GB2550161A

GB2550161A - Vehicle and method

Info

Publication number: GB2550161A
Application number: GB1608186.1A
Authority: GB
Inventors: Osborn Russell; Valero Thomas; Roques Olivier
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2016-05-10
Filing date: 2016-05-10
Publication date: 2017-11-15
Anticipated expiration: 2036-05-10
Also published as: GB2550161B; GB201608186D0

Abstract

A vehicle 1 having a torque generating machine, e.g. engine 4, connected to driven wheels WD by a decoupling mechanism, such as a multi-plate clutch 12 which is operable to couple/decouple transmitting means, e.g. drive shaft 8, from the wheels WD. A controller 2 having at least one electronic processor P controls operation of the engine 4 and the clutch 12. When a vehicle glide opportunity is identified, the electronic processor P activates a driveline disconnect gliding mode by opening the clutch12 to decouple the drive shaft 8 from driven wheels WD and then reduce a speed of the engine 4. When the gliding mode is no longer appropriate, the processor P controls the speed of the engine 4 to reduce a speed differential across the clutch 12 and when the speeds are substantially equal the clutch 12 closed to couple the drive shaft 8 to the wheels WD. Also claimed is a method of controlling the transmittal of torque from an engine 4 along a driveline 6 to one or more driven wheel WD of the vehicle 1.

Description

VEHICLE AND METHOD

TECHNICAL FIELD

The present disclosure relates to a vehicle and a method. More particularly, but not exclusively, the present disclosure relates to a vehicle having a driveline including a decoupling mechanism for selectively decoupling one or more driven wheel from a torque generating machine; and to a method of controlling the transmittal of torque from a torque generating machine to one or more driven wheel.

BACKGROUND

It is known to disconnect a vehicle driveline and to reduce an operating speed of an internal combustion engine to reduce fuel consumption. This strategy is known variously as vehicle gliding, vehicle sailing, idle coasting etc. The operating mode is referred to herein as a gliding mode.

An example of a known driveline disconnect strategy is disclosed in the Applicant’s earlier UK patent application GB1316183.1. A rear-wheel drive vehicle 1 having a powertrain 3 is illustrated in Figure 1. The powertrain 3 comprises an internal combustion engine 4, a transmission 5 and a driveline 6. When a gliding mode is activated, the driveline 6 is decoupled from the internal combustion engine 4. The operating speed of the internal combustion engine 4 can then be reduced, for example to operate at idle, to provide improved fuel efficiency. When the internal combustion engine 4 is decoupled, the driveline 6 is rotated by a torque applied by the driven wheels WD (the rear wheels in the present arrangement). The dynamic operating states of the respective components when the vehicle 1 is operating in a conventional gliding mode are illustrated in Figure 1. A vehicle 1 having a front-wheel drive arrangement is illustrated in Figure 2. The front-wheel drive vehicle 1 can also operate in a gliding mode by decoupling the driveline 6 from the internal combustion engine 4. When the driveline 6 is decoupled, the driveline 6 is rotated by a torque applied by the driven wheels WD (the front wheels in the present arrangement). The dynamic operating states of the respective components when the vehicle 1 is operating in a conventional gliding mode are illustrated in Figure 2.

The relationship between the operating loads on a vehicle 1 travelling down a 2% negative gradient is illustrated in Figure 3. The loads are expressed as the torque within a powertrain of the vehicle 1. The positive (accelerating) forces acting on the vehicle 1, represented by a first arrow pointing in the direction of travel (from left to right in Figure 2), comprise: an engine torque A delivered in dependence on a driver torque request; and an effective torque B derived from the road gradient. The sum of the engine torque A and the effective torque B represents a total torque at the wheels of A+B. The negative (decelerating) forces acting on the vehicle 1, represented by a second arrow pointing in the opposite direction (from right to left in Figure 2), comprise: an aerodynamic torque C; a road loss torque D; an engine loss torque E; a transmission loss torque F; and a driveline loss torque G. The total negative torque is -(C+D+E+F+G); and the total positive torque is (A+B). A first difference between the positive torque and the negative torque is calculated as follows: (A+B)-(C+D+E+F+G). When the gliding mode is activated, the driveline 6 is disconnected from the internal combustion engine 4 and the total torque comprises a positive torque comprising the effective torque B; and a negative torque comprising the aerodynamic torque C, the road loss torque D, the transmission loss torque F and the driveline loss G. The internal combustion engine 4 is disconnected from the driveline 6 so the engine loss torque E is not applied. A second difference between the positive torque and the negative torque is calculated as follows: (B)-(C+D+F+G). The internal combustion engine can operate at a lower speed, for example idle, or can be switched off.

