SE541437C2

SE541437C2 - Method and system for controlling transmission of torque in a vehicle

Info

Publication number: SE541437C2
Application number: SE1750352A
Authority: SE
Inventors: Erik Gustafsson; Fredrik Jarngren; Georg Åhrberg
Original assignee: Scania Cv Ab
Priority date: 2017-03-24
Filing date: 2017-03-24
Publication date: 2019-10-01
Also published as: SE1750352A1; DE102018001728A1

Abstract

The present invention relates to a method for controlling transmission of torque in a vehicle (100),the vehicle (100) including:a drivetrain for transmitting torque between a power source (101) and at least one drive wheel of the vehicle (101), anddriver manoeuvrable means (118), wherein torque to be transmitted by the drivetrain is controllable in dependence of an electrical signal representing a position of the driver manoeuvrable means (118),the method including:- detecting if a change in torque to be transmitted by the drivetrain is demanded by means of the driver manoeuvrable means (118),- predicting a torque that is expected to arise in the drivetrain if controlling the change in transmission of torque as demanded by the driver manoeuvrable means (118), and- influencing the change in transmission of torque of the drivetrain based on said prediction.

Description

METHOD AND SYSTEM FOR CONTROLLING TRANSMISSION OF TORQUE IN A VEHICLE Field of the invention The present invention relates to vehicles, and in particular to a method and system for controlling transmission of torque in a vehicle. The present invention also relates to a vehicle, as well as a computer program and a computer-readable medium that implement the method according to the invention.

Background of the invention There exist various kinds of vehicle transmissions. For example, vehicle transmissions can be of a fully automatic kind, where a vehicle control system controls gear changing operations. The gearboxes being used in these systems may consist of automated manual transmissions where the vehicle control system automatically controls gear shifting in “manual” gearboxes.

There also exist manual transmissions where the vehicle driver is in control of the gear changing operation. A change of gear in manual transmissions is often performed through the use of a driver controllable clutch, oftentimes through the use of a clutch pedal. Automatic clutches can also be used in automated manual transmissions, in which case clutch operation when changing gear is controlled by the vehicle control system and not by the driver. There also exist systems having automated manual transmissions, where driver controllable means such as a clutch pedal is present and which may be used when starting the vehicle from standstill. When the vehicle has been set in motion, subsequent changes of gear can be arranged to be controlled completely by the vehicle control system without driver interaction and without further manoeuvring of the clutch, i.e. changes of gear being performed with the drivetrain closed. Hence, in this case, the clutch is completely controlled by the driver using a clutch pedal being directly (mechanically) linked to the clutch servo.

The present specification relates to systems where the driver manoeuvrable means such as a clutch pedal or accelerator is used to control transmission of torque in a drivetrain, e.g. by controlling torque transmitting means such as a clutch or other torque transmitting means, or power delivered by a power source. With regard to torque transmitting means, the torque transmitting means are not controlled directly through the use of a mechanical or hydraulic linkage. Instead, e.g. the torque transmitting means is controlled through the use of clutch-by-wire (CBW) systems. In clutch-by-wire systems an electrical signal representing e.g. a clutch pedal position is translated into a corresponding request for torque transmission, such as a corresponding clutch movement. For example, a position sensor or other suitable means may be used to detect a position of the driver manoeuvrable means, such as e.g. the position of a clutch pedal. An electrical signal representing this position is then translated into a corresponding driver request regarding e.g. clutch operation, and the vehicle control system controls e.g. the actual clutch movement in dependence of the signal representing the position of the clutch pedal. The actual clutch movement, consequently, is not mechanically linked to movements of the driver manoeuvrable means.

Systems of this kind may provide advantages in the operation of the vehicle.

Summary of the invention It would be advantageous to achieve a method and system that reduces the risk for excessive load in the drivetrain in situations when the driver engages torque transmission between a power source and vehicle drive wheels through control of torque transmission means using driver manoeuvrable means. To better address this concern a method and system having the features defined in the independent claims are provided.

The present invention relates to a method for controlling transmission of torque in a vehicle, the vehicle including: a drivetrain for transmitting torque between a power source and at least one drive wheel of the vehicle, and driver manoeuvrable means, wherein torque to be transmitted by the drivetrain is controllable in dependence of an electrical signal representing a position of the driver manoeuvrable means, the method including: - detecting if a change in torque to be transmitted by the drivetrain is demanded by means of the driver manoeuvrable means, - predicting a torque that is expected to arise in the drivetrain if controlling the change in transmission of torque as demanded by the driver manoeuvrable means, and - influencing the change in transmission of torque of the drivetrain based on said prediction.

There exist various kinds of transmission systems, where a change of gear may be performed manually or automatically. The transmission systems, irrespective whether of a manual gearshift or automatic gearshift kind, may include a clutch or other torque transmission means that may be used to selectively disengage, i.e. interrupt, torque transmission through the drivetrain. Such systems may further comprise driver manoeuvrable means for allowing driver manoeuvring of the torque transmitting means. For example, a further pedal in addition to e.g. an accelerator and a brake pedal may be utilised. Such driver manoeuvrable means for controlling torque transmitting means may also be present in hybrid vehicles.

The torque transmitting means may be controlled by the driver manoeuvrable means where a signal, such as an electrical signal, may be used to represent a position of the driver manoeuvrable means, such as e.g. a clutch pedal position, where the vehicle control system then controls the torque transmitting means on the basis of the position signals.

Torque transmitting means may further be engaged from a disengaged state. When the transmission of torque is disengaged, there is an interruption in the transmission of torque between power source and gearbox. Transmission of torque may be commenced by engaging the torque transmitting means. If the torque transmitting means are engaged from a disengaged state in which torque transmission is interrupted, the torque transmission in the drivetrain may in some situations increase from essentially zero level to a higher level. The amount of torque that will arise in the drivetrain following engagement may depend e.g. on prevailing driving conditions. In addition, the manner in which the torque transmitting means is engaged may have a substantial impact on the load that the drivetrain is subjected to. This is because the torque levels being reached as a result of the engagement to a large extent will depend also on dynamic torques that may arise when drivetrain components are accelerated by the commenced transmission of torque. If the driver manoeuvers the driver manoeuvrable means for controlling the torque transmitting means in a manner that results in sudden increases in the transmittable torque, a substantial load may be imposed on the drivetrain, largely caused by dynamic torques. This load may reach levels that is potentially damaging to components of the vehicle and may impose excessive wear. In addition, such engagements of the torque transmitting means may be perceived as discomforting to the driver.

