Vehicle apparatus and method

Abstract

The present invention relates to a vehicle (1) having a torque generating machine (4); and one or more driven wheel (W.sub.D). A driveline (6) is provided for transmitting torque from the torque generating machine (4) to said one or more driven wheel. The driveline (6) includes a torque transmitting means (8). A first decoupling mechanism (11) is operable to decouple the torque transmitting means (8) from the torque generating machine (4). The first decoupling mechanism (11) is closed to couple the torque transmitting means (8) to the torque generating machine (4) and is opened to decouple the torque transmitting means (8) from the torque generating machine (4). A second decoupling mechanism (12) is operable to decouple the torque transmitting means (8) from the one or more driven wheel. The second decoupling mechanism (12) is closed to couple the torque transmitting means (8) to the one or more driven wheel and is opened to decouple the torque transmitting means (8) from the one or more driven wheel. A controller (2) is provided having at least one electronic processor for controlling operation of the first and second decoupling mechanisms (11, 12). The at least one electronic processor (P) is configured to close the first decoupling mechanism (11), to determine a target operating speed of the torque generating machine (4), to control the operating speed of the torque generating machine (4) in dependence on the determined target operating speed and to close the second decoupling mechanism (12) when the operating speed of the torque generating machine (4) at least substantially matches the determined target operating speed. The present invention also relates to a corresponding method of controlling first and second decoupling mechanisms (11, 12) to control the transmittal of torque from a torque generating machine (4) to one or more driven wheel of a vehicle (1).

Claims

1. A vehicle comprising: a torque generating machine; at least one driven wheel; a driveline for transmitting torque from the torque generating machine to said at least one driven wheel, the driveline comprising a torque transmitting means; a first decoupling mechanism operable to decouple the torque transmitting means from the torque generating machine, wherein the first decoupling mechanism is closed to couple the torque transmitting means to the torque generating machine and is opened to decouple the torque transmitting means from the torque generating machine; a second decoupling mechanism operable to decouple the torque transmitting means from the at least one driven wheel, wherein the second decoupling mechanism is closed to couple the torque transmitting means to the at least one driven wheel and is opened to decouple the torque transmitting means from the at least one driven wheel; and a controller comprising at least one electronic processor for controlling operation of the first and second decoupling mechanisms, wherein the at least one electronic processor is configured to: close the first decoupling mechanism; determine a target operating speed of the torque generating machine; after closing the first decoupling mechanism, control the operating speed of the torque generating machine in dependence on the determined target operating speed; and close the second decoupling mechanism when the operating speed of the torque generating machine at least substantially matches the determined target operating speed.

2. The vehicle as claimed in claim 1, wherein the first decoupling mechanism comprises first torque input means and first torque output means, wherein the first decoupling mechanism accommodates slip between the first torque input means and the first torque output means.

3. The vehicle as claimed in claim 1, wherein the at least one electronic processor is configured to determine the target operating speed of the torque generating machine in dependence on a wheel speed signal.

4. A vehicle as claimed in claim 1, wherein the second decoupling mechanism comprises second torque input means and second torque output means, wherein the second decoupling mechanism is a non-slip mechanism.

5. The vehicle as claimed in claim 4, wherein the second decoupling mechanism comprises one or more of the following set: a torque converter, a single-plate clutch, a multi-plate clutch, a synchronizer, a hydrostatic coupling and a magnetic coupling.

6. The vehicle as claimed in claim 1, comprising a transmission coupled to the torque generating machine, wherein the first decoupling mechanism is incorporated into the transmission.

7. The vehicle as claimed in claim 1, comprising a transmission coupled to the torque generating machine, wherein the first decoupling mechanism is disposed between the torque generating machine and the transmission or between the transmission and the torque transmitting means.

8. The vehicle as claimed in claim 1, wherein the first decoupling mechanism comprises one or more of the following set: a torque converter, a single-plate clutch, a multi-plate clutch, a synchronizer, a hydrostatic coupling and a magnetic coupling.

