WO2004097266A1

WO2004097266A1 - Drive transmission

Info

Publication number: WO2004097266A1
Application number: PCT/GB2004/001779
Authority: WO
Inventors: Richard Taylor
Original assignee: Volkswagen Aktiengesellshaft
Priority date: 2003-04-28
Filing date: 2004-04-23
Publication date: 2004-11-11
Also published as: DE112004000668T5; GB2415022B; GB2415022A; GB0521042D0

Abstract

A dual clutch transmission (14) includes a first clutch (18), input shaft (22) and gear set (26) and a second clutch (20), input shaft (24) and gear set (28). The dual clutch transmission (14) is switchable between a mode in which, during a shift between gears both clutches (18) and (20) engage during the shift and a mode where only one clutch (18) or (20) engages at any time. As a result a limp-home mode and improved AMT shift regime are obtained.

Description

Drive Transmission

The invention relates to a drive transmission; in particular a drive transmission comprising first and second clutches.

One known form of drive transmission is a dual clutch transmission such as the DSG transmission used in the Audi TT. A typical dual clutch transmission is shown schematically in Figure 1. In a vehicle system designated generally 10, a drive from an engine 12 is coupled to the wheels 16 (not shown) via a dual clutch transmission designated generally 14. The transmission 14 includes first and second clutches 18 and 20 and respective first and second input shafts 22 and 24. The input shafts 22 and 24 carry respective first and second gear sets 26 and 28. In the embodiment shown the first gear set 26 carries gears 1, 3, 5 and 7 (designated schematically) and the second gear set 28 carries gears reverse, 2, 4 and 6 (designated schematically). A gear of either or both gear sets 26, 28 is selectively engagable with a corresponding gear of an output gear set 30 on an output shaft 32 which is coupled to the vehicle wheels by an appropriate intermediate linkage. It will be appreciated that the arrangement shown is simplified and in practice the arrangements may be more complex although operating on the same principal. For example the clutches 18, 20 can be mounted co-axially.

In operation, where the vehicle is for example in fifth gear, the first clutch 18 is fully engaged with the engine 12, with the relevant gear of gear set 26 engaging the relevant gear of gear set 30 on the output shaft 32. The second clutch 20 is fully disengaged from the engine 12 but can be engaged with the output shaft 32 by means of a gear in the gearset 28 and the second input shaft 24. If a gear shift is required (for example to fourth gear) and the required gear on the second input shaft 24 is not already engaged with the output shaft 32, then with the second clutch 20 remaining disengaged from the engine 12, the appropriate gear of the second gear set 28 is synchronised with the relevant gear of the output gear set 30 and then engaged such that clutch 20 spins freely and not in synchronisation with the engine speed. In the downshift from fifth to fourth gear, the second clutch 20 will typically be rotating faster than the engine speed and so, to synchronise the engine speed with the speed of the second clutch 20, the first clutch 18 is disengaged until slipping starts at which point the engine speed rises. As the engine speed approaches the second clutch speed the second clutch 20 is engaged and the first clutch 18 disengaged.

As explained with reference to Figure 1, an input shaft 22, 24 is provided for each gear set 26, 28. A shift rail 34 is provided to shift a selector fork 36 between a neutral position and an engaged position in which a synchroniser clutch 38 is moved into engagement with a gear on an input shaft, which is itself already in engagement with a gear of the output gear set 30. To move a selector fork 36, hydraulic fluid is passed through conduits to actuate an associated actuator 40 connected to the shift rail 34 and hence cause the associated selector fork 36 to move as required and the associated synchroniser clutch 38 to move into engagement with a gear on an input shaft.

The transmission includes various sensors which for the purpose of clarity, are not shown in Fig. 1. The sensors include a shift rail position sensor, an input shaft speed sensor and a clutch pressure sensor. The shift rail position sensor allows the position of the shift rail to be determined at any time providing diagnostic information concerning the current state of the transmission as well as control feedback information as to whether a desired movement has taken place. The input shaft speed sensor provides information relevant to synchronisation of the various components and can be used in conjunction with an engine speed and/or output shaft speed sensor as appropriate. The clutch pressure sensor provides an indication of the hydraulic pressure in the clutch allowing diagnostic data to be collected as well as failure prediction. The transmission is controlled by a controller (not shown) which can be, for example, an engine control unit. Based on the implicit or explicit driver demand, and the sensed shift rail position, clutch pressure and shaft speeds, shifts are controlled by the ECU and failures or potential failures are detected.

Referring to Figure 2 the variation in engine speed (v) against time (t) can be seen in more detail for one particular case of a dual clutch shift. While the vehicle is in fifth gear the engine speed is at a lower speed vl . At a time tl the first clutch begins to gradually disengage at the beginning of the shift operation. At a time t2 when the engine speed v2 has increased to the speed of the second clutch, the second clutch engages and the first clutch disengages fully in a coordinated manner. Accordingly a smooth torque transfer is obtained without torque interruption in which the first clutch is used to control the engine speed. The operation is governed by appropriate actuators and sensors. However a problem arises with this known system in the event that there is component or shift rail failure.

