Patent Description:
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.

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

The lay shafts are coupled by output gears <NUM> to a drive shaft <NUM> leading to the wheels of the vehicle. The output gear <NUM> carried by lay shaft <NUM> is connected to the output gear <NUM> carried by drive shaft <NUM> as shown by the dotted line that runs between the output gears <NUM>. The position of output gear <NUM> carried by drive shaft <NUM> would in practice be positioned out of the plane of the page of <FIG> so as to connect to both other output gears <NUM>. The output gears <NUM> are shown as being connected to the layshafts <NUM>, <NUM> at their ends closest to the clutches <NUM>, <NUM>. The output gears <NUM> could be connected to the layshafts <NUM>, <NUM> at their ends farthest from the clutches <NUM>, <NUM>.

The inner intermediate shaft <NUM> carries shaft gears <NUM> which mesh with drive gears <NUM>. The ratios provided by gears <NUM> and <NUM> in combination implement a first set of gear ratios between the driven shaft <NUM> and the drive shaft <NUM>. A selected one of those gear ratios can be implemented by actuating main clutch <NUM> so as to couple the drive shaft <NUM> to the inner intermediate shaft <NUM> and by actuating one of the dog clutches <NUM> so as to couple the appropriate one of the drive gears <NUM> to one of the lay shafts. Similarly, the outer intermediate shaft <NUM> carries shaft gears <NUM> which mesh with drive gears <NUM> to implement a second set of gear ratios between the driven shaft <NUM> and the drive shaft <NUM>. Lay shaft <NUM> is also shown as carrying a drive gear <NUM> that functions as a reverse gear. Not shown in <FIG> is a further reverser gear that connects drive gear <NUM> to its respective shaft gear <NUM>. This reverser gear causes layshaft <NUM> to rotate in the opposite rotational direction when reverse gear <NUM> is engaged, for a given rotational direction on driven shaft <NUM>, compared to the other gears carried by layshaft <NUM>. As with output gear <NUM> carried by drive shaft <NUM>, the reverser gear may be positioned out of the plane of the page of <FIG>.

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 clutch <NUM> to 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 gears <NUM>, <NUM> and more shaft gears being required to be carried by the layshafts <NUM>, <NUM> and intermediate shafts <NUM>, <NUM>. 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.

<CIT> discloses a gearbox configured for use in a vehicle comprising a first power source that is configured to rotate in a first rotational direction and a second power source that is configured to rotate in both the first rotational direction and a second rotational direction opposite to the first rotational direction.

<CIT>, published after the priority date of the present application, discloses another gearbox.

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 configured for use in a vehicle comprising a first power source that is configured to rotate in a forward direction and a second power source that is configured to rotate in both the first rotational direction and a second rotational direction opposite to the first rotational direction, the gearbox comprising: a first main clutch; a second main clutch which is actuatable independently of the first main clutch; an input shaft for connection to the first and second power sources; an outer intermediate shaft removably coupled to the input shaft by the second main clutch, and carrying a first set of shaft gears; an inner intermediate shaft removably coupled to the input shaft by the first main clutch, and 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 a first output gear, a second lay shaft carrying a second set of drive gears and a second output gear, 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; a plurality of coupling mechanisms, wherein at least two drive gears on a lay shaft share a common coupling mechanism for selectively coupling the two drive gears to the layshaft; wherein the first set of shaft gears are 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 are coupled to respective drive gears to provide a second set of gear ratios of the plurality of gear ratios, each gear ratio of the first and second sets of gear ratios being a forward gear ratio; characterised in that the gearbox further comprises an output shaft configured to be coupled to the wheels of a vehicle by a differential, each lay shaft being coupled to the output shaft by a respective one of the first and second output gears, and the first output gear is positioned along the first lay shaft between
two of the first set of drive gears and the second output gear is positioned along the second lay shaft between two of the second set of drive gears.

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 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. 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.

Successive gear ratios may alternate between the first set of gear ratios and the second set 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 first main clutch may have a first mode in which the first main clutch provides for positive torque transfer from the input shaft to
the inner intermediate shaft and a second mode in which the first main clutch permits independent motion of the input shaft and the inner intermediate shaft; and the second main clutch may have a first mode in which the second main clutch provides for positive torque transfer from the input shaft to the outer intermediate shaft and a second mode in which the second main clutch permits independent motion of the input shaft and the outer intermediate shaft.

