Patent Publication Number: US-2022235535-A1

Title: Working Machine

Description:
FIELD 
     The present teachings relate to a working machine, for example an electric or hybrid working machine. 
     BACKGROUND 
     Working machines (e.g. excavators, backhoe loaders, telehandlers, skid steer loaders etc.) typically include a number of hydraulically actuated devices, and a hydraulically driven ground engaging structure such as wheels or a pair of endless tracks. Depending on the particular working machine, a range of different hydraulically actuated devices may be provided, such as a working arm, stabilizer legs, a dozer blades, hydraulically powered steering, and these devices are operable by receiving a flow of hydraulic fluid from a hydraulic pump. 
     In such known working machines, propelling the working machine on the ground engaging structure and supplying hydraulic fluid for the hydraulically actuated devices are provided by separate motor-transmission arrangements. This approach requires both of the electric motors to be independently sized and results in inefficient packing on the working machine. 
     The present teachings seek to overcome or at least mitigate one or more problems associated with the prior art. 
     SUMMARY 
     A first aspect of the teachings provides an electric or hybrid working machine comprising: a ground engaging structure for propelling the working machine; an electrical source of power; an electric motor arrangement configured to be powered by the electrical source of power, the electric motor arrangement comprising at least one electric motor; one or more hydraulically actuated devices; a hydraulic pump configured to supply hydraulic fluid to the one or more hydraulically actuated devices; and a transmission operable to transmit drive from the electric motor arrangement to the ground engaging structure and the hydraulic pump, wherein the transmission comprises a first input member connected to a first electric motor of the electric motor arrangement and configured to be driven thereby, a drive train comprising a first input gear connected to the first input member, and a coupling device connected between the first input member and the first input gear to selectively adjust transmission of drive to the hydraulic pump and the ground engaging structure. 
     Advantageously, the combination of both hydraulic and traction function on the same transmission has been found to allow a low voltage solution to be used for the motor to deliver high voltage motor performance and remove redundancy in the machine. The inclusion of the coupling device allows the distribution of transmission between the hydraulics and traction to be optimized. For smaller machines, the use of one motor has been found to be advantage for packing reasons where two separate motors cannot be accommodated. 
     The coupling device may be configured to selectively couple and decouple transmission of drive to the hydraulic pump and the ground engaging structure based on whether the working machine is in a working mode or a travelling mode. 
     Advantageously, this enables the distribution of transmission to be optimized depending on the predetermined drive requirements associated with different modes of operation. 
     The coupling device may be configured to selectively decouple transmission of drive from the first input member to the ground engaging structure when the working machine is substantially stationary or wherein the working machine is travelling at a speed below a predetermined threshold, e.g. a low speed. 
     Advantageously, this enables a hydraulic pump speed to be maintained whilst the tractive speed requirement tends to zero, and for the hydraulic pump to be driven by the first electric motor arrangement independent of the ground engaging structure. 
     The coupling device may be configured to selectively decouple transmission of drive from the first input member to the hydraulic pump when the working machine is in a travelling mode and/or when demand for hydraulic supply to the one or more hydraulically actuated devices is low (i.e. below a pre-determined threshold). 
     Advantageously, this enables the transmission to the ground engaging structure to be prioritized when there is a greater requirement for tractive drive than hydraulic drive, e.g. when the working machine is being driven. 
     The coupling device may be configured to selectively couple transmission of drive from the first input member to the hydraulic pump and the ground engaging structure, when the working machine is in the working mode. 
     Advantageously, this enables drive to be transmitted to both the hydraulic pump and the ground engaging structure when there is such a requirement. 
     The working machine may comprise a controller configured to control the selective coupling and decoupling of the coupling device depending on the mode of operation of the working machine. 
     The controller may be configured to determine: when the working machine is travelling at a speed below the predetermined threshold; when the working machine is travelling at a speed above the predetermined threshold; and/or the demand of the one of more hydraulically actuated devices for hydraulic fluid supply. 
