SE1150860A1 - Device and method for controlling the propulsion of a motor vehicle - Google Patents

Description

Despite the driver braking at idle speed to prevent the drive wheels of the vehicle from locking.

In this case, relatively high driving forces can occur before disengagement takes place, especially when propelling the vehicle in low gears where the vehicle has a relatively strong engine, which can be perceived as unpleasant for the driver.

Using a procedure where disconnection takes place on the basis of a prevailing engine speed can create some uncertainty for the driver as the disconnection is not always perceived as predictable. In some driving cases, a driver must brake quite hard for disengagement to be performed. In other driving cases, it may be sufficient for the driver to brake fairly marginally for disengagement to be performed. Said disadvantages experienced by drivers can also be exacerbated by the fact that the engines of different vehicles can be individually calibrated, which of course affects drivers who in their daily work switch between different vehicles in a vehicle fleet.

US 2001049576 describes a method of a motor vehicle in which the vehicle is propelled by so-called crawling. In this case, a clutch of the vehicle's transmission is partially disengaged for a certain period of time during braking of the vehicle, whereby the clutch is completely disengaged after said elapsed time.

WO 03089264 describes a method for being able to steplessly regulate the speed of a vehicle at low speeds where a minimum gear step of the vehicle transmission is engaged by disengaging the vehicle engine from the vehicle gearbox to varying degrees.

WO 2007030044 describes a system of a motor vehicle where disengagement of the vehicle's propulsion takes place on the basis of a braking force of the vehicle. SUMMARY OF THE INVENTION There is a need to provide a method of disengaging a motor vehicle propulsion where the above disadvantages are reduced.

An object of the present invention is to provide a new and advantageous method for automatically disengaging the propulsion of a motor vehicle.

Another object of the invention is to provide a new and advantageous device and a new and advantageous computer program for automatically disengaging the propulsion of a motor vehicle.

A further object of the invention is to provide a method, an apparatus and a computer program for providing an alternative automatic disengagement of a motor vehicle propulsion.

A further object of the invention is to provide a method, an apparatus and a computer program for effecting automatic disengagement of a motor vehicle propulsion where said disengagement is more predictable and independent of the selected gear stage of a transmission of the vehicle.

A further object of the invention is to provide a method, an apparatus and a computer program for achieving improved performance of a motor vehicle.

These objects are achieved with a method for automatically disengaging a motor vehicle propulsion by means of a clutch of a driveline of the vehicle, according to claim 1. According to one aspect of the invention, there is provided a method for automatically disengaging a motor vehicle propulsion by means of a clutch of a driveline of the vehicle. The method includes the steps of - continuously determining a prevailing driving force for propulsion of the vehicle, and - automatically opening said clutch when said driving force exceeds a predetermined value to disengage the propulsion of the vehicle. Said driving force can advantageously be calculated continuously in an accurate and robust manner. Said driving force may be a calibrated driving force which can be continuously determined in any suitable manner. Said driving force can be the engine component of a prevailing driving force of the vehicle and thus not a force resultant that acts against the ground of the vehicle's driving wheel.

This provides a method for automatically disengaging a motor vehicle propulsion by means of the vehicle driveline coupling which is more predictable than in prior art where disengagement occurs on the basis of a prevailing engine speed. This also provides a method for automatically disengaging a motor vehicle propulsion by means of the vehicle driveline coupling as is independent of a calibration of the engine of the vehicle.

In this case, a method is also provided for automatically disengaging the propulsion of a motor vehicle by means of a coupling of a driveline of the vehicle which takes into account the entire driveline configuration of the vehicle.

The innovative procedure is applicable to vehicles with a final gear. The innovative method is applicable to vehicles that have a gearbox. The innovative method is applicable to vehicles which do not have a distribution gearbox. In this case, a method is thus provided for automatically disengaging a motor vehicle propulsion by means of the vehicle's driveline coupling which is versatile. The method is also applicable to vehicles having two conventional gearboxes in a driveline thereof. The method is also applicable to vehicles using hybrid operation, i.e. vehicles equipped with different types of energy storage, such as e.g. batteries, for the propulsion of said vehicles.

