Abstract:
An oil supply system for a transmission includes a transmission casing; a transmission shaft disposed in the transmission casing; a plurality of gears relatively rotatably fitted on the transmission shaft; an oil passage axially formed in the transmission shaft; a trough portion formed on an inside wall of the transmission casing so as to receive oil splashed from the gears; and a connection passage formed in a side wall of the transmission casing and extending downwardly from the trough portion to the oil passage. The oil passage is opened at outer peripheral portions of the transmission shaft adjacent to the gears, and opened at one axial end of the transmission shaft. The trough portion is disposed above the transmission shaft and is extended axially along the transmission shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 10/603,750, filed Jun. 26, 2003 now abandoned, which is a continuation of application Ser. No. 09/942,556, filed Aug. 31, 2001, now U.S. Pat. No. 6,616,563, issued Sep. 9, 2003, the entire disclosures of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure of a transmission comprising a belt-type continuously variable transmission (hereafter referred to as ‘CVT’), which is suitable for a working vehicle. 
     2. Background Art 
     A conventional working vehicle, e.g., a truck, includes a belt-type CVT connecting an output shaft of an engine and an input shaft of the transmission such that rotation of the output shaft of the engine is transmitted to its axles and drives them. In this vehicle structure, a sensing mechanism is provided at the CVT and detects rotary speed or load of the engine so as to automatically steplessly reduce/increase the speed reduction ratio according to the increase/decrease of rotary speed of the engine or the decrease/increase of the engine load. 
     In addition, it is well-known to laterally mount an engine on a vehicle so as to locate its crankshaft perpendicular to the longitudinal direction of the vehicle and in parallel to an input shaft of a transmission, an output shaft of the transmission, and axles. This described vehicle structure especially facilitates interposing a belt-type CVT between the crankshaft of the engine and the input shaft of the transmission because both shafts are parallel to each other. Moreover, the transmission in this vehicle structure may transmit power via economical spur wheels because shafts therein are disposed parallel to one another. Therefore, the vehicle structure is advantageous in contributing to the reduction of assembly and material costs. 
     An object of the invention is to provide a transmission for a working vehicle that is simplified so that the manufacturing costs can be more and more reduced. 
     Further, conventional transmissions with differential locking mechanisms provide a shaft for operating the differential locking mechanism that is axially, slidably supported and is disposed parallel to the axles. The differential locking slider is engaged with a fork fixed onto the shaft so as to slide the differential locking slider integrally with the shaft, thereby switching between a differential-locking mode and a differential-unlocking mode. 
     However, in the above conventional structure, the fork engaged with the differential locking slider is apt to be large, thereby inhibiting miniaturization of the transmission. And, because a space inside of the transmission housing is required for straightly moving such a large fork back and forth at a set stroke to operate the differential locking slider, further miniaturization of the transmission is difficult. 
     BRIEF SUMMARY OF THE INVENTION 
     The transmission of the present invention is applied to a working vehicle having an engine mounted on a bodywork frame such that a crankshaft of the engine is disposed horizontal to the ground and is perpendicular to the longitudinal direction of the vehicle. The transmission comprises an input shaft for receiving power of the engine through a CVT, an output shaft disposed in parallel with the input shaft, a pair of left and right axles aligned with and extending out opposite to each other and in parallel with the output shaft, a differential connecting the left and right axles with each other in a differential manner, a transmission housing containing the differential, a pair of left and right axle housings mounted onto left and right faces of the transmission housing respectively, each of which houses each of the pair of axles, having mounting portions for mounting to the bodywork frame, and a wet-type disc brake device provided around a portion of the axles covered by the axle housings. Therefore, a load, which is applied to drive wheels fixed on the axles, can be supported by the transmission housing through the axle housings, thereby simplifying the structure of a vehicle. And, in comparison with the conventional structure having an output of a differential that is transmitted to the drive wheels through universal joints and a dry-type brake device, manufacturing costs can be reduced. Furthermore, due to the wet type disc brake device, durability and reliability of the brake device can be improved. 
