Patent Abstract:
A transmission arrangement including a torque converter, a first shaft fixed to rotate with a turbine of the torque converter about an axis, a second shaft fixed to rotate with a casing of the torque converter about said axis, a gear mounted on the first shaft and being fixed to rotate with the first shaft and a clutch selectively engageable to cause the first shaft to be fixed to rotate with the second shaft and being selectively disengageable to allow the first shaft to rotate relative to the second shaft, the clutch being rotatable about said axis.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates to a transmission arrangement, in particular a transmission arrangement including a torque converter. The present invention also relates to a power arrangement, in particular a power arrangement including a prime mover and a transmission arrangement. 
     BACKGROUND OF THE INVENTION 
     Transmission systems are known whereby a prime mover, such as an internal combustion engine, drives a torque converter which in turn drives a gearbox having multiple ratios. When such a transmission is used on a vehicle, the gearbox will typically have a plurality of forward gears and one or more reverse gears. The advantage of the torque converter is that the torque being transmitted from the prime mover is multiplied. The disadvantage is that the torque converter itself absorbs energy, which energy cannot therefore be used to propel the vehicle. 
     In order to overcome this problem torque converters can be fitted with lock-up clutches. US2003/0186768 shows an example of torque converter with a lock-up clutch. The torque converter has a casing to which is attached an impeller. Rotatable relative to the casing is a turbine. A friction clutch operably acts between the turbine and an inside part of the casing to prevent rotation of the turbine relative to the casing under certain circumstances. 
     Typically the lock-up clutch is used in the high gears, for example top gear, when shock loads from the wheels of the vehicle to the torque converter are less significant. When the vehicle is used in a low gear, for example bottom gear, then the shock loads coming from the wheels are correspondingly higher and accordingly the torque capacity of the lock-up clutch may not be sufficient to withstand these loads. Thus, whilst a lock-up clutch reduces wasted energy in the high gears, it may not be able to reduce wasted energy in the low gears. Further, providing a lock-up clutch within a torque converter casing is expensive. In particular the valves used to engage and disengage the lock-up clutch are expensive. 
     Whilst it is possible to provide multiplate lock-up clutches in a torque converter casing, so as to allow the torque converter to lock-up in all gears, such multiplate lock-up clutches are considerably more expensive than the single plate lock-up clutch shown in US2003/0186768. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved transmission including a torque converter. 
     Thus, according to the present invention there is provided a transmission arrangement including a torque converter, a first shaft fixed to rotate with a turbine of the torque converter about an axis, a second shaft fixed to rotate with a casing of the torque converter about said axis, a gear mounted on the first shaft and being fixed to rotate with the first shaft and a clutch selectively engageable to cause the first shaft to be fixed to rotate with the second shaft and being selectively disengageable to allow the first shaft to rotate relative to the second shaft, the clutch being rotatable about said axis. 
     The gear may be positioned axially between the torque converter and the clutch. 
     The transmission arrangement may include a third shaft fixed to rotate with the second shaft about a said axis wherein the clutch is supported by the third shaft. 
     The second shaft may include a spline in engagement with a further spline of the third shaft so as to fix the third shaft to rotate with the second shaft and the clutch may be positioned axially between the torque converter and one or both of the spline and further spline. 
     The second shaft may have a first end proximate the torque converter and a second end remote from the torque converter, the first and second ends may define a second shaft length and the gear may be positioned axially closer to the first end than the second end. 
     An axial distance from the first end of the second shaft to the gear may be less than 40% of the second shaft length. 
     The torque converter may define a plane which is positioned axially between the first end and the second end. 
     The gear may engage a further gear mounted on a fourth shaft rotatable about a second axis, the gear and further gear defining a gear plane, the fourth shaft including one or more additional gears, each defining an additional gear plane wherein the gear plane is positioned between the or each additional gear plane and a plane defined by the torque converter. 
     The fourth shaft may include one or more additional clutches, each defining an additional clutch plane wherein the gear plane is positioned between the or each additional clutch plane and the plane defined by the torque converter. 
     The transmission arrangement may include a multispeed gearbox driven by a said gear. 
     The said gear may be the only gear which transmits power from the torque converter to the multispeed gearbox. 
     The second shaft may be in permanent driving connection with an oil pump input drive. 
     The oil pump input drive may be engaged with the third shaft. 
