WO2004005744A1

WO2004005744A1 - A method and device for controlling a disk clutch

Info

Publication number: WO2004005744A1
Application number: PCT/SE2003/000929
Authority: WO
Inventors: Anders Eriksson; Svante Karlsson; Erik Lauri; Marcus Steen
Original assignee: Volvo Lastvagnar Ab
Priority date: 2002-07-05
Filing date: 2003-06-05
Publication date: 2004-01-15
Also published as: SE0202137L; SE524456C2; US7300384B2; EP1532379A1; AU2003242073A1; US20050170933A1; SE0202137D0

Abstract

Method and device for controlling the position of an automatic disk clutch (3) as a function of the position of a throttle lever (48, 49) arranged in the vehicle, the method being employed when starting the vehicle from stationary or virtually from stationary, in which the primary function of the disk clutch (3) is to transmit motive force from an internal combustion engine (1) arranged in a vehicle to an input shaft (7 ) of a stagegeared gearbox (9). The position (48, 49) of the disk clutch is also controlled as a function of at least one of the parameters: vehicle weight, tractive resistance of the vehicle and the selected transmission ratio between the gearbox input shaft and the driving wheels of the vehicle.

Description

14338, DS, 04-07-2002

A method and a device for controlling a disk clutch

BACKGROUND OF THE INVENTION The present invention relates to a method of controlling an automatic disk clutch according to the preamble to claim 1 below, the disk clutch being arranged in a motor vehicle in order to transmit motive force from an internal combustion engine to a gearbox. The invention also relates to a device for the said method according to the preamble to claim 7.

DESCRIPTION OF THE PRIOR ART

Automatic gearboxes of the automatic stagegeared gearbox type have become ever more common in heavier vehicles with the increasing development of microprocessor systems, making it possible, with a control computer and a number of control devices, such as servomotors, for example, to precisely regulate the engine speed, engagement and disengagement of an automatic disk clutch between engine and gearbox, and gearbox clutch members in relation to one another, so that smooth gear changes are always achieved at the correct engine speed. The advantage with this type of automatic gearbox compared to a conventional automatic gearbox made up of planetary gear trains and having a hydrodynamic torque converter on the inlet side lies partly in the fact that it is simpler and more robust and can be manufactured at substantially lower cost than the conventional automatic gearbox, especially where used in heavy vehicles, and partly in that it affords greater efficiency, which means scope for reduced fuel consumption.

A stagegeared gearbox usually comprises an input shaft, an intermediate shaft, which has at least one toothed gear meshing with a toothed gear on the input shaft, and main shaft with toothed gears, which mesh with toothed gears on the intermediate shaft. The main shaft is then further connected to an output shaft coupled to the driving wheels via a prop shaft, for example. Each pair of toothed gears has a different gear ratio from another pair of gears in the gearbox. Different transmission ratios are obtained in that different pairs of gears transmit the torque from the engine to the driving wheels.

The development of computer technology has also had an impact on electronic control and feedback systems for a vehicle engine, and these systems have become more precise, faster and more adaptable to prevailing engine and environmental conditions. The entire combustion process can be precisely controlled according to any operating situation. The vehicle's throttle lever (an accelerator pedal, for example), which primarily controls the fuel supply to the engine, controls the vehicle's engine via electrical wiring and electronic signals. The throttle lever is therefore equipped with sensors for detecting the throttle lever position, that is to say what throttle opening is required.

In the process of starting or maneuvering the vehicle an automatic disk clutch as described above is usually controlled by means of information on the position of the throttle lever, the rotational speed of the engine, the engine output torque, the position of the disk clutch and from a reference position of the disk clutch, which is selected on the basis of when the disk clutch just begins to transmit torque (traction position) , this position being relatively easy to define. A torque typically transmitted in the reference position may be in the order of 30 Nm. The engine output torque is mostly calculated from the quantity of fuel injected into the engine. In the starting sequence and maneuvering the vehicle is typically started from stationary or a virtually stationary state, and the engine commences the sequence at idling speed. The position of the disk clutch and hence the degree of engagement, which determines the torque transmitted from the engine to the gearbox, primarily depends on where the driver positions the throttle lever. The reference position of the disk clutch is used to give the driver of the vehicle more accurate control of the vehicle starting in that the disk clutch assumes the reference position immediately a starting gear is selected. Thus in many situations the driver experiences only a small flat spot, if any, when the accelerator pedal is depressed. The driver therefore obtains a theoretically direct response and the vehicle in principle starts to move as soon as the accelerator pedal starts to be depressed.

