VARIABLE RATE SHOCK ABSORBER

Abstract: A variable rate shock absorber comprising a tubular working cylinder (10) destined to be mounted on a suspended part of a vehicle, a piston rod assembly (24) slideably received in the working cylinder (10) and having an end (34) destined to be mounted on a fixed part of a vehicle, the piston rod assembly (24) having at its free end a piston member (48) cooperating with the working cylinder (10) 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 and lower working chambers and electromagnetic valve means (62) disposed between the upper working chamber (44) and a reservoir (18) and selectively actuatable to allow fluid flow therebetween, the valve means (62) comprising a first member (80 ; 114) slideably mounted with respect to a second member (72 ; 116) between a closed position and an open position, characterised in that the first member (80,114) is moveable into at least one partially open position, the position defined by at least one stepped valve surface (94 ; 100 ; 126) formed on one member (80 ; 116).

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 it is desirable to be able to change the response characteristics, or rate of stiffness of a vehicle's shock absorber 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-3 039 566 describes a hydraulic shock absorber in which a solenoid valve simultaneously vents the upper and lower working chambers to a reservoir, thus to selectively change the characteristics of the suspension. This arrangement had the disadvantage that the shock absorber structure was complex and that it needed special electrical control circuitry for the valve. Document GB-A-2 159 604 discloses a hydraulic shock absorber according to the preamble of Claim 1. This shock absorber presents only two levels of damping forces. On the other hand, using stepped valve surfaces in order to obtain predetermined flow restrictions is known from JP-U-57-11 54 68. However these stepped valve surfaces are not used for a shock absorber It is therefore an object of the present invention to provide a variable rate shock absorber of simple structure and in which the control circuitry for the valve is minimized. According to the present invention there is provided a variable rate shock absorber comprising a tubular working cylinder destined to be mounted on a suspended part of a vehicle, a piston rod assembly slideably received in the working cylinder and having an end destined to be mounted on a fixed part of a vehicle, the piston rod assembly having at its free end a piston member cooperating with working cylinder to divide the interior thereof into an upper and a lower working chamber, valve means in the piston member to permit controlled two-way flow between the upper and lower working chambers and electromagnetic valve means disposed between the upper working chamber and a reservoir and selectively actuatable by a control circuit to allow fluid flow therebetween, the valve means comprising a first member slideably mounted with respect to a second member between a closed position and an open position, the first member being slideable relative to an opening formed in the second member and which forms part of the fluid passage between the upper working chamber and the reservoir. According to the invention, the first member is moveable into partially open positions which are defined by a first and a second stepped valve surfaces, and a fully open position defined by a third stepped valve surface, and the control circuit comprises four resistances which are selectively arrangeable in parallel, in series or in two parallel pairs, the selected arrangement corresponding respectively to a selected desired position of the first member. The invention will now be described by way of example with reference to the accompanying drawings, in which : Figure 1 is a longitudinal section through a shock absorber, in accordance with the invention ; Figures 2, 2A and 2B are detailed views of a part of Figure 1 showing the electrovalve in accordance with the invention and shown by reference numeral 2 in Figure 1 and Figure 3 and 3A to 3D are diagrams of electric control circuits for the present shock absorber. As shown in Figure 1, the variable rate shock absorber 8 which, in the example shown, is of the bi-tube type, 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 the 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 opened 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 opened 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. As shown Figure 2, 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 form 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 83 of the valve member 80 is immediately adjacent the leading edge 84 of part 70 of the core member 68. The valve member 80 allows fluid to pass between the interior 92 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 atmospheric pressure. The valve member 80 is formed with first, second and third annular surfaces 100, 102 and 104. The first and second annular surfaces 100 and 102 have similar axial lengths -c- and -d- which allow the valve member 80 to be positioned with any point along the annular surfaces 100 and 102 adjacent the edge of annular groove 98 to form a given restriction. The first and second annular surfaces 100 and 102 give two possible predetermined restrictions to fluid flow past the valve member 80. Displacement of the valve member 80 to a point where the third annular surface 104 is adjacent the edge of annular groove 98 forms the open position where the restriction, and hence the pressure drop across it, are negligible. Thus, the valve member 80 can be selectively moved, with no great precision, into four different positions corresponding to different operating characteristics of the shock absorber. These four positions may be described as closed, first restriction, second restriction and open. In the illustrated rest position of the valve member 80, the end of the valve member extends beyond the annular groove 98 so that a portion of the valve member having its full diameter, which closely corresponds to that of bore 82, closes the fluid passage between the interior 92 of the cylinder 36 and passage 91. Activation of the solenoid coil 64 to a given first level will cause the valve member 80 to be drawn back against the force of the spring 86 into a first position where the first annular surface 100 is located opposite the edge of annular groove 98. This position is shown in Figure 2A. Such an opening will allow fluid passage at a rate proportional to the restriction defined between the edge of the annular groove 98 and the first surface 100. As the first surface 100 is of constant diameter it is immaterial which point along the axial length -c- is moved into position opposite the edge of the annular groove 98 ; the resulting restriction of thickness -t-, which is presented to fluid passage, will be the same. So it is not necessary to position the valve member 80 with any great precision. Thus, as will be described below, the electric control circuit for the solenoid coil 64 can be minimized. If the solenoid coil 64 is actuated to a second, higher level the valve member 80 will be drawn back further against the force of spring 86 into a second position in which the second surface 102 is located opposite to the edge of annular groove 98. This position defines a second restriction. If the solenoid coil 64 is actuated to a third higher level, the valve member 80 will be drawn back into a third position. This position is shown in Figure 2B and is considered as the open position of the valve member 80 where the restriction, and hence the pressure drop across it, are negligible. In Figures 3, 3A and 3B are shown possible electrical control circuits for the above described embodiment. Figure 3 shows the circuit corresponding to the closed position of the valve member in which a zero voltage is applied to the solenoid coil 64. In Figure 3A four resistances 132, 134, 136 and 138 are arranged in two parallel pairs and a positive continuous voltage, 12 volts in the example shown, is applied across the resistances to the solenoid coil 64. It is envisaged that the four resistances be of substantially similar impedance. The coil intensity, I, in this situation, which corresponds to an intermediate open position of the valve member is represented by the formula I = V 2R where V is the applied voltage and R is the coil resistance. The applied voltage would, in use, come from the vehicle battery and any variation in this voltage would simply cause the valve member to be displaced slightly relative to its means intermediate position. Any such minor displacement of the valve member would not affect the restriction due to the previously described length of the first surface 100. Figure 3B shows the circuit which produces the open position of the valve member. In this circuit the four resistances 132, 134, 136 and 138 are arranged in parallel and a positive continuous voltage is applied across them. In this circuit the coil intensity I is defined as I = V R where V is the applied voltage and R is the coil resistance. In this case the value of I is twice that of Figure 3A. Figure 3C shows the circuit necessary to produce a second intermediate position of the valve member. In this case the four resistances 132, 134, 136 and 138 are arranged in series. In this case the coil intensity I = V 4R Finally Figure 3D shows an example of an electrical switching circuit which could be used to produce the resistance arrangements of the previous figures. Thus, it will be seen that the valve arrangement of the present invention allows the production of a variable rate shock absorber whose construction is simple and whose cost is relatively low. The electrically control circuit associated with the shock absorber is also simple and of low cost. It is envisaged that the valve assembly may be provided in a fluid passage at another point in the shock absorber for example in a chamber located below the relief valve member 16 or at the free end of the piston assembly 24. In any embodiment it is simply necessary to locate the valve member in the fluid passage between the upper working chamber and a fluid reservoir formed in the shock absorber. It is further envisaged that the valve member 80 may be slideably mounted around the outside of an inner core member. Thus, with the present invention, it is possible to provide satisfactory modification of the suspension characteristics to meet the essential motoring needs with the minimum of components.

