GB2509736A

GB2509736A - System and method for controlling engagement of a clutch when a vehicle is at standstill and based on the gradient on which the vehicle stands

Info

Publication number: GB2509736A
Application number: GB1300480.9A
Authority: GB
Inventors: Pascal Tissot; Rodolphe Querelle; Cyrille Bridier
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2013-01-11
Filing date: 2013-01-11
Publication date: 2014-07-16
Also published as: GB201300480D0; CN103921785A

Abstract

A method for controlling engagement of a clutch (3, Figure 1) for coupling a transmission (5, Figure 1) to an engine (4, Figure 1) of a vehicle (1, Figure 1) includes determining a standstill status of the vehicle 100, deterÂmining the longitudinal acceleration of the vehicle whilst the vehicle (1) is in the standstill status. Determining a gradient from the longitudinal acceleration 102, 104 and determining that a signal representative of a status of a brake pedal indicates that the brake pedal is inactive 106. If the gradient is greater than a first predefined threshold 109, an uphill mode is activated 110 and the clutch (3) is engaged in accordance with the uphill mode. If the gradient is less than a seÂcond predefined threshold 111, a downhill mode 113 is activated and the clutch (3) is engaged in accordance with the downhill mode.

Description

GM Global Technology Operations LLC System and method for controlling engagement of a clutch for coupling a transmission to an engine of a vehicle The present invention relates to a system and a method for controlling engagement of a clutch for coupling a transmission to an engine of a vehicle.

In a conventional automatic transmission, a coupling device is provided to couple a crank-shaft of an engine, such as an internal combustion engine, to the transmission gearing that establishes torque flow paths to the vehicle wheels. The coupling device may be provided as a torque converter included in the driveline between the crankshaft and the transmission or it may be a starting clutch located between the engine and the input shaft of transmission or a starting clutch, which is located inside the transmission as one of the range of clutches applied in the forward and/or reverse gears.

US 7,044,888 B2 discloses a clutch control strategy in which a starting clutch is slipped during vehicle launch to achieve a high torque and minimise vehicle driveline excitation.

The control strategy commences when the engine power increases from idle speed as throttle position changes or when the vehicle starts moving in a creep condition, i.e. when the vehicle launches without acceleration pedal demand.

However, further methods for controlling the engagement of a clutch are desirable.

A method for controlling engagement of a clutch for coupling a transmission to an engine of the vehicle is provided that comprises the following: determining a standstill status of the vehicle, determining the longitudinal acceleration of the vehicle whilst the vehicle is in the standstill status, calculating a gradient from the longitudinal acceleration, determining that a signal representative of a status of a brake pedal indicates that the brake pedal is inactive, and if the gradient is greater than a first predefined threshold activating an uphill mode and engaging the starting clutch in accordance with the uphill mode, or if the gradient is less than a second predefined threshold, activating a downhill mode, and engaging the staffing clutch in accordance with the downhill mode.

The method takes into account the gradient of the surface on which the vehicle is posi-tioned during the standstill status of the vehicle in order to determine whether the vehicle is to take off in a direction uphill or downhill so that the starting clutch can be activated in ac-cordance with an uphill mode or a downhill mode, respectively. This enables the vehicle to be started in either an uphill creep mode or an uphill launch mode or a downhill creep mode or a downhill launch mode such that the clutch engagement is better suited to the desired mode. Clutch engagement may include properties such as clutch engagement timing and clutch slippage The clutch engagement may be adjusted to limit the level of starting clutch slip and dissi-pated power and also to provide safe behaviour, for example a hill hold brake function.

Clutch engagement may also be adjusted to improve vehicle launch and creep on hills to provide improved performance and drivability. Limiting clutch slip may prevent the clutch from overheating. This feature may be used to reduce the clutch hardware sizing.

The above method is used if the vehicle is to take off in a forwards direction uphill or down-hill. In an embodiment, the method further comprises determines if a forwards gear ratio and if a forwards gear ratio is selected, the uphill mode is activated if the gradient is greater than the first predefined threshold, or the downhill mode is activated if the gradient is less than the second predefined threshold.

