SE540472C2

SE540472C2 - Method and system for controlling a clutch of a vehicle

Info

Publication number: SE540472C2
Application number: SE1550533A
Authority: SE
Inventors: Jarngren Fredrik; Gustafsson Erik
Original assignee: Scania Cv Ab
Priority date: 2015-04-30
Filing date: 2015-04-30
Publication date: 2018-09-18
Also published as: DE102016004799A1; SE1550533A1

Abstract

The invention relates to a method for controlling a clutch (106) of a vehicle (100) comprising driver manoeuvrable means (118), e.g. a clutch pedal, manoeuvring the clutch and being movable between a first end position (A) and a second end position (B). Transmittable torque of said clutch (106) is controlled on the basis of the position of said driver manoeuvrable means (118). The method includes, for a plurality of different magnitudes of at least one force forming at least part of the driving resistance (F) of said vehicle (100):- controlling said clutch (106) such that transmittable torque of at least one position in a first portion (ΔX) of said movement region (A-B) of said driver controllable means (118) gives rise to a propelling force on the vehicle drive wheels (113, 114) substantially corresponding to the magnitude of said at least one force (F).

Description

METHOD AND SYSTEM FOR CONTROLLING A CLUTCH OF A VEHICLE Field of the invention The present invention relates to vehicles, and in particular to a method and system for controlling a clutch of a vehicle. The present invention also relates to a vehicle, as well as a computer program and a computer program product 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 completely 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. Clutches can also be used in automated manual transmissions, in which case clutch operation 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 still present and used e.g. when starting the vehicle from standstill. When the vehicle has been set in motion, use of the clutch in subsequent changes of gear can be controlled completely by the vehicle control system without driver interaction .

Irrespective of the particular kind of transmission being used driver comfortability is oftentimes an aspect of interest when designing a vehicle powertrain. For example, it is essential that the vehicle behaves as expected by the driver when being driven on roads.

Such vehicle behaviour can relate to various different aspects and, for example, relate to the manner in which the vehicle behaves when performing a start from standstill and when being manoeuvred with high precision, e.g. when manoeuvring the vehicle to and from loading docks/loading bays. Situations of this kind often involve operation of a clutch, and it is essential that the clutch transmits torque in an expected manner so that the vehicle thereby also behaves as expected by the driver.

Summary of the invention It is an object of the present invention to provide a method and system that facilitates clutch operation in particular when starting a vehicle from standstill and when operating the vehicle at low speeds. This object is achieved by a method according to claim 1.

According to the present invention, it is provided a method for controlling a clutch of a vehicle, the vehicle including a clutch for selectively transmitting torque to and/or from a first power source, said vehicle further including driver manoeuvrable means for manoeuvring a clutch, said driver manoeuvrable means being movable in a movement region between a first end position and a second end position, transmittable torque of said clutch being controlled by a vehicle control system on the basis of the position of said driver manoeuvrable means in said movement region. The method includes, for a plurality of different magnitudes of at least one force forming at least part of the driving resistance of said vehicle: - controlling said clutch on the basis of the position of said driver manoeuvrable means in said movement region in dependence of the magnitude of said at least one force, further including: - controlling said clutch such that transmittable torque of at least one position in a first portion of said movement region of said driver controllable means gives rise to a propelling force on the vehicle drive wheels substantially corresponding to the magnitude of said at least one force.

The driver manoeuvrable means can, for example, be a clutch pedal. The magnitude of said at least one force can be an estimated magnitude, and according to one embodiment of the invention the estimation of the magnitude of said at least one force is part of the method according to the invention.

Likewise, a device according to the invention can be arranged to perform the estimation. According to one embodiment said at least one force is represented by the vehicle driving resistance.

As was mentioned above, it is important that vehicles behave as expected by the driver, e.g. in situations when manoeuvred through the use of a clutch. For example, when manoeuvring a vehicle in places where space is limited, the manoeuvring of the vehicle often involve a number of driver controlled openings and closings of the clutch. It is also important that the vehicle behaves as expected e.g. when performing a start from standstill. Manoeuvring in situations according to the above often involves a partially open clutch, i.e. the clutch is slipping. That is, the output shaft of the power source (e.g. a combustion engine) rotates at a different speed than the gearbox input shaft, and hence the clutch is only partially engaged.

