WO2007030042A1

WO2007030042A1 - Method and device for controlling a clutch in a vehicle

Info

Publication number: WO2007030042A1
Application number: PCT/SE2005/001306
Authority: WO
Inventors: Marcus Steen; Sixten Berglund; Svante Karlsson; Erik Lauri
Original assignee: Volvo Lastvagnar Ab
Priority date: 2005-09-08
Filing date: 2005-09-08
Publication date: 2007-03-15
Also published as: EP1928716A4; JP2009507702A; EP1928716A1; JP4804536B2

Abstract

Method and device for controlling a clutch (3) in a vehicle comprising as long as the displacement of a throttle control (13) remains within a preselected throttle control creep speed range or a brake control (9) remains within a preselected brake control creep speed range, and a first displaced position is selected within one of said ranges, said first displaced position corresponding to a first vehicle creep speed, a control unit (10, 12, 14, 16) maintains said first vehicle creep speed by controlling at least one of brake actuator, engine and clutch actuator as long as the throttle control or the brake control remains substantially in said first displaced position.

Description

Method and device for controlling a clutch in a vehicle

TECHNICAL FIELD OF THE INVENTION

The present invention relates to controls for automatic clutches associated with vehicular drivetrains and, in particular, to controls for enhanced slow-speed operation (marshalling) of vehicles provided with automatic clutches and automated mechanical transmission systems, in which transmission systems the automatic clutches can be incorporated.

More particularly, the present invention relates to a method and device to simplify handling of a vehicle at marshalling, i. e. especially at vehicle velocities where the engine would run under idle speed (creep speed) if not the clutch would be arranged to slip, and where the vehicle preferably is equipped with a automated transmission system as defined in the preamble of claim 1, the features of which are well- known in this art.

The present invention also relates to a computer program for executing such a method with a computer.

STATE OF THE ART

Vehicular automated master friction clutches, including automated clutches providing start-from-stop operation, and automated mechanical transmission systems utilizing the same are well known in the prior art. Such systems, when utilized in heavy-duty vehicles such as trucks, tractor-semitrailers and buses, typically include mechanical transmissions having 9 to 18 or more forward gear ratios of the types illustrated e. g. in

WO2004/023003 and WO03/038314. With a two-pedal

(accelerator pedal and brake pedal) automated transmission system it is possible to drive the vehicle at creep speed and control the velocity of the vehicle O

even if the velocity is below synchronous engine idle speed, i. e. rotation speed of transmission input shaft is below engine idle speed preferably when the transmission has the lowest gear ratio engaged.

When a driver of such vehicle tries to reverse close to something e. g. dischargable loader/container, loading dock or trailer it is often difficult to control the speed of the vehicle, when moving with creep speed (i. e. below synchronous engine idle speed). According to prior art, one way to control the creep speed in a vehicle with a two-pedal automated transmission system, is to brake the vehicle down to desired creep speed, and then control the vehicle speed by depressing the brake pedal and accelerator pedal at the same time and each pedal with varying degree, dependent on desired/needed propulsive power. Since lowest gear is engaged and vehicle speed is below corresponding synchronous engine idle speed the system will control the slip of the clutch accordingly. To control the clutch slip with the brake pedal and accelerator pedal is not an easy thing to do when the driver at the same time must control the steering wheel and at which direction the vehicle, perhaps e. g. connected with a trailer with two axles (where the front axle of the trailer is turnable) is moving. The handling problems of the vehicle increases even more if the road surface is bumpy, soft or gives a varying travel resistance in some way. The problem is that it is difficult to control the speed of the vehicle to a desired fixed creep speed. Either the risk is that the speed will become to high and the vehicle will bang into said something that the driver wants to move close to or the vehicle will stop before it reaches the desired position.

