the mounting bolt 34 and the other end sealingly and slideably receives the free end 74 of cylinder 36. The core member 68 is formed from two parts of magnetic material 70 and 72 which are joined together by a ring 76 of non-magnetic material, for example bronze. An annular air gap 78 is defined between the opposing edges of the two parts 70 and 72 of the core member 68. A cylindrical valve member 80 is slideably mounted in a longitudinal bore 82 formed in the core member 68 and has a length such that, in the illustrated rest position, an end of the valve member 80 is immediately adjacent the leading edge 84 of part 70 of the core member 68. The valve member 80 is urged towards its illustrated rest position by a spring 86 which is located between two non-magnetic bushes 88 and 90. At its end remote from spring 86 the valve member 80 has a longitudinally extending groove 92 which communicates by way of passage 94 with a longitudinal bore 96 extending through the valve member 80. The bore 96 is in fluid communication with the interior 98 of cylinder 36. When the solenoid coil 64 is actuated and the valve member 80 moves against the force of spring 86, the closed end of groove 92 comes into fluid communication with a passageway 102 formed in part 72 of core member 68. Actuation of the solenoid coil 64 thus causes a fluid passageway to be opened between the interior 98 of cylinder 36 and the annular space 46. In use the annular volume 44 and the working chamber 56 are filled with a hydraulic fluid while the annular reservoir 18 is only partially filled with hydraulic fluid. The remaining portion of the annular reservoir 18 is filled with air or gas at a pressure above or equal to atomospheric pressure. In operation, the piston member 48 will assume a nominal position intermediate the extremities of the inner cylinder 14. In the event that the wheel associated with the shock absorber encounters a bump, a force will be applied to the free end of the shock absorber tending to displace the outer shell 10 and inner cylinder 14 upwardly towards the mounting bolt 34 attached to vehicle's frame. This force will produce a pressure differential across the piston member 48. If the wheel associated with the shock absorber falls into a hole, the free end of the shock absorber will be subjected to a force tending to displace the outer shell 10 and the inner cylinder 14 vertically downwards, away from the mounting bolt 34 which is secured to the bodywork of the vehicle, with the shock absorber in extension. This force will cause a pressure differential across the piston member 48 and the spring loaded valve 54, causing the oil to flow through the permanent passage 52 of the piston member 48, which will allow the said movement. In turn, the pressure differential across the valve member 16 will cause the oil to flow between the annular reservoir 18 and working chamber 56 which will compensate for the volume increase formed by the extension of the shock absorber. When the wheel encounters a bump, the operation of the shock absorber is symmetrical to that indicated above, the roles of the valve member 16 and the piston member 48 being reversed. When the wheel falls into a hole and the solenoid valve is not activated, the fluid pressure is maximum in the annular volume 44, the oil being compressed between the upper seal and the piston, rising towards the former, the shock absorber being extended. The stiffness of the shock absorber can be changed by activating the solenoid valve 62 to vent the annular volume 44 to the reservoir 18 through the cylinder 36 and the cylindrical part 38. Referring to Figure 2, when the solenoid coil 64 is not activated the valve member 80 is urged by spring 86 into its rest position in abutment against a ring 104 fixedly mounted in the bore 82 of core member 68. In this position passageway 102 is closed by the valve member 80. Activation of the solenoid coil 64 causes the valve member 80 to move against the force of spring 86 towards a position in which a shoulder 106 on an end of the valve member 80 comes into contact with an annular abutment 108 formed in the bore 82. The controlled displacement of valve member 80 opens a controlled fluid passage between the interior 98 of cylinder 36, which is in fluid communication with the interior of cylindrical part 38 and the annular space 46. When the wheel encounters a bump and the solenoid valve is not activated, the fluid pressure is a maximum in the chamber 56 and since the diameters of the passages 17 and 19 and the stiffness of springs 25 and 27 are selected, so that the pressure drop through the valve member 16 is greater than through the piston, then the pressure in the annular volume 44 is greater than that of the reservoir 18. Since the fluid flow through the passages 58 is proportional to the pressure differential across the piston member 48, during extension, the movement of the piston member is controlled by the pressure in the annular volume 44. Activation of the solenoid valve 62 evacuates the annular volume 44 to the reservoir 18, thereby reducing the pressure differential in the piston member 48. As a result, the fluid flow through the piston is lower, the energy dissipation by viscous friction through the piston is lower whereby the stiffness of the shock absorber in extension is reduced. During compression, the displacement of the piston is controlled by the pressure in the chamber 56 and the pressure differential across the valve member 16. Activation of the solenoid valve 62 evacuates the annular volume 44, the pressure of which is greater, to the reservoir 18, the pressure of which is lower, thereby increasing the pressure differential across the piston. In this way the flow rate from the chamber 56 to the annular volume 44 increases and the pressure in the chamber 56 is reduced. Thereby the pressure differential across the valve member decreases, the energy disipation by viscous friction thereacross is less, which reduces the stiffness of the shock absorber in compression. In this way the solenoid valve controlling the fluid flow rate from the annular volume 44 to the reservoir 18 may be used to reduce the