     The power arrangement may include a prime mover having an output shaft and a transmission arrangement wherein the output shaft is fixed to rotate with the casing. 
     The prime mover may be an internal combustion engine, in particular an internal combustion engine having reciprocating pistons, for example a compression ignition engine such as a diesel engine. 
     The gear may be positioned on an opposite side of the torque converter to the prime mover. The clutch may be positioned on an opposite side of the torque converter to the prime mover. 
     The clutch may be positioned externally relative to the casing. 
     The output shaft may be fixed to rotate with and engage and drive a flywheel which is fixed to rotate with and engage and drive a flex plate which is fixed to rotate with and engage and drive the casing. 
     The transmission arrangement may be incorporated into a working machine. The transmission arrangement may drive the ground engaging structure of the working machine. The ground engaging structure may be tracks or may be wheels. When the ground engaging structure is a set of front wheels and a set of rear wheels then the front or rear wheels may be selectively driven by the transmission arrangement either independently or together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is an enlarged view of part of a transmission arrangement according to the present invention, and 
         FIG. 2  is a view of a machine including the transmission arrangement of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 2  there is shown a working machine (or material handling machine)  1  including a prime mover  2  in the form of a diesel engine, a bell housing  3  and a gear box  14 . In this case, the working machine  1  is a back hoe loader, having a back hoe  4  and a loading shovel  5 . The working machine has ground engaging means in the form of rear wheels  6  and front wheels  7 . The diesel engine  2  can drive the rear wheels  6  via the gear box, thereby propelling the vehicle. The gear box has a plurality of forward gears and a plurality of reverse gears. An output  15  from the gearbox is drivingly coupled to the rear wheels, for example via a crown wheel and pinion and differential assembly and shafts. 
     The gear box may selectively be able to drive the front wheels  7  (as will be described below). 
     Positioned between the engine and the gear box and within bell housing  3  is a torque converter  12 . 
       FIG. 1  shows a transmission arrangement  10  including the torque converter  12  and the gear box  14 . 
     The torque converter is a non lock-up torque converter, that is to say a torque converter without an internal lock-up clutch. 
     As best seen in  FIG. 1 , the torque converter  12  includes a casing (also known as shell)  20  within which is positioned an impeller  22  and a turbine  24 . Also mounted within the casing is a reaction element  26  which is held against rotation under torque conversion conditions by a conventional over running device  28 , such as a sprag type one way clutch. Bolts  30  secure the turbine side  24 A of the casing  20  to a flex plate  32 . Further bolts  34  secure the flex plate  32  to a fly wheel  36  of the prime mover  2 . 
     The turbine  24  is connected to a first shaft  40  via a turbine mounting ring  25 . 
     Transmission of power from the prime mover  2  to the turbine  24  is conventional and need not be described in detail, however, in summary rotation of the flywheel  36  of the prime mover  2  causes the flex plate  32  to rotate the casing  20 . As the casing rotates then the vanes of the impeller  22  rotate and fluid within the torque converter causes the blades of the turbine  24  to rotate, though at a slower speed than the speed of rotation of the prime mover  2 . 
     The casing  20  includes a boss  42  secured rotationally fast therewith via weld  44 . Boss  42  has a central splined recess  43 . A second shaft  50  has an end  50   b  with splines  51  that engages with the splined recess  43  thereby ensuring that shaft  50  is rotationally fast with boss  42 , and in particular is rotationally fast with flywheel  36  of the prime mover (via the turbine side  24 A of the casing and the flex plate  32 ). 
     Turning to  FIG. 1 , the first shaft  40  is rotatably supported in bearings  65 . End  40 A of first shaft  40  has an external spline  46  which is engaged with an internal spline  25 A of the turbine mounting ring  25 . A gear  47  is mounted on the first shaft  40  via a spline arrangement  48 . 
     As will be appreciated, the gear  47  is fixed to rotate with the first shaft  40 , which in turn is fixed to rotate with the turbine  24 . 
     The first shaft also includes a clutch housing portion  49  which supports the clutch  17 . 
     The second shaft  50  includes a first end  50 A and a second end  50 B. As mentioned above, the first end  50 A includes a spline  51 . Proximate the second end  50 B the second shaft  50  includes an external spline  52 . 
