WO1996010492A2

WO1996010492A2 - Improvements in transmission systems for vehicles

Info

Publication number: WO1996010492A2
Application number: PCT/GB1995/002346
Authority: WO
Inventors: Simon David Stevens
Original assignee: Lucas Industries Public Limited Company
Priority date: 1994-10-04
Filing date: 1995-10-03
Publication date: 1996-04-11
Also published as: WO1996010492A3; GB9419953D0

Abstract

A transmission system for a two-pedal vehicle incorporating a gearbox (5) provided with a manual gear lever, a clutch (7) having an operating lever (18), and a clutch management system (15) comprising an electronically controlled hydraulic actuator (17) mounted on the gearbox and acting on the operating lever, is disclosed. Means are incorporated for utilising information from the clutch management system to control the engine (8) during gearshifts, thereby removing the need for the driver to release the accelerator pedal for a gear change to be accomplished.

Description

IMPROVEMENTS IN TRANSMISSION SYSTEMS FOR VEHICLES

This invention relates to improvements in transmission systems for vehicles.

In known transmission systems for vehicles power from an engine is transmitted to a driven axle through a gearbox of a manual or automatic type in order to change the drive ratio between the engine and the axle to achieve a desired road speed for the vehicle. This is known as "gear change" achieved by a "gear shift". Normally a manual gearbox is operated by a gear lever in conjunction with the operation of a pedal-operated clutch which disconnects the drive between the gearbox and the axle to enable a gear shift to take place and with the accelerator pedal released, at least when changing up, so that the engine revolutions match the road speed. In a transmission system including an automatic gearbox, no pedal-operated clutch is provided and the gearbox includes an arrangement of centrifugal clutches which are operable to cause the gearbox to change gear automatically, up or down, in response to a given engine torque. Such gearboxes include a manual selector lever which enables the gearbox to select an initial park (P), drive (D), or reverse (R) mode, and at least two lower gear forward drive positions. Each mode can be selected manually, and the drive modes can be selected at will, for example to prevent the gearbox from changing between one gear and another for a given road condition.

A further known transmission system for a two-pedal vehicle incorporates a clutch management system (CMS) which replaces the clutch pedal and its mechanical connection to the clutch with an electronically controlled, hydraulic actuator. This combines the benefits of two-pedal driving with fuel economy and driver control of a manual transmission. The car is driven exactly as a normal manual but the clutch operation is carried out automatically.

The clutch management system consists of an hydraulic actuator mounted on the gearbox and acting on the clutch operating lever, a pump and valve block, an electronic control unit and various sensors. The standard clutch is retained, and the gear box is provided with a standard gear lever. The sensor measures engine and clutch speeds, gear lever position and force, and clutch position. The clutch position is a controlled closed loop using the other inputs to determine the target position. A pressure sensor controls the hydraulic pump and accumulator to maintain the correct operating pressure. A switch on the car bonnet is used to disable clutch engagement when the accelerator is operated from the engine compartment, during servicing for instance. If the car had been left in gear then it would otherwise have moved unexpectedly without this switch.

The system is tuned to match the best clutch operation by a driver. It allows pull away from rest in first and second gears. A winter mode may be selected to allow the use of higher gears and reduce the possibility of wheelspin. The system is of particular benefit in stop-start traffic conditions when the car may be left in second gear and inched forwards using only the accelerator. Engine braking is available with the additional feature of limiting engine speed by slipping the clutch if too low a gear is selected. A small and closely controlled amount of clutch slip is introduced under light load conditions. This uses the clutch as a friction damper in the drivetrain reducing shunt for improved smoothness. This slip is not apparent to the driver. The automated clutch is able to move at a higher speed than when driver actuated. Hence gear shift times may be reduced with performance benefits. It is claimed that the clutch plate life is unaffected by the fitment of clutch management system since its use is always accurately controlled.

A Controlled-Area Network (CAN) interface may be developed in the form of an additional circuit board in the control unit. The clutch management is 'programmed to accept a disengage clutch request from the master controller. Gear lever position, clutch position, and gear shift in progress signals are transmitted.

In such a system for a two-pedal vehicle, gear change can only effected after the accelerator pedal has been released sufficiently to enable the automatic clutch to open. If therefore follows that a gear change cannot be achieved if the vehicle is accelerating.