Claims: 1. A variable rate shock absorber comprising a tubular working cylinder (10) destined to be mounted on a suspended part of a vehicle, a piston rod assembly (24) slideably received in the working cylinder (10) and having an end (34) destined to be mounted on a fixed part of a vehicle, the piston rod assembly (24) having at its free end a piston member (48) cooperating with the working cylinder (10) 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 and lower working chambers and electromagnetic valve means (62) disposed between the upper working chamber (44) and a reservoir (18) and selectively actuatable by a control circuit to allow fluid flow therebetween, the valve means (62) comprising a first member (80) slideably mounted with respect to a second member (68) between a closed position and an opened position, the first member (80) being slideable relative to an opening (98) formed in the second member (68) and which forms part of the fluid passage between the upper working chamber (44) and the reservoir (18), characterised in that said first member is moveable into partially open positions which are defined by a first (100) and a second (102) stepped valve surfaces, and a fully open position defined by a third stepped valve surface (104), and in that said control circuit comprises four resistances (132, 134, 136, 138) which are selectively arrangeable in parallel, in series or in two parallel pairs, the selected arrangement corresponding respectively to a selected desired position of the first member. 2. Shock absorber as claimed in Claim 1 characterized in that said valve surfaces (100, 102, 104) are formed on the first member (80), the intermediate positions being defined between the opening (98) and the first and second valve surfaces (100, 102).

Inventors: SIMON BACARDIT, JUAN
Applicants: BENDIX ESPANA S.A.
Application year: 1988
Main classification: F16F9
IPC codes: B60G17, F16F9