The crown wheel of the differential may be positioned so that it cuts through a plane defined by the drive gears at the end of the layshaft closest to where the input shaft is removably coupled to the inner and outer intermediate shafts.

According to a second aspect of the present invention there is provided a vehicle comprising a gearbox as described above.

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 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 scope of the claims.

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> shows a vehicle <NUM>. Vehicle <NUM> comprises a drivetrain <NUM>. The drivetrain <NUM> comprises a first power source <NUM>. The first power source <NUM> may be an internal combustion engine <NUM>. The first power source <NUM> may be coupled to at least one wheel <NUM> of the vehicle <NUM> by other elements of the drivetrain <NUM> for the transference of a first power source torque, generated by the first power source <NUM>, from the first power source <NUM> to the drive wheels <NUM> of the vehicle <NUM>.

The vehicle may comprise a plurality of wheels <NUM>, <NUM> for supporting the vehicle <NUM> on a surface. Some of those wheels may be drive wheels <NUM> and some of those wheels may be non-drive wheels <NUM>. It will be appreciated that any configuration of drive <NUM> and non-drive wheels <NUM> may be used depending on the particular drive characteristics required by the vehicle <NUM>.

The first power source <NUM> comprises a first drive shaft <NUM>. The first power source <NUM> may be configured to cause the first drive shaft <NUM> to rotate about its axial direction.

The rotation of the first drive shaft <NUM>, due to its coupling to the wheels <NUM> of the vehicle <NUM>, may cause the vehicle <NUM> to move. The first power source <NUM>, in normal operation, may only be capable of causing the first drive shaft <NUM> to rotate in one rotational direction. 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 shaft <NUM> can only rotate in that one rotational direction when in normal operation. when the first power source is being instructed to generate a first power source torque. The first power source <NUM> may be configured to only generate a drive torque when causing the first drive shaft <NUM> to 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 shaft <NUM> is 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 drivetrain <NUM> also comprises a second power source <NUM>. The second power source <NUM> may be coupled to at least one wheel of the vehicle <NUM> by other elements of the drivetrain <NUM> for the transference of a second power source torque, generated by the second power source <NUM>, from the second power source <NUM> to the drive wheels <NUM> of the vehicle <NUM>. The second power source <NUM> may be an electric motor configured to provide a drive torque and/or receive a drive torque.

The second power source <NUM> comprises a second drive shaft <NUM>. The second power source <NUM> may be configured to cause the second drive shaft <NUM> to rotate about its axial direction. The rotation of the second drive shaft <NUM>, due to its coupling to the wheels <NUM> of the vehicle <NUM>, may cause the vehicle <NUM> to move. The second power source <NUM>, in normal operation, may be capable of causing the second drive shaft <NUM> to rotate in both rotational directions. 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 source <NUM> may be a reversible direction electrical machine.

The vehicle may comprise one or more fuel stores <NUM>. The fuel stores may be a fuel tank, or a battery.

The second power source <NUM> may be coupled to a transmission <NUM>. The transmission may comprise an input shaft <NUM> and an output shaft <NUM>. The second drive shaft <NUM> is coupled to the input shaft <NUM> of transmission <NUM>. The input shaft <NUM> may also be known as the driven shaft <NUM> of the transmission <NUM>. The transmission <NUM> may comprise one or more clutches to select how and when the input shaft <NUM> is connected to the output shaft <NUM>. The transmission <NUM> may permit the selection between a plurality of gear ratios at which the input shaft <NUM> is connected to output shaft <NUM>. The second power source <NUM> is coupled to the input shaft <NUM> of the transmission <NUM>. The second drive shaft <NUM> of the second power source <NUM> may be coupled to the transmission <NUM> without the means of a clutch so that rotation of second drive shaft <NUM> always causes a rotation of the input shaft of the transmission <NUM>. The second drive shaft <NUM> can be connected to the input shaft <NUM> of the transmission so that, in operation, the second drive shaft <NUM> is constantly capable of imparting a torque on the input shaft <NUM>. As pictured, the second power source may be directly connected to the input shaft <NUM>. Alternatively, the second power source may be connected by one or more gears. The second power source may be connected to the input shaft <NUM> by a transfer mechanism. The transfer mechanism may comprise one or more gears to transfer torque from the second power source to the input shaft <NUM>. The transmission <NUM> may be any suitable transmission; for instance, the transmission <NUM> may be as described herein.