     The input shaft is disposed closer to the engine than said axles in the longitudinal direction of the vehicle. Therefore, the position of the input shaft, while keeping a required distance from the axles, can be lower than that when being above the axles. Due to this arrangement, even if the amount of lubricating oil in the transmission housing is small, splash lubrication for the input shaft can be sufficient. Consequently, the amount of lubricating oil can be saved, thereby reducing manufacturing costs and weight of the transmission. And, when the present invention is applied to a transmission of a truck, its deck can be located at a low position, thereby improving capacity of the deck and sinking the center of gravity of the truck. 
     The transmission further comprises a drive train which can switch the rotational direction of the output shaft in relation to the rotational direction of the input shaft, wherein the drive train drivingly connects the input shaft with a portion of the output shaft, which is nearer to one end of the output shaft, a prime rotary object provided on the output shaft nearer to other end of the output shaft, a follower rotary object serving as an input means of said differential, the follower rotary object being engaged with the prime rotary object, and a centrifugal governor for changing the output of the engine according to the variation of the rotational speed of the input shaft, the centrifugal governor being disposed at a portion of the input shaft facing toward the prime rotary object. Therefore, by the adoption of the centrifugal governor which is smaller and less expensive than a torque governor, manufacturing costs of the transmission can be saved and compactness thereof can be improved. And, because the centrifugal governor is placed at empty space inside of the transmission housing, a layout of the transmission can be simple and space-saving, thereby further improving compactness of the transmission. 
     The transmission further comprises a pair of left and right transmission housing parts into which the transmission housing is laterally dividable through a surface which is perpendicular to a longitudinal direction of said axles, wherein the differential is supported at its left and right portions by the left and right transmission housing parts, respectively, and bearings provided at outer ends of the respective axle housings, wherein the bearings support outward portions of the axles projecting leftward and rightward from the differential. Therefore, because the differential can be directly supported by the transmission housing without intervention of the axles, when manufacturing of the transmission, a convenient assembling method (i.e., a method of putting in axles after fixing the differential to the transmission housing by joining together of left and right housing parts) can be adopted. Furthermore, since outward portions of the axles are supported by the axle housings through the bearings, the weight of the vehicle can be surely supported by the axles through the axle housings. 
     A portion of at least one of said the housings to be attached to the transmission housing is expanded so as to be bowl-like shaped. The wet-type disc brake is disposed in the bowl-like shaped portion of the axle housing, and an arm for operating the wet-type disc brake is disposed outside the bowl-like shaped portion of the axle housing. Therefore, because a room which houses the wet-type disc brake (i.e. the bowl-like shaped portion) is integrally formed with the axle housing, manufacturing costs of the transmission can be reduced. And, because the arm for operating the wet-type disc brake is disposed outside the bowl portion of the axle housing, the operating system from the arm to wet-type disc brake can be compactly and simply formed. 
     A transmission of a working vehicle comprises a differential, a transmission housing containing the differential, a pair of left and right axles connected with each other in a differential manner by the differential, an axle housing mounted onto one of left and right faces of the transmission housings to support one of the axles, wherein a joint space is formed in a joint portion between the transmission housing and the axle housing, a differential locking slider which can switch between a differential mode for connecting the left and right axles with each other in a differential manner and a differential-locking mode for integrally connecting the axles, a friction disc provided on the axle supported by the axle housing, and a pressure member which pushes the friction disc so as to brake the axle, wherein the pressure member and the differential locking slider are disposed substantially coaxially with each other in the joint space. Therefore, the differential locking slider and the pressure member can be arranged in a compact length of longitudinal direction of the axles, thereby contributing to space-saving of the transmission. 
     A guide portion for axially slidably supporting said pressure member is provided in a flanged portion formed on an outer side wall of the transmission housing for mounting the axle housing, the differential locking slider is disposed in the guide portion, and a round wall of the guide portion is partly notched such that an arm for operating the differential locking slider is inserted through the notched portion. Therefore, because the pressure member is supported by the guide portion and the differential locking slider is located inside of the guide portion, both of them can be apportioned between inside and outside of the guide portion in a compact mass. And, because the round wall of the guide portion is partly notched and the arm for operating the differential locking slider is inserted through the notched portion, the simple structure for operating the differential locking slider located in the guide portion from the outside of the guide portion can be achieved. 