If the vehicle is to take off in a reverse direction uphill or downhill, then the opposite condi-tions for the predefined thresholds of the gradient apply and the alternative method is used.

In the alternative method, a method for controlling engagement of a clutch for coupling a transmission to an engine of a vehicle comprises the following: determining a standstill status of the vehicle, determining the longitudinal acceleration of the vehicle whilst the vehicle is inthe standstill status, determining a gradient from the longitudinal acceleration, determining that a signal representative of a status of a brake pedal indicates that the brake pedal is inactive, and if the gradient is less than a first predefined threshold, activating an uphill mode, and engaging the clutch in accordance with the uphill mode, or if the gradient is greater than a second predefined threshold, activating a downhill mdde, and engaging the clutch in accordance with the downhill mode: The alternative method may further compiise determining if a backwards gear ratio is se-lected, and if a backwards gear ratio is selected, activating the uphill mode if the gradient is less than the first predefined threshold, or activating the downhill mode if the gradient is greater than the second predefined threshold.

The vehicle may take off in either a creep mode or a launch mode. A creep condition is de-termined if the brake pedal is inactive and an acceleration pedal is inactive. If the uphill mode is active, an uphill creep mode is activated, or if the downhill mode is active, a down-hill creep mode is activated. In both embodiments of the creep condition, a vehicle speed is maintained that is greater than zero and less than a predetermined value.

A launch condition is determined if the brake pedal is inactive, the acceleration pedal is active and a demanded engine torque is greater than a predefined value. If the uphill mode is active, an uphill launch condition is activated, or if the downhill mode is active, a downhill launch mode is activated.

In an embodiment, upon activating the uphill mode, a brake pressure is maintained for a predefined time period after the signal representative of the status of the brake pedal indi-cates that the brake pedal is inactive. Upon expiry of the predefined time period, the clutch is activated and applied to couple the transmission to the engine. The uphill mode, there-fore, includes an ithproved hill hold brake function due to the maintenance of the brake pressure for a predefined time period after the brake pedal is inactive in order to prevent the vehicle from rolling backwards.

In a further development of this embodiment, the engine speed or engine torque is in- creased as a function of the gradient compared to a predetermined engine speed or prede-termined engine torque used in a normal mode. In this sense, a normal mode indicates a mode, which is used when the gradient is determined to be less than the first predefined threshold and greater than the second predefined threshold. Within these thresholds of the gradient, the vehicle is positioned on a surface with a very small gradient. Increasing the engine speed or engine torque as a lunction of the gradient further decreases the likelihood that the vehicle will roll backwards upon activation of the clutch.

The control of the clutch may be calibrated depending on engine torque and engine speed.

In order to link the engine torque TE to the engine speed WE. a K-factor method is defined.

The engagement of the internal starting clutch is controlled in accordance with this law.

ft0s 2 K can be a calibratable value given by tables entered in the calibration software. K will be interpolated between the k1 values of the matrix, depending on the accelerator driver re-quest.

The desired engine speed or engine torque may be determined as a function of gradient by use of a look up table including specific K4actor values for uphill creep or uphill launch.

The predefined time period may be determined as a function of the gradient and, may be increased for increasing uphill gradients. The predefined time period may be taken from a lookup table saved in a memory of control system, which carries out the method, for exam-ple.

Upon activating the downhill mode, the engine speed or the engine torque may be reduced as a function of the gradient compared to a predetermined engine speed or engine torque used in a normal mode. This embodiment takes into account that gravity assists movement of the vehicle in downhill mode so that less engine torque or engine speed is required to initiate movement of the vehicle. Specific K-factors for downhill creep or downhill launch may be used.

The uphill mode may comprise an uphill creep mode and/or the downhill mode may com-prise a downhill creep mode, which are activated when a creep condition of the vehicle is determined.

