Low-level damping valve and method for a semi-active hydraulic damper

Abstract: A semi-active hydraulic damper (10) includes a solenoid valve assembly (66) mounted in a valve boss (68) mounted on an exterior surface of the damper (10), for controlling fluid flow through a bypass channel (54) in the damper (10). A separate blow-off valve assembly (64) is provided in the valve boss (68) in series with the solenoid valve assembly (66) to provide low-level damping when the bypass channel (54) is open.

Description: The present invention relates generally to controllable hydraulic dampers for vehicular suspension. In particular, the present invention is concerned with a low-level damping valve mounted in series with a solenoid valve in a semi-active suspension actuator as specified in the preamble of claim 1, as disclosed in WO-A-91/10077. For purposes of this specification, an active suspension system includes an actuator capable of modifying the force between a vehicular body and a wheel assembly in response to a control in real time to produce a desired suspension behavior. A semi-active suspension system is similar but uses an actuator (a damper) which provides only damping or dissipative forces in real time wherein the suspension system generates its own force. Additionally, an on/off semi-active damper has only two operating modes with fixed force/velocity damping curves: a first mode having a low damping force ("soft") when a solenoid valve of the damper is open; and a second mode having a high damping force ("firm") when the solenoid valve of the damper is closed. A continuously variable semi-active damper has a continuous range of damping modes between minimum and maximum settings. Semi-active dampers include electric solenoid valves capable of switching a damper between operating modes at frequencies preferably at least twice the resonant wheel vibration frequency to achieve real-time control of wheel and body motions. Semi-active dampers are also known as "fast shocks" and as "real-time dampers." Passive hydraulic dampers (shock-absorbers and struts) include a reciprocable piston and piston rod slidably mounted in a fluid-filled cylinder. The piston divides the interior of the cylinder into upper and lower chambers. A valve assembly in the piston provides a restricted fluid path between the chambers. A reservoir tube concentrically mounts and co-operates with the cylinder to form a fluid reservoir. The lower end of the cylinder is closed by a compression, base valve assembly. During a compression stroke, fluid travels from the lower chamber through the piston valve assembly to the upper chamber. An amount of fluid equal to the increasing rod volume in the upper chamber travels through the base valve assembly to the reservoir. During a rebound stroke, fluid travels from the upper chamber through the piston valve assembly to the lower chamber. Also, fluid travels from the reservoir through the base valve assembly to the lower chamber to compensate for the rod volume. The restriction of fluid flow through the piston and base valve assemblies provides the level of damping in a damper. A semi-active damper uses a bypass channel between the upper chamber and the reservoir in a well-known manner. As described above, a semi-active damper incorporates either an on/off or continuously variable solenoid valve assembly to control fluid flow in the bypass channel. When the solenoid valve assembly is opened, fluid travels from the upper chamber to the reservoir through the bypass channel. This re-direction of fluid flow changes the damping characteristic of the damper to a "soft" setting, since the bypass channel permits fluid flow with less restriction than the piston and base valve assemblies. When the solenoid valve assembly is closed, fluid is forced to flow through the piston and base valve assemblies in the usual manner, resulting in a "firm" setting. Semi-active dampers can be tuned so that the vehicle experiences a boulevard-type ride when operating in the soft mode. It has been determined that a certain amount of low damping is desirable at such conditions to improve vehicle handling. The art continues to seek improvements. It is desirable to provide low-level damping in a semi-active damper to enhance ride control. A hydraulic damper according to the present invention is characterised by the features specified in the characterising portion of claim 1. The present invention includes a low-level damping valve mounted in series with a solenoid valve in a semi-active damper. The low-level damping valve includes a blow-off valve assembly which receives fluid from a bypass channel. When the solenoid valve is opened, fluid flows first through the low-level damping valve and then through the solenoid valve to reach a reservoir. This fluid path provides low-level damping to enhance ride control. The invention and how it may be performed are hereinafter particularly described, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view of a semi-active hydraulic damper including a low-level damping valve according to the present invention mounted in series with a solenoid valve assembly; Figure 2 is a sectional view of a second embodiment of a low-level damping valve according to the present invention, removed from the damper of Figure 1 for purposes of clarity of illustration; Figure 3 is a graph illustrating typical force-velocity damping curves for the semi-active damper of Figure 1; and Figure 4 is an enlarged sectional view of the low-level damping valve of Figure 1 shown exploded from the solenoid valve assembly, a spacer and a seal cup, all of which are received by a valve boss provided on the hydraulic damper. A semi-active hydraulic damper is indicated generally at 10 in Figure 1. The damper 10 includes an outer reservoir tube 12 closed at its lower end by an end cap 14. A mounting fitting 16 is