In addition to dynamic torques arising from engagement and disengagement of torque transmitting means, driver manoeuvring of driver manoeuvrable means such as an accelerator may also impact the load that the drivetrain is subjected to. The driver may demand a change in torque to be delivered by the power source, such as an internal combustion engine, where a demand for a sudden increase or decrease in torque to be delivered by the power source may result in a substantial load being imposed on the drivetrain, e.g. caused by dynamic torques arising from sudden acceleration of drivetrain components. According to embodiments of the invention, the risk of undesired torque levels arising in the drivetrain may be reduced.

According to the invention, this may be accomplished by a method in which it is detected if a change in torque to be transmitted by the drivetrain is demanded by means of the driver manoeuvrable means. For example, it can be detected if engagement of the torque transmitting means is demanded by means of the driver manoeuvrable means. That is, it may be detected that the driver initiates an engagement of the torque transmitting means, where this detection, for example, may be accomplished by monitoring an electrical signal representing the position of the driver manoeuvrable means, where changes in the electrical signal may be translated into a corresponding movement, i.e. change in position, of the driver manoeuvrable means. The detection may be performed, e.g. by the vehicle control system, or in any other suitable way. According to embodiments of the invention, it may be detected in a similar manner if the driver demands a change in torque to be delivered by the power source by monitoring an electrical signal representing the position of the driver manoeuvrable means controlling the demand for torque, such as an accelerator.

If a demand for engagement of the torque transmitting means, or a demand for a change in torque to be delivered by the power source, is detected, a torque that is expected to arise in the drivetrain if controlling the change in torque to be transmitted by the drivetrain as demanded by the driver manoeuvrable means is predicted. The change in transmission of torque, such as the engagement of the torque transmitting means or change in request for torque from the power source, may be influenced based on this prediction.

If it is predicted that the torque that is expected to arise in the drivetrain would give rise to potentially harmful torque levels if controlling the change in transmission of torque according to the driver demand, the engagement of the torque transmitting means may e.g. be influenced to reduce the torque levels that is expected to arise.

For example, if the transmission of torque is interrupted, i.e. there is no ongoing transmission of torque, the power source may be rotating at one speed of rotation while rotatable drivetrain components downstream the torque transmitting means may e.g. be stationary or rotating at a different speed of rotation.

If the driver engages torque transmission between power source and vehicle drive wheels in a manner that results in a sudden increase in transmittable torque by the torque transmitting means, e.g. by rapidly releasing a depressed clutch pedal, this may give rise, in particular, to high dynamic torques that may be harmful and which may also give rise to discomforting jerks and/or drivetrain oscillations. The dynamic torque arises from acceleration of drivetrain components, where the acceleration is caused by drivetrain components rotating at different speeds of rotation being brought into synchronisation by the engagement of the torque transmitting means.

The invention may be utilised to reduce torque levels, such as dynamic torque levels, to thereby reduce excess stress on the drivetrain by influencing the engagement of the torque transmitting means. Torque levels that arise in the drivetrain as a consequence of the engagement of the torque transmitting means may be reduced to lower levels than had prevailed if the engagement of the torque transmitting means had been controlled completely as demanded by the driver manoeuvrable means.

When influencing engagement of the torque transmitting means, this may comprise applying a limit to the rate of change of the transmittable torque of the torque transmitting means, where the limited rate of change may reduce dynamic torque levels. The influencing may also comprise delaying and/or prolonging a time of engagement of the torque transmitting means in relation to a time of engagement if engagement would be controlled as demanded by the driver manoeuvrable means. Similarly, a change in the demand for torque from the power source may be influenced such that the rate of change when reducing or increasing torque to be delivered by the power source is reduced in comparison to a rate of change according to the driver demand. In this way, e.g. accelerations of drivetrain components can be reduced, which may reduce the dynamic torque that the drivetrain is subjected to when engaging the torque transmitting means.

Consequently, negative effects from undesired driver behaviour when engaging the torque transmitting means or changing a request for power from the power source may be reduced. With regard to requests for torque from the power source, the driver demand may also be influenced by controlling the clutch such that only a limited torque can be transmitted. The transmission of torque to drivetrain components downstream the clutch cannot exceed the currently transmittable torque. Higher torques than the transmitted torque may still arise downstream the clutch, but limiting transmittable torque may be utilised to reduce acceleration of components downstream the clutch, thereby limiting arising of dynamic torques downstream the clutch.

According to embodiments of the invention, if it is determined that the rate of change of the driver demanded torque in the drivetrain is below a limit, no influence may be applied.

According to embodiments of the invention, the rate of change of driver demanded torque in the drivetrain is determined based on the signal representing the position of the driver manoeuvrable means, for example based on a change of the position of the driver manoeuvrable means. In addition or alternatively, a rate of change of the position of the driver manoeuvrable means, in combination with a representation of the effect on the transmission of torque of the drivetrain caused by the manoeuvring of the driver manoeuvrable means may be utilised. Using e.g. a rate of change of the position of the driver manoeuvrable means the change of the transmission of torque by the drivetrain can be predicted e.g. for an imminent period of time, and if it is determined that the torque will exceed some limit/level in this period of time, the change in the transmission of torque may be influenced, e.g. to limit the dynamic torque that will arise.

When detecting a driver demand for a change in torque to be transmitted by the drivetrain a delay may be imposed in the control of the torque transmission to allow the effect of controlling torque transmission according to the driver demand to be evaluated and influenced if required. Further, various possible driver actions for different driving situations may be simulated for a vehicle, where the simulation may be performed in the vehicle or in a system distinct from the vehicle. Potentially harmful driver demands/behaviours may be identified and used as input when determining whether to influence the change in transmission of torque as demanded by the driver. The simulation may be performed e.g. for different vehicle speeds, different road inclinations, and/or different vehicle loads. The driver demand may then be compared with such determined undesired demands, and when an undesired driver manoeuvring is detected, this manoeuvring can be used as the prediction that torque will reach undesired levels. Hence no explicit estimation of the torque expected to arise need to be estimated.

