SE542746C2

SE542746C2 - Method, Computer Program and Control Unit for Accelerating a Motor Vehicle at an Acceptable Wear on the Vehicle's Clutch

Info

Publication number: SE542746C2
Application number: SE1851484A
Authority: SE
Inventors: Martin Jakobsson; Mikael Ögren
Original assignee: Scania Cv Ab
Priority date: 2018-11-29
Filing date: 2018-11-29
Publication date: 2020-07-07
Also published as: DE102019007231A1; SE1851484A1

Abstract

A method, a driveline control unit and a computer program product for accelerating a motor vehicle (V) from an initial velocity (v) to a target velocity (v) while gradually engaging a clutch.A motor vehicle’s (V) driveline accelerates the vehicle (V) from an initial velocity (v) to a target velocity (v) in response to a set of input parameters (v, v, m, F, L). Specifically, a minimum acceleration (a) is determined, which is required to reach the target velocity (v) at an acceptable wear on the vehicle’s (V) clutch (125). The minimum acceleration (a) is determined based on the set of input parameters, which includes a driving resistance (F) for the vehicle (V), a weight (m) of the vehicle (V), a maximal amount of energy (L) absorbable by the clutch (125), and a velocity difference (Δν) between the initial and target velocities (v, v). A control signal (S) controls the driveline (120) to cause the vehicle (V) to accelerate from the initial velocity (v) to the target velocity (v) at least as fast as specified by the minimum acceleration (a).

Description

Method, Computer Program and Control Unit for Accelerating a Motor Vehicle at an Acceptable Wear on the Vehicle’s Clutch TECHNICAL FIELD The invention relates generally to automatic speed control in motor vehicles. In particular, the present invention concerns a method for accelerating a motor vehicle, a driveline control unit implementing this method and a vehicle containing the driveline control unit. The invention also relates to a computer program product and a non-volatile data carrier.

BACKGROUND In autonomously controlled vehicles, it is common practice to accelerate from a standstill relatively quickly in order to minimize the wear on the vehicle’s clutch. If the vehicle carries passengers, such an acceleration may, however, be experienced as uncomfortable by the passengers. Here, a milder acceleration would be preferable. Nevertheless, this causes more wear on the clutch, and complicates determining appropriate service intervals for the clutch.

US 2013/0281260 discloses systems and methods for assisted direct start control. An example method varies engine torque, forward clutch engagement pressure, and wheel brake pressure during a vehicle launch responsive to longitudinal vehicle grade to improve launch performance.

WO 2010/047652 describes a method for speed control of an engine of a motor vehicle with automatic transmission at the time of engaging a clutch of the vehicle when setting the vehicle in motion. The method involves: - requesting a desired clutch torque; - determining current clutch torque of the clutch and a closing rate for the clutch at the time of engaging it; - determining a dynamic torque increase required for providing the engine speed increase required when engaging the clutch at said closure rate; - determining, on the basis of parameters comprising said current clutch torque and said dynamic torque increase, a necessary engine torque for achieving said requested clutch torque; - determining from said necessary engine torque for the engine a necessary engine speed for achieving said requested clutch torque; - raising the engine speed to the necessary engine speed if the necessary engine speed is greater than a predetermined engine speed.

Thus, different solutions are known for controlling motor vehicles to accelerate automatically. However, there is yet no such method, which ensures that the clutch does not experience excessive wear.

SUMMARY One object of the present invention is therefore to offer an enhanced solution for accelerating a motor vehicle to a target velocity while gradually engaging the clutch, so that at a target velocity, the clutch can be fully engaged.

According to one aspect of the invention, this object is achieved by a method performed in a driveline control unit, which method involves accelerating a motor vehicle from an initial velocity, for example from a standstill position, to the target velocity. A set of input parameters is obtained in the driveline control unit; and based on the set of input parameters, the control unit controls the vehicle to accelerate from the initial to the target velocity. Specifically, a processing circuitry in the control unit determines a minimum acceleration, which is required to reach the target velocity at an acceptable wear on a clutch in the vehicle. The minimum acceleration is determined based on the set of input parameters, which includes a driving resistance for the vehicle, a weight of the vehicle, a maximal amount of energy absorbable by the clutch, and a velocity difference between the initial and target velocities. A control signal is generated, which is configured to control a driveline in the vehicle to cause the vehicle to accelerate from the initial velocity to the target velocity at least as fast as specified by the minimum acceleration.