EP0731294 describes a vehicular system for enhanced creep control in a vehicle equipped with automated start-from-stop clutch control. The enhanced creep _ r> _ control is activated via a shift selector 60 or a button 62. When the enhanced creep control is activated the clutch will be caused to slip such that input shaft speed will equal engine speed multiplied by the accelerator pedal position (T) divided by the reference accelerator pedal position (T_REF) . In the enhanced creep mode, creep controls are effective over an expanded range of accelerator pedal positions, such as from about 0% to 75% accelerator pedal displacement, to provide easier control of low-speed vehicle operation. The throttle position is proportional to the fuelling of the engine (i. e. driving force), which means that the driver have to continuously adapt the throttle displacement position to control vehicle speed and if negative travel resistance occurs, the driver will have to apply the brakes.

One object of the present invention is to make it easier for the driver to control the vehicle speed during creep mode, thus making it easier to handle the vehicle during e. g. marshalling. Another object of the present invention is to fully automatize engagement and disengagement of creep mode in a vehicle equipped with a two pedal automated transmission system, and thus making it simpler for the driver to handle the vehicle.

SUMMARY OF THE INVENTION

The solution of the problem according to the invention with regard to the method according to the invention is described in patent claim 1 and with regard to the device in patent claim 7. Patent claims 2 to 6 and 8 to 16 describe preferred embodiments and developments of the arrangement according to the invention.

The method for controlling a clutch in a vehicle according to the invention comprises a clutch in a vehicle comprising a fuel controlled internal combustion engine, a manually controlled throttle control displaceable between 0% and 100% displaced positions, a service brake system with brakes and brake actuators for controlling the brakes, a manually controlled brake control displaceable between 0% and 100% displaced positions, a multiple-speed transmission having an input shaft, said clutch being drivingly interposed between an output shaft of the engine and said input shaft, a clutch actuator for causing said clutch to be fully engaged, fully disengaged or partially engaged, at least one control unit for receiving input signals including signals indicative of vehicle speed, engaged ratio of said transmission, rotational speed of said engine, rotational speed of said input shaft and displacement of said throttle control or brake control, and for processing said signals in accordance with programmed logic rules to issue command output signals to said engine, for torque request, and to system actuators including at least said clutch actuator and brake actuator. The method is characterized in that as long as the displacement of said throttle control remains within a preselected throttle control creep speed range or said brake control remains within a preselected brake control creep speed range, and a first displaced position is selected within one of said ranges, said first displaced position corresponding to a first vehicle creep speed, said at least one control unit maintains said first vehicle creep speed by controlling at least one of said engine, said brake actuator and said clutch actuator as long as the throttle control or the brake control remains substantially in said first displaced position.

A major advantage of the arrangement according to the invention is that the driver will not need to control the displacement of the throttle control or the brake control to maintain a selected speed. Instead, the control unit according to the invention controls and regulates the fuelling of the engine, the clutch actuator and the brake actuators automatically and in the best way to maintain selected creep speed, independent of vehicle travel resistance and the variation of the vehicle travel resistance during creep speed manoeuvring of the vehicle. The driver will just have to hold the throttle control or the brake control in a fixed displaced position to get a certain vehicle creep speed. This simplifies the handling of the vehicle during e. g. marshalling.

In a preferred embodiment of the method according to the invention said at least one control unit is causing operation in a creep control mode upon sensing;

-unsynchronized speed over the output shaft, the clutch and the input shaft, -lowest available transmission ratio engaged,

-and a selected displacement of said throttle control within said throttle control creep speed range that has an extension between 0% and up to a first predetermined limit.

The advantage of this is that when said conditions are fulfilled the system according to the invention will automatically engage said creep mode and the driver will control the vehicle by choosing a throttle control position and thus choosing a vehicle creep speed connected to that particular throttle position. The throttle control creep speed range can be between 0% and up to a first predetermined limit, where the first predetermined limit preferably can be from 30% to 50%.

In another preferred embodiment of the method according to the invention said at least one control unit is causing operation in a creep control mode upon sensing:

-synchronized speed over the output shaft, the clutch and the input shaft,

-lowest available transmission ratio engaged, -decreasing vehicle speed near corresponding rotational engine idle speed, -and a selected displacement of said brake control is within said brake control creep speed range that has an extension between 0% and up to a second predetermined limit.