The demand for a change in torque to be transmitted by the drivetrain may be detected, for example, if it is detected a movement of the driver manoeuvrable means. For example, it may be detected a movement of the driver manoeuvrable means controlling the torque transmitting means from a position representing a complete interruption of the transmission of torque towards a position representing a request for a full transmissibility of torque. The driver manoeuvrable means may, for example, be manoeuvrable by the driver in a movement region between a first end position, representing a request for a full transmissibility of torque, and a second end position, representing a complete interruption of the transmission of torque. Hence, initiation of engagement of the torque transmitting means may be detected when it is detected a change in position of the driver manoeuvrable means from a position representing a complete interruption in the transmission of torque of the torque transmitting means towards a position representing a higher transmittable torque.

According to embodiments of the invention, the prediction of the torque arising in the drivetrain comprises estimating if the torque that will arise in the drivetrain will exceed a predetermined torque limit, where the change in transmission of torque of the drivetrain is influenced only if the estimation indicates that the predetermined torque limit will be exceeded. In this way, the driver requested change in torque can be arranged to be influenced only when harmful and/or discomforting situations potentially may arise.

The torque that is expected to arise in the drivetrain may be estimated as a torque comprising at least partly a dynamic torque that is expected to arise if changing transmission of torque as demanded by the driver manoeuvrable means. In general, a power source may apply a static torque to the drivetrain which e.g. is determined by the amount of fuel being injected. However, as was mentioned above, when rotatable components are accelerated this gives rise to a dynamic torque that depend on the moment of inertia of the component(s) being accelerated and the acceleration. If high accelerations of drivetrain components occur, this may give rise to high dynamic torques. Hence, by taking the dynamic torque that will arise from e.g. engagement of the torque transmitting means into account a more accurate determination of the load that the drivetrain will be subjected to can be taken into consideration when determining whether to influence the change in transmission of torque.

The expected dynamic torque may be estimated based on a simulation of the drivetrain, e.g. utilising a mathematical representation of the drivetrain, where resulting dynamic torques arising in the drivetrain may be simulated/estimated given relevant input parameters such as a torque being transmitted by the torque transmitting means and/or twisting of drivetrain components. Estimation of torques in the drivetrain is a straightforward act to the person skilled in the art, and so is also the generation of drivetrain representations.

The prediction of the torque may also be based on a request for power from the power source. The request for power influence the static torque that is applied to the drivetrain and may also influence the dynamic torque that may arise when engaging the torque transmitting means, since the static torque produced by the power source may accelerate components.

When influencing the engagement of the torque transmitting means, the influencing may be performed such that a maximum torque being transmitted by the torque transmittable means as a result of the engagement is kept below a predetermined torque limit e.g. until rotating components have been synchronised to an extent where further engagement will not result in a maximum torque exceeding the predetermined torque limit.

Further, engagement of the torque transmitting means can be influenced, e.g. by more slowly engaging the torque transmitting means, such that an acceleration of a rotational speed of at least one powertrain component is kept below an acceleration limit, thereby ensuring that undesired dynamic torque levels do not arise.

The engagement of the torque transmitting means can be arranged to be influenced for as long as otherwise a maximum torque in the drivetrain is expected to exceed the predetermined torque limit.

According to embodiments of the invention, the driver manoeuvrable means comprises a pedal to be manoeuvred by a foot of the driver, for example a clutch pedal or accelerator.

The torque transmitting means may comprise a clutch such as a friction clutch. The torque transmitting means for controlling transmission of torque to/from a power source may also be of other designs. For example, a conventional clutch may be replaced by torque transmitting means comprising one or more electrical machines and suitable gearing, where such other kind of torque transmitting means still may be arranged e.g. between a power source such as an internal combustion engine and a gearbox, e.g. a gearbox comprising distinct gears. With regard to such other torque transmitting means, the gearing may e.g. comprise one or more planetary gears, or other suitable gearing, where the electrical machine(s) and power source such as an internal combustion engine may be arranged in a torque balanced relationship such that when no torque is applied by the electrical machine, this limits the torque that can be transmitted by the power source to the gearbox to essentially zero, and where a higher applied torque by the electrical machine allows a higher transmission of torque from the power source, where the torque that can be applied by the power source may be the torque applied by the electrical machine times a factor. In this embodiment, the vehicle may comprise a power source in the form of an internal combustion engine, while functionality resembling a slipping clutch may be obtained by controlling transmission of torque by the electrical machine.

Driver manoeuvrable means such as a pedal may then be used, where a first end position, such as a released pedal, may represent a request for a high, maximally transmittable torque, similar to a closed clutch, and a second end position, such as depressed pedal, may represent an interrupted transmission, e.g. zero torque, by controlling the electrical machine to deliver e.g. zero torque. The electrical machine may be controlled to provide varying transmittable torque to/from the power source in dependence of the position of the driver manoeuvrable means. The driver may in addition control speed of rotation of the power source through the use of simultaneous operation of an accelerator. Solutions of this kind allows different speeds of rotation of the power source and gearbox input shaft, where the speeds of rotation will be brought into synchronism as higher torque is applied. Solutions of this kind may e.g. be used when embodiments of the invention are implemented in hybrid vehicles, such as electric hybrid vehicles.

Further, as is appreciated by the person skilled in the art, torque transmitting means such as clutches and other means may be of various designs, and the particular design, e.g. whether the clutch is a friction clutch or not, is not of relevance to the present invention. The present invention may be applicable in any system providing clutch-by-wire functionality, irrespective of whether an actual clutch is present.

It will be appreciated that the embodiments described in relation to the method aspect of the present invention are all applicable also for the system aspect of the present invention. That is, the system may be configured to perform the method as defined in any of the above described embodiments. Further, the method may be a computer implemented method.

Further characteristics of the present invention and advantages thereof are indicated in the detailed description of exemplary embodiments set out below and the attached drawings.

