Patent Publication Number: US-6986295-B2

Title: Transmission for work vehicle having PTO function

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a transmission for a work vehicle having PTO function for transmitting a force to an implement mounted on a vehicle body. 
   2. Description of the Related Art 
   With the transmission of the above-noted type, conventionally, as known from e.g. Japanese Patent Application “Kokai” No.: Sho. 58-102848 (FIGS. 1 and 3), a drive force from an engine is divided between a vehicle traveling force and an implement driving force through first and second multiple-plate friction clutches and an intermediate transmission shaft included in the first multiple-plate friction clutch, respectively. The implement driving force from the intermediate transmission shaft is inputted to a PTO change-speed mechanism housed in a transmission case, so that the force is subjected to a change-speed operation by this PTO change-speed mechanism and then this speed-reduced force is transmitted to a rear PTO shaft. On the other hand, the vehicle traveling force from the first and second multiple-plate friction clutches is subjected to an auxiliary change-speed operation by an auxiliary change-speed mechanism including small and large gears mounted on a change-speed shaft and a shift gear mounted on a bevel-pinion shaft and then this force is transmitted to a rear-wheel differential mechanism. 
   In the case of this conventional work vehicle transmission having PTO function, in the number of speeds available from the auxiliary change-speed mechanism is to be increased, this will result in enlargement of the auxiliary change-speed mechanism, thus requiring a large space for accommodating the mechanism. This then requires enlargement of the differential case. Such enlargement of the differential case results in increase of the wheel base of the vehicle. For avoiding such increase of wheel base, there arises the necessity of reducing the length of the transmission case which is formed separately from the differential case and which accommodates such mechanisms as a main change-speed unit for traveling, a reduction mechanism for the implement. However, if the length of the transmission case is reduced, this will impose significant restriction in the spatial arrangement of the above-described components accommodated within the case. 
   In the case of a further conventional transmission known from Japanese Utility Model Application “Kokai” No. Hei. 1-11550 (FIGS. 3 and 5), a rear PTO shaft (shown at 1 in FIGS. 3 and 5 of the document) is disposed at a rear portion of the vehicle body and a mid PTO shaft (shown at 3 in FIGS. 3 and 5) is disposed forwardly of the rear PTO shaft. With this arrangement, for instance, if a lawn mower implement is disposed between the front wheels and the rear wheels and a grass collector and a blower are disposed on the rear portion of the vehicle body, the lawn mower implement can be driven by the mid PTO shaft and the blower can be driven by the rear PTO shaft so that grass or lawn cut by the mower can be drawn by the blower to be collected into the collector. With the work vehicle having this type of transmission, there often occurs a situation of the lawn mower implement being driven by the force from the mid PTO shaft. For this reason, it is necessary to transmit high-speed force to the mid PTO shaft and to dispose this mid PTO shaft at a low position. Further, the force from the engine is transmitted to a transmission gear (shown at 38 in FIGS. 3 and 5) and force from this transmission gear is transmitted from a switchover slider (shown at 36 in FIGS. 3 and 5) through a retaining portion and a transmission shaft (shown respectively at 37 and 11 in FIGS. 3 and 5) to the rear PTO shaft. The force from the transmission gear (shown at 38 in FIGS. 3 and 5) is transmitted via the switchover slider (shown at 36 in FIGS. 3 and 5) through transmission gears (shown at 35, 42 in FIGS. 3 and 5) to the mid PTO shaft disposed at the low position. In this case, the transmission gears are set to provide an accelerating gear ratio for transmitting a high-speed force to the mid PTO shaft. With the transmission of the above construction, a transmission gear is mounted coaxially relative to a transmission gear receiving the power from the engine, which transmission gear is meshed with a transmission gear mounted on the mid PTO shaft. In this case, there is a limit in possible enlargement of the transmission gear for transmitting high-speed force to the mid PTO shaft (this is probably attributable to the fact the transmission gear acts as a point of force division between the force to the rear PTO shaft and the force to the mid PTO shaft). Hence, it is necessary to allow transmission of high-speed force to the mid PTO shaft by minimizing the diameter of the transmission gear mounted on the mid PTO shaft. However, if this transmission gear (shown at 3 in FIGS. 3 and 5) mounted on the mid PTO shaft is reduced in diameter, this will result in corresponding rising of the disposing position of the mid PTO shaft. 