9. The vehicle as claimed in claim 1, wherein the torque generating machine comprises an internal combustion engine.

10. The vehicle as claimed in claim 1, wherein the controller is configured to activate a driveline disconnect gliding mode by opening the first decoupling mechanism to decouple the torque transmitting means from the torque generating machine and opening the second decoupling mechanism to decouple the torque transmitting means from the at least one driven wheel.

11. A method of controlling first and second decoupling mechanisms to control a transmittal of torque from a torque generating machine to at least one driven wheel of a vehicle; the method comprising: opening the first decoupling mechanism to decouple torque transmitting means from the torque generating machine; opening the second decoupling mechanism to decouple the torque transmitting means from the at least one driven wheel; closing the first decoupling mechanism; determining a target operating speed of the torque generating machine; after closing the first decoupling mechanism, controlling the operating speed of the torque generating machine in dependence on the determined target operating speed; and closing the second decoupling mechanism when the operating speed of the torque generating machine at least substantially matches the determined target operating speed.

12. The method as claimed in claim 11, comprising determining the target operating speed of the torque generating machine in dependence on a wheel speed signal.

13. The method as claimed in claim 11, wherein the second decoupling mechanism comprises second torque input means and second torque output means; the method comprising at least substantially matching a rotational speed of the second torque input means and the second torque output means and then closing the second decoupling mechanism.

14. The method as claimed in claim 11, comprising activating a driveline disconnect gliding mode by opening the first decoupling mechanism to decouple the torque transmitting means from the torque generating machine and opening the second decoupling mechanism to decouple the torque transmitting means from the at least one driven wheel.

15. A controller comprising at least one processor configured to implement the method of claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

(2) FIG. 1 shows a schematic representation of the main components of a conventional rear-wheel drive vehicle;

(3) FIG. 2 shows a schematic representation of the main components of a conventional front-wheel drive vehicle;

(4) FIG. 3 shows a schematic representation of the forces acting on a vehicle when operating in a gliding mode;

(5) FIG. 4 shows a schematic representation of a vehicle configured to operate in a driveline disconnect gliding mode in accordance with an embodiment of the present invention;

(6) FIG. 5 shows a schematic representation of the dynamic operating states of the components in the driveline of the vehicle shown in FIG. 4 when operating in said driveline disconnect gliding mode;

(7) FIG. 6 shows a schematic representation of the loads on the vehicle shown in FIG. 4 when operating in the said driveline disconnect gliding mode;

(8) FIG. 7 shows a schematic representation of a front-wheel drive vehicle operating in a driveline disconnect gliding mode in accordance with an embodiment of the present invention;

(9) FIG. 8 shows a schematic representation of the transmission and front differential of the front-wheel drive vehicle shown in FIG. 7; and

(10) FIG. 9 shows a schematic representation of a four-wheel drive vehicle operable in a driveline disconnect gliding mode in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

(11) A vehicle 1 comprising a controller 2 according to an embodiment of the present invention will now be described with reference to FIGS. 4, 5 and 6. The controller 2 is configured selectively to activate and deactivate a driveline disconnect gliding mode. In the present embodiment, the vehicle 1 is a rear-wheel drive automobile having driven wheels W.sub.D disposed at the rear. It will be appreciated that the invention described herein is not limited to this drive configuration. Moreover, the invention can be implemented in different types of vehicle.

(12) As illustrated in FIG. 4, the vehicle 1 comprises a powertrain 3 for generating a traction force to propel the vehicle 1. The powertrain 3 comprises an internal combustion engine 4, a transmission 5 and a driveline 6. The internal combustion engine 4 is arranged in a longitudinal configuration (North South) in the vehicle 1. The transmission 5 is an automated transmission comprising one or more internal friction brake; and one or more multi-plate clutch. The transmission 5 is controlled by a transmission control module (TCM) 7. The driveline 6 is arranged to transmit torque from the internal combustion engine 4 to driven wheels W.sub.D. In the present embodiment, the driveline 6 is configured to transmit torque to the rear wheels of the vehicle 1. The powertrain 3 could optionally also include an electric traction machine (not shown) for supplying a traction force to said driven wheels W.sub.D.

