Compact gearbox and e-reverse

A gearbox comprising: an outer intermediate shaft carrying a first set of shaft gears; an inner intermediate shaft carrying a second set of shaft gears, the inner intermediate shaft running concentrically within the outer intermediate shaft; a first lay shaft carrying a first set of drive gears and an output gear positioned along the first lay shaft between two of the first set of drive gears, a second lay shaft carrying a second set of drive gears and an output gear positioned along the second lay shaft between two of the second set of drive gears, each drive gear being coupled to a respective shaft gear to together provide a plurality of gear ratios between the intermediate shafts and the output shaft; and an output shaft, each lay shaft being coupled to the output shaft by the respective output gear.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of and claims priority under 35 U.S.C. § 371 to PCT Application No. PCT/GB2017/050989, filed on Apr. 10, 2017, which claims priority to German Application No. DE 20 2016 101 867.6, filed on Apr. 8, 2016. The contents of both of these priority applications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

This invention relates to a gearbox and to a vehicle comprising first and second power sources.

BACKGROUND

A typical road vehicle has a source of drive, such as an internal combustion engine, which is connected to the vehicle's wheels through a gearbox. The road vehicle may have a hybrid powertrain in which case the source of drive may be an internal combustion engine working in conjunction with at least one electric machine that can operate as an electric motor. The gearbox allows the driver to select the drive ratio between an output shaft of the power source and a drive shaft leading to the wheels.

SUMMARY

Increasing numbers of vehicles have dual clutch transmissions (DCTs).FIG. 1shows a conventional DCT gearbox. The gearbox has a driven shaft1which is connected to the crankshaft of an engine. The driven shaft is connected to a clutch housing2so that the clutch housing rotates with the driven shaft. The clutch housing contains a pair of main clutches3,4. The main clutches are arranged so that they can be actuated independently to couple the driven shaft to either an inner intermediate shaft5or an outer intermediate shaft6. The inner intermediate shaft runs concentrically within the outer intermediate shaft. The gearbox has two lay shafts7,8. Each lay shaft carries a number of drive gears9,10. The drive gears can spin freely about their lay shaft or can be coupled to their lay shaft by a respective dog clutch11.

The lay shafts are coupled by output gears12to a drive shaft13leading to the wheels of the vehicle. The output gear12carried by lay shaft7is connected to the output gear12carried by drive shaft13as shown by the dotted line that runs between the output gears12. The position of output gear12carried by drive shaft13would in practice be positioned out of the plane of the page ofFIG. 1so as to connect to both other output gears12. The output gears12are shown as being connected to the layshafts7,8at their ends closest to the clutches3,4. The output gears12could be connected to the layshafts7,8at their ends farthest from the clutches3,4.

The inner intermediate shaft5carries shaft gears14which mesh with drive gears10. The ratios provided by gears14and10in combination implement a first set of gear ratios between the driven shaft1and the drive shaft13. A selected one of those gear ratios can be implemented by actuating main clutch3so as to couple the drive shaft1to the inner intermediate shaft6and by actuating one of the dog clutches11so as to couple the appropriate one of the drive gears10to one of the lay shafts. Similarly, the outer intermediate shaft6carries shaft gears15which mesh with drive gears9to implement a second set of gear ratios between the driven shaft1and the drive shaft13. Lay shaft7is also shown as carrying a drive gear16that functions as a reverse gear. Not shown inFIG. 1is a further reverser gear that connects drive gear16to its respective shaft gear15. This reverser gear causes layshaft7to rotate in the opposite rotational direction when reverse gear16is engaged, for a given rotational direction on driven shaft1, compared to the other gears carried by layshaft7. As with output gear12carried by drive shaft13, the reverser gear may be positioned out of the plane of the page ofFIG. 1.

Successive gear ratios alternate between the first set and the second set so that, for example, the inner intermediate shaft provides even gear ratios and the outer intermediate shaft carries odd gear ratios. That characteristic allows the gearbox to provide quick up and down shifts. When drive is being provided through one gear, the next gear ratio up or down can be pre-selected by actuating the appropriate dog clutch11to couple the drive gear for the next gear ratio to its lay shaft. Then the main clutches can be operated so as to decouple the intermediate shaft for the active gear ratio from the driven shaft and to couple the intermediate shaft for the next gear ratio to the driven shaft. Those operations of the main clutches can be done quickly, or even in an overlapping way, allowing the gearbox to provide substantially uninterrupted power during shifts.

