Actuation systems

An actuation system for a vehicle in which a pump (10b) draws fluid from a reservoir (10a) to supply one or more first consumers, such as steering valve (50). One of more second consumers, such as a clutch actuator (12), are actuated via a solenoid valve (12a) from an accumulator (10c) charged by the pump. The solenoid valve connects each second actuator (12) to the accumulator or to the reservoir. When the pressure in the accumulator is below a predetermined charge pressure, flow to the first consumer is restricted to a level sufficient to ensure effective operation of the first consumer, while generating a back pressure sufficient to ensure charging of the accumulator. The flow restriction to the first consumer may be achieved by the solenoid valve (12a) or by a separate charging valve (20).

This invention relates to fluid pressure operated actuation systems and in 
particular, though not exclusively, to such actuation systems for the 
operation of vehicle clutches used in semi-automatic transmissions of the 
form described in, for example, the Applicants earlier European patents 
Nos. 0038113, 0043660, 0059035 and 0101220 and other fluid pressure 
operated functions. 
Actuation systems are already known in which a pump supplies pressurised 
fluid to interconnected closed centre and open centre circuits each of 
which includes at least one consumer and the closed centre circuits 
includes an accumulator which is charged by the pump. 
Problems arise with such actuating systems in that the operation of the 
open centre circuit is often affected by the charging of the accumulator 
in the closed centre circuit. 
It is an object of the present invention to provide an actuating system 
which at least mitigates the above problem. 
Thus according to the present invention there is provided an actuation 
system comprising: 
a pump which draws fluid from a reservoir; 
one or more first consumers actuated from the pump; 
one or more second consumers actuated via valve means from an accumulator 
charged by the pump; 
the valve means being operable to connect the or each second consumer to 
the accumulator or to the reservoir thus actuating the second consumers 
and also being operable in response to accumulator pressure levels below a 
predetermined charge level to restrict the flow of fluid to the or each 
first consumer to a level sufficient to ensure effective operation of the 
or each first consumer whilst generating a back pressure sufficient to 
ensure charging of the accumulator. 
By restricting the flow to the first consumer(s) when charging of the 
accumulator is required in the above manner unaffected operation of the 
first consumer(s) is ensured. 
Both the first and second consumers may be actuated via the valve means. 
The valve means may include a first valve having a valve member (such as a 
spool) which is displaceable both to connect the second consumer(s) to the 
accumulator or reservoir and also to restrict the flow of fluid to the 
first consumer(s). 
The valve member may be displaced by a solenoid which is activated by a 
control means which controls operation of the second consumer(s) and also 
by signals from an accumulator pressure level sensor. Alternatively the 
displacement of the valve member in response to the accumulator pressure 
level falling below the predetermined charge level could be achieved by 
the action of fluid pressure on the valve member. 
Where a spool type valve member is used in the first valve means the spool 
may be provided with one or more grooves or other formation through which 
the restricted flow to the first consumer(s) takes place. 
In an alternative construction the valve means may include a first valve 
having a valve member which is displaced both to connect the second 
consumer(s) to the accumulator or reservoir and also to control the rate 
of charging of the accumulator. 
The actuation system may include a separate charging valve means to 
restrict the flow of fluid to the or each first consumer at accumulator 
pressure levels below a predetermined charge level. 
The actuation system may also include a second valve means to limit the 
pressure level to which the accumulator can be charged. Conveniently this 
second valve means may comprise a charging valve and venting valve 
arrangement of the form 94 20983.0 the disclosure of which is hereby 
included in the present application.

Referring to FIG. 1, the clutch actuation system includes a powerpack 10 
which supplies pressurised fluid to a first consumer in the form of an 
open centre power steering valve 50 and a second consumer in the form of 
an actuator 12 for a and a second consumer in the form of an actuator 12 
for a clutch operating slave cylinder 11. Both consumers are supplied via 
a value means in the form of a solenoid operated fluid flow control valve 
12a. The slave cylinder 11 acts on a clutch actuating lever 13 which in 
turn operates a clutch release bearing 14. 