(13) The driveline 6 comprises a torque transmitting means for transmitting torque from the internal combustion engine 4 to the driven wheels W.sub.D. In the present embodiment, the torque transmitting means is in the form of a drive shaft 8. The drive shaft 8 is selectively coupled to the driven wheels W.sub.D by first and second rear half shafts 9, 10. The vehicle 1 comprises a first decoupling mechanism 11 and a second decoupling mechanism 12. The first and second decoupling mechanisms 11, 12 are disposed at opposite ends of the drive shaft 8 and, as described herein, can be controlled independently of each other. As described herein, the controller 2 is configured to control operation of the first and second decoupling mechanisms 11, 12.

(14) The first decoupling mechanism 11 comprises a first input means in the form of a first input shaft; and a first output means in the form of a first output shaft. The internal combustion engine 4 transmits an input torque to the first input shaft; and the first output shaft transmits an output torque to the drive shaft 8. The first decoupling mechanism 11 is operable selectively to couple and decouple the drive shaft 8 from the internal combustion engine 4. The first decoupling mechanism 11 is opened to decouple the first input shaft from the first output shaft, thereby decoupling the drive shaft 8 from the internal combustion engine 4. Conversely, the first decoupling mechanism 11 is closed to couple the first input shaft to the first output shaft, thereby coupling the drive shaft 8 to the internal combustion engine 4. The first decoupling mechanism 11 is implemented by controlling operation of the transmission 5, for example by opening a clutch in the transmission 5 to disconnect the drive shaft 8 from the internal combustion engine 4. In a variant, the first decoupling mechanism 11 can be separate from the transmission 5. For example, the first decoupling mechanism 11 can be disposed between the drive shaft 8 and the transmission 5; or between the internal combustion engine 4 and the transmission 5.

(15) The second decoupling mechanism 12 comprises a second input means in the form of a second input shaft; and a second output means in the form of a second output shaft. The drive shaft 8 transmits torque to the second input shaft; and the second output shaft transmits a torque to first and second rear half shafts 9, 10 to drive the driven wheels W.sub.D. The second output shaft can, for example, transmit torque to a rear differential 13 configured to transmit torque to the first and second rear half shafts 9, 10. When the internal combustion engine 4 is decoupled from the drive shaft 8 (i.e. the first decoupling mechanism 11 is open), the first and second rear half shafts 9, 10 transmit torque to the second output shaft of the second decoupling mechanism 12. The second decoupling mechanism 12 is operable to decouple the drive shaft 8 from the driven wheels W.sub.D. The second decoupling mechanism 12 is closed to couple the second input shaft to the second output shaft, thereby coupling the drive shaft 8 to the driven wheels W.sub.D. Conversely, the second decoupling mechanism 12 is opened to decouple the second input shaft from the second output shaft, thereby decoupling the drive shaft 8 from the driven wheels W.sub.D. In the present embodiment the second decoupling mechanism 12 comprises a multi-plate clutch. The multi-plate clutch allows slip between the second input shaft and the second output shaft to compensate for the different rotational speeds of the drive shaft 8 and the first and second rear half shafts 9, 10 when the driveline disconnect gliding mode is deactivated. In a modified arrangement, the second decoupling mechanism 12 can comprise first and second clutch mechanisms associated with the first and second rear half shafts 9, 10 respectively. The first and second clutch mechanisms can, for example, be incorporated into the rear differential 13.

