DE102014216973B4 - Method of limiting the amount of energy dissipated in a friction clutch during clutch engagement - Google Patents

Abstract

A method of limiting the amount of energy loss in a friction clutch (13) of a motor vehicle (5) drivingly coupling an engine (10) to a transmission (12) during engagement of the clutch (13) while the transmission (12) is in is in progress, the method comprising generating a target engine speed (N _T ) and controlling the engine (10) based on the target engine speed (N _T ), the target engine speed (N _T ) being a target clutch slip speed (N _TSL ) that based on a combination of a current input speed (N _I ) to the transmission (12) and a transition speed based on the engagement state of the clutch (13), the transition speed being a function of the clutch engagement state between a maximum value when the clutch engagement state is disengaged , and a minimum value when the clutch engagement state is fully engaged.

Description

This invention relates to on-highway vehicles, and more particularly to a method of limiting the amount of energy dissipated in a friction clutch drivingly connecting an engine to a transmission during a period of time that the clutch is engaged.

It is known that once a friction clutch is disengaged, there may be a speed differential between the engine and an input to the transmission that is eliminated when the clutch is fully engaged. The synchronization of engine and transmission input speeds while a gear is engaged in the transmission generates energy that is dissipated as heat in the clutch.

This is a particular problem when the driver demands a high level of torque from the engine during the clutch engagement phase. The high torque level typically results in "engine howl" when the clutch is partially engaged due to the difficulty in accurately synchronizing accelerator and clutch pedal movements. “Engine howl” occurs when the engine speed increases rapidly due to the presence of a high level of output torque and no significant load to resist acceleration of the engine, as is the case when the clutch is disengaged or partially engaged .

Heat generation within the friction clutch is becoming an increasing problem due to the fact that clutch torque capacities are being reduced to meet modern packaging requirements.

Heat generation is a particular problem during a power downshift because engine speed must increase during the shift to allow it to synchronize with the input to the transmission at the end of the downshift. If the rate of change of engine speed towards the end of clutch engagement is too rapid, then driveline drag and acceleration disturbance will be felt by the driver.

It is desirable, particularly in the case of a power downshift, for engine speed to be slightly higher than transmission speed at the end of clutch engagement, as this gives the driver a sense of urgency and improves acceleration.

In the DE 101 39 558 A1 a drive arrangement of a motor vehicle is described in which a drive shaft of a drive motor can be connected via a separating clutch to an input shaft of a step change transmission, with the clutch being disengaged, a speed of the output shaft of the drive motor is tracked to a target speed, which depends on a speed of the input shaft of the step change transmission, and wherein upon clutch engagement, the target speed is adjusted based on the speed of the input shaft and a speed offset.

In the DE 10 2006 029 044 B4 a method for supporting the starting of a motor vehicle with a manual transmission and a manually operated clutch is described, with a rate of change of a clutch pedal position being detected for determining a target starting torque of the engine and an adjustment factor for the target starting torque being determined from a speed deviation from a target idling speed and the detected rate of change becomes.

In the DE 10 2011 102 427 A1 describes a motor vehicle drive device with an internal combustion engine, a friction clutch and a transmission, as well as a method for controlling the internal combustion engine, according to which a speed adjustment of the internal combustion engine is initiated if information about a gear stage change, a clutch position change, a minimum vehicle speed or a maximum vehicle acceleration is available in order to to enable a comfortable gear stage change.

It is an object of the invention to provide a method for limiting the amount of energy dissipated in a friction clutch during engagement of the friction clutch.

According to a first aspect of the invention, there is provided a method of limiting the amount of energy loss in a motor vehicle friction clutch drivingly coupling an engine to a transmission during engagement of the clutch while the transmission is in gear, the method generating a desired engine speed and controlling the engine based on the desired engine speed, the desired engine speed being a desired clutch slip speed based on a combination of a current input speed to the transmission and a transition speed based on the engagement state of the clutch.

The transition speed varies between as a function of the clutch engagement state a maximum value when the clutch engaged state is disengaged and a minimum value when the clutch engaged state is fully engaged.

The engine may be controlled to adjust the current engine speed to the desired engine speed.

The method may further include generating a launch engine speed for use in launching the road motor vehicle from rest, and the target engine speed may be the maximum of the target launch engine speed and the target clutch slip speed.

The target launch engine speed may be the lowest predicted engine speed for producing a vehicle launch with low energy dissipation in the clutch.

Alternatively, the target launch engine speed may be one of a range of predicted engine speeds for producing a vehicle launch with low energy loss in the clutch.

The state of engagement of the clutch may be determined based on the position of a clutch pedal.

According to a second aspect of the invention, there is provided a system for limiting energy loss in a motor vehicle friction clutch drivingly coupling an engine to a transmission during clutch engagement while the transmission is in gear, the system comprising an electronic control unit for controlling the engine and a clutch slip controller for generating a target engine speed for use in controlling the engine based on the target engine speed, the target engine speed comprising a target clutch slip speed based on a combination of a current input speed to the transmission and a transition speed based on the engagement state of the clutch is.

The transmission has an input that is driven by the clutch, the clutch is actuated by a clutch pedal, a clutch pedal position sensor is used to determine clutch engagement, and the desired clutch slip speed is based on a combination of a current speed of the input into the transmission and a transition speed based on the position of the clutch pedal.