We are aware of EP-A-361 943 which discloses an automatic transmission system for a vehicle. The system is electronically controlled and incorporates a gear transmission and a friction clutch. A target gear position is determined in accordance with stored data. Before a gear shift is automatically executed, detector data is used to determined whether the vehicle is accelerating. The signal for shifting the transmission to the target gear position is delivered only if the vehicle is not accelerating. Thus, when the driver presses hard on the accelerator pedal to accelerate the vehicle, the normal series of operations to change gear, up, are not carried out. This automatic selection is deliberately inhibited when the vehicle is accelerating to prevent gear change from taking place. The operation for shifting up can be carried out only after completion of the acceleration phase, controlled by the driver releasing the accelerator.

According to one aspect of our invention in a transmission system for an engine powered two-pedal vehicle incorporating a gearbox provided with a manual gear lever, a clutch having an operating lever, and a clutch management system (CMS) comprising an electronically controlled hydraulic actuator acting on the operating lever, control means are incorporated for utilising information from the clutch management system to control the engine during gearshifts, thereby removing the need for the driver to release the accelerator pedal for a gear change to be accomplished.

The hydraulic actuator may be mounted on the gear box.

Such control means, which comprises a powershift, has the advantage that, in order to change gear, it is only necessary to operate the gear lever normally to complete a gearshift, irrespective of the fcrce being applied to the accelerator pedal at that particular time. Furthermore, no additional hardware has to be provided for carrying out the powershift function.

When the driver begins a gear shift, the gear lever is moved in the required direction. This is detected by the clutch management system using force switches in the gear lever. It sends a signal to a master controller to indicate that a gear shift is in progress. The master controller then sends a "lowest wins" demand to an Electronic Programmed Injection Control (EPIC) to reduce the engine power. The clutch management system interprets this as the driver lifting his foot off the accelerator and disengages the clutch allowing the driver to move the gear lever to the next position. When the gear selection is complete, the clutch management system cancels its shift in progress signal and the master controller returns control to the driver by cancelling its EPIC demand. The clutch is then re-engaged. The master controller's demand to EPIC is the result of logic to ramp the engine power down to idle, wait for the shift to complete, and then ramp the power back to the driver's demand. The driver may notice a momentary resistance as he moves the gear lever. This is due to the delay between the operation of a force switches and the releasing of the clutch. It is not possible to disengage the gears under power due to the forces on the gears themselves.

The powershift feature means that the clutch management system is put to full use in saving driver effort. It can be difficult to synchronise lifting off the accelerator and moving the gear lever to achieve a smooth gear shift with the standard clutch management. This is avoided with powershift. It does have the disadvantage of preventing double declutching but the driver can still carry out a normal gear shift by lifting off as normal.

When a vehicle is provided with an anti-lock hydraulic braking system (ABS) which is adapted to control automatically the behaviour of a braked wheel on a surface having a relatively low co-efficient of friction, ABS is at its most effective on such a low friction surface, when the clutch is disengaged. This disconnects the inertia and torque output of the engine from the powertrain allowing the wheels to respond more quickly to the brakes and the road surface.

According to another aspect of our invention, therefore, in an anti-lock hydraulic braking system (ABS) for a vehicle incorporating means for controlling automatically the behaviour of a braked wheel, the braking system is integrated into a vehicle provided with a manual gear lever, a clutch having an operating lever, and a clutch management system comprising an electronically controlled hydraulic actuator acting on the operating lever, the clutch management system is adapted to receive signals from the ABS indicating that ABS is active, such signals, in turn, cause the clutch to be disengaged.

This enables ABS to become most effective since the clutch is disengaged to disconnect the inertia and torque output of the engine from the powertrain.

The clutch management system treats the signal from ABS as a normal gearchange request, using its standard software to make the disengagement and subsequent re-engagement as refined as possible.

Specifically the signal from ABS is received by a master controller of the clutch management system and operates the clutch as described above. Such a system may be integrated into a system having a power shift feature in accordance with the first aspect of this invention.

Conveniently the ABS active and disengage requests are sent over the CAN, thereby avoiding the need for additional hardware. Two embodiments of our invention are illustrated in the accompanying drawings in which: -

Figure 1 is a layout of a two-pedal vehicle incorporating a power shift system and provided with a master controller Electronic Programmed Injection Control (EPIC), and a Clutch Management System (CMS) and a Master Controller;

Figure 2 is a flow chart for the power shift system of Figure 1;

Figure 3 is a layout of an ABS de-clutch system incorporating a Master Controller, and a Clutch Management System (CMS);

Figure 4 is a flow chart for the ABS de-clutch system of Figure 3; and

Figure 5 is a flow chart showing the step of smoothing the transitions during clutch disengagement and re-engagement for the systems of Figures 1 and 3.

