Shock absorbers

The present invention provides a shock absorber of monotube or twin-tube configuration wherein the piston within the shock absorber includes an electromagnetically operable bypass valve, the electromagnetically operable valve being controlled remotely from the outside of the shock absorber via an electrical connection which extends along the piston rod. In a twin tube configuration according to the present invention, the foot valve assembly also includes an electromagnetically operable bypass valve which is remotely controlled from the outside of the shock absorber via an electrical connection. These electrical connections do not affect the overall design of the shock absorber and can thus be easily included in a vehicle design. Further, these electrical connections can be connected to a microprocessor so that the shock absorber valves are controlled by the microprocessor dependent upon the values of certain parameters, e.g. speed, load, fed to the microprocessor from appropriate sensors.

The present invention relates to shock absorbers for use in automotive 
vehicles. 
More particularly the present invention relates to telescopic shock 
absorbers. All such telescopic shock absorbers comprise a piston which is 
axially movable in a cylinder, the piston incorporating valves for 
restricting the flow of fluid therethrough as the piston moves along the 
cylinder. The valves are so designed to provide a greater resistance in 
one direction of piston movement than the other. However, these valves are 
usually preset during manufacture and the setting of these valves is not 
suitable for all vehicle load conditions, surfaces over which the vehicle 
may be driven, and/or speeds. 
To cater to a certain extent, for varying loads, road surfaces etc, shock 
absorbers have been produced with adjustable piston valves and/or with 
additional controlled valves. However such valves have been adjustable 
externally of the shock absorber, either manually or electro-mechanically. 
Thus, manual or electro-mechanical controls have had to be provided on the 
outside of the shock absorber, thereby increasing the overall size of the 
shock absorber. This is clearly disadvantageous as space-saving is an 
important consideration in vehicle suspension design. 
An aim of the present invention is to provide a shock absorber which allows 
for the remote adjustment of the piston valves without increasing the 
overall outer configuration of the shock absorber. 
According to the present invention there is provided a telescopic shock 
absorber comprising a piston which is axially slidable within a cylinder, 
an electromagnetically controlled valve being arranged to provide a fluid 
flow path bypassing the piston when desired. 
Thus, the electromagnetically controlled valve may have a wire connection 
through the piston and a piston rod connected to the piston, to the 
outside where the wire can extend to a remote location from which the 
valve can be controlled. This wire connection adds virtually nothing to 
the size of the shock absorber and thus does not affect the suspension 
design. Further it is possible to efficiently seal the shock absorber 
around the wire, whereas it is difficult to provide adequate sealing 
around a movable mechanical linkage. 
Electromagnetically operated valves may be incorporated in the pistons of 
monotube or twin-tube shock absorbers and preferably are in addition to 
the existing piston valves. The electromagnetic valve thus provides an 
additional flow path in parallel with the conventional flow path through 
the piston. The effect of this additional flow path is to provide for a 
change in the setting characteristic by increasing or decreasing the 
pressure drop across the piston. The normal setting for the de-energised 
electromagnetic valve is for the valve to be closed. When energized the 
increased total flow through the piston results in a lower resistance to 
piston movement at a given piston velocity. 
In twin-tube telescopic shock absorbers which basically comprise two 
elongate hollow cylinders, the cylinders being coaxially arranged with 
respect to each other, one within the other, a foot valve is provided at 
one end of the inner cylinder, a piston being axially movable within the 
inner cylinder and being connected with a piston rod which extends out of 
the other end of the inner cylinder. The foot valve controls the flow of 
fluid between the inner cylinders and the annular cavity formed between 
the cylinders, which acts as a fluid reservoir. Conventionally two valves 
are provided in the foot valve assembly, each valve allowing for fluid 
flow in a different direction and restricting fluid flow to a different 
extent. These valves are preset during design and manufacture of the shock 
absorber, but clearly they cannot provide the required performance for all 
types of terrain and/or load. 
It is an aim of the present invention to provide a shock absorber 
additionally having an adjustable foot valve, to thus cater for different 
performance requirements. 
According to the present invention there is provided a telescopic shock 
absorber comprising a piston which is axially slidable within a cylinder, 
an electromagnetically controlled valve being arranged to provide a fluid 
flow path bypassing the piston when desired. 
According to a further feature of the present invention there is provided a 
twin tube telescopic shock absorber comprising a pair of coaxially aligned 
cylinders, one cylinder being located within the other, a foot valve 
assembly being located at one end region of the inner cylinder to control 
fluid flow between the inner cylinder and the annular cavity between the 
cylinders, and a piston being axially slidably arranged within said inner 
cylinder, an electromagnetically controlled valve being arranged to 
provide a fluid path bypassing the piston when desired, and the foot valve 
assembly also incorporating an electromagnetically operable valve, said 
valves being controllable from a remote location outside the shock 
absorber. 
