GB2318848A

GB2318848A - Motor vehicle automatic clutch control

Info

Publication number: GB2318848A
Application number: GB9721204A
Authority: GB
Inventors: Klaus Kuepper; Michael Salecker; Franz Kosik; Gunter Worner
Original assignee: Daimler Benz AG; LuK Getriebe Systeme GmbH
Current assignee: Daimler Benz AG; LuK Getriebe Systeme GmbH
Priority date: 1996-10-10
Filing date: 1997-10-08
Publication date: 1998-05-06
Anticipated expiration: 2017-10-08
Also published as: ITMI972294A1; FR2754494A1; IT1295304B1; GB2318848B; BR9704996A; GB9721204D0; DE19744051A1; FR2754494B1

Abstract

In a motor vehicle with a manually-controlled gearbox (4) and an automatically-operated clutch (3) which is disengaged when a sensor device (14) detects a manual activation of the gear shift lever (13), the clutch is not disengaged unless the engine torque is less than a boundary value in order to avoid engine flare. The boundary value is a variable dependent on the rate of release of the accelerator pedal, to allow for a delay in the reduction of torque when the accelerator depression is reduced. The torque is calculated from the accelerator or throttle position as well as other parameters.

Description

MOTOR VEHICLE The invention relates to a motor vehicle with a motor, a gearbox and an automated torque transfer system, such as a clutch wherein the gearbox transmission ratio can be manually selected by means of an operating element, such as for example a shift lever, wherein a sensor device detects a manual activation of the operating element and passes a signal representing an activation on to a control unit, the control unit is in signal connection with sensors and where applicable other electronics units wherein the control unit determines the engine torque and a sensor detects a load lever position of a load lever, such as accelerator pedal, the control unit detects from at least one signal a characteristic value of a driver-side activation of an element and a control signal can be produced by the control unit whereupon the torque transfer system is disengaged by means of an actor during activation of the operating element.

In the case of vehicles having an automated torque transfer system such as clutch the closed clutch provides in the drive train with an engaged gear the force transfer from the engine to the gearbox and to the drivable wheels which are mounted on the output side. If a change in the gearbox transmission ratio is initiated by the driver such as can be carried out by means of the operating element, the clutch has to be disengaged.

With an activation of the operating element a sensor detects such activation and passes a signal representing an activation onto the control unit. The control unit can disengage the clutch when activation has been detected. With unintended activation of the operating element and with a high engine torque this disengagement can lead to an uncomfortable oversewing of the engine. With such motor vehicles it is known from US PS 5 099 969 that a shift process desired by the driver is only allowed through activation of the operating element if during activation of the operating element the engine torque is below a boundary value. If the engine torque is above a boundary value the shift process is prevented and the clutch is not disengaged.

This can however be disadvantageous if changing gear is carried out with a rapid shift process although the engine torque has not yet dropped below the boundary value. Even with rapid shift processes with a quick release of the load lever , as a result of inertia of the system and internal time constants the engine torque cannot drop rapidly at will below the boundary value although the driver starts or carries out the activation of the shift lever as a rule at the same time as relaxing the load lever, such as accelerator pedal.

The object of the invention is to provide a motor vehicle wherein with an automated torque transfer system rapid shift processes can be carried out and the drawbacks of the prior art are reduced or overcome. More particularly a shift process is to be allowed or prevented in dependence on the driver-side activation of for example an operating element for gear change and/or load lever.

The object of the invention is further to provide a motor vehicle with automated torque transfer system wherein the gearbox stages of the gearbox can be shifted safely and functionally reliably in substantially all relevant operating situations.

This is achieved according to the invention in that the control signal is produced when during activation of the operating element the engine torque understeps a predefinable boundary value wherein the value of the predefinable boundary value can be changed in dependence on at least one characteristic value of the motor vehicle.

It can be expedient according to the invention if the predefinable boundary value can be changed in dependence on the alteration speed d/dt of a characteristic value It can likewise be advantageous if the predefinable boundary value can be changed as a function of a characteristic value such as of the alteration speed of the load lever position.

It can furthermore be advantageous if the predefinable boundary value can be changed within predefinable limits.

It is likewise advantageous if the predefinable boundary value is increased as a function of the alteration speed of a characteristic value in the event of the driver cancelling the load lever position, such as with a driver-side release of the load lever.