The powerpack 10 includes a reservoir 10a, an electrically driven pump 10b, 
an accumulator 10c and a non return valve 10d. 
Actuator 12 includes a piston 17 which divides the actuator into two 
chambers 18 and 19 which are connected with solenoid valve 12a and slave 
cylinder 11 respectively. Thus pressurisation of chamber 18 displaces 
piston 17 which expels fluid out of chamber 19 to operate slave cylinder 
11 and displace clutch operating lever 13 to disengage the associated 
clutch. 
Displacement of clutch operating lever 13 is measured by a sensor in the 
form of a rotary potentiometer 44 whose output is fed to an electrical 
control unit 36. Control unit 36 also receives other vehicle operating 
parameter inputs, designated S in FIG. 1, and issues commands to the 
solenoid 12b of valve 12a to connect the actuator 12 to accumulator 10c or 
reservoir 10a. 
Full constructional and operational details of the electronic control unit 
36 etc. can be found in the Applicants previously referred to European 
patent nos. and will not therefore be given here. 
Solenoid operated valve 12a comprises an outer portion 30 which is inserted 
into a bore 31 in a housing 15 and remains stationary therein. Outer 
portion 30 defines, in conjunction with bore 31, annular feed passages 35 
and 36 which are connected respectfully with the accumulator 10c and the 
actuator 12. Two further annular feed passages 51 and 52 are also defined 
in a similar manner, feed passage 51 being connected with pump 10b and 
passage 52 with steering valve 50. 
Within outer valve portion 30 is disposed an axially movable landed spool 
37 which, when the solenoid valve 12a is not actuated it is maintained in 
the position shown in FIG. 1 by return springs 38 and 39 respectively. 
Return spring 39 acts against a threaded nut 40 whose axial position 
within a threaded bore 41 controls the spring loading on spool 37 as 
described in the Applicants co pending application no. 9308539.7. 
When the spool 37 is in the FIG. 1 position, spool land 42 cuts off 
communication between annular feed passages 35 and 36 so that the chamber 
18 of actuator 12 is not pressurised by the powerpack 10. In this spool 
position feed passage 36 communicates with reservoir 10a via flow path X 
and return line 43. 
Spool 37 also includes an additional land 53 provided with an axial groove 
54 which extends part way along land 53. With the spool 37 in the FIG. 1 
position, annular feed passage 51 is in unrestricted communication with 
feed passage 52 via path Y over shoulder 55 in bore 30a within which spool 
37 slides. 
The actuation system is completed by a pressure level sensor 56 which 
provides electrical signals to control unit 36 indicative of the pressure 
level of the fluid in accumulator 10c. Typically if the pressure level in 
the accumulator falls below 20 bar this is taken as an indication by 
control unit 36 that charging of the accumulator is necessary and a 
pressure level of say 40 bars indicates a fully charged accumulator. 
The above described actuation system operates as follows. 
With the spool 37 in the FIG. 1 position, as previously indicated, actuator 
12 is not pressurised by accumulator 10c so that the clutch operated by 
the release bearing 14 is engaged. To disengage the clutch the solenoid 
12b of valve 12a is actuated to axially displace spool 37 to the right, as 
viewed in FIG. 1, so that land 42 opens up a communication between annular 
feed passages 35 and 36 and closes off the return path X to reservoir 10a 
thus connecting chamber 18 of actuator 12 with accumulator 10c so that 
piston 17 is displaced to the right, as viewed in FIG. 1, thus displacing 
fluid out of chamber 19 of actuator 12 into slave cylinder 11 to operate 
clutch release bearing 14 to disengage the clutch. 