It would be advantageous to broaden the range of operating conditions in which the driveline could be decoupled from the internal combustion engine. It is against this backdrop that the present invention has been conceived.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a vehicle operable selectively to couple and decouple a driveline; and to a method of selectively coupling and decoupling a driveline of a vehicle as claimed in the appended claims.

According to a further aspect of the present invention there is provided a vehicle comprising: a torque generating machine; one or more driven wheel; a driveline comprising a torque transmitting means for transmitting torque from the torque generating machine to said one or more driven wheel; a decoupling mechanism operable to decouple the torque transmitting means from the one or more driven wheel, wherein the decoupling mechanism is closed to couple the torque transmitting means to the one or more driven wheel and is opened to decouple the torque transmitting means from the one or more driven wheel; and a controller comprising at least one electronic processor for controlling operation of the torque generating machine and the decoupling mechanism; wherein the at least one electronic processor is configured to: open the decoupling mechanism to decouple the torque transmitting means from the one or more driven wheel and to reduce an operating speed of the torque generating machine; and control the operating speed of the torque generating machine to reduce a speed differential across the decoupling mechanism and to close the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel.

The decoupling mechanism may be opened when a driveline disconnect gliding mode is activated; and may be closed when the driveline disconnect gliding mode is terminated. The activation and termination of the driveline disconnect gliding mode is performed while the vehicle is in motion. By reducing the operating speed of the torque generating machine when the driveline disconnect gliding mode is active, the use of stored energy may be reduced. The reduction in the operating speed of the torque generating machine typically results in a speed differential across the decoupling mechanism. In order to terminate the driveline disconnect gliding mode, the controller is configured to control the operating speed of the torque generating machine before closing the decoupling mechanism. At least in certain embodiments, the decoupling mechanism may be closed to couple the torque transmitting means to the one or more driven wheel without providing a separate decoupling mechanism to disconnect the torque transmitting means from the torque generating machine. Thus, at least in certain embodiments, the driveline disconnect gliding mode may be implemented by a single decoupling mechanism operable selectively to decouple the torque transmitting means from the one or more driven wheel. By way of example, in an embodiment comprising an internal combustion engine and a transmission, it is not necessary to provide a decoupling mechanism to decouple the transmission from the internal combustion engine.

The at least one processor may reduce the operating speed by stopping the torque generating machine; and may control the operating speed by re-starting the torque generating machine.

The vehicle may comprise a transmission connected to the torque generating machine. The transmission may have a plurality of drive ratios. The torque generating machine, the transmission and the torque transmitting means may be connected in series. The decoupling mechanism may be remote from the transmission and the torque generating means. The torque transmitting means may be disposed between the transmission and the decoupling mechanism. The transmission may be permanently drivingly connected to the torque generating machine. The torque transmitting means may be permanently drivingly connected to the transmission.

The at least one electronic processor may be configured to determine a target operating speed of the torque generating machine; and to control an operating speed of the torque generating machine in dependence on the determined target operating speed. The target operating speed may be determined so as to minimise the speed differential across the decoupling mechanism. At least in certain embodiments, the target operating speed may be determined such that the speed differential may be at least substantially zero. The target operating speed may be determined at least substantially to match the input and output speeds of the decoupling mechanism.

The at least one processor may be configured to close the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel when the operating speed of the torque generating machine at least substantially matches the determined target operating speed.

The at least one electronic processor may be configured to determine the target operating speed of the torque generating machine in dependence on a wheel speed signal of said one or more driven wheel and/or a torque demand signal.

In arrangements in which the vehicle comprises a transmission, the at least one electronic processor may be configured to determine an operating speed of the torque generating machine for reducing the speed differential across the decoupling mechanism in respect of each drive ratio of the transmission. The at least one electronic processor may set the target operating speed as one of the determined operating speeds which falls within a predefined operating speed range. The predefined operating speed range may define an upper speed threshold and a lower speed threshold for the torque generating machine. The upper and lower speed thresholds may be defined to protect the torque generating machine.