It can likewise be expedient if with a cancellation of the load lever position, such as with a driver-side release of the load lever, the predefinable boundary value is increased as a function of the alteration speed of the load lever position.

It is expedient if the predefinable boundary value is increased as a function of a negative alteration speed of a characteristic value.

Furthermore it is advantageous if the predefinable boundary value remains unchanged with a positive alteration speed of a characteristic value.

According to a further aspect of the invention it is expedient if with a driver-side activation of the load lever, such as with a driver-side increase in the load lever position, the predefinable boundary value is reduced as a function of the alteration speed of a characteristic value, such as load lever position.

It can be advantageous according to the invention if the predefinable boundary value is reduced with a positive alteration speed of a characteristic value.

It can equally be expedient if the predefinable boundary value MGre=Z for the engine torque is changed according to MGrenz = Mo - k * da/dt with a starting value M0 of the predefinable boundary value, a constant k and the alteration speed d/dt of a characteristic value Furthermore it can be expedient if the predefinable boundary value MGrenz for the engine torque is changed according to Arenz = Mo - , d/dt,...) * d/dt with a starting value Mo of the predefinable boundary value, a function k(,d/dt,...) and the alteration speed d/dt of a characteristic value wherein the variable k(...) is a function of , d/dt and/or of possibly other values, such as for example the time t.

It can likewise be expedient if the predefinable boundary value after increasing or reducing in dependence on a characteristic value as a function of the time is returned again to a predefinable ideal value M,.

It is further expedient if the predefinable boundary value after increasing or reducing in dependence on a characteristic value as a function of the time with a predefinable time delay is returned again to a predefinable ideal value .

It is likewise advantageous if a characteristic value is for example a load lever position, a throttle valve position, an injection time and/or an injection volume.

According to a further idea it can be advantageous if instead of the engine torque a value representing the engine torque is monitored and when this value understeps a boundary value when the operating element is activated the clutch is disengaged.

Furthermore the invention relates to a method for controlling an automated torque transfer system when used within a motor vehicle.

The invention will now be explained with reference to the drawings in which: Figure 1 is a diagrammatic illustration of a vehicle; Figure 2 is a block circuit diagram; Figure 3 is a diagram; Figure 4 is a diagram and Figure 5 is a block circuit diagram.

Figure 1 shows a vehicle 1 in a diagrammatic view with a motor 2, such as drive unit, a torque transfer system 3, such as clutch and a gearbox 4. On the output side of the gearbox 4 is a drive shaft 5, differential 6 and the driven axles 7a and 7b wherein the wheels 8a, 8b are driven by the driven axles 7a and 7b. The vehicle can be provided for example with a shiftable four-wheel drive. This is however not illustrated in Figure 1.

The torque transfer system 3, such as for example friction clutch, magnetic powder clutch or torque converter with converter bridging clutch is shown in Figure 1 as a torque transfer system mounted in the drive train between the motor 2 and gearbox 4 wherein the torque transfer system 3 can also be mounted on the output side after the gearbox 4 as can be expedient for example in the case of an continuously variable transmission (CVT).

The torque transfer system 3 consists in the illustration of Figure 1 of a clutch disc with friction linings 3b, a pressure plate 3c as well as a clutch cover 3d and a plate spring 3e. These parts of the torque transfer system can be mounted on a flywheel 3a wherein these can also be assembled with the flywheel 3a as a premountable unit. The flywheel 3a can also be a so-called twin mass flywheel which provides a torsion damper between the primary and secondary mass. The plate spring 3e is biased by means of the disengagement bearing 3f for engaging or disengaging the clutch whereby through the biasing of the plate spring tongues by means of the disengagement bearing 3f the clutch can be changed or set in a position which is for example the fully engaged or fully disengaged state or a state between these two boundary states. The torque transferable by the torque transfer system 3 can be set and fixed anywhere in the area between zero and the maximum value.

The disengagement bearing 3f is operated in the embodiment of Figure 1 by means of a disengagement lever 9 wherein the disengagement lever is operated through a hydraulic path with slave cylinder 10, hydraulic line 11 and actor 12. The actor 12 contains a servo device 12a which in the case of a use of a hydraulic path contains a master cylinder and a drive unit for operating the master cylinder. Furthermore the actor 12 contains an electronic unit 12b such as control unit which receives the incoming signals from for example sensor devices, sensors or other electronics units, stores them, retrieves them from memories and/or processes them and produces control signals in order to control the actor so that the torque transfer system is engaged or disengaged.