The electronic control unit controls the speed of the engine to match the desired clutch slip speed.

The transition speed may vary between a maximum value when the clutch pedal is fully depressed and a minimum value when the clutch pedal is fully released.

The system may further include a launch controller to generate a target launch engine speed for launching the vehicle from rest, and the target engine speed is the maximum of the target launch engine speed and the target clutch slip speed and the engine is controlled by the electronic control unit based on the target engine speed.

The target launch engine speed generated by the launch controller may be the lowest predicted engine speed for producing a successful vehicle launch with low energy dissipation in the clutch.

Alternatively, the target launch engine speed generated by the launch controller may be one of a range of predicted engine speeds for producing a successful vehicle launch with low energy loss in the clutch.

According to a third aspect of the invention, there is provided a motor road vehicle incorporating a system constructed in accordance with the second aspect of the invention.

• 1a ein schematisches Diagramm eines Straßenkraftfahrzeugs gemäß einem dritten Aspekt der Erfindung mit einem System gemäß einem zweiten Aspekt der Erfindung ist;
• 1b ein schematisches Diagramm einer Drehmomentsteuereinheit, die einen Teil des in 1a gezeigten Systems bildet, ist;
• 2a ein Diagramm ist, das die Änderung des Kupplungseinrückzustandes während eines Lastherunterschaltens zeigt;
• 2b ein Diagramm ist, das für dieselbe Zeitachse wie 2a den Gangzustand während des Lastherunterschaltens zeigt;
• 2c ein Diagramm ist, das für dieselbe Zeitachse wie 2a eine unregulierte Kraftmaschinendrehzahl, eine Getriebeeingangsdrehzahl und eine Sollkraftmaschinendrehzahl für das Lastherunterschalten zeigt;
• 3a ein Diagramm ist, das den Gangzustand während eines Fahrzeuganfahrens zeigt;
• 3b ein Diagramm ist, das für dieselbe Zeitachse wie 3a die Änderung des Kupplungseinrückzustandes während des Anfahrens zeigt;
• 3c ein Diagramm ist, das für dieselbe Zeitachse wie 3a eine unregulierte Kraftmaschinendrehzahl, eine Getriebeeingangsdrehzahll, eine Sollkupplungsschlupfdrehzahl und eine Sollkraftmaschinendrehzahl für das Anfahren zeigt;
• 4 ein Diagramm ist, das für dieselbe Zeitachse wie 2a eine unregulierte Kraftmaschinendrehzahl, eine Getriebeeingangsdrehzahl und eine Sollkraftmaschinendrehzahl für ein Lasthochschalten zeigt;
• 5 eine schematische Darstellung von verschiedenen Kupplungspedalpositionen und der resultierenden Kupplungseinrückzustände ist;
• 6 ein Ablaufplan hoher Ebene eines ersten Verfahrens zum Begrenzen der Menge an Energie, die in einer Reibungskupplung verloren geht, gemäß einem ersten Aspekt der Erfindung ist;
• 7 ein Ablaufplan hoher Ebene eines zweiten Verfahrens zum Begrenzen der Menge an Energie, die in einer Reibungskupplung verloren geht, gemäß einem ersten Aspekt der Erfindung ist; und
• 8 ein Verfahren zum Kombinieren des in 6 und 7 gezeigten ersten und zweiten Verfahrens ist.

The invention will now be described by way of example with reference to the accompanying drawings, of which:

• 1a Figure 12 is a schematic diagram of a motor road vehicle according to a third aspect of the invention having a system according to a second aspect of the invention;
• 1b a schematic diagram of a torque control unit, which is part of the in 1a system shown is;
• 2a Fig. 12 is a diagram showing the change in clutch engagement state during a power downshift;
• 2 B is a chart that is for the same timeline as 2a shows the gear state during the power downshift;
• 2c is a chart that is for the same timeline as 2a an unregulated engine speed, a transmission input speed number and a target engine speed for the power downshift;
• 3a Fig. 12 is a diagram showing the gear state during vehicle launch;
• 3b is a chart that is for the same timeline as 3a shows the change in clutch engagement state during launch;
• 3c is a chart that is for the same timeline as 3a Figure 12 shows an unregulated engine speed, a transmission input speed, a desired clutch slip speed, and a desired engine speed for launch;
• 4 is a chart that is for the same timeline as 2a Figure 12 shows an unregulated engine speed, a transmission input speed, and a desired engine speed for a power upshift;
• 5 Figure 12 is a schematic representation of various clutch pedal positions and the resulting clutch engagement states;
• 6 Figure 12 is a high level flowchart of a first method for limiting the amount of energy dissipated in a friction clutch in accordance with a first aspect of the invention;
• 7 Figure 12 is a high level flowchart of a second method for limiting the amount of energy dissipated in a friction clutch in accordance with a first aspect of the invention; and
• 8th a method of combining the in 6 and 7 shown first and second method.

In 1 a road motor vehicle 5 is shown with four road wheels 6 and an engine 10 which drives a manual transmission 12 via a friction clutch 13 . The clutch 13 is actuated by a clutch pedal (not shown) through an actuating mechanism (not shown) of any known type as is well known in the art. An input to the clutch 13 rotates at a speed N _E equivalent to the speed of the engine 10 and an output from the clutch 13 rotates at a speed N _I equivalent to the speed of the input shaft of the manual transmission 12 . When the clutch 12 is fully engaged, there is essentially no slip across the clutch 13 and thus the input and output speeds of the clutch are equal and the engine speed is equal to the input speed to the transmission 12 ( _NE = N _I ).