Thus, this design of gearbox can be capable of providing smooth and fast gearshifts. However, there is a general desire for these gearboxes to include a larger number of gear ratios. This may be to improve performance, driveability, comfort and/or emissions. The increase in gear ratios can increase the overall length of such gearboxes due to more drive gears9,10and more shaft gears being required to be carried by the layshafts7,8and intermediate shafts5,6. Such increased length can be problematic as it increases the size within the vehicle that is required for such a gearbox. This increase in size may mean the width of a vehicle needs to be increased in a transverse engine vehicle. This increase in size can also be problematic for mid- and rear-engine vehicles because it can increase the overall length of the vehicle which may not be desirable for performance reasons such as handling.

Therefore, there is a need for alternative designs of gearbox and designs of vehicle.

According to a first aspect of the present invention there is provided a gearbox comprising: an outer intermediate shaft carrying a first set of shaft gears; an inner intermediate shaft carrying a second set of shaft gears, the inner intermediate shaft running concentrically within the outer intermediate shaft; a first lay shaft carrying a first set of drive gears and an output gear positioned along the first lay shaft between two of the first set of drive gears, a second lay shaft carrying a second set of drive gears and an output gear positioned along the second lay shaft between two of the second set of drive gears, each drive gear being coupled to a respective shaft gear to together provide a plurality of gear ratios between the intermediate shafts and the output shaft; and an output shaft, each lay shaft being coupled to the output shaft by the respective output gear.

The output gears of the first and second lay shafts may be positioned so that the drive gears of the first and second sets that are coupled to shaft gears carried by the outer intermediate shaft are to one side, along the respective lay shaft, of the output gears of the first and second lay shafts and the drive gears of the first and second sets that are coupled to shaft gears carried by the inner intermediate shaft are to the other side, along the respective lay shaft, of the output gears of the first and second lay shafts. The gearbox may comprise at least two drive gears to each side of the output gear of the first lay shaft. The gearbox may comprise at least two drive gears to each side of the output gear of the second lay shaft.

The gearbox may comprise a plurality of coupling mechanisms. The coupling mechanisms may be configured to selectively couple at least one respective drive gear to the lay shaft of the drive gear. The coupling mechanisms may have a first mode in which the coupling mechanism couples a respective first drive gear to the lay shaft that carries the drive gear, and a second mode in which the coupling mechanism permits the first drive gear to rotate freely about the lay shaft. At least one coupling mechanism may have a third mode in which the coupling mechanism couples a respective second drive gear to the lay shaft that carries the first drive gear and permits the first drive gear to rotate freely about the lay shaft, and the first mode may permit the second drive gear to rotate freely about the lay shaft. At least two drive gears on a lay shaft may share a common coupling mechanism for selectively coupling the two drive gears to the layshaft. The drive gears on the first lay shaft may be divided into pairs and each pair shares a common coupling mechanism for selectively coupling the drive gears to the first lay shaft. The drive gears on the second lay shaft may be divided into pairs and each pair may share a common coupling mechanism for selectively coupling the drive gears to the second lay shaft. The output gears of the first and second lay shafts may be positioned so that the output gears are not between two drive gears being selectively coupled to the respective lay shaft by a common coupling mechanism.

The first set of shaft gears may be coupled to respective drive gears to provide a first set of gear ratios of the plurality of gear ratios, and the second set of shaft gears may be coupled to respective drive gears to provide a second set of gear ratios of the plurality of gear ratios. Successive gear ratios may alternate between the first set of gear ratios and the second set of gear ratios.

Each of the plurality of gear ratios may have the same rotational relationship between a rotation of the intermediate shafts and a rotation of the output shaft. A rotation of each intermediate shaft in one rotational direction may cause the output shaft to rotate in the same rotational direction at each of the plurality of gear ratios. The rotation of each intermediate shaft in a first rotational direction may cause the output shaft to rotate in an opposite direction to the first rotational direction at each of the plurality of gear ratios. The output shaft may be coupled to an output gear, and the output gear of the output shaft may be coupled to each of the output gears of the first and second lay shafts.

The gearbox may comprise: an input shaft; a first main clutch having a first mode in which the first main clutch provides for positive torque transfer from the input shaft to the outer intermediate shaft and a second mode in which the first main clutch permits independent motion of the input shaft and the outer intermediate shaft; and a second main clutch having a first mode in which the second main clutch provides for positive torque transfer from the input shaft to the inner intermediate shaft and a second mode in which the second main clutch permits independent motion of the input shaft and the inner intermediate shaft.

