GB2353339A

GB2353339A - A transmission system controller which with a gear engaged disengages a clutch to prevent stalling

Info

Publication number: GB2353339A
Application number: GB0018804A
Authority: GB
Inventors: Robin John Warren
Original assignee: LuK Lamellen und Kupplungsbau GmbH
Current assignee: LuK Lamellen und Kupplungsbau GmbH
Priority date: 1999-08-16
Filing date: 2000-08-02
Publication date: 2001-02-21
Anticipated expiration: 2020-08-02
Also published as: GB9919178D0; FR2797613A1; ITMI20001890A0; ITMI20001890A1; IT1318767B1; GB0018804D0; GB2353339B; JP2001074133A; DE10036257A1

Abstract

A transmission system comprises a multi ratio gearbox 12 with a gear engaging mechanism 25 and a main drive clutch 14 having clutch actuating means 38, 22, 20. The mechanism 25 and the clutch actuating means are controlled by an electronic controller 36 which signals the mechanism to maintain an engaged gear while the vehicle is decelerating with the vehicle speed above a second gear threshold value. When the vehicle speed falls below the second gear threshold value the controller 36 commands the mechanism 25 to change down from the currently held gear to second gear and to maintain second gear while the vehicle is decelerating. Also during deceleration, while the vehicle speed is below the second gear threshold value, the controller 36 activates the clutch actuating means to disengage the clutch 14 so as to maintain engine speed above a predetermined minimum value, thereby preventing the engine from stalling. This system prevents unexpected jolts by inhibiting shift down when a driver is about to accelerate the vehicle.

Description

2353339 VEHICLE TRANSMISSIONS The present invention relates to automated

manual or semi-automatic transmissions, but could be applied to fully automated transmission. The said transmission systems have a main drive clutch, such as a start-up clutch and/or gear change clutch, and clutch actuation means for controlling the state of engagement of the clutch, a multi-ratio gear box and a gear engaging mechanism for engaging an operative ratio of the gearbox.

The British patent GB 2302377B discloses an automated manual transmission system with means of automated priority control over a manually engaged gear ratio, whereby this priority control gives priority to a signal over another signal or overrides it, plus means to engage a more appropriate ratio for the current operating conditions if a predetermined operating condition occurs while in manual mode.

Typical operating conditions in which such a system would automatically override the manually engaged gear would include:

1. when a predetermined engine speed is exceeded; or 2. when the engine speed falls below a predetermined minimum level Alternatively, automatic override of a manually engaged gear may be implemented when the vehicle speed increases above a specified maximum threshold value or falls below a specified minimum threshold value for the currently engaged gear.

Similarly with fully automated transmission systems, gear changes are carried out in accordance with shift maps which set the specified maximum and minimum vehicle speed values for each gear.

With the systems disclosed above, when the vehicle is decelerating, conditions may determine that an automatic shift down is required, just as the 2 driver is about to accelerate the vehicle. An automatic shift down under such circumstances would, at least, result in a delay in the response by the vehicle to the activation of the accelerator and may result in an unexpected jolt as the vehicle accelerates in the lower gear.

According to one aspect of the present invention a vehicle transmission system comprises a main drive clutch, clutch actuation means for controlling the state of engagement of the clutch, a multi-ratio gear box, a gear engaging mechanism for engaging an operative ratio (gear) of the gear box and an electronic control means to control the clutch actuation means and/or the gear engaging mechanism. The control means include means to sense the gear engaged, the speed of an engine which is connected, for example, to the gearbox via the clutch, the vehicle speed and the degree of opening of a throttle control valve for the engine, the control means being arranged when the vehicle is decelerating to:

i) hold the engaged gear, while the vehicle speed is above a predetermined second gear threshold value; and ii) change down from a higher currently engaged gear to second gear when the vehicle speed falls below the second gear threshold value, the second gear being held while the vehicle is decelerating with the vehicle speed below the second gear threshold value; the control means causing the clutch actuation means to disengage the clutch to maintain the engine speed above a predetermined minimum value.

In accordance with the present invention a shift down from a higher currently engaged gear to second gear only occurs when the vehicle speed drops below the second gear threshold value, the risk of a shift down when the driver is about to accelerate is consequently very much reduced.

With the transmission system disclosed above automatic shift down from second gear to first gear is inhibited, the second gear being held until the vehicle comes to rest unless there is manual intervention.

3 According to a preferred embodiment of the present invention the control means may cause an automatic shift down from second gear to first gear if the throttle is opened beyond a predetermined threshold value but above a predetermined first gear threshold value and the vehicle continues to decelerate below the first gear threshold value. Such operating conditions would indicate that the driver wishes to accelerate but that second gear represents too high a transmission ratio (too high a gear) the system will thus reduce the gear ratio (the gear) so that the vehicle will accelerate away more effectively.

According to a further preferred embodiment of the present invention the control means may cause an automatic shift down from second gear to first gear if the brakes are applied and the vehicle speed is below a predetermined first gear threshold value, indicating that it is the driver's intention to stop the vehicle.