Brief description of the drawings Fig. 1A illustrates a powertrain of an exemplary vehicle; Fig. 1B illustrates an example of a control unit in a vehicle control system; Fig. 1C illustrates a clutch pedal of the exemplary vehicle of Fig. 1A.

Fig. 2 illustrates an exemplary method according to embodiments of the invention.

Fig. 3 illustrates an exemplary clutch pedal characteristic of a vehicle in which the present invention can advantageously be utilised.

Figs. 4A-D illustrates arising and limitation of dynamic torque in a drivetrain.

Detailed description of exemplary embodiments As has been explained above, according to embodiments of the invention, it is detected if a change in torque to be transmitted by the drivetrain is demanded by driver manoeuvrable means, where the driver manoeuvrable means may e.g. be means controlling torque transmitting means or e.g. an accelerator for requesting torque from a power source. Embodiments of the invention will, however, be exemplified below primarily with reference to a demand for change of torque to be transmitted by the drivetrain using torque transmitting means. The examples may in an analogous manner be applied when requesting a change for torque to be delivered by a power source, e.g. when torque transmitting means such as a clutch, if present, are closed.

Further with regard to torque transmitting means, as was mentioned above, embodiments of the invention are applicable not only to systems comprising a clutch but to any kind of system where controllable torque transmitting means are used to control transmission of torque to and/or from a power source using driver manoeuvrable means. As was further mentioned above, such systems may e.g. include systems where an electrical machine and gearing are used to replace functionality of a conventional clutch, e.g. in electric hybrid vehicles.

However, in the following detailed description, for reasons of simplicity, embodiments of the invention are exemplified for a system where a clutch is controlled by driver manoeuvrable means. Furthermore, the driver controllable means for controlling a clutch is exemplified by a clutch pedal in the following detailed description. The present invention is, however, applicable for any kind of driver controllable means for controlling a clutch, where the driver controllable means is movable in a movement region.

Fig. 1A schematically depicts a powertrain of an exemplary vehicle 100. The powertrain comprises a power source, in the present example a combustion engine 101, which, in a conventional manner, is connected via an output shaft of the combustion engine 101, normally via a flywheel 102, to a gearbox 103 via a clutch 106. An output shaft 107 from the gearbox 103 propels drive wheels 113, 114 via a final drive 108, such as a common differential, and drive axles 104, 105 connected to said final drive 108.

The combustion engine 101 is controlled by a vehicle control system via a control unit 117. The clutch 106 and gearbox 103 are also controlled by the vehicle control system by means of a control unit 116. According to the present example, the clutch comprises a dry clutch where a friction element (disc) 110 is connected to, and rotates with, a first gearbox element, e.g. an input shaft 109 of the gearbox 103. The friction element 110 selectively engages the flywheel 102, or any other suitable rotating part of the combustion engine 101 , to transmit torque to/from the combustion engine 101, i.e. between combustion engine 101 and powertrain components downstream of the clutch 106, such as to/from at least one of the drive wheels 113, 114 via the gearbox 103.

The engagement of the friction element 110 with the engine flywheel 102 is controlled by means of a pressure plate 111 by means of a lever arm 112, which is manoeuvred by a clutch actuator 115.

In fully mechanical systems where the clutch is controlled directly by means of a clutch pedal, the clutch pedal is mechanically linked to the clutch. For example, the clutch pedal can be mechanically linked to the lever arm in order to directly control movement of the friction element. That is, a movement of the clutch pedal is mechanically linked to the clutch, and a movable clutch element, such as friction element moves in synchronism with the clutch pedal. It is to be understood that the exemplified clutch is merely an example, and that clutches, irrespective of whether the clutch constitutes part of a clutch-by-wire system or is controlled mechanically by driver controllable means, may be of various designs. For example, the clutch actuator may be arranged coaxially with the gearbox input shaft.

According to clutch-by-wire systems, such as the presently exemplified system, opening and closing of the clutch 106 may be controlled by the driver using driver manoeuvrable means such as a clutch pedal 118. In this case, however, the clutch pedal does not directly control the influence of the clutch actuator 115 on the lever arm 112 by a mechanical link. Instead, the clutch is controlled by the vehicle control system in dependence of one or more signals representing the clutch pedal 118 position.

Since the actual movement of the lever arm 112 is not mechanically linked to the clutch pedal 118 this means, in turn, that the clutch pedal 118 position, instead, is used as a request for a particular transmittable torque, e.g. represented by clutch friction element/actuator position, which is then, by means of the vehicle control system, translated into an actual clutch movement via the clutch actuator 115. Hence actual manoeuvring of the clutch, i.e. the positioning of the lever arm 112 in the present example, is performed by the vehicle control system when the clutch is driver controlled, where this manoeuvring is dependent on the clutch pedal 118 position.

However, since the actual manoeuvring is under the control of the vehicle control system, this allows that the clutch may also be controlled by the vehicle control system completely independent from the clutch pedal. The clutch may hence be controlled according to different modes, where actual clutch movement is always performed by the vehicle control system, but where the movement in a driver controlled mode is performed on the basis of signals representing the position of the clutch pedal, and in an automatic mode clutch movement is performed independently from the current position of the clutch pedal.

An exemplary clutch pedal 118 is schematically shown in Fig. 1C. The clutch pedal 118 is movable within a movement region defined by two end positions A, B, defining an angular range a. The clutch pedal 118 position in said movement region can be determined, e.g. by means of a suitable sensor, such as, a potentiometer or an angle sensor 119 or any other suitable kind of sensor which determines the current position of the clutch pedal 118 in the movement region in which the clutch pedal is movable. When the clutch pedal 118 is fully released, i.e. not manoeuvred by the driver, it is in a state of rest in position A, e.g. by means of a spring force, where position A represents a fully closed clutch. Position B represents a fully depressed clutch pedal and hence a fully open clutch. Fig. 1A also discloses an accelerator pedal 130 by means of which the driver requests power from the internal combustion engine 101.