The transmission 12 in this case drives the front wheels 6 of the motor vehicle 5 via a final drive 16, but it will be appreciated that the invention is equally applicable to all wheel drive and rear wheel drive motor vehicles.

An electronic control unit 20 is provided to control the operation of the engine 10 in response to a number of inputs 14,15,17,18,19.

A first input is an engine speed sensor 14 that provides a signal to electronic control unit 20 indicative of engine speed (N _E ).

A second input is a gear selected sensor (SGS) 15 which provides an input to the electronic control unit 20 indicative of at least one gear currently engaged and in some cases also an indication of a gear to be engaged.

A third input is a clutch pedal position sensor 17 which provides an input indicative of current clutch pedal position (C _P ). Clutch pedal position is used in the case of this example to derive the state of engagement of the clutch 13, but it will be appreciated that other methods of deriving the state of clutch engagement could be used, such as a release bearing displacement sensor or a system pressure sensor in the case of a hydraulically actuated clutch 13 The preferred method is to use the clutch pedal position sensor 17 because it is cost effective and because such sensors usually already exist for other control functions.

A fourth input is a ground speed sensor 18, which in this case is a common sensor used by an anti-lock braking system, but could be any type of sensor used to sense the speed of the driveline downstream of the transmission 12.

A fifth input is an accelerator pedal position sensor 19 which is used to provide an input of requested torque T _D from a motor vehicle 5 driver.

In the case of this example, the speed N _I of the input shaft to the transmission 12 is derived based on the gear ratio selected and the vehicle speed, but in other embodiments a separate speed sensor could be provided.

During normal use, the electronic control unit 20 controls the engine 10 in response to a torque request from the driver as communicated by the accelerator pedal sensor 19 . In this case, the engine 10 is a diesel engine, and thus as more torque is requested, the amount of fuel supplied by a fuel injection system 11 and the timing of injecting the fuel into the engine are varied to meet the requested demand . In the case of a spark-ignited engine, various methods can be used to vary the torque output from the engine, as is well known in the art.

The electronic control unit 20 includes a clutch slip control unit (CSC) 25 whose function is to limit the amount of energy dissipated in the clutch 13 during a clutch 13 engagement phase.

The electronic control unit 20 is operable to modulate the torque demand on the engine 10 during engagement of the clutch 13 such that engine howl is reduced, thereby limiting the amount of energy dissipated in the clutch 13 . In one embodiment, the electronic control unit 20 comprises a torque control unit, which is shown schematically in FIG 1b is shown, the effect of which is to limit the driver torque request T _D as derived from the accelerator pedal position sensor 19 when the torque request T _D produces a higher than desired engine speed N _E . The desired engine speed is set by the CSC 25 and the torque demand limit function could also be integrated as part of the CSC 25 .

In the torque limiter, the in 1b As shown, the current level of torque request T _ECur is reduced by δ when the current engine speed is greater than the engine speed target N _T set by the CSC 25 . If the current engine speed is not greater than the target engine speed N _T set by the CSC 25, then the driver demanded torque T _D is used. The value of δ can be a fixed or variable value. In the case of a variable value, it could be based on the difference between the current engine speed and the desired engine speed.

The operation of the CSC 25 is as follows, when the signal from the clutch pedal sensor 17 indicates that the clutch 13 is disengaged and the signal from the SGS 15 indicates that a gear is selected, the CSC 25 is operable to achieve an engine speed target N _T for to set the engine 10 for the current clutch pedal position _CP .

5 FIG. 12 shows, in schematic form, various clutch engagement states as they relate to clutch pedal position _CP .

In a first zone of clutch pedal positions, the clutch pedal 23 is designated as released (R). In the released zone, the state of the clutch 13 is always engaged.

In a second zone of clutch pedal positions, the clutch pedal is designated as pressed (P). In the stepped zone, the state of the clutch 13 changes from an engaged state to a released state. The "slipping point" of the clutch 13 always occurs in the depressed zone. It is in the engaged zone that the majority of the heat generating slip occurs due to the partially engaged condition of the clutch 13 .

In a third zone of clutch pedal positions, the clutch pedal is referred to as depressed (D). In the depressed zone the driver has moved the clutch pedal a large amount from its normal rest position and in the depressed zone the clutch 13 is always disengaged. In the depressed zone, no heat is generated in the clutch 13 since it is disengaged.

In one example, the relative clutch pedal percentage limit for the released zone was 0 to 20% of the total clutch pedal travel, the relevant clutch pedal percentage limits for the pressed zone were 20% to 85% of the total clutch pedal travel, and the relevant clutch pedal percentage limit for the depressed zone was 85% to 100% of total clutch pedal stroke. The bite point occurred at 75% clutch pedal position. It can be seen that between the bite point and the start of the depressed zone, the clutch pedal slip occurs, but the transmitted torque is insufficient to move the motor vehicle 5 .

The "R", "P" and "D" zones are established as part of a calibration process for the clutch position sensing system and the values given are only examples of possible calibrated values.