It will be appreciated that the above axial movement of spool 37 results in 
the previously unrestricted flow path Y now taking place via the axial 
groove 54. The groove 54 is sized such that the volume flow rate available 
to steering valve 50 is still maintained at a sufficiently high level to 
ensure an unaffected operation of valve 50 whilst at the same time causing 
a build up of back pressure on the pump side of the valve 12a which is 
sufficient to charge the accumulator 10c. 
Should pressure sensor 56 indicate that charging of accumulator 10c is 
necessary (as a result of the pressure level having fallen below a 
predetermined charge level--typically 20 bars) when the clutch actuator 12 
is not being actuated control unit 36 issues a signal to solenoid 12b to 
displace spool 37 to the right thus bringing groove 54 into the flow path 
Y so that charging of the accumulator 10c can take place without any 
effect on the operation of steering valve 50 and without actuating slave 
cylinder 11. 
Thus the restricted flow to steering valve 50 via groove 54 is introduced 
into the steering circuit when spool 37 is moved by control unit 36 to 
operate actuator 12 or, if actuator 12 is not under operation, when 
pressure level sensor 56 indicates that charging of the accumulator is 
necessary. 
The present invention thus provides an actuating system in which the 
operation of the open centre steering valve 50 is not effected by the 
charging of the accumulator. 
With the actuating system described above there is nothing to control the 
level to which the accumulator 10c could be charged by pump 10b when the 
steering is being operated. This may result in the accumulator (which is 
preferably kept at a pressure level of 30-40 bars) being charged to 
pressure levels well above 100 bars as a result of back pressure 
generating on the pump side of steering valve 50 since pressure levels 
well above 100 bars can be generated in the steering circuit when the 
valve 50 is in, for example, the full lock position. 
If desired, the above problem of high accumulator charging pressures can be 
overcome by the use of a second valve means 60, shown in dotted detail in 
FIG. 1, in the line to the accumulator 10c. 
Conveniently, as shown in FIG. 2 the second valve means 60 may comprise a 
charging valve 114 and venting valve 117 arrangement of the form described 
in the previously referred to co-pending application Ser. No. 9420983.0. 
The charging valve 114 comprises a spool 120 with a waisted portion 121 
which controls communication between charging ports 122 and 123 depending 
on the axial position of the spool. One end 124 of spool 120 is acted upon 
by the charging pressure on the accumulator side of non-return valve 10d. 
The other end of spool 120 is formed as rod 125 which is operative to 
unseat a ball valve member 126 of venting valve 117 which is normally held 
against an associating venting seat 127 by a spring 128. A main spool 
control spring 129 also acts on spool 120 to bias the spool to the right 
as viewed in FIG. 2. 
As will be evident from the above, the accumulator pressure acting on end 
124 of spool 120 acts against the combined action of main spool control 
spring 129, light spring 128 and the charging pressure acting on venting 
valve member 126. The effective cross sectional areas of the end 124 of 
spool 120 and the area of valve member 126 exposed to the charging 
pressure are arranged to be substantially different (typically two to one 
in favour of the end 124 of the spool). Because of the high differential 
areas used, as soon as the accumulator pressure has risen sufficiently to 
open venting valve 117 the pressure surrounding ball valve member 126 
drops dramatically so that the force acting to the right on spool 120 also 
drops dramatically and the accumulator pressure acting on the end 124 of 
spool 120 ensures a rapid movement of the spool to the left to close off 
charging port 123. This provides a large force holding venting valve 
member 126 open so that the pressure on the pump side of non return valve 
10d is vented to the sump 10a via a line 30. This ensures a clear cut-off 
level at which the charging of accumulator 10c is cut-off by spool 120. 
Similarly it is necessary for the accumulator pressure to fall to a 
relatively low level compared with the level at which charging of the 
accumulator is cut-off by spool 120 before spring 129 displaces spool 120 
to open charging port 123 and recommence charging of the accumulator 10c. 
Thus the cut-off of charging and commencement of charging are clearly and 
efficiently controlled by charging valve 114 and venting valve 117 to 
provide clear and distinct cut-off and recharging pressure levels. 