When the clutch is slipping part of the work produced by the power source is dissipated over the clutch, usually in the form of friction losses. The clutch slip, consequently, allows the vehicle to be propelled at lower speeds than would otherwise be possible, and hence facilitates manoeuvring at higher accuracy.

However, clutch plates often engage and disengage in a nonlinear manner, i.e. the clutch has a non-linear characteristic. That is, the relation between transmittable torque and position of the movable clutch element(s) being used to control the transmittable torque is not linear.

Manoeuvring of the clutch in a desired manner can therefore still be difficult due to this non-linearity, e.g. in order to transmit precisely the amount of torque that is required to propel the vehicle in a manner intended by the driver in order to avoid unexpected accelerations/decelerations. Also, the driving conditions may vary substantially from one situation to another, e.g. having as result that the required torque to be transmitted by the clutch e.g. to overcome the driving resistance may differ to a great extent from one situation to another.

Correspondingly, this means that actual clutch pedal movement, e.g. when setting a vehicle in motion, may vary substantially in dependence of the current driving resistance. Such variations are increased due to the non-linearity according to the above. The driving resistance represents the resultant force that must be overcome in order to accelerate the vehicle and/or set the vehicle in motion from standstill. The driving resistance may vary substantially from one situation to another, e.g. in dependence on vehicle speed, load (vehicle mass) and road inclination.

Oftentimes the operation of the clutch, such as the manoeuvring of a clutch friction element, and hence the engagement of the clutch, is controlled by driver manoeuvrable means such as a clutch pedal that is mechanically linked to the clutch movable elements. This means that the clutch operation is constrained by the characteristics of the mechanical linkage.

The present invention, however, relates to systems where the driver manoeuvrable means is not used to control the clutch directly through the use of a mechanical linkage, but, instead, clutch-by-wire systems. In clutch-by-wire systems an electrical signal representing e.g. a clutch pedal position is translated into a corresponding clutch movement. For example, a position sensor or other suitable means can 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 clutch operation, and the vehicle control system controls the actual clutch movement on the basis 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.

In general, from a driver perspective, a clutch-by-wire system behaves in a manner similar to systems having a mechanical linkage according to the above, but clutches of this kind can also be controlled fully automatically by the vehicle control system, e.g. in automated manual transmissions (AMT).

According to the present invention, it has been realized that drivability with regard to operation of the clutch can be improved in vehicles having a clutch-by-wire system.

According to the present invention, this is accomplished by the use of a method which changes the dependency between the position of the driver manoeuvrable means and resulting transmittable torque of the clutch. The dependency is changed such that a particular position of the driver manoeuvrable means, e.g. a particular clutch pedal position, is arranged to correspond to a propelling force on the drive wheels that substantially or precisely meet said at least one force forming part of the vehicle driving resistance, such as e.g. the current driving resistance. According to one embodiment said position can be any position in a specific portion of the movement region, This is further arranged to be fulfilled for a plurality of magnitudes of the at least one force (driving resistance). That is, the current driving resistance may be arranged to always be met by a corresponding transmittable torque at the same clutch pedal position irrespective of the actual magnitude of the driving resistance.

According to one embodiment, the dependency is arranged such that the transmittable torque of the clutch of said particular position is arranged to always correspond to the current driving resistance of the vehicle. The driver controllable means for controlling a clutch is, in general, movable in a movement region between a first end position and a second end position, where the opening/closing of the clutch is dependent on the position of said driver controllable means.

Consequently, according to the present invention, the said particular position of the driver manoeuvrable means will result in different transmittable torques in dependence of the variations in driving resistance.

Consequently, the driver of the vehicle can always be aware of e.g. the clutch pedal position at which the clutch will transmit a torque corresponding to propelling force corresponding to the current driving resistance. In this way, irrespective of whether the vehicle is e.g. heavily loaded or less heavily loaded, and irrespective of whether the vehicle is starting from standstill on a horizontal surface or in an uphill inclination, one and the same clutch pedal position can be arranged to always, or substantially always, correspond to the driving resistance prevailing at the particular situation. Consequently the driver will always be able to know at which clutch pedal position vehicle motion will begin.