     The working machine may comprise a first sensor arrangement associated with the hydraulically actuated devices. The first sensor arrangement may for example, be configured to detect whether a hydraulically actuated device is being operated. The sensor arrangement may also be configured to detect the required flow rate of hydraulic fluid to the one or more hydraulically actuated devices. 
     The working machine may comprise a second sensor arrangement associated with the ground engaging. The second sensor arrangement may be configured to detect the speed of movement of the ground engaging structure. 
     The electric motor arrangement may comprise a second electric motor configured to be powered by the electrical source of power and the transmission comprises a second input member connected to the second electric motor and configured to be driven thereby. The coupling device may be configured to selectively decouple the first input gear from the first input member to inhibit transmission of drive between the first input member and the second input member when: the working machine is substantially stationary; the working machine is travelling at a speed below a predetermined threshold; when the working machine is in the travelling mode; and/or when demand for hydraulic supply to the one or more hydraulically actuated devices is below a predetermined threshold value. 
     Advantageously, this enables the ground engaging structure and hydraulic devices to be driven independently depending on the drive requirements. This has been found to increase the overall efficiency of the transmission. 
     The electric motor arrangement may comprise a second electric motor configured to be powered by the electrical source of power and the transmission comprises a second input member connected to the second electric motor and configured to be driven thereby. When the working machine is in working mode, the coupling device may be configured to selectively couple the first input gear to the first input member such that drive can be transmitted between the first input member and the second input member. 
     Advantageously, this enables the transmission of the ground engaging structure and the hydraulic devices to be combined when certain operating conditions have been met. 
     The coupling device may be any one of a torque converter, a fluid coupling or a slipping clutch. 
     Advantageously, this enables transmission of drive to the hydraulic pump even when the machine stalls. Additionally, if a torque converter is used, the torque output may be increased. 
     The transmission may comprise a lock up clutch configured to engage when the working machine is in a travelling mode. 
     The lock up clutch may be configured to engage when the working machine is travelling above a pre-determined speed. 
     Advantageously, this engages/attaches the motor and the transmission when their speeds are nearly equal, which results in an increase in efficiency. 
     The electric motor arrangement may comprise a second electric motor configured to be powered by the electrical source of power. 
     Advantageously, inclusion of a second motor has been found to enable the motor sizing for one or both of these services to be reduced compared to having separate transmission paths. Additionally, the use of multiple motors in one transmission has been found to reduce the required voltage and/or number of transmission ratios. 
     The transmission may comprise a second input member connected to the second electric motor and configured to be driven thereby. 
     The drive train may comprise a second input gear connected to the second input member. 
     Advantageously, this arrangement enables drive to be transmitted from both the first and second electric motor arrangements to both the hydraulic pump and the ground engaging structure. 
     The first electric motor may be configured to drive the hydraulic pump and the second electric motor is configured to drive the ground engaging structure. 
     The transmission may comprise a first output member connected to the hydraulic pump and a second output member connected to the ground engaging structure, and wherein the first and second output members may be configured to transmit drive from the electric motor arrangement. 
     The first input gear may be connected to the first output member via a coupling element. The first output member may be directly connected to the hydraulic pump. 
     The drive train may comprise a first output gear connected to the second output member. 
     Drive may be transmitted from the second input member to the second output member via the second input gear and the first output gear. 
     Advantageously, such an arrangement is a simple way of transmitting drive from the input members to both the hydraulic pump and the ground engaging structure. 
     The electric motor arrangement may comprise a second electric motor configured to be powered by the electrical source of power. The first electric motor may be connected to a first transfer shaft, and the second electric motor may be connected to a second transfer shaft. The first transfer shaft and the second transfer shaft may be configured to transmit drive to the first input member. 
     The working machine may comprise a body supported on the ground engaging structure. 
     The body may comprise an undercarriage supported on the ground engaging structure and a superstructure mounted to the undercarriage. 
     The superstructure may be rotatably mounted to the undercarriage. 
     The one or more hydraulically actuated devices may comprise a first working arm mounted to the body, and/or at least one stabilizer leg mounted to the body, and/or a dozer blade mounted to the body. 