The present invention is advantageous where the vehicle uses a so-called off-road mode for propelling said vehicles. In this case, lower gears than normal are generally used to propel the vehicle.

The method may further comprise the step of: - continuously determining said prevailing driving force on the basis of the torque of the engine of the vehicle. By continuously determining said driving force, a method according to the invention is hereby obtained which can in a very accurate manner determine at what time the coupling of the vehicle is to be opened in order to avoid engine stoppage. By determining the driving force on the basis of a prevailing motor torque, a very accurate method according to the invention can be achieved since the motor torque can be determined on with high accuracy. Furthermore, a prevailing engine torque of the vehicle can be determined by continuous calculations in a control unit of the vehicle, which provides a cheap solution according to the invention since no expensive sensors or components are needed to determine said prevailing engine torque.

The method may further comprise the step of: - continuously determining said prevailing driving force on the basis of a gear ratio of a gearbox of the vehicle with respect to a current gear, a gear ratio of a gearbox of the vehicle, a gear ratio of a final gear of the vehicle and a wheel radius. By continuously determining said driving force, a method according to the invention is hereby obtained which can in a very accurate manner determine at what time the coupling of the vehicle is to be opened in order to make the innovative method repeatable and thus achieve good drivability. By determining the driving force of a gear ratio of a gearbox of the vehicle with respect to a current gear, a gear ratio of a gearbox of the vehicle, a gear ratio of a final gearbox of the vehicle and a wheel radius, a very accurate method according to the invention can be achieved. parameters are known at any given time. These parameters are constants, which is why said determination of said driving force is not computationally difficult. In this case, a cheap solution according to the invention is provided since no expensive sensors or components are needed to determine said parameters.

The method may alternatively include the step of: - continuously determining said prevailing driving force on the basis of a gear ratio of a gearbox of the vehicle with respect to a current gear, a gear ratio of a final gear of the vehicle and a wheel radius. By continuously determining said driving force, a method according to the invention is hereby obtained which can in a very accurate manner determine at what time the coupling of the vehicle is to be opened in order to make the innovative method repeatable and thus achieve good drivability. By determining the driving force of a gear ratio of a gearbox of the vehicle with respect to a current gear, a gear ratio of a final gear of the vehicle and a wheel radius, a very accurate method according to the invention can be achieved since these parameters are known at any given time. These parameters are constants, which is why said determination of said driving force is not computationally difficult. In this case, a cheap solution according to the invention is provided since no expensive sensors or components are needed to determine said parameters.

The method may further comprise the step of: - automatically opening the coupling when said predetermined value is exceeded for a predetermined period of time. In this case, a method is provided for automatically disengaging the propulsion of a motor vehicle by means of the coupling of the vehicle's driveline which shows a certain redundancy. By conditioning disconnection with a validation period, the risk of incorrect disconnection can be minimized. Hereby a more robust method is provided according to an aspect of the invention. Said predetermined time period may be within a time interval of 1-5 seconds. Said predetermined time period may be shorter than 1 second. Said predetermined time period may be longer than 5 seconds, e.g. 10 seconds. (0) seconds. In this case, a method is provided which can open the clutch in a distinct manner. The said predetermined time period can be zero in the vehicle. This can be advantageous in certain safety-critical applications and driving cases where the clutch should be opened immediately when the driving force exceeds said predetermined value.

Said predetermined value may be in a range of 15-25 kN (kilo Newton). This range may be applicable to trucks or buses. According to one example, said predetermined value is 20 kN.

Said predetermined value may be in the range 1500-2500 N (Newton). This range may be applicable to passenger cars.

It should be noted that said predetermined threshold value may be any suitable value. Said predetermined threshold value may be greater than 25 kN. Said predetermined threshold value may be less than 15 kN.