When a vehicle is set in motion from standstill this, unless the vehicle takes off in a downhill slope, in general occurs when the transmittable torque of the clutch gives rise to a vehicle propelling force on the vehicle drive wheels that exceeds the prevailing driving resistance. These forces include rolling resistance, air resistance and influence of the force of gravity. For example, when the driver manoeuvrable means is a clutch pedal, the dependency, such as clutch pedal characteristic, is made to depend on said at least one force forming part of the driving resistance.

According to one embodiment of the present invention, control according to the present invention is only utilized when the driving resistance is such that the driving resistance in itself is not capable of setting the vehicle in motion in the desired direction of travel.

According to one embodiment, the clutch pedal characteristic is further controlled such that variations in transmittable torque as a function of movement of the driver manoeuvrable means is reduced about said position or portion of movement region. In this way, driveability is further improved to the driver.

Further, as is appreciated by the person skilled in the art, clutches 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 is applicable in any clutch-by-wire system.

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 the present invention.

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

Fig. 4A illustrates a first exemplary clutch pedal characteristic according to the present invention.

Fig. 4B illustrates a second exemplary clutch pedal characteristic according to the present invention.

Fig. 5 illustrates a further clutch pedal characteristic according to the present invention.

Detailed description of exemplary embodiments The driver controllable means for controlling a clutch is exemplified for 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.

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 the 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 consists of 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 systems where the clutch 106 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 112 in order to directly control movement of the friction element 110. It is to be understood, however, 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 109.

According to the disclosed system, opening and closing of the clutch 106 may still be controlled by the driver using a clutch pedal 118, however with the difference that the influence of the clutch actuator 115 on the lever arm 112 is controlled by the vehicle control system on the basis of signals representing the clutch pedal 118 position.

That is, the actual movement of the lever arm 112 is no longer 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 clutch operation, which is then, by means of the vehicle control system, translated into an actual clutch movement via the clutch actuator 115. Still, the positioning of the lever arm 112 is dependent on the clutch pedal 118 position.

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 ?. The clutch pedal 118 position in said movement region can be determined, e.g. by means of a suitable sensor, such as, for example, 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.

The present invention takes advantage of the fact that the clutch pedal is not physically linked to the clutch so that the clutch pedal characteristic, i.e. the relationship between clutch pedal position and transmittable torque over the clutch, can be adapted to a particular situation. This is accomplished by controlling the clutch, e.g. by controlling the dependency of the movement of the friction element 110 and/or the lever arm 112 in relation to clutch pedal 118 movement such that transmittable torque of one and the same clutch pedal position always, or at least for a plurality of different situations where different driving resistances prevail, result in a propelling force of the vehicle drive wheels that corresponds, or substantially corresponds, to the vehicle driving resistance. As is explained below, the driving resistance can at least in some instances be considered to be represented by at least one force forming part of the driving resistance, e.g. when this force constitutes a major portion of the driving resistance. 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 said communication bus system and other wiring, partly indicated by interconnecting lines in Fig. 1A.

The present invention can 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 the present 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 normally adapted to receive sensor signals from various parts of the vehicle 100. The control unit 116 will, for example, receive signals from clutch pedal position sensor 119 and clutch actuator 115. Further, the control unit will receive signals representing, or signals from which can be determined, the current driving resistance and/or one or more forces forming part of the current driving resistance, of the vehicle 100. 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 consist of 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 program product, wherein said computer program product 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, consist of 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.1B, wherein the control unit can comprise a processing unit 120, which can consist of, 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 112 is equipped with devices 122, 123, 124, 125 for receiving and transmitting input and output signals, respectively. These input and output signals can 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 can consist of 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, the present invention relates to a method and system where the influence of the clutch pedal (or other suitable means for manoeuvring the clutch) on the clutch is arranged to differ according to at least one force forming part of the current driving resistance of the vehicle 100.

According to the present example, the influence of the clutch pedal is arranged to depend on the magnitude of the driving resistance. In step 201, it is determined whether the characteristic of the clutch pedal 118 is to be controlled according to the current driving resistance. The method remains in step 201 for as long as this is not the case, and continues to step 202 when the clutch pedal characteristic is to be controlled on the basis of the current driving resistance.