provided on the end cap 14 for securing the damper 10 to a vehicular road wheel assembly (not illustrated) in a well-known manner. A seal cover 18 is welded or otherwise secured to an upper end of the reservoir tube 12. A fluid-filled inner cylinder 20 is spaced inwardly from and concentric with the reservoir tube 12. An intermediate tube 22 is concentrically mounted about the inner cylinder 20 as described below. The volume between the intermediate tube 22 and the reservoir tube 12 forms a fluid reservoir 24. A piston 26 is slidably mounted inside the inner cylinder 20 and divides the interior volume of the inner cylinder 20 into an upper chamber 28 and a lower chamber 30. The piston 26 includes well-known internal valving 32 which provides a restricted flow path between the lower chamber 30 and the upper chamber 28 as the piston 26 reciprocates in the inner cylinder 20. A well-known compression valve assembly 34 secured to and closing the lower end of the inner cylinder 20 controls the flow of fluid between the reservoir 24 and the lower chamber 30 during operation of the damper 10 as described below. A piston rod 36 is attached at its inner end to the piston 26 and is connected at its upper end (not illustrated) to bodywork (not illustrated) of a vehicle in any conventional manner. The piston rod 36 passes through a rod guide 38 press-fitted onto an upper end of the inner cylinder 20 and held in position by the seal cover 18. An annular bearing 40 is fitted into a central passage of the rod guide 38 and receives the piston rod 36. A high-pressure seal ring 42 is provided about the rod guide 38 adjacent the bearing 40. A low-pressure seal assembly 44 is seated on the rod guide 38 and has sealing contact with the piston rod 36 to prevent loss of hydraulic fluid from the damper 10 as the piston 26 reciprocates in the inner cylinder 20 during operation. A return passage 45 is provided in the outer circumference of the rod guide 38 for fluid which leaks past the high-pressure seal ring 42 to return to the reservoir 24. A tube seal adapter 46 preferably formed from a suitable polymeric material is press-fitted onto a lower end of the inner cylinder 20. A circumferential shoulder 48 of the adapter 46 receives a lower end of the intermediate tube 22. An upper end of the intermediate tube 22 is press-fitted onto an intermediate diameter portion 50 of the rod guide 38. Ports 52 (only one of which is illustrated in Figure 1) are formed in the rod guide 38 to provide fluid communication between the upper chamber 28 and an annular bypass channel 54 formed by the volume between the inner cylinder 20 and the intermediate tube 22. The tube seal adapter 46 blocks the lower end of the bypass channel 54 and forms a fluid seal. A sleeve 56 which can include longitudinal ribs 58 is press-fitted onto the intermediate tube 22 and includes an opening 60 aligned with an opening 62 provided in the intermediate tube 22. Openings 60 and 62 provide fluid communication between the bypass channel 54 and a low-level damping valve assembly 64 mounted in series with a solenoid valve assembly 66. A valve boss 68 is welded to the reservoir tube 12 and includes internal threads for receiving the solenoid valve assembly 66. The low-level damping valve assembly 64 is housed in a hollow, cylindrical seal cup 70 having a protruding inlet portion 72 which is urged into openings 60 and 62 as the solenoid valve assembly 66 is threaded inwardly into the valve boss 68. A valve cage indicated generally at 76 is a generally cylindrical member having a stem 78 at a first end and an annular skirt 80 at a second end. A retainer flange 82 is provided between the stem 78 and the skirt 80. An annular elastomeric isolator 84 is provided between an inner end surface of the seal cup 70 and the retainer flange 82. A ring-like spacer 86 is provided between the retainer flange 82 and the innermost end of the solenoid valve assembly 66. As the solenoid valve assembly 66 is threaded inwardly to engage the spacer 86 against the retainer flange 82, the elastomeric isolator 84 is compressed and provides a fluid seal between the valve cage 76 and the seal cup 70. A relief valve indicated generally at 88 is a substantially cylindrical member including an opening 90 and gate 92 in an inner portion slidably received in the stem 78 and a circumferential stop flange 94 formed about its central portion. The relief valve 88 is inserted inside the annular skirt 80 so that the stop flange 94 rests on an inner surface of the stem 78. A helical coil spring 96 is provided about the outer portion of the relief valve 88. A first end of the spring 96 is seated against the stop flange 94. A second end of the spring 96 is seated against a slotted retainer 98 held in place by a crimped end 100 of the skirt 80. The solenoid valve assembly 66 includes an inlet portion 102 in fluid communication with the low-level damping valve assembly 64 and an annular outlet portion 104 in communication with the reservoir 24. When the solenoid valve assembly 66 is energized by a controller (not illustrated), an internal passage (not illustrated) is opened which permits the one-way passage of fluid from the inlet portion 102 to the outlet portion 104. When the solenoid valve assembly 66 is not energized, fluid flow is blocked through its internal passage. Without the low-level damping valve assembly 64, opening the solenoid valve assembly 66 changes the damping force provided by the damper 10 from a "firm" mode to a "soft" mode by routing fluid through the bypass channel 54 to the reservoir 24 instead of through the compression valve assembly 34. The force-velocity curves illustrated in Figure 3 illustrate such firm and soft damping characteristics. The inclusion of the present low-level damping valve assembly 64 in series with the solenoid valve assembly 66 changes the damping characteristics