This method is advantageous because, in addition to ensuring that no more than an acceptable amount of energy is absorbed by the clutch, the method enables predicting the clutch wear very precisely. Consequently, a service scheme for the clutch can be made highly accurate.

According to one embodiment of this aspect of the invention, the minimum acceleration is determined in proportion to the driving resistance, and in a quadratic relation to the velocity difference.

Preferably, the minimum acceleration, amin, is determined as: Image available on "Original document" where Fe is the driving resistance, L is the maximal amount of energy absorbable by the clutch with respect to the acceptable wear, ?? is the velocity difference between the initial and target velocities, and m is the weight of the vehicle.

Thereby, an acceleration value can be calculated, which reflects a constant velocity increase from the initial to the target velocity, and guarantees that the clutch does not experience any unnecessary wear.

According to another embodiment of this aspect of the invention, the maximal amount of energy absorbable by the clutch is either a constant figure, or a variable parameter. In the former case, the constant figure is set to an empirically verified magnitude for the specific clutch; and the latter case, the parameter is determined based on a current temperature of the clutch, a service interval for the clutch and/or a fuel consumption constraint. Hence, the minimal acceleration can be calculated with further improved precision.

According to still another embodiment of this aspect of the invention, the driving resistance, in turn, contains: a road inclination factor, an air resistance parameter and/or a rolling resistance parameter. This allows for a dynamic and high-quality assignment of the driving resistance. As a result, the minimal acceleration can also be determined more appropriately.

According to yet another embodiment of this aspect of the invention, the target velocity is a highest velocity at which the clutch is fully engaged. In other words, the clutch may be fully engaged at a velocity below the target velocity. This is associated with an even lower clutch wear, however presumably also a somewhat poorer comfort for any passengers in the vehicle.

According to a further aspect of the invention the object is achieved by a computer program containing instructions which, when executed on at least one processor, cause the at least one processor to carry out the above-described method.

According to another aspect of the invention, the object is achieved by a non-volatile data carrier containing such a computer program.

According to yet another aspect of the invention, the above object is achieved by a driveline control unit adapted to be included in a vehicle for accelerating the vehicle from an initial velocity to a target velocity while gradually engaging a clutch in the vehicle. The driveline control unit is configured to obtain a set of input parameters, and based thereon, control the vehicle to accelerate from the initial to the target velocity. A processing circuitry in the control unit is specifically configured to determine a minimum acceleration required to reach the target velocity at an acceptable wear on the clutch. The minimum acceleration is determined based on the set of input parameters, which comprises a driving resistance for the vehicle, a weight of the vehicle, a maximal amount of energy absorbable by the clutch, and a velocity difference between the initial and target velocities. The processing circuitry is further configured to generate a control signal configured to control the vehicle to accelerate from the initial velocity to the target velocity at least as fast as specified by the minimum acceleration. The advantages of this control unit, as well as the preferred embodiments thereof, are apparent from the discussion above with reference to the proposed method.

According to still another aspect of the invention, the object is achieved by a vehicle including the proposed control unit for detecting faults in a driver-assistance system of the vehicle.

Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

Figure 1 schematically depicts a vehicle at an initial position when travelling at an initial velocity and at a later point in time when travelling at a target velocity; Figure 2 shows a block diagram over a driveline control unit according to one embodiment of the invention; and Figure 3 illustrates, by means of a flow diagram, the general method according to the invention.