The transition from step 201 to step 202 can, for example, be performed each time the vehicle 100 is set in motion, or is about to be set in motion from standstill, such as e.g. when a movement of the clutch pedal in a clutch closing direction is detected. The transition from step 201 to step 202 can also be arranged to take place when the vehicle 100 is in motion and a clutch pedal movement is detected and/or when being manoeuvred through the use of a partially open clutch, i.e. when the clutch is slipping.

According to one embodiment, the method according to the present invention is carried out each time a movement of the clutch pedal is detected, and according to one embodiment each time a movement of the clutch pedal is detected while simultaneously the vehicle speed is below some suitable speed limit, such as e.g. 30 km/h.

In step 202 the current driving resistance of the vehicle 100 is determined. As was mentioned above, the driving resistance represents the combination forces that must be overcome in order to accelerate the vehicle. The driving resistance is often estimated by one or more vehicle functions, and is therefore often already available on the vehicle communication bus system, and hence can be established in a straightforward manner. Alternatively the driving resistance of the vehicle can be arranged to be determined by, or on demand of, the control unit in which the present invention is implemented. The driving resistance can be estimated in any suitable manner, and plural examples of estimating the driving resistance can be found in the prior art. For example, the driving resistance can be estimated as: FDrive_res= FAir Res+ FRoll Res+ FGrav(1) Where: FAir Resrepresents the air resistance, FRoll Resrepresents the rolling resistance, and FGravrepresents the force resulting from the influence of gravity.

These forces can be estimated in any known conventional manner. Further forces may also be included in the model, such as e.g. powertrain friction losses. Such losses can also be arranged to be included e.g. as part of the rolling resistance. The respective influences of the various forces are highly dependent on the current driving conditions, and therefore, according to one embodiment, only one or two forces need to be considered. For example, when the vehicle 100 performs a start from standstill the air resistance will be negligible due to its high vehicle speed dependency.

Similarly, the force resulting from the influence of gravity is highly dependent on road inclination as well as vehicle mass, and can be neglected, e.g., on level ground.

As was mentioned above, the estimation of the driving resistance and forces forming part of the driving resistance is highly straightforward, and therefore not explained further in detail herein.

In step 203 a clutch pedal 118 characteristic for use is determined based on the determined driving resistance. Fig. 3 illustrates an example of a characteristic Pchar1for an exemplary clutch of a kind that can be used in a vehicle of Fig. 1A. The y-axis denotes the transmittable torque, i.e. the torque that the clutch 106 can transmit between combustion engine 101 and further powertrain components, such as drive wheels, downstream the clutch. In general, with regard to clutch characteristics, the x-axis denotes clutch position, which can be determined in any suitable manner, and, for example, be represented by the clutch actuator position and/or the lever arm position. Clutch characteristics are, in general, stored in the vehicle control system, e.g. for use when the clutch is automatically controlled by the vehicle control system, e.g. in automatic manual transmissions (AMT), so that, for example, smooth gear changes and/or starts of the vehicle can be obtained.

Furthermore, clutch characteristics are often subject to changes as the clutch wears, and/or due to changes in temperature, which might render the vehicle control system to perform adaptions of the clutch characteristic when found suitable. Such adaptions are well described in the prior art.

According to the present example, however, the x-axis does not represent actual clutch position, but according to the present example, instead, the graph is used to disclose transmittable torque as a function of the 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 oftentimes 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. The lever arm can be used to pull out the friction element by applying a force to the friction element when opening the clutch. Tmaxrepresents the maximum torque that can be transmitted by means of the present combination of clutch and combustion engine, which in general is limited by the maximum torque that the combustion engine 101 can deliver. According to the figure, the distance A-B consequently represents the movement region A-B in fig. 1C of the clutch pedal.

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.

The exact amount of torque that can be transmitted at each friction element position depends on the clutch characteristic, i.e. the relation between transmittable torque and friction element position. This relation might resemble the relation Pchar1shown in Fig. 3, and may vary from clutch to clutch and which, as mentioned, needs to be estimated (adapted) at regular intervals.

As was mentioned, in the present example, the x-axis represents the clutch pedal position and not clutch position and the characteristic Pchar1hence being a clutch pedal characteristic, i.e. transmittable torque as a function of the clutch pedal 118 position.