The advantage of this is that when said conditions are fulfilled the system according to the invention will automatically engage said creep mode and the driver will control the vehicle by choosing a brake control position and thus choosing a vehicle creep speed connected to that particular brake position. The brake control creep speed range can be between 0% and up to a second predetermined limit, where the second predetermined limit preferably can be from 30% to 50%.

In a further preferred embodiment of the method according to the invention said at least one control unit is causing deactivation of the creep control mode upon sensing one of: -zero vehicle speed,

-or that a new displacement of said throttle control or brake control is selected that has a value that is outside said throttle control creep speed range or brake control creep speed range.

An advantage of this is that when one of said above conditions is met the creep mode will be deactivated and the vehicle will be driven in normal known operational mode.

In a further preferred embodiment of the method according to the invention said at least one control unit is receiving input signals indicative of power consumption of, in the vehicle arranged, one or more accessory units. The embodiment is characterized in that said at least one control unit is using said input signals indicative of power consumption of one or more accessory units as one of the input signals for maintaining said first vehicle creep speed by controlling said fuelling. The advantage of this is that the control unit takes into account power consumptions coming from other consumers than the propulsion of the vehicle. The system will be able to better hold a chosen vehicle creep speed during a creep speed drive.

The above mentioned embodiments are also present in corresponding device claims. Further advantageous embodiments of the invention emerge from the dependent patent claims following patent claim 1 and claim 7 respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater detail below with reference to accompanying drawings which, for the purpose of exemplification, show further preferred embodiments of the invention and also the technical background.

Figure 1 shows diagrammatically a view of an embodiment of the invention.

Figure 2 shows diagrammatically a diagram over how vehicle creep speed is related to the displacement of the brake control or throttle control respectively. Figure 3 shows tables with examples over different control displacements and related transmission output speed. Figure 4 shows an apparatus, which is used according to at least one embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Figure 1 shows a vehicle 1 with a drive line comprising a fuel controlled internal combustion engine 2, a clutch 3, a multiple-speed transmission 4 having an input shaft (not shown) , propeller shaft 5, and a pair of driven wheels 6. The driving force from the engine 2 is transmitted by the clutch 3, the gearbox 4 and the propeller shaft 5 out to the driven wheels 6 in a known manner. The vehicle 1 is also equipped with a pair of front wheels 7, which preferably are steerable and controlled by a driver of the vehicle through a steering system (not shown) in a known manner.

The vehicle 1 is further equipped with a service brake system for retarding the vehicle. Service brakes with brake actuators 8 are controlled in a known manner by the driver through a manually controlled brake control 9 displaceable between 0% and 100% displaced positions, where 0% means that the brake control is released and the brakes are released, and 100% means that the brake control is pressed down to its maximum and the vehicle is retarded with maximum possible braking power. In the shown embodiment the brake control 9 is a foot brake pedal. For retarding the vehicle the driver presses the brake control 9 and a brake signal is generated and transmitted to a brake control unit 10. The brake control unit then instantly demands braking power by activating the brake actuators 8 for controlling the brakes. The transmittal of the braking signal from the brake control unit to the brake actuators is indicated in figure 1 by wire 11, thus the connection all the way out to the brakes and brake actuators 8 are not shown.

The fuelling of the engine 2 is controlled by an engine control unit 12 that controls an engine fuelling device (not shown) . When the driver demands more propulsive power he can do so by pressing the throttle control 13 to displacement positions between 0% and 100%. 100% displacement gives maximum available response from the engine 2. When 0% displacement the engine 2 will be fuelled and controlled by an idle speed regulator (not shown) in a known manner. In the shown embodiment the throttle control signal reaches the engine control unit 12 via a vehicle control unit 14 and a vehicle data network 15. The network 15 integrates in a known manner the communication between the different control units in the vehicle.