The gearbox 4 is a gearbox wherein a difference can be made between various gearbox transmission ratios such as gears, by means of an operating element 13. In order to select one gearbox transmission ratio from a plurality of same the operating element 13 is brought into the position provided for same or is operated in a manner and way proposed for same. This activation can be carried out manually or automatically. The operating element for manual activation by the driver can be formed as shift lever or as an electronic element.

The device for disengaging the torque transfer system can as illustrated above be carried out by means of a pressurised medium system wherein the pressurised medium system can be a hydraulic system, pneumatic system or another fluid-operated system. The disengagement member can also be in these cases a central disengagement member operated by pressurised medium. Furthermore the activation can also be through mechanical means such as for example electromotorized through rod linkage.

A sensor device 14 can be mounted or attached to the operating element 13 whereby activation of the operating element is detected through this sensor unit 14. The detection of an operation can be carried out by measuring a force acting on the operating element or by measuring a position, change in position or speed or acceleration.

Furthermore the activation can be detected on overstepping a boundary or threshold value during movement or activation of the operating element.

The sensor or sensor device 14 can be a sensor dependent on path or speed or acceleration or force and which detects or can detect a movement of the operating element or an element connected therewith or a force on the operating element or on an element connected therewith.

Furthermore a sensor 15 can be mounted on the gearbox 4 to detect the position of the engaged gear by sensing for example the position of shift elements inside the gearbox.

The sensors, such as throttle valve sensors 16, such as wheel speed or speed sensor 17 (vehicle speed sensor), engine speed sensor 18 and further sensors can be provided in or on the vehicle and can be connected to the control unit through signal lines. A door sensor which detects whether the door is opened can also be mounted on the vehicle.

The control unit can calculate characteristic values from the data of the sensors wherein these characteristic values are the sensor signals themselves or values derived or processed by same or signals, such as for example alteration speeds of the characteristic values or of sensor signals, such as gradients which can be used for evaluating a driver-side shift intent. These alteration speeds or gradients can be calculated for example through numerical processes, such as though difference quotients. The control unit 12 detects from these sensor data and other data as well as from system input values the driving state and generates a control signal for operating the torque transfer system 3 if a shift intent is considered to exist.

As characteristic values are used sensor signals or signals processed or derived from same, such as for example the load lever position, the alteration speed of the load lever position and/or other processed or filtered signals. The characteristic value thus represents a value for a driverside activation of an operating element. The alteration speed of the load lever position is thus a characteristic value for the operation of the accelerator pedal by the driver.

If the operating element of the gearbox is activated by the driver then the torque transfer system is disengaged by means of the control unit and actor in that a control signal is generated to open the torque transfer system. This takes place as a rule only when the calculated or determined engine torque is smaller or equal to a predefinable boundary value Mren: of the engine torque. Furthermore a shift intent by the driver can be suppressed or considered as not given if the determined engine torque exceeds the boundary value ArenZ- The motor vehicle 1 further has an accelerator pedal 20, such as load lever, as well as an operating element for a brake 21, such as operating brake, as well an operating element 22 for a brake such as parking brake. At least one sensor 23 is mounted on the load lever 20 to determine the position or activation of the load lever. It can also be determined thereby whether an activation exists or does not exist. As a sensor for determining whether or not the pedal or load lever is activated can also be considered an idling switch which is switched on when the pedal is not activated and which is switched off when the pedal is activated. This idling switch can be replaced electronically by the activation determined by the sensor in that an operating bit can be used when the sensor 23 detects a non-disappearing activation.

A brake switch 24 can be mounted on the operating element of the operating brake 21 to detect whether the brake is activated. A brake switch of this kind can also be mounted on the operating element 22 for the parking brake wherein the sensor 25 detects whether the parking brake is activated.

The sensor unit 23 of the load lever 20 is in signal connection with an engine electronics 30 so that the engine speed and the engine torque is controlled according to the process provided above by the engine electronics 30 through activation of the accelerator pedal or through activation of the load lever.