Fig. 3 further discloses a clutch pedal position Xdrive_res1that corresponds to a transmittable torque Tdrive_res1that must be transmitted in order to meet the driving resistance according to a first exemplary driving resistance Fdrive_res1. As was explained above, the driving resistance may vary substantially from one situation to another, e.g. in dependence of whether the vehicle 100 is heavily loaded or not, and whether the vehicle 100 is on level ground or in an uphill section of road. Consequently the clutch pedal 118 position at which the transmittable torque corresponds to the torque required to overcome the driving resistance will vary from one situation to another. This means that the clutch will behave quite differently from one situation to another, since e.g. the clutch pedal movement that is required from a fully open clutch until the vehicle starts moving, i.e. until the transmittable torque corresponds to a drive wheel force that is equal to or overcomes the current driving resistance of the vehicle may differ substantially from one situation to another since the difference in driving resistance may be considerable.

This is also exemplified in Fig 3. Apart from the first exemplary driving resistance Fdrive_res1, corresponding to the required transmittable torque Tdrive_res1, fig. 3 also discloses the situation for a second exemplary driving resistance Fdrive_res2. According to this second example, the driving resistance Fdrive_res2corresponds to a required transmittable torque Tdrive_res2, which is achieved at a clutch pedal position Xdrive_res2· Consequently, the required transmittable torques in the fig. 3 examples differs from each other, and this is also the case for the clutch pedal motion that is required to set the vehicle in motion. When the required transmittable torque is Tdrive_res1, the clutch pedal 118 must be moved a portion ?Xdrive_res1of the total movement region A-B of the clutch pedal 118.

Similarly, when the required transmittable torque is Tdrive_res2, the clutch pedal 118 must be moved a portion ?Xdrive_res2of the total movement region A-B of the clutch pedal 118.

As can be seen from the figure, larger clutch pedal motions are in general required for higher transmittable torques, Tdrive_res1> Tdrive_res2, than for comparatively lower transmittable torques . The bigger the difference is, i . e . the bigger the difference between the vehicle driving resistance Fdrive_resin different situations, the bigger the difference in clutch pedal movement.

This means that the vehicle 100 behaviour when the clutch pedal 118 is being manoeuvred may be quite different for different driving resistances, e.g. when setting the vehicle in motion from standstill. Differences of this kind can be mitigated or eliminated through the use of the present invention.

When the clutch 106 is controlled by the vehicle control system the clutch pedal characteristic can, in principle, be set to any desirable characteristic, since the actual position of the clutch is controlled independently from the actual pedal position. This is utilised by the present invention and in step 203 the clutch pedal characteristic is set to a characteristic that is determined on the basis of the determined driving resistance. According to the present example, the clutch pedal characteristic is set to a characteristic where the transmittable torque at a position Xdrive_res, shown in fig. 3, is set to correspond to the prevailing vehicle driving resistance, i.e. a transmittable torque that gives rise to a propelling force on the vehicle drive wheels that corresponds to the current driving resistance.

Consequently, according to the invention, the clutch pedal characteristic can be controlled such that a single particular position Xdrive_resin the clutch pedal movement region A-B is arranged to e.g. always correspond to the clutch pedal position where the transmittable torque results in a probe telling force precisely at or about which the vehicle will be set in motion.

This is exemplified in Figs. 4A-B. Fig. 4A discloses the example of fig. 3 where a transmittable torque Tdrive_res1is required to meet the current driving resistance. According to this example, the clutch pedal characteristic is adapted in step 203 such that the clutch pedal characteristic Pchar1of fig. 3, shown with dashed line in fig. 4A, is displaced in the direction according to the arrows 402 in fig. 4A, thereby forming a characteristic Pchar2· In this way, the characteristic is changed so that the transmittable torque will equal the torque Tdrive_res1at the position Xdrive_resinstead of at the position Xdrive_res1. Hence, according to fig. 4A, the transmittable torque is increased at the clutch pedal position Xdrive_resin comparison to fig. 3.