     External spline  52  engages an internal spline  61  of a third shaft  60 . Third shaft  60  is supported on bearings  62  and  63 . Third shaft  60  has a first end  60 A upon which is mounted a clutch  17 . The third shaft also has a second end  60 B which includes an internal spline  64 . An oil pump  18  (shown schematically in  FIG. 1 ) includes an oil pump drive  18 A which has an external spline  18 B. Spline  18 B is engaged with spline  64  of the third shaft. 
     As will be appreciated, the third shaft is fixed to rotate with the second shaft. The second shaft is fixed to rotate with the torque converter casing  20 . The torque converter casing  20  is fixed to rotate with the flywheel. The flywheel is fixed to rotate with the output shaft (crankshaft)  8  of the prime mover  2  by virtue of the flywheel being bolted to the crankshaft via bolts  9 . 
     Bearing  65  supports the third shaft relative to the second shaft. 
     In summary, the turbine  24 , first shaft  40  and gear  47  are all rotationally fast with each other. The crank shaft  8 , flywheel  36 , torque converter casing  20 , second shaft  50  and third shaft  60  and oil pump drive  18 A are all rotationally fast with each other. First shaft  40 , second shaft  50 , third shaft  60  and clutch  17  all rotate about axis A. Crank shaft  8  and torque converter  12  also rotate about axis A. 
     Gear  47  engages a further gear  70  which is mounted on a fourth shaft  71  which rotates about axis B. Mounted to the left (when viewing  FIG. 1 ) of the further gear  70  is gear  72  and gear  73 , clutch  72 A and clutch  73 A. The torque converter  12  defines a plane P 1 . The gear  47  defines a plane P 2 . Gear  72  defines a plane P 3 . Clutch  72 A defines a plane P 4 . Clutch  73 A defines plane P 5 . Gear  73  defines a plane P 6 . 
     Gear  47  defines the sole input into the gearbox  14 . Power from the prime mover can be transmitted to gear  47  in one of two ways: 
     a) with clutch  17  disengaged power is transmitted from the crank shaft  8  through the flywheel  36  through the flexplate  32  through the casing  20  through the impeller  22  through the turbine  24  through the turbine mounting ring  25  through splines  25 A, through splines  40 A, through the right hand part (when viewing  FIG. 1 ) of the first shaft  40  through the spline arrangement  48  to the gear  47 . Under these circumstances, because the power is being transmitted via the torque converter, the first shaft  40  will be rotating slightly slower than the crank shaft  8 . Accordingly, because the third shaft will be rotating at crank shaft speed, then the first end  60 A of the third shaft will be rotating at a different speed to clutch housing portion  49 , and this is possible since clutch  17  is disengaged. 
     b) with clutch  17  engaged, then power from the crankshaft is transmitted through the flywheel  36 , through the flexplate  32 , through the casing  20 , through the boss  42 , through the spline recess  43 , through spline  51 , through the second shaft  50 , through the spline  52 , through the spline  61 , through the third shaft  60 , through engaged clutch  17 , through clutch housing portion  49 , through the left-hand part (when viewing  FIG. 1 ) of the first shaft  40 , through the spline arrangement  48  to gear  47 . 
     Under these circumstances, the first and second shafts will both be rotating at the same speed and accordingly the impeller and turbine will also be rotating at the same speed. Because the impeller and turbine will be rotating at the same speed, then the torque converter will not be able to transmit any power (since the torque converter relies on a mismatch of rotational speeds of the impeller and turbine to transmit power and no such mismatch exists). 
     Thus, gear  47  is either directly driven (when clutch  17  is engaged) or is torque converter driven (when clutch  17  is disengaged). Under either circumstance, gear  47  transmits power to gear  70  which is rotationally fast with shaft  71 . When forwards motion of the working machine  1  is required, clutch  72 A is disengaged, and clutch  73 A is engaged. This results in gear  73  becoming rotationally fast with shaft  71  and thereby transmitting power from gear  70 , through shaft  71 , through clutch  73 A, through gear  73  and through gear  74  and on through the rest of the forward gears within the gear box, depending upon which forward gear ratio is selected. 
     When it is required to reverse the working machine  1 , then clutch  73 A is disengaged and clutch  72 A is engaged. This results in gear  47  turning gear  70  which in turn turns shaft  71  which turns clutch  72 A which turns gear  72  (which is now rotationally fast with shaft  71 ), which turns reverse idler  75  (shown in a developed position in  FIG. 1  for ease of understanding), which in turn is engaged with and turns gear  76 , which turns the rest of the gearbox in whichever reverse gear is selected. 