The at least one electronic processor may be configured to select one of said plurality of drive ratios associated with the target operating speed; and to control the transmission to engage the selected one of said plurality of drive ratios before closing the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel. The at least one electronic processor may be configured to control the transmission to engage the selected drive ratio and to control the operating speed of the torque generating machine at least substantially to match the determined target operating speed. The at least one electronic processor may be configured to close the decoupling mechanism only when these conditions are satisfied. If the torque generating machine is to be re-started, the at least one processor may be configured to control the transmission to engage a drive ratio suitable for starting the torque generating machine. For example, the at least one processor may control the transmission to engage a low drive ratio. Once the torque generating machine has started, the at least one processor may control the transmission to engage the selected drive ratio. In certain scenarios, the selected drive ratio may be the same as the drive ratio engaged for starting. However, the selected drive ratio will usually be different from the drive ratio engaged for starting.

The decoupling mechanism may comprise torque input means and torque output means. The decoupling mechanism may be configured to accommodate slip between the torque input means and the torque output means. The torque input means may comprise an input shaft; and the torque output means may comprise an output shaft.

The decoupling mechanism may comprise 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.

The torque generating machine may comprise an internal combustion engine. In certain embodiments, the torque generating machine may comprise an internal combustion engine and an electric machine.

The torque transmitting means may be in the form of a drive shaft. The drive shaft may extend longitudinally.

The at least one processor may be configured to activate a driveline disconnect gliding mode by opening the decoupling mechanism to decouple the torque transmitting means from the one or more driven wheel. The at least one processor may be configured to terminate the driveline disconnect gliding mode by closing the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel.

According to a further aspect of the present invention there is provided a method of controlling the transmittal of torque from a torque generating machine along a driveline to one or more driven wheel of a vehicle, the driveline comprising a torque transmitting means; wherein the method comprises: operating a decoupling mechanism to decouple the torque transmitting means from the one or more driven wheel and reducing an operating speed of the torque generating machine; controlling the operating speed of the torque generating machine to reduce a speed differential across the decoupling mechanism and then re-coupling the torque transmitting means to the one or more driven wheel. The torque transmitting means may be decoupled from the one or more driven wheel when a driveline disconnect gliding mode is activated. The torque transmitting means may be re-coupled to the one or more driven wheel when a driveline disconnect gliding mode is terminated.

At least in certain embodiments, reducing the operating speed of the torque generating machine may comprise stopping the torque generating machine. Controlling the operating speed of the torque generating machine may comprise re-starting the torque transmitting means.

The method may comprise determining a target operating speed of the torque generating machine and controlling the operating speed of the torque generating machine in dependence on the determined target operating speed. The target operating speed of the torque generating machine may be determined so as to reduce the speed differential across the decoupling mechanism. At least in certain embodiments, the target operating speed may be determined to minimise the speed differential. The target operating speed may be determined at least substantially to match the input and output speeds of the decoupling mechanism. Thus, the target operating speed may be determined such that the speed differential across the decoupling mechanism is at least substantially zero.

The method may comprise operating the decoupling mechanism to re-couple the torque transmitting means to the one or more driven wheel when the operating speed of the torque generating machine at least substantially matches the determined target operating speed.

The method may6 comprise determining the target operating speed of the torque generating machine in dependence on a wheel speed of the one or more driven wheel and/or a torque demand signal.

The method may comprise, in respect of a plurality of available drive ratios, determining an operating speed of the torque generating machine for reducing the speed differential across the decoupling mechanism; and setting the target operating speed as one of the determined operating speeds falling within a predefined operating speed range. The plurality of drive ratios may be provided by a transmission connected to the torque generating machine. The method may comprise selecting the drive ratio associated with the target operating speed; and engaging the selected drive ratio and then re-coupling the torque transmitting means to the one or more driven wheel.

The method may comprise engaging the selected drive ratio and then controlling the operating speed of the torque generating machine at least substantially to match the determined target operating speed. Once the operating speed of the torque generating machine at least substantially matches the determined target operating speed, the method may comprise closing the decoupling mechanism to re-couple the torque transmitting means to the one or more driven wheel. If the method comprises re-starting the torque generating machine, a drive ratio suitable for starting may initially be engaged. For example, a low drive ratio may be selected to facilitate re-starting the torque generating machine. The selected drive ratio may be engaged once the torque generating machine has started. In certain scenarios, the selected drive ratio may be the same as the drive ratio engaged for starting. However, the selected drive ratio will usually be different from the drive ratio engaged for starting. The operating speed of the torque generating machine may be at least substantially matched to the determined target operating speed after engaging the selected drive ratio. The method may then comprise operating the decoupling mechanism to re-couple the torque generating machine to the one or more driven wheel.