   SUMMARY OF THE INVENTION 
   In view of the above, a primary object of the present invention is to provide a transmission for a work vehicle having PTO function, which allows transmission of PTO driving force in speed reduced state to the rear PTO shaft and which also allows the differential case area to be formed compact. Further, in the case of a type of transmission in which a rear PTO shaft is disposed at a rear portion of a vehicle body and a mid PTO shaft is disposed forwardly of the rear PTO shaft, an object of the invention is to allow the mid PTO shaft to be disposed at a as low as possible position and to allow transmission of high-speed force to the mid PTO shaft also. 
   For accomplishing the above-noted objects, a transmission for a work vehicle having PTO function, according to the present invention, comprises:
         a first transmission shaft for receiving engine power through a PTO power train;   a second transmission shaft for receiving the engine power through a traveling power train, said second transmission shaft being coupled to a rear differential mechanism;   a third transmission shaft coupled to a rear PTO;   a fourth transmission shaft for receiving force from the second transmission shaft;   a first gear transmission mechanism for transmitting the force from the first transmission shaft to the third transmission shaft;   said first gear transmission mechanism including;
           an input gear mounted on the first transmission shaft,   an output gear mounted on the third transmission shaft, and   a relay gear loosely mounted on the second transmission shaft for transmitting the force from the input gear to the output gear;   
           a second gear transmission mechanism for transmitting the force from the second transmission shaft to the fourth transmission shaft; and   said second gear transmission mechanism including;
           an input gear mounted on the second transmission shaft,   an output gear mounted on the fourth transmission shaft, and   a relay gear loosely mounted on the third transmission shaft for transmitting the force from the input gear to the output gear.   
               

   With the above-described construction, the relay gear of the first gear transmission mechanism for transmitting the force of the first transmission shaft as the PTO driving force to the third transmission shaft utilizes the second transmission shaft for its loose (rotatable) mounting thereof. And, the relay gear of the second transmission mechanism for transmitting the force of the second transmission shaft as the vehicle traveling force to the fourth transmission shaft utilizes the third transmission shaft for its loose (rotatable) mounting thereof. With this, the rear wheel differential area of the transmission is formed compact. 
   According to one preferred embodiment of the present invention, the transmission further comprises a mid PTO shaft and a third gear transmission mechanism for transmitting the force from the first gear transmission mechanism to the mid PTO shaft, and said third gear transmission mechanism includes an output gear mounted on the mid PTO shaft, a first relay gear loosely mounted on the third transmission shaft for receiving the force from the first gear transmission mechanism and a second relay gear loosely mounted on the fourth transmission shaft and meshing with said first relay gear and said output gear. 
   With the above construction, the third transmission shaft and the fourth transmission shaft are interposed between the second transmission shaft coupled to the rear wheel differential mechanism and the mid PTO shaft, and the force from the first gear transmission mechanism is transmitted via the third gear transmission mechanism to the mid PTO shaft. Accordingly, the mid PTO shaft can be disposed at a low position. 
   With the invention&#39;s feature as above, the gear ratio of the third gear transmission mechanism can be selected relatively freely. Hence, high-speed force may be transmitted to the mid PTO shaft. In this case, since the output gear of the third transmission mechanism has a small diameter, there is obtained another auxiliary advantage that the outer peripheral portion of the output gear does not project significantly downward from the mid PTO shaft (i.e. the case covering the mid PTO shaft and the input gear does not project downward significantly). 
   According to a further preferred embodiment of the present invention, said first transmission shaft mounts a PTO clutch. With this, by selectively operating this PTO clutch into a transmitting condition or a non-transmitting condition, the third transmission shaft coupled to the rear PTO and the mid PTO shaft can be driven or stopped as the same time. Therefore, in the case of the aforementioned construction in which a lawn mower implement is disposed between the front wheels and the rear wheels and a grass collector and a blower are disposed on the rear portion of the vehicle body, the lawn mower can be driven by the mid PTO shaft and the blower can be driven by the rear PTO shaft so that grass or lawn cut by the mower can be drawn by the blower to be collected in the collector, by selectively operating the PTO cutch into the transmitting condition or the non-transmitting condition, the mower implement and the blower can be driven or stopped at the same time. 