The present invention is particularly suited to automated manual or semiautomated transmission systems where down shifting in accordance with the present invention would automatically override the manually engaged gear, in the absence of appropriate manual action. In such circumstances means may be provided by which the driver could override the automatic override, should the driver wish to maintain the manually selected gear for some reason.

With fully automated transmission systems, the above described down shift procedure would replace the more conventional down shift control, based on shift maps which give minimum and maximum vehicle velocities for the gear ratios.

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 schematic view of an automated transmission system in accordance with the present invention.

4 Figure 2 shows a downshift pattern for a conventional automated transmission system, and Figure 3 shows a downshift pattern for an automated transmission system in accordance with the present invention.

Automated gears are principally gears which can be changed both manually and automatically via an actuation device, whereby the selection of the gear can be made by the driver or by a control unit, whereby then the transmission ratio can be adjusted via an actuator (activation unit) and therefore the transmission ratio of the gear can be changed manually or under automatic control by activating the actuator. In the case of semi-automatic gears, the manual selection of the transmission ratio can be initiated by the driver, whereby the performance of the selection of the transmission ratio is then implemented via an actuator. In this way the selection of the gear engaged is set by the driver and performance is controlled by the system.

Figure 1 shows an engine 10 with a starter and associated starter circuit 10a, which is coupled through the clutch 14, such as a main friction drive clutch, and a gearbox input shaft 15, to a gearbox 12, such as for example a multi speed synchromeshed lay shaft-type gearbox. Fuel is supplied to the engine by a throttle 16 which includes a throttle vale 18, operated by the accelerator pedal 19. The invention is equally applicable to electronic or mechanical fuel injection petrol or diesel engines.

The clutch 14 is actuated, for example, via a release fork 20, or a clutch release unit arranged concentrically around the gear shaft, which is operated, for example by a hydraulic slave cylinder 22, under the control of a clutch actuator control means 38. Activation may also be via an electric motor.

Reference should be made on this matter to DE 195 04 847 the contents of which expressly forms a part of the disclosure content of the present application.

A gear selector lever 24 operates in a shift 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 shift 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 'Y' 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 'Y' position provides a command to cause the gearbox to shift up one gear ratio; and momentary movement of the gear lever 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 shift 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 the applicant's prior patent specification no.

W097105410, the content of which expressly forms a part of the disclosure of the current application.

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 6 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 the applicant's prior patent specifications EP0038113,

EP0043660, EP0059035, EP0101220 and W092/13208, the content of which expressly forms a part of the disclosure of the present application.

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

A warning element, such as a buzzer 50, is connected to the control unit to warnlindicate to the vehicle operator as certain operating conditions occur. In addition to 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., The control unit 36 also monitors the current gear engaged by manual operation of gear lever 24, by means of sensor 32 and the vehicle operating conditions, for example vehicle speed by means of sensor 42, the vehicle speed being dependent on the driven plate speed and the gear engaged, and the engine speed by means of sensor 26. If the control unit 36 determines that the gear engaged manually is not appropriate for the vehicle operating conditions, then the control unit 36 may automatically override the manually engaged gear and engage a more appropriate gear.

With transmission systems proposed hitherto, for example as disclosed in BB 2 302 37713, the content of which expressly forms a part of the disclosure of the current application, the control unit 36 would typically increase or decrease the manually selected gear ratio by one increment, so that for example, if the current manually engaged gear was fourth and the engine speed fell below a predetermined level, the control unit 36 would automatically 7 shift down one gear, to third; or alternatively, if the engine speed exceeds a predetermined maximum value, the control unit 36 would automatically shift up one ratio to fifth. More than one automatic shift may of course be made, where operating conditions require, so that the gear may be shifted automatically from fourth to third and then second. Rather than engine speed such systems may automatically shift gear as a function of vehicle speed, shifts occurring when the vehicle speed exceeds or falls below predetermined values for each gear. Such systems provide a step-wise shift in the gear rations, as illustrated in Fig. 2.

Under certain operating conditions, for example where the driver is decelerating gradually to a halt, several automatic changes will be required if the driver does not intervene manually. This may present problems if the driver is decelerating due, for example to traffic conditions, but has the intention to accelerate away as soon as it is safe to do so. Under such conditions, the control unit 36 may decide that a change down is appropriate, just as the driver is about to accelerate. If the gear change is occurring as the accelerator pedal 19 is depressed, as if actuated, then as the clutch 14 will be at least partially disengaged, there is likely to be a delay in response to depression of the accelerator pedal 19, while if the lower gear has already been engaged, there is likely to be an unexpected jolt as the vehicle accelerates away in the lower gear.

In accordance with the present invention if the vehicle is decelerating and the speed of the vehicle is in excess of a predetermined second gear threshold value V2nd, then the current manually engaged gear, for example, third, fourth or fifth is held and the control unit 36 takes no action to control overriding and altering this gear. If however the vehicle speed falls below the second gear threshold value V2nd then the control unit 36 causes the gear selector mechanism 25 to automatically engaged second gear as illustrated in Fig. 3.