     The pressure member is rotatable along said round wall of said guide portion by a brake operating shaft supported by said axle housing, and a cam body, which thrusts the pressure member in correspondence to as rotational degree of the pressure member, is supported around the round wall of the guide portion. Therefore, since the pressure member rotates while it is guided by an outer peripheral surface of the round wall of the guide portion, a special structure for axial alignment of the pressure member can be eliminated. And, since the cam body is supported around the round wall of the guide portion, the compact structure that the pressure member pushes the friction discs by axially sliding while rotating can be achieved. 
     A rotational axis of the arm for operating the differential locking slider is disposed at a position which is offset from a virtual plane containing the rotational axis of said pressure member, and the brake operating shaft is placed in parallel with the axles on a opposite side to the arm with the virtual plane between. Therefore, an operating system of the differential locking slider and an operating system of the brake device can be compactly arranged and can avoid interruptions with each other, thereby miniaturizing the transmission. 
     Furthermore, the transmission further comprises an input shaft projecting outward from one of left and right sides of said transmission housing and a follower pulley constituting a belt-type CVT disposed onto an outward projecting portion of the input shaft, wherein said differential locking slider is disposed at a position nearer to the other of the left and right sides of the transmission housing. Therefore, an operating system of the differential locking slider can be disposed in a position wherein the operating system can avoid interruptions with the CVT, thereby improving the compactness of the transmission. 
     An oil supply system for the transmission comprises a transmission casing, an output shaft disposed in the transmission casing, a plurality of gears relatively rotatably fitted on the output shaft, an oil passage axially formed in the output shaft, a trough portion formed on an inside wall of the transmission casing so as to receive oil splashed from the gears, and a connection passage formed in a side wall of the transmission casing and extending downwardly from the trough portion to the oil passage. The oil passage is opened at outer peripheral portions of the output shaft adjacent to the gears, and opened at one axial end of the output shaft. The trough portion is disposed above the output shaft and extended axially along the output shaft. In one embodiment, the plurality of gears includes a normal gear and a reverse gear, and an automatic continuously variable belt transmission is disposed outside the transmission casing. The normal gear and the reverse gear are drivingly interposed between the belt transmission and the output shaft so that either the normal gear or the reverse gear is selectively fixed to the output shaft so as to determine one of opposite rotary directions of the output shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a general side view of a truck to which a transmission of the present invention is applied. 
         FIG. 2  is a sectional rear elevation showing the general structure of the transmission and axles. 
         FIG. 3  is a grossly enlarged sectional rear elevation showing the structure in a transmission housing. 
         FIG. 4  is a side view of the transmission. 
         FIG. 5  is a sectional side view of the transmission. 
         FIG. 6  is a sectional side view of the transmission when modified axle housings are attached. 
         FIG. 7  is a general side view of a truck having a transmission wherein a differential locking mechanism is provided. 
         FIG. 8  is a sectional rear development showing the structure in a transmission housing. 
         FIG. 9  is a perspective view showing the state wherein axle housings are detached from a transmission housing. 
         FIG. 10  is a sectional rear view showing a transmission of the type which receives power from an electric motor. 
         FIG. 11  is a segmentary perspective view showing the structure for holding friction discs to an axle housing in the brake device of the transmission of electric motor type. 
         FIG. 12  is a grossly enlarged sectional rear development mainly showing the structure of a clutch fork shaft and an idle gear. 
         FIG. 13  is a sectional side view showing the structure that a differential shift arm is inserted through a partly notched portion of the guide portion. 
         FIG. 14  is a sectional side view mainly showing the structure of a direction-switching shaft. 
         FIG. 15  is a perspective view showing a right housing member composing the transmission housing. 
         FIG. 16  is a perspective view showing a pressure member. 
         FIG. 17  is a sectional plan development showing brake control shafts. 
         FIG. 18  is a sectional rear view showing the structure for leading lubricating oil to an output shaft. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A truck  1  as an embodiment of the present invention is shown in  FIG. 1 . A bodywork frame  10  is disposed in the longitudinal direction of the vehicle. An engine  3  is mounted on the bodywork frame  10  at the rear of an operator&#39;s seat  2 . The engine  3  is disposed such that its crankshaft (as an output shaft of the engine)  6  is horizontally oriented perpendicular to the longitudinal direction of the vehicle. 