   According to a still further preferred embodiment of the present invention, the transmission further comprises a mid PTO clutch interposed between the third gear transmission mechanism and the mid PTO shaft. With this construction, by selectively operating this mid PTO clutch into the transmitting condition or the non-transmitting condition, the mid PTO shaft can be driven or stopped independently. Therefore, in case no implement is provided between the front and rear wheels but an implement is provided at a rear portion of the vehicle body, by operating the mid PTO clutch into the non-transmitting condition, such inconvenience of the mid PTO shaft being driven unnecessarily can be avoided. 
   According to a still further preferred embodiment of the present invention, said relay gear of the first gear transmission mechanism includes a gear portion meshing with the input gear of the first gear transmission mechanism, a further gear portion meshing with the output gear of the first gear transmission mechanism and a still further gear portion meshing with the first relay gear of the third gear transmission mechanism. With this construction, the construction of the first gear transmission mechanism for transmitting the force to both the third transmission shaft and the third gear transmission mechanism can be formed compact. 
   Further and other features and advantages of the present invention will become apparent upon reading the following detailed disclosure of the invention with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an overall side view of a tractor, 
       FIG. 2  is a schematic showing an inside of a transmission case, 
       FIG. 3  is a side view in vertical section showing vicinity of a PTO transmission gear of the transmission case and an output case, 
       FIG. 4  is a front view in vertical section showing the vicinity of a PTO transmission gear of the transmission case and the output case, 
       FIG. 5  is a schematic of a transmission relating to a further embodiment of the invention, and 
       FIG. 6  is a section view showing a rear area of the transmission relating to the further embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a tractor, as an example of a work vehicle, having a vehicle body supported on front wheels  1  and rear wheels  2 , an engine  3  mounted on the body and a transmission case  4  mounted also on the body and connected to the engine  3 . As shown in  FIG. 1  and  FIG. 2 , the transmission case  4  comprises an interconnected assembly of a first case portion  4   a , a second case portion  4   b , a third case portion  4   c  and a fourth case portion  4   d  in the mentioned order from the front side of the case. 
   Next, a vehicle traveling power train for transmitting engine power to the rear wheels  2  will be described. 
   As shown in  FIG. 2 , the first case portion  4   a  accommodates therein a main clutch  5  which receives the power from the engine  3 . The second case portion  4   b  of the transmission case  4  accommodates transmission gears  6 ,  7  and a hydrostatic stepless change-speed unit (HST)  8 . And, the force from the main clutch  5  is transmitted via the transmission gears  6 ,  7  to an input shaft  8   a  of the HST  8 . This HST  8 , when moved from its neutral position, can change speed of the force in stepless manner to a high speed side or to low speed side. 
   As shown in  FIG. 2 , the third case portion  4   c  of the transmission case  4  accommodates therein transmission shafts  9 ,  10 , and an output shaft  8   e  of a hydraulic motor  8   c  of the HST  8  is coupled via a coupling  11  to the transmission shaft  9 . This transmission shaft  9  fixedly mounts thereon a low speed gear  12 , a mid speed gear  13  and a high speed gear  14 . Whereas, the transmission shaft  10  loosely or rotatably mounts thereon transmission gears  15 ,  16  which are meshed with the low speed gear  12  and the high speed gear  14 . A shift gear  17  is mounted, via a splined connection, on this transmission shaft  10  to be slidable thereon and rotatable therewith. These constitute a gear change-speed unit for changing the rotation of the output shaft  8   e  of the hydraulic motor  8   c  of the HST  8  in three speeds by sliding the shift gear  17  for meshing the transmission gears  15 ,  16  and the mid speed gear  13 . And, a speed-changed output from this unit is then transmitted to the transmission shaft  10 . That is to say, this gear change-speed unit, the HST  8  and the transmission shaft  10  together constitute a traveling power train section  100  as a forward half portion of the vehicle traveling power train. 