Any controller or controllers described herein may suitably comprise a control unit or computational device having one or more electronic processors. Thus the system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller” or “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. A first controller may be implemented in software run on one or more processors. One or more other controllers may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

Figure 1 shows a schematic representation of the main components of a conventional rear-wheel drive vehicle;

Figure 2 shows a schematic representation of the main components of a conventional front-wheel drive vehicle;

Figure 3 shows a schematic representation of the forces acting on a vehicle when operating in a gliding mode;

Figure 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;

Figure 5 shows a schematic representation of the dynamic operating states of the components in the driveline of the vehicle shown in Figure 4 when operating in said driveline disconnect gliding mode; and

Figure 6 shows a schematic representation of the loads on the vehicle shown in Figure 4 when operating in the said driveline disconnect gliding mode.

DETAILED DESCRIPTION A vehicle 1 comprising a controller 2 according to an embodiment of the present invention will now be described with reference to Figures 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 WD 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.

As illustrated in Figure 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 WD. 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 WD.

The driveline 6 comprises a torque transmitting means for transmitting torque from the internal combustion engine 4 to the driven wheels WD. In the present embodiment, the torque transmitting means is in the form of a drive shaft 8. A first end of the drive shaft 8 is permanently drivingly connected to the transmission 5 to transmit torque generated by the internal combustion engine 4 to the driveline 6. A second end of the drive shaft 8 is selectively coupled to the driven wheels WD by first and second rear half shafts 9, 10. The vehicle 1 comprises a decoupling mechanism 12 operable to decouple the drive shaft 8 from the driven wheels WD. The decoupling mechanism 12 is disposed at the rear of the drive shaft 8. As described herein, the controller 2 is configured to control operation of the decoupling mechanism 12.

The decoupling mechanism 12 comprises input means in the form of an input shaft; and output means in the form of an output shaft. The drive shaft 8 transmits torque to the input shaft; and the output shaft transmits a torque to first and second rear half shafts 9, 10 to drive the driven wheels WD. The 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. The decoupling mechanism 12 is operable to decouple the drive shaft 8 from the driven wheels WD. The 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 WD. Conversely, the 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 WD. In the present embodiment the decoupling mechanism 12 comprises a multi-plate clutch. The multi-plate clutch allows slip between the input shaft and the 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 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.

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 SAct to a vehicle communications network COM to activate a driveline disconnect gliding mode. In dependence on the activation signal SACt, the 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 the decoupling mechanism 12 and reducing the operating speed of the internal combustion engine 4, the rotational speed of the drive shaft 8 decreases. If the internal combustion engine 4 is shut down during the driveline disconnect gliding mode, the drive shaft 8 may come to rest. As the driveline 6 is not coupled to the driven wheels WD when the 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.

With reference to Figure 4, the at least one processor P is configured to receive a wheel speed signal SWh, an internal combustion engine speed signal Sice and a torque request signal STQ. The wheel speed signal SWh is generated by at least one wheel speed sensor 14 associated with the driven wheels WD of the vehicle 1. The internal combustion engine speed signal Sice is generated by a crankshaft speed sensor 15. The torque request signal STQ is generated in dependence on a pedal position sensor 16 associated with a throttle pedal 17. The torque request signal STq 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.

In dependence on said activation signal SACT, the decoupling mechanism 12 is 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 driven wheels WD. The internal combustion engine 4 is shut down by inhibiting the combustion cycle. As shown in Figure 5, when the decoupling mechanism 12 is open and the internal combustion engine 4 is shut down, the drive shaft 8 comes to rest. It will be appreciated that the first and second rear half shafts 9, 10 continue to rotate since the rotation of the driven wheels WD transmits an input torque. In certain variants, the transmission control module (TCM) 7 may control operation of the transmission 5 to engage neutral. For example, the transmission control module (TCM) 7 may detect the activation signal SAct published to the communications network COM and, in dependence on said activation signal SACt, the transmission control module (TCM) 7 may engage neutral.

The operating loads acting on the vehicle 1 when the driveline disconnect gliding mode has been activated are shown schematically in Figure 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 driven wheels WD. 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.