Fig. la shows the fundamental correlation between the position of the accelerator pedal and the torque transmitted to the input shaft of the gearbox according to the prior art. When the accelerator pedal is fully released and a starting gear is selected the disk clutch assumes the reference position and a certain torque is therefore transmitted to the input shaft of the gearbox. The more the driver depresses the accelerator pedal the more torque is transmitted to the gearbox and an acceleration of the vehicle is obtained. Fig. lb correspondingly shows basically how, according to the prior art, the position of the disk clutch depends on the position of the accelerator pedal. With the accelerator pedal released the reference position (RF) is assumed, and from the reference position the disengagement diminishes the more the accelerator pedal is depressed, which gives the increasing torque transmission according to Fig. la. The maximum position in Fig. lb denotes the clutch in the fully engaged position.

The reference position and the predefined correlation between accelerator pedal position and disk clutch position functions well in most driving situations. The torque transmission to the gearbox input shaft for a certain clutch position is, however, affected by wear, changes in the coefficient of friction of the disks and variations in the thickness of the disks due to temperature fluctuations, so that the torque transmitted for a certain clutch position may differ somewhat from one starting sequence to another. This can effect the reference position and the flat spot may increase, which leads to an inferior throttle accuracy in the starting sequence. Other and in most situations even more decisive factors are variations in the total weight of the vehicle equipment and the tractive resistance of the vehicle, in which the road gradient, the rolling resistance and the aerodynamic resistance all play a part. Where the actual traction position of a disk clutch ultimately ends up, therefore depends on several factors and may in certain cases vary greatly between two different starting sequences. The driver in certain situations therefore experiences an unsatisfactory throttle accuracy in the handing of the vehicle during the starting sequence due to variations in clutch wear, the coefficient of friction of the disks, the thickness of the disks, the vehicle weight and the tractive resistance of the vehicle.

There is therefore a need, in a vehicle equipped with an automatic disk clutch, to control the work of the clutch more accurately in order to achieve greater throttle accuracy of the vehicle in the starting sequence and maneuvering. This is the primary object of the invention described below.

SUMMARY OF THE INVENTION

The means of achieving the object of the invention in respect of the method and the device according to the invention are described in claim 1 and claim 7 respectively. The other claims describe preferred embodiments and developments of the method according to the invention (2 to 6) and the device according to the invention (8 to 9) . The method according to the invention describes a method for controlling the position of an automatic disk clutch as a function of the position of a throttle lever arranged in the vehicle, the method being used in starting the vehicle from stationary or a virtually stationary state, and in which method the main function of the disk clutch is to transmit motive force from an internal combustion engine arranged in the vehicle to an input shaft to a stagegeared gearbox arranged in the vehicle. The invention is characterized in that the position of the disk clutch is also controlled as a function of at least one of the parameters: vehicle weight, tractive resistance of the vehicle and the selected transmission ratio between the gearbox input shaft and the driving wheels of the vehicle.

The device according to the invention describes a device for controlling the position of a disk clutch, the primary function of which disk clutch is to transmit motive force from an internal combustion engine arranged in a vehicle to the input shaft of a stagegeared gearbox arranged in the vehicle, the device comprising a throttle lever position sensor for a throttle lever arranged in the vehicle, means of determining the tractive resistance of the vehicle, means of determining the vehicle weight and means of determining the selected transmission ratio between the gearbox input shaft and the driving wheels of the vehicle, all of which means and position sensors are coupled to a control unit and in which the control unit is designed to control the position of the disk clutch as a function of a signal from the throttle lever position sensor. The device is characterized in that the control unit is designed, when starting the vehicle from stationary or virtually from stationary, to control the position of the disk clutch also as a function of the signal from at least one of the said means of determining the tractive resistance of the vehicle, means of determining the vehicle weight and means of determining the selected transmission ratio between the gearbox input shaft and the driving wheels of the vehicle.

The advantage of the method and the device according to the invention is that they afford the driver better control of the vehicle in the starting sequence, such control being unaffected by varying vehicle weight, transmission ratio or tractive resistance, since the invention takes account of these parameters.

According to an advantageous second embodiment of the method and the device according to the invention a torque characteristic with the torque values and associated disk clutch position assumed is stored in the control unit. When a clutch position matching a required transmitted torque is attained, the transmitted torque is measured and the control unit registers any new transmitted torque to the relevant clutch position. A

"slow" adjustment of the torque characteristic is achieved.

The advantage of this is that even parameters slowly varying over time, such as changes in the coefficient of friction of the disks due to wear are allowed for in the adjustment of the disk clutch position.