The clutch actuation system of FIG. 3 is basically the same as that of FIG. 
1 with the exception that in FIG. 3 the accumulator 10c is charged via 
annular feed passages 51 and 52 (see path Y') and power steering valve 50 
is fed for convenience via charging valve 80 via permanently open feed 
passage 51. Components of FIG. 3 similar to those of FIG. 2 have been 
similarly numbered. 
When the spool 37 is in the FIG. 3 position, spool land 42 cuts off 
communication between annular feed passages 35 and 36 so that the chamber 
18 of actuator 12 is not pressurised by the powerpack 10. In this spool 
position feed passage 36 communicates with reservoir 10a via flow path X 
and return line 43. and annular feed passage 51 is in unrestricted 
communication with feed passage 52 via path Y' so that the charging rate 
of accumulator 10c is not restricted. 
Pressure level sensor 56 provides electrical signals to actuate, via 
control unit 36, charging valve 80 with a parallel coupled flow restrictor 
81. 
Typically if the pressure level in the accumulator falls below 20 bar 
sensor 56 closes charging valve 80 to divert flow to the steering valve 50 
via flow restriction 81. This causes a back pressure to build up on the 
pump side of valve 80 which ensures adequate charging of accumulator 10c 
whilst still ensuring effective operation of steering valve 50. 
The actuation system also includes a pressure sensor 90 which produces an 
output signal to control unit 36 when the pressure in the steering valve 
circuit has risen to 2 to 3 bar thus indicating that the steering valve 50 
is operative. Operating pressures of 80-100 bar are not uncommon in such 
steering valve circuits when the valve is in the full-lock condition. 
The actuation system of FIG. 3 operates as follows. 
With the spool 37 in the FIG. 3 position, as previously indicated, actuator 
12 is not pressurised by accumulator 10c so that the clutch operated by 
the release bearing 14 is engaged. To disengage the clutch the solenoid 
12b of valve 12a is actuated to axially displace spool 37 to the right, as 
viewed in FIG. 3, so that the land 42 opens up a communication between 
annular feed passages 35 and 36 and closes off the return path X to 
reservoir 10a thus connecting chamber 18 of actuator 12 with accumulator 
10c so that piston 17 is displaced to the right as viewed in FIG. 3, thus 
displacing fluid out of chamber 19 of actuator 12 into slave cylinder 11 
to operate clutch release bearing 14 to disengage the clutch. 
It will be appreciated that the above axial movement of spool 37 results in 
the previously unrestricted accumulator charging path Y' now taking place 
via the axial groove 54 in land 53. The groove 54 is sized such that the 
volume flow rate available to charge accumulator 10c ensures that 
sufficient flow is still available to steering valve 50 to ensure 
unaffected operation of valve 50. 
Should pressure sensor 56 indicate that charging of accumulator 10c is 
necessary (as a result of the pressure level having fallen below a 
predetermined charge level--typically 20 bar) control unit 36 issues a 
signal to charging valve 80 to switch flow through the restrictor 81 to 
build up a back pressure to ensure charging of the accumulator 10c can 
take place at a rate which will not effect the operation of steering valve 
50. 
When sensor 90 sends a signal to control unit 36 indicating operation of 
steering valve 50, control unit 36 issues a signal to the solenoid 12b of 
valve 12a to move spool 37 to the right sufficient to restricting the 
charging flow to accumulator 10c using groove 54 without actuating slave 
cylinder 11. Thus uneffected operation of steering valve 50 can take place 
during charging of accumulator 10c. With a more sophisticated control unit 
36 the spool 37 may not necessary be displaced on every occasion when the 
steering valve 50 is operating. For example, if the steering valve is 
making small steering connection either side of the straight ahead 
position, the control unit could be set up to permit unrestricted charging 
of the accumulator. 