According to a second aspect of the present invention there is provided vehicle comprising: a transmission comprising an input shaft configured to rotate in a first rotational direction and second rotational direction opposite to the first rotational direction; a first power source comprising a first drive shaft, the first power source being configured to cause the first drive shaft to rotate in a third rotational direction; a second power source comprising a second drive shaft coupled to the input shaft, the second power source being configured to cause the second drive shaft to rotate in the third rotational direction and a fourth rotational direction opposite to the fourth rotational direction; a first clutch having a first mode in which the first clutch provides for torque transfer between the first drive shaft and the second drive shaft and a second mode in which the first clutch permits independent motion of the first drive shaft and the second drive shaft; wherein the vehicle is configured to cause the first clutch to enter the first mode to permit the first power source to cause the input shaft to rotate in the first rotational direction, and cause the first clutch to enter the second mode to permit the second power source to cause the input shaft to rotate in the second rotational direction.

The vehicle may be configured to cause the first clutch to enter the second mode to permit the second power source to cause the input shaft to rotate in the first rotational direction independently of the first power source. When the first clutch is in the first mode, the first power source and second power source may together cause the input shaft to rotate in the first rotational direction.

The transmission may comprise an output shaft, wherein the transmission may be configured to provide drive from the input shaft to the output shaft at a plurality of gear ratios, and at each gear ratio a rotation of the input shaft in the first rotational direction may cause a rotation of the output shaft in a particular same rotational direction for each gear ratio. At each gear ratio a rotation of the input shaft in the first rotational direction may cause a rotation of the output shaft in the first rotational direction. At each gear ratio a rotation of the input shaft in the first rotational direction may cause a rotation of the output shaft in the second rotational direction.

The vehicle may be configured to cause the first clutch to enter the first mode to permit the first power source to cause the vehicle to move in a primary motion direction of the vehicle. The vehicle may be configured to cause the first clutch to enter the second mode to permit the second power source to cause the vehicle to move in a reverse motion direction of the vehicle. The vehicle may be configured to cause the first clutch to enter the second mode to permit the second power source to cause the vehicle to move in the primary motion direction of the vehicle independently of the first power source. The second drive shaft may be coupled to the first clutch and input shaft by a transfer mechanism.

The first power source may be an internal combustion engine configured to provide a drive torque to the first drive shaft. The first power source may be an internal combustion engine configured to provide a drive torque to the first drive shaft and/or receive a drive torque therefrom. The second power source may be an electric motor configured to provide a drive torque to the second drive shaft. The second power source may be an electric motor configured to provide a drive torque to the second drive shaft and/or receive a drive torque therefrom.

When the first clutch is in the first mode, a rotation of the first drive shaft in the third rotational direction may cause the input shaft to rotate in the first rotational direction. A rotation of the second drive shaft in one of the third and fourth rotational directions may cause the input shaft to rotate in the first rotational direction, and a rotation of the second drive shaft in the other of the third and fourth rotational directions may cause the input shaft to rotate in the second rotational direction. The vehicle may comprise a gearbox as described herein as the transmission.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art.

The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

One aspect of the present invention relates to a gearbox comprising an outer intermediate shaft carrying a first set of shaft gears and an inner intermediate shaft carrying a second set of shaft gears, the inner intermediate shaft running concentrically within the outer intermediate shaft. The gearbox comprises a first lay shaft carrying a first set of drive gears and an output gear positioned along the first lay shaft between two of the first set of drive gears, and a second lay shaft carrying a second set of drive gears and an output gear positioned along the second lay shaft between two of the second set of drive gears, where each drive gear is coupled to a respective shaft gear to together provide a plurality of gear ratios between the intermediate shafts and the output shaft. The gearbox also comprises an output shaft, each lay shaft being coupled to the output shaft by the respective output gear.