The creep condition may be determined when the brake pedal is inactive and an accelera-tion pedal is inactive. The uphill creep mode is activated if the gradient is greater than the first predefined value or the downhill creep mode is activated if the gradient is less than a second predefined threshold. The vehicle speed is maintained at a value that is greater than zero and less than a predetermined value, for example 5 km/h. This ensures that the vehicle creeps slowly, even when the acceleration pedal is inactive. The uphill creep mode or downhill creep mode may be useful whilst parking the vehicle or in heavy traffic, for ex-ample1 so that the driver does not constantly have to move between the acceleration pedal and the brake pedal in order to maintain a low speed.

In an embodiment, the method further comprises determining if an uphill launch condition of the vehicle is desired, If an uphill launch condition of the vehicle is determined, an uphill launch mode is activated. The uphill condition may be determined when the brake pedal is inactive, the acceleration pedal is active, a demanded engine torque is greater than a pre- defined value and the gradient is greater than the first predefined threshold. This combina-tion of features may be taken as an indication that the vehicle is likely to launch in an uphill situation.

In the uphill launch mode, an uphill clutch slip control mode may be used to engage the clutch. For example, specific uphill K-factors may be applied; In a further embodiment, it is determined whether a downhill launch condition of the vehicle is desired. If the downhill launch condition is determined, a downhill launch mode is activat-ed. The downhill launch condition may be determined when the brake pedal is inactive, acceleration pedal is active, a demanded engine torque is greater than a predefined value and the gradient is less than a second predefined threshold, which together indicate that vehicle take off in a downhill situation is desired. In the downhill launch mode, a downhill clutch slip control mode is used to engage the clutch. For example, specific downhill K-factors may be applied.

The method according to one of the embodiments described above may be used for engag-ing different types of clutches, for example, a starting clutch within the gearbox of the transmission or clutch positioned between the gearbox and the crankshaft, such as a torque converter, or a dual mass flywheel of a dual clutch transmission.

The methods according to the embodiments described above may be useful for controlling the engagement of an internal starting clutch, i.e. when a clutch within the gearbox is used in place of a standard torque convertor.

Starting clutch transmissions may have reduced torque gain in comparison with transmis-sions with a torque convertor. This means that during vehicle take off, the transmitted torque is lower in the case of a starting clutch transmission. The impact is double on hill conditions: reduced performance and possible rollback in uphill case.

Therefore, a dedicated strategy for starting clutch transmission taking into account the slope indication to enhance performance and drivability is particularly useful for a starting clutch transmission. This strategy may be used to integrate an anti roll-back control method during vehicle launches in uphill condition in order to limit the level of starting clutch slip and dissipated power and to provide a safe behavior.

A system for controlling engagement of the clutch for coupling transmission to an engine of a vehicle is also provided. The system comprises an input for receiving a signal representa- tive of a standstill of the vehicle, an input for receiving a signal representative of the longitu-dinal acceleration of the vehicle, an input for receiving a signal representative of the status of a brake pedal and an input for receiving a signal representative of the status of an accel- erator pedal. The system also comprises means for determining a gradient from the longi- tudinal acceleration and an output for providing an output signal to maintain the brake pros-sure fora predefined period after the signal representative of the status of the brake pedal indicates that the brake pedal is inactive if the condition is met that the signal representative of the longitudinal acceleration indicates that the gradient is greater than a first predefined threshold value. After expiry of predetermined period, the control unit provides an output signal to engage the clutch and to couple the transmission to the engine. Alternatively if the signal representative of the longitudinal acceleration indicates that the gradient is less than a second predefined threshold value, an output signal is provided to engage the clutch to couple the transmission to the engine.

The system may further comprise memory for storing values of engine speed or engine torque as a function of gradient. The system may further comprise an output for providing a signal to an engine control unit to control the engine speed or the engine torque is a func-tion of gradient. This embodiment can be used to further improve the hill hold brake feature and prevent roll-back of the vehicle.