     At the rear of the engine  3 , a transmission  4  of the present invention is supported by the bodywork frame  10  through a pair of axle housings  80  (described below). A pair of left and right slender flat boards are disposed in a longitudinal direction of the vehicle and parallel to each other, and the rear end portion of the flat boards are connected with each other, thereby forming the bodywork frame  10  having a U-shape in a plan view. As shown in  FIG. 2 , axle housings  80  are fixed onto the bodywork frame  10  such that a housing  31  of the transmission  4  is located between the left and right flat boards. 
     A deck frame  10   a  is disposed above the transmission  4  and the engine  3 , and is supported by the bodywork frame  10 , such that the truck can carry loads. 
     An input shaft  5  of the transmission  4  projects leftward from the transmission housing  31 . The input shaft  5  is connected to the output shaft  6  of the engine  3  through a belt-type automatically continuous variable transmission (hereinafter referred to as CVT)  7 . A pair of left and right rear axles  8  project outward from both left and right sides of the transmission housing  31 . Each of rear wheels  9  as drive wheels is provided at the outer end of each of the rear axles  8 . 
     A front transaxle case (not shown) is supported at a front portion of the vehicle. The front transaxle case houses a pair of left and right front axles  11 , and a differential (not shown) which connects the front axles  11  with each other in a differential manner. Each of the front axles  11  supports each of front wheels  12  at its outer end. The front wheels  12  are steerable by a steering wheel  13  disposed at the front of the operator&#39;s seat  2 . 
     A switching lever  19 , which is operated to select the direction of travel between forward and backward, is disposed at the side of the steering wheel  13 . A speed-changing pedal  21  is provided at the front of the operator&#39;s seat  2 , and is linked with a throttle valve (not shown) which adjusts the volume of injected fuel. By changing the degree of opening of the throttle valve according to degree of depressing of the speed-changing pedal  21 , the output speed of the engine  3  can be increased or reduced. 
     The power, which is transmitted from the output shaft  6  to the input shaft  5  of the transmission  4  through the CVT  7 , is transmitted into the transmission housing  31  through the input shaft  5 . The power passes through a power transmission way which forming the transmission  4 , and is finally transmitted to the rear wheels  9  through the rear axles  8 , thereby driving the truck  1 . 
     A pair of brake devices (not shown in  FIG. 1 ) are provided in the axle housings  80  so as to brake the pair of left and right rear axles  8 , respectively. Each of the brake devices  22  can be operated by each of a pair of brake control arms  23  which are supported rotatably on each of the left and right axle housings  80 . The brake control arms  23  are interlocked with only one brake pedal (not shown) disposed in the vicinity of the speed-changing pedal  21 , such that the left and right rear axles  8  are braked at the same time by depressing the brake pedal. 
     Next, description will be given on the structure in the transmission housing  31  in accordance with  FIG. 2 . 
     The transmission housing  31 , which houses the transmission  4 , is formed of a pair of left and right housing members  31 L and  31 R (serving as transmission housing parts) which are joined to each other at their flat and peripheral joint faces in a plane which is perpendicular to a longitudinal direction of the rear axles  8 . In the transmission housing  31 , the input shaft  5 , a centrifugal governor  34  which detects the rotational speed of the input shaft  5 , a differential  32  which connects the left and right rear axles  8  in a differential manner, and a direction-of-travel switching mechanism  35  operated by the switching lever  19 , and so on are disposed. 
     The input shaft  5  is laterally and rotatably supported at the midway portion in a vertical direction of the transmission housing  31 . One end of the input shaft  5  projects laterally outward from a left side of the transmission housing  31 . A follower split pulley  36  is provided on the outward projecting portion of the input shaft  5 , such that the follower split pulley  36  serves as an output section of above-mentioned belt-type CVT  7 . 
     The follower split pulley  36  is formed of two pulley members  36   a  and  36   b  which are connected with each other forming torque cam as shown in  FIG. 3 . The two pulley members  36   a  and  36   b  approach each other when torque which resists the rotation of the engine  3  (e.g. torque generated at the rear wheels  9  when the truck  1  climbs a hill) increases, such that an effective diameter of the follower split pulley  36  increases so as to increase the speed reduction ratio of the CVT  7 . 