Therefore, if the clutch pedal position C _P is indicated as depressed by the clutch pedal sensor 17 and the SGS 15 indicates that a gear is engaged, it can be concluded that heat is lost when the clutch 13 is subsequently engaged and thus the CSC 25 is active to limit the amount of energy lost in the clutch 13 .

The CSC 25 determines a target engine speed N _T for the engine 10 during the engagement process. This is done using the current vehicle speed and the selected gear ratio to generate a predicted value for the input speed N _I of the input shaft of the transmission 12 . The predicted input speed N _I is then used in combination with a transition speed N _LSL based on the current clutch pedal position _CP to generate a value for the target clutch slip speed N _TSL . The transition speed N _LSL varies based on the clutch pedal position C _P .

Therefore, the target clutch slip speed N _TSL = (N _I + N _LSL )

It can be appreciated that the relationship between the clutch pedal position C _P and the transient speed N _LSL can be any desired relationship.

The value for N _LSL can be stored as a relationship between clutch pedal position C _P and transient speed N _LSL in the form of a look-up table, or could be repeatedly calculated using an algorithm.

If the system has only one CSC 25, then the value of the target clutch slip speed N _TSL is used as the target engine speed N _T .

Once a value for N _T is generated by the CSC 25, the electronic control unit 20 uses this value to control the torque request T _E to the engine 10 to bring the engine speed N _E toward the desired engine speed N _T . In a situation where the driver's torque request T _D produces an engine speed N _E that is lower than the target engine speed N _T , it is used directly to control the engine 10 . However, if the current driver torque request T _D produces an engine speed that is higher than the target engine speed N _T , the driver torque request T _D is modified or limited to allow the engine speed to converge with the target engine speed N _T .

It will be appreciated that engine speed N _E is not necessarily equal to desired engine speed N _T because engine 10 may not be able to decelerate fast enough to track changes in desired engine speed N _T , but engine speed N _E is constrained by the target engine speed N _T , thereby limiting the amount of energy to be dissipated in the clutch 13 by reducing the speed difference across the clutch 13 .

While the CSC 25 is active, the engine 10 is not responding to the excessive torque requests from the driver that would cause the engine speed _NE to exceed the desired engine speed N _T . In this manner, engine speed _NE flare-up during clutch engagement is avoided and thus the energy lost is less than if flare-up were allowed to occur.

The relationship between clutch pedal position C _P and engine transition speed N _LSL may vary continuously for the full range of clutch pedal stroke. However, it is preferable if a small difference is provided between the target engine speed N _T and the input shaft speed N _I , such as 50 ^rpm , even when the clutch pedal position is in the released zone. It can be seen that eventually the engine speed N _E equals the input shaft speed N _I and this occurs when the clutch pedal position C _P is in the released zone. This is because the CSC 25 only provides a target engine speed N _T and does not establish an actual engine speed N _E .

It can be seen that the desired engine speed N _T is not a fixed value but is updated cyclically based on the clutch pedal position C _P and the current input speed N _I to the transmission 12 .

The electronic control unit 20 further includes a launch control unit 28 in this example, but may include only the CSC 25 in other embodiments.

The function of the launch controller 28 is to generate a target launch speed N _TL for the engine 10 that is designed to provide a good launch with low energy dissipation in the clutch 13 . The target launch speed N _TL set by the launch controller 28 is such that using an engine speed below the target launch speed N _TL is likely to result in a failed launch due to either poor engine 10 response or engine 10 stalling.

It will be appreciated that the structure shown is exemplary in nature and that the CSC 25 and launch controller 28 could be separate units and need not be part of a single electronic controller and that the functionality of these controllers could be created in any other way. Further, it is recognized that the functionality of the CSC 25 and launch controller 28 could be provided by software and that they cannot be physical entities.

2a until 2c show a typical power downshift and how the slip controller CSC 25 works to limit the energy lost in the clutch 13.

In 2c line "A" is that for a representative engine speed without speed control, line "B" is the target engine speed N _T set by the CSC 25 (N _T = N _TSL ), and line N _I is the input speed into the Transmission 12. Actual engine speed _NE is close to, but not necessarily coincident with, line “B”. It can be seen that 2a until 2c are schematic in nature and do not necessarily represent an actual power downshift.

At time "0" the clutch pedal 23 is moved away from its rest position towards the fully depressed position and the clutch state changes from fully engaged to fully released.

At time "1" a lower gear is selected while the clutch 13 is fully disengaged (in the depressed zone) and the CSC 25 becomes active and in this case sets the target engine speed N _T = N _I + 300 ^rpm .

Between time "1" and time "2", the clutch pedal 23 is released from the depressed zone, entering the depressed zone at time "2", and the clutch state changes from disengaged to a partially engaged state, wherein the "Grinding point" (BP) is reached at time "3". In the case of the example shown, the value of the target engine speed N _T remains constant during this period at N _I +300 ^rpm . In other examples, the relationship between the input speed N _I and the desired engine speed N _T varies continuously once the clutch pedal's pressed zone is entered.

At time “4”, the clutch pedal 23 is still in the depressed zone, but the clutch 13 is almost fully engaged. The engine transition speed N _LSL is set by the CSC 25 from this clutch pedal position until the clutch pedal is fully released to a constant speed (50 ^rpm ) above the current input shaft speed N _I of the transmission 12, and thus the target engine speed N _T tracks the input speed N _I , however, is set 50 min ^-1 higher.