The output for providing the output signal to maintain the brake pressure for the predefined period may be coupled to a brake control unit of the vehicle, such as an ABS system.

The input for receiving the signal representative of the longitudinal acceleration of the vehi- cle may be coupled to a yaw sensor, which may be further coupled to stability control sys-tems of the vehicle.

The system can also include memory storing a table for correlating the longitudinal acceler-ation of vehicle with the gradient on which the vehicle is positioned during standstill of the vehicle. The system may comprise further tables indicating the desirable engine speed or engine torque or K-factors as a function of the gradient.

The standstill of the vehicle may be determined by a signal indicating that the vehicle speed and the vehicle acceleration is zero.

In a further embodiment, a control system comprises an engine control module, a transmis-sion control module, an engine input speed sensor, an engine output speed sensor and a brake control module and the system according to one of the embodiments described above. The system of the embodiments described above may be part of the transmission control module or may be provided as a separate control unit.

A vehicle is also provided which includes an engine coupled to a transmission by engage-ment of a clutch, in particular, an internal starting clutch, using apparatus and/or a system according to one of the embodiments described above.

A computer program for carrying out the method according to one of the embodiments de-scribed herein is also provided. The computer program may be provided as a computer program product or may be stored in memory of a product such as control module of the vehicle, for example a transmission control module.

Embodiments will now be described, with reference to the accompanying drawings.

Figure 1 illustrates a schematic diagram of a vehicle including a system for controlling en-gagement of the clutch according to a first embodiment, Figure 2 illustrates the system for controlling engagement of the clutch according to the first S embodiment, Figure 3 illustrates calculation of a gradient from the longitudinal acceleration of vehicle, Figure 4 illustrates a diagram illustrating different operation modes of the vehicle including a hill hold brake request, Figure 5 illustrates effects of a comparison system and a system with an extended hill brake hold function, Figure 6 illustrates a flow diagram for engaging a clutch in a drive mode, Figure 7 illustrates a flow diagram for engaging a clutch in a reverse mode, and Figure 8 illustrates a table of hill start strategy for differing hill conditions.

Figure 1 illustrates a schematic diagram of a vehicle 1 including a system 2 for controlling engagement of a clutch 3 according to a first embodiment. In this particular embodiment, take off of the vehicle 1 is achieved by a controlled slip of an internal starting clutch (Internal Friction Launch) and not by a torque converter However, the system and methods de- scribed herein can also be used to control a torque convertor including a dual clutch config-uration.

The vehicle 1 includes an internal combustion engine 4 which is coupled to a transmission including gearbox 6 which comprises a number ofgear ratios. One of the clutches within the gearbox 6 provides a starting clutch 3, which may also be denoted as an internal friction launch clutch. The system 2 includes a transmission control module 7 for controlling switch-ing between the gear ratios as well as the starting clutch 3 and an engine control module 8 for controlling the internal combustion engine 4. The system further includes an input speed sensor 9 with which the engine speed and engine torque can be measured and an output speed sensor 10. The transmission S provides torque paths to wheels 11 of the vehicle so as to drive the wheels 11. In this embodiment, the transmission control module 7 controls engagement of the clutch 3.

A clutch pressure control strategy for take off is defined which takes into account three dif- fering road slope conditions; a flat road condition, a downhill condition and an uphill condi-tion. An uphill condition may be more constraining compared to the other cases, because the torque to be transmitted is much higher and the dissipated energy is higher as well. The three differing road slope conditions are selected depending on the slope of the road on which the vehicle stands still as determined from the longitudinal acceleration of the vehicle at rest.

Figure 2 illustrates the system 2 for controlling engagement of the clutch 3 according to the first embodiment. As is illustrated in Figure 2, the vehicle 1 comprises an inertial sensor 12 providing information related to longitudinal, lateral and yaw accelerations. This inertial sen-sor 12 is usually used only by the brake control module 13 to improvethe stability of the vehicle. However, this information is also used by the system 2 to control engagement of the clutch 3.