Another aspect of the present invention relates to a vehicle comprising a transmission comprising an input shaft configured to rotate in a first rotational direction and a second rotational direction opposite to the first rotational direction, a first power source comprising a first drive shaft, the first power source being configured to cause the first drive shaft to rotate in a third rotational direction, and a second power source comprising a second drive shaft coupled to the input shaft, the second power source being configured to cause the second drive shaft to rotate in the third rotational direction and a fourth rotational direction opposite to the fourth rotational direction. The first power source may only be capable of driving the first drive shaft in the third rotational direction. The second power source may be capable of driving the second drive shaft in both the third rotational direction and the fourth rotational direction opposite to the third rotational direction. The vehicle comprises a first clutch having a first mode in which the first clutch provides for torque transfer between the first drive shaft and the second drive shaft and a second mode in which the first clutch permits independent motion of the first drive shaft and the second drive shaft, wherein the vehicle is configured to cause the first clutch to enter the first mode to permit the first power source to cause the input shaft to rotate in the first rotational direction, and cause the first clutch to enter the second mode to permit the second power source to cause the input shaft to rotate in the second rotational direction.

An internal combustion engine to which the principles described herein may apply is not limited in its configuration and could be a straight, flat or V-engine having any number of cylinders.

FIG. 2shows a vehicle20. Vehicle20comprises a drivetrain21. The drivetrain21comprises a first power source22. The first power source22may be an internal combustion engine22. The first power source22may be coupled to at least one wheel23of the vehicle20by other elements of the drivetrain21for the transference of a first power source torque, generated by the first power source22, from the first power source22to the drive wheels23of the vehicle20.

The vehicle may comprise a plurality of wheels23,31for supporting the vehicle1on a surface. Some of those wheels may be drive wheels23and some of those wheels may be non-drive wheels31. It will be appreciated that any configuration of drive23and non-drive wheels31may be used depending on the particular drive characteristics required by the vehicle1.

The first power source22comprises a first drive shaft23. The first power source22may be configured to cause the first drive shaft23to rotate about its axial direction. The rotation of the first drive shaft23, due to its coupling to the wheels23of the vehicle20, may cause the vehicle20to move. The first power source22, in normal operation, may only be capable of causing the first drive shaft23to rotate in one rotational direction. E.g. in a forward direction but not in a reverse direction. This may be because the first power source is configured such that the first drive shaft23can only rotate in that one rotational direction when in normal operation. E.g. when the first power source is being instructed to generate a first power source torque. The first power source23may be configured to only generate a drive torque when causing the first drive shaft23to rotate in one rotational direction. In the case of an internal combustion engine, this occurs because the ignition of a combustion mixture inside the engine causes a crankshaft of the engine to rotate in one direction. The internal combustion engine is not capable of using the ignition of the combustion mixture to cause the crankshaft to rotate in the opposite rotational direction. Thus, an internal combustion engine in operation is only capable of rotating its drive shaft in one rotational direction. The first power source may be an electric motor that is only capable of developing the first power source torque when the first drive shaft23is rotating in one rotational direction. Thus, the first power source may be a single direction electric motor. It should be noted that whilst some single direction electrical machines may be capable of causing its drive shaft to rotate in an opposite rotational direction if given the correct inputs such single direction electrical machines tend to run non-optimally, may generate low power and/or may be dangerous to operate in such a way.

The drivetrain21also comprises a second power source24. The second power source24may be coupled to at least one wheel of the vehicle20by other elements of the drivetrain21for the transference of a second power source torque, generated by the second power source24, from the second power source24to the drive wheels23of the vehicle20. The second power source24may be an electric motor configured to provide a drive torque and/or receive a drive torque.

The second power source24comprises a second drive shaft25. The second power source25may be configured to cause the second drive shaft25to rotate about its axial direction. The rotation of the second drive shaft25, due to its coupling to the wheels23of the vehicle20, may cause the vehicle20to move. The second power source23, in normal operation, may be capable of causing the second drive shaft25to rotate in both rotational directions. E.g. in both a forward direction and in a reverse direction. In the case of an electrical machine, this can occur because it can use electrical inputs to generate electromagnetic fields to cause a rotor that it coupled to the second drive shaft to rotate in either rotational direction. Thus, the second power source24may be a reversible direction electrical machine.

The vehicle may comprise one or more fuel stores40. The fuel stores may be a fuel tank, or a battery.