Similarly, fig. 4B discloses the example of fig. 3 where a transmittable torque Tdrive_res2is required to meet the current driving resistance. In this situation, the clutch pedal characteristic is adapted in step 203 such that the clutch pedal characteristic Pchar1of fig. 3 is, instead, displaced in the direction according to the arrows 404 in fig. 4B, i.e. opposite the direction of displacement in fig. 4A. In this way, the characteristic is, instead, changed to a characteristic Pchar3where the transmittable torque will equal the torque Tdrive_res2at the position Xdrive_resinstead of at the position Xdrive_res2. Hence, according to fig. 4B, the transmittable torque is decreased at the clutch pedal position Xdrive_res Image available on "Original document" comparison to fig. 3.

The disclosed method can, for example, be arranged to determine a clutch pedal characteristic that always results in a transmittable torque resulting in a propelling force on the vehicle drive wheels equalling the vehicle driving resistance at the clutch pedal position Xdrive_res. Furthermore, according to the disclosed example, the clutch pedal characteristics Pchar2have been displaced in a direction parallel to the Pos-axis of the figure. According to one embodiment, the clutch pedal characteristics are instead displaced in parallel to the T-axis, i.e. "raised" or "lowered" in the figure such that the transmittable torque fulfils the criteria according to the above. According to one embodiment, it is only ensured that the transmittable torque equals the desired transmittable torque at the desired position, while the remainder of the clutch pedal characteristic can be adapted in any suitable manner. For example, the characteristic may be adapted such that the slope (changes in transmittable torque per unit distance movement of the clutch pedal) becomes suitable e.g. towards fully opened and fully closed positions.

Consequently, according to the present invention, the driver will always be aware of the clutch pedal position Xdrive_resthat corresponds to the current driving resistance Fdrive_res, i.e. the position where there is an equilibrium of the forces acting on the vehicle. Hence the driver will also be aware of the clutch pedal position where the vehicle will be set in motion (from standstill) or begin to accelerate, since a movement from the clutch pedal position Xdrive_reswill change the transmittable torque, and at least an increase in transmittable torque from clutch pedal position Xdrive_reswill set the vehicle in motion.

According to the above example, the transmittable torque corresponding to the vehicle driving resistance is controlled to always be obtained at a particular clutch pedal position, Xdrive_res. According to one embodiment of the present invention, the control is only utilized e.g. when the driving resistance is below some suitable value and/or above some suitable value. For example, it may not always be desired that the invention is utilized when the driving resistance is very high or very low. At least not if this may result in clutch pedal characteristics where the remaining available portion of the movement region for controlling torques above and/or below the torque corresponding to the driving resistance may be too small to ensure satisfactory control of the clutch.

Furthermore, according to one embodiment of the invention, a single position Xdrive_resaccording to the above is not used, but instead, the clutch is controlled such that the transmittable torque corresponding to the vehicle driving resistance instead is controlled to be within a particular portion of the movement region A-B. For example, this portion may vehicle e.g. 2%, 5% or 10% of the total movement region of the clutch pedal 118, e.g. centered about the position Xdrive_res. In this way, the clutch pedal may still behave from a driver point of view substantially as if the same position always results in a transmittable torque meeting the vehicle driving resistance, while the vehicle control system more easy may find a clutch pedal characteristic that fulfils set criteria. This is exemplified by the portion ?Xdrive_resof fig. 4B.

The clutch 106 can be arranged to be controlled according to the determined clutch pedal characteristic, e.g. Pchar2or Pchar3, step 204, e.g. for as long as the clutch is slipping, and the method can be ended e.g. when the clutch has been completely closed, or completely opened, determined in step 205. The method is then ended in step 206. Alternatively the method can be arranged to continuously return to step 201 from step 204 in order to update the clutch pedal characteristic in dependence of changes in driving resistance during an ongoing clutch slip.

Furthermore, according to one embodiment of the invention, the position Xdrive_resand/or region about a position Xdrive_res, in the movement region A-B can be arranged to be driver controlled. That is, the driver may be allowed to, e.g. by means of the vehicle control system, set the clutch pedal position at which the driving resistance is to be met irrespective of the actual magnitude of the driving resistance. In this way, the clutch behaviour can be adapted individually according to the preferences of different drivers.