The procedure is easy to implement in existing motor vehicles. Software for automatic disengagement of a motor vehicle's propulsion by means of a coupling of a driveline of the vehicle can be installed in a control unit of the vehicle during its manufacture. A buyer of the vehicle can thus be given the opportunity to choose the function of the procedure as an option. Alternatively, software including program code for performing the innovative procedure may be installed in a control unit of the vehicle when upgrading at a service station. In this case, the software can be loaded into a memory in the control unit. Implementation of the innovative method is thus cost-effective, in particular since no additional sensors or other components need to be installed in the vehicle according to an aspect of the invention. The required hardware is already the vehicle today. presently provided in the Invention thus provides a cost effective solution to the above problems.

Software that includes program code for automatically disengaging the propulsion of a motor vehicle by means of a coupling of a driveline of the vehicle can be easily updated or replaced. Furthermore, different parts of the software that include program code to perform the innovative procedure can be replaced independently. This modular configuration is advantageous from a maintenance perspective.

According to one aspect of the invention, there is provided a device for automatically disengaging the propulsion of a motor vehicle by means of a coupling of a driveline of the vehicle. The device comprises means for continuously determining a prevailing driving force for propelling the vehicle, and means for automatically opening said clutch when said driving force exceeds a predetermined value for disengaging the propulsion of the vehicle.

The device may further comprise: - means for continuously determining said prevailing driving force on the basis of the torque of the vehicle's engine.

The device may further comprise: - means for continuously determining said prevailing driving force on the basis of a gear ratio of a gearbox of the vehicle with respect to a current gear, a gear ratio of a gearbox of the vehicle, a gear ratio of a final gearbox of the vehicle and a wheel radius.

The device may alternatively comprise: means for continuously determining said prevailing driving force on the basis of a gear ratio of a gearbox of the vehicle with respect to a current gear, a gear ratio of a final gear of the vehicle and a wheel radius.

The device may further comprise: - means for automatically opening the coupling when said predetermined value is exceeded for a predetermined period of time.

Said predetermined time period can be zero seconds. Said predetermined time period may be within a time interval of 1-5 seconds. Said predetermined value may be in a range of 15-25 kN.

The above objects are also achieved with a motor vehicle comprising the device. The motor vehicle can be a truck, bus or car.

The motor vehicle can be a wheel loader, forestry machine or a vehicle that is adapted for operation in a mine.

According to one aspect of the invention, there is provided a computer program for automatically disengaging a motor vehicle propulsion by means of the vehicle driveline coupling, said computer program comprising program code stored on a computer readable medium for causing an electronic control unit or another computer connected to the electronic control unit. to perform the steps according to any one of claims 1-7.

According to one aspect of the invention, there is provided a computer program for automatically disengaging a motor vehicle propulsion by means of the vehicle driveline clutch, said computer program comprising program code for causing an electronic control unit or another computer connected to the electronic control unit to perform the steps of any of claims 1-7 . According to one aspect of the invention, there is provided a computer program product comprising a program code stored on a computer readable medium for performing the method steps according to any one of claims 1-7, when said computer program is run on an electronic control unit or a computer. another computer connected to the electronic control unit.

Additional objects, advantages and novel features of the present invention will become apparent to those skilled in the art from the following details, as well as through the practice of the invention. While the invention is described below, it should be understood that the invention is not limited to the specific details described. Those skilled in the art having access to the teachings herein will recognize and incorporate within other further applications, modifications areas, which are within the scope of the invention. SUMMARY DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and further objects and advantages thereof, reference is now made to the following detailed description which is to be read in conjunction with the accompanying figures, in which like reference numerals refer to like parts in the various figures, and in which: 1 schematically illustrates a vehicle, according to an embodiment of the invention; Figure 2 schematically illustrates a subsystem of the vehicle shown in Figure 1, according to an embodiment of the invention; Figure 3a schematically illustrates a flow chart of a method, according to an embodiment of the invention; Figure 3b schematically illustrates in further detail a flow chart of a method, according to an embodiment of the invention; and Figure 4 schematically illustrates a computer, according to an embodiment of the invention. DETAILED DESCRIPTION OF THE FIGURES Referring to Figure 1, a side view of a vehicle 100 is shown. The exemplary vehicle 100 consists of a tractor 110 and a trailer 112.

The vehicle can be a heavy vehicle, such as a truck or a bus. The vehicle can alternatively be a car.