Another known type of transmission is an automated manual transmission (AMT) for example of the type sold by Alfa Romeo™ under the trade name "Selespeed"™. In an AMT a single clutch and associated gear pack couples with an output gear pack. When a gear change is required the clutch disengages, the new gears synchronise and the clutch re-engages. A problem with AMT's is that, during gear changes, there is a significant torque interrupt as well as a rapid change in engine speed when the clutch re-engages at the end of the shift. To overcome these problems previous approaches have been to speed up the synchronisation process which can damage the related components, or to control engine speed separately which can give rise to additional control requirements.

The invention is set out in the appended claims.

As the dual clutch transmission is switchable between dual engagement (where during a shift both clutches are at least temporarily engaged simultaneously) or separate engagement (where the clutches engage mutually exclusively) gear shift modes, shifts between gears common to a single clutch are possible allowing a limp-home capability in the event of failure of a component. In addition AMT style shifts can be carried out at any time if desired with reduced torque loss/engine speed variation effects when compared with a standard single clutch AMT transmission.

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

Fig. 1 is a schematic diagram of a known dual clutch transmission;

Fig. 2 is a graph of engine speed (v) versus time (t) during a dual clutch transmission (DCT) gearshift;

Fig. 3 is a block diagram showing the principal components of a transmission according to the present invention;

Fig. 4 is a flow diagram illustrating a control approach according to the present invention; and Fig. 5 is a graph of torque (τ) against time (t) during an AMT gearshift.

In overview the invention provides a transmission which is freely switchable between a conventional torque transfer DCT style shift and one in which the clutch or clutches fully disengage prior to a gear change and re-engage after synchronisation such that there is separate, rather than simultaneous engagement. As a result greater flexibility in potential gearshift modes is available. AMT style shifts are improved as there is less torque interrupt because synchronisation of a second gear pack with the output shaft can be achieved while a first gear pack is still engaged. In addition, if a component such as one of the gear packs fails then the remaining clutch and gear pack can engage and disengage and provide a limp-home capability.

Referring to Fig. 3, a schematic view of the principal components according to the invention are shown. A control unit 50 controls a DCT 52 of any appropriate type. The DCT has sensors 54, 56 (although any appropriate number of sensors may be included) which detect component failure as discussed in more detail below. The sensors may be dedicated failure sensors or failure can be inferred from readings taken by conventional DCT sensors such as the shift rail position sensor, input shaft speed sensor and clutch pressure sensor. The DCT further includes control actuators 58, 60 (again any number of actuators may in fact be used) to compensate for failures again as discussed in more detail below, where once again the conventional actuators can be used. The ECU 50, sensors 54, 56 and actuators 58, 60 are all of any appropriate known type as will be well known to the skilled person, for example of the typed used in the Audi TT DSG transmission.

Operation of the DCT system in order to deal with component failure can be understood with reference to Fig. 4. At block 70 the ECU detects a failure via sensors 54, 56. Possible failure types are discussed in more detail below. At block 72 the relevant control strategy is identified dependent on the failure type. At block 74 the control strategy is implemented by the ECU making use of the actuators 58, 60. The failure types can be, for example, an actuator failure relevant to a specific gear, a shift rail failure or a clutch failure. Accordingly the control strategy will be dependent on the failure type. One instance is where an individual gear has failed in which case the control strategy will be to skip the failed gear. For example if second gear fails while disengaged then on an upshift from first gear the control strategy will be to disengage the relevant clutch (clutch 18 in Fig. 1), synchronise third gear with the output shaft 32 and then re-engage clutch 18, thus skipping the failed gear.

The failed gear can be detected by monitoring the shift rail position via the shift rail sensor and/or the input shaft speed which will not show synchronisation.

Alternatively, if there is a shift rail failure, for example a gear cannot be disengaged (gear fails engaged) from the output shaft 32 or if the shift rail fails, then the corresponding clutch is permanently disengaged from the engine and the other clutch and associated gears used on their own. This type of failure is detected from an incorrect shift rail position measurement via the shift rail sensor and /or from in incorrect input shaft speed. So, for example, or if the shift rail 24 in Fig. 1 fails then the clutch 20 is disengaged and the clutch 18 is used as described above to shift between gears 1, 3, 5 and 7 on the gear set 26. If possible, all gears on the shaft are i.e. withdrawn from operation for example by controlling the hydraulic actuators appropriately.

A further possibility is clutch failure. If the clutch fails in an open position then all gears on the input shaft are disabled and the other clutch and gears used in the similar manner as for shift rail failure. Clutch failure is detected from an incorrect clutch pressure identified by the clutch pressure sensor. Alternatively the conventional control algorithms determining operation of the system will detect the corresponding loss of control from the incorrect or conflicting feedback signals received. If the clutch fails closed, which is detected in a similar manner, a similar control strategy is adopted but further incorporating an AMT style shift, disengaging the failed clutch prior to engagement of the other clutch and associated gears.

