GB2373553A

GB2373553A - Depressurisation of transmission accumulator on shut-down

Info

Publication number: GB2373553A
Application number: GB0107041A
Authority: GB
Inventors: Ole Jonny Waerp; Morten Gunnerud; Fred Hemmingsen; Karl Frode Ring; Torgeir Sundet
Original assignee: LuK Lamellen und Kupplungsbau GmbH
Current assignee: LuK Lamellen und Kupplungsbau GmbH
Priority date: 2001-03-21
Filing date: 2001-03-21
Publication date: 2002-09-25
Anticipated expiration: 2021-03-21
Also published as: GB0107041D0; FR2822513A1; ITMI20020592A0; FR2822513B1; ITMI20020592A1; GB2373553B

Abstract

An automated transmission system has a hydraulic circuit including an accumulator 124, a control valve 120, actuators 22, 114 and 115 to control a clutch 14 and/or gear engagement mechanism 110-113 and an electric pump 123 for recharging the accumulator 124. Electronic controller 36 controls valve 120 actuation to supply pressurised fluid to the actuators according to system gear change requirements. On powering down of the system following keying-off, the actuators are connected through control valve 120 to drain 12, powering of the pump 123 is inhibited and the control valve 120 is cycled to supply fluid from the accumulator to one or more actuators and from there to drain to reduce pressure in the accumulator 124 to below a predetermined value. Safety checks are made before repressurisation.

Description

AUTOMATED TRANSMISSION SYSTEMS The present invention relates to automated transmission systems and in particular to fully or semi automated transmission systems or to manual transmission systems with automatic clutch control, in which actuation of the clutch and/or gear selector mechanisms is under control of an electronically controlled fluid pressure actuator.

Automated transmission systems of this type, for example as described in W097/05410 and W097/40300, to the disclosure of which explicit reference is made and whose content is expressly incorporated in the disclosure content of the present application, include a fluid pressure accumulator with pump means to charge the accumulator. Fluid pressure actuators within the system are normally connected to drain when the transmission system is keyed-off. However, pressure is normally retained in the accumulator for actuation of the clutch and/or gear shift actuators, when the system is next keyed-on.

The retention of fluid pressure in the system when the system is keyedoff may present hazards if, for example the system is dismantled or the electronic control circuits tampered with or fail, causing actuators to operate unexpectedly. In particular, when the vehicle is parked on a slope in gear, with no parking brake applied, the inadvertent release of the clutch in this manner would permit the vehicle to roll down the slope.

In order to avoid this possibility it is proposed that at key-off when the vehicle is left in gear, the pressure in the accumulator should be reduced to a level which is insufficient to disengage the clutch According to one aspect of the present invention, an automated transmission system comprises a fluid pressure circuit including a fluid pressure accumulator, a control valve and a fluid pressure actuator to control engagement of a clutch, an electronic control means to control actuation of the control valve, to supply fluid under pressure to the actuator in accordance with gear change requirements of the transmission system and an electric pump for recharging the accumulator, the actuator on powering down of the system following keying-off being connected to drain; the control means on keying-off of the system when the system is

left in gear and before powering down of the system inhibiting energisation of the pump and causing cycling of the control valve, to supply fluid under pressure from the accumulator to the clutch actuator and from there to drain, in order to reduce pressure in the accumulator to below a predetermined value.

In the manner described above, recycling of the control valve while the pump is inhibited will cause the pressure in the accumulator to be reduced below the predetermined value at which the pressure is insufficient to cause disengagement of the clutch.

According to a preferred embodiment of the invention pressure in the accumulator is reduced by repeatedly moving the clutch between its fully engaged position and a position at which the clutch is partially disengaged but is still capable of transmitting torque in excess of the engine braking torque.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a semi-automated transmission system in accordance with the present invention; Figure 2 illustrates a hydraulic control circuit for an automated transmission system in accordance with the present invention showing a main control valve in a first position; Figure 3 illustrates part of the hydraulic control circuit illustrated in Fig. 2 showing the main control valve in a second position; Figure 4 illustrates part of the hydraulic circuit illustrated in Fig. 2 showing the main control valve in a third position; and Figure 5 shows a flow diagram of a transmission system in accordance with the present invention.