The system 2 also comprises a first sensor 14 for sensing whether the brake pedal is acti-vated or inactive, a second sensor 15 for sensing whether the accelerator pedal is activated or inactive and a third sensor 16 for determining if the vehicle is in standstill.

When the vehicle 1 is stopped, which is the initial state before the launch or creeping of the vehicle, the longitudinal acceleration is provided by the inertial sensor 12 to the system 2.

An indication of the slope or gradient of the road can be obtained from the longitudinal ac-celeration through a calculation as illustrated in Figure 3.

Figure 3 illustrates that the longitudinal acceleration (mis2) = g*sin. which enables the an-gle -to be calculated. From this angle, the slope or gradient of the surface on which the vehicle is stopped can be calculated, for example as a percentage. A lockup table may be stored in memory of the system including this information.

For example, an uphill mode may be used for controlling clutch engagement for gradients higher than a first predefined value, such as +3% and a downhill mode may be used for hill percentages less than a second predefined threshold value, for example, -3%. Within these two threshold values a normal mode may be used in which the gradient is not taken into account when engaging the clutch to provide a creep capability or a vehicle launch.

The system 2 may include a lookup table 17 from which the gradient of the surface on which the vehicle is situated can be gained from the longitudinal acceleration. The system may include one or more lookup further tables 18 in its memory which include K-factors for different gradients. These tables 18 enable the system 2 to send a signal to the engine con- trol module B to increase the engine torque if the vehicle 1 is to take St uphill or to de-crease the engine torque if the vehicle 1 is to take off downhill.

One or more of the lookup tables 19 may also include clutch slippage values as a function of gradient. These tables 19 enable the system to send a signal to the transmission control unit to increase clutch slippage if the vehicle 1 is to take off uphill or to decrease clutch slip-page if the vehicle I is to take off downhill.

Based on the indication of the slope or gradient of the surface on which the vehicle 1 is stopped, the system 2 may provide a hill brake hold function by sending a signal to the brake control module 13, which controls the vehicle brakes, to maintain the brake pressure for a given time after the brake pedal sensor 14 indicates that the brake released in order that the vehicle 1 remains at standstill on the hill.

The uphill mode may include a function known as an extended hill hold brake request, as is illustrated in figure 4. Figure 4 illustrates the driver brake request 20, the driver acceleration request 21, the extended hill hold brake request 22 generated by the system according to embodiments of the invention and the actual brake action 23 during standstill mode 24, creep mode 25 and the launch mode 26.

During the standstill mode 24, the driver depresses the brake pedal so that it is active, the accelerator pedal is inactive and the brake is applied. The longitudinal acceleration of the vehicle is measured during standstill mode 24. Upon release of the brake pedal by the driv-er at a time 27, the creep mode 25 is entered if the accelerator pedal remains inactive.

However, rather than reducing the brake pressure immediately after the brake pedal is re-leased by the driver, an extended hill hold brake request 28 is sent by the system 2 to the brake control module to maintain the brake pressure for a predetermined period of time.

When the driver depresses the accelerator pedal and the driver brake request is inactive at time 29, launch mode 26 is started. The hill hold brake request continues for a predeter-mined period of time, and upon expiry of this predetermined amount of time at time 30, the brake pressure is reduced as indicated by the actual brake action. At this point, the driver has requested enough torque from the engine to prevent roll-back of vehicle upon release of the brake pressure by the transmission control module 7.

Figure 5 illustrates the effects of a comparison system and a system including an extended hill brake hold function. In the comparison example illustrated on the left, after the brake pedal is released, the brake pressure is reduced and the vehicle rolls backwards indicated by the increased vehicle speed in the region "roll-back". In the system on the right, the brake pressure is reduced only after an additional extended hold time period of 0.7 seconds after release of the brake pedal and rollback is prevented. Also the dissipated energy is lower for the system with the extended hill brake hold function at 53 kJ rather than 66 kJ for the comparison system.

