Patent Publication Number: US-2007111838-A1

Title: Transmission

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority to United Kingdom Patent Application No. GB0521539.7 filed Oct. 22, 2005, which is incorporated in its entirety by reference herein.  
     BACKGROUND TO THE INVENTION  
      This invention relates to a transmission and more particularly to a transmission known as an infinitely variable transmission (“IVT”) in which the speed of an output shaft or other output member is infinitely variable irrespective of the speed of a, typically engine driven, input member. Such a transmission is typically used for off-road vehicles including tractors and working machines, such as excavating and/or loading machines.  
      In an IVT, drive is typically achieved by using a combination of mechanical and hydraulic components to provide a drive train in which, with the engine at a set speed, the output speed of the output shaft is dependent upon the input from a hydraulic motor, or variator. Hydraulic motors have been used because of their well established reliability and durability, which are important factors for a transmission for an off-road vehicle.  
     SUMMARY OF THE INVENTION  
      According to a first aspect of the invention we provide a transmission including a first input member which in use is rotatably driven by a first prime mover, a second input member which in use is rotatably driven by a second prime mover, a rotatable output member from which drive is provided to a driven structure, the first input member driving a driven member and there being a drivable member drivable by the second input member, the driven member and the drivable member being coupled though an intermediate structure which carries the output member, drive being transmitted from the first input member to the output member when torque is input to the second input member from the second prime mover, and wherein the second prime mover is an electrically driven switched reluctance motor.  
      By virtue of the second prime mover being an electrically driven switched reluctance motor, advantages over conventional hydraulic motor variators can be realized.  
      With known IVTs, with hydraulic motor variators, in order to provide adequate power over the whole range of off-road vehicle speeds, both when the vehicle is required to perform a work operation, as well as to enable the vehicle to be driven along a road at an adequate speed, it is necessary to provide selectable gears, which may be selectively engagable e.g. using clutches. This is because of the limitations in terms of speed and torque which can be achieved using a hydraulic motor as a variator. However a suitable electrical motor may provide for much greater variation of speed, and as a result, the number of selectable gears required to provide power over the whole vehicle speed operating range, may be at least reduced, or the requirement for selectable gears may be avoided altogether. Thus the output member may directly drive the driven structure without the intermediary of selectable gears.  
      Switched reluctance motors are relatively efficient, and are able to provide constant torque drive over a very large speed range, for example, up to 25000 rpm, and are mechanically relatively simple in construction. Even when driven at very low rotational speeds, switched reluctance motors provide full-rated torque, and these may be made in a variety of different geometrical configurations to suit different transmission packaging requirements.  
      Thus a switched reluctance motor, despite prejudices which have restricted development of IVTs to the use of primarily hydraulic motors and selectable gears, is an ideal secondary prime mover, or variator, for an IVT transmission.  
      In a preferred arrangement, electrical power for the electrically driven motor is provided from a generator which is driven by the first prime mover. For example, a rotor of the generator may coupled to or integral with, and be rotated with the first input member of the transmission which is driven by the first prime mover. The generator may be any kind of electrically generating machine, but preferably is a switched reluctance electrical generating machine.  
      The electrically driven switched reluctance second prime mover motor may be operated alternatively as a generator too, if desired, to produce electrical power e.g. for storage, when the first prime mover is being operated but the transmission is not transmitting drive to the output member. A large range of output member speeds, for forward and reverse drive, may be realized as the switched reluctance motor may readily be driven at high speeds and in either direction of rotation.  
      Various other advantages may be realized.  
      It will be appreciated that off-road vehicles, like on-road vehicles, require a source of electrical power, such as an alternator, to provide power for vehicle systems. With the transmission in accordance with the invention however, the generator which provides power for the electrically driven second prime mover may be used to provide power for vehicle systems, thus avoiding the need for any separate alternator.  
      Where the first prime mover is an engine, the off-road vehicle typically will have a starter motor, but with a transmission in accordance with the invention, initial drive to start the engine may be achieved through the transmission from the second prime mover, thus avoiding the need for a separate engine starter motor.  
      In one embodiment, the first and second input members may include drive shafts.  
      The driven member, driven from the first input member may include a sun gear which is rotatable about a main transmission axis, whilst the drivable member which may be driven by the second input member, may include a ring gear which is rotatable about the main transmission axis radially outwardly of the sun gear. The intermediate structure may provide at least one planet gear which meshes with each of the sun gear and the ring gear, the intermediate structure being rotatable about the main transmission axis and carrying the output member which is rotatable about the main transmission axis too, as the intermediate structure rotates.  
      The first input member may include a drive gear which meshes with a driven gear which is fast with a driven shaft of the transmission which carries the sun gear. The second input member may include a drivable gear which meshes with a driven gear which is rotatable relative to the driven shaft on which the sun gear is carried, the driven gear which meshes with the drivable gear being fast with the ring gear.  