(16) The controller 2 comprises at least one electronic processor P configured to execute a set of computational instructions stored on a non-transitory computer readable media. The controller 2 monitors one or more vehicle dynamic conditions, such as vehicle acceleration and/or speed; and one or more vehicle operating parameters, such as output torque from the internal combustion engine 4. The controller 2 is configured to identify a vehicle glide opportunity when the measured dynamic condition(s) differs from a desired vehicle dynamic condition for the current vehicle operating parameter(s). The controller 2 can also check to identify a positive torque request indicative of a driver intention to maintain the current vehicle dynamic conditions. When these conditions are satisfied, the controller 2 publishes an activation signal S.sub.ACT to a vehicle communications network COM to activate a driveline disconnect gliding mode. In dependence on the activation signal S.sub.ACT, the first decoupling mechanism 11 is opened to decouple the drive shaft 8 from the internal combustion engine 4; and the second decoupling mechanism 12 is opened to decouple the drive shaft 8 from the first and second rear half shafts 9, 10. A powertrain control module (PCM) also operates to reduce the torque request of the internal combustion engine 4. The internal combustion engine 4 can operate at idle during the driveline disconnect gliding mode or can be shut down by inhibiting the combustion cycle. By opening both the first and second decoupling mechanisms 11, 12, the rotational speed of the drive shaft 8 decreases and, depending on the duration of the driveline disconnect gliding mode, can come to rest. As the driveline 6 is not coupled to the driven wheels W.sub.D when the second decoupling mechanism 12 is open, the total losses acting on the vehicle 1 can be reduced. At least in certain embodiments, this enables activation of the driveline disconnect gliding mode over a broader range of operating conditions.

(17) With reference to FIG. 4, the at least one processor P is configured to receive a wheel speed signal S.sub.WH, an internal combustion engine speed signal S.sub.ICE and a torque request signal S.sub.TQ. The wheel speed signal S.sub.WH is generated by at least one wheel speed sensor 14 associated with the driven wheels W.sub.D of the vehicle 1. The internal combustion engine speed signal S.sub.ICE is generated by a crankshaft speed sensor 15. The torque request signal S.sub.TQ is generated in dependence on a pedal position sensor 16 associated with a throttle pedal 17. The torque request signal S.sub.TQ comprises a torque demand signal generated by a driver of the vehicle 1 when the throttle pedal 17 is depressed. Alternatively, or in addition, the torque demand signal can be generated by a cruise control system, for example to match a target vehicle speed.

(18) The transmission control module (TCM) 7 detects the activation signal S.sub.ACT published to the communications network COM. In dependence on said activation signal S.sub.ACT, the transmission control module 7 controls operation of the internal clutches in the transmission 5 to decouple the drive shaft 8 from the transmission 5. The second decoupling mechanism 12 is also opened to disconnect the drive shaft 8 from the first and second rear half shafts 9, 10. The drive shaft 8 is thereby disconnected from the internal combustion engine 4 and from the driven wheels W.sub.D. The first and second decoupling mechanisms 11, 12 can be opened concurrently or sequentially to activate the driveline disconnect gliding mode. The internal combustion engine 4 is shut down by inhibiting the combustion cycle. As shown in FIG. 5, when the first and second decoupling mechanisms 11, 12 are open, the drive shaft 8 comes to rest. The operating speed of the internal combustion engine 4 can be reduced, for example to an idle speed. It will be appreciated that the first and second rear half shafts 9, 10 continue to rotate since the rotation of the driven wheels W.sub.D transmits an input torque.