DETAILED DESCRIPTION To the left, Figure 1 schematically depicts a motor vehicle V at an initial position when travelling at an initial velocity vo. To the right, the vehicle V is depicted at a later point in time when traveiling at a target velocity vt. Typically, the initial velocity vo is zero; and for a heavy motor vehicle, e.g. a truck or a bus, the target velocity vt is given by the engine’s idling speed and the currently selected gear. However, according to the invention, any other values of the initial velocity vo and the target velocity vt are equally well conceivable, provided that vt > vo.

The vehicle V has a driveline, which in Figure 1 is illustrated by the reference sign 120. The driveline 120 contains the components of the vehicle’s V power train between the transmission and the differential. The driveline 120 may thus include a drive shaft and a universal joint.

Figure 1 also symbolically shows a clutch 125 in the vehicle V, i.e. a mechanical device that is configured to engage and disengage power transmission from the engine’s driving shaft to a driven shaft of the driveline 120.

The vehicle V further contains a driveline control unit 110, which, via a control signal Sctri, is configured to cause the vehicle V to accelerate from an initial velocity vo to a target velocity vt while gradually engaging the clutch 125. To this aim, the driveline control unit 1 10 is configured to obtain a set of input parameters based upon which the acceleration is controlled.

Referring now to Figure 2, we see a block diagram over the driveline control unit 110 according to one embodiment of the invention. The driveline control unit 110 is preferably implemented in one or more so-called ECUs (Electronic Control Units) in the vehicle V, which ECUs exchange data and instructions with other units, sensors and actuators in the vehicle V via a CAN (Controller Area Network) bus, or analogous internal communications network.

The driveline control unit 110 contains a processing circuitry 112 and a non-volatile data carrier 114, which is communicatively connected to the processing circuitry 112. The non-volatile data carrier 114, in turn, includes a computer program product 115 containing software for executing the below described method when run on the processing circuitry 112. In response to control by the software, the processing circuitry 112 is specifically configured to determine a minimum acceleration amin, which is required to reach the target velocity vt at an acceptable wear on the clutch 125 when starting from the initial velocity vo.

As the clutch is used 125, i.e. engaged and disengaged, it suffers some physical degradation/deterioration. More precisely, during the process of engaging the clutch 125, e.g. at start from a standstill, or in connection with gear shifting, various surfaces within the clutch 125 slide against one another in order to gradually transfer more power to the driveline, and thus attain a comfortable and safe operation of the vehicle. Depending on the degree of sliding of said surfaces against one another, the clutch 125 suffers more or less from the physical degradation/ deterioration. In this disclosure, the term acceptable wear is meant to define how much of this sliding that can be tolerated in order to not cause excessive wear on the clutch 125, and, at the same time, accomplish a comfortable and safe operation of the vehicle.

The processing circuitry 112 determines the minimum acceleration amin based on the set of input parameters, which, in turn, contains a driving resistance Fe for the vehicle V, a weight m of the vehicle V, a maximal amount of energy L absorbable by the clutch 125, and a velocity difference ?? between the initial and target velocities vo and vt. I.e., if the initial velocity vo is zero, the velocity difference ?? becomes equal to the target velocity vt. The maximal amount of energy L absorbable by the clutch 125 may basically be expressed in terms of how much heat that can be dissipated through the clutch 125. As will be discussed below, this energy may be represented by either a constant figure or a dynamic parameter.

The driving resistance Fe is composed by any external causes to that have a decelerating effect on the vehicle’s V propulsion. Consequently, the driving resistance Fe may comprise a road inclination factor (i.e. a gradient or slope measure), an air resistance parameter and/or a rolling resistance parameter.

After having determined the minimum acceleration amin, the processing circuitry 112 generates the control signal Sctri, which is configured to control the vehicle V to accelerate from the initial velocity vo to the target velocity vt at least as fast as specified by the minimum acceleration amin. In other words, a quicker acceleration than the minimum acceleration amin is also acceptable.

Analogously, according to one embodiment of the invention, the target velocity vt is the highest velocity at which the clutch 125 shall be fully engaged. I.e., from a clutch-wear point-of-view, it is equally acceptable to have the clutch fully engaged at any velocity below the target velocity vt.