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 WD. Specifically, the controller 2 closes the decoupling mechanism 12 to couple the drive shaft 8 to the driven wheels WD 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 WD. 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 decoupling mechanism 12 allows slip between the second input shaft and the second output shaft. However, the controller 2 is configured to reduce the speed differential across the decoupling mechanism 12 (i.e. the difference in the rotational speed of the input shaft and the output shaft of the decoupling mechanism 12) prior to closing the decoupling mechanism 12. At least in certain embodiments, the controller 2 is configured at least substantially to match the rotational speed of the input shaft and the output shaft of the decoupling mechanism 12 such that the speed differential is substantially zero. The operation of the controller 2 to reduce the speed differential across the decoupling mechanism 12 will now be described.

The rotational speed of the output shaft is determined in dependence on the wheel speed signal SWh for the driven wheels WD. The controller 2 determines a target operating speed of the internal combustion engine 4 such that the rotational speed of the input shaft at least substantially matches that of the output shaft. The target operating speed is dependent on the selected drive ratio of the transmission 5. An operating speed range (comprising an upper speed threshold and a lower speed threshold) may be predefined for the internal combustion engine 4, for example to remain within normal operating conditions. The controller 2 may be configured to control the transmission 5 to engage a drive ratio to ensure that the target operating speed of the internal combustion engine 4 is within the predefined speed range. For example, the controller 2 may determine an operating speed of the internal combustion engine 4 based on each of the available drive ratios of the transmission 5. The controller 2 may then select a drive ratio which provides a target operating speed which is within the predefined speed range. The controller 2 outputs an engine speed request signal to the internal combustion engine 4 specifying the target operating speed; and also a transmission control signal to the transmission control module (TCM) 7 to engage the selected drive ratio. It will be understood that the target operating speed is determined at least substantially in real time in dependence on the wheel speed signal SWh-

As outlined above, when the driveline disconnect gliding mode is activated, the internal combustion engine 4 is shut down and the decoupling mechanism 12 is open such that the drive shaft 8 is decoupled from the driven wheels WD. The control strategy implemented by the control 2 in order to terminate the driveline disconnect gliding mode will now be described. While the decoupling mechanism 12 is open, the controller 2 outputs a transmission control signal to the transmission control module (TCM) 7 requesting that a drive ratio is engaged for starting the internal combustion engine 4. The drive ratio typically corresponds to a low gear. The controller 2 then requests that the internal combustion engine 4 is re-started. Once the internal combustion engine 4 has started, the controller 2 outputs a transmission control signal to request that the selected drive ratio is engaged. The transmission 5 engages the selected drive ratio in conventional manner. Once the selected drive ratio is engaged, the controller 2 outputs the engine speed request signal specifying the target operating speed of the internal combustion engine 4. When the operating speed of the internal combustion engine (4) at least substantially matches the determined target operating speed, the rotational speed of the input shaft at least substantially matches the rotational speed of the output shaft of the decoupling mechanism 12. The controller 2 outputs a control signal to close the decoupling mechanism 12, thereby drivingly connecting the drive shaft 8 to the first and second rear half shafts 9, 10 and the driven wheels WD.

In a variant of the above embodiment, the controller 2 is configured to output a transmission control signal to the transmission control module (TCM) 7 to engage the selected drive ratio and then to re-start the internal combustion engine 4. In this variant, it is not necessary to change the gear ratio after starting the internal combustion engine 4. Since the decoupling mechanism 12 is initially open (such that the drive wheels WD are decoupled from the internal combustion engine 4), the internal combustion engine 4 can be started with the selected gear ratio pre-engaged. The controller 2 then outputs the engine speed request signal specifying the target operating speed of the internal combustion engine 4. When the operating speed of the internal combustion engine (4) at least substantially matches the determined target operating speed, the rotational speed of the input shaft at least substantially matches the rotational speed of the output shaft of the decoupling mechanism 12. The controller 2 outputs a control signal to close the decoupling mechanism 12, thereby drivingly connecting the drive shaft 8 to the first and second rear half shafts 9, 10 and the driven wheels WD. At least in certain embodiments, the time taken to re-couple the internal combustion engine 4 to the driven wheels WD may be reduced.

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.

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.

Claims

CLAIMS:

1. A vehicle comprising: a torque generating machine; one or more driven wheel; a driveline comprising a torque transmitting means for transmitting torque from the torque generating machine to said one or more driven wheel; a decoupling mechanism operable to decouple the torque transmitting means from the one or more driven wheel, wherein the decoupling mechanism is closed to couple the torque transmitting means to the one or more driven wheel and is opened to decouple the torque transmitting means from the one or more driven wheel; and a controller comprising at least one electronic processor for controlling operation of the torque generating machine and the decoupling mechanism; wherein the at least one electronic processor is configured to: open the decoupling mechanism to decouple the torque transmitting means from the one or more driven wheel and to reduce an operating speed of the torque generating machine; and control the operating speed of the torque generating machine to reduce a speed differential across the decoupling mechanism and to close the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel.