Between time "2" and time "4", the clutch pedal position _CP is in the depressed zone and the clutch 13 is engaged.

At time “5” the clutch 13 enters the released zone and at time 6 the clutch 13 is fully engaged and the engine speed _NE is synchronized with the input shaft speed _NI .

Note that as time elapses from time “2” to time “4”, the difference between the target engine speed N _T and the input shaft speed N _I of the transmission 12 is gradually reduced to provide a controlled and smooth gear change.

Since the energy dissipated in the clutch 13 is related to the area enclosed by the lines "A" and "N _I " for the case without controlled slip, and "B" and "N _I " for the case with controlled slip, assuming that at all times the engine speed N _E is equal to the target engine speed N _T , which is not necessarily the case since the actual engine speed is not directly controlled. Therefore, the energy lost in the clutch 13 is reduced by an amount substantially equivalent to the area above line "B" bounded by lines "A" and "B" (actually real engine speed N _E ( not shown) and bounded by line A).

Therefore, a significant reduction in energy lost in the clutch 13 is obtained compared to the unconstrained engine speed situation, and this lower energy loss results in lower clutch temperatures and clutch wear.

3a until 3c' show a typical standstill launch and how the slip control unit CSC 25 can be used to reduce or limit the energy dissipated in the clutch 13 .

In 3c and 3c' line “A” is that for a representative engine speed with no slip control, line “B” is a target engine speed N _T for the engine 10 during launch, line “C” is a target force engine speed N _TSL generated by the clutch slip control unit 25 and the line N _I is the transmission input speed. It can be seen that 3a until 3c' are schematic in nature and do not necessarily represent an actual launch.

At time "0" the clutch pedal 23 is in the released zone and is beginning to move away from its rest position toward the fully depressed position. Since the vehicle speed is zero at this point in time, the electronic control unit 20 deduces that the functionality required is that required to launch the vehicle 5 from standstill.

Between time "0" and time "1", the clutch state changes from engaged to disengaged and the clutch pedal 23 moves to a fully depressed position at a time between time "0" and time "1".

At time “1” a starting gear such as e.g. B. the first gear is selected while the clutch 13 is fully disengaged, and the operation of the clutch slip control unit 25 and the launch control unit 28 begins.

The CSC 25 sets a target engine speed N _TSL equal to N _I + 300 ^rpm , and since N _I = 0 during this period, the value of N _TSL = 300 ^rpm . The launch controller 28 sets a target launch speed N _TL which in this case is 1200 ^rpm but in practice is a range of speed values. The target engine speed N _T for the engine 10 is set to the maximum of N _TL or N _TSL , resulting in a target engine speed _NT = 1200 ^RPM in this case. The engine 10 starts accelerating to reach this target engine speed, which in this case it reaches at time “3”, which in this case corresponds to the time when the slip point of the clutch 13 is reached.

At time "2" the clutch pedal 23 enters the depressed zone and the clutch 23 is partially engaged, but a bite point (BP) has not been reached and the values for _NT , N _TL and N _TSL remain from time "1" to at time "3".

At time "3" the clutch pedal 23 has been moved from the depressed zone to the depressed zone and the clutch state changes from disengaged to a partially engaged state referred to as the "slip point" where propulsion begins to take place.

Between time "3" and time "4", the value of the target launch speed N _TL remains the same, but the value of the target clutch slip speed N _TSL increases with increasing transmission input speed N _I , but not as rapidly as the rate of increase in input speed N _I , since the operation of the CSC 25 is such that it causes the target clutch slip speed N _TSL to converge with the input speed N _I during this period. The target engine speed N _T is still equal to N _TL since N _TL > N _TSL .

At time “4” the clutch 13 is virtually engaged and the target engine speed N _T is still based on the target launch speed N _TL set by the launch controller 28 at a speed determined to be the optimum value for launch.

At time “4”, the clutch pedal 23 is still in the depressed zone, but the clutch 13 is almost fully engaged. The engine transition speed N _LSL is set by the CSC 25 from this clutch pedal position until the clutch pedal is fully released to a constant speed (50 ^rpm ) above the current input shaft speed N _I of the transmission 12, and thus the target engine speed N _TSL tracks the input speed N _I , but is set 50 min ^-1 higher.

Engine speed N _E is not fully synchronized with input shaft speed N _I and target clutch slip speed N _TSL generated by slip control unit 25 is still less than target engine speed N _T set by launch control unit 28 .

Therefore, at time "4" the relationship between the input speed N _I and the clutch pedal position _CP changes such that for clutch pedal positions C _P equal to or less than this are displaced, a constant speed difference of 50 ^rpm for the clutch slip speed target N _TSL is determined. It will be appreciated that this change could take place in a different clutch pedal position and is unrelated to the fact that in this case the driver starts moving the clutch pedal 23 at this point in time using the same clutch pedal position.

At time “5” the clutch 13 is moved into the released zone and is fully engaged and the engine speed _NE is synchronized with the input shaft speed N _I at time “6”.

In the region between time “4” and time “5”, the target engine speed N _T changes from a target value N _TL set by the launch controller 28 to a target speed N _TSL set by the CSC 25 because the target speed N _TSL , which is determined by the CSC 25, exceeds the target speed N _TL derived from the launch controller 28 at any point during this period.