     The ground engaging structure may be provided in the form of front and rear wheels or a pair of endless tracks. 
     The first input member may be a first input shaft, and/or the second input member may be a second input shaft, and/or the first output member may be a first output shaft and/or the second output member may be a second output shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of a working machine according to an embodiment; 
         FIG. 2  is a schematic representation of a drive arrangement of the working machine of  FIG. 1 ; and 
         FIG. 3  is a schematic representation of an alternative drive arrangement of the working machine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) 
     Referring firstly to  FIG. 1 , a working machine according to an embodiment is indicated at  10 . In the illustrated embodiment, the working machine  10  is an excavator, but it will be appreciated that in alternative embodiments the working machine may be a telehandler, backhoe loader, skid steer loader, or any other suitable working machine. 
     The working machine  10  includes a body. The body includes an undercarriage  12 , and a superstructure  14  mounted to the undercarriage  12 . In some arrangements, the working machine  10  may not include an undercarriage  12  and superstructure  14  and instead may include an operator structure  16  mounted onto a chassis of the body. 
     The working machine  10  includes an operator structure  16  from which an operator is able to operate the working machine  10 . The operator structure  16  is provided on the superstructure  14 . In the illustrated embodiment, the operator structure  16  is a cab, but in alternative arrangements it will be appreciated that a cab may not be provided and the operator structure  16  may include a frame and an operator sear, or may only include an operator seat. 
     In the illustrated embodiment, the superstructure  14  is rotatably mounted to the undercarriage  12 . In alternative arrangements of the working machine  10 , it will be appreciated that the superstructure  14  may not be rotatable relative to the undercarriage  12 . In the present arrangement, the operator structure  16  is rotatably mounted to the superstructure  14 . However, it will be understood that in some alternative arrangements of the working machine  10 , the operator structure  16  may not be rotatable relative to the superstructure  14   
     The working machine  10  has one or more hydraulically actuated devices for performing functions of the working machine  10 . 
     A working arm  18  is rotatably mounted to the superstructure  14  for performing working operations. The working arm  18  is pivotable about a substantially horizontal axis. The working arm  18  is mounted via kingpost arrangement  20 . Mounting the working arm  18  via a kingpost enables the working arm to rotate about a substantially vertical axis relative to the body (i.e. the superstructure  14 ). Movement or operation of the working arm  18 , e.g. pivoting, rotating, extending/retracting, crowding in/out, is actuated by hydraulic fluid, and so the working arm  18  is a first hydraulically actuated device. 
     The working arm  18  has a working implement  22  mounted at the distal end thereof. In the illustrated embodiment, the working implement  22  is a bucket, but in alternative arrangements any suitable working implement may be used such as forks, a shovel, a sweeper, a grapple etc. Movement or operation of the working implement  22 , e.g. bucket curl/dump, pivoting etc., is actuated by hydraulic fluid, and so the working implement  22  is a second hydraulically actuated device. 
     The working machine  10  is provided with a dozer blade  24 . The dozer blade  24  is provided on the undercarriage  12  of the working machine  10 . Raising and lowering of the dozer blade  24  is actuated by hydraulic actuator  25 , and so the dozer blade  24  is a third hydraulically actuated device. 
     The working machine  10  is provided with a pair of stabilizing legs  28 . The stabilizing legs  28  are provided on the undercarriage  12  of the working machine  10 . Raising and lowering of the stabilizer legs  28  is actuated by hydraulic actuator  26 , and so the stabilizer legs  28  are a fourth hydraulically actuated device. 
     Further examples of hydraulically actuated devices for a working machine are: a hydraulic power steering device (not shown) for assisting with movement of steered axles or articulation actuators; a spring applied hydraulically released brake for parking the working machine; and hydraulic shock absorbers. 
     Each of the hydraulically actuated devices are supplied with hydraulic fluid from a hydraulic fluid reservoir along a hydraulic fluid flow path driven by a hydraulic pump  30 . 