The starting clutch launch and creeping control strategies can be adjusted by extending the hill brake hold feature to the specific needs of the starting clutch device. The transmission control unit takes control on hill brake hold in creep or launch mode by sending requests to the brake control module. The slope is taken into account to improve hill creep capability and hill launch performance and driveability.

The detection of conditions leading to activate the hill control strategy is described in con-nection with Figures 6 and 7. Hill start strategies for differing hill conditions are summarized in the table illustrated in Figure 8. The drive case is considered in Figure 6 and the reverse case in Figure 7. The uphill or downhill strategy is only considered when vehicle take off is started from standstill, i.e. the vehicle is in a standstill mode.

Figure 6 illustrates a flow diagram for engaging a clutch in a forwards drive mode.

As long as the vehicle is in Standstill Mode 100 the slope based on longitudinal acceleration is recorded 101. This value is stored in StandStillslope.

Considering the drive case, if the value of the detected slope is over a defined threshold (noted ThrslopeDefPoso in drive) in box 102 then the default stage UpHillIJef is set to true in box 103. If the value of the detected slope is below another defined threshold (noted ThrSlopeDefNegD in drive) in box 104 then the default stage DwnHillDef is set to true in box 105.

As soon as brake is released in box 106 the Creeping Mode 107 is active. A timer is started S (UpownHillTimer) in box 108. If the value of the slope detected in Standstill Mode is above a given threshold (noted ThrSlopeCreepPosD in drive) in box 109, then uphill creeping stage is activated and UpHilICrp is set to true in box 110. If the value of the slope detected in Standstill Mode is below another defined threshold (noted ThrSlopeCreepwegD in drive) in box 111 then downhill creeping stage is activated and Downl-lillCrp is set to true in box 113.

If the driver accelerates over a defined threshold in box 114 the Launch Mode is active 115.

If the value of the slope detected in Standstill Mode is above a given threshold (noted ThrSlopeLaunchPosD in drive) in box 116! the delay of the request is considered in box 117. If this driver request appears after a given delay (noted MaxUpDwnHillDelayD in drive) it is considered that the driver does not want to launch the vehicle in uphill condition and the method ends, otherwise the uphill launch stage is activated and tJpHillLnc is set to true in box 118. If the value of the slope detected in Standstill Mode is below a given threshold (noted ThrSlopeLaunchNegD in drive) in box 119, the downhill launch stage is activated and UpDwnHillLnc is set to true in box 120.

Figure 7 illustrates a flow diagram for engaging a clutch in a reverse mode.

Considering the reverse case, if the value of the detected slope is below a defined thresh- old (noted ThrSlopeDefNegR in reverse) in box 121 then the default stage is set and Up-HilIDef is set to true in box 122. If the value of the detected slope is above another defined threshold (noted ThrSlopeDefPosR in reverse) in box 123 then the default stage is set and DwnHilIDef is set to true in box 124. As soon as brake is released in box 125, the Creeping Mode is active in box 126. A timer is started (UpDwnHillTimer) in box 127.

If the value of the slope detected in Standstill Mode is below a given threshold (noted ThrSlopeCreepuegR in reverse) in box 128 then uphill creeping stage is activated and Up-HillCrp is set to true in box 129. If the value of the slope detected in Standstill Mode is above another defined threshold (noted ThrSlopeCreepPosR in reverse) in box 130 then downhill creeping stage is activated and DownHillCrp is set to true in box 131. If the driver accelerates over a defined threshold in box 132, the Launch Mode is active in box 133.

If the value of the slope detected in Standstill Mode is below a given threshold (noted ThrSlopeLaunchNegR in reverse) in box 134, the delay of the request is considered. If this driver request appears after a given delay (noted MaxUpDwnHillDelayR in reverse) in box 135, it is considered that the driver does not want to launch the vehicle in uphill condition and the method ends, otherwise the uphill launch stage is activated and UpHillLnc is set to true in box 136. Otherwise if the value of the slope detected in Standstill Mode is above a given threshold (noted ThrslopeLaunchPosR in reverse) in box 137, the downhill launch stage is activated and UpDwnHillLnc is set to true in box 138.

