Abstract:
A multi-ratio tractor transmission system including a series arrangement of a speed changing gearbox and a range changing gearbox. The system is selectively operable in a field working automatic mode and a road working automatic mode, wherein the transmission can only operate automatically within its speed change gearbox when the system is operating in the field working automatic mode.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of application Ser. No. 11/275,680, filed 24 Jan. 2006, which application claims priority under 35 USC § 119 to United Kingdom Patent Application Number 0502867.5 filed on 11 Feb. 2005, both of which are herein incorporated by reference in their entirety as if fully set forth below. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention   
       [0002]    This invention relates to multi-ratio tractor transmissions which have an automated mode of operation. 
       BRIEF SUMMARY OF THE INVENTION  
       [0003]    According to the present invention there is provided multi-ratio tractor transmission system comprising a series arrangement of a speed changing gearbox and a range changing gearbox, the system being selectively operable in a field working automatic mode and a road working automatic mode, wherein the transmission can only operate automatically within its speed change gearbox when the system is operating in the field working automatic mode. 
         [0004]    The speed changing box may be a multi-ratio epicyclic unit and the range change box may be a synchromesh unit. With such series arrangements it is desirable to provide some so-called “speed matching” capability when the overall control of the active transmission ratio ensures that when a range change is made the ratio selected in the speed changing box is also adjusted to ensure that the ratio provided by the overall transmission is the next overall available ratio in the transmission. 
         [0005]    The transmission system may be operable in a speed-matching mode wherein the ratio of the speed changing gearbox is automatically selected so as to deliver the next overall available ratio in the transmission in response to the operator changing the ratio of the range changing gearbox. Therefore, when a range change occurs, the overall control of the transmission adjusts the ratio of the speed changing box to ensure that the ratio provided by the overall transmission is the next overall available ratio in the transmission. When in these “speed matching” zones the ratio changes must be commanded by the operator. 
         [0006]    In a preferred embodiment, the engine speed at which the transmission changes up in ratio when operating automatically can being selectable by the operator. The engine speed at which the transmission changes up in ratio may be selectable within a pre-defined range. Typically this change-up speed may be variable between say 1600 rpm and 2200 rpm. 
         [0007]    The speed at which the transmission changes down when in the automatic mode may conveniently be linked to the selected change-up speed. For example, the change down may be arranged to be initiated when the engine speed has fallen to 20% below the selected change-up speed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]    One embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0009]      FIG. 1  show diagrammatically the controls for a multi-ratio tractor transmission in accordance with the present invention; 
           [0010]      FIG. 2  shows a perspective view of a controller for the multi-ratio tractor transmission of the present invention, and 
           [0011]      FIG. 3  shows the layout of the control zones of the controller of  FIG. 2  more clearly. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0012]    Referring to  FIG. 1  this show in diagrammatic form the controls of a multi-ratio tractor transmission in which an engine  10  drives a multi-ratio epicyclic gearbox  11  in series with forward and reverse clutches F and R and a multi-ratio synchromesh gearbox  12  whose output  13  drives the wheels of the tractor via suitable differentials and final drive gears etc which are not shown. 
         [0013]    Typically the epicyclical gearbox  11  will provide six ratios and the synchromesh gearbox  12  will provide four range ratios. These ratios are changed hydraulically by pressurised fluid provided from a hydraulic source  14  which includes a hydraulic pump etc. The ratio changes are controlled by solenoid operated hydraulic control valves  15  associated with epicyclic gearbox  10  and similar valves  16  associated with synchromesh box  12 . These valves are in turn operated by electrical signals from a microprocessor control unit  17  via lines  18  and  19  respectively. 
         [0014]    The forward and reverse clutches F and R are also hydraulically operated with pressure from source  14  and are controlled by solenoid operated valves  20  and  21  respectively via lines  22  and  23 . 
         [0015]    Microprocessor control unit  17  receives inputs from the following driver operated controls and from other sensors on the tractor. 
         [0016]    A so-called shuttle lever  24 , designed to be operated by the driver&#39;s left hand, controls both the direction of motion of the tractor (i.e. forward or reverse) and also the operative ratio in the selected direction. A sensor (not shown) which indicates the position of lever  24  is connected to microprocessor control unit  17  via line  28 . Lever  24  has a central neutral zone  25  (shown in  FIG. 1 ), a forward zone of operation  26  and a reverse zone of operation  27 . When in the forward zone of operation  26  the associated transmission can be changed up a ratio in the forward direction each time the lever  24  is moved in the UF direction and down a ration each time the lever  24  is moved in the DF direction. Similarly when in the reverse zone of operation the associated transmission can be changed up a ratio in the reverse direction each time the lever  24  is moved in the UR direction and down a ratio each time the lever  24  is moved in the DR direction. These movements of lever  24  trigger all the necessary operations of the ratio changing valves  15  and  16  and the clutch valves  20  and  21  to make the requested ratio changes The lever  24  also disengages the operative forward or reverse clutch (F, R) if the lever is pulled up towards the operator, as indicated by arrow  24   a.    