The operation of the launch controller 28 is to examine and maintain the engine speed N _E between upper and lower limits selected to provide an optimal launch with minimal excess energy production.

If the CSC 25 were used alone for vehicle launch, then the engine 10 would likely stall or respond very slowly since the target speed N _TSL based on the engine transition speed N _LSL and N _I would be lower than the engine speed N _E required is to start the motor vehicle 5 successfully.

However, if a launch controller 28 is used alone, then this would inhibit engine speed N _E at the end of launch when N _E = N _I , thereby limiting motor vehicle 5 acceleration.

The effect of the combination of the two control units 25, 28 can best be seen with reference to 3c' be understood, which is an enlargement of the area "X" contained in 3c is shown.

The control of the target engine speed N _T is based on using the higher of the engine speed N _TL derived from the launch controller 28 and the target engine speed N _TSL derived from the slip controller 25 .

Therefore, to the left of point “P” is in 3c' N _TL is the higher of the two speed limits N _TSL , N _TL and thus the target engine speed N _T is set to that level.

The engine speed launch limit N _TL can either be a predefined fixed value for the motor vehicle 5 or can be determined based on the current situation of the motor vehicle 5, such as its weight and whether it is on an up slope, down slope, or on level ground.

To the right of point "P", the value of the engine speed limit N _TSL generated by the CSC 25 is greater than the launch speed limit N _TL from the launch controller 28, and so this is used as the target engine speed N _T instead of the target launch speed N _TL .

It can be seen that if only the launch speed limit N _TL is used, then the engine 10 cannot accelerate above speed N _TL if the launch controller 28 is active and it remains active during a positive speed differential between engine speeds N _E and the input speed N _I into the transmission 12 consists.

Therefore, when a slip occurs due to the driver moving the clutch pedal 23, the engine speed N _E is never equal to the input speed N _I and energy is lost in the clutch 23 until the driver releases the clutch pedal 23 completely. Using the CSC 25, however, it is possible to continue accelerating while maintaining only a small amount of slip, thereby providing a smooth end to the launch phase with good acceleration without excessive energy loss in the clutch 23. In this case, therefore, the driver moving the clutch does not limit the acceleration of the vehicle 5 to the same extent as when the target launch speed N _TL is used.

As before, the transient speed N _LSL produced by the CSC 25 varies with clutch pedal position C _P .

As before, a significant reduction in energy dissipated in the clutch 13 is obtained, resulting in lower clutch temperatures and less clutch wear.

4 shows a representative diagram for a power upshift. The clutch location and gear shift diagrams have been omitted but would be similar to those in 2a and 2 B shown, except that in the case of 2 B the gear change is an upshift, not a downshift.

In 4 line “A” is that for a representative engine speed with no speed control, line “B” is a desired engine speed N _T for the engine 10 during the transition, and line N _I is the transmission input speed. It can be seen that 4 is schematic in nature and does not necessarily represent an actual gear change.

At time "0" the clutch pedal 23 is moved away from its rest position towards the fully depressed position and the Clutch state changes from engaged to disengaged.

At time "1" a higher gear is fully selected while the clutch 13 is disengaged, the input shaft speed N _I falls due to the higher gear ratio and as the vehicle begins to decelerate.

The CSC 25 becomes active at time "1" when the gear is selected and begins to check the engine speed N _E and bring it to the target engine speed N _T .

As the clutch pedal 23 transitions from the depressed zone to the depressed zone, that is, between times “1” and “2”, the transitional engine speed limit N _LSL is set to 300 ^rpm and thus the target engine speed N _T is over 300 ^rpm of the current input shaft speed N _I and thus tracks the input shaft speed N _I as shown.

At time "3" the clutch pedal 23 is in the depressed zone and the clutch condition is a partially engaged condition referred to as the "slip point" where drive begins to occur. The transient speed N _LSL is now varied based on the clutch pedal position _CP until at time "4" the clutch 13 is virtually engaged, and the transient speed N _LSL is then maintained by the CSC 25 at a constant value above the current input shaft speed N _I des Transmission 12 held until the end of engagement.

At time "5" the clutch 13 is engaged and the clutch pedal position enters the released zone and at time "6" the clutch pedal 23 is fully released and the engine speed _NE synchronizes with the input shaft speed _NI .

Between times “1” and “6”, the CSC 25 is active and reduces the engine speed N _E to the target engine speed N _T indicated by line “B”.

As before, the energy dissipated in the clutch 13 is directly related to the area enclosed by the lines "A" and " _NI " for the case with no controlled slip, and "B" and " _NI " for the case with controlled slip in relation. In fact, it is the area enclosed by the actual engine speed _NE and N _I , but as the engine speed _NE approaches the target engine speed N _T , the area bounded by "B" and "N _I " is a good approximation.

Therefore, the energy lost in clutch 13 is reduced by an amount equivalent to the area above line "B" bounded by lines "A" and "B", which is a significant reduction in the energy lost in clutch 13 lost energy and leads to lower clutch temperatures and less clutch wear.

It will be appreciated that the transition speed N _LSL may vary in any way with respect to the clutch pedal position C _P provided that the difference between the target clutch slip speed N _TSL and the input speed N _I decreases as the clutch pedal moves from pressed to released position is moved.