stiffness of the shock absorber in the desired degree when the valve is open, both in the extension and in the compression movements. During the rebound or when the wheel falls into a hole, a force is generated tending to displace the housing and inner cylinder downwardly away from mounting bolt 34. This force increases the fluid pressure in the annular volume 44 above the piston member 48. When the solenoid valve 62 is actuated, the annular volume 44 is vented to the reservoir 18. Therefore, the movement of the piston member 48 is controlled primarily by the fluid flow trough relief valve 16 from the reservoir 18 to the working chamber 56. The size of the fluid passages of the relief valve 16 which control the rate of fluid flow from the reservoir 18 to the working chamber 56 can be selected to decrease the stiffness of the shock absorber by the desired amount when the solenoid valve is open. As shown in Figure 2 the longitudinally extending groove 92 has an end 112 extending at right angles to the axis 114 of the valve member 80. In the illustrated rest position the end 112 lies adjacent an edge of a chamfered surface 116 which leads to the passageway 102. The chamfered surface 116 lies on the core member 68 which has the result that a force F is exerted on the fixed core member 68. The force F has virtually no influence on the throttling value. Figures 3a and 3b show a variant in which the internal structure of the shock absorber has been simplified with respect to that shown in Figure 1. The solenoid valve 62 is located in an extension 401 of the outer shell 10 as opposed to in the tubular strut 26 in the previous embodiment. The shock absorber comprises a single inner tube 403 which corresponds to the second cylindrical part 38 of the embodiment of Figure 1 in which two telescoping tubes were necessary due to the location of the solenoid valve. The inner tube 403 is received in a sleeve 405 which is fixed in, and passes through the valve member 16. The interior of the inner tube 403 communicates with the interior of the sliding valve member 80 of the solenoid valve 62. As in the case of the previous embodiment, when the solenoid coil 64 is actuated, valve member 80 moves against spring 86 and progressively opens passageway 102 between the interior of the inner tube 403 and a chamber 407 which is defined by the extension 401 of the outer shell 10. The chamber 407 is in permanent communication with the annular reservoir 18 and may communicate with the working chamber, as in the case of the previous embodiment, by way of passages 17 and 19. The interior of the inner tube 403 is in fluid communication with the annular space 46 which is, itself, in fluid communication with the annular volume 44 by way of aperture 42. The operation of this embodiment is analogous to that of the embodiment of Figure 1.

Claims: A variable rate shock absorber comprising a tubular working cylinder (14) destined to be mounted on a suspended part of a vehicle, a piston rod assembly (24) slideably received in the working cylinder (14) and having an end (34) destined to be mounted on a fixed part of a vehicle, the piston rod assembly having at its free end a piston member (48) cooperating with the working cylinder (14) to divide the interior thereof into an upper (44) and a lower working chamber (56), valve means in the piston member (48) to permit controlled two-way flow between the upper (44) and lower (56) working chambers, and solenoid valve means (62) disposed between one of the working chambers and an annular space (18) and selectively actuatable to allow fluid flow therebetween, the solenoid valve means (62) comprising a tubular valve member (80) slideably mounted with respect to a core member (68) and slideable in response to actuation of a solenoid coil (64) generating a magnetic field to open an orifice (102), characterized in that said core member (68) is formed from two parts (70, 72) of magnetic material which are separated by a non-magnetic material so that the valve member (80) closes the generated magnetic field between said two parts (70, 72), in that said valve member (80) is progressively displaceable against a spring (86) under the effect of the magnetic induction produced by said solenoid coil (64) in order to variably open said orifice (102) between a fully closed and a fully open position, and in that the tubular valve member (80) is mounted in a bore (82) formed in the core member (68), the core member (68) having an opening (102) therein which is defined in part by a chamfered surface (116), the valve member (80) having an edge (112) which cooperates with the chamfered surface (116) to form the said variable orifice. A shock absorber as claimed in Claim 1, characterised in that it further comprises an outer shell (10) circumscribing the working cylinder (14) and defining therebetween a reservoir (18), valve means (16), located at an end of the working cylinder (14) defining an extremity of the lower working chamber (56) and allowing controlled two-way flow between the lower working chamber (56) and the reservoir (18), the solenoid valve means (62) being located in an independant passage (36,38 ; 403) between the upper working chamber (44) and the reservoir (18). A shock absorber as claimed in Claim 2, characterised in that the passage (36,38) comprises two telescopingly arranged tubes (36,38) extending through an axial passage (46) in the piston rod assembly (24). A shock absorber as claimed in Claim 2, characterised in that the passage (403) comprises a tube (403) one end of which is mounted on the valve means (16) the other end of which is slideably received in an axial passage (46) in the piston rod assembly (24). A shock absorber as claimed in Claim 4, characterised in that the solenoid valve means (62) is located in a chamber (407) formed in an extension of the outer shell (10) defined on the opposite side of the valve means (16) to the lower working chamber (56), the chamber (407) being in fluid communication with the reservoir (18).

Inventors: SIMON BACARDIT, JUAN
Applicants: BENDIX ESPANA S.A.
Application year: 1987
Main classification: F16F9
IPC codes: B60G17, F16F9