The second power source24may be coupled to a transmission26. The transmission may comprise an input shaft27and an output shaft28. The second drive shaft25is coupled to the input shaft27of transmission26. The input shaft27may also be known as the driven shaft27of the transmission26. The transmission26may comprise one or more clutches to select how and when the input shaft27is connected to the output shaft28. The transmission26may permit the selection between a plurality of gear ratios at which the input shaft27is connected to output shaft28. The second power source24is coupled to the input shaft27of the transmission26. The second drive shaft24of the second power source24may be coupled to the transmission26without the means of a clutch so that rotation of second drive shaft24always causes a rotation of the input shaft of the transmission26. The second drive shaft24can be connected to the input shaft27of the transmission so that, in operation, the second drive shaft24is constantly capable of imparting a torque on the input shaft27. As pictured, the second power source may be directly connected to the input shaft27. Alternatively, the second power source may be connected by one or more gears. The second power source may be connected to the input shaft27by a transfer mechanism. The transfer mechanism may comprise one or more gears to transfer torque from the second power source to the input shaft27. The transmission26may be any suitable transmission; for instance, the transmission26may be as described herein.

The output shaft28of the transmission26is coupled to drive wheels23by at least one differential29. A vehicle may comprise more than one differential, for example, when the vehicle has more than two drive wheels. The differential29allows for independently variable rotational speeds of each of the drive wheels for a given input torque in dependence on the resistance presented by each drive wheel.

The drivetrain21also comprises a first clutch30. The first clutch30controls the coupling of the first power source22to the second power source25. In particular, the first clutch30controls the coupling of the first drive shaft to the second drive shaft. The first clutch30has a first mode in which the first clutch provides for torque transfer between the first drive shaft and the second drive shaft. E.g. when the first clutch is at least partially engaged and permits torque flow from one side of the first clutch30to the other side of first clutch30. The first clutch30has a second mode in which the first clutch permits independent motion of the first drive shaft23and the second drive shaft25. E.g. when the first clutch30is disengaged and does not permit torque flow from one side of the first clutch30to the other side of first clutch30. Thus, when the first clutch is in the first mode the first power source22is connected to the transmission26by means of the second power source25being connected to the transmission26. The first power source22can therefore cause the input shaft27of the transmission26to rotate when the first clutch30is in the first mode, but not when the first clutch30is in the second mode.

The arrangement of the first power source22, first clutch30and second power source24so that the second power source is constantly connected to the transmission and the first power source is selectively connected to the transmission via the first clutch means that the vehicle can select whether the transmission, and thus the wheels, are driven by both the first power source and second power source or just the second power source. This is advantageous where the second power source24can generate a torque whilst rotating the second drive shaft25in either rotational direction, because it can mean that the second power source24can be used to drive the vehicle in both forward and reverse directions relative to the surface on which the vehicle rests. Stated differently, the second power source24can cause the output shaft28of the transmission26, when the transmission26is in a mode where torque transfer is permitted between the input and output shafts27,28of the transmission26, to rotate in both rotational directions. Thus, the second power source can be used for both forward and reverse drive. As the first drive shaft23of the first power source22is only capable of being driven in one rotational direction, and not in the other rotational direction. The first power source22may resist its drive shaft being driven in the other rotational direction or may even inhibit the rotation of its drive shaft in the other rotational direction. Therefore, the presence of the first clutch30means that the first power source22can be disengaged from the second power source25and from the transmission26prior to the second power source25rotating in the other rotational direction.

The above configuration is advantageous because it means that transmission26does not need to be equipped with a mechanism that permits the rotational direction of the input shaft27relative to the output shaft28to be reversed. Stated differently, transmission26may be provided with only forward gears. I.e. gears that all cause the output shaft28to rotate in one rotational direction for a given rotation of the input shaft27in a particular rotational direction. This means that the transmission26needs at least one fewer gearings in the transmission which thus reduces the length of the transmission, or permits the substitution of the reverse gearing for another forward gearing.

Within the body32of the vehicle20is a seat33for a driver. When a driver is sat in the seat20he can reach a throttle pedal34with his foot. The throttle pedal is pivotable about its rearmost end relative to the body of the vehicle. Its forward end is biased upwardly by spring35to an uppermost position where it hits a stop, and can be pressed down by the driver's foot to a lowermost position where it hits another stop. The pedal is thus constrained to be movable only between the uppermost position (“0%”) and the lowermost position (“100%”). A position detector36is attached to the pedal and senses the angle of deflection of the pedal. It will be appreciated that other throttle controls could be used instead of the throttle pedal34to gather the target drive demand from the drivetrain21of the vehicle requested by the driver. For instance, the vehicle could comprise a hand operated control as a throttle control. The vehicle may also calculate the target drive demand autonomously, for example, by means of an adaptive cruise control system.