According to an advantageous third embodiment of the method and the device according to the invention the position of the disk clutch is directly controlled through measurement of the transmitted torque.

The advantage of this is that all parameters, that is to say variations in the clutch wear, the coefficient of friction of the disks, disk thickness, vehicle weight and the tractive resistance of the vehicle, for example, are taken into account. The driver will therefore at all times experience the same response for a certain throttle lever position regardless of variations in parameters. Any flat spot on the throttle lever when controlling the starting sequence is eliminated.

Further advantageous embodiments of the invention are set forth in the succeeding dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in more detail below with reference to the drawings attached, which by way of example show further preferred embodiments of the invention and the prior art.

Fig. la and lb show the fundamental correlation between transmitted torque and throttle lever position, and between clutch position and accelerator pedal position according to the prior art .

Fig. 2 shows a schematic diagram of an embodiment of a device for controlling an automatic disk clutch according to the invention, the disk clutch being arranged between an engine and an automatic stagegeared gearbox .

Fig. 3a and 3b show the fundamental correlation between transmitted torque and throttle lever position, and between clutch position and accelerator pedal position according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Fig. 2, 1 denotes a six-cylinder internal combustion engine, for example a Diesel engine, the crankshaft 2 of which is coupled to a single-disk dry clutch generally denoted by 3, which is enclosed in a clutch cover 4. Depending on the magnitude of the maximum torque to be transmitted by the clutch, the clutch may have more than one disk and pressure plate 12. The crankshaft 2 is rotationally fixed to the clutch housing 5 of the clutch 3, while the disk 6 thereof is rotationally fixed to an input shaft 7, which is rotatably supported in a gearbox housing 8 of a gearbox generally denoted by 9. A main shaft 10 and an intermediate shaft 11 are also rotatably supported in the housing 8.

Servo devices (not shown) in the gearbox, which engage and disengage the different gears in the gearbox 9, are controlled by an electronic control unit 45 as a function of control unit input signals representing various engine and vehicle data. Among other things, the control unit 45 comprises a microcomputer with memory units. In the embodiment shown the throttle lever 48 is an accelerator pedal, but it may also feasibly be some form of manually controlled throttle, for example a throttle on the steering wheel . The position of the throttle lever is obtained from an angle sensor 49, which is coordinated with the pedal arm 51 of the throttle lever 48 pivotally mounted on a shaft 50. When the gear selector 46 is in the manual shift position gear shifting is performed at the driver's command via the gear selector 46. The control unit 45, via an engine control unit 15, may also control the fuel injection, that is to say the engine torque or engine speed, as a function of the throttle lever position and the air admission to a pneumatic piston-cylinder device 47, which controls the clutch 3. The position of the automatic clutch 3 is obtained by a position sensor 17.

The degree of engagement of the disk clutch 3 may be divided into several different levels or positions. The traction position is the position of the clutch 3 when it is transmitting just sufficient motive force from the engine 1 to the gearbox 9 that the vehicle can just start to move forwards from stationary. A known method of identifying the traction position is shown, for example, in SE 9903117-1. A typical value for the traction position is a clutch position which transmits approximately 30 Nm.

At the initiation of a starting sequence, for example the selection of a starting gear either by the driver or by the automatic control system, the control unit 45 according to one embodiment of the invention, determines a set-point value for the position of the disk clutch 3 on the basis of prevailing conditions. The control unit 45 picks up signals relating to the parameters: throttle lever position, vehicle weight, tractive resistance and selected transmission ratio between the input shaft 7 of the gearbox 9 and the drive wheels in order to ascertain the prevailing conditions for the starting sequence. The said parameters are collated in a manner known in the art and this will not be discussed further in this application.

The set-point value for the clutch position is determined so that for a given throttle lever position the clutch 3 assumes a more engaged position given a higher vehicle weight and/or greater tractive resistance and/or higher starting gear (lower transmission ratio) , and correspondingly a less engaged position given a lower vehicle weight and/or lower tractive resistance and/or lower gear. Fig. 3b shows the principle of how the control unit 45 selects a set- point value from the said input parameters. If the position of the throttle lever 48 is L, the vehicle is light, a low starting gear is selected and the tractive resistance is low, so the less engaged position X is selected as set-point value of the clutch position. If, at the same throttle opening L, on the other, the vehicle is heavy, a high starting gear is selected and the tractive resistance is high, the position Y is selected as the set-point value for the clutch 3. Consequently a more engaged position which transmits more torque to the input shaft 7 of the gearbox 9. The vehicle weight, the tractive resistance and the starting gear selected very often vary from one starting sequence to another, which for a given accelerator pedal position, for example L, means that the set-point value for the clutch position can, according to the example shown, vary between the position X and Y. The maximum permitted value and the minimum permitted value for the set-point value of the clutch 3 for a certain accelerator pedal position are determined from the capacity of the disk clutch 3, the engine 1 and the transmission (gearbox 3, prop shaft, rear axle with constituent components) . At zero throttle opening, that is to say with the accelerator pedal 48 fully released, the control system 45 selects a set-point value for the clutch position in the range RF1 to RF2 (see Fig. 3b) . The control system 45 may also select a more disengaged position at zero throttle opening, if the control system does not receive signals indicating that the driver intends to start the vehicle, for example if the control system detects that the driver is keeping the vehicle brake pedal depressed.