Furthermore, the present invention can also be utilised in combination with the invention disclosed in the parallel Swedish patent application SE155XXXX-X, with the title "METHOD AND SYSTEM FOR CONTROLLING A CLUTCH OF A VEHICLE II", and having the same inventors and the same filing date as the present invention. According to the invention disclosed in this parallel application, the clutch is also controlled in dependence of the position of the drivel manoeuvrable means such as e.g. a clutch pedal in the movement region A-B. In particular, a control is used where the characteristic of the clutch pedal can be adapted such that e.g. changes in transmittable torque as function of clutch pedal movement can be reduced when moving the clutch pedal in a region about the position at which the transmittable torque equals, or substantially equals, e.g. the current driving resistance.

When used in combination with the present invention, a particular clutch pedal position, or at least one position in a portion of the clutch pedal movement region, will always correspond to the current driving resistance. In addition, the clutch pedal characteristic about this position is adapted according to the above-referenced application such that e.g. changes in transmittable torque about this position/region is controlled in a manner that further facilitates clutch operation for the driver.

For example, the change in transmittable torque as a function of clutch pedal movement about the clutch pedal position corresponding to the current driving resistance can be reduced. This is exemplified in fig. 5, which discloses a situation corresponding to the fig. 4B example. In fig. 5 the clutch pedal characteristic Pchar4has not only been displaced such that transmittable torque at the position Xdrive_rescorrespond to the current driving resistance. In addition, the transmittable torque is further controlled such that the derivative of the clutch pedal characteristic about the position Xdrive_resis reduced in a portion of the movement region A-B about the clutch pedal position Xdrive_res. The corresponding fig. 3 characteristic Pchar1is shown by dashed line. The change in transmittable torque can be controlled such that the change in transmittable torque for a first movement of said driver manoeuvrable means about said first portion of said movement region A-B and/or the position Xdrive_resis controlled to be below some suitable change in transmittable torque.

Consequently, when combining the present invention with the solution disclosed in the above-referenced patent application a combined solution is obtained which not only enables the driver to always know where in the clutch pedal movement region that the transmittable torque will correspond to the current driving resistance. The control of the vehicle will also be further improved by reducing variations in transmittable torque as a function of the movement about this clutch pedal position.

Finally, the present invention has been described above for a particular example of a vehicle, but is applicable for any vehicle in which driver manoeuvrable means are used to control a clutch, the clutch being any kind of suitable clutch comprising any kind of elements, and hence not necessarily a clutch of the kind exemplified above, for as long as the manoeuvring of the clutch can be accomplished independently from the manoeuvring of the driver manoeuvrable means.

Claims

1. Method for controlling a clutch of a vehicle (100), the vehicle (100) including a clutch (106) for selectively transmitting torque to and/or from a first power source (101), said vehicle (100) further including driver manoeuvrable means (118) for manoeuvring a clutch (106), said driver manoeuvrable means (118) being movable in a movement region (A-B) between a first end position (A) and a second end position (B), transmittable torque of said clutch (106) being controlled by a vehicle control system on the basis of the position of said driver manoeuvrable means (118) in said movement region (A-B), the method being characterised in, for a plurality of different magnitudes of at least one force forming at least part of the driving resistance ( Fdrive_res) of said vehicle (100): - controlling said clutch (106) on the basis of the position of said driver manoeuvrable means (118) in said movement region (A-B) in dependence of the magnitude of said at least one force ( FDrive_res) , further including : - controlling said clutch (106) such that transmittable torque of at least one position in a first portion ( ?XDrive_res) of said movement region (A-B) of said driver controllable means (118) gives rise to a propelling force on the vehicle drive wheels (113, 114) substantially corresponding to the magnitude of said at least one force ( Fdrive_res) .

2. Method according to claim 1, further including, when controlling said clutch (106): - controlling said clutch (106) on the basis of the position of said driver manoeuvrable means (118) in said movement region (A-B) according to a first dependency (Pchar1) for a first magnitude of said at least one force ( Fdrive_res) , and - controlling said clutch (106) on the basis of the position of said driver manoeuvrable means (118) in said movement region (A-B) according to a second dependency (Pchar2), being different from said first dependency, (Pchar1) for a second magnitude, being different from said first magnitude of said at least one force ( Fdrive_res), such that according to said dependencies transmittable torque of at least one position in said first portion ( ?XDrive_res) of said movement region (A-B) of said driver controllable means (118) gives rise to a propelling force on the vehicle drive wheels (113, 114) substantially equalling the magnitude of said at least one force ( Fdrive_res ) .