The clutch 3 and its clutch actuator 17 and the transmission 4 are controlled by a transmission control unit 16. The clutch 3 can be of the dry disk clutch type and the transmission 4 can be of the automated mechanical transmission type, both well documented in prior art (see e. g. WO2004/023003 and WO03/038314) . The clutch actuator 17 may be operatively coupled to a movable one of the clutch disks (not shown) for control of the clutch from full disengagement through partial engagement to full engagement. In a typical vehicular application, clutch actuator 17 may be electrical, hydraulic, mechanical, pneumatic, or some combination thereof, and typically is position- or pressure- controlled. The clutch actuator 17 controls the degree of clutch engagement according to a clutch engagement signal from the transmission control unit 16 and preferably is a closed-loop-type device providing feedback signals to the transmission control unit 16. The different clutch engagement positions are chosen dependent on demanded torque transfer from the engine 2 to the transmission 4.

All mentioned control unites are connected to the data network 15, thus information can be shared between the different control units.

When the vehicle 1 is standing still, or almost still

(i. e. unsynchronized speed over the output shaft, the clutch and the input shaft) and the driver of the vehicle needs to drive in a vehicle creep speed, the driver can preferably manually choose the lowest available gear speed ratio for starting the vehicle. According to the invention, when the driver depresses throttle control 13 to a position within said throttle control creep speed range, the creep speed mode will be engaged and the vehicle will start to move and accelerate to the vehicle creep speed corresponding to that particular chosen throttle control position. If the throttle control creep speed range is between e. g. 0% and 50% displaced position and the throttle control is moved to a position within said range the vehicle control unit 14 will register said position.

The vehicle control unit 14 then sends the information about said position out on the data network 15 and, thus makes the information available for other control units connected to the network 15, such as the the transmission control unit 16, which picks up the throttle control displacement information. With the manually chosen lowest available starting gear and the throttle control within said range the transmission control unit will, accordning to the invention, interpret said throttle control position and chosen gear as a demand to drive with a certain vehicle creep speed. The transmission control unit 16 will demand the torque needed from the engine control unit 12 to start the vehicle and accelerate it to the demanded creep speed, that corresponds to a engine rotational speed below engine idling speed. The engine control unit 12 controls the fuelling of the engine 2 in a known manner. When the engine is idling the fuelling is preferably controlled by an idling speed regulator (not shown) . The transmission control unit 16 will control the clutch actuator 17 for controlling the clutch engagement as a function of incoming signals indicative of vehicle speed, engaged ratio of said transmission, rotational speed of said engine, rotational speed of said input shaft. The transmission control unit will further according to the invention also send signals to the brake control unit 10, demanding braking power when needed to hold said demanded creep speed. The brake control unit 10 will send signals to the brake actuators 8 for braking the vehicle 1. Thus, if the vehicle travels on approximately horizontal ground and suddenly will be moving over a bump, the vehicle will experience an increase in the travel resistance of the vehicle 1 when a first wheel pair(e. g wheels 6 if the vehicle moves backwards over the bump) hits the bump.

According to the invention the vehicle will aim at holding the demanded creep speed even if the travel resistance suddenly increases. The transmission control unit 16 will increase the amount of torque transferred to the transmission 4 and the driving wheels 6 by a slight clutch engagement increase. When the first wheel pairs comes to the top of the bump the vehicle travel resistance will decrease and the vehicle will begin to accelerate. Sensing the incipient acceleration of the vehicle 1 the transmission control unit 16 will send signals to the clutch actuator 17 to decrease the amount of torque transferred to the transmission and at the same time send signals to the brake control unit 10 to brake the vehicle. The effect from the braking will influence the vehicle speed faster than the increased disengagement of the clutch 3, and thus the demanded creep speed will be maintained. During the time the creep mode is engaged the engine 2 will run at idling speed. There could be exceptions to this when starting the vehicle, depending on the vehicle travel resistance at the start of the vehicle 1.

The driver can change the throttle control position during engaged creep speed mode to another position within said throttle control creep speed range and thus getting another vehicle creep speed.

To disengage the creep speed mode the driver only has to press the throttle control beyond the throttle control creep speed range, i. e. in the given example beyond 50% displaced throttle position. This, the driver can do if he is demanding higher vehicle speed than vehicle creep speed. Alternatively if the driver wants to stop the vehicle he will only have to press the brake control to stop the vehicle and disengage the creep speed mode.