Here, the term "link" refers to a communication link which may be a physical line, such as an optoelectronic communication line, or a non-physical line, such as a wireless connection, for example a radio or microwave link.

Referring to Figure 2, a subsystem 299 of the vehicle 100 is shown.

The subsystem 299 is arranged in the tractor 110. The tractor may be equipped with a two-pedal system for propelling the vehicle. The subsystem 299 consists of an internal combustion engine 230. The internal combustion engine 230 may be a diesel engine.

The internal combustion engine 230 has an output shaft 235 which is connected to a clutch 240. The clutch 240 may be a suitable automatic clutch of friction type, e.g. comprising two slats.

A clutch actuator (not shown) is provided to actuate the clutch 240 in such a way that a desired torque is transmitted through the clutch 240 in the vehicle driveline for propelling said vehicle. The clutch actuator is arranged to set the clutch 240 so that it is completely open, partially closed (slippage of the clutch) or completely closed.

The clutch 240 has an output shaft 245 which is connected to a gearbox 250. The gearbox 250 has an output shaft which is coupled to a distribution gearbox 280. The distribution gearbox 280 has an output shaft which is coupled to an end gear 285. The end gear 285 is coupled to two drive wheels 260a and 260b via drive shafts 255a and 255b, respectively. A torque generated by the engine 230 can be transmitted via the shaft 235, the clutch 240, the shaft 245, the gearbox 250, the transmission gearbox 280 and the final gear 285 to the drive wheels 260a and 260b. According to an alternative embodiment, the vehicle lacks said gearbox 280.

Said gearbox 250 and distribution gearbox 280 are arranged to have a number of different selectable gears lgb and ltg, respectively, which are described in further detail below. The final gear 285 has a gear ratio ldg.

Said drive wheels 260a and 260b have a certain wheel radius Rw. Said radius Rw of the drive wheels 260a and 260b may be e.g. 0.5 m. The drive wheels 260a and 260b may have a suitable wheel radius, which may be greater or less than 0.5 m.

It should also be noted that the vehicle may be equipped with a number of drive wheel pairs, and not necessarily just a pair of drive wheels shown with reference to the exemplary embodiment in Figure 2. Thus, the vehicle 100 may be equipped with e.g. two or three pairs of drive wheels.

A first control unit 200 is arranged for communication with the motor 230 via a link 231. The first control unit 200 is arranged for communication with the clutch 240 via a link 241. In this case, the first control unit 200 can be closed at 240 by means of the first 200 is communication with the gearbox 250 via a link 251. The first control unit actuates a clutch actuator. The control unit arranged for 200 is arranged to control operation of the motor 230. The first control unit is arranged to control operation of the clutch 240, i.e. by influencing a degree of closure of the clutch actuator in a desired manner. The first control unit 200 is arranged to control the operation of the gearbox 250, e.g. by actuating a gearbox of the gearbox 250. The first control unit 200 is arranged to control the operation of the gearbox 280, e.g. by influencing a gear ratio of the gearbox 280. The first control unit 200 is for this purpose signal connected to the gearbox 280 via a link (not shown).

The first control unit 200 has a number of drivers for propelling the vehicle, which are stored in one or more memories therein. A driver refers to the so-called off-road driving. According to this driver, e.g. lower gear ratios of the vehicle's gearbox than are normally selected. Said driver for off-road driving can be advantageous when driving where the ground is uneven, e.g. in the form of slopes or depressions. Said driver for off-road driving can be advantageous when driving where the ground is slippery, such as e.g. on winter road or muddy road. Said driver for off-road driving can be advantageous when driving on loose ground, such as e.g. gravel road or sand. Said driver for off-road driving can be advantageous when driving where the ground is uneven insofar as it e.g. is rocky. Said driver for off-road driving can be advantageous when driving where objects are present on the ground, e.g. in the form of loose tree branches. Said driver for off-road driving can be advantageous when driving in off-road, e.g. in a case where the vehicle is a Forestry Machine or a commercial vehicle such as e.g. a wheel loader. Said off-road driver can in several different situations be advantageous for propelling a timber truck.