To summarize, as soon as hill condition is activated, the default flag corresponding to uphill or downhill is set to true. It respectively corresponds to UpHilEDef or DownHillDef. On basis of these flags, dedicated strategies are considered which take into account slope indication to improve hill creep capability and hill launch performance and driveability and potentially extend the hill brake hold request, if present.

In an uphill condition, in StandStill Mode, the driver brakes, this is the initial state He de-cides to takeoff and first releases the brake. Creeping Mode is activated. In this example it is considered that the slope is big enough to activate flags (UpHillCrp is true and UpHilILnc is true). Before expiration of delay, the driver accelerates and launch Mode is active. As long as conditions are not met, a brake request is sent, and finally the brake request is re-leased when conditions are met.

Figure 8 summarizes hill start strategy for differing hill conditions. For Creep Drive Downhill (DwnHiIICrp is true, DwnkillDef is true), the engine speed level or engine torque request is reduced as a function of hill percentage. For Creep Drive Uphill (UpHiIICrp is true, UpHiliDef is true), the extended Hill Brake Hold and/or interruption request as a function of hill per-centage, when "Hill Brake Hold" was previously active, is performed. Additionally, a higher engine speed level or engine torque request function of hilt percentage may be used.

For Launch Drive Downhill (DwnHilILnc is true, DwnHiIIDef is true), a Downhill Clutch Slip control mode using a specific Downhill K-factor table is activated. For Launch Drive Uphill (IJpHiIlLnc is true, UpHiliDef is true), an extended Hill Brake Hold request, when "Hill Brake Hold" was previously active, is activated and an Uphill Clutch Slip control mode using a specific Uphill K-factor table is used.

For Creep Reverse Downhill (DwnHillCrp is true, DwnHillDef is true), engine speed level or engine torque request is lowered as a function of hill percentage. For Creep Reverse Uphill (UpHillCrp is true! UpHilIDef is true), the extended Hill Brake Hold request and/or interrup-tion request as a function of hill percentage, when "Hill Brake Hold" was previously active, is used. A higher engine speed level or engine torque request function of hill percentage may also be used.

For Launch Reverse Downhill (DwnHillLnc is true, DwnHillDef is true), a Downhill Clutch Slip control mode using a specific Downhill K-factor table is used. For Launch Reverse Up-hill (UpHillLnc is true, UpHiliDef is true), an extended Hill Brake Hold Request when "Hill Brake Hold" was previously active is used. An uphill Clutch Slip control mode using a spe-cific Uphill K-factor table may be used in addition.

For extended Default Strategy Uphill (UpHilIDef is true), the extended Hill Brake Hold re-quest when "Hill Brake Hold" was previously active is used. For extended Default Strategy Downhill(DwnHillDef is true), no specific action is taken so that the normal mode may be used.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient roadmap for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment1 without departing from the scope as set forth in the appended claims and their legal equivalents.