In the system illustrated in the layout of Figure 1, front wheels 1, 2 of two-pedal controlled vehicle are driven by a front axle comprising a pair of stub axles 3, 4 controlled by a gear box 5, having a manual gear-change lever 6. A clutch 7 is positioned between and transmits drive between a transverse engine 8 and the gearbox 5. The front wheels 1, 2 are steered from a steering wheel 9 through a steering mechanism 10. A first foot pedal 11 operates the accelerator, and a second foot pedal 12 operates the braking system through an hydraulic master cylinder 13.

Operation of the engine 8 in response the pedal 11 is controlled by an EPIC 14. A CMS 15 controls operation of the clutch 7 by means of an hydraulic actuator 17 mounted on the gearbox 5 and acting on an operating lever 18 for the clutch 7.

Signals to and from the EPIC 14 and the CMS 15 are integrated by an electronic master controller 16 defining a power shift.

An hydraulic pump 19, an accumulator 20, and valve block 21 pr vide pressure for operating the actuator 17.

Various sensors are incorporated to measure the speeds of the engine 8 and the clutch 7, the position of, and the force acting on, the clutch lever 18, and the position of the clutch 7.

The position of the clutch 7 is a controlled closed loop using the other inputs to determine the target position.

A pressure sensor controls the pressure of the hydraulic pump 19 and accumulator 20 to maintain the correct operating pressure.

Forces switches are provided in the gear lever 6 to send signals to the master controller 16 to indicate that a gear shift is in progress. In operation, for normal gear change, the driver lifts his foot from the accelerator pedal and selects the appropriate gear. The CMS 15 opens the clutch 7 to enable the gear change to take place.

On the other hand should the driver wish to change gear with the engine accelerating, for example to increase speed to overtake another vehicle, then he simply operates the gear lever 6 to select the appropriate lower gear. The power shift comes into effect in that the force switches send signals to the CMS 15 in turn sending a corresponding signal to the master controller 16. The master controller 16 recognises the signal and, as a result, sends a "lowest wins" signal to the EPIC 14 in turn to close the accelerator to prevent the engine from over-revving. The CMS 15 interprets the signals as the force on the accelerator pedal 11 being reduced, and opens the clutch 7.

After gear change has been accomplished, the forces on the force switches reduce, the CMS 15 cancels its signal and the clutch re-engages or closes, with the master controller 16 cancelling its signal to the engine 8. Thus power is automatically restored to the engine 3 by the EPIC to provide acceleration.

Th-e driver may notice a momentary resistance as he moves the gear lever 6. This is due to the delay between the operation of the force switches and releasing the clutch 7.

The operational steps of the master controller 16, the EPIC 14, and the CMS 15 during power shift are explained in the flow chart illustrated in Figure 2 of the accompanying drawings. Specifically the "lowest wins" throttle demand to permit the gear change, followed, after the change has been accomplished, by the restoration of engine power when effective throttle demand equals the driver's throttle demand, is explained.

In the system illustrated in the layout of Figure 3, front wheels 41,42 of a two-pedal controlled vehicle are driven by a front axle comprising a pair of stub axles 43,44 controlled by a gearbox 45 which may be controlled by a manually-operable gear lever. A clutch 47 is positioned between and transmits drive between a transverse engine 48 and the gear box 45. The front wheels 41,42 are steered from a steering wheel 49 through a steering mechanism 50.

A first foot pedal 51 operates the accelerator, and a second foot pedal 52 operates an hydraulic master cylinder 53, in turn to initiate an hydraulic anti-lock braking system (ABS) 54.

A CMS 55 controls operation of the clutch 47 by means of an hydraulic actuator 57 mounted on the gearbox 45 and acting on an operating lever 58 for the clutch 47.

Signals from the CMS 55 and ABS 54 are integrated by an electronic master controller 56.

An hydraulic pump 59, an accelerator 60 and a valve block 61, provide pressure for operating the clutch 47 under the control of the CMS 55, and for re-applying the brakes during ABS.

When the brakes are applied normally by operation of the master cylinder 53 the ABS 54 is inoperative. However, should the vehicle then travel onto a surface having a significantly lower co-efficient of friction, signals indicative of an incipient wheel skid condition are sent to the ABS 54 from wheel speed sensors. In turn signals from the ABS 54 are passed to the master controller 56 which recognises that the ABS 54 is active and, as a result, initiates operation of the CMS 55 to open the clutch 47 thereby disconnecting the drive to the wheels 41,42.

The ABS 54 then becomes most effective in relieving the braking pressure and correcting the behaviour of the braked wheels, not only controlling the brakes on the wheels 41,42 but also braked rear wheels 61,62 of the vehicle, by modulating the supply of hydraulic fluid to the brake on an unstable wheel.