   As shown in  FIGS. 2 and 3 , the fourth case portion  4   d  of the transmission case  4  accommodates therein a rear wheel transmission shaft  18  (to be referred to as “second transmission shaft” hereinafter) and a rear wheel differential mechanism  19  directly coupled with this second transmission shaft  18 . Further, the transmission shaft  10  is coupled via a coupling  20  to this second transmission shaft  18 . With the above-described construction in operation, the power of the engine  3  is transmitted to the rear wheels  2  via the main clutch  5 , the HST  8  (the output shaft  8   e  of the hydraulic motor  8   c  of the HST  8 ) (steplessly changed in speed to high speed side in the forward drive direction and to high speed side in the reverse drive direction), the transmission shafts  9 ,  10  (changed in three speeds), the second transmission shaft  18  and the rear wheel differential mechanism  19 . 
   Next, a transmission line to the front wheels  1  will be described. 
   As shown in  FIGS. 2 and 3 , a transmission gear  21  is fixedly mounted on the second on the second transmission shaft  18 . The fourth case portion  4   d  of the transmission case  4  accommodates therein a transmission shaft (to be referred to as “third transmission shaft” hereinafter)  22 . A transmission gear  23  rotatably mounted on the third transmission gear shaft  22  is meshed with the transmission gear  21 . As shown in  FIGS. 1 ,  2  and  3 , an output case  24  is connected to a lower portion of the fourth case portion  4   d  of the transmission case  4 . This output case  24  accommodates therein a fourth transmission shaft  25  as a front wheel transmission shaft. As shown in  FIG. 4 , the fourth transmission shaft (front wheel transmission shaft)  25  and the third transmission shaft  22  are disposed at a right/left center C of the vehicle body. 
   As shown in  FIGS. 2 ,  3  and  4 , a shift gear  26  is fitted, by a splined connection, on the front wheel transmission shaft  25  to be slidable thereon and rotatable therewith. The shift gear  26  is slidable to a transmission position to be meshed with the transmission gear  23  and a released position released from this transmission gear  23 . Further, the front wheel transmission shaft (fourth transmission shaft)  25  includes a detent mechanism  27  for retaining the shift gear  26  at the transmitting position (the position shown in  FIG. 3 ) or at the released position (a position on the right side from the position shown in  FIG. 3 ). In this embodiment, the second gear transmission mechanism  60  for transmitting the force from the second transmission shaft  18  to the front wheel transmission shaft (fourth transmission shaft)  25  consists essentially of the transmission gear (input gear)  21 , the further transmission gear (relay gear)  23  and the shift gear (output gear)  26 . 
   As shown in  FIG. 4 , to the left side of the output case  24 , a control shaft  28  is rotatably supported. And, an arm  28   a  secured to this control shaft  28  is meshed with the shift gear  26 . A control rod  29  connected to the control shaft  28  projects upward from the left side of a floor  30  (see  FIG. 1 ). Then, when the control rod  29  is pulled up, the control shaft  28  operates the shift gear  26  into the transmitting position. When the control rod  29  is pushed down, the control shaft  28  operates the shift gear  26  into the released, i.e. non-transmitting, position. With the above-described construction, the force of the second transmission shaft  18  is transmitted to the front wheels  1  via the transmission gears  21 ,  22 , the shift gear  26 , the front wheel transmission shaft (fourth transmission shaft)  25  and a front wheel differential mechanism not shown). 
   Next, there will be described a rear PTO shaft  31  having a rear PTO coupling (to be referred to also as “rear PTO”) at a free end thereof. 
   As shown in  FIGS. 2 ,  3  and  4 , this rear PTO shaft  31  is accommodated in the fourth case portion  4   d  of the transmission case  4 . And, the third transmission shaft  22  is coupled via a coupling  32  to this rear PTO shaft  31 . The rear PTO shaft  31  projects rearward from the fourth case portion  4   d  of the transmission case  4 . 
   As shown in  FIGS. 2 and 3 , the third case portion  4   c  of the transmission case  4  accommodates therein a transmission shaft  33 . A pump shaft  8   d  of a hydraulic pump  8   b  of the HST  8  is coupled via a coupling  34  to this transmission shaft  33 . That is, the pump shaft  8   d  receiving the engine power and the transmission shaft  33  together constitute a PTO power train section  200  as a forward half portion of the PTO driving power train. The fourth case portion  4   d  of the transmission case  4  accommodates therein a transmission shaft (to be referred to as “first transmission shaft”)  35 . And, between this first transmission shaft  35  and the transmission shaft  33 , there is provided a PTO clutch  36 . This PTO clutch  36  includes an engaging portion  36   a  splined on the transmission shaft  33  to be rotatable therewith and slidable thereon, a further engaging portion  36   b  splined on the first transmission shaft  35  to be rotatable therewith and slidable thereon, and a spring  36   c  for urging the engaging portion  36   a  toward the further engaging portion  36   b.    