The failure types, the manner in which the failure is detected and the control strategy are explained in more detail in the following table:

TABLE

In addition to implementation of the non-simultaneous engagement strategy in the event of failure detection, the ECU may accept a command to implement such a strategy from driver demand. The driver demand can either be a specific request from a driver via a suitable interface, or a detected requirement from driver input in relation, for example, to gear shifts or acceleration demand.

As described above, when the DCT switches to AMT mode then, upon a gearshift, a first clutch will disengage fully before a second clutch re-engages. For example in an upshift from first to second gear, referring to Fig. 1, initially the clutch 18 is engaged and the clutch 20 is disengaged. When second gear is requested the second gear of the gear pack 28 synchronises with the respective gear of the output shaft 32. Meanwhile the first clutch 18 disengages. Subsequently the second clutch 20 engages. Because the second gear is on a separate input 24, it can begin synchronisation before the first clutch 18 disengages. Indeed a preferred control strategy is to identify a likely next gear (for example: if engine speed is increasing then the next uplift can be pre- selected) and to synchronise the idle shaft to the preselected gear.

As a result the shift can be carried out significantly more quickly with a corresponding reduction in torque interruption. This can be understood with reference to Fig. 5 which is a graph of torque (τ) against time (t). In conventional AMT operation as the first clutch disengages the torque transferred drops to zero at a time TI . When the first clutch re-engages torque increases again at a time T2 defining a zero torque window Wl during which the new gear is selected. According to the present invention, as the second gear is on a separate shift rail it can already be selected and does not need to wait for the first clutch to be disengaged. As a result the torque will start increasing at a time T3 earlier than T2 as shown by the broken line trace defining a shorter zero torque window W2. This aspect can be combined with control of engine speed during torque interrupt using existing AMT strategies to improve the shift quality on re-engagement.

It will be appreciated that the invention can be applied in relation to any dual shaft transmission having appropriate sensors and actuators defining an appropriate control regime and with a suitably configured mechanical hydraulic actuation system. The invention can apply to any engine and drive type as appropriate.

Claims

1. A drive transmission comprising first and second clutches switchable between a simultaneous engagement gearshift mode and a separate engagement gear shift mode.

2. A transmission as claimed in claim 1 in which the simultaneous engagement gearshift mode is a dual clutch transmission mode.

3. A transmission as claimed in claim 2 in which the first and second clutches are coupled to respective first and second transmission shafts providing respective gear coupling to a common output.

4. A transmission as claimed in claim 3 in which the separate engagement gearshift mode comprises at least one of a shift between gears on a common shaft or a shift between gears on respective shafts.

5. A transmission as claimed in claim 4 in which, for a shift between gears on respective shafts, a gear on a first shaft is arranged to synchronise to the common output before a clutch on a second shaft is fully disengaged.

6. A transmission as claimed in claim 5 in which the gear on the first shaft is pre-selected and synchronised before the second shaft clutch begins disengagement

7. A transmission as claimed in any preceding claim switchable to a separate engagement gearshift mode on detection of transmission component failure.

8. A transmission as claimed in claim 7 in which the component comprises a transmission shaft or rail.

9. A transmission as claimed in claim 7 when dependent on claim 3 in which the component is a transmission shaft or rail.

10. A transmission as claimed in claim 9 in which the transmission rail or shaft component is a gear.

11. A transmission as claimed in any of claims 8 to 10 in which the separate engagement gearshift mode is a limp-home mode.

12. A transmission as claimed in any of claims 7 to 11 further comprising a sensor arranged to sense a transmission component failure and a controller to control switching of the transmission between gear shift modes.

13. A transmission as claimed in any preceding claim in which the transmission is switchable upon driver demand.

14. An engine including a drive transmission as claimed in any preceding claim.

15. A vehicle including an engine as claimed in claim 14.

16. A method of controlling a drive transmission having first and second clutches comprising switching the transmission between a simultaneous engagement gear shift mode and a separate engagement gear shift mode.

17. A method as claimed in claim 16 comprising sequentially engaging respective clutches in the mutually separate gearshift mode.

18. A method as claimed in claim 17 in which, before a first clutch is fully disengaged, a gear associated with a second clutch is synchronised to an output shaft before sequential engagement.

19. A method as claimed in claim 18 in which the second clutch gear is synchronised before the first clutch begins disengagement.

20. A method as claimed in claim 17 comprising sequentially engaging and reengaging the same clutch in the separate engagement gear shift mode.

21. A method as claimed in claim 16 comprising the step of engaging the separate engagement gearshift mode upon failure detection.

22. A method as claimed in claim 21 in which the separate engagement gearshift mode comprises a krnp-home mode.

23. A method as claimed in claim 16 comprising switching between gearshift modes upon driver demand.

24. A computer program comprising instructions for implementing a method as claimed in any of claims 16 to 23.

25. A computer readable medium storing a computer program as claimed in claim 24.

26. An engine control unit configured to operate under the instructions of a computer program as claimed in claim 24.

27. A transmission or method substantially as herein described with reference to the drawings.