      In such a construction, because drive may continuously be applied from the first prime mover, even though the output member should not rotate unless the second prime mover is actuated, due to innate resistances in the transmission, the vehicle may “creep” i.e. be driven very slowly, when vehicle movement is not required. Although a driver may halt such creep by the use of a brake, desirably an isolating clutch is provided which may selectively be disengaged to disengage drive from the first input member to the driven member, to prevent any unintentional creeping of the vehicle when drive is not required.  
      The transmission may be for a vehicle such as a tractor or working machine, which may be driven both on and off-road.  
      According to a second aspect of the present invention we provide a vehicle which includes a ground engaging structure though which drive may be transmitted from a prime mover to the ground to move the vehicle over the ground, and wherein a transmission is provided, the transmission being in accordance with the first aspect of the invention.  
      The transmission may include a drive splitting assembly for transmitting drive from the output member of the transmission to each of first and second pairs of ground engaging driving wheels or track driving wheels as required. The drive splitting assembly may include a shaft carrying a gear which meshes with and is driven from an output gear of the output member of the transmission. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Embodiments of the invention will now be described with the aid of the accompanying drawings in which:  
       FIG. 1  is a diagrammatic illustration of a tractor which may embody the invention;  
       FIG. 2  is an illustrative sectional view of a transmission in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Referring to  FIG. 1 , an off-road vehicle  10 , namely a tractor in this example, includes a body  11  and a driven ground engaging structure  12  including a two pairs of ground engaging wheels, namely a pair of front drive wheels  13  and a pair of rear drive wheels  14 . All of the wheels  13 ,  14  are drivable by a transmission  18  to which drive power is primarily provided by a first prime mover being in this example, an internal combustion engine  20 .  
      Referring also to  FIG. 2 , the transmission  18  includes a first input member  22  which includes a drive shaft, which is coupled to the engine  20 , and a second input member  24  which also includes a drive shaft, and is connected to or integral with a rotor shaft  25  of a second prime mover  26  which is an electrically driven motor, and more particularly, is a switched reluctance motor.  
      The drive shaft of the first input member  22  carries a rotor R of an electrical power generating machine  27  which in this example is a switched reluctance generating machine. The drive shaft of the first input member  22  also carries a rotatable clutch member  30  which rotates with the drive shaft of the first input member  22 , and when clutch plates  32  of an isolating clutch  34  are moved into engagement with the clutch member  30 , a drive gear  35  is constrained to rotate with the drive shaft of the first input member  22 . The drive gear  35  meshes with a driven gear  36  which is fast with a driven shaft  38  which is centred on a main transmission axis A of the transmission  18 . Thus when the isolating clutch  34  is engaged, and when the engine  20  is operating, the driven shaft  38  rotates with the first input member  22 .  
      The driven shaft  38  carries and is fast with a sun gear  40 , which in this example is splined or otherwise non-rotatably fixed to the driven shaft  38 .  
      The second input member  24  includes a drivable gear  42  which meshes with a driven gear  43  which is rotatable about the main transmission axis A, relative to the driven shaft  38 . The driven gear  43  which meshes with the drivable gear  42  is fast with a drivable member  45  which in the present example is a ring gear  45 . The ring gear  45  thus is rotatable about the main transmission axis A radially outwardly of the sun gear  40 .  
      An intermediate structure  48  is provided between the ring gear  45  and the sun gear  40 , and includes at least one, but preferably a plurality of, e.g. at least three, planet gears  50 ,  51 . In  FIG. 2 , two planet gears  50 ,  51  are seen in cross-section, each of which is rotatable about its own respective axis  50   a,    51   a  relative to a carrier  55  of the intermediate structure  48 . The carrier  55  and planet gears  50 ,  51  of the intermediate structure  48  are all rotatable about the main transmission axis A as hereinafter described, to rotate a rotatable transmission output member  56  which is coupled to the driven structure i.e. the ground engaging structure  12  of the vehicle  10  to drive the drive wheels  13 ,  14 .  
      To enable drive to be transmitted to both the front pair  13  and rear pair  14  of the drive wheels, the output member  56  includes an output gear  57  which drives an intermediate gear  58  carried on a lay shaft  59  of a drive splitting assembly  60 . The intermediate gear  58  in turn drives a final shaft  61  with an integral final drive gear  63  which meshes with the intermediate gear  58 . The final shaft  61  of the drive splitting assembly  60  is coupled e.g. via a differential, to each of the front and rear pairs of drive wheels  13 ,  14 .  
      Use of the transmission  18  is as follows.  
      With the engine  20  speed set, power is provided to the first input member  22  and the generator  27  generates electrical power. The set speed may be a constant engine speed, although an engine controller may adjust the engine speed to provide optimum performance, minimal emissions, or fuel economy depending on what is required, according to sensed conditions such as load.  