(19) The operating loads acting on the vehicle 1 when the driveline disconnect gliding mode has been activated are shown schematically in FIG. 6. The first arrow 19 (pointing from left to right) represents the positive forces acting on the vehicle 1. The same deceleration rate is achievable by activating the driveline disconnect gliding mode in accordance with an aspect of the present invention. The effective torque B is delivered by virtue of the negative gradient on which the vehicle 1 is travelling. The positive contribution of the engine torque A is removed since the transmission 5 selects neutral and the internal combustion engine 4 is slowed to idle speed or is stopped. The second arrow 20 (pointing from right to left) represents the negative (i.e. decelerating) forces. The negative contributions of the engine loss torque E and the transmission loss torque F are removed. The driveline loss torque G is at least partially removed since the drive shaft 8 is decoupled from the internal combustion engine 4 and the driven wheel W. The total positive torque is provided by the effective torque B, and the total negative torque comprises the aerodynamic torque C and the road loss torque D, i.e. (C+D). A second difference between the positive torque and the negative torque is calculated as follows: (B)(C+D). By removing the driveline loss torque G, the range of operating conditions in which the driveline disconnect gliding mode can usefully be activated is increased, for example to allow activation at smaller gradients.

(20) The controller 2 monitors the vehicle dynamic conditions and the vehicle operating parameters to determine when the driveline disconnect gliding mode is no longer appropriate (i.e. when the effective torque B is no longer sufficient to compensate for the aerodynamic torque C and the road loss torque D. The controller 2 then deactivates the driveline disconnect gliding mode. The controller 2 implements a first control strategy to couple the drive shaft 8 to the driven wheels W.sub.D and to the internal combustion engine 4. Specifically, the controller 2 closes the second decoupling mechanism 12 to couple the drive shaft 8 to the driven wheels W.sub.D by the first and second rear half shafts 9, 10. The drive shaft 8 is decoupled during the driveline disconnect gliding mode and has a lower rotational speed than the driven wheels W.sub.D. Indeed, the rotational speed of the drive shaft 8 may be zero (0) during the driveline disconnect gliding mode. The multi-plate clutch arrangement of the second decoupling mechanism 12 allows slip between the second input shaft and the second output shaft. The second decoupling mechanism 12 closes and the rotational speed of the drive shaft 8 increases in proportion to the rotational speed of the first and second rear half shafts 9, 10 which are drivingly connected to the driven wheels W.sub.D. The controller 2 initiates an engine start-up procedure, for example by activating a starter motor (not shown), to re-start the internal combustion engine 4. The engine start-up procedure can be performed concurrently with closing of the second decoupling mechanism 12. After the second decoupling mechanism 12 is closed, the controller 2 determines the rotational speed of the drive shaft 8. The rotational speed of the drive shaft 8 could be measured directly, for example using a dedicated speed sensor. However, in the present embodiment the rotational speed of the drive shaft 8 is determined in dependence on the measured wheel speed (as indicated by the wheel speed signal SWH) which is proportional to the rotational speed of the drive shaft 8. The controller 2 then determines a target operating speed for the internal combustion engine 4 at least substantially to match the rotational speed across the first decoupling mechanism 11. The controller 2 outputs an engine speed request signal in dependence on the determined target operating speed. Once the operating speed of the internal combustion engine 4 at least substantially matches the target operating speed, the controller 2 outputs a control signal to close the first decoupling mechanism 11. The driveline 6 is thereby re-coupled to the internal combustion engine 4 and to the driven wheels W.sub.D.

(21) The control strategy described above to terminate the driveline disconnect gliding mode requires that the second decoupling mechanism 12 allows slip between the second input shaft and the second output shaft to accommodate the different rotational speeds of the drive shaft 8 and the first and second rear half shafts 9, 10 when the driveline disconnect gliding mode is deactivated. In the present embodiment, the second decoupling mechanism 12 comprises a multi-plate clutch to allow slip. A first variant which does not require the second decoupling mechanism 12 to provide slip will now be described. In the first variant, the second decoupling mechanism 12 can, for example, comprise a dog clutch disposed in series with an output of a differential; or a dog clutch disposed between a ring gear and a differential carrier. The controller 2 is configured to activate the driveline disconnect gliding mode by opening the first and second decoupling mechanisms 11, 12 to decouple the drive shaft 8. The first and second decoupling mechanisms 11, 12 may be opened simultaneously to decouple the drive shaft 8 or sequentially. Alternative control strategies implemented for the first variant to deactivate the driveline disconnect gliding mode will now be described. In a further variant, if the internal combustion engine 3 is stopped and comes to rest during the driveline disconnect gliding mode, the first decoupling mechanism 11 can be closed concurrent with or before the internal combustion engine 3 is re-started. This control strategy would allow the drive shaft 8 to be coupled to the internal combustion engine 3 when the rotational speeds are similar, potentially both zero.