     Next, description will be given on the centrifugal governor  34 . 
     This centrifugal governor  34 , disposed around a portion of the input shaft  5  facing toward a later-discussed output gear  51 , comprises a governor weight  71 , a lifter  72 , a governor fork  73 , a rotation shaft  74  and an output arm  75 . The governor weight is a sensor which is rotated outward according to centrifugal force so as to detect the rotational speed of the input shaft  5 . The lifter  72  is slidden axially at the same time when the governor weight  71  rotates outward. The governor fork  73  is engaged with the lifter  72 . The rotation shaft  74  is supported rotatably at the ceiling of the transmission housing  31 . The output arm  75  is disposed on the outside of the transmission housing  31  so as to rotate integrally with the rotation shaft  74 . 
     The output arm  75  is interlocked with the throttle valve of the engine  3  through a linkage, such that the centrifugal governor  34  detects the rotational speed of the input shaft  5  and adjusts the volume of injected fuel, thereby changing the output of the engine  3  according to the variation of the rotational speed of the input shaft  5 . 
     Next, description will be given on the direction-of-travel switching mechanism  35  serving as a drive train to allow switching the rotational direction of the output shaft  37  in relation to the rotational direction of the input shaft  5 . 
     The input shaft  5  is notched on its periphery so as to form two gears, i.e., a forward drive gear  39  and a reverse drive gear  40 . The output shaft  37  is disposed parallel to the input shaft  5  (and the rear axles  8 ). Around a portion of the output shaft  37  which is nearer to the left end of the output shaft  37 , a forward follower gear  43  is relatively rotatably disposed, and a clutch gear  44  are not relatively rotatably but axially slidably disposed. The forward follower gear  43 , which is constantly engaged with the forward drive gear  39 , is notched on its side face so as to form a toothed portion  43   a , thereby being engaged/disengaged with/from a toothed portion  44   a  formed on the side face of the clutch gear  44  facing the toothed portion  43   a.    
     An idle gear  45 , designated by a phantom line in  FIG. 3 , is constantly engaged with the reverse drive gear  40 . The clutch gear  44  also can be engaged/disengaged with/from the idle gear  45 . 
     The clutch gear  44  is axially slid so as to engage with either the forward follower gear  43  or the idle gear  45 , thereby selectively bringing the output shaft  37  into a regularly directed rotation or a reversely directed rotation. 
     As shown in  FIG. 5 , a clutch fork shaft  48  is straightly, slidably disposed adjacent to the clutch gear  44 , and a clutch fork  49  is fixed onto the clutch fork shaft  48  and is engaged with the clutch gear  44 . A control shaft  60  is vertically and rotatably supported at the ceiling of the transmission housing  31  so as to slide the clutch fork shaft  48 . An arm  61  is fixed onto a bottom portion of the control shaft  60  and an apex portion of the arm  61  is engaged with a groove formed on the clutch fork shaft  48 . A top portion of the control shaft  60  projects upward, and an operating arm  62  is fixed onto the upward projecting portion of the control shaft  60 . The operating arm  62  is interlocked with the above-mentioned switching lever  19 , thereby allowing the clutch gear  44  to slide to a forward position or a backward position. 
     A portion of the output shaft  37 , which is nearer to the right end of the output shaft  37 , is notched on its periphery so as to form the output gear  51  serving as a prime rotary object, thereby transmitting the rotation of the output shaft  37  to the differential  32 . 
     The differential  32  is constructed normally for differentially connecting inner end portions of the pair of rear axles  8 , which extend oppositely to each other. In detail, as shown in  FIG. 3 , the differential  32  comprises a hollow differential casing  52 , a ring gear  53 , a pinion shaft  54 , two pinions  55 , and two differential side gears  56 . The differential casing  52  is disposed coaxially with the rear axles  8 , and rotatably supported at its left and right portions by the left and right housing members  31 L and  31 R through bearings  111 , respectively. The ring gear  53 , serving as a follower rotary object, is fixed around the differential casing  52  and is engaged with the output gear  51  of the output shaft  37 . The pinion shaft  54  is disposed in the differential casing  52  perpendicular to the rear axles  8  so as to be rotatable integrally with the differential casing  52 . The pinions  55 , which are bevel gears, are disposed oppositely to each other and rotatably supported on the pinion shaft  54 . Each of the differential side gears  56  which are bevel gears is fixed onto an inner end of each of the rear axles  8  so as to engage with both the pinions  55 . 