The CMS 55 treats the signal from ABS 54 as a normal gear change request, using its standard software to make the disengagement and subsequent re-engagement as smooth as possible.

A flow chart explaining the operational steps of the master controller 56 and the CMS 55 is illustrated in Figure 4 of the accompanying drawings.

In the ABS system described above with reference to Figures 3 and 4 the CMS 55 may be provided only to achieve clutch release under ABS control. However it may be incorporated in:-

1. A vehicle of the two-pedal control type in which the standard clutch pedal mechanism is omitted and gear change is achieved manually by operation of the gear lever, after foot pressure has been relieved from the accelerator pedal; or 2. A vehicle of the two-pedal control type having a power shift feature as described above in the first aspect of the invention and with reference to Figures 1 and 2 of the accompanying drawings.

The braking systems illustrated in the layout of Figures 1 and 2, and Figures 3 and 4, may be modified to smooth the transitions during clutch disengagement and re-engagement. This means that the momentary resistance notices by the driver as he moves the gear lever will become less noticeably. This modification is achieved by suitable ramping in and out of the throttle position, and hence power, during gear changing.

This modification is illustrated in the flow chart of Figure 5 and from which it will be noted that after shift has been initiated it is "ramped down to zero", and the shift is completed followed by "ramping up to driver" .

This has the effect that:

Gearchange in process equals the flag set by CMS gear lever force sensor.

Gearshift complete equals new gear fully engaged, gear change in progress flag cleared.

Claims

1. A transmission system for an engine powered two-pedal vehicle incorporating a gearbox (5) provided with a manual gear lever (6), a clutch (7) having an operating lever (18), and a clutch management system (CMS) (15) comprising an electronically controlled hydraulic actuator (17) acting on the operating lever, characterised in that control means are incorporated for utilising information from the clutch management system to control the engine (8) during gearshifts, thereby removing the need for the driver to release the accelerator pedal (11) for a gear change to be accomplished.

2. A transmission system according to claim 1, characterised in that the hydraulic actuator (17) is mounted on the gearbox (5).

3. A transmission system according to claim 1 or claim 2, characterised in that the control means comprises a powershift (16) which is adapted to integrate signals to and from the CMS (15) and an Electronic Programmed Injection Control (EPIC) (14) .

4. A transmission system according to any preceding claim, characterised in that force switches are provided to the gear lever (6), and, upon manual operation of the gear lever, the CMS (15) is adapted to detect signals in the force switches and send such signals to a master controller defining the powershift (16), in turn to send a "lowest wins" signal to the EPIC (14) to reduce engine power, the CMS (15) in response to such signals acting to disengage the clutch (7) to allow the gear lever (6) to move to the next position.

5. A transmission system according to claim 4, characterised in that when gear selection is complete the CMS (15) is adapted to cancel its "shift in process" signal and the master controller (16) then returns control to the driver by cancelling its EPIC demand.

6. A transmission system according to claim 4, characterised in that the demand from the master controller (16) to the EPIC (14) comprises the result of logic to ramp the power of the engine (8) back to the demand of the driver, and wait for the shift to complete, and then ramp the power back to driver's demand.

7. An anti-lock hydraulic braking system (ABS) for a vehicle incorporating ABS means (54) for controlling automatically the behaviour of a braked wheel, the braking system is integrated into a vehicle provided with a manual gear lever, a clutch (47) having an operating lever (58), and a clutch management system (CMS) (55) comprising an electronically controlled hydraulic actuator (57) acting on the operating lever, characterised in that the clutch management system (55) is adapted to receive signals from the ABS means (54) indicating that ABS is active, such signals in turn, causing the clutch (47) to be disengaged.

8. An anti-lock hydraulic braking system according to claim 7, characterised in that the CMS (55) is adapted to treat the signal from ABS as a normal gearchange request.

9. An anti-lock hydraulic braking system according to claims 8 or 9, characterised in that a master controller (56) of the CMS(55) is adapted to receive the signal from the ABS means (54) to operate the clutch.

10. An anti-lock hydraulic braking system according to claim 9, characterised in that active and disengage requests from the ABS means (54) are sent over an existing Controlled-Area Network (CAN) interface in the master controller (56).

11. A engine powered vehicle of the two-pedal type incorporating a transmission system according to any of claims 1-6, and an anti-lock hydraulic braking system (ABS) according to any of claims 7-10, characterised in that the ABS means (54) is integrated into the master controller (56) to avoid the need for additional hardware.