The first control unit 200 is arranged to continuously determine a prevailing driving force for propulsion of the vehicle 100, and automatically open the clutch 240 when said driving force exceeds a predetermined value for disengaging the propulsion of the vehicle. The first control unit is arranged to continuously determine a prevailing driving force of the vehicle on the basis of the parameters the engine Torque Me, a gear ratio lgb of the gearbox 250 of the vehicle with respect to a current gear, a gear ratio ltg of the gearbox 280 of the vehicle, a gear ratio ldg of an end gear 285 of the vehicle and a wheel radius Rw of the drive wheels 260a and 100b of the vehicle. The first control unit is alternatively arranged to continuously determine a prevailing driving force of the vehicle on the basis of the parameters engine torque Me, a gear ratio lgb of the gearbox 250 of the vehicle with respect to a current gear, a gear ratio ldg of a final gear 285 of the vehicle and a wheel radius Rw of the drive wheels 260a and 260b in the vehicle 100.

According to one embodiment, the driving force of the vehicle is defined according to equation 1 below: Fdriv = (Me * | gb * | tg * | dg) / Rw (1) In a case where the vehicle's powertrain lacks a transmission, the vehicle's driving force is defined according to equation 2 below: Fdrivqiviengb * idgvRw ( 2) Said motor torque Me can be the flywheel torque of the motor, which can be continuously determined (calculated) in a known manner.

The prevailing gear ratio lgb of the gearbox is something of a discrete value within a predetermined range, e.g. 1-16. There is for each vehicle provided a set of discrete predetermined gears, which set of course depends on the configuration of the driveline.

The prevailing gear ratio ltg of the gearbox 280 is something of a discrete value within a predetermined range, e.g. 0.5-3. For each vehicle there is provided a set of discrete predetermined gears ltg, which set of course depends on the configuration of the driveline.

The gear ratio ldg of the final gear 285 is something of a discrete value within a predetermined range, e.g. 1-5.

The drive wheel radius Rw is a constant, e.g. 0.5 meters. According to another embodiment, the first control unit 200 is arranged to calculate the driving force Fdrive on the basis of the parameters engine torque Me, a gear ratio lgb of a gearbox of the vehicle with respect to a current gear and a wheel radius RW of the drive wheels of the vehicle.

Depending on a configuration of the vehicle 100, the driving force Fdriv can be calculated appropriately. According to one embodiment, the driving force Fdriv is calculated on the basis of a torque of an electric machine (not shown), which can be driven by e.g. an energy storage, for propelling the vehicle 100.

A second control unit 210 is arranged for communication with the first control unit 200 via a link 201. The second control unit 210 may be detachably connected to the first control unit 200. The second control unit 210 may be a control unit external to the vehicle 100. The second control unit 210 may be arranged to perform the innovative method steps according to the invention. The second control unit 210 can be used to upload software to the first control unit 200, in particular software for performing the innovative method. The second control unit 210 may alternatively be arranged for communication with the first control unit 200 via an internal network in the vehicle. The second control unit 210 may be arranged to perform substantially similar functions as the first control unit 200, such as e.g. to continuously determine a prevailing driving force for propulsion of the vehicle, and automatically open the clutch when the driving force exceeds a predetermined value for disengaging the vehicle's propulsion. The subsystem 299 comprises a two-pedal system comprising a conventional accelerator control 270, for example an accelerator pedal, and a brake pedal. The throttle control 270 is signal-connected to the first control unit 200 via a link 271. The driver can request a desired coupling torque Req T by means of the throttle control 270.

The propulsion of the motor vehicle can be controlled by the driver 270 by means of the throttle control 270, where a coupling torque is requested by the driver by means of throttle. Figure 3a schematically illustrates a flow chart of a method for automatically disengaging a motor vehicle propulsion by means of a clutch of a driveline of the vehicle, according to an embodiment of the invention.

The method comprises a first method step S301. Step S301 comprises the steps of: - continuously determining a prevailing driving force for propulsion of the vehicle, and - automatically opening said clutch when said driving force exceeds a predetermined value for disengaging the propulsion of the vehicle. After step S301, the procedure is terminated.