When the driver is sat in the seat20he can also reach a gear selector with his hand. The gear selector36permits the driver to indicate a desired gear ratio for the transmission26. The gear selector36may enable the driver to select a gear ratio one higher or one lower than the current gear ratio of the transmission26. The gear selector may also be configured to permit the driver to select an automatic mode of operation for the transmission where the current gear ratio between the input shaft27and the output shaft28is selected by the vehicle20in dependence on the current operating conditions of the vehicle. For instance, the speed, current drive demand and/or the torque required to fulfil that drive demand. The gear selector may also be configured to permit the drive to select a reverse drive mode in which the vehicle is capable of moving in a reverse direction to the normal motion direction of the vehicle. The normal motion direction may be the direction in which the driver faces when sitting in seat33.

The operation of the vehicle is regulated by a Vehicle Control Unit (VCU)37. The VCU37comprises a processor38and a non-volatile memory39. The VCU37may comprise more than one processor38and more than one memory39. The memory39stores a set of program instructions that are executable by the processor, and reference data such as look-up tables that can be referenced by the processor in response to those instructions. The processor38may be configured to operate in accordance with a computer program stored in non-transitory form on a machine readable storage medium. The computer program may store instructions for causing the processor to perform the operations of the VCU37in the manner described herein. The VCU37may be formed of a number of control units, such an Engine Control Unit, Power Source Control Unit, Gearbox Control Unit, and/or Dynamics Control Unit.

The VCU37is coupled to the position detector23to receive from it the detected position of the throttle pedal34. The VCU37is coupled to the power sources22,24to receive from them data relating to the operation of the power sources22,24. For instance, the current RPM of the power sources, operating temperature and/or operating parameters. The VCU37also transmits to the power sources22,24control information that regulates the operation of the power sources22,24. That control information could, for example, include the amount of fuel and/or air to be charged in each inlet stroke, valve and ignition timings, turbo boost level, output power level, and other data relating to the control of an electrical machine.

The VCU37is also coupled to first clutch30to control the connection between the first power source22and the second power source25.

The program instructions stored by the memory define a mechanism whereby the VCU37can determine a set of output parameters for controlling the power sources22,24and first clutch30in response to a set of input parameters it has received and/or computed. In the present example, the VCU may follow a two-stage process to determine the output parameters. First, in response to at least some of the input parameters (including, for example, throttle position and a representation of throttle direction) the VCU determines a target drive demand from the power sources22,24. The drive demand can conveniently be a torque demand, but it could be expressed in other ways such as power demand or fuel used per unit time. Second, using a pre-stored model of the behaviour of the power sources the VCU determines the outputs needed to cause the power sources22,24to satisfy that drive demand. It then transmits those outputs to the power sources22,24and to first clutch30to cause the power sources22,24and first clutch30to behave in accordance with the computed drive demand. These stages are repeated frequently: typically 20 or more times per second, to generate a series of output values reflecting up-to-date input values.

The VCU37may therefore select which of the first and second power sources22,24are to drive the vehicle at any given time. This selection is made, in part, using first clutch30. If the VCU determines that the vehicle needs to reverse, the VCU may be configured to (i) cause the first clutch30to disengage the first power source from the second power source by causing the first clutch to enter the second mode where independent motion of the first drive shaft23and second drive shaft25is permitted, and (ii) cause the second power source to rotate in one rotational direction which causes the output of the transmission to rotate in a rotational direction that causes the vehicle to reverse. The VCU37may determine the vehicle needs to reverse based on inputs received from the gear selector36or in response to an autonomous driving mode deciding it needs to reverse. If the VCU37determines that the vehicle needs to move in a forwards direction, the VCU37may be configured to select between (i) the second power source24driving the transmission26on its own (with first clutch in the second mode), (ii) the second power source24driving the transmission26in conjunction with the first power source22(with first clutch in the first mode), and/or (iii) the first power source22driving the transmission26and second power source22either idling or drawing power from first power source22. The VCU37may select between these different modes depending on the drive demand and also the operating mode of the vehicle (e.g. if it is operating in a power saving mode or in a high performance mode).

FIG. 3shows a drivetrain50. As described with reference toFIG. 2, the drivetrain50comprises a first power source22, second power source24, first clutch30, and transmission26. An example gearbox51that could be used as the transmission26will now be described with reference toFIG. 3.