     The undercarriage  12  is connected to a ground engaging structure  32 . The ground engaging structure includes wheels  32   a ,  32   b . The wheels  32   a ,  32   b  are mounted to the undercarriage  12  via first and second drive axle assemblies. The second drive axle assembly is fixed with respect to the undercarriage  12 , whereas the first drive axle assembly is capable of limited articulation, thereby permitting the wheels to remain in ground contact, even if the ground is uneven. The wheels  32   a ,  32   b  are typically provided with off-road pneumatic tires. In this embodiment, both drive axle assemblies are steer axles, but this may not always be the case. In alternative arrangements, the ground engaging structure  32  may include a pair of endless tracks. 
     When an operator wishes to move the working machine  10 , the operator can use controls such as the steering wheel, a foot brake, a foot clutch, a foot accelerator, forward and reverse levers and a gear box having forward and reverse gears to move the working machine  10  over the ground. When it is necessary to move the working machine  10  a distance from one location to another location, the dozer blade  24  and stabilizer legs  28  will be lifted above ground level and the working machine  10  can be driven. This corresponds to the working machine  10  being in a moving mode or state. 
     When the operator wishes to use the working machine  10 , i.e. to carry out a working operation, the working machine  10  is considered to be in a working mode or state. When using the working machine  10  may be substantially stationary or the working machine  10  may be travelling at a low speed below a predetermined threshold. In this condition, some or all of the ground engaging structure may be lifted off the ground by operation of stabilizer legs  28  and/or lowering of the dozer blade  24  into engagement with the ground. 
     Referring to  FIG. 2 , a drive arrangement of the working machine  10  is illustrated. The drive arrangement includes an electric motor arrangement and a transmission. 
     The working machine  10  has an electrical source of power  33 . In the present arrangement, the electrical source of power  33  is a battery. The electrical source of power  33  provides power to an electric drive arrangement  34 . The electric motor arrangement  34  is configured to drive the hydraulic pump  30  to power the hydraulically actuated devices. The electric motor arrangement  34  is configured to drive the ground engaging structure  32  to propel the working machine  10 . 
     The working machine  10  may be considered to be an electric working machine  10 . In alternative arrangements, the working machine may also include an internal combustion engine, e.g. to charge the electrical source of power  33 , and so may be a hybrid working machine. 
     The electric motor arrangement includes a first electric motor  36  and a second electric motor  38 . Incorporating a plurality of electric motors has been found to reduce both the required voltage of each of the electric motors and the number of transmission ratios. 
     The first electric motor  36  is configured to drive the hydraulic pump  30 . The first electric motor  36  is able to be adjusted to vary the output of the hydraulic pump  30  to meet the hydraulic fluid demand of the hydraulically actuated devices. The second electric motor  38  is configured to drive the ground engaging structure  32 . It shall be appreciated that in alternative embodiments, the first electric motor  36  may be configured to drive the ground engaging structure  32 , and the second electric motor  38  may be configured to drive the hydraulic pump  30 . 
     The working machine  10  includes a transmission  35 . The transmission  35  is operable to transmit drive from the electric motor arrangement  34  to the ground engaging structure  32  and to the hydraulic pump  30 . 
     The transmission  35  includes a first input member  40  that is connected to the first electric motor  36  so as to be driven thereby. The transmission  35  includes a second input member  46  that is connected to the second electric motor  38  so as to be driven thereby. In order to transmit drive to the hydraulic pump  30  and the ground engaging structure  32 , the transmission  35  includes a first output member  52  connected to the hydraulic pump  30 , and a second output member  54  connected to the ground engaging structure  32 . The input and output members  40 ,  46 ,  52  and  54  each define a longitudinal axis, and each of the longitudinal axes are parallel to one another. 
     The transmission  35  includes a drive train to facilitate transmission of drive. In the embodiment, the drive train enables the transmission of drive between the input and output members  40 ,  46 ,  52  and  54 . The drive train includes a first input gear  44  connected to the first input member  40 . The drive train includes a second input gear  48  connected to the second input member  46 . The drive train includes a third input gear  50  connected to the second input member  46 . The third input gear  50  is spaced apart from the second input gear  48 . In order to transmit drive to the second output member  54 , the drive train includes at least one output gear. In this embodiment, the drive train includes a first output gear  58  and a second output gear  60  connected to the second output member  54  and spaced apart. 