         [0017]    The transmission is also controllable by a control lever  30  which when moved in the upward direction U and held displaced in this direction causes the transmission to progressively shift up through the six ratios provided by epicyclical gearbox  11  and, if a range change is required in synchromesh gearbox  12 , the drive can be disconnected by pressing button  31  on the end of lever  30  to disengage either the forward or reverse drive clutch F or R depending on which clutch is currently operative. Thus, with the lever  30  displaced in the upward direction U each pressing of button  31  causes the transmission to shift up a range in the gearbox  12 . The transmission can be caused to shift quickly up through the ratios provided by box  11  by quickly pulsing the lever  30  in direction U, each pulsing movement of lever  30  producing a change up in ratio. Similarly, movement of lever  30  in the down change direction D results in progressive changes down in ratio with the same facility to quickly change down one ratio at a time by pulsing the lever  30  in the D direction. Also each pressing of the button  31  with the lever displaced in the downward direction D causes the transmission to shift down a range in gearbox  12 . Lever  30  is provided with a position sensor  30   a  which is connected to control unit  17  via line  32 . 
         [0018]    A hand throttle lever  33  is also provided which sets the engine speed and which is mechanically linked with a throttle pedal  33   a  which has a sensor  33   b  which is connected to control unit  17  via line  34 . A clutch pedal  35  is also provide which when pressed disconnects the operative forward or reverse clutch F or R to disconnect drive through the transmission. This pedal, which also has a sensor  35   a  connected with the control unit  17 , is used primarily when starting the vehicle and as an emergency method of disconnecting drive. 
         [0019]    A further transmission controller is provided in the form of a dial  40  (see  FIGS. 2 and 3  ) which has a datum indicator  41  which is rotatable in two selection zones, a field working zone  42  entered by clockwise rotation from a central position  43  and a road working zone  44  entered by anti-clockwise rotation from central position  43 . 
         [0020]    When in the dial is set in the central position  43  the transmission operates in a manual selection mode in which there is no matching of the speed when a range changes occur. Thus, for example, if the transmission is in the sixth speed of the epicyclic box  11 , and the range is changed (by operating button  31 ) from range  1  to range  2 , the transmission will change to operating in the sixth ratio of box  11  and range  2  which is not the next higher transmission ratio overall. When the dial is in the central position  43  basic protection is provided to prevent ratios being engaged which could result in overspeeding of the transmission or engine. 
         [0021]    Either side of the central position  43  are two so-called “speed matching” zones  45  and  46  in which the above problem when changing between ranges is automatically catered for and the transmission selects the appropriate transmission in box  11  and box  12  to ensure that the next overall ratio of the transmission is selected. 
         [0022]    Still further from the central position  43  are two so-called “autodrive” zones  47  and  48  in which the transmission operates as an automatic transmission with the speed at which the ratios are changed up being selected by the position of the dial  40  so that, for example, speed changes at between 1600 rpm and 2200 rpm can be selected by the driver. 
         [0023]    When the tractor is operating with the dial set in the autodrive field working zone  47  the transmission can only operated automatically for changes within the epicyclic box  11  at the selected change up speed. This change up speed can by varied on the go by the operator in a continuous manner for all speeds in the 1600 to 2200 rpm range. If a range change is required the button  31  must be depressed. 
         [0024]    When the transmission is operating with the dial set in the autodrive road working zone  48  the transmission can be operated automatically for all ratio changes in box  11  and all range changes in box  12  without the need to operate the button  31 . Again these changes are made at the speed selected on dial  40  which can again be changed in continuous manner on the go. 
         [0025]    With the dial  40  in the field working zone  42  the lever  24  can only select ratio changes in the epicyclic box  11  and any range changes would require the use of pedal  35  or button  31  to disconnect the drive through the transmission. 
         [0026]    The console in which dial  40  is mounted also includes a set of indicator lights  50  which indicate which range is currently operating. 
         [0027]    The speeds at which the transmission changes down when operating automatically may conveniently be linked to the selected change-up speed. For example, the change down speed may be arranged to be initiated when the engine speed has fallen to 20% below the selected change-up speed. 
         [0028]    Although the invention has been described above in relation to a control member in the form of a dial  40 , the control member may take any other convenient form. For example, it may comprise a lever moveable linearly in opposite direction from a control position in its field and road working zones.