(22) A second control strategy for deactivating the driveline disconnect gliding mode will now be described. The controller 2 determines a target operating speed for the internal combustion engine 4 in dependence on the measured wheel speed of the driven wheels W.sub.D. In particular, the target operating speed is determined such that the input rotational speed of the first decoupling mechanism 11 is substantially the same as the input rotational speed of the second decoupling mechanism 12 (which is proportional to the wheel speed of the driven wheels W.sub.D). When the operating speed of the internal combustion engine 4 matches the target operating speed, the first decoupling mechanism 11 is closed. The first decoupling mechanism 11 accommodates slip, thereby allowing the rotational speed of the drive shaft 8 to increase progressively to match the input rotational speed of the first decoupling mechanism 11. By controlling the operating speed of the internal combustion engine 4, the rotational speed of the drive shaft 8 can be at least substantially matched to the output rotational speed of the second decoupling mechanism 12. Once the rotational speed have been matched, the second decoupling mechanism 12 is closed to re-couple the drive shaft 8 to the driven wheels W.sub.D via the first and second rear half shafts 9, 10. By controlling the operating speed of the internal combustion engine 4 to synchronise the rotational speed of the drive shaft 8 to the output rotational speed of the second decoupling mechanism 12, a non-slip coupling mechanism can be utilised.

(23) A third control strategy for deactivating the driveline disconnect gliding mode will now be described. The internal combustion engine 4 is re-started. The first decoupling mechanism 11 is closed to couple the drive shaft 8 to the internal combustion engine 4. The first decoupling mechanism 11 accommodates slip, thereby allowing the rotational speed of the drive shaft 8 to increase progressively to match the input rotational speed of the first decoupling mechanism 11. The controller 2 then determines a target operating speed for the internal combustion engine 4 in dependence on the measured wheel speed of the driven wheels W.sub.D. The target operating speed is determined such that the input rotational speed of the first decoupling mechanism 11 is substantially the same as the input rotational speed of the second decoupling mechanism 12 (which is proportional to the wheel speed of the driven wheels W.sub.D). When the operating speed of the internal combustion engine 4 matches the target operating speed, the second decoupling mechanism 12 is closed to re-couple the drive shaft 8 to the driven wheels W.sub.D via the first and second rear half shafts 9, 10. By controlling the operating speed of the internal combustion engine 4, the rotational speed of the drive shaft 8 can be at least substantially matched to the input rotational speed of the second decoupling mechanism 12. It will be understood that controlling the operating speed of the internal combustion engine 4 to synchronise the rotational speed of the drive shaft 8 to the input rotational speed of the second decoupling mechanism 12 allows use of a non-slip coupling mechanism.

(24) The second and third control strategies are both applicable to the variant of the second decoupling mechanism 12 described above which does not permit slip between the second input shaft and the second output shaft. It will be appreciated, however, that the second control strategy could also be applied to arrangements in which the second decoupling mechanism 12 does permit slip.

(25) The vehicle 1 in the above embodiment has a rear-wheel drive arrangement. The invention described herein is equally applicable to a vehicle 1 having a front-wheel drive arrangement. A further embodiment of the present invention implemented in a vehicle 1 having a front-wheel drive arrangement will now be described with reference to FIGS. 7 and 8. Like reference numerals will be used for like components in the description of this arrangement.