If, while third, fourth or fifth gears are held, or after automatically shifting down to second gear, the engine speed fails below a predetermined value, for example the engine idle speed, the control means 36 will cause the clutch 8 actuation means 38, 22, 20 to disengage the clutch and prevent the engine from stalling.

If when the second gear is engaged the throttle is opened beyond a threshold value ajo, while the vehicle speed is above a predetermined first gear threshold value V1st, this value being lower than the second gear threshold value V2nd, and the vehicle continues to decelerate to a speed below V1st, then the control means 36 will automatically shift from second gear to first gear (as illustrated by the broken line in figure 3) permitting the vehicle to accelerate away.

Furthermore, when second gear is engaged and the vehicle speed fails below the first gear threshold value V1st, while the vehicle brake 58 is applied, the control means 36 will automatically shift from second gear to first gear (as illustrated by the broken line in figure 3) so that the vehicle may be brought to a rest.

In this manner, under normal control, the transmission system according to the present invention will only shift down when the vehicle speed fails below the second gear threshold value V2nd, thus reducing the risk that an automatic shift down will occur when the driver wishes to accelerate the vehicle.

Various modifications may be made without departing from the invention. For example, while in the above embodiment hydraulic means are used for actuation of the clutch and gear engaging mechanism, other suitable actuators, for example pneumatic or electrical means, for example electric motors or solenoids may be used.

The present invention is also applicable to automated manual transmission systems and fully automated transmission systems.

9 A power transmission system for vehicles has a main drive clutch 14, clutch actuation means 38, 22, 20 to control the state of engagement of the clutch 14, a gearbox with several transmission ratios 12, a gear engaging mechanism 25 for engaging an operative ratio of the gearbox and an electronic control means 36 to control the clutch actuation means 38, 22, 20 and the gear engaging mechanism 25. The control means 36 are designed in such a way that the engaged gear is held whilst the vehicle is decelerating but the vehicle speed is above a predetermined second gear threshold value and changes down from a higher currently engaged gear to second gear when the vehicle speed fails below the second gear threshold value, the second gear being held while the vehicle is decelerating with the vehicle speed below the second gear threshold value and whereby the control means 36 causes the clutch actuation means 38, 22, 20 to disengage the clutch 14 to keep the engine speed above a predetermined minimum value.

The patent claims submitted with the application are proposed formulations without prejudice to the achievement of further patent protection. The applicant reserves the right to submit claims for further combinations of characteristics, previously only disclosed in the description andlor drawings.

References back used in sub-claims refer to the further development of the subject of the main claim by the characteristics of the respective subclaim; they are not to be understood as a waiver with regard to achieving independent item protection for the combination of characteristics in the related sub-claims.

Since the subject of the sub-claims can form separate and independent inventions with reference to the prior art on the priority date, the applicant reserves the right to make them the subject of independent claims or of division declarations. Furthermore, they may also contain independent inventions which demonstrate a design which is independent of one of the objects of the preceding sub-claims.

The embodiments are not to be considered a restriction of the invention. Rather, a wide range of amendments and modifications is possible within the scope of the current disclosure, especially those variations, elements and combinations and/or materials which, for example, the expert can learn by combining individual ones together with those in the general description and embodiments in addition to characteristics and/or elements or process stages described in the claims and contained in the drawings with the aim of solving a task thus leading to a new object or new process stages or sequences of process stages via combinable' characteristics, even where they concern 10 manufacturing, testing and work processes.

Claims

1 Vehicle transmission system comprising a main drive clutch, clutch actuation means for controlling the state of engagement of the clutch, a multi-ratio gear box, a gear engaging mechanism for engaging an operative ratio of the gearbox and an electronic control means to control the clutch actuation means and the gear engaging mechanism; the control means including means to sense the gear engaged, the speed of an engine, the vehicle speed and the degree of opening of a throttle control valve for the engine, the control means being arranged when the vehicle is decelerating to:

i) hold the engaged gear, while the vehicle speed is above a predetermined second gear threshold value; and ii) change down from a higher currently engaged gear to second gear when the vehicle speed fails below the second gear threshold value, the second gear being held while the vehicle is decelerating with the vehicle speed below the second gear threshold value; the control means causing the clutch actuation means to disengage the clutch to maintain the engine speed above a pre-determined minimum value.

2. A transmission system according to claim 1 in which the predetermined minimum value of engine speed is the engine idle speed.

3. A transmission system according to claim 1 or 2 in which the control means is arranged to change from second gear if when the vehicle speed is below the second gear threshold value but above a predetermined first gear threshold value, the throttle is opened beyond a predetermined threshold value but the vehicle continues to decelerate to a speed below the first gear threshold value.

12

4. A transmission system according to any one of the preceding claims in which the control means will shift down from second gear to first gear if the vehicle speed is below a predetermined first gear threshold value and a brake of the vehicle is applied.

5 5. A transmission system in which the gear ratios are normally manually engaged, the control means shifting down from the manually engaged gear to second or first gear in accordance with the preceding claims.

6. A transmission system according to claim 5 in which means is provided for manually overriding the automatic shift down of the gears.

7. A transmission system substantially as described herein, with reference to and as shown in figs 1 and 3.