The invention gives the driver a traction position suited to a certain starting sequence, which eliminates any flat spot on the accelerator pedal 48 by adjusting the starting sequence, that is to say a flat spot between the driver starting to depress the accelerator pedal 48 to an accelerator pedal position in which the torque transmitted is just sufficiently large for the vehicle to start moving. By means of the invention the traction position is attained immediately on starting to depress the accelerator pedal 48.

The transmission control system 45 adjusts the position of the clutch 3 to the position determined by the set- point value function using the position sensor 17. The set-point value is continuously calculated during a starting sequence and can afterwards be modified during a starting sequence, for example depending on whether the driver varies the throttle opening during the starting sequence.

In this embodiment of the invention the torque transmitted to the input shaft 7 of the gearbox 9 may vary somewhat for two different but comparable starting sequences with the same vehicle weight, tractive resistance, transmission ratio and accelerator pedal position. This is because of possible changes in the coefficient of friction of the disks 6, changes in the disk thickness due to temperature fluctuations and any other factors that are difficult to predict. The advantage compared to the prior art is obvious, however, since the control system determines the set- point value from the parameters that have the greatest effect on the ultimate traction position of the clutch 3, that is to say, the vehicle weight, the tractive resistance and the transmission ratio.

According to a second advantageous embodiment of the invention a torque sensor 16 is arranged on the gearbox input shaft 7 (see Fig. 2) . The torque sensor 16 may be of the type in which the shaft 7 is magnetized with a special magnetic pattern. The magnetic pattern is deformed when the shaft 7 is twisted (due to an applied torque) . The measuring circuit of the torque sensor 16 comprises one or more coils which are located around the shaft 7 where the magnetic pattern is situated. The measuring circuit registers the changes in the magnetic pattern and delivers an electrical signal which corresponds to the torque applied. This torque sensor is of the proximity type and is known in the art. Stored in the control system 45 for this embodiment of the invention is a table (torque characteristic of the disk clutch 3) in which a certain clutch position is assumed to correspond to a predetermined value for the torque transmitted to the gearbox input shaft 7. By means of the said table the control unit 45 determines a set-point value for the transmitted torque and corresponding clutch position from the given parameters. Fig. 3a basically shows that if the position of the throttle levers 48 is L, the vehicle is light, a low starting gear is selected and the tractive resistance is low, giving the set-point value MX for the transmitted torque. According to the table stored in the control unit 45, we see, as is shown in Fig. 3b, that the corresponding clutch position assumed is X. The control unit adjusts the clutch position to the set-point value X with the aid of the position sensor 17. When the clutch 3 has assumed the position according to the set-point value, the control system 45 registers this by means of the position sensor 17 and registers the transmitted torque by means of the torque sensor 16. The torque value MX previously assumed for the clutch position X is replaced by a new measured transmitted torque. The control unit 45 continuously updates the torque values in the table during a starting sequence. When the accelerator pedal 48 next assumes the position L and a transmitted torque MX is consequently required, the clutch position may have been adjusted so that the torque actually transmitted corresponds better to what is required. Thus a gradual adjustment of the torque characteristic of the clutch 3 is obtained, which in addition to vehicle weight, tractive resistance, transmission ratio and accelerator pedal position also takes account of changes in the coefficient of friction of the disks 6, and any other factors that are difficult to predict and which vary slowly over time. Consequently more rapid changes such as changes in disk thickness due to temperature fluctuations are more difficult to capture with this embodiment.