     The first input member  40  is connected to the first electric motor  36  at a first end thereof, and to the first input gear  44  at a second end. The first output member  52  is connected at a first end to the first input gear  44  of the first input member  40 . The first output member  52  is directly connected to the hydraulic pump  30  at a second end. A first coupling element  56  is used to couple the first output member  52  to the first input gear  44 . As such, drive is transmitted from the first electric motor  36  to the hydraulic pump  30 . In alternative embodiments, the coupling element  56  may be used to couple the first input member to the first input gear, and the first input gear may instead be connected to the first output member. 
     The first input gear  44  and the second input gear  48  are in meshing engagement so as to transmit drive between the first input member  40  and the second input member  46 . Put another way, the first input gear  44  and the second input gear  48  are aligned along the transmission such that they inter-engage. 
     The transmission  35  is configured to transmit drive from the second input member  46  to the second output member  54  via the second and third input gears  48 ,  50 , and the first and second output gears  58 ,  60 . The second input gear  48  and the first output gear  58  are in meshing engagement such that drive is transmitted therebetween. The third input gear  50  and the second output gear  60  are in meshing engagement such that drive is transmitted therebetween. 
     The second output member  54  is connected, either directly or indirectly, to the ground engaging structure  32 . The second output member  54  may be directly or indirectly connected to the first axle assembly associated with the first set of wheels  32   a , and the second axle assembly associated with the second set of wheels  32   b.    
     The second output member  54  is provided in the form of two output shafts. The first output gear  58  is connected to one of the output shafts, and the second output gear  60  is connected to the other one of the output shafts. The two output shafts are rotationally locked together. The two output shafts are coupled together using a second coupling element  62 . However, it shall be appreciated that in alternative embodiments the second output member may be provided as a single output shaft. 
     A coupling device  42  is provided to selectively adjust transmission of drive to the hydraulic pump  30  and the ground engaging structure  32 . The coupling device  42  is connected between the first input gear  44  and the first input member  40 . The coupling device  42  is connected to the input member  40  associated with the hydraulic pump  30 . In alternative embodiments, the coupling device  42  may be connected to the input member associated with the ground engaging structure  32 . 
     The coupling device  42  may be any one of a torque converter, a fluid coupling and a slipping clutch. The use of any one these coupling devices enables transmission of drive to the hydraulic pump  30  even when the machine stalls, and enables both independent and combined transmission. In the embodiment described below, the coupling device  42  is a torque converter. This is advantageous because the torque output may be increased. 
     In an alternative embodiment, the transmission of the first electric motor and the second electric motor may be combined prior to transmitting drive to the first input member. For example, a first transfer shaft connected to the first electric motor, and a second transfer shaft connected to the second electric motor, could both transmit drive to the first input member. The selective coupling and decoupling of the coupling device would therefore occur after the combination of drive from the first and second motors. 
     The transmission  35  includes a lock up clutch. The lock up clutch is configured to be used (i.e. to be operational) when the working machine is in a travelling mode. Put another way, the lock up cutch engages/activates when the working machine is in travelling mode, e.g. when travelling at high machine speed, and hydraulic demand is low. The lockup clutch is located in front of the torque converter and has the advantage of preventing slip at high speeds. 
     The coupling device  42  is configured to selectively couple and decouple transmission of drive. The coupling device  42  is configured to selectively couple and decouple transmission of drive to the hydraulic pump  30  and the ground engaging structure  32 . The coupling and decoupling of the transmission of drive is dependent on whether the working machine  10  is in a working mode or a travelling mode. This enables the distribution of transmission to be optimized depending on the different modes of operation of the working machine  10 . 
     When the working machine  10  is in a working mode, the predetermined drive requirement of the ground engaging structure  32  will be low, or at a minimum. The transmission  35  is therefore configured to priorities distribution of drive to the hydraulic pump  34 . The coupling device  42  selectively decouples transmission of drive from the first input member  40  to the ground engaging structure  32 . The predetermined threshold may be in the range of 0 km/h to 10 km/h. 