Preferably, the processing circuitry 112 is configured to determine the minimum acceleration amin in proportion to the driving resistance Fe and in a quadratic relation to the velocity difference ??. More precisely, the minimum acceleration amin may be determined as: Image available on "Original document" where Fe is the driving resistance, L is the maximal amount of energy absorbable by the clutch 125, ?? is the velocity difference between the initial velocity vo and target velocity vt, and m is the weight of the vehicle V.

According to one embodiment of the invention, the processing circuitry 112 is configured to either treat the maximal amount of energy L absorbable by the clutch 125 as a constant figure, or as a dynamic parameter.

If the maximal amount of energy L absorbable by the clutch 125 is regarded as a constant figure, this figure is preferably set to an empirically verified magnitude considering the design of the clutch. In general, this means that for a large and relatively robust clutch, L is comparatively high; and vice versa for a smaller and less robust clutch.

If the maximal amount of energy L absorbable by the clutch 125 is regarded as dynamic parameter; this parameter, in turn, may be determined based on a current temperature of the clutch 125, a service interval for the clutch 125 and/or a fuel consumption constraint. For example, if the current temperature of the clutch 125 is already relatively high, L is set to a somewhat smaller figure than if the clutch temperature had been lower. The service interval for the clutch 125 may influence the maximal amount of energy in such a manner that, typically, L can be set to a higher value for a clutch with shorter service intervals than for an identical clutch with less frequent service occasions. The fuel consumption constraint may influence the maximal amount of energy such that a lower allowed fuel consumption raises L, and vice versa.

In order to sum up, and with reference to the flow diagram in Figure 3, we will now describe the general method according to the invention for accelerating a motor vehicle from an initial velocity to a target velocity while gradually engaging the vehicle’s clutch.

A first step 310, checks if a set of input parameters have been received in the form of: a driving resistance for the vehicle, a weight of the vehicle, a maximal amount of energy absorbable by the clutch, and a velocity difference between the initial and target velocities. If the set of input parameters has been received, a step 320 follows; and otherwise, the procedure loops back and stays in step 310.

In step 320, a minimum acceleration is determined, i.e. a smallest constant velocity increase from the initial velocity to the target velocity. The minimum acceleration is determined based on the set of input parameters, for example in proportion to the driving resistance, and in a quadratic relation to the velocity difference.

Thereafter, in a step 330, a control signal is generated, which is configured to control a driveline in the vehicle to cause the vehicle to accelerate from the initial velocity to the target velocity at least as fast as specified by the minimum acceleration.

Subsequently, the procedure loops back to step 310.

All of the process steps, as well as any sub-sequence of steps, described with reference to Figure 3 above may be controlled by means of at least one programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system, or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital Video/Versatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EPROM (Erasable Programmable Read-Only Memory), an EEPROM (Electrically Erasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal which may be conveyed directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

The term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components. However, the term does not preclude the presence or addition of one or more additional features, integers, steps or components or groups thereof.

The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

1. A method performed in a driveline control unit (110) for accelerating a motor vehicle (V) from an initial velocity (vo) to a target velocity (vt) while gradually engaging a clutch (125) in the vehicle (V), the method comprising: obtaining a set of input parameters (vo, vt, m, Fe, L), and controlling the vehicle (V) to accelerate from the initial to the target velocity based on the set of input parameters, characterized by determining, in a processing circuitry (112) of said control unit (110), a minimum acceleration (amin) required to reach the target velocity (vt) at an acceptable wear on the clutch (125), the minimum acceleration (amin) being determined based on the set of input parameters, which comprises a driving resistance (Fe) for the vehicle (V), a weight (m) of the vehicle (V), a maximal amount of energy (L) absorbable by the clutch (125), and a velocity difference (??) between the initial and target velocities (vo, vt), and generating a control signal (Sctri) configured to control a driveline (120) in the vehicle (V) to cause the vehicle (V) to accelerate from the initial velocity (vo) to the target velocity (vt) at least as fast as specified by the minimum acceleration (amin).