The output shaft <NUM> of the transmission <NUM> is coupled to drive wheels <NUM> by at least one differential <NUM>. A vehicle may comprise more than one differential, for example, when the vehicle has more than two drive wheels. The differential <NUM> allows 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 drivetrain <NUM> also comprises a first clutch <NUM>. The first clutch <NUM> controls the coupling of the first power source <NUM> to the second power source <NUM>. In particular, the first clutch <NUM> controls the coupling of the first drive shaft to the second drive shaft. The first clutch <NUM> has a first mode in which the first clutch provides for torque transfer between the first drive shaft and the second drive shaft. when the first clutch is at least partially engaged and permits torque flow from one side of the first clutch <NUM> to the other side of first clutch <NUM>. The first clutch <NUM> has a second mode in which the first clutch permits independent motion of the first drive shaft <NUM> and the second drive shaft <NUM>. when the first clutch <NUM> is disengaged and does not permit torque flow from one side of the first clutch <NUM> to the other side of first clutch <NUM>. Thus, when the first clutch is in the first mode the first power source <NUM> is connected to the transmission <NUM> by means of the second power source <NUM> being connected to the transmission <NUM>. The first power source <NUM> can therefore cause the input shaft <NUM> of the transmission <NUM> to rotate when the first clutch <NUM> is in the first mode, but not when the first clutch <NUM> is in the second mode.

The arrangement of the first power source <NUM>, first clutch <NUM> and second power source <NUM> so 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 source <NUM> can generate a torque whilst rotating the second drive shaft <NUM> in either rotational direction, because it can mean that the second power source <NUM> can 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 source <NUM> can cause the output shaft <NUM> of the transmission <NUM>, when the transmission <NUM> is in a mode where torque transfer is permitted between the input and output shafts <NUM>, <NUM> of the transmission <NUM>, to rotate in both rotational directions. Thus, the second power source can be used for both forward and reverse drive. As the first drive shaft <NUM> of the first power source <NUM> is only capable of being driven in one rotational direction, and not in the other rotational direction. The first power source <NUM> may 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 clutch <NUM> means that the first power source <NUM> can be disengaged from the second power source <NUM> and from the transmission <NUM> prior to the second power source <NUM> rotating in the other rotational direction.

The above configuration is advantageous because it means that transmission <NUM> does not need to be equipped with a mechanism that permits the rotational direction of the input shaft <NUM> relative to the output shaft <NUM> to be reversed. Stated differently, transmission <NUM> is provided with only forward gears. gears that all cause the output shaft <NUM> to rotate in one rotational direction for a given rotation of the input shaft <NUM> in a particular rotational direction. This means that the transmission <NUM> needs 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 body <NUM> of the vehicle <NUM> is a seat <NUM> for a driver. When a driver is sat in the seat <NUM> he can reach a throttle pedal <NUM> with 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 spring <NUM> to 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 ("<NUM>%") and the lowermost position ("<NUM>%"). A position detector <NUM> is 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 pedal <NUM> to gather the target drive demand from the drivetrain <NUM> of 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 seat <NUM> he can also reach a gear selector with his hand. The gear selector <NUM> permits the driver to indicate a desired gear ratio for the transmission <NUM>. The gear selector <NUM> may enable the driver to select a gear ratio one higher or one lower than the current gear ratio of the transmission <NUM>. 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 shaft <NUM> and the output shaft <NUM> is selected by the vehicle <NUM> in 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 seat <NUM>.