     When the working machine  10  is in the working mode, there is a drive requirement of both the hydraulically actuated devices and the ground engaging structure  32 . The working machine  10  is operating in working mode when the speed of the working machine  10  is above the predetermined threshold. It is therefore advantageous that the electric drive arrangement  34  transmits drive to both the ground engaging structure  32  and the hydraulic pump  30  simultaneously. The coupling device  42  is therefore configured to selectively couple transmission of drive from the first input member  40  to both the hydraulic pump  30  and the ground engaging structure  32 . 
     When the working machine  10  is in travelling mode and/or when demand for hydraulic supply to the one or more hydraulically actuated devices is low, the transmission  35  is configured to priorities the distribution of drive to the ground engaging structure  32 . The coupling device  42  is therefore configured to selectively decouple transmission of drive from the first input member  40  to the hydraulic pump  30 . 
     The working machine  10  includes a controller configured to control the selective coupling and decoupling of the coupling device  42  based on the operational mode of the working machine  10 . The controller is therefore configured to determine the speed of the working machine  10  and to compare it to the predetermined threshold, and to monitor the demand of the one or more hydraulically actuated devices for hydraulic fluid supply. The controller is configured to determine the mode and operating condition of the working machine  10 , and operate the coupling device  42  to selectively couple and decouple and transmission accordingly. Alternatively, operation of the transmission  35  may be manually controlled by the operator. 
     In order to detect the conditions of the working machine  10 , the working machine may include a sensor arrangement (not shown). The working machine  10  may include a first sensor arrangement associated with the hydraulically actuated devices. The first sensor arrangement may for example, be configured to detect whether a hydraulically actuated device is being operated. The sensor arrangement may also be configured to detect the required flow rate of hydraulic fluid to the one or more hydraulically actuated devices. The working machine  10  may include a second sensor arrangement associated with the ground engaging structure  32 . The second sensor arrangement may be configured to detect the speed of movement of the ground engaging structure  32 . 
     Operation of the coupling device  42  is described below. 
     When the working machine  10  is in the working mode, it is advantageous for transmission of drive to the hydraulic pump  30  and the ground engaging structure  32  to be independent of one another. When the working machine  10  is in the travelling mode and/or when demand for hydraulic supply to the one or more hydraulically actuated devices is low, it is advantageous for transmission of drive to the hydraulic pump  30  and the ground engaging structure  32  to be independent of one another. 
     The coupling device  42  is configured to selectively decouple the first input gear  44  from the first input member  40 . Transmission of drive between the first input member  40  and the second input member  46  is therefore inhibited. The hydraulic pump  30  is driven by the first electric motor  36 , and the ground engaging structure  32  is independently driven by the second electric motor  38 . 
     This enables the first and second motors  36 ,  38  to drive the hydraulic pump  30  and the ground engaging structure  32  at different speeds depending on the drive requirements of the mode of operation. For example, if the working machine  10  is stationary or moving at low speed and one of the hydraulically actuated devices is being operated, the output of the second electric motor  38  is can be reduced. The output of the first electric motor  36  can then be increased such that the output of the hydraulic pump  30  matches the demand of the one or more hydraulically actuated devices for hydraulic fluid supply. If the working machine  10  is in travelling mode and the demand for hydraulic fluid is low, the output of the first electric motor  36  can be reduced and the output of the second electric motor  36  can be increased to match the drive requirement of the ground engaging structure  32 . 
     When the working machine  10  is in working mode, there is a demand for drive to both the hydraulic pump  30  and the ground engaging structure  32 . It is therefore advantageous for transmission of drive to the ground engaging structure  32  and the hydraulic pump  30  to be combined. The coupling device  42  is configured to selectively couple the first input gear  44  to the first input member  40 . Transmission of drive to the first input member  40  and the second input member  46  is therefore combined. As such, both the first and second motors  36 ,  38  may be driven to optimize the efficiency of transmission. 