With specific reference to 6 1, a first embodiment 100 of a method for the amount of energy dissipated in a friction clutch during clutch engagement is shown, which is particularly suitable for use in the case of power-on gear shifting.

The method begins in box 110 and then proceeds to box 120 where it is checked whether the transmission 12 is in gear and whether the clutch 13 is disengaged.

If the clutch pedal position C _P indicates that the clutch 13 is not disengaged or is not currently in gear, then the method cycles around box 120. It can be seen that a gear must be engaged for an input speed N _Ides Transmission 12 is determined unless a separate speed sensor is provided, and further it can be seen that substantially no energy can be lost in the clutch 13 while the transmission 12 is in neutral.

If the conditions of box 120 are met, the method advances to box 130 where the current input speed N _I of the transmission 12 is determined. It will be appreciated that this could be a direct measurement using a sensor or could be derived from the vehicle speed using the current gear ratio selected and the effective gear ratio between the transmission 12 and the road.

From Box 130 the method advances to Box 140 where the current clutch engagement state is determined based on the clutch pedal position _CP .

Then, in box 150, the value of _CP is used to calculate a current value of the desired force to determine the rail speed N _T . As previously discussed, the desired engine speed N _T is based on a combination of the current input speed N _I and a value N _LSL generated by the CSC 25 based on the clutch pedal position Cp.

Therefore, target engine speed N _T = N _TSL = (N _I + N _LSL )

That is, since only one target clutch slip speed N _TSL is generated in this case, it is used as the target engine speed N _T .

Proceeding from box 150 to box 160, a check is made to see if the current engine speed N _E , as sensed by the engine speed sensor 14, is greater than the desired engine speed N _T .

If the current engine speed _NE is not greater than the desired engine speed N _T , the method proceeds to box 180 where it is checked whether the current engine speed _NE is equal to the current input speed _NI and if so, ends method 100 at box 190, but if not, the method returns to box 130.

If in box 160 the current engine speed N _E as sensed by the engine speed sensor 14 is determined to be greater than the desired engine speed N _T , the method advances to box 170 .

At box 170, the electronic control unit 20 controls the engine 10 to the desired engine speed N _T . In most cases, this will involve dampening or reducing the driver demand for torque to allow the engine 10 to slow down in a passive manner, but may also include active engine braking such as braking. B. applying a load to the engine 10 via an attached electric generator or compressor, or by closing a throttle valve or engine brake.

From box 170 the method returns to box 130 and the subsequent boxes are executed again.

It can be seen that the target engine speed N _T is not constant during engagement, but rather is updated cyclically as the value of the target clutch slip speed N _TSL changes. A cycle time of around 10 ms is possible for this cyclic update.

With specific reference to 7 Shown is a second embodiment 200 of a method for limiting the amount of energy dissipated in a friction clutch during clutch engagement, particularly suitable for use in the event of a vehicle launch.

The method begins in box 210 and then proceeds to box 215 which checks to see if the transmission 12 is in gear and if the clutch 13 is disengaged.

If the clutch pedal position C _P indicates that the clutch 13 is not disengaged or is not currently in gear, then the method cycles around box 215. It can be seen that a gear must be engaged for an input speed N _Ides Transmission 12 is determined unless a separate speed sensor is provided, and further it can be seen that substantially no energy can be lost in the clutch 13 while the transmission 12 is in neutral.

If the conditions of box 215 are met, the method advances to box 220 where a desired engine launch speed N _TL is established based either on stored parameters or by direct calculation. A range of target launch speeds can be set to provide a successful launch with low energy dissipation in the clutch 13 .

From Box 220 the method proceeds to Box 230 where the current input speed N _I of the transmission 12 is determined. It will be appreciated that this could be a direct measurement using a sensor or could be derived from the vehicle speed using the current gear ratio selected and the effective gear ratio between the transmission 12 and the road. The current clutch pedal position _CP is also in this case determined in box 230 based on the output from the clutch pedal position sensor 17, but this could be determined separately.

From Box 230 the method advances to Box 240 where the current clutch pedal position C _P is used in combination with the current input speed N _I to generate a value of the desired clutch slip speed N _TSL . $${\text{N}}_{\text{TSL}}=\left({\text{N}}_{\text{I}}+{\text{N}}_{\text{LSL}}\right).$$

Then in box 250 the value of N _TL from the launch controller 28 is compared to the value of N _TSL received from the CSC 25 .

If the value of N _TL is greater than the value of N _TSL , then the value of N _TL is used for the desired engine speed N _T as indicated in box 260, otherwise the value of N _TSL is used for the desired engine speed N _T as is given in box 270.

From Box 260 the method advances to Box 265 to check whether the current engine speed N _E is substantially equal to the current input speed N _I to the transmission 12 and if so, the method 200 ends in Box 290. It can be seen that a very small difference between engine speed N _E and input speed N _I is possible and this test is intended to check that the engine 10 and transmission 12 are synchronized, meaning that slip control is no longer required .

If in box 265 it is determined that the current engine speed N _E is not equal to the current input speed N _I to the transmission 12, the method returns to box 230 and subsequent boxes are executed again.

Returning to Box 270, the method advances from Box 270 to Box 280 to check if the current engine speed _NE is substantially equal to the current input speed _NI to the transmission 12, and if so the method ends 200 in box 285.

If it is determined in box 280 that the current engine speed _NE is not equal to the current input speed _NI to the transmission 12, the method returns to box 230 and subsequent boxes are executed again.