Preferably, the electromagnetically operated valve in the foot valve 
assembly provides an additional flow path in parallel to the opposite 
direction flow paths provided by the usual two valves. With the valve 
de-energised the valve is closed allowing the foot valve to operate 
conventionally. However, when energised the additional flow path is open 
in both flow directions, thereby reducing the resistance to flow. 
In a preferred embodiment, the electromagnetic valve in the foot valve 
assembly comprises an electromagnet which is connected by an electrical 
wire to a remote control outside the shock absorber. The electromagnet 
acts on an elongate hollow tube which passes through the foot valve 
assembly and is axially movable relative thereto. In the normal position 
with the electromagnet de-energised, the hollow tube is retracted to close 
off lateral ports in the tube. However, when energised, the electromagnet 
moves the hollow tube to expose the lateral ports and to thus provide a 
flow path through the foot valve assembly in addition to that provided by 
the conventional valves. 
The above described electromagnetic foot and piston valves provide the 
required adjustment to cater for the desired performance having regard to 
speed, load and terrain. Further the or each electromagnetic valve may be 
controlled automatically dependent, for example, upon speed, load etc as 
monitored by appropriate sensors.

FIG. 1 illustrates part of a twin-tube shock absorber comprising an inner 
cylinder 1 and an outer cylinder 3, said tubes 1,3 being coaxially aligned 
with each other. 
Within the inner cylinder 1 is located a piston assembly 5 mounted on a 
piston rod generally designated 7. The piston assembly 5 comprises a 
cylindrical piston 9 which has a central bore 11 which engages snugly over 
a reduced diameter end region 13 of the piston rod 7. An end cap 15 screw 
threadedly engages the end region 13 of piston rod 7 to hold the piston 9 
on piston rod 7. Trapped between the end cap 15 and piston 9 are an 
annular spacer 17 and a valve closure member 19, the valve closure member 
19 controlling fluid flow through bore 20 and being biassed to the 
illustrated closed position by a spring 21 which also engages an outwardly 
extending flange 23 on end cap 15. As seen in FIG. 1, the closed position 
for closure member 19 still provides a bleed gap 25 due to spacer 17. A 
further bore or bores 27 also extends axially through piston 9 and an 
annular closure member 29 is located directly over further bore 27 and 
trapped between piston 9 and a shoulder 31 on the piston rod 7. This 
annular closure member 29 has an aperture 33 which is aligned with bore 20 
and a small bore 35 aligned with further bore 27. A further annular 
closure plate 37 is located on piston rod 7 so as to be axially movable 
therealong when an electromagnet 39 also located on piston rod 7, is 
energised; a spring 41 biassing the further annular closure plate 37 
against closure member 29. This further annular closure plate 37 is 
cutaway at 43 to expose aperture 33 and bore 20, but closes off small bore 
35 when biassed against annular closure member 29. 
Control and power for the electromagnet 39 is provided via electric cable 
wire 45, wire 45 extending through an axial bore 47 in piston rod 7 to the 
outside of the shock aborber. The exit of the wire 45 from the shock 
absorber can be simply sealed reliably and the wire fed to any desired 
remote location; the exit of the wire from the shock absorber not 
increasing the size of the shock absorber and thus not affecting 
suspension design. 
With the electromagnet de-energised, closure plate 37 is held by spring 41 
against closure member 29. In this condition upward movement of the piston 
9 i.e. outward movement of piston rod 7, will cause fluid to flow through 
cutaway 43, aperture 33 and bore 20 and to deflect closure member 19 
against spring 21. This fluid flow is therefore restricted by closure 
member 19. Downward movement of the piston 9 causes closure member 19 to 
return to the illustrated position, bleed gap 25 allowing a very small 
leakage path for fluid back along bore 20. However during this downward 
movement of the piston, fluid can flow along further bore 27 and deflect 
both closure member 29 and closure plate 37 against spring 41, allowing 
restricted fluid flow. 
When the electromagnet 39 is energised, the closure plate 37 is lifted off 
closure member 29 against spring 41, exposing small bore 35. In this 
condition fluid can flow through further bore 27 and small bore 35 in 
either direction of piston movement. In particular, the flow path is 
increased for upward movement of the piston, thus reducing the resistance 
to piston movement at a particular piston speed. Thus by energising the 
electromagnet 39, the performance of the shock absorber can be adjusted to 
suit changing speed, load etc., without the requirement for bulky external 
control means on the shock absorber. 