Again as described in relation to FIG. 1, if desired, the problem of high 
accumulator charging pressures can be overcome by the use of a second 
valve means 60, shown in dotted detail in FIG. 3, in the line to the 
accumulator 10c. 
Conveniently, the second valve means 60 may comprise a charging valve 114 
and venting valve 117 arrangement similar to that described in relation to 
FIG. 2. 
Referring to FIG. 4 this shows an actuation system employing such a 
charging valve 114 and venting valve 117 arrangement the charging valve 
114 comprising a spool 120 with two waisted portions 121a and 121b as 
compared with the single waisted portion 121 in FIG. 2. Waisted portion 
121a controls communications between charging ports 122 and 123 depending 
on the axial position of the spool. Waisted portion 121b and an associated 
axially extending flow restricting groove 181a control flow through a 
steering port 181 which performs the function of resrictor 81 in the FIG. 
3 construction. 
One end 124 of spool 120 is acted upon by the charging pressure on the 
accumulator side of non-return valve 10d. The rod end 125 of spool 120 is 
operative to unseat ball valve member 126 of venting valve 117 which is 
normally held against an associating venting seat 127 by a spring 128. A 
main spool control spring 129 also acts on spool 120 to bias the spool to 
the left as viewed in FIG. 4. 
As will be evident from the above, the accumulator pressure acting on end 
124 of spool 120 acts against the combined action of main spool control 
spring 129, light spring 128 and the charging pressure acting on venting 
valve member 126. The effective cross sectional areas of the end 124 of 
spool 120 and the area of valve member 126 exposed to the charging 
pressure are arranged to be substantially different (typically two to one 
in favour of the end 124 of the spool). Because of the high differential 
areas used, as soon as the accumulator pressure has risen sufficiently to 
open venting valve 117 the pressure surrounding ball valve member 126 
drops dramatically so that the force acting to the left on spool 120 also 
drop dramatically and the accumulator pressure acting on the end 124 of 
spool 120 ensures a rapid movement of the spool to the right to close off 
charging port 123. This provides a large force holding venting valve 
member 126 open so that the pressure on the pump side of non return valve 
10d is vented to the sump 10a via a line 30. This ensures a clear cut-off 
level at which the charging of accumulator 10c is cut-off by spool 120. 
Similarly it is necessary for the accumulator pressure to fall to a 
relatively low level compared with the level at which charging of the 
accumulator is cut off by spool 120 before spring 129 displaces spool 120 
to open charging port 123 and recommence charging of the accumulator 10c. 
Thus the cut-off of charging and commencement of charging are clearly and 
efficiently controlled by charging valve 114 and venting valve 117 to 
provide clear and distinct cut-off and recharging pressure levels. 
As will be apparent from the above, flow restricting groove 181a 
co-operates with steering port 181 to restrict the flow of fluid to 
steering valve 50 when charging port 123 is open and accumulator 10c is 
being charged by pump 10b. This restriction of the steering circuit is 
removed when spool 120 is moved to the right to close off port 123. 
Thus in the FIG. 4 construction the extra waisted portion 121b, on spool 
120 with its co-operating steering port 181 and groove 181a replace the 
function of charging valve 80, restrictor 81 and pressure sensor 56 in the 
FIG. 3 construction. 
FIG. 5 shows part of a modified form of the system shown in FIG. 4 in which 
pressure sensor 90 which operates the solenoid valve 12a is replaced by a 
pressure tapping 200 from the steering circuit between steering valve 50 
and charging/venting valve 114/117. Tapping 200 is connected with an 
auxiliary piston 201 which acts on the end of the spool 37 of valve 12a to 
displace spool 37 when the pressure level in tapping 200 indicates that 
the steering valve 50 is being operated thus restricting the potential 
charging rate of accumulator 10c. 
The solenoid actuation of spool 37 to control the pressure supplied to 
actuator 12 is still retained down the centre of piston 201 as indicated 
diagrammatically at 12b in FIG. 5.