   As shown in  FIGS. 2 and 3 , the second transmission shaft  18  rotatably mounts a PTO transmission gear  37 . This PTO transmission gear  37  comprises an integrated assembly of an input gear portion  37   a , a rear PTO gear portion  37   b  and a mid PTO gear portion  37   c . The input gear portion  37   a  of the PTO transmission gear  37  is meshed with a transmission gear  35   a  mounted on the first transmission shaft  35 . The rear PTO gear portion  37   b  is meshed with a transmission gear  38  fixed on the third transmission shaft  22 . Hence, in this embodiment, a first gear transmission mechanism  50  for transmitting the force of the first transmission shaft  35  to the third transmission shaft  22  includes the transmission gear (input gear)  35   a , the transmission gear (output gear)  38 , and the input gear portion  37   a  and the rear PTO gear portion  37   b  of the PTO transmission gear  37  acting as a relay gear loosely mounted on the second transmission shaft  18 . 
   With the above-described construction in operation, as shown in  FIGS. 2 and 3 , the power of the engine  3  is transmitted to the rear PTO shaft  31  via the main clutch  5 , the HST  8  (the pump shaft  8   d  of the hydraulic pump  8   b  of the HST  8 ) (the HST  8  does not effect any change speed, but the force transmitted to the input shaft  8   a  thereof is outputted directly from the HST  8  (the output shaft  8   d  of the hydraulic pump  8   b  of the HST  8 )), the transmission shaft  33 , the PTO clutch  36  (under the transmitting condition), the first transmission shaft  35 , the transmission gear  35   a , the PTO transmission gear  37 , the transmission gear  38  and the third transmission shaft  22 . 
   As shown in  FIGS. 2 and 3 , when the engaging portion  36   a  is operated to be released from the engaging portion  36   b  in the PTO clutch  36 , this PTO clutch  36  is operated into the non-transmitting condition, so that the rear PTO shaft  31  is stopped. Further, in the transmitting condition of the PTO clutch  36 , if a significant load is applied to the rear PTO shaft  31 , the engaging portion  36   a  is slid against the urging force of the spring  36   c  to be released from the engaging portion  36   b , whereby the PTO clutch  36  is automatically operated into the non-transmitting condition. 
   Next, the mid PTO shaft  39  will be described. 
   As shown in  FIGS. 1 ,  2 ,  3  and  4 , in the output case  24 , at a position downwardly of the front wheel transmission shaft  25  and offset to the right side from the right/left center C of the vehicle body, this mid PTO shaft  39  is provided. The mid PTO shaft  39  projects forwardly from the output case  24 . With this, the mid PTO shaft  39  is disposed forwardly of the rear PTO shaft  31 . 
   As shown in  FIGS. 2 ,  3  and  4 , the third transmission shaft  22  rotatably mounts a transmission gear  40 . This transmission gear  40  is meshed with the mid PTO gear portion  37   c  of the PTO transmission gear  37 . The front wheel transmission shaft  25  rotatably mounts a large mid gear  41 , which is meshed with the transmission gear  40 . The mid PTO shaft  39  rotatably mounts a small transmission gear  42 , which is meshed with the mid gear  41 . 
   As shown also in  FIGS. 2 ,  3  and  4 , a shift member  43  is splined on the mid PTO shaft  39  to be rotatable therewith and a slidable thereon. This shift member  43  is slidable to a transmitting position to be meshed with the transmission gear (input gear)  42  and a released position released therefrom. Further, the mid PTO shaft  39  includes a detent mechanism  44  for retaining the shift member  43  at the transmitting position (the position shown in  FIG. 3 ) or the non-transmitting position (position on the right slide from the position shown in  FIG. 3 ). 