The operation of the vehicle is regulated by a Vehicle Control Unit (VCU) <NUM>. The VCU <NUM> comprises a processor <NUM> and a non-volatile memory <NUM>. The VCU <NUM> may comprise more than one processor <NUM> and more than one memory <NUM>. The memory <NUM> stores 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 processor <NUM> may 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 VCU <NUM> in the manner described herein. The VCU <NUM> may 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 VCU <NUM> is coupled to the position detector <NUM> to receive from it the detected position of the throttle pedal <NUM>. The VCU <NUM> is coupled to the power sources <NUM>, <NUM> to receive from them data relating to the operation of the power sources <NUM>, <NUM>. For instance, the current RPM of the power sources, operating temperature and/or operating parameters. The VCU <NUM> also transmits to the power sources <NUM>, <NUM> control information that regulates the operation of the power sources <NUM>, <NUM>. 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 VCU <NUM> is also coupled to first clutch <NUM> to control the connection between the first power source <NUM> and the second power source <NUM>.

The program instructions stored by the memory define a mechanism whereby the VCU <NUM> can determine a set of output parameters for controlling the power sources <NUM>, <NUM> and first clutch <NUM> in 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 sources <NUM>, <NUM>. 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 prestored model of the behaviour of the power sources the VCU determines the outputs needed to cause the power sources <NUM>, <NUM> to satisfy that drive demand. It then transmits those outputs to the power sources <NUM>, <NUM> and to first clutch <NUM> to cause the power sources <NUM>, <NUM> and first clutch <NUM> to behave in accordance with the computed drive demand. These stages are repeated frequently: typically <NUM> or more times per second, to generate a series of output values reflecting up-to-date input values.

The VCU <NUM> may therefore select which of the first and second power sources <NUM>, <NUM> are to drive the vehicle at any given time. This selection is made, in part, using first clutch <NUM>. If the VCU determines that the vehicle needs to reverse, the VCU may be configured to (i) cause the first clutch <NUM> to 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 shaft <NUM> and second drive shaft <NUM> is 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 VCU <NUM> may determine the vehicle needs to reverse based on inputs received from the gear selector <NUM> or in response to an autonomous driving mode deciding it needs to reverse. If the VCU <NUM> determines that the vehicle needs to move in a forwards direction, the VCU <NUM> may be configured to select between (i) the second power source <NUM> driving the transmission <NUM> on its own (with first clutch in the second mode), (ii) the second power source <NUM> driving the transmission <NUM> in conjunction with the first power source <NUM> (with first clutch in the first mode), and/or (iii) the first power source <NUM> driving the transmission <NUM> and second power source <NUM> either idling or drawing power from first power source <NUM>. The VCU <NUM> may 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> shows a drivetrain <NUM>. As described with reference to <FIG>, the drivetrain <NUM> comprises a first power source <NUM>, second power source <NUM>, first clutch <NUM>, and transmission <NUM>. An example gearbox <NUM> that could be used as the transmission <NUM> will now be described with reference to <FIG>.

Gearbox <NUM> comprises an input shaft <NUM> and an output shaft <NUM>. Input shaft <NUM> is connected to second power source <NUM> and first clutch <NUM>. Input shaft <NUM> is connected to a clutch housing <NUM> so that the clutch housing rotates with the input shaft <NUM>. Gearbox <NUM> comprises a pair of main clutches <NUM>, <NUM>. The pair of main clutches <NUM>, <NUM> are contained in the clutch housing. The main clutches are arranged so that they can be actuated independently to couple the input shaft <NUM> to either an inner intermediate shaft <NUM> or an outer intermediate shaft <NUM>. The inner intermediate shaft <NUM> runs concentrically within the outer intermediate shaft <NUM>.

The gearbox <NUM> comprises two lay shafts <NUM>, <NUM>. First lay shaft <NUM> carries a first set of drive gears <NUM>. Each drive gear <NUM> of the first set of drive gears <NUM> can rotate freely about the first lay shaft <NUM> or can be coupled to the first lay shaft <NUM> by a coupling mechanism <NUM>. Second lay shaft <NUM> carries a second set of drive gears <NUM>. Each drive gear of the second set of drive gears <NUM> can rotate freely about the second lay shaft <NUM> or can be coupled to the second lay shaft <NUM> by a coupling mechanism <NUM>.