(26) As shown in FIG. 7, the vehicle 1 comprises a powertrain 3 for generating a traction force to propel the vehicle 1. The powertrain 3 comprises an internal combustion engine 4, a transmission 5 and a driveline 6. The internal combustion engine 4 is arranged in a transverse configuration (East West) in the vehicle 1. The transmission 5 is an automated transmission comprising one or more internal friction brake; and one or more multi-plate clutch. The driveline 6 is arranged to transmit torque from the internal combustion engine 4 to driven wheels W.sub.D. In the present embodiment, the driveline 6 is configured to transmit torque to the front wheels of the vehicle 1.

(27) The driveline 6 comprises a torque transmitting means for transmitting torque from the internal combustion engine 4 to the driven wheels W.sub.D. With reference to FIG. 8, the torque transmitting means comprises a front differential 21 drivingly connected to the transmission 5. In particular, the front differential 21 comprises an input ring gear 22 which meshes with an output gear 23 of the transmission 5. The front differential 21 comprises first and second output shafts 24, 25 coupled to respective first and second front half shafts 26, 27. In use, the first and second front half shafts 26, 27 transmit torque to the driven wheels W.sub.D of the vehicle 1.

(28) In accordance with the other embodiments described herein, the vehicle 1 comprises a first decoupling mechanism 11 and a second decoupling mechanism 12. The first and second decoupling mechanisms 11, 12, can be selectively opened to decouple the front differential 21 from the driveline 6 when the vehicle 1 is operating in a driveline disconnect gliding mode. The first and second decoupling mechanisms 11, 12 can be controlled independently of each other. For example, the first and second decoupling mechanisms 11, 12 can be opened simultaneously or sequentially. As described herein, the controller 2 is configured to control operation of the first and second decoupling mechanisms 11, 12.

(29) The transmission 5 transmits an input torque to the input ring gear 22; and the differential transmits an output torque to the front half shafts 26, 27. The first decoupling mechanism 11 is operable selectively to couple and decouple the front differential 21 to the transmission 5.

(30) The first decoupling mechanism 11 is incorporated into the transmission 5. The first decoupling mechanism 11 may be associated with a transmission input shaft 28 which is connected to the internal combustion engine 4. This arrangement of the first decoupling mechanism is denoted by the reference 11a in FIG. 8. Alternatively, the first decoupling mechanism 11 may be incorporated into the transmission 5, for example by selecting neutral or opening a transmission clutch, as denoted by the reference 11b in FIG. 8. In a further alternative, the first decoupling mechanism 11 may be incorporated into the transmission 5 before a gear driving an intermediate shaft 29 within the transmission 5, as denoted by the reference 11c in FIG. 8. Alternatively, the first decoupling mechanism 11 may be incorporated into the intermediate shaft of the transmission 5, as denoted by the reference 11d in FIG. 8. These variations on the first decoupling mechanism 11 may be incorporated into the other embodiments described herein.

(31) The front differential 21 transmits torque to the first and second front half shafts 26, 27 to drive the driven wheels W.sub.D. The second decoupling mechanism 12 is operable selectively to couple and decouple the first and second output shafts 24, 25 to the respective first and second front half shafts 26, 27. The second decoupling mechanism 12 in the present embodiment comprises first and second output decoupling mechanisms 12a, 12b which can be opened to decouple the first and second output shafts 24, 25 from the first and second front half shafts 26, 27. The second decoupling mechanism 12 is operable to decouple the transmission 5 and the front differential 21 from the driven wheels W.sub.D. The second decoupling mechanism 12 in this embodiment is operable to disconnect both sides of the front differential 21. The first and second output decoupling mechanisms 12a, 12b may be operated together or independently of each other. The first and second output decoupling mechanisms 12a, 12b in the present embodiment are incorporated into the front differential 21. However, it will be appreciated that the first and second output decoupling mechanisms 12a, 12b may be separate from the front differential 21, for example disposed between the front differential 21 and the first and second front half shafts 26, 27.