As was mentioned above, the clutch may be controlled in dependence of the clutch pedal (driver manoeuvrable means). However, an advantage of clutch-by-wire systems is that the clutch may also be controlled by the vehicle control system independently from the clutch pedal. This is also oftentimes utilized, e.g. to allow the vehicle to be driven as a two pedal (accelerator, brake pedal) vehicle if so desired, where the clutch pedal can be used to provide additional control as was described above. According to embodiments of the invention, it is provided a method and system that may provide additional safety against harmful engagements of the torque transmitting means from arising and/or increase driver comfortability when engaging torque transmitting means. An exemplary method 200 of the present invention is shown in Fig. 2, which method can be implemented at least partly e.g. in the control unit 116 for controlling the clutch 106 and gearbox 103. As indicated above, the functions of a vehicle are, in general, controlled by a number of control units, and control systems in vehicles of the disclosed kind generally comprise a communication bus system consisting of one or more communication buses for connecting a number of electronic control units (ECUs), or controllers, to various components on board the vehicle. Such a control system may comprise a large number of control units, and the control of a specific function may be divided between two or more of them.

For the sake of simplicity, Fig. 1A depicts only control units 116-117, but vehicles 100 of the illustrated kind are often provided with significantly more control units, as one skilled in the art will appreciate. Control units 116-117 are arranged to communicate with one another and various components via the communication bus system and other wiring, partly indicated by interconnecting lines in Fig. 1A.

Embodiments of the invention may be implemented in any suitable control unit in the vehicle 100, and hence not necessarily in the control unit 116. The control of the clutch 106 according to embodiments of the invention will usually depend on signals being received from other control units and/or vehicle components, and it is generally the case that control units of the disclosed type are adapted to receive sensor signals from various parts of the vehicle 100. The control unit 116 may, for example, receive signals from clutch pedal position sensor 119 and clutch actuator 115. Further, the control unit may receive signals representing driver request for power from the internal combustion engine, such as by means of the accelerator pedal 130. The control unit may also receive signals e.g. with regard to a speed of rotation of the gearbox input shaft 109 and/or other signals from which speeds of rotation of drivetrain components may be determined. Control units of the illustrated type are also usually adapted to deliver control signals to various parts and components of the vehicle, e.g. to control the clutch actuator 115.

Control of this kind is often accomplished by programmed instructions. The programmed instructions typically comprise a computer program which, when executed in a computer or control unit, causes the computer/control unit to exercise the desired control, such as method steps according to the present invention. The computer program usually constitutes a part of a computer-readable medium, wherein said computer-readable medium comprises a suitable storage medium 121 (see Fig. IB) with the computer program 126 stored on said storage medium 121. The computer program can be stored in a non-volatile manner on said storage medium. The digital storage medium 121 can, for example, comprise any of the group comprising: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk unit etc., and be arranged in or in connection with the control unit, whereupon the computer program is executed by the control unit. The behaviour of the vehicle in a specific situation can thus be adapted by modifying the instructions of the computer program.

An exemplary control unit (the control unit 116) is shown schematically in Fig. 1 B, wherein the control unit may comprise a processing unit 120, which may comprise, for example, any suitable type of processor or microcomputer, such as a circuit for digital signal processing (Digital Signal Processor, DSP) or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC). The processing unit 120 is connected to a memory unit 121, which provides the processing unit 120, with e.g. the stored program code 126 and/or the stored data that the processing unit 120 requires to be able to perform calculations. The processing unit 120 is also arranged so as to store partial or final results of calculations in the memory unit 121.

Furthermore, the control unit 116 is equipped with devices 122, 123, 124, 125 for receiving and transmitting input and output signals, respectively. These input and output signals may comprise waveforms, pulses or other attributes that the devices 122, 125 for receiving input signals can detect as information for processing by the processing unit 120. The devices 123, 124 for transmitting output signals are arranged so as to convert calculation results from the processing unit 120 into output signals for transfer to other parts of the vehicle control system and/or the component (s) for which the signals are intended. Each and every one of the connections to the devices for receiving and transmitting respective input and output signals may comprise one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Oriented Systems Transport) or any other bus configuration, or of a wireless connection.

Returning to the exemplary method 200 illustrated in Fig. 2, the method starts in step 201. As was mentioned above, embodiments of the invention relate to a method and system having an aim to reduce the risk of harmful torques arising in the drivetrain when engaging torque transmitting means such as a clutch. In addition, driver comfortability may be increased. The method according to embodiments of the invention may be arranged to be carried out only if the speed of the vehicle is below some predetermined speed, or when the vehicle is standing still. In such situations excessive torques may more frequently arise from engagement of the torque transmitting means. This is because large differences in speed of rotation of drivetrain components may prevail at low vehicle speeds and/or when the vehicle is standing still. However, high dynamic torques may also arise irrespective of vehicle speed e.g. when there is a step in the transmittable torque of the torque transmitting means. According to embodiments of the invention, the method is always carried out when detecting a demand for engaging the clutch 106.

In step 201 it is determined whether the torque transmitting means, in this case the clutch 106, is disengaged. According to embodiments of the invention, it is required that the clutch 106 is fully open, i.e. the transmission of torque is completely interrupted such as when friction plate 110 does not contact flywheel 102. According to embodiments of the invention, the method is carried out when there is a difference in speed of rotation over the clutch 106. The method remains in step 201 for as long as this is not the case, while the method continues to step 202 when the clutch 106 is disengaged.

In step 202 it is determined whether an engagement of the clutch 106 is demanded. If this is not the case, the method returns to step 201 while the method continues to step 203 when an engagement is demanded. Whether or not an engagement of the clutch is demanded may be detected, for example, by detecting a movement of the clutch pedal 118 from the position B (Fig. 1C) representing a complete interruption of the transmission of torque towards the position A representing a request for a full transmissibility of torque, i.e. representing a closed drivetrain. The movement may further be detected by the vehicle control system monitoring an electrical signal representing the position of the clutch pedal 118. As was mentioned, it may be required that a clutch motion from a fully open position is detected, but it may also be sufficient that a motion is detected from any position towards position A, for as long as there is a difference in speed of rotation over the clutch, i.e. no or limited torque is transmittable by the clutch, since when the clutch is capable of transmitting higher torques than currently is being transmitted by the drivetrain there will be no difference in speed of rotation between internal combustion engine and gearbox input shaft.