2. A vehicle as claimed in claim 1, wherein reducing the operating speed comprises stopping the torque generating machine; and controlling the operating speed comprises restarting the torque generating machine.

3. A vehicle as claimed in claim 1 or claim 2 comprising a transmission having a plurality of drive ratios; the transmission being drivingly connected to the torque generating machine.

4. A vehicle as claimed in claim 3, wherein the transmission is permanently drivingly connected to the torque generating machine.

5. A vehicle as claimed in any one of claims 1 to 4, wherein the at least one electronic processor is configured to determine a target operating speed of the torque generating machine; and to control an operating speed of the torque generating machine in dependence on the determined target operating speed.

6. A vehicle as claimed in claim 5, wherein the at least one processor is configured to close the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel when the operating speed of the torque generating machine at least substantially matches the determined target operating speed.

7. A vehicle as claimed in claim 5 or claim 6, 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 of said one or more driven wheel and/or a torque demand signal.

8. A vehicle as claimed in any one of claims 5, 6 or 7 when dependent directly or indirectly on claim 3, wherein, in respect of each of the plurality of drive ratios of the transmission, the at least one electronic processor is configured to determine an operating speed of the torque generating machine for reducing the speed differential across the decoupling mechanism; and to set the target operating speed as one of the determined operating speeds which falls within a predefined operating speed range.

9. A vehicle as claimed in claim 8, wherein the at least one electronic processor is configured to select one of said plurality of drive ratios associated with the target operating speed; and to control the transmission to engage the selected one of said plurality of drive ratios before closing the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel.

10. A vehicle as claimed in any one of the preceding claims, wherein the decoupling mechanism comprises torque input means and torque output means, wherein the decoupling mechanism accommodates slip between the torque input means and the torque output means.

11. A vehicle as claimed in any one of the preceding claims, wherein the 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.

12. A vehicle as claimed in any one of the preceding claims, wherein the torque generating machine comprises an internal combustion engine.

13. A vehicle as claimed in any one of the preceding claims, wherein the at least one processor is configured to activate a driveline disconnect gliding mode by opening the decoupling mechanism to decouple the torque transmitting means from the one or more driven wheel; and to terminate the driveline disconnect gliding mode by closing the decoupling mechanism to couple the torque transmitting means to the one or more driven wheel.

14. A method of controlling the transmittal of torque from a torque generating machine along a driveline to one or more driven wheel of a vehicle, the driveline comprising a torque transmitting means; wherein the method comprises: operating a decoupling mechanism to decouple the torque transmitting means from the one or more driven wheel and reducing an operating speed of the torque generating machine; controlling the operating speed of the torque generating machine to reduce a speed differential across the decoupling mechanism and then re-coupling the torque transmitting means to the one or more driven wheel.

15. A method as claimed in claim 14, wherein reducing the operating speed of the torque generating machine comprises stopping the torque generating machine; and controlling the operating speed of the torque generating machine comprises re-starting the torque transmitting means.

16. A method as claimed in claim 15 comprising determining a target operating speed of the torque generating machine and controlling the operating speed of the torque generating machine in dependence on the determined target operating speed.

17. A method as claimed in claim 16 comprising operating the decoupling mechanism to re-couple the torque transmitting means to the one or more driven wheel when the operating speed of the torque generating machine at least substantially matches the determined target operating speed.

18. A method as claimed in claim 16 or claim 17 comprising determining the target operating speed of the torque generating machine in dependence on a wheel speed of the one or more driven wheel and/or a torque demand signal.

19. A method as claimed in any one of claims 16, 17 or 18 comprising, in respect of a plurality of available drive ratios, determining an operating speed of the torque generating machine for reducing the speed differential across the decoupling mechanism; and setting the target operating speed as one of the determined operating speeds falling within a predefined operating speed range.

20. A method as claimed in claim 19, comprising selecting the drive ratio associated with the target operating speed; and engaging the selected drive ratio and then re-coupling the torque transmitting means to the one or more driven wheel (WD).

21. A controller comprising at least one processor (P) configured to implement the method described in any one of claims 14 to 20.

22. A vehicle substantially as herein described with reference to the accompanying figures.

23. A method substantially as herein described with reference to the accompanying figures.