In an alternativ embodiment an automatic gear selection mode is chosen by the driver through a not shown gear selection lever. The transmission control unit 16 then picks up the information about the throttle control position from the network 15 chosen by the driver and, if the throttle control position is within said range, interprets the signal as that a certain creep speed is demanded. The transmission control unit will then automatically choose the lowest available gear ratio as a starting gear and creep speed gear. During start and driving in creep speed mode said actuators and said fuelling of the engine 2 will be controlled as in the embodiment mentioned above to maintain demanded and selected vehicle creep speed.

The vehicle creep speed mode can also be engaged when the vehicle is travelling with speed above creep speed and controlled by the brake control 9. The conditions for engaging creep speed by the brake control 9 is that the rotational speed over the engine output shaft, the clutch 3 and the transmission input shaft has to be synchronized, lowest available transmission ratio engaged, the vehicle speed is near corresponding rotational engine idle speed and decreasing, and a selected displacement of said brake control has to be within said brake control creep speed range. that has an extension between 0% and up to a first predetermined limit. The input signals for said conditions are measured in a known manner and in the same way as mentioned in the throttle control embodiment above. If the brake control creep speed range is between e. g. 0% and 30% displaced position and the brake control is moved to a position within said range the brake control unit 10 will register said position. The brake control unit 10 then sends the information about said brake control position out on the data network 15 and, thus makes the information available for the transmission control unit 16, which picks up the brake control displacement information. With said above mentioned conditions sensed and the brake control within said range the transmission control unit 16 will, according to the invention, interpret said brake control position and said conditions as a demand to drive with a certain vehicle creep speed. The transmission control unit 16 controls said actuators and engine fuelling during creep mode in the same manner as in the throttle control embodiment above. Also in this embodiment the driver can change brake control position within said brake control creep speed range and, thus, getting another vehicle creep speed. Preferably automatic mode is chosen for the transmission. Alternatively the driver can chose the lowest available gear manually.

To disengage the creep speed mode the driver only has to press the brake control 9 beyond the brake control creep speed range, i. e. in the given example beyond 30% displaced throttle position, and thus stopping the vehicle 1. Alternatively the driver can release the brake control and the vehicle will accelerate to a vehicle speed corresponding to engine idle speed when the clutch 3 is fully engaged, i. e. synchronous speed over engine output shaft, clutch 3 and transmission input shaft.

Figure 2 shows through curve A a preferred relationship between vehicle creep speed and throttle control position. In the same figure 2 curve b shows a preferred relationship between vehicle creep speed and brake control position. Vehicle speed corresponding to engine idle speed when the clutch 3 is fully engaged, i. e. synchronous speed over engine output shaft, clutch 3 and transmission input shaft, is indicated by the horizontal dotted line. X% and the vertical dotted line indicates upper limit for throttle control creep speed range or brake control creep speed range. selected displacement of said throttle control within said throttle control creep speed range that has an extension between 0% and up to a first predetermined limit

Figure 3 shows two tables with examples of which transmission output shaft speed the vehicle 1 will get when a certain throttle or brake control displacement within said creep speed ranges is chosen. For example a by the driver selected brake control displacement of 20% gives a transmission output shaft speed of 5 rpm.

Figure 4 shows an apparatus 500 according to one embodiment of the invention, comprising a nonvolatile memory 520, a processor 510 and a read and write memory

560. The memory 520 has a first memory part 530, in which a computer program for controlling the apparatus

500 is stored. The computer program in the memory part 530 for controlling the apparatus 500 can be an operating system.

The apparatus 500 can be enclosed in, for example, a control unit, such as the control unit 16. The data- processing unit 510 can comprise, for example, a microcomputer .

The memory 520 also has a second memory part 540, in which a program for controlling the creep mode function according to the invention is stored. In an alternative embodiment, the program for controlling the creep mode function is stored in a separate nonvolatile data storage medium 550, such as, for example, a CD or an exchangeable semiconductor memory. The program can be stored in an executable form or in a compressed state.

When it is stated below that the data-processing unit 510 runs a specific function, it should be clear that the data-processing unit 510 is running a specific part of the program stored in the memory 540 or a specific part of the program stored in the nonvolatile recording medium 550.