In the case of this example, the setpoint starting speed N _TL that has been set once is retained for the duration of the starting. However, in other embodiments, the value for the target launch speed may be updated cyclically as is the value for the target clutch slip speed N _TSL . A cycle time of around 10 ms is possible for this cyclic update.

With specific reference to 8th is shown as the in 6 and 7 methods shown can be combined to provide a method usable for either vehicle launch or power-on gear shifting.

The method 300 determines in box 310 whether the vehicle 5 is moving and if so, proceeds to box 320 which initiates a transfer to box 110 in 6 and if it is not moving, the method advances from Box 310 to Box 330 which involves a transfer to Box 210 in 7 is.

It will be appreciated that the methods shown and described are exemplary in nature and that the invention is not limited to the exact combination of method steps or sequence shown and described.

In summary, the method provides a desired engine speed N _T for the engine 10 that is based at least in part on the state of engagement of the clutch 13 .

When the clutch 13 is disengaged, a large difference (N _E - N _I ) in speed between the engine 10 and the input to the transmission 12 is allowed, but as the clutch 13 approaches full engagement, the allowable difference in the speed (N _E - N _I ) is reduced.

Preferably, a small positive difference between the target engine speed N _T and the input speed N _I is maintained even when the clutch 13 is fully engaged to provide a positive feel for the final stages of engagement.

By reducing the allowable difference in speed between the engine 10 and the input to the transmission 12 (N _E - N _I ) based on clutch engagement state, a smoother transition is provided and there is less risk of driveline drag.

It will be appreciated by those skilled in the art that, while the invention has been described by way of example with reference to one or more embodiments, it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention, such as defined by the appended claims.

Claims (13)

A method of limiting the amount of energy loss in a friction clutch (13) of a motor vehicle (5) drivingly coupling an engine (10) to a transmission (12) during engagement of the clutch (13) while the transmission (12) is in is in progress, the method comprising generating a desired engine speed (N _T ) and controlling the power engine (10) based on the target engine speed (N _T ), wherein the target engine speed (N _T ) is a target clutch slip speed (N _TSL ) that is calculated based on a combination of a current input speed (N _I ) to the transmission (12) and a transition speed is determined based on the engagement state of the clutch (13), the transition speed varying as a function of the clutch engagement state between a maximum value when the clutch engagement state is disengaged and a minimum value when the clutch engagement state is fully engaged. procedure after claim 1 wherein the engine (10) is controlled to adjust the current engine speed (N _E ) to the target engine speed (N _T ). Procedure according to one of Claims 1 until 2 , the method further comprising generating a launch engine speed for use in launching the road motor vehicle (5) from rest and the target engine speed (N _T ) is the maximum of the target launch engine speed (N _TL ) and the target clutch slip speed (N _TSL ). procedure after claim 3 , wherein the target launch engine speed (N _TL ) is the lowest predicted engine speed for producing a vehicle launch with low energy loss in the clutch (13). procedure after claim 3 , wherein the target launch engine speed (N _TL ) is one of a range of predicted engine speeds for producing a vehicle launch with low energy loss in the clutch (13). Procedure according to one of Claims 1 until 5 wherein the state of engagement of the clutch (13) is determined based on the position of a clutch pedal. A system for limiting energy loss in a friction clutch (13) of a motor vehicle (5) drivingly coupling an engine (10) to a transmission (12) during engagement of the clutch (13) while the transmission (12) is in gear the system having an electronic control unit (20) for controlling the engine (10) and a clutch slip control unit (25) for generating a target engine speed (N _T ) for use in controlling the engine (10) based on the target engine speed (N _T ) wherein the target engine speed (N _T ) is a target clutch slip speed (N _TSL ) calculated based on a combination of a current input speed (N _I ) to the transmission (12) and a transition speed based on the state of engagement of the clutch (13) is determined, the transmission (12) having an input driven by the clutch (13), the clutch (13) being actuated by a clutch pedal, a clutch pedal position sensor (17) being used to detect the engagement state of the clutch ( 13) and the target clutch slip speed (N _TSL ) is based on a combination of a current input speed to the transmission (12) and a transition speed based on the position of the clutch pedal. system after claim 7 wherein the electronic control unit (20) controls the speed of the engine to match the target clutch slip speed (N _TSL ). system after claim 7 or claim 8 wherein the transition speed varies between a maximum value when the clutch pedal is fully depressed and a minimum value when the clutch pedal is fully released. system according to one of the Claims 7 until 9 , the system further comprising a launch controller (28) to generate a target launch engine speed (N _TL ) for launching the vehicle (5) from rest, and the target engine speed (N _T ) the maximum of the target launch engine speed (N _TL ) and the target clutch slip speed (N _TSL ) and the engine is controlled by the electronic control unit (20) based on the target engine speed (N _T ). system after claim 10 , wherein the target launch engine speed (N _TL ) produced by the launch controller (28) is the lowest predicted engine speed for producing a successful vehicle launch with low energy loss in the clutch (13). system after claim 10 wherein the target launch engine speed (N _TL ) produced by the launch controller (28) is one of a range of predicted engine speeds for producing a successful vehicle launch with low energy loss in the clutch (13). Road motor vehicle with a system according to any of Claims 7 until 12 .

Images