FIG. 2 shows part of a monotube shock absorber comprising a hollow 
cylindrical casing 49 within which a piston assembly 51 is axially 
slidable. The piston assembly 51 comprises a cylindrical piston 53 having 
two valve bores 55 and 57 extending axially therethrough. Flexible valve 
closure members 59 and 61 allow fluid to flow only in opposite directions 
through bores 55 and 57 respectively, and thus provide for conventional 
operation of the shock absorber. 
A piston rod assembly 63 extends through a central axial bore 65 in piston 
53, and is secured thereto. The piston rod assembly 63 has a central 
axially extending bore 67 which connects with three cavities 69, 71 and 73 
in the illustrated embodiment. Cavity 69 is towards the free end 75 of the 
piston rod and connects with the shock absorber space 77 in front of 
piston 53 by a bore 79 which extends laterally of the piston rod. Cavity 
69 also presents a planar valve seat 80 against which a tubular valve 
closure member 81 can engage. Tubular valve closure member 81 extends 
through bore 67 and cavities 71 and 73. In cavity 71 tubular closure 
member 81 has a laterally outwardly extending annular flange 83 against 
which a spring 85 engages to bias the valve closure member 81 against 
valve seat 80. Tubular valve closure member 81 has a blind bore 87 
extending for part of its length, the blind bore being open at the end of 
the closure member 81 which engages valve seat 80 and connecting with 
cavity 71 via lateral ports 89. Cavity 71 connects via lateral bore 91 
with the shock absorber space 93 behind piston 53. 
The solid part 95 of the tubular closure member 81 extends into cavity 73 
wherein an electromagnet 97 is housed, the electromagnet 97 being powered 
and controlled via a wire 99, the wire extending via bore 67 to outside 
the shock absorber and requiring no bulky control means on the outside of 
the shock absorber. When the electromagnet is de-energised, the spring 85 
holds closure member 81 against valve seat 80, closing the additional path 
91, 71, 89, 87, 69, 79 across the piston 53. However, when the 
electromagnet 97 is energised the tubular closure member 81 is moved 
axially in bore 67 lifting the tubular closure member 81 off valve seat 80 
and opening said additional flow path. Thus by operation of the 
electromagnet the shock absorber performance can be changed. Further the 
small dimension of the wall thickness of the tubular closure member means 
that a relatively weak spring is required to both close and hold this 
additional path closed, against fluid pressure. 
By providing restrictors (not shown) in either or both lateral bores 79 and 
91, the degree of setting resistance can be preset. These restrictors may 
be in the form of a one way arrangement with a restricted bypass. By these 
means, the setting change for rebound and compression can be varied. 
FIG. 3 shows part of a twin-tube shock absorber such as illustrated in FIG. 
1, incorporating a foot valve generally designated 101. This foot valve 
101 comprises an end plug 103 secured in the inner cylinder 105 of the 
shock absorber, and separating the inner cylinder space from the annular 
reservoir cavity 107 formed between the inner cylinder 105 and outer 
cylinder 109. Conventionally, end plug 103 has two concentric series of 
axially extending valve bores 111 and 113 which are controlled by valve 
closure members 115 and 117 respectively so as to allow fluid flow in 
opposite directions, one valve providing a greater resistance to fluid 
flow than the other. 
Fixedly mounted in the shock absorber below the end plug 103 is an 
electromagnet 119 which is powered and controlled via a wire (not shown) 
which extends to the outside of the shock absorber, allowing for simple 
remote control. Extending through the centre of the electromagnet 119 and 
through a central bore 120 in end plug 103, is a tubular valve spool 121. 
The valve spool 121 has an axially extending blind bore 123 which is open 
beneath the electromagnet 119 and has lateral ports 125 and 127. At the 
closed end of the valve spool 121, a lateral flange 129 is provided, this 
flange 129 engaging the upper face of end plug 103 to close lateral ports 
125 under the biassing action of a spring 131 which engages between a 
lateral extension 133 of the spool 121, and the electromagnet 119. With 
the valve spool 121 in this position, the shock absorber performs 
conventionally in respect of foot valve 101. However, if the electromagnet 
119 is energised the spool 121 moves axially against spring 131, to open 
an additional flow path via lateral ports 125 and 127, and bore 123, 
across end plug 103. Thus the performance of the foot valve can be varied 
as required. 
The above described foot valve 101 can be used in a shock absorber with the 
electromagnetic piston valve arrangement of the present invention, or with 
a conventional electromechanically adjustable or non-adjustable piston 
valve arrangement, as desired. The control of the foot valve can be 
effected manually or automatically dependent upon vehicle operating 
parameters e.g. load, speed etc, as monitored by appropriate sensors. 
The present invention thus provides a shock absorber wherein the 
performance can be adjusted as desired, the shock absorber requiring no 
bulky major external design changes which could affect the suspension 
design configuration.