From the signals, such as measuring data or system input values entering into the control unit 12 it is possible to determine the ensuing engine torque. The ensuing engine torque is the actual engine torque plus or minus the torques which are absorbed or delivered by the secondary assemblies.

Secondary assemblies can be for example the air conditioning unit or centrifugal force accumulator. Furthermore drag torques can also be taken into consideration.

Furthermore it can be detected whether an activation of the operating element 13 exists and whether a brake 21, 22 is activated and whether the accelerator pedal, such as load lever is operated. The control unit 12 detects a shift intent through an activation of the operating element 13 from the incoming signals of the sensors 14 and/or 15. Whether the shift intent is evaluated or accepted as a wish to change gear by the control unit and a control signal is produced for opening the clutch depends on the system parameters.

It is for example not expedient in every situation that a shift intent signal is also evaluated so that a shift process takes place. As a rule as a condition for a desired gear change or for shifting into neutral it is required that the engine torque is smaller than a predefinable boundary value and/or that the operation of the load lever is smaller than a predefinable boundary value, that is for example that the load lever is not activated and the idling switch signals this.

If the control unit 12 detects from its input signals, such as sensor values and other signals , an activation by the driver of the operating element, such as a shift intent this is first checked before the clutch is disengaged in controlled or regulated manner.

It is expedient if the shift intent is prevented by the control unit if the engine torque exceeds a certain boundary value wherein the boundary value can be varied in dependence on at least one characteristic value. The engine torque intended for this minus for example the drag torques and torques based on secondary consumers is compared by the control unit with a predefinable boundary value and if the engine torque exceeds the boundary value a shift intent is evaluated as inadmissible and the torque transfer system is not disengaged. This should prevent faulty releases since it is assumed that the driver would not want to change gear whilst he requires torque (power).

With shift processes carried out rapidly on the driver side where the operating element 13 is operated quickly and the load lever 20 is released or taken back relatively rapidly on the driver side it can happen under certain circumstances that the engine torque M;ot cannot drop quickly enough below the boundary value mores and the control unit 12 evaluates the shift intent as not existing and the clutch is not disengaged although the driver is deliberately introducing a shift process through activating the operating element.

The cause for a non-instantaneous reduction of the engine torque Mtwith a cancelling of the load lever is for example the mass inertia of the rotating masses of the engine.

Furthermore a certain time lasts until the driver has reduced the load lever at least so far that the resulting engine torque lies below the predefinable boundary value. This lasts a certain time even if the engine electronics and the engine could react immediately.

The engine torque is calculated inter alia from the position or setting of the load lever respectively from the resulting throttle valve position and/or injection time or volume. It reacts however with a certain time delay on the input signal.

If thus the driver reduces the throttle valve angle to the zero value in order to prepare for a gear change then a certain time lapses until the engine torque reduces below the boundary value mentioned above. During this time the clutch is not opened and a shift process is at least impeded.

The driver begins as a rule the activation of the operating element substantially at the same time as a reduction of the load lever. Thus the start of the operating movement is made difficult since the clutch is closed or engaged.

Figure 2 shows a block circuit diagram 100 in which block 101 indicates the activation or cancellation by the driver of the load lever or another element. This signal for cancellation is delayed in block 102 by system-conditioned dead times before a reaction can take place on the part of the engine electronics or engine. In block 103 the engine torque is calculated which likewise takes time. Furthermore inertias of the engine have to be overcome before the desired engine torque required by the driver is issued in block 104.

Figure 3 shows a diagram 200 in which the load lever position 201, a shift lever operating signal 202, an engine torque 203 and a boundary value for the engine torque 204 are shown as a function of the time. At time to,205 the load lever is drawn back by the driver or the activation is reduced and at the same time the operating element of the gearbox is operated on the driver side to change gear, as can be seen through the reduction of the signals 201 and 202 from the time point 205. The engine torque 203 is substantially constant up to time point 207 and is reduced from time point 207. The time difference between the time point 205 and time point 207 is produced for example from inertias and dead times.

The engine torque is from time point t1 206 below the boundary value 204 for the engine torque and from this time point a shift process is regarded as present. At this time point the activation of the operating element in the case of the shift process is however as a result of for example a rapid shift speed already practically completely carried out although the clutch was closed hitherto. In this example it is clear that an increase in the boundary value to for example the value 208 would be advantageous.