The data-processing unit 510 is tailored for communication with the memory 550 through a data bus 514. The data-processing unit 510 is also tailored for communication with the memory 520 through a data bus 512. In addition, the data-processing unit 510 is tailored for communication with the memory 560 through a data bus 511. The data-processing unit 510 is also tailored for communication with a data port 590 by the use of a data bus 515.

The method according to the present invention can be executed by the data-processing unit 510, by the data- processing unit 510 running the program stored in the memory 540 or the program stored in the nonvolatile recording medium 550.

The invention is applicable both to lowest forward and backward gear.

It is possible to in one embodiment only have the throttle control to work as an creep speed mode initiating control according to the invention. In another embodiment instead only the brake control would work as an creep speed mode initiating control according to the invention.

The upper limit for the creep speed ranges for both throttle control and brake control is predetermined and can preferably be between 30% and 50%. The lower limit of said ranges starts preferably just above 0% displaced position.

In an alternative embodiment of the invention the creep mode can be deactivated first after a new displacement of said throttle control or brake control is selected that has a value that is outside said throttle control creep speed range or brake control creep speed range, and that the vehicle, after said new displacement has occurred, has travelled a predetermined distance, that e. g. can be 10 metres.

The throttle control can be an accelerator pedal controlled with the foot of the driver or some kind of hand regulated control (e. g. button, knob, lever) . The brake control can be a brake pedal controlled with the foot of the driver or some kind of hand regulated brake control (e. g. button, knob, lever).

In an alternative embodiment of the invention the driver first activates the creep mode according to above mentioned embodiments, i. e. with the throttle control or brake control and selects a certain vehicle creep speed. When the vehicle creep speed is selected the driver locks the selected creep speed with another control, that can e. g. be the cruise control of the vehicle. Thus, the driver would not need to hold the throttle control or brake control in a certain displacement to maintain a certain creep speed and can now fully concentrate on the steering of the vehicle. To stop the vehicle and disable creep mode the driver can preferably press the brake pedal.

The different functions of the control units disclosed in the embodiments can be distributed between the control units in many different ways. The number of control units can also be varied, which means that the connections between the different components in the systems can be varied in many ways . The invention must not be regarded as being limited to the exemplary embodiments described above, a number of further variants and modifications being feasible without departing from the scope of the following claims.

Claims

PATENT CLAIMS

1. Method for controlling a clutch (3) in a vehicle comprising a fuel controlled internal combustion engine (2) , a manually controlled throttle control

(13) displaceable between 0% and 100% displaced positions, a service brake system with brakes and brake actuators (8) for controlling the brakes, a manually controlled brake control (9) displaceable between 0% and 100% displaced positions, a multiple- speed transmission (4) having an input shaft, said clutch (3) being drivingly interposed between an output shaft of the engine (2) and said input shaft, a clutch actuator (17) for causing said clutch (3) to be fully engaged, fully disengaged or partially engaged, at least one control unit (10, 12, 14, 16) for receiving input signals including signals indicative of vehicle speed, engaged ratio of said transmission, rotational speed of said engine, rotational speed of said input shaft and displacement of said throttle control or brake control, and for processing said signals in accordance with programmed logic rules to issue command output signals to said engine, for torque request, and to system actuators including at least said clutch actuator (17) and brake actuator (8), said method characterized in that: as long as the displacement of said throttle control (13) remains within a preselected throttle control creep speed range or said brake control (9) remains within a preselected brake control creep speed range, and a first displaced position is selected within one of said ranges, said first displaced position corresponding to a first vehicle creep speed, said at least one control unit (10, 12, 14, 16) maintains said first vehicle creep speed by controlling at least one of said engine, said brake actuator and said clutch actuator as long as the throttle control or the brake control remains substantially in said first displaced position.

2. A method as in claim 1, characterized in that said at least one control unit is causing operation in a creep control mode upon sensing; -unsynchronized speed over the output shaft, the clutch and the input shaft,

-lowest available transmission ratio engaged, -and a selected displacement of said throttle control within said throttle control creep speed range that has an extension between 0% and up to a first predetermined limit.