Figure 1 of the accompanying drawings shows an engine 10 with a starter and associated starter circuit 1 osa which is coupled through the main drive

friction clutch 14 to a multi-speed synchromeshed lay shaft-type gearbox 12, via a gearbox input shaft 15. Fuel is supplied to the engine by a throttle 16 which includes a throttle valve 18, operated by accelerator pedal 19. The invention is equally applicable to electronic or mechanical fuel injection petrol or diesel engine.

The clutch 14 is actuated by a release fork 20 which is operated by a hydraulic slave cylinder 22, under the control of a clutch actuator control means 38.

A gear selector lever 24 operates in a gate 50 having two limbs 51 and 52 joined by a cross track 53 extending between the end of limb 52 and intermediate of the ends of limb 51. The gate 50 defines five positions; "R"at the end of limb 52 ;"N"intermediate of the ends of the cross track 53 ;"S"at the junction of limb 51 with the cross track 53; and"+"and "-"at the extremities of limb 51. In limb 51 the lever 24 is biased to the central"S"position. The"N"position of the selector lever 24 corresponds to neutral ; "R"corresponds to selection of reverse gear ;"S" corresponds to selection of a forward drive mode; momentary movement of the lever to the"+"position provides a command to cause the gearbox to shift up one gear ratio; and momentary movement of the gear lever 24 to the"-"position provides a command to cause the gearbox to shift down one gear ratio.

The positions of the lever 24 are sensed by a series of sensors, for example micro switches or optical sensors, positioned around the gate 50.

Signals from the sensors are fed to an electronic control unit 36. An output from the control unit 36 controls a gear engaging mechanism 25, which engages the gear ratios of the gearbox 12, in accordance with movement of the selector lever 24 by the vehicle operator. The gear engaging mechanism 25 may, for example, comprise hydraulic rams and solenoid control valves to move selector members to engage and disengage the various gear ratios, for example as disclosed in patent specification WO97/05410 the disclosure of which is incorporated herein by reference thereto.

In addition to signals from the gear selector lever 24, the control unit 36 receives signals from:

sensor 19a indicative of the degree of depression of the accelerator pedal 19 ; sensor 30 indicative of the degree of opening of the throttle control valve 18; sensor 26 indicative of the engine speed; sensor 42 indicative of the speed of the clutch driven plate ; sensor 34 indicative of the clutch slave cylinder position; and sensor 32 indicative of the gear ratio selected.

The control unit 36 utilises the signals from these sensors to control actuation of the clutch 14 during take-up from rest and gear changes, for example as described in patent specifications EP0038113, EP0043660, EP0059035, EPO 10 1220 and WO92/13208 to the disclosure of which explicit reference is made and whose content is expressly incorporated in the disclosure content of the present application.

In addition to the above mentioned sensors, control unit 36 also receives signals from a vehicle speed sensor 52, ignition switch 54 and brake switch 56 associated with the main braking system, for example the footbrake 58 of the vehicle.

A buzzer 50 is connected to the control unit 36 to warn/indicate to the vehicle operator as certain operating conditions occur. In addition or in place of the buzzer 50 a flashing warning light or other indicating means may be used. A gear indicator 60 is also provided to indicate the gear ratio selected.

As illustrated in Figs. 2 to 4, a hydraulic circuit for control of the clutch 14 and gear engagement mechanism 25 of the transmission system disclosed above comprises a main solenoid operated flow control valve 120 for selectively connecting clutch slave cylinder 22 and/or hydraulic gear engagement actuators 114 and 115, to a hydraulic fluid pressure accumulator 124 or to a reservoir 126. Accumulator 124 is charged to a predetermined pressure and is maintained above a minimum operating pressure, when the system is keyed on by means of an electrically driven pump 123, via a non return valve 124a. A pressure transducer 160 monitors the pressure in the accumulator 124 and the pump 123 is

controlled by the electronic control unit 36 to maintain pressure in the accumulator 124 above the predetermined minimum operating pressure.

The main control valve 120 has a spool 150 which is displaced against a spring 151 by means of a solenoid 120a. The spool 150 is displaceable by solenoid 120a under control of control unit 36, to one of three positions.