Figure 4 shows a diagram 300 in which a load lever position 301 or a value equivalent to this is shown as a function of the time t. Furthermore the boundary value 302, renz for the engine torque is shown as a function of the time. The value lies with low load lever alteration speeds at the value Mo wherein at high load lever alteration speeds the value of MGr,nz rises according to curve 302a. With maximum load lever alteration speeds the curve 302a reaches its maximum. If the load lever is substantially nil then the increased value is again reduced from MGre2z to the value M,. The curves 303 and 304 show a path from MGrenz in the case of the reduction. The curve 303 corresponds to a normal reduction and the curve 304 shows a path of a reduction where a filter function produces a time delay.

As already mentioned above a detection of a shift intent is carried out by means of at least one sensor which detects the movement of an operating element and/or the position of an operating element and/or the speed and/or the acceleration of an operating element. Furthermore a sensor of this kind can also detect directly or indirectly the force action on the operating element. By using a path sensor in the area of the operating element and a path sensor in the area of the shift elements inside the gearbox it is possible with the existence of elasticities in the force path between the operating element and the shift elements inside the gearbox to carry out also a differential path measurement in order to obtain a force-proportional or force-representing signal which can be used to evaluate a shift intent.

The shift intent signal as already described is a digital signal, that is a, shift intent exists or is evaluated as not existing or does not exist. Furthermore the shift intent signal can be determined or calculated and processed as a continuous signal with values between a minimum value and a maximum value. Just before reaching, exceeding or understepping the signal relating to a release threshold or a predefinable boundary value for releasing a shift intent the clutch torque can be reduced.

The clutch is with a slight activation below the shift intent threshold already slightly opened so that the reaction to a shift intent signal can be adapted by the driver according to the operating speed of the operating element.

The transition from "slow opening" of the torque transfer system to 'rapid opening up" of the torque transfer system would then be continuous after the driver-side activation of the operating element. Also a continuous transition would exist in the time path of opening during changing gear.

A slight opening of the clutch would have to take place on understepping a first boundary value wherein a complete opening of the clutch would only take place on understepping a second boundary value.

In this operating state a short term slip phase can occur prior to opening of the torque transfer system whilst the drive train is set tension-free so that the build up of vibration of the input side of the gearbox is counteracted.

This means that an at least slight opening of the torque transfer system with a detected movement of the operating element is already controlled although the predefinable threshold value for detecting a shift intent has still not been exceeded. The amount of this at least slight opening can be selected in dependence on the filtered or processed signal values wherein the typical vibrations of the shift lever ought to remain unconsidered.

Figure 5 shows a block circuit diagram 400 for explaining the process according to the invention for use inside the motor vehicle according to the invention. In block 400 the process is started. In block 402 it is asked whether there is a driver-side activation of the operating element. If this is the case then it proceeds in block 403 , if this is not the case then the process for this time step or this interval is ended in block 408.

In block 403 the engine torque is determined or detected whereby the engine torque can be determined from system input values or for example can be obtained from other electronics units though a signal line or data bus.

In block 404 the load lever position is determined or a value representing same or an equivalent value. Furthermore the alteration speed or gradient of this value is determined or calculated. These values can where applicable also be obtained by another electronics unit through a signal line or a data bus.

In block 405 the boundary value for the engine torque or a value representing same is determined whereby this is preferably determined according to Mores: = Mo - k ( ,d/dt,...)* d/dt wherein Mo is a starting value, k is a variable value which can depend on , -d/dt, or other values and is a value at least representing the load lever position and d/dt is the alteration speed of this value. k can be a linear, nonlinear or any function of the parameters or can be a constant.

In block 406 it is determined whether the engine torque EJI, is smaller than this determined boundary value M < Grenz If this is the case in block 407 the clutch is deliberately disengaged by the control unit by means of the actor before the process is ended in block 408.

This process can be repeated cyclically with a predefinable rhythm rate.

The patent claims filed with the application are proposed wordings without prejudice for achieving wider patent protection. The applicant retains the right to claim further features disclosed up until now only in the description and/or drawings.

References used in the sub-claims refer to the further design of the subject of the main claim through the features of each sub-claim; they are not to be understood as dispensing with obtaining an independent subject protection for the features of the sub-claims referred to.

The subjects of these sub-claims however also form independent inventions which have a configuraticn independent of the subjects of the preceding sub-claims.