     Next, the axle housings  80 , each of which supports each of the rear axles  8 , will be described. 
     The two axle housings  80  are formed in the same cylindrical shape. As shown in  FIG. 2 , an inner end of each of the axle housings  80  is symmetrically fixed onto each of left and right sides of the transmission housing  31 , so as to cover an opening portion formed on each of the left and right side faces of the transmission housing  31 . An outer end of each of the axle housings  80  projects outward along the rear axles  8 . A supporting portion is formed at the projecting end portion of each of the axle housings  80  so as to support an outward portion of each of the rear axles  8  by a bearing  110 . Thus, a portion of each rear axle  8  adjacent to its proximal end is covered at a certain length with each axle housing  80 . 
     A top portion of the supporting portion of each of the axle housings  80  is formed into a mounting portion  80   a  having a horizontally flat shape. The mounting stay  81  in a flat-board-like shape, which is fixed onto a bottom end of the bodywork frame  10 , is fixed onto the mounting portion  80   a  by screwing bolts so as to support the axle housings  80  by the bodywork frame  10 . In such a structure, a load applied to the rear wheels  9  can be supported by the transmission housing  31  through the axle housings  80 , thereby simplifying the structure of a vehicle. 
     As shown in  FIG. 3 , left and right brake devices  22 , for braking the rear axles  8 , is provided around portions of the rear axles  8  covered by the axle housings  80 , respectively. Portions of the axle housings  80  to be attached to the transmission housing  31  are expanded so as to be bowl-like shaped. Each of brake devices  22  is housed in each of bowl-like shaped portions  80   b.    
     In each of the brake devices  22 , first friction disc  91  are axially slidably but not relatively rotatably provided onto the rear axle  8 . And, second friction discs  92  are slidably but not relatively rotatably engaged with the axle housing  80 . Each of the first friction discs  91  and each of the second friction discs  92  are arranged alternately. A pressure member  93  is fitted axially slidably and rotatably onto the transmission housing  31  for pressuring the multi-layered friction discs  91  and  92 . Cam grooves are formed on the pressure member  93 , and each of steel balls  94 , serving as cam bodies, is intervened between each of the cam grooves and the axle housing  80 . A brake control shaft  96  is rotatably supported by the axle housing  80 , and a cam is formed at one end portion of a brake control shaft  96  in a D-shape (not shown) so as to push an arm  95  formed at a top portion of the pressure member  93 . The above-mentioned brake control arm  23  is fixed onto one end of the brake control shaft  96 , which projects outward from the axle housing  80 . The brake control arm  23  is disposed outside above-mentioned bowl-like shaped portion  80   b.    
     In this structure, when the brake control arm  23  is operated, the brake control shaft  96  is rotated and the above-mentioned D-shape cam pushes the arm  95  so as to rotate the pressure member  93 . By the action of cam between the cam groove and the steel ball  94 , the pressure member  93  is slidden axially and make the friction discs  91  and  92  engage with one another, thereby braking the rear axle  8 . 
     The axle housings  80  and the transmission housing  31  are filled with oil, i.e., the brake devices  22  are of a wet type, thereby being improved in its durability and reliability. 
     The input shaft  5  is displaced from a position above the rear axles  8  so as to be nearer to the engine  3  than the rear axles  8  in the longitudinal direction of the vehicle such that the position of the input shaft  5  can be lowered in the transmission housing  31 . Consequently, even if the amount of the filled oil is small and oil level OL is low, splash lubrication for the input shaft  5  by the rotation of the ring gear  53  of the differential  32  can be sufficient because the input shaft  5  is located at the low position. 
     Various modification of the above-mentioned embodiment is possible. For example, as shown in  FIG. 6 , the structure that axle housings  80 ′ are fixed onto the transmission housing  31  leaning forward or backward so as to locate the brake control arm  23  at a low position, may be available. 
     Next, description will be given on a transmission  4 ′ wherein a differential locking mechanism is provided. A truck to which the transmission  4 ′ is applied is shown in  FIG. 7 . 