In a first position of main control valve 120 as illustrated in Fig. 2, the working chamber of clutch slave cylinder 22 is vented to reservoir 126 around land 155 of spool 150 via flow path Z and supply line 165 is connected to the reservoir 126 between lands 157 and 158.

In a second position of the control valve 120 the spool 150 is displaced to the right as illustrated in Fig. 3. The working chamber of clutch slave cylinder 22 remains vented to reservoir 126 via flow path Z. Line 165 is however isolated from the reservoir 126 by land 158 and is connected to the pressure accumulator 124 between lands 157 and 158.

In a third position of the control valve 120 the spool 150 is further displaced to the right, as illustrated in Fig. 3. Flow path Z is closed and the working chamber of clutch slave cylinder 22 is connected to the pressure accumulator 124 between lands 156 and 157. Line 165 remains connected to the accumulator 124.

Line 165 connects the gear engaging mechanism 25 to the hydraulic fluid pressure accumulator 124 or to reservoir 126, depending on the position of the main control valve 120. The gear engaging mechanism 25 comprises a selector member 110 which is engagable with three shift rails 111,112 and 113 which are movable axially to engage gear ratios of the gearbox 15. Shift rail 111 would typically engage first and second gear ratios; shift rail 112 engage third and fourth gear ratios; and shift rail 113 engage fifth gear ratio and reverse'R'.

The selector member 110 is movable in a first direction X by means of a first fluid pressure operated actuator 114 to align the selector member 110 with one of the shift rails 111, 112 or 113 and thereby select the pair of gears associated with that selector rail. The selector member 110

may then be moved in a second direction Y by means of a second fluid pressure operated actuator 115, to move the shift rail 111, 112 or 113 axially in either direction to engage one of the gear ratios associated therewith.

The actuators 114 and 115 each comprise a double acting ram with an operating rod 114a, 115a respectively, which is operatively connected with the selector member 110. The operating rod 114a extends from one side of a piston 116 of actuator 114, so that the working surface on the rod end of the piston 116 is smaller than that on the opposite head end.

Similarly for actuator 115, an operating rod 115a extends from one side of a piston 117, the operating surface on the rod end of piston 117 being smaller than that of the opposite head end. In view of the differential areas on the sides of the pistons 116 and 117, if both sides are connected to the accumulator 124, the pistons 116 and 117 will be displaced along the actuators 114 and 115 respectively to extend the associated operating rods 114a and 115a. If however the head end side of the pistons 116 and 117 are connected to the reservoir 126, while the rod end sides of pistons 116 and 117 are connected to the accumulator 124, the pressure differential across pistons 116 and 117 will cause them to be displaced along the actuators of 114 and 115 respectively to contract the associated operating rods 114a and 11 5a.

The supply of hydraulic fluid to the rod end of pistons 116 and 117 is controlled directly by the main control valve 120. The supply of hydraulic fluid to the head end of pistons 116 and 117 is controlled from the main control valve 120 by two further solenoid operated proportional flow control valves 121 and 122 respectively. The valves 121 and 122 connect the head end side of pistons 116 and 117 to the main control valve 120 or to the reservoir 126.

The proportional flow control valves 120,121 and 122 are controlled by the electronic control unit 36 to apply appropriate pressures to opposite sides of pistons 116 and 117 to control movement of the pistons 116 and 117 and the associated operating rods 114a and 115a to select and engage the required gear ratio as disclosed in WO97/0541 0 or W097/40300 to the disclosure of which explicit reference is made and

whose content is expressly incorporated in the disclosure content of the present application.

Potentiometers 127 and 128 are connected to the operating rods 114a and 115a respectively, to provide a signal indicative of the position of the associated operating rods. Signals from potentiometers 127 and 128 are fed to the control unit 36 to provide an indication of the position of the operating rods 114a and 115a, for each of the gear ratios of the gearbox and also to indicate the position of the operating rod 11 5a when the selector member 110 is in a neutral plane. The transmission system may thus be calibrated so that predetermined position signals from potentiometers 127 and 128 correspond to engagement of each of the gear ratios of gearbox 15.

The measurements from the potentiometers 127 and 128 may then be used by a closed loop control system, to control valves 120,121 and 122 to move the operating rods 114a and 115a to the predetermined positions to engage the desired gear ratio.