   Hence, in this embodiment, a third gear transmission mechanism  70  for transmitting the force of the first gear transmission mechanism  50  i.e. the force from the PTO transmission gear  37 , to the mid PTO shaft  39  includes the transmission gear (output gear)  42  having the shift member  43 , the transmission gear (first relay gear)  40  meshed with the mid PTO gear portion  37   c  of the PTO transmission gear  37  and loosely mounted on the third transmission shaft  22 , and the mid gear (second relay gear)  41  meshed with the first relay gear  40  and the output gear  42  and loosely mounted on the fourth transmission shaft  25 . 
   As shown in  FIG. 4 , to the right side of the output case  24 , a control shaft  45  is rotatably supported. And, an arm  45   a  secured to this control shaft  45  is engaged with the shift member  43 . A control rod  46  connected to the control shaft  45  projects upward from the left side of the floor  30  (see  FIG. 1 ). Then, when the control rod  46  is pulled up, the control shaft  45  operates the shift member  43  into the transmitting position. When the control rod  46  is pushed down, the control shaft  45  operates the shift member  43  into the released, i.e. non-transmitting, position. 
   With the above-described construction, when the force is transmitted to the rear PTO shaft  31 , at the same time, as shown in  FIGS. 2 and 3 , the force of the first transmission shaft  35  is transmitted to the mid PTO shaft  39  via the transmission gear  35   a , the PTO transmission gear  37 , the transmission gear  40 , the mid gear  41 , the input gear  42  and the shift member  43 . Further, when the PTO clutch  36  is operated into the non-transmitting condition, the rear PTO shaft  31  and the mid PTO shaft  39  are stopped. Further, in the transmitting condition of the PTO clutch  36 , if a significant load is applied to the rear PTO shaft  31  or the mid PTO shaft  39 , the engaging portion  36   a  is slid against the urging force of the spring  36   c  to be released from the engaging portion  36   b , whereby the PTO clutch  36  is automatically operated into the non-transmitting condition. Moreover, under the transmitting condition of the PTO clutch  36  (i.e. the condition when the force is transmitted to the rear PTO shaft  31  and the mid PTO shaft  39 ), if the shift member  43  is operated into the non-transmitting condition, the mid PTO shaft  39  alone can be stopped. 
   In this case, as shown in  FIGS. 2 and 3 , for instance, if the rear PTO gear portion  37   b  of the PTO transmission gear  37  is designed to have ‘15’ (fifteen) teeth and the transmission gear  38  is designed to have ‘27’ (twenty seven) teeth, then, the mid PTO gear portion  37   c  of the PTO transmission gear  37  is designed to have ‘22’ (twenty two) teeth, the transmission gear  40  is designed to have ‘21’ (twenty one) teeth, the mid gear  41  is designed to have ‘36’ (thirty six) teeth, and the input gear  42  is designed to have ‘11’ (eleven) teeth, respectively. With these settings, a force of a higher speed than the rear PTO shaft  31  is transmitted to the mid PTO shaft  39  (for instance, 540 rpm for the rotation of the rear PTO shaft  31  and 2000 rpm for the rotation of the mid PTO shaft  39 ). 
   A further embodiment of the transmission relating to the present invention will be described next with reference to  FIGS. 5 and 6 . 
   Relative to the foregoing embodiment, this further embodiment differs in that the mid PTO shaft is eliminated. Therefore, the third gear transmission mechanism  70  is also absent in this further embodiment. Correspondingly, the PTO transmission gear  37  used in the foregoing embodiment comprising the integrated assembly of the input gear portion  37   a , the rear PTO gear portion  37   b  and the mid PTO gear portion  37   c  is now replaced by a different PTO transmission gear  370  comprising an integrated assembly of an input gear portion  371  and a rear PTO gear portion  372  alone. The rest of the construction is identical to that of the foregoing embodiment, hence, will not be described, with only the reference numerals being provided in the figures. 
   In addition to the tractor described above, the invention&#39;s transmission can be applied also to any other agricultural vehicle or machinery such as a rice planter, a farm managing machine or vehicle or to any construction work machine or vehicle. 
   The present invention may be embodied in any other manner than described above. Various modifications thereof will be apparent to those skilled in the art, without departing the essential features thereof defined in the appended claims.