     Referring to  FIG. 3 , an alternative drive arrangement of the working machine  10  is illustrated. Similar parts to the embodiment of  FIG. 2  are labelled by like reference numerals with prefix “1”. The differences with respect to the embodiment of  FIG. 2  are discussed below. 
     The drive arrangement includes an electric motor arrangement and a transmission. The electric motor arrangement  34  includes a single electric motor  136 . It may be particularly advantageous to include a single electric motor in small machines where space is particularly limited. The electric motor  136  is configured to drive both the hydraulic pump  130  and the ground engaging structure  32 . The drive train includes an additional output gear  164  connected to the first output member  152 . The electrical source of power  133  provides power to the electric motor  136 . 
     The working machine  10  includes a transmission  135 . The transmission  135  includes the first input member  140  connected to the connected to the electric motor  136  to be driven thereby. In order to transmit drive to the hydraulic pump  130  and the ground engaging structure  32 , the transmission  135  includes the first output member  152  connected to the hydraulic pump  130 , and the second output member  154  connected to the ground engaging structure  32 . The input and outputs members  140 ,  152  and  154  each define a longitudinal axis, and each of the longitudinal axes are parallel to one another. 
     The transmission  135  also includes the drive train to facilitate transmission of drive between the input and output members  140 ,  152  and  154 . The drive train includes the first input gear  144  connected to the first input member  140 . An additional output gear  164  is also connected to the first output member  154 , and an additional transfer gear  166  is provided. The drive train also includes the first output gear  158  and the second output gear  160  connected to the second output member  154  and spaced apart. 
     The first input member  140  is connected to the electric motor  136  at the first end, and to the first input gear  144  at the second end. The first coupling element  156  is provided to couple the first input member  140  to the output gear  164 , and to couple the first output member  152  to the first input gear  142 . As such, drive is transmitted from the electric motor  136  to the hydraulic pump  130 . 
     The first input gear  144  and the first output gear  158  are positioned adjacent one another so as to transmit drive from the first input member  140  to the second output member  154 . Put another way, the first input gear  144  and the first output gear  158  are aligned along the transmission such that they mesh together and transmit drive therebetween. 
     The transmission is configured to transmit drive between the first output member  152  and the second output member  154 . This transmission of drive occurs via the transfer gear  166 . The output gear  164 , the transfer gear  166  and the second output gear  160  are in alignment along the transmission  135  such that they mesh together and drive is transmitted therebetween. 
     The second output member  154  may be directly or indirectly connected to the first axle assembly associated with the first set of wheels  32   a , and the second axle assembly associated with the second set of wheels  32   b.    
     The input and output members of this embodiment are shafts. However it shall be appreciated that in alternative embodiments, the input and output members may be any suitable device, for example belts or chains. 
     The second output member  154  is provided in the form of a single output shaft  154 . However, in alternative embodiments, the second output member may be provided in the form of two output shafts coupled together. 
     The coupling device  142  is provided to selectively adjust the transmission of drive to the hydraulic pump  130  and the ground engaging structure  32 . Similarly to the first embodiment, the coupling device  142  is connected between the first input member  140  and the first input gear  144 . 
     Operation of the coupling device  142  is described below. 
     When the working machine  10  is in a working mode and there is demand for hydraulic supply to one or more of the hydraulically actuated devices it is advantageous for transmission of drive to the hydraulic pump  130  to occur independent of transmission to the ground engaging structure  132 . As such, the coupling device  142  is configured to selectively decouple the first input gear  144  from the first input member  140 , and to selectively decouple the output gear  164  from the second input member  152 . This enables the electric motor  136  to drive the hydraulic pump  130  to meet the demand of the one or more hydraulically actuated devices, whilst inhibiting transmission of drive to the ground engaging structure  32 . 
     Alternatively, when the working machine is in working mode, there is a demand for drive to both the hydraulic pump  130  and the ground engaging structure  32 . The coupling device  142  is therefore configured to selectively couple the first input gear  144  to the first input member  140 , and to selectively couple the output gear  164  from the second input member  152 . 
     Although the teachings have been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope as defined in the appended claims.