With the main control valve 120 in the position illustrated in Fig. 1, which represents the de-energised condition of the solenoid 1 20a, both the clutch slave cylinder 22 and the gear engaging mechanism 25 via line 165 will be connected to the reservoir 126. The clutch slave cylinder 22 and actuators 114 and 115 will thereby be depressurised.

Upon movement of the main control valve 120 to its second position the clutch actuator remains depressurised but the gear engagement mechanism 25 is pressurised. Appropriate control of the solenoids 121 a and 122a by control unit 36 as disclosed in W097/05410 or W097/40300 may then cause actuators 114 and 115 to select and engage an appropriate gear ratio.

Movement of the main control valve 120 to its third position connects the working chamber of clutch slave cylinder 22 to accumulator 124 thereby disengaging the clutch 14.

The clutch slave cylinder 22 and gear engagement mechanism 25 may thus be controlled by appropriate manipulation of solenoids 120a, 121 a

and 122a, by the control unit 36, to effect gear changes at take-up from rest or while the vehicle is on the move.

When the transmission system is keyed-off solenoids 120a, 121 a and 1 22a will eventually be de-energised so that the clutch slave cylinder 22 and gear engagement mechanism actuators 114 and 115 are depressurised. Pressure in accumulator 124 which has been maintained above a predetermined minimum working pressure while the system has been keyed-on will, however, be maintained above its minimum working pressure.

In accordance with the invention and as illustrated in Fig. 5, if at key-off and before the system is powered down, sensor 32 indicates that a gear ratio is engaged, the pump 123 is disabled while the solenoid 120a is energised to cycle the control valve 120 between its first and third positions. In this manner the working chamber of the clutch slave cylinder 22 will be repeatedly connected to the accumulator 124 and then to reservoir 126, moving the clutch 14 between its fully engaged position and a partially released position in which the clutch is still capable of transmitting torque in excess of the engine braking torque. Hydraulic fluid is thereby pumped from the accumulator 124 via slave cylinder 22 to reservoir 126. The energising current for solenoid 120a may be applied as a sinuous or square wave function This is continued until the pressure in the accumulator 124 falls below the predetermined value at which the pressure in accumulator 124 is not sufficient to operate the clutch slave cylinder 22 to disengage the clutch. The system is then powered down.

If at key-off sensor 32 indicated that no gear is engaged, then after a suitable time-out period, the system may be powered down without discharging accumulator pressure.

Upon subsequent keying-on of the system, after appropriate safety checks have been made, the pump 123 may be energised to bring the accumulator 124 up to the minimum working pressure.

Various modifications may be made without departing from the invention.

For example, while the invention has been described with reference to a semi-automated transmission system in which both the clutch and gear engagement mechanism are hydraulically actuated, the invention may also be used with fully automated transmission systems or with manual transmission systems having automated clutch actuation. Furthermore, such systems need have only the clutch actuated by hydraulic means.

Claims

CLAIMS.

1. An automated transmission system comprising a fluid pressure circuit including a fluid pressure accumulator, a control valve and a fluid pressure actuator to control engagement of a clutch, an electronic control means to control actuation of the control valve, to supply fluid under pressure to the actuator in accordance with gear change requirements of the transmission system and an electric pump for recharging the accumulator, the actuator on powering down of the system following keying-off being connected to drain; the control means on keying-off of the system when the system is left in gear and before powering down inhibiting energisation of the pump and causing cycling of the control valve, to supply fluid under pressure from the accumulator to the clutch actuator and from there to drain, in order to reduce pressure in the accumulator to below a predetermined value.

2. An automated transmission system according to claim 1 in which at keying-off of the system, the control means is adapted to cause the clutch actuator to repeatedly move the clutch between a fully engaged position and a partially disengaged position, the clutch in the partially disengaged position still being capable of transmitting torque in excess of the engine braking torque, until the pressure in the accumulator falls below a predetermined minimum value.

3. An automated transmission system according to claim 1 or 2 in which at subsequent keying-on of the system, the control unit is adapted to carry out safety checks on the system and only after such checks are successfully completed, energise the pump to charge the accumulator to a predetermined working pressure.

4. An automated transmission system substantially as disclosed herein with reference to, and as shown in, figures 1 to 5 of the accompanying drawings.