Claims

Claims 1. A method for controlling engagement of a clutch (3) for coupling a transmission (5) to an engine (4) of a vehicle (1), comprising: determining a standstill status of the vehicle (1), determining the longitudinal acceleration of the vehicle (1) whilst the vehicle (1) is in the standstill status, determining a gradient from the longitudinal acceleration, determining that a signal representative of a status of a brake pedal indicates that the brake pedal is inactive, and if the gradient is greater than a first predefined threshold, activating an uphill mode, and engaging the clutch (3) in accordance with the uphill mode, or if the gradient is less than a second predefined threshold, activating a downhill mode, and engaging the clutch (3) in accordance with the downhill mode.
2. A method for controlling engagement of a clutch (3) for coupling a transmission (5) to an engine (4) of a vehicle (1), comprising: determining a standstill status of the vehicle (1), determining the longitudinal acceleration of the vehicle (1) whilst the vehicle (1) is in the standstill status, determining a gradient from the longitudinal acceleration, determining that a signal representative of a status of a brake pedal indicates that the brake pedal is inactive, and if the gradient is less than a first predefined threshold, activating an uphill mode, and engaging the clutch (3) in accordance with the uphill mode, or if the gradient is greater than a second predefined threshold, activating a downhill mode, and engaging the clutch (3) in accordance with the downhill mode.
3. The method according to claim 1, further comprising determining if a forwards gear ratio and if a forwards gear ratio is selected, activating the uphill mode if the gradient is greater than the first predefined threshold, or activating the downhill mode if the gradi-ent is less than the second predefined threshold.
4. The method according to claim 2, further comprising determining if a backwards gear ratio is selected, and if a backwards gear ratio is selected, activating the uphill mode if the gradient is less than the first predefined threshold, or activating the downhill mode if the gradient is greater than the second predefined threshold.
The method according to claim 1 or claim 2, further comprising upon activating the uphill mode, maintaining a brake pressure for a predefined time period after the signal representative of the status of the brake pedal indicates that the brake pedal is inac- tive, and upon expiry of the predefined time period, activating the clutch (3) and cou-pling the transmission (5) to the engine (4).
6. The method according to claim 3, further comprising increasing the engine speed or the engine torque as a function of the gradient com-pared to a predetermined engine speed or a predetermined engine torque used in a normal mode.
7. The method according to claim 5 or claim 6, wherein the predefined time period is determined as a function of the gradient.
8. The method according to one of claims 1 to 4, wherein in the downhill mode, the engine speed or the engine torque is reduced as a function of the gradient compared to a predetermined engine speed or engine torque used in a normal mode.
9. The method according to one of claims ito 5, further comprising determining a creep condition if the brake pedal is inactive and an acceleration pedal is inactive, if the uphill mode is active, activating an uphill creep mode, or if the downhill mode is active, acti- vating a downhill creep mode, and maintaining a vehicle speed that is greater than ze-ro and less than a predetermined value.
10. The method according to claim 7, further comprising determining a launch condition if the brake pedal is inactive, the acceleration pedal is active, a demanded engine torque is greater than a predefined value, if the uphill mode is active, activating an uphill launch condition, or if the downhill mode is active, activating a downhill launch mode.
11. The method according to claim 8, wherein in the uphill launch mode, an uphill clutch slip control mode is used to engage the clutch, or in the downhill launch mode, a downhill clutch slip control mode is used to engage the clutch.
12. The method according to one of claims Ito 12, wherein the clutch (3) is a starting clutch within a gearbox of the transmission or a clutch posi-tioned between the gearbox and the crankshaft.
13. A system (2) for controlling engagement of a clutch (3) for coupling a transmission (5) to an engine (4) of a vehicle (1), comprising: an input for receiving a signal representative of a standstill of the vehicle, an input for receiving a signal representative of the longitudinal acceleration of the vehicle, an input for receiving a signal representative of a status of a brake pedal, an input for receiving a signal representative of a status of an accelerator pedal, means for determining a gradient from the longitudinal acceleration of the vehicle, an output for providing an output signal to maintain the brake pressure for a pre-defined period after the signal representative of the status of the brake pedal indicates that the brake pedal is inactive, if the gradient is greater than a first predefined thresh- old value, and, after expiry of the predefined period, providing an output signal to en-gage the clutch (3) and to couple the transmission (5) to the engine (4), or if the gradient is less than a second pre-defined threshold value, providing an out-put signal to engage the clutch (3) to couple the transmission (5) to the engine (4).
14. The apparatus according to claim 13, further comprises an output for providing a signal to an engine control module (8) to control the engine speed or the engine torque as a function of the gradient.
15. A vehicle comprising an engine (4), a transmission (5) and a system (2) for controlling engagement of a clutch (3) for coupling the transmission (5) to the engine (4) of a vehi-cle (1) according to claim 13 or claim 14.