3. A method as in claim 1, characterized in that said at least one control unit is causing operation in a creep control mode upon sensing:

-synchronized speed over the output shaft, the clutch and the input shaft, -lowest available transmission ratio engaged,

-decreasing vehicle speed near corresponding rotational engine idle speed,

-and a selected displacement of said brake control is within said brake control creep speed range that has an extension between 0% and up to a first predetermined limit.

4. A method as in one of the preceding claims, characterized in that said at least one control unit is causing deactivation of the creep control mode upon sensing one of: -zero vehicle speed,

5. A method as in one of the preceding claims, where said at least one control unit is receiving input signals indicative of power consumption of, in the vehicle arranged, one or more accessory units, characterized in that said at least one control unit is using said input signals indicative of power consumption of one or more accessory units as one of the input signals for maintaining said first vehicle creep speed by controlling said fuelling.

6. A method as in one of the preceding claims, characterized in that said first and second predetermined limits both are 30% to 50%.

7. A vehicle (1) comprising a fuel controlled internal combustion engine (2), a manually controlled throttle control (13) displaceable between 0% and 100% displaced positions, a service brake system with brakes and brake actuators (8) for controlling the brakes, a manually controlled brake control (9) displaceable between 0% and 100% displaced positions, a multiple-speed transmission (4) having an input shaft, said clutch (3) being drivingly interposed between an output shaft of the engine (2) and said input shaft, a clutch actuator (17) for causing said clutch (3) to be fully engaged, fully disengaged or partially engaged, at least one control unit (10, 12, 14, 16) for receiving input signals including signals indicative of vehicle speed, engaged ratio of said transmission, rotational speed of said engine, rotational speed of said input shaft and displacement of said throttle control or brake control, and for processing said signals in accordance with programmed logic rules to issue command output signals to said engine, for torque request, and to system actuators including at least said clutch actuator (17) and brake actuator (8), characterized in that said throttle control (13) or brake control (9) having a preselected creep speed range, where each displaced position within said range is corresponding to a certain vehicle creep speed, said at least one control unit (10, 12, 14, 16) is arranged to maintain a selected vehicle creep speed corresponding to a displaced position within said range by controlling at least one of said engine, said brake actuator and said clutch actuator as long as the throttle control or the brake control remains substantially in a displaced position within said range.

8. A vehicle as in the preceding claim, characterized in that said at least one control unit is arranged to cause operation in a creep control mode upon sensing;

-unsynchronized speed over the output shaft, the clutch and the input shaft,

-lowest available transmission ratio engaged, -and a selected displacement of said throttle control within said creep speed range that has an extension between 0% and up to a predetermined limit.

9. A vehicle as in claim 7, characterized in that said at least one control unit is arranged to cause operation in a creep control mode upon sensing:

-decreasing vehicle speed near corresponding rotational engine idle speed,

-and a selected displacement of said brake control is within said creep speed range that has an extension between 0% and up to a predetermined limit.

10. A vehicle as in one of claims 7 to 9, characterized in that said at least one control unit is arranged to cause deactivation of the creep control mode upon sensing one of:

-zero vehicle speed,

11. A vehicle as in one of claims 7 to 10, where said at least one control unit is arranged to receive input signals indicative of power consumption of, in the vehicle arranged, one or more accessory units, characterized in that said at least one control unit is arranged to use said input signals indicative of power consumption of one or more accessory units as one of the input signals for maintaining said first vehicle creep speed by controlling said fuelling.

12. A vehicle as in one of claims 7 to 11, characterized in that said predetermined limit is 30% to 50%.

13. A vehicle as in one of claims 7 to 12, characterized in that said creep speed range has different values for the range limits depending on if the control creep speed range is for the throttle control or for the brake control.

14. A computer program comprising a program code for executing the method as claimed in claim 1, when said computer program is executed on a computer.

15. A computer program product comprising a program code, stored on a computer-readable medium, for executing the method as claimed in claim 1, when said computer program is executed on the computer.

16. A computer program product directly loadable into an internal memory in a computer, which computer program product comprises a computer program for executing the method as claimed in claim 1, when said computer program on the computer program product is executed on the computer.