(32) The controller 2 in this further embodiment is configured to implement the first control strategy described herein. When the driveline disconnect gliding mode is activated, the first and second decoupling mechanisms 11, 12 are open such that the front differential 21 and the transmission 5 are decoupled from the driveline 6. In further variants, the second decoupling mechanism 12 can comprise one or more non-slip mechanisms. The controller 2 can be configured to implement the second and third control strategies described herein to deactivate the driveline disconnect gliding mode.

(33) In certain modified arrangements, the second decoupling mechanism 12 may provide a single-side disconnect. The second decoupling mechanism 12 may comprise a single output decoupling mechanism (either the first output decoupling mechanism 12a or the second output decoupling mechanism 12b) which may be opened to decouple the front differential 21. In this arrangement, the front differential 21 may rotate when the output decoupling mechanism 12 is opened.

(34) In a further modified arrangement, the second decoupling mechanism 12 may be associated with the input ring gear 22 of the front differential 21. This arrangement of second decoupling mechanism is denoted by the reference 12c in FIG. 8. The second decoupling mechanism 12c is opened to decouple the input ring gear 22. Conversely, the second decoupling mechanism 12c is closed to couple the input ring gear 22.

(35) At least some of the features described herein with reference to the front differential 21 may be incorporated into the rear differential 13 described with reference to the rear-wheel drive embodiments of the present invention. For example, the second decoupling mechanism 12 described with reference to the front differential 21 may be incorporated into the rear differential 13 to enable the first and second rear half shafts 9, 10 to be selectively coupled and decoupled.

(36) The vehicle 1 may comprise one or more electric traction motor. The vehicle 1 may, for example, be a Mild Hybrid Electric Vehicle (MHEV) or a Plug-in Hybrid Electric Vehicle (PHEV). The one or more electric traction motor may, for example, be incorporated into the transmission 5 or the driveline 6. The one or more electric traction motor could, for example, be coupled to the transmission input shaft 28, the transmission intermediate shaft or the transmission output shaft.

(37) Aspects of the invention described herein could also be implemented in a four-wheel drive vehicle having front and rear driven wheels W.sub.D. A vehicle 1 having four-wheel drive and comprising first and second decoupling mechanisms 11, 12 in accordance with an embodiment of the present invention is shown in FIG. 9. The vehicle 1 comprises a transfer case 30 drivingly connected to the transmission 5. A front driveshaft 31 connects the transfer case 30 to the first and second front half shafts 26, 27. The first decoupling mechanism 11 is incorporated into the transfer case 30 and is operable to disconnect the front driveshaft 31 from the transfer case 30. The second decoupling mechanism 12 comprises first and second output decoupling mechanisms 12a, 12b associated with the first and second front half shafts 26, 27 respectively. When the vehicle 1 is operating in a driveline disconnect gliding mode, the first decoupling mechanism 11 is opened to disconnect the transfer case 30 from the front driveshaft 31; and the first and second output decoupling mechanisms 12a, 12b are opened to disconnect the first and second front half shafts 26, 27 from the front driveshaft 31. The front driveshaft 31 may thereby be disconnected from the internal combustion engine 3 and the front driven wheels W.sub.D when the driveline disconnect gliding mode is activated. It will be appreciated that additional decoupling mechanisms may be provided for disconnecting the driveshaft 8 from the rear driven wheels W.sub.D. For example, the mechanisms described herein with reference to the rear-wheel drive vehicle 1 shown in FIG. 5 may be implemented in the four-wheel drive vehicle 1 shown in FIG. 9. The four-wheel drive function of the vehicle 1 may be permanently engaged. Alternatively, the four-wheel vehicle function of the vehicle 1 may be selectively four-wheel drive, for example operating in two-wheel drive under normal operating conditions. The activation of the driveline disconnect gliding mode may be controlled in dependence on whether the vehicle 1 is operating in four-wheel drive or two-wheel drive.

(38) It will be appreciated that various changes and modifications can be made to embodiments described herein without departing from the scope of the present invention.