3. Method according to claim 2, said dependency being a representation of the transmittable torque of said clutch (106) as a function of the position of said driver manoeuvrable (118) means in said movement region (A-B).

4. Method according to any one of claims 1-3, further including: - controlling said clutch such that said first portion ( ?XDrive_res) of said movement region (A-B) constitutes a portion corresponding to any of: 0-2% of the total movement in said movement region (A-B), 0-5% of the total movement in said movement region (A-B), 0-10% of the total movement in said movement region (A-B).

5. Method according to any one of the claims 1-4, further including: - controlling said clutch (106) such that, for said magnitudes of said at least one force (Fdrive_res), transmittable torque at substantially a same first position (XDrive_res) of said movement region (A-B) of said driver controllable means (118) gives rise to a propelling force on the vehicle drive wheels (113, 114) substantially equalling the magnitude of said at least one force (Fdrive_res).

6. Method according to any one of the claims 1-5 further including: - controlling said clutch (106) according to any one of the claims 1-5 when a positive propelling force on said drive wheels is required to set the vehicle in motion in an intended direction of travel.

7. Method according to any one of the claims 1-6, further including: - controlling said clutch (106) according to any one of the claims 1-6 irrespective of the magnitude of said at least one force.

8. Method according to any one of the claims 1-7, further including: - controlling said clutch according to any one of the claims 1-7 when the magnitude of said at least one force at most equals a first magnitude.

9. Method according to any one of the claims 1-8, wherein the location of said first portion of said movement region (A-B) and/or said first position in said movement region (A-B) is controllable by a driver of the vehicle.

10. Method according to any one of the claims 1-9, wherein said at least one force (Fdrive_res) is an estimation of at least one of: rolling resistance, air resistance, force resulting from the influence of gravity.

11. Method according to any one of claims 1-10, wherein said at least one force is an estimation of the driving resistance ( Fdrive_res) of said vehicle ( 100 ) .

12. Method according to any one of the preceding claims, further including: - reducing variations in transmittable torque of said clutch (106) as a function of movement of said driver controllable means (118) about said first portion ( ?XDrive_res) of said movement region (A-B) and/or said first position ( XDrive_res) in said movement region (A-B).

13. Method according to claim 12, further including: - reducing said change in transmittable torque of said clutch (106) such that the change in transmittable torque for a first movement of said driver manoeuvrable means about said first portion ( ?XDrive_res) of said movement region (A-B) and/or said first position ( XDrive_res) in said movement region (A-B) is controlled to be below a first change in transmittable torque.

14. Computer program comprising program code that, when said program code is executed in a computer, causes said computer to carry out the method according to any of claims 1-13.

15. Computer program product comprising a computer-readable medium and a computer program according to claim 14, wherein said computer program is contained in said computer-readable medium.

16. System for controlling a clutch of a vehicle (100), the vehicle (100) including a clutch (106) for selectively transmitting torque to and/or from a first power source (101), said vehicle (100) further including driver manoeuvrable means (118) for manoeuvring a clutch (106), said driver manoeuvrable means (118) being movable in a movement region (A-B) between a first end position (A) and a second end position (B), transmittable torque of said clutch (106) being controlled by a vehicle control system on the basis of the position of said driver manoeuvrable means (118) in said movement region (A-B), the system being characterised in means for, for a plurality of different magnitudes of at least one force forming at least part of the driving resistance ( Fdrive_res) of said vehicle (100): - controlling said clutch (106) on the basis of the position of said driver manoeuvrable means (118) in said movement region (A-B) in dependence of the magnitude if said at least one force ( Fdrive_res); and - controlling said clutch (106) such that transmittable torque of at least one position in a first portion ( ?XDrive_res) of said movement region (A-B) of said driver controllable means (118) gives rise to a propelling force on the vehicle drive wheels (113, 114) substantially corresponding to the magnitude of said at least one force ( Fdrive_res) .

17. Vehicle, characterised in that it comprises a system according to claim 16.