of the damper 10. When the solenoid valve assembly 66 is energized and opened, fluid from the bypass channel 54 first flows through the low-level damping valve assembly 64 and then through the solenoid valve assembly 66 to reach the reservoir 24. The spring-biased relief valve 88 acts as a blow-off element and provides a restriction as fluid flows to the solenoid valve assembly 66. As a result, the damper 10 provides a low level of damping as depicted in Figure 3. It is understood that the low-level damping valve assembly 64 can be tuned to provide a desired low-level damping rate. A second embodiment of the present low-level damping valve assembly is indicated generally at 108 in Figure 2. The assembly 108 has been removed from the damper 10 of Figure 1 for clarity and would be substituted for the first low-level damping valve assembly 64. The valve assembly 108 includes a cup-like valve cage 110 having a central orifice 112 in a forward wall 114. The forward wall 114 engages the elastomeric isolator 84 as the solenoid valve assembly 66 is threaded inwardly in the valve boss 68 and into contact with a crimped end 116 of the valve cage 110 which secures a slotted retainer 118. The spacer 86 illustrated in Figure 1 is not required when valve assembly 108 is mounted in series with the solenoid valve assembly 66. A valve plate 120 includes an annular, coined sealing surface 122 urged against the forward wall 114 by a first end of a spring 124. The second end of the spring 124 is seated on the retainer 118. A circumferential flange 126 is provided on the valve plate 120. When the solenoid valve assembly 66 is opened, fluid from the bypass channel 54 flows through the orifice 112 and forces the sealing surface 122 away from the forward wall 114. Fluid is directed past the flange 126, which acts as a self-centering element for the valve plate 120, and the retainer 118 to reach the solenoid valve assembly 66 and the reservoir 24. It is appreciated that the valve assembly 108 can be tuned to provide a desired low-level damping rate. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail of these embodiments without departing from the scope of the claims of the invention.

Claims: A hydraulic damper (10) for a vehicular suspension comprising a fluid-filled inner cylinder (20); a piston (26) slidably mounted in the inner cylinder (20) and dividing the inner cylinder (20) into upper and lower chambers (28,30); piston valving means (32) for controlling fluid flow through the piston (26); a reservoir tube (12) concentrically surrounding the inner cylinder (20) and co-operating therewith to form a fluid reservoir (24); a bypass channel (54) formed between the inner cylinder (20) and the reservoir (24) for receiving fluid from the upper chamber (28); solenoid valve means (66) for controlling fluid flow in the bypass channel (54); blow-off valve means (64) mounted in series with the solenoid valve means (66) to provide low-level damping when the solenoid valve means (66) is energized; and a seal cup (70) having an inlet (72) in fluid communication with the bypass channel (54), the seal cup (70) being slidably received in a valve boss (68) mounted on an exterior surface of the reservoir tube (12); the blow-off valve means (64) being inserted into the seal cup (70), having a valve element (88) biased to a closed position by spring means (96), and being opened by fluid pressure to provide said low-level damping; and said solenoid valve means (66) being housed separately from the blow-off valve means, and being secured to the valve boss (68); characterised in that the hydraulic damper comprises compression valve means (34) for controlling fluid flow between the lower chamber (30) and the reservoir (24); in that the blow-off valve means (64) is mounted upstream of the solenoid valve means (66); and in that the solenoid valve means (66) is secured to the valve boss (68) downstream of the blow-off valve means (64), and has an inlet portion (102) for receiving fluid from the opened blow-off valve means (64) and an outlet portion (104) directing fluid to the reservoir (24) when the solenoid valve means (66) is energized. A hydraulic damper (10) according to claim 1, in which the blow-off valve means (64) includes a valve cage (76) housing the spring-biased valve element (88). A hydraulic damper (10) according to claim 2, in which the valve element (88) is a valve stem having an opening (90) and a gate (92) in fluid communication with the bypass channel (54). A hydraulic damper (10) according to claim 2, in which the valve element is a plate (120) having a circumferential flange (126). A hydraulic damper (10) according to claim 1, in which the inlet portion (72) of the solenoid valve means (66) is received within the seal cup (70). A hydraulic damper (10) according to claim 1, in which the bypass channel (54) is formed between the inner cylinder (20) and an intermediate tube (22) mounted concentrically about the inner cylinder (20). A hydraulic damper (10) according to claim 6, in which a tube seal adapter (46) formed from a polymeric material is press-fitted to lower ends of the inner cylinder (20) and the intermediate tube (22) so as to seal the bypass channel (54) from the reservoir (24). A hydraulic damper (10) according to claim 1, in which an elastomeric isolator (84) is provided between the seal cup (70) and the blow-off valve means (64). A hydraulic damper (10) according to claim 1, in which the valve boss (68) includes internal screwthreads which mate with external screwthreads provided on the solenoid valve means (66).

Inventors: DERR RANDALL L, DOURSON STEPHEN EDWARD, KELLER CHRIS FRED JR, MORGAN WILLIAM SWAN, DERR, RANDALL L., DOURSON, STEPHEN EDWARD, KELLER, CHRIS FRED, JR., MORGAN, WILLIAM SWAN
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1992
Main classification: F16F9
IPC codes: B60G17, F16F9