Gearbox51comprises an input shaft27and an output shaft28. Input shaft27is connected to second power source24and first clutch30. Input shaft27is connected to a clutch housing52so that the clutch housing rotates with the input shaft27. Gearbox51comprises a pair of main clutches52,53. The pair of main clutches52,53are contained in the clutch housing. The main clutches are arranged so that they can be actuated independently to couple the input shaft27to either an inner intermediate shaft55or an outer intermediate shaft56. The inner intermediate shaft55runs concentrically within the outer intermediate shaft56.

The gearbox51comprises two lay shafts57,58. First lay shaft57carries a first set of drive gears59. Each drive gear59of the first set of drive gears59can rotate freely about the first lay shaft57or can be coupled to the first lay shaft57by a coupling mechanism60. Second lay shaft58carries a second set of drive gears61. Each drive gear of the second set of drive gears61can rotate freely about the second lay shaft58or can be coupled to the second lay shaft58by a coupling mechanism62.

Each coupling mechanism60,62having a first mode in which the coupling mechanism60,62couples a drive gear59,61to a lay shaft57,58so that the drive gear59,61rotates with the lay shaft57,58and a second mode in which the coupling mechanism60,62permits the drive gear to rotate freely about the lay shaft57,58. Conveniently, each coupling mechanism60,62could be a dog clutch, optionally with a synchromesh mechanism to facilitate it being engaged. A coupling mechanism60,62may be shared between a pair of drive gears59,61as illustrated inFIG. 3. The coupling mechanism60,62may therefore have three modes:A first mode in which the coupling mechanism60,62couples a first drive gear59,61of a set of drive gears59,61to the respective lay shaft57,58and permits a second drive gear59,61of the same set of drive gears59,61to rotate freely about the lay shaft57,58.A second mode in which the coupling mechanism60,62permits both first and second drive gears59,61of the set of drive gears to rotate freely about the lay shaft57,58.A third mode in which the coupling mechanism60,62couples the second drive gear59,61of the set of drive gears59,61to the respective lay shaft and permits the first drive gear59,61of the set of drive gears59,61to rotate freely about the lay shaft57,58.

In the example illustrated inFIG. 3, dog clutches operate between the lay shaft59,61and a pair of the drive gears59,61. The dog clutches have a pair of toothed rings63,64associated with each drive gear59,61which can be set so as to mate with each other or to be free of each other. Toothed rings64are rotationally fast with the layshaft57,58. Toothed rings63are rotationally fast with the drive gears59,61. The dog clutches, and thus also the coupling mechanisms, can be moved between their modes by selectors (not shown).

Each of the first and second lay shafts57,58are coupled to the output shaft by respective output gears65,66. A first output gear65is carried by first lay shaft57. A second output gear66is carried by second lay shaft58. A third output gear67is carried by output shaft28. Third output gear67meshes with the first and second output gears65,66. Each output gear65,65,67is rotationally fast with its respective shaft57,58,28. Thus, when a lay shaft rotates so does the output shaft. The connection between first output gear65and third output gear67is shown by dotted line68because in practice output shaft28and third output gear67would be offset from the plane in which the figure is drawn to permit connection between the third output gear67and the first and second output gears65,66.

The outer intermediate shaft56carries a first set of shaft gears70. The shaft gears70each mesh with a respective one drive gear59,61of the first and second sets of drive gears59,61. The shaft gears70may mesh with a drive gear of the first set of drive gears59and a drive gear of the second set of drive gears61as shown by drive gears59aand61a. Such a configuration reduces the length of the gearbox51by reducing the number of shaft gears70that are required to connect with the sets of drive gears. The shaft gears may be rotationally fast with the outer intermediate shaft56.

The inner intermediate shaft55carries a second set of shaft gears71. The shaft gears71each mesh with a respective one drive gear59,61of the first and second sets of drive gears59,61. The shaft gears71may mesh with a drive gear of the first set of drive gears59and a drive gear of the second set of drive gears61as shown by drive gears59aand61a. Again, such a configuration reduces the length of the gearbox51by reducing the number of shaft gears71that are required to connect with the sets of drive gears. The shaft gears may be rotationally fast with the inner intermediate shaft55.