Each coupling mechanism <NUM>, <NUM> having a first mode in which the coupling mechanism <NUM>, <NUM> couples a drive gear <NUM>, <NUM> to a lay shaft <NUM>, <NUM> so that the drive gear <NUM>, <NUM> rotates with the lay shaft <NUM>, <NUM> and a second mode in which the coupling mechanism <NUM>, <NUM> permits the drive gear to rotate freely about the lay shaft <NUM>, <NUM>. Conveniently, each coupling mechanism <NUM>, <NUM> could be a dog clutch, optionally with a synchromesh mechanism to facilitate it being engaged. A coupling mechanism <NUM>, <NUM> may be shared between a pair of drive gears <NUM>, <NUM> as illustrated in <FIG>. The coupling mechanism <NUM>, <NUM> may therefore have three modes:.

In the example illustrated in <FIG>, dog clutches operate between the lay shaft <NUM>, <NUM> and a pair of the drive gears <NUM>, <NUM>. The dog clutches have a pair of toothed rings <NUM>, <NUM> associated with each drive gear <NUM>, <NUM> which can be set so as to mate with each other or to be free of each other. Toothed rings <NUM> are rotationally fast with the layshaft <NUM>, <NUM>. Toothed rings <NUM> are rotationally fast with the drive gears <NUM>, <NUM>. 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 shafts <NUM>, <NUM> are coupled to the output shaft by respective output gears <NUM>, <NUM>. A first output gear <NUM> is carried by first lay shaft <NUM>. A second output gear <NUM> is carried by second lay shaft <NUM>. A third output gear <NUM> is carried by output shaft <NUM>. Third output gear <NUM> meshes with the first and second output gears <NUM>, <NUM>. Each output gear <NUM>, <NUM>, <NUM> is rotationally fast with its respective shaft <NUM>, <NUM>, <NUM>. Thus, when a lay shaft rotates so does the output shaft. The connection between first output gear <NUM> and third output gear <NUM> is shown by dotted line <NUM> because in practice output shaft <NUM> and third output gear <NUM> would be offset from the plane in which the figure is drawn to permit connection between the third output gear <NUM> and the first and second output gears <NUM>, <NUM>.

The outer intermediate shaft <NUM> carries a first set of shaft gears <NUM>. The shaft gears <NUM> each mesh with a respective one drive gear <NUM>, <NUM> of the first and second sets of drive gears <NUM>, <NUM>. The shaft gears <NUM> may mesh with a drive gear of the first set of drive gears <NUM> and a drive gear of the second set of drive gears <NUM> as shown by drive gears 59a and 61a. Such a configuration reduces the length of the gearbox <NUM> by reducing the number of shaft gears <NUM> that are required to connect with the sets of drive gears. The shaft gears may be rotationally fast with the outer intermediate shaft <NUM>.

The inner intermediate shaft <NUM> carries a second set of shaft gears <NUM>. The shaft gears <NUM> each mesh with a respective one drive gear <NUM>, <NUM> of the first and second sets of drive gears <NUM>, <NUM>. The shaft gears <NUM> may mesh with a drive gear of the first set of drive gears <NUM> and a drive gear of the second set of drive gears <NUM> as shown by drive gears 59a and 61a. Again, such a configuration reduces the length of the gearbox <NUM> by reducing the number of shaft gears <NUM> that are required to connect with the sets of drive gears. The shaft gears may be rotationally fast with the inner intermediate shaft <NUM>.

The ratios provided by first set of shaft gears <NUM> and drive gears <NUM>, <NUM> in combination implement a first set of gear ratios between the input shaft <NUM> and output shaft <NUM>. A selected one of those gear ratios can be implemented by actuating first main clutch <NUM> so as to couple the input shaft <NUM> to the inner intermediate shaft <NUM> and by actuating one of the coupling mechanisms <NUM>, <NUM> so as to couple the appropriate one of the drive gears <NUM>, <NUM> to one of the lay shafts <NUM>, <NUM>. Similarly, outer intermediate shaft <NUM> can implement a second set of gear ratios between the input shaft <NUM> and output shaft <NUM> by actuating second main clutch <NUM> so as to couple the input shaft <NUM> to the inner intermediate shaft <NUM> and by actuating one of the coupling mechanisms <NUM>, <NUM> so as to couple the appropriate one of the drive gears <NUM>, <NUM> to one of the lay shafts <NUM>, <NUM>. 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 gearbox <NUM> shown in <FIG>, 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. 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 gearbox <NUM>.