In step 203 it is determined whether the engagement of the torque transmitting means is to be influenced. As was mentioned, the engagement of the clutch may be arranged to always be influenced, while according to embodiments of the invention the engagement of the clutch 106 may be arranged to be influenced only when some criteria is fulfilled.

For example, engagement of the clutch 106 may be arranged to be influenced only if it is determined that the engagement of the clutch will give rise to potentially harmful torque levels in the drivetrain. In step 203, therefore, a representation of the torque that is expected to arise in the drivetrain if engaging the clutch according to the driver request may be predicted in order to determine whether the torque is likely to exceed a limit that is considered to potentially be harmful.

When the clutch 106 is open there is no ongoing transmission of torque since the transmission of torque is interrupted. If the vehicle 100 is standing still the internal combustion engine output shaft, and thereby flywheel 102, will rotate at the current speed of rotation of the internal combustion engine 101. The gearbox input shaft 109, on the other hand will, at least if gears are engaged, be standing still. This also applies to the propeller shaft 107 and drive shafts 104, 105. If the driver then suddenly removes the foot from the clutch pedal 118, or otherwise attempts to close the clutch in a manner such that transmittable torque of the clutch 106 rapidly increases, e.g. by rapidly releasing the clutch pedal 118, this will impose a torque load that not only comprises any static torque produced by the internal combustion engine, i.e. work produced by injection of fuel, but which to a large extent, or even primarily, will consist of a dynamic torque.

The dynamic torque is generated by acceleration of the drivetrain/powertrain components. The acceleration may arise when differing speeds of rotation of the flywheel and gearbox input shaft are brought into synchronisation as the clutch engages and transmittable torque of the clutch increases. For example, if the internal combustion engine is rotating at one speed, and the gearbox input shaft is rotating at another, these speeds of rotation will forcedly be brought into synchronism when the clutch closes. If the clutch closes rapidly, the acceleration will be high, thereby giving rise to a high torque. In the present example, if the clutch is suddenly closed, the internal combustion engine will be braked by the still standing drivetrain, thereby being subjected to a high negative acceleration when the internal combustion engine strives to set the vehicle in motion by twisting and accelerating the gearbox input shaft. Similarly, drivetrain components may be accelerated when the request for torque from the power source rapidly changes, e.g. by the driver suddenly depresses or releases an accelerator. Accelerations of drivetrain components may result in a high dynamic torque being applied to the drivetrain. The size of the dynamic torque will depend on the moment of inertia of rotating/moving parts of the internal combustion engine, which may be substantial.

The dynamic torque caused by the moment of inertia and acceleration of a drivetrain component may be determined as: Image available on "Original document" Where ? is the acceleration of the drivetrain component, and J is the moment of inertia, e.g. of the component being accelerated. The dynamic torque can be determined for drivetrain components downstream of the clutch when such are being accelerated. If the acceleration is high, the resulting dynamic torque may be high, and may exceed the maximum torque for which the drivetrain is designed, thereby potentially harming drivetrain components.

In step 203, therefore, at least the arising dynamic torque may be estimated. This may be accomplished in any suitable manner. Factors such as moment of inertia are in general well known for the components of the drivetrain and internal combustion engine, and as was mentioned above, the dynamic torque caused by the moment of inertia and acceleration of one or more drivetrain components may be estimated based on a mathematical representation of the drivetrain, where resulting dynamic torques may be estimated given relevant input parameters that may also take into account twisting and torque applied by the vehicle drive wheels that may counteract rotation and give rise to oscillations as illustrated below. For example, if there is an indication that there will be a sudden increase in transmittable torque of the clutch, e.g. determined by monitoring the movement of the clutch pedal, the predicted increase in transmittable torque may be used to estimate the dynamic torques that arise as a consequence.

For as long as the transmittable torque is maintained low, a high difference in speed of rotation over the clutch may be maintained, and thereby also keeping acceleration of drivetrain components limited. If, however, transmittable torque is increased at a high rate, such as by suddenly releasing the clutch pedal, a high acceleration may be inevitable and high dynamic torques thereby arise.

This is illustrated in figs. 4A-D. In fig. 4A dashed line 401 illustrates a step increase in transmittable torque of the clutch. According to the illustrated situation, the vehicle is standing still and the torque increase is insufficient to overcome the driving resistance, i.e. torque applied by the drive wheels, and set the vehicle in motion. Hence the vehicle will continue to be standing still in spite of applied torque. Line 402 illustrates the resulting dynamic torque that arises on the gearbox input shaft from the sudden increase in torque. As can be seen from fig. 4A the dynamic is considerably higher than the torque that is actually applied to the gearbox input shaft by the internal combustion engine, which is delimited by the currently transmittable torque of the clutch. Figure 4B illustrates the gearbox input shaft acceleration that gives rise to the dynamic torque, starting from zero since the vehicle is at stand still. Since the applied torque is insufficient to overcome the driving resistance the acceleration caused by the step in transmittable torque twists the gearbox input shaft, giving rise to an oscillating acceleration and thereby oscillating dynamic torque. In this way, due to the sudden increase in torque, harmful torque levels may arise. As was mentioned the arising dynamic torques may be estimated from a mathematical representation of the drivetrain in combination with relevant input parameters. This may be performed e.g. when clutch manoeuvring is detected, but according to embodiments of the invention harmful situations may be identified beforehand e.g. in the vehicle development stage in which case the vehicle control system need not perform any actual estimations of the torque that arises but instead the vehicle control system may identify situations that may give rise to harmful torque levels. For example, simulations beforehand may have identified situations which may give rise to harmful dynamic torques, and when such situations are identified and actions may be taken according to the invention. These actions may include a limitation of the rate at which transmittable torque of the clutch is increased.