Figure 3b schematically illustrates in further detail a flow chart of a method for automatically disengaging a motor vehicle propulsion by means of a coupling of a driveline of the vehicle, according to an embodiment of the invention.

The method comprises a first method step S310. Method step S310 includes the step of continuously determining a prevailing driving force for propulsion of the vehicle. Said prevailing driving force can e.g. determined on the basis of the parameters engine torque Me, gear ratio lgb of a gearbox 250 of the vehicle with respect to a current gear, a gear ratio ltg of a gearbox 280 of the vehicle, a gear ratio ldg of an end gear 285 of the vehicle and a wheel radius Rw of the drive wheels 260 at 100. After S310 procedure step S320. the vehicle process step is performed a subsequent method step S320 includes the step of automatically opening said clutch when said driving force exceeds a predetermined value THforce to disengage the vehicle propulsion. According to one embodiment, the coupling 240 is opened when said predetermined value is exceeded for a predetermined period of time THtime. 10 15 20 25 30 17 Said predetermined threshold value THforce may be any suitable value. Said predetermined threshold value THforce may be greater than 25 kN.

Said predetermined threshold value THforce may be less than 15 kN.

Said predetermined threshold value THforce may be within a range of 15-25 kN.

Said predetermined time period THtime may be within a time interval of 1-5 seconds. Said predetermined time period THtime may be shorter than 1 second. Said predetermined time period THtime may be longer than 5 seconds, e.g. 10 seconds.

After the procedure step s320, the procedure is terminated.

Referring to Figure 4, there is shown a diagram of an embodiment of a device 400. The controllers 200 and 210 described with reference to Figure 2 may in one embodiment include the device 400. The device 400 includes a non-volatile memory 420, a data processing unit 410, and a read / write memory 450. The non-volatile memory 420 has a first memory portion 430 in which a computer program, such as an operating system, is stored to control the operation of the device 400. Further, the device 400 includes a bus controller, a serial communication port , I / O means, an A / D converter, a time and date input and transfer unit, an event counter and an interrupt controller (not shown). The non-volatile memory 420 also has a second memory portion 440.

A computer program P is provided which includes routines for automatically disconnecting the propulsion of a motor vehicle by means of a clutch of a driveline of the vehicle.

The program P includes routines for continuously determining a prevailing driving force Fdrive for propelling the vehicle 100. The program P includes routines for automatically opening the vehicle clutch 240 when said driving force Fdrive exceeds a predetermined value THforce for disengaging the vehicle's propulsion.

The program P includes routines for continuously determining said prevailing driving force Fdriv on the basis of the engine torque Me.

The program P comprises routines for continuously determining said prevailing driving force Fdriv on the basis of a gear ratio lgb of a gearbox 250 of the vehicle with respect to a current gear, a gear ratio ltg of a gearbox 280 of the vehicle, a gear ratio ldg of a final gear 285 of the vehicle and a wheel radius Rw.

The program P alternatively comprises routines for continuously determining said prevailing driving force Fdriv on the basis of a gear ratio lgb of a gearbox 250 of the vehicle with respect to a current gear, a gear ratio ldg of a final gear 285 of the vehicle and a wheel radius Rw.

The program P can be stored in an executable manner or in a compressed manner in a memory 460 and / or in a read / write memory 450.

When it is described that the data processing unit 410 performs a certain function, it is to be understood that the data processing unit 410 performs a certain part of the program which is stored in the memory 460, or a certain part of the program which is stored in the read / write memory 450.

The data processing device 410 can communicate with a data port 499 via a data bus 415. The non-volatile memory 420 is intended for communication with the data processing unit 410 via a data bus 412. The separate memory 460 is intended to communicate with the data processing unit 410 via a data bus 411. Read / write memory 450 is arranged to communicate with the data processing unit 410 via a data bus 414. To the data port 499, e.g. links 201, 231, 241, 251 and 271 are connected (see Figure 2).

When data is received on the data port 499, it is temporarily stored in the second memory part 440. The data processing unit 410 is prepared to perform code execution in a manner described above.