The ratios provided by first set of shaft gears70and drive gears59,61in combination implement a first set of gear ratios between the input shaft27and output shaft28. A selected one of those gear ratios can be implemented by actuating first main clutch53so as to couple the input shaft27to the inner intermediate shaft55and by actuating one of the coupling mechanisms60,61so as to couple the appropriate one of the drive gears59,61to one of the lay shafts57,58. Similarly, outer intermediate shaft56can implement a second set of gear ratios between the input shaft27and output shaft28by actuating second main clutch54so as to couple the input shaft27to the inner intermediate shaft56and by actuating one of the coupling mechanisms60,61so as to couple the appropriate one of the drive gears59,61to one of the lay shafts57,58. Successive gear ratios alternate between the first set and the second set so that, for example, the inner intermediate shaft provides odd gear ratios and the outer intermediate shaft carries even gear ratios.

In the gearbox51shown inFIG. 3, no reversing gears are provided therefore all of the gear ratios provided by the gearbox have the same rotational relationship between the input shaft and output shaft. They could all be described as forward gears. I.e. for a given rotation direction of the input shaft the output shaft always rotates in the same rotation direction irrespective of the gear ratio chosen. None of the gear ratios may be provided with a reversing gear. The input shaft and output shaft may always rotate in the same rotational direction or opposite rotation direction irrespective of the gear ratio chosen depending on the gearing provided inside the gearbox51.

The gearbox51is advantageous when combined with the first and second power sources because no reverse gear is required when using the first and second power sources as the second power source can drive the vehicle in reverse and so the gearbox can be shorter because it does not require a reverse gear, or the space on the shafts that was occupied by a reverse gear can be occupied instead by another forward gear.

The first and second output gears65,66carried by first and second lay shafts57,58respectively are positioned along their respective lay shafts between two of the drive gears on each shaft. The first and second output gears65,66may be positioned along their respective lay shafts57,58so that there are an equal number of drive gears to each side of the output gears. The first output gear and second output gear may each have a different number of drive gears to each side of them. This may occur where the gearbox has an odd number of gear ratios and so the intermediate shafts each have a different number of shaft gears.

The first and second sets of drive gears59,61may be split into two groups: a first group that are coupled to the first set of shaft gears70carried by the outer intermediate shaft56and a second group that are coupled to the second set of shaft gears71carried by the inner intermediate shaft55. The first and second output gears65,66may be positioned on their respective lay shaft in between the first group and the second group of shaft gears.

At least some of the drive gears may share a coupling mechanism60between a pair of drive gears. One or both of the output gears65,66may be positioned along its respective lay shaft57,58so as not to be between any of those pairs of drive gears. The output gears65,66may have at least one pair of drive gears that share a common coupling mechanism to each side of the output gear65,66along its respective lay shaft57,58.

As shown inFIG. 3, the gearbox may have eight gear ratios. Four of those gear ratios being provided by the coupling of drive gears on first lay shaft57with shaft gears on the intermediate shafts55,56and four of those gear ratios being provided by the coupling of drive gears on second lay shaft58with shaft gears on the intermediate shafts5556. The drive gears on first lay shaft57are divided into pairs with each pair being coupled to and disengaged from the first lay shaft by a respective coupling mechanism60. The drive gears on second lay shaft58are divided into pairs with each pair being coupled to and disengaged from the second lay shaft58by a respective coupling mechanism. This means there are half as many coupling mechanisms as drive gears per lay shaft. The output gear65,66of each lay shaft is positioned along the output gear's respective lay shaft57,58in between the pairs of drive gears59,61so as to have one pair of drive gears59,61to each side of each output gear.

This position means that the overall length of the drivetrain50can be made more compact because the connection from the output shaft28to the drive wheels can be positioned closer to the portion of the gearbox housing the lay shafts rather than requiring its own space in the drivetrain50. This is especially advantageous in mid-engine vehicles where the gearbox is usually placed over or behind the rear axle of the vehicle. Thus, the ability to move the connection between the output shaft28of the gearbox51closer to the gearbox and thus to the rear of the vehicle can improves the ability to package the drivetrain50within the vehicle. This is particularly true where the input shaft27and output shaft28accept a connection from the same direction.

In the case shown inFIG. 3, the input shaft27and output shaft28accept a connection to other drivetrain components in the same direction. Coupled to the output shaft28is a differential29. The position of the output gears65,66,67between the drive gears59,61means that the differential29can be packaged closer to the drive gears at the end of the lay shafts closest to where the input and output shafts27,28accept a connection. The crown wheel72of the differential29may be positioned so that it cuts through a plane defined by the drive gears at end of the lay shafts closest to where the input and output shafts27,28accept a connection. This positioning reduces the overall length of the gearbox51and differential29package.