The gearbox <NUM> is 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 gears <NUM>, <NUM> carried by first and second lay shafts <NUM>, <NUM> respectively are positioned along their respective lay shafts between two of the drive gears on each shaft. The first and second output gears <NUM>, <NUM> may be positioned along their respective lay shafts <NUM>, <NUM> so 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 gears <NUM>, <NUM> may be split into two groups: a first group that are coupled to the first set of shaft gears <NUM> carried by the outer intermediate shaft <NUM> and a second group that are coupled to the second set of shaft gears <NUM> carried by the inner intermediate shaft <NUM>. The first and second output gears <NUM>, <NUM> may 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 mechanism <NUM> between a pair of drive gears. One or both of the output gears <NUM>, <NUM> may be positioned along its respective lay shaft <NUM>, <NUM> so as not to be between any of those pairs of drive gears. The output gears <NUM>, <NUM> may have at least one pair of drive gears that share a common coupling mechanism to each side of the output gear <NUM>, <NUM> along its respective lay shaft <NUM>, <NUM>.

As shown in <FIG>, the gearbox may have eight gear ratios. Four of those gear ratios being provided by the coupling of drive gears on first lay shaft <NUM> with shaft gears on the intermediate shafts <NUM>, <NUM> and four of those gear ratios being provided by the coupling of drive gears on second lay shaft <NUM> with shaft gears on the intermediate shafts <NUM><NUM>. The drive gears on first lay shaft <NUM> are divided into pairs with each pair being coupled to and disengaged from the first lay shaft by a respective coupling mechanism <NUM>. The drive gears on second lay shaft <NUM> are divided into pairs with each pair being coupled to and disengaged from the second lay shaft <NUM> by a respective coupling mechanism. This means there are half as many coupling mechanisms as drive gears per lay shaft. The output gear <NUM>, <NUM> of each lay shaft is positioned along the output gear's respective lay shaft <NUM>, <NUM> in between the pairs of drive gears <NUM>, <NUM> so as to have one pair of drive gears <NUM>, <NUM> to each side of each output gear.

This position means that the overall length of the drivetrain <NUM> can be made more compact because the connection from the output shaft <NUM> to 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 drivetrain <NUM>. 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 shaft <NUM> of the gearbox <NUM> closer to the gearbox and thus to the rear of the vehicle can improves the ability to package the drivetrain <NUM> within the vehicle. This is particularly true where the input shaft <NUM> and output shaft <NUM> accept a connection from the same direction.

Claim 1:
A gearbox configured for use in a vehicle comprising a first power source that is configured to rotate in a first rotational direction and a second power source that is configured to rotate in both the first rotational direction and a second rotational direction opposite to the first rotational direction, the gearbox comprising:
a first main clutch (<NUM>);
a second main clutch (<NUM>) which is actuatable independently of the first main clutch (<NUM>);
an input shaft (<NUM>) for connection to the first and second power sources;
an outer intermediate shaft (<NUM>) removably coupled to the input shaft (<NUM>) by the second main clutch (<NUM>), and carrying a first set of shaft gears (<NUM>);
an inner intermediate shaft (<NUM>) removably coupled to the input shaft (<NUM>) by the first main clutch (<NUM>), and carrying a second set of shaft gears (<NUM>), the inner intermediate shaft running concentrically within the outer intermediate shaft;
a first lay shaft (<NUM>) carrying a first set of drive gears (<NUM>) and a first output gear (<NUM>), a second lay shaft (<NUM>) carrying a second set of drive gears (<NUM>) and a second output gear (<NUM>), 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;
a plurality of coupling mechanisms (<NUM>;<NUM> ;<NUM>), wherein at least two drive gears on a lay shaft share a common coupling mechanism for selectively coupling the two drive gears to the layshaft;
wherein the first set of shaft gears are 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 are coupled to respective drive gears to provide a second set of gear ratios of the plurality of gear ratios, each gear ratio of the first and second sets of gear ratios being a forward gear ratio;
characterised in that the gearbox further comprises an output shaft (<NUM>) configured to be coupled to the wheels of a vehicle by a differential, each lay shaft being coupled to the output shaft by a respective one of the first and second output gears, and the first output gear is positioned along the first lay shaft between two of the first set of drive gears and the second output gear is positioned along the second lay shaft between two of the second set of drive gears.