Parts of the methods described herein may be performed by the device 400 by means of the data processing unit 410 running the program stored in the memory 460 or the read / write memory 450. When the device 400 runs the program, the methods described herein are executed.

The foregoing description of the preferred embodiments of the present invention has been provided for the purpose of illustrating and describing the invention. It is not intended to be exhaustive or to limit the invention to the variations described. Obviously, many modifications and variations will occur to those skilled in the art. The embodiments were selected and described to best explain the principles of the invention and its practical applications, thereby enabling those skilled in the art to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims (18)

10 15 20 25 30 20 PATENT REQUIREMENTS A method for automatically disengaging a motor vehicle (100; 110) propulsion by means of a coupling (240) of a driveline of the vehicle characterized by the steps of - continuously determining a prevailing driving force (Fdrive) for propelling the vehicle (100; 110), and - automatically open said clutch (240) when said driving force (Fdriv) exceeds a predetermined value (THforce) to disengage the vehicle's propulsion. The method of claim 1, further comprising the step of: - continuously determining said prevailing driving force (Fdriv) on the basis of the torque (Me) of the vehicle engine. A method according to claim 1 or 2, further comprising the step of: - continuously determining said prevailing driving force (Fdriv) on the basis of a gear ratio (lgb) of a gearbox (250) of the vehicle with respect to a current gear, a gear ratio (ltg) of a gearbox (280) of the vehicle, a gear (ldg) of a final gear (285) of the vehicle and a wheel radius (RW). A method according to any one of claims 1-3, further comprising the step of: - automatically opening the clutch (240) when said predetermined value (THforce) is exceeded for a predetermined period of time (THtime). The method of claim 4, wherein said predetermined time period (THtime) is zero (0) seconds. The method of claim 4, wherein said predetermined time period (THtime) is within a time interval of 1-5 seconds. 10 15 20 25 30 21 A method according to any one of the preceding claims, wherein said predetermined value (THforce) is in a range of 15-25 kN. Device for automatically disengaging the propulsion of a motor vehicle by means of a coupling (240) of a driveline of the vehicle characterized by - means (200; 210; 400) for continuously determining a prevailing driving force (Fdrive) for propelling the vehicle, and - means (200; 210; 400) to automatically open said clutch (240) when said driving force (Fdrive) exceeds a predetermined value (THforce) to disengage the vehicle's propulsion. The device according to claim 8, further comprising: - means (200; 210; 400) for continuously determining said prevailing driving force (Fdriv) on the basis of the torque (Me) of the vehicle engine. Apparatus according to claim 8 or 9, further comprising: - means (200; 210; 400) for continuously determining said prevailing driving force (Fdriv) on the basis of a gear ratio (lgb) of a gearbox (250) of the vehicle with respect to a current gear, a gear (ltg) of a gearbox (280) of the vehicle, a gear (ldg) of a final gear (285) of the vehicle and a wheel radius (Rw). 11.. Device according to any one of claims 8-10, further comprising: - means (200; 210; 400) for automatically opening the coupling (240) when said predetermined value (THforce) is exceeded for a predetermined period of time (THtime). The device of claim 11, wherein said predetermined time period (THtime) is zero (0) seconds. 10 15 20 25 22 The device of claim 11, wherein said predetermined time period (THtime) is within a time interval of 1-5 seconds. Device according to any one of claims 8-13, wherein said predetermined value (THforce) is in a range 15-25 kN. Motor vehicle (100; 110) comprising a device according to any one of claims 8-14. A motor vehicle (100; 110) according to claim 15, wherein the motor vehicle is something of a truck, bus or passenger car. A computer program (P) for automatically disengaging a motor vehicle (100; 110) propulsion by means of the vehicle driveline coupling (240), said computer program (P) comprising program code for causing an electronic control unit (200; 400) or another computer ( 210; 400) connected to the electronic control unit (200; 400) for performing the steps according to any one of claims 1-7. A computer program product comprising a program code stored on a computer readable medium for performing the method steps of any of claims 1-7, when said computer program is run on an electronic control unit (200; 400) or another computer (210; 400) connected to the electronic control unit (200; 400).