      Where the isolating clutch  34  is engaged but the switched reluctance motor  26  is inoperative, the driven shaft  38  will be rotated, and the sun gear  40  will rotate about the main transmission axis A thereby causing the planet gears  50 ,  51  to rotate about their respective axes  50   a  and  51   a . Thus the ring gear  45  will rotate but the carrier  55  of the intermediate structure  48  will remain stationary. Thus drive is not transmitted to the output member  56 , and the vehicle  10  remains stationary.  
      Because the ring gear  45  meshes with the planet gears  50 ,  51 , their rotation will rotate the ring gear  45  and in turn the drivable gear  42  and second input member  24  will be rotated transmitting drive to the rotor shaft  25  of the switched reluctance motor  26  which will idle.  
      However, upon the switched reluctance motor  26  being actuated, such that drive or resistance to drive is transmitted to the ring gear  45 , the carrier  55  of the intermediate structure  48 , and hence the output member  56  will be constrained to rotate about the main transmission axis A, thus transmitting drive from the engine  11  to the driven ground engaging structure  12 .  
      For a particular first input member  22  speed, the speed and direction of rotation of the intermediate structure  48  and hence output member  56  will depend entirely upon the speed and direction of rotation of the second input member  24 , which by virtue of the second prime mover  26  being a switched reluctance motor, may readily be varied between zero speed and very high rotational speed, and in either direction of rotation, whilst providing full or at least near full-rated torque over the whole of its speed operating range. If the engine speed, i.e. speed of the first input member  22  is adjusted by an engine controller to optimize performance and/or reduce emissions and/or improve economy, for conditions experienced, the second prime mover  26  speed may readily be adjusted to maintain a constant output member  56  speed.  
      Electrical power for the switched reluctance motor  26  may be provided by the generator  27  which is driven by the first prime mover  20 .  
      Switched reluctance motors have particular requirements and in particular a source of cooling. Cooling may be provided by cooling fluid which passes through a cooler of the vehicle  10 , such as an engine radiator R, or otherwise.  
      The physical configuration of the switched reluctance motor  26  need not be as shown, but may be varied to a wide degree e.g. to provide a shorter fatter or thinner longer motor  26  as required, to suit different packaging requirements for different vehicles  10 .  
      Switched reluctance motors require an electronic controller, which may be situated close to the motor  26 , or remote therefrom as is suitable.  
      Various modifications may be made without departing from the scope of the invention.  
      Although the transmission  18  has been described for use in a vehicle which is a tractor  10 , the transmission is suitable for use for other kinds of vehicles including working machines such as excavators and/or loaders, any of which may be operated off-road, and which may be driven on-road. In each case, such a vehicle will have services powered by pumped hydraulic fluid. If desired, a hydraulic pump may be driven from the first input member  22 , at a position at the end of the drive shaft of the first input member  22 , remote from the engine  20 , and as indicated at H in the drawing.  
      Because wide variation of output member  56  speed and in forward or reverse, can be achieved using a switched reluctance motor  26  as a variator, it will be appreciated that there is no need to provide selectable gears to change gear ranges to suit different required drive speeds. Thus the driven ground engaging structure  12  may be driven directly from the output member  56  by which we mean without any intermediate selectable gears, whilst high on-road speeds may be achieved, as well as lower off-road speeds, with full engine torque being available throughout the entire speed range.  
      In an alternative transmission arrangement, drive from the first input member  22  may be transmitted to the sun gear  40  otherwise than as described. Moreover drive may be transmitted from the second input member  24  to the ring gear  45  may be achieved otherwise than as described.  
      If desired, instead of an intermediate structure  56  with planet gears  50 ,  51 , some other gearing arrangement may be provided, in which input from the second prime mover is required for drive to be transmitted from the first prime mover to the output member of the transmission.  
      If desired, when the engine  20  is operative but drive is not required, the idling switched reluctance motor  26  may be used as an electrical generator to generate electrical power for storage in a vehicle battery and/or for use in powering other vehicle systems.  
      If desired, during engine  20  start up, the isolating clutch  34  may be engaged and the switched reluctance motor  26  actuated to transmit drive to the first input member  22 , so that the vehicle  10  requires no starter motor.  
      When a group of device elements, materials, compositions, or components is disclosed herein, it is understood that all individual members of any such groups and all subgroups thereof are disclosed separately. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. Every combination of components described or exemplified herein can be used to practice the invention, unless otherwise stated. Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure.  
      The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.  
      One of ordinary skill in the art will appreciate that device elements and materials and methods of use other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such device elements, materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.  
      All references cited herein are hereby incorporated by reference to the extent that there is no inconsistency with the disclosure of this specification.