Figure 4C illustrates the situation of figure 4A but where instead the increase 404 in transmittable torque is controlled according to embodiments of the invention to occur more slowly, i.e. the rate of change is reduced. That is, the clutch is closed at a slower rate than the driver demands. As can be seen from figure 4D there is substantially no acceleration 406 of the gearbox input shaft and the resulting drivetrain torque 405 substantially corresponds to the torque increase and hence the load on the drivetrain is reduced. Consequently, according to embodiments of the invention, sudden/fast closings of the clutch may be prohibited and transmittable torque be arranged to increase more slowly. Various potentially harmful driver behaviours may be identified e.g. through simulations beforehand, and when the control system identifies the possible arising of such a situation closing of the clutch may be influenced.

When and to which extent the clutch will engage may be determined e.g. through the use of a clutch characteristic. Fig. 3 illustrates an example of a characteristic Pchar1for an exemplary clutch of a kind that may be used in a vehicle of Fig. 1 A. The y-axis denotes transmittable torque T, i.e. the torque that the clutch 106 can transmit between combustion engine 101 and gearbox 103 input shaft. In general, with regard to clutch characteristics, the x-axis denotes clutch position, such as clutch actuator position and/or lever arm position. The x-axis may also represent clutch pedal 118 position.

The origin, “0”, represents the clutch open position, i.e. a position where the clutch pedal 118, and usually friction element (the lever arm/the clutch actuator) is at its one extreme position, position B in Fig. 1C. This corresponds to a fully depressed clutch pedal 118, and the friction element 110 being completely disconnected from the combustion engine 101, i.e. being positioned to the right as in Fig. 1A. Conversely, the “closed clutch” position represents a fully released clutch pedal. That is, position A in Fig. 1C, and the friction element 110 being as close to the flywheel as possible and thereby pressed against the flywheel, for example by the aid of a spring action.

Tmax represents the maximum torque that can be transmitted. The friction element 110, when the clutch is fully open, is normally at a distance from the engine's flywheel so that closing of the clutch involves the friction element, and hence the clutch pedal, initially moving a distance x1 before actually contacting the flywheel. Once the friction element precisely contacts the flywheel, at the contact point CP, torque transfer between the engine and rest of the powertrain can commence. The more the clutch closes from this point (i.e the more strongly the friction element 110 engages the flywheel 102, the more torque can be transmitted over the clutch 106.

Hence, a characteristic of the kind shown in fig. 3 may be used to determine when the clutch will engage, and also the manner in which transmittable torque will change as the clutch closes. The speed at which the clutch pedal closes may be monitored, e.g. from the signals representing clutch pedal position, and thereby it may also be identified, e.g. through the use of a characteristic according to fig. 3, or simply through the use of the manoeuvring of the driver manoeuvrable means, potentially harmful situations. For example, if a speed of closing of the clutch is estimated based on the ongoing clutch motion, and closing may be presumed to continue at the same speed and the resulting drivetrain torque may be predicted for a period of time t, and if the torque at any point during this time t exceeds a torque limit it may be determined that the closing of the clutch is to be influenced. A delay in the actual controlling of the clutch according to the driver demand may be imposed to allow the determination to be made.

Hence, if it is determined in step 203 that the engagement of the torque transmitting means is to be influenced, the method continues to step 204. Otherwise the method may continue to step 207 where it is determined if the clutch is closed. The method may then be arranged to return to step 203 for as long as this is not the case. In this way it can be ensured that the closing of the clutch may be influenced in situations where at first no influence is required, but where it may be determined later in the closing of the clutch that influencing is in fact required, e.g. because the driver suddenly increases the speed of closing the clutch. When the clutch has closed the method can be ended in step 206.

In step 204 it is determined a suitable control of the engagement of the clutch, where the clutch preferably is controlled such that the clutch closes at a slower speed than requested by the driver manoeuvrable means, e.g. as illustrated with reference to figs 4A-D. The control of the clutch 106 when being influenced according to the method is also commenced in step 204. This influence may be accomplished by controlling the clutch actuator / friction plate differently from the control that is requested by the clutch pedal, so that the clutch closes as if the clutch pedal had been released more slowly.

As was explained above, a slower closing of the clutch will result in a slower increase in transmittable torque and the gearbox input shaft will accelerate more slowly.

Hence, the speed of rotation of the gearbox input shaft may be brought into synchronism in a more controllable manner, giving rise to less acceleration of components and thereby less dynamic torque.

Furthermore, potentially harmful driver behaviour using the accelerator may also be identified e.g. beforehand in which case similar measures may be taken. With regard to dynamic torques arising from sudden changes in the request for torque from the vehicle power source, such as an internal combustion engine, the drivetrain may be protected by reducing the rate of change in comparison to the driver demand but also by controlling the clutch such that at most a predetermined torque can be transmitted, since the internal combustion engine cannot apply a higher torque to the drivetrain downstream the clutch than the clutch currently can transmit. Furthermore, the clutch may be maintained at least partly open, i.e. with a reduced transmittable torque until the vehicle 100 has been set in motion to an extent giving a gearbox input shaft speed of rotation essentially corresponding to the speed of rotation of the internal combustion engine 101 so that the clutch 106 may be closed without giving rise to undesired changes, such as an increase to an undesired torque level, in the transmission of torque.

In step 205 it is determined whether influence of the engagement of the clutch 106 is to be continued, e.g. in case the clutch 106 is still not engaged and/or because the difference in speed of rotation over the clutch 106 is still above some predetermined threshold that may result in undesired acceleration if the clutch 106 is abruptly closed. If influence of the engagement of the clutch is to be continued, the method may e.g. return to step 204, where the control may be adjusted if required, e.g. by increasing transmittable torque. If it is determined that the speed of rotation of the internal combustion engine no longer is to be influenced, e.g. due to the clutch having engaged, the method is ended in step 206. According to embodiments of the invention, consequently, the clutch 106 may be arranged to close more slowly than requested by the driver to thereby reduce the risk for undesired situations arising.

Furthermore, as was stated above, embodiments of the invention are applicable also when the torque transmitting means is of designs other than a clutch, such as torque transmitting means comprising one or more electrical machines and suitable gearing. Designs of this kind may provide functionality of a clutch, where such functionality may be controlled by driver manoeuvrable means e.g. in the form of a pedal. An example of a system of this kind is disclosed in the International application PCT/SE16/050538, with the title “A drive system for a vehicle" and having the same applicant as the present application. This referenced application is incorporated herein by reference.