In a further preferred embodiment of the invention the torque sensor 16 is used for direct and hence rapid adjustment of torque transmitted to the input shaft 7 of the gearbox 9. Stored in the transmission system 45 is a correlation between transmitted torque and corresponding accelerator pedal position according to Fig. 3a. Following previous examples, the throttle lever position L is selected in the case of a light vehicle with low starting gear and low tractive resistance. As shown in Fig. 3a, this gives the set- point value MX for the transmitted torque. With the aid of the torque sensor 16, the control system 45 adjusts the clutch position so that the transmitted torque MX required by the accelerator pedal 48 is obtained. During a starting sequence the control system 45 continuously adjusts the clutch position in order to obtain the transmitted torque required by the accelerator pedal 48. Consequently a rapid adjustment of the clutch position is obtained in order to achieve the required transmitted torque as a function of vehicle weight, tractive resistance, transmission ratio and accelerator pedal position, irrespective of changes in the coefficient of friction of the disks, changes in disk thickness due to temperature fluctuations and any other factors which are difficult to predict and which vary rapidly or slowly over time.

The invention is not limited to the lowest forward gear of the vehicle but can also be applied to all gears in the gearbox including reverse gears.

The functions of the control unit 45 may be performed by two or more control units.

Claims

1. A method for controlling the position of an automatic disk clutch (3) as a function of the position of a throttle lever (48, 49) arranged in the vehicle, the method being employed when starting the vehicle from stationary or virtually from stationary, in which method the primary function of the disk clutch (3) is to transmit motive force from an internal combustion engine (1) arranged in a vehicle to an input shaft (7) of a stagegeared gearbox (9) arranged in the vehicle, characterized in that the position of the disk clutch (48, 49) is also controlled as a function of at least one of the parameters: vehicle weight, tractive resistance of the vehicle and selected transmission ratio between the gearbox input shaft (7) and the driving wheels of the vehicle.

2. The method as claimed in claim 1, characterized in that a set-point value for the position of the disk clutch (3) is determined as a function of the position of the throttle lever (48) and at least one of the said parameters and that the disk clutch (3) is thereafter set to the position that corresponds to the set-point value.

3. The method as claimed in claim 1, characterized in that a required torque transmitted to the gearbox input shaft (7) is determined as a function of the position of the throttle lever (48) and at least one of the said parameters and that the position of the disk clutch (3) is controlled according to a measurement of the torque actually transmitted to the gearbox input shaft (7) in order to achieve the required transmitted torque.

4. The method as claimed in claim 3, characterized in that the required transmitted torque is represented by a stored disk clutch position and that the disk clutch (3) is adjusted to the stored position, and that when the stored position is attained the transmitted torque is measured and stored together with the relevant clutch position attained, so that each clutch position matching a transmitted torque is subsequently modified or adjusted.

The method as claimed in claim 3, characterized in that the transmitted torque is continuously measured and that the measured torque is used for direct adjustment of the position of the disk clutch (3) until the measured torque attains the same value as the required transmitted torque.

The method as claimed in any one of the preceding claims, characterized in that the method of control is performed after the starting gear has been selected in the vehicle starting sequence from stationary or virtually from stationary.

A device for controlling the position of a disk clutch (3) , the primary function of which disk clutch (3) is to transmit motive force from an internal combustion engine (1) arranged in a vehicle to an input shaft (7) of a stagegeared gearbox (9) arranged in the vehicle, the device comprising a throttle lever position sensor (49) for a throttle lever (48) arranged in the vehicle, means of determining the tractive resistance of the vehicle, means of determining the vehicle weight and means of determining the selected transmission ratio between the input shaft (7) of the gearbox (9) and the driving wheels of the vehicle, all of which means and position sensors are coupled to a control unit (45) , and in which the control unit is designed to control the position of the disk clutch (3) as a function of a signal from the throttle lever position sensor

(49) , characterized in that the control unit (45) is designed, when starting the vehicle from stationary or virtually from stationary, to control the position of the disk clutch (3) also as a function of the signal from at least one of the said means of determining the tractive resistance of the vehicle, means of determining the vehicle weight and means of determining the selected transmission ratio between the gearbox input shaft (7) and the driving wheels of the vehicle

The device for controlling a disk clutch as claimed in claim 7, characterized in that the torque sensor (16) is arranged on the input shaft (7) of the gearbox (9) and that the control unit (45) is designed to continuously compare the torque measured by the torque sensor (16) with the torque required from the throttle lever (48) to the input shaft (7) of the gearbox (9) and to adjust the position of the disk clutch (3) so that the measured torque becomes the required torque.

The device for controlling a disk clutch as claimed in claim 7, characterized in that the control unit (45) is designed to store a table containing the transmitted torque and the matching position of the disk clutch and that the control unit (45) subsequently updates each torque matching a disk clutch position by measuring the transmitted torque in the relevant disk clutch position by means of a torque sensor (16), which is arranged on the gearbox input shaft (7) .