     As will be appreciated, gear  47  is positioned axially between the torque converter  12  and the clutch  17 . The clutch  17  is positioned axially between the torque converter and splines  52  and associated splines  61 . 
     Thus, consideration of the transmission path with direct drive (i.e. with clutch  17  engaged) shows that power is transmitted from spline  51 , along almost the entire length of the second shaft to spline  52 , i.e. power is transmitted over length M of the second shaft. However, in direct drive the power now has to be transferred from spline  52  to gear  47  via the third shaft, clutch  17  and left hand most portion of the first shaft, in other words the power has to be transmitted over length N. Thus, the effective length over which power has to be transmitted along shafts from spline  51  to gear  47  is equal to M+N. Making the effective length of the shafts over which power has to be transmitted (M+N) relatively large gives certain advantages when power is being transmitted in direct drive mode (i.e. with clutch  17  engaged). A relatively large effective shaft length (M+N) creates a greater torsional flexibility than if the effective length of the shaft were shorter. This torsional flexibility is advantageous when the prime mover is an internal combustion engine. Thus, it is known for internal combustion engines, in particular piston type (or reciprocating type) internal combustion engines have torque fluctuations as the fuel in each cylinder is sequentially ignited. On non-torque converter vehicles, it is known to provide a torsional damper (such as circumferentially orientated springs) in a clutch so as to prevent, or reduce the torque fluctuations from the engine being transmitted to the gearbox. If such torque variations are transmitted to the gearbox then this can result in a noisy gearbox. 
     When power is transmitted through the torque converter of the present invention, then engine torque variations are naturally damped out by the torque converter itself. 
     One advantage of the present invention is that for certain embodiments it is not necessary to have any separate torsional damper arrangement because the effective length of the shaft (M+N) is arranged to be relatively long and those parts of the shafts (the second shaft, the third shaft, and the left-hand portion of the first shaft) can be arranged to have a torsional national frequency which is lower than an idling speed of the engine. As such, not only does the relatively long effective length (M+N) result in less torsional vibration being transmitted to the gearbox  14  at speeds at or above engine idle, it is also possible for the overall natural frequency of the first, second and third shafts to be lower than an idle speed of the engine and therefore the effective shaft length (N+M) will never continuously run at a natural frequency, and will only momentarily pass through a natural frequency upon engine start up or engine stop. 
     Consideration of  FIG. 1  shows that the transmission arrangement has been designed to increase the effective length (M+N) of the shaft. Thus, the gear  47  is positioned axially between the torque converter and the clutch. The clutch  17  is positioned axially between the torque converter and the spline coupling between the second and third shaft (splines  52  and  61 ). The gear  47  is positioned closer to first end  50 A than it is to second end  50 B of the second shaft. In particular the actual distance from the first end  50 A to the gear  47  is less than 40% of the length L of the second shaft. The plane P 1  defined by the torque converter is positioned axially between the first and second ends of the second shaft. The plane P 2  defined by gear  47  is positioned nearer to plane P 1  of the torque converter than planes P 3 , P 4 , P 5  and P 6 . Thus, by positioning gear  47  to the right of gear  72  and  74  and clutches  72 A and  73 A requires the left-hand portion of the first shaft between gear  47  and clutch housing portion  49  to be lengthened to span this distance thereby increasing the effective length (M+N) of the shaft. 
     As mentioned above, shaft  3  also drives an oil pump which, in some embodiments, has a damping effect. Thus, any torque fluctuations which may be transmitted from the engine along the second shaft may then be damped by the second shaft as it powers the oil pump. As such the torque fluctuations will be reduced and therefore fewer torque fluctuation will be transmitted onward through third shaft and clutch  17  and the left-hand portion of the first shaft to the gearbox thereby resulting in a quieter gearbox. The oil pump may be used to operate hydraulic rams  80  or other hydraulic surfaces of the working machine. 
     For the avoidance of doubt, a component is fixed to rotate with another component when that component cannot rotate relative to the other component. In other words, when rotating, the component and the other component both rotate at the same speed. The phrase “rotationally fast with” means the same as “fixed to rotate with”. 
     The clutches shown in the figures are multi plate clutches, though in further embodiments this may not be the case.

Technology Classification (CPC): 5