In systems of this kind, an internal combustion engine may e.g. be connected to a gearbox input shaft through a planetary gearing, where an electrical machine is also connected to the planetary gearing. The internal combustion engine may be connected e.g. to a sun gear of the planetary gearing, while the gearbox may be connected to a carrier, and the electrical machine is connected to a ring gear.

According to solutions of the referenced application, the internal combustion engine may be rotating independently from the speed of rotation of the gearbox input gear. Further, the electrical machine and the internal combustion engine may be arranged in a torque balanced relationship such that when no torque is applied by the electrical machine, this limits the torque that may be transmitted by the internal combustion engine to zero.

When applied torque is increased by the electrical machine, a higher torque may be transmitted by the internal combustion engine to the gearbox input shaft, and the higher the transmission of torque the closer the speeds of rotation will be. When the electrical machine applies a torque equal to or exceeding the torque that will be transmitted by the drivetrain the speeds of rotation of the internal combustion engine and gearbox will be in synchronisation.

Consequently, the increase in transmittable torque may be influenced according to embodiments of the invention also in systems of this kind when engaging the torque transmitting means, such as by controlling an increase in the torque applied by the electrical machine in response to e.g. a driver manoeuvred pedal that provides functions similar to that of a clutch pedal in a manner that more slowly increases the torque applied by the electrical machine. The vehicle may be a hybrid vehicle, such as an electric hybrid vehicle, or any other kind of vehicle having torque transmitting means of this kind.

Embodiments of the invention may also be utilised in systems where an electrical machine is connected to e.g. a gearbox input shaft and where an accelerator controls a demand for torque from the electrical machine. A change in demand for torque from the electrical machine using the accelerator may be influenced according to the above.

Finally, embodiments of the invention have been described above mainly for a particular example of a vehicle, but is applicable for any vehicle in which driver manoeuvrable means are used to control torque transmitting means. The torque transmitting means may be of any suitable kind comprising any kind of elements, such as a clutch or other kind of solution, for as long as the manoeuvring of the torque transmitting means may be accomplished independently from the manoeuvring of the driver manoeuvrable means.

Claims

1. Method for controlling transmission of torque in a vehicle (100), the vehicle (100) including: a drivetrain for transmitting torque between a power source (101) and at least one drive wheel of the vehicle (101), and driver manoeuvrable means (118), wherein torque to be transmitted by the drivetrain is controllable in dependence of an electrical signal representing a position of the driver manoeuvrable means (118), the method including: - detecting if a change in torque to be transmitted by the drivetrain is demanded by means of the driver manoeuvrable means (118), - predicting a torque that is expected to arise in the drivetrain if controlling the change in transmission of torque as demanded by the driver manoeuvrable means (118), and - influencing the change in transmission of torque of the drivetrain based on said prediction to reduce the risk for excessive load in the drivetrain.

2. Method according to claim 1, - wherein the influencing comprises limiting a rate of change of an increase or decrease in transmission of torque of the drivetrain.

3. Method according to claim 1 or 2, - wherein the prediction is based on the signal representing the position of the driver manoeuvrable means.

4. Method according to any one of the preceding claims, wherein the prediction is based on a simulation and/or mathematical representation of the drivetrain.

5. Method according to any one of the preceding claims, - wherein the prediction comprises comparing the demanded change in torque to be transmitted by the drivetrain with at least one predetermined demand, and - influencing the change in transmission of torque of the drivetrain based on said comparison.

6. Method according to any one of the preceding claims, wherein the prediction comprises estimating if the torque expected to arise in the drivetrain will exceed a predetermined torque limit, and wherein the change in transmission of torque is influenced if said estimation indicates that the predetermined torque limit will be exceeded.

7. Method according to any one of the preceding claims, wherein: - estimating the torque that is expected to arise in the drivetrain as a torque at least partly comprising a dynamic torque that is expected to arise if changing the torque to be transmitted as demanded by the driver manoeuvrable means (118).

8. Method according to any one of the preceding claims, further including: - estimating a maximum torque that is expected to arise in the drivetrain if changing the transmission of torque as demanded by the driver manoeuvrable means (118) during a period of time T following said detection, and - influencing the change in transmission of torque based on the estimated maximum torque.

9. Method according to any one of the preceding claims, the vehicle including torque transmitting means (106) for selectively transmitting torque between the power source (101) and the at least one drive wheel of the vehicle (100), wherein transmittable torque of the torque transmitting means (106) is controllable in dependence of the electrical signal representing a position of the driver manoeuvrable means (118), wherein the detection comprises detecting if a change in torque to be transmitted by the drivetrain is demanded by means of the driver manoeuvrable means (118), and the influencing comprises influencing the engagement of the torque transmitting means (106) based on the prediction.

10. Method according to claim 9, wherein influencing engagement of the torque transmitting means (106) comprises delaying and/or reducing the rate of increase of transmittable torque of the torque transmitting means (106) in relation to the rate of increase of transmittable torque if engagement would be controlled as demanded by the driver manoeuvrable means (118).

11. Method according to claim 9 or 10, wherein engagement of the torque transmitting means is influenced such that an acceleration of a rotational speed of at least one powertrain component is kept below an acceleration limit.

12. Computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of the preceding claims.

13. Computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of the claims 1-11.

14. System for controlling transmission of torque in a vehicle (100), the vehicle (100) including: a drivetrain for transferring torque between a power source (101) and at least one drive wheel of the vehicle (101), and driver manoeuvrable means (118), wherein torque to be transmitted by the drivetrain is controllable in dependence of an electrical signal representing a position of the driver manoeuvrable means (118), the system including: - means configured to detect if a change in torque to be transmitted by the drivetrain is demanded by means of the driver manoeuvrable means (118), - means configured to predict a torque that is expected to arise in the drivetrain if controlling the change in transmission of torque as demanded by the driver manoeuvrable means (118), and - means configured to influence the change in transmission of torque of the drivetrain based on said prediction to reduce the risk for excessive load in the drivetrain.

15. Vehicle comprising a system according to claim 14.