2. The method according to claim 1, comprising determining the minimum acceleration (amin): in proportion to the driving resistance (Fe), and in a quadratic relation to the velocity difference (??).

3. The method according to claim 2, comprising determining the minimum acceleration (amin) as: Image available on "Original document" where Fe is the driving resistance, L is the maximal amount of energy absorbable by the clutch (125), ?? is the velocity difference between the initial and target velocities, and m is the weight of the vehicle (V).

4. The method according to any one of the preceding claims, wherein the maximal amount of energy (L) absorbable by the clutch (125) is: a constant figure, or determined based on at least one of a current temperature of the clutch (125), a service interval for the clutch (125) and a fuel consumption constraint.

5. The method according to any one of the preceding claims, wherein the driving resistance (Fe) comprises at least one of: a road inclination factor, an air resistance parameter and a rolling resistance parameter.

6. The method according to any one of the preceding claims, wherein the target velocity (vt) is a highest velocity at which the clutch (125) is fully engaged.

7. The method according to any one of the preceding claims, wherein the initial velocity (vo) is zero.

8. A computer program product (115) loadable into a non-volatile data carrier (114) communicatively connected to the processing circuitry (112), the computer program product (115) comprising software for executing the method according any of the claims 1 to 7 when the computer program product (115) is run on the processing circuitry (112).

9. A non-volatile data carrier (114) containing the computer program product (1 15) of the claim 8.

10. A driveline control unit (110) adapted to be comprised in a motor vehicle (V) for accelerating the vehicle (V) from an initial velocity (vo) to a target velocity (vt) while gradually engaging a clutch (125) in the vehicle (V), the driveline control unit (110) being configured to: obtain a set of input parameters (vo, vt, m, Fe, L), and control the vehicle (V) to accelerate from the initial to the target velocity based on the set of input parameters characterized in that the control unit (110) comprises a processing circuitry (112) configured to: determine a minimum acceleration (amin) required to reach the target velocity (vt) at an acceptable wear on the clutch (125), the minimum acceleration (amin) being determined based on the set of input parameters, which comprises a driving resistance (Fe) for the vehicle (V), a weight (m) of the vehicle (V), a maximal amount of energy (L) absorbable by the clutch (125), and a velocity difference (??) between the initial and target velocities (vo, vt), and generate a control signal (Sctri) configured to control the vehicle (V) to accelerate from the initial velocity (vo) to the target velocity (vt) at least as fast as specified by the minimum acceleration (amin).

11. The driveline control unit (110) according to claim 10, wherein the processing circuitry (112) is configured to determine the minimum acceleration (amin): in proportion to the driving resistance (Fe), and in a quadratic relation to the velocity difference (??).

12. The driveline control unit (110) according to claim 11, wherein the processing circuitry (112) is configured to determine the minimum acceleration (amin) as: Image available on "Original document" where Fe is the driving resistance, L is the maximal amount of energy absorbable by the clutch (125), ?? is the velocity difference between the initial and target velocities, and m is the weight of the vehicle (V).

13. The driveline control unit (1 10) according to any one of the claims 10 to 12, wherein the processing circuitry (112) is configured to either: treat the maximal amount of energy (L) absorbable by the clutch (125) as a constant figure, or determine the maximal amount of energy (L) absorbable by the clutch (125) based on at least one of a current temperature of the clutch (125), a service interval for the clutch (125) and a fuel consumption constraint.

14. The driveline control unit (1 10) according to any one of the claims 10 to 13, wherein the driving resistance (Fe) comprises at least one of: a road inclination factor, an air resistance parameter and a rolling resistance parameter.

15. The driveline control unit (1 10) according to any one of the claims 10 to 14, wherein the initial velocity (vo) is zero.

16. The driveline control unit (1 10) according to any one of the claims 10 to 15, wherein the target velocity (vt) is a highest velocity at which the clutch (125) is fully engaged.

17. A vehicle (V) comprising a driveline (120) and the driveline control unit (110) according to any one of claims 10 to 15 for controlling the driveline (120).