The invention is not restricted to the embodiment of the description. Rather numerous modifications and alterations are possible within the framework of the invention, more particularly those variations, elements and combinations and/or materials which are inventive for example through combination or modification of individual features or elements or method steps contained in the drawings and described in connection with those in the general description and embodiments and claims and lead through combinable features to a new subject or to new method steps or sequence of method steps where they relate to manufacturing, testing and work processes.

Claims

PATENT CLAIMS

1. Motor vehicle with a motor, a gearbox and an automated torque transfer system, such as a clutch wherein the gearbox transmission ratio can be manually selected by means of an operating element, such as for example a shift lever, wherein a sensor device detects a manual activation of the operating element and passes a signal representing an activation on to a control unit, the control unit is in signal connection with sensors and where applicable other electronics units, wherein the control unit determines the engine torque and a sensor detects a load lever position of a load lever, such as an accelerator pedal, and a control signal can be produced by the control unit whereupon the torque transfer system is disengaged by means of an actor during activation of the operating element, characterised in that the control signal is produced if during activation of the operating element the engine torque understeps a predefinable boundary value wherein the value of the predefinable boundary value can be changed in dependence on at least one characteristic value of the motor vehicle.

2. Motor vehicle according to claim 1 characterised in that the predefinable boundary value can be changed in dependence on the alteration speed d/dt of a characteristic value

3. Motor vehicle according to claim 1 characterised in that the predefinable boundary value can be changed as a function of the alteration speed of the load lever position.

4. Motor vehicle according to one of claims 1 to 3 characterised in that the predefinable boundary value can be changed within predefinable limits.

5. Motor vehicle according to one of claims 1 to 3 characterised in that the predefinable boundary value is increased as a function of the alteration speed of a characteristic value in the event of the driver cancelling the load lever position, such as with a release by the driver of the load lever.

6. Motor vehicle according to one of claims 1 to 3 characterised in that with a cancellation of the load lever position, such as with a release by the driver of the load lever, the predefinable boundary value is increased as a function of the alteration speed of the load lever position.

7. Motor vehicle according to one of claims 1 to 3 characterised in that the predefinable boundary value is increased as a function of a negative alteration speed of a characteristic value.

8. Motor vehicle according to one of claims 1 to 3 characterised in that the predefinable boundary value remains unchanged with a positive alteration speed of a characteristic value.

9. Motor vehicle according to claim 3 characterised in that with a driver-side operation of the load lever, such as with a driver-side increase in the load lever position, the predefinable boundary value is reduced as a function of the alteration speed of a characteristic value such as the load lever position.

10. Motor vehicle according to one of claims 1 to 3 characterised in that the predefinable boundary value is reduced in the event of a positive alteration speed of a characteristic value.

11. Motor vehicle according to one of claims 1 to 3 characterised in that the predefinable boundary value MGrenz for the engine torque is changed according to MGrenz = Mo - k * d/dt with a starting value Mo of the predefinable boundary value, a constant k and the alteration speed d/dt of a characteristic value

12. Motor vehicle according to one of claims 1 to 3 characterised in that the predefinable boundary value MGrenz for the engine torque is changed according to MGrenz = Mo - k( d d/dt, ...) * d/dt with a starting value Mo of the predefinable boundary value, a function k(,d/dt,...) and the alteration speed d/dt of a characteristic value

13. Motor vehicle according to one of the preceding claims, characterised in that the predefinable boundary value after an increase or reduction in dependence on a characteristic value as a function of the tirne is returned again to a predefinable ideal value M,.

14. Motor vehicle according to one of the preceding claims, characterised in that the predefinable boundary value after an increase or reduction in dependence on a characteristic value as a function of the time with a predefinable time delay such as filtering, is returned again to a predefinable ideal value M,.

15. Motor vehicle according to one of the preceding claims characterised in that a characteristic value is for example a load lever position, a throttle valve position, an injection time and/or an injection volume.

16. Motor vehicle in a modification of the preceding claims, characterised in that instead of the engine torque a value representing the engine torque is monitored and when this value understeps a boundary value when the operating element is activated the clutch is disengaged.

17. Motor vehicle substantially as herein described with reference to the accompanying drawings.

18. Method for controlling an automated torque transfer system when used within a motor vehicle according to one of the preceding claims.