     As shown in  FIGS. 8 and 9 , each of the left and right housing members  31 L and  31 R is formed at its outer side wall into each of left and right cylindrically flanged portions  31 La and  31 Ra which are extended laterally outward. The outer end surface of each of the cylindrically flanged portions  31 La and  31 Ra is formed into a vertical flat joint face, on which the above-mentioned axle housing  80  is mounted. 
     As shown in  FIG. 8 , a hole  97  is formed on the side wall of the right housing member  31 R, and one end portion of an input shaft  5 ′ of the transmission  4 ′ is supported in the hole  97  through a bearing. As shown in  FIG. 10 , a mounting surface  98 , onto which an electric motor  99  is mounted through a bracket  100 , is formed on an outer face of the side wall around of the hole  97  of the right housing member  31 R. Namely, the housing members  31 L and  31 R are available for both of an engine type and an electric motor type. Reference numerals  101  in  FIGS. 8 and 9  designate as mounting bosses formed on the right housing member  31 R for screwing the bracket  100  onto the mounting surface  98 . 
     In the engine type shown in  FIG. 8 , which receives power from the engine  3  through the CVT  7 , the input shaft  5 ′ projects outward through the side wall of the left housing member  31 L, and the hole  97  in the right housing member  31 R is closed by a cover  102 . 
     On the other hand, in the electric motor type shown in  FIG. 10 , an input shaft  5 ″ projects outward through the hole  97  and is connected with a motor shaft  103  of the electric motor  99  through a coupler  104 . In this type, a cover  106  closes a hole  105  in the left housing member  31 L. 
     In the electric motor type, the direction-of-travel switching mechanism  35  (as provided in the engine type) is removed, and the input shaft  5 ″ and an output shaft  37 ′ are constantly engaged with each other through a gear  44 ′. Because, the electric motor  99  itself can bring the input shaft  5 ″ into a regularly directed rotation or a reversely directed rotation selectively. 
     The engine type will be described in accordance with  FIG. 12  and greater. As shown in  FIG. 12 , the idle gear  45  in the direction-of-travel switching mechanism  35  is supported rotatably on a shaft  14 . A left end of the shaft  14  is supported by a boss formed on the inner face of the side wall of the left housing member  31 L. As shown in  FIGS. 12 ,  14 , and  15 , the joint surface, which is formed on the left housing member  31 L to join with the right housing member  31 R, partly projects inward of the transmission housing  31 . A support plate  30  is screwed to the projected portion, and a right end of the shaft  14  is inserted and fitted into a circular hole  30   a  formed in the support plate  30 . 
     In this structure, the shaft  14  is rattle-free because the both ends of the shaft  14  are supported. And, the shaft  14  is not required to be so long as a whole width of the transmission housing  31 , thereby improving compactness. Other mechanics (in this embodiment, the rotation shaft  74  and the governor fork  73  of the centrifugal governor  34 ) can be placed in such formed empty space. 
     As shown in  FIGS. 8 and 12 , a forward follower gear  43  and a backward follower gear  44  are relatively rotatably supported around the output shaft  37 ′. The forward follower gear  43  is constantly engaged with the forward drive gear  39  formed around the input shaft  5 ′, and backward follower gear  44  is with the reverse drive gear  40  through the idle gear  45 . 
     Between the two follower gears  43  and  44 , a clutch slider  47  is not relatively rotatably but axially slidably disposed around the output shaft  37 ′. The clutch slider  47  is axially slidden so as to engage with either the forward follower gear  43  or backward follower gear  44 , thereby selectively bringing the output shaft  37 ′ into a regularly directed rotation or a reversely directed rotation. Also, the clutch slider  47  can be located at its neutral position where it engages with none of the two gears  43  and  44 . 
     The clutch fork shaft  48  is straightly slidably supported by the transmission housing  31 , as shown in  FIG. 12 . The clutch slider  47  is engaged with the clutch fork  49  which is fixed onto the midway portion of the clutch fork shaft  48 . 
     As shown in  FIGS. 9 and 14 , a direction-switching shaft  50  is vertically supported at the ceiling of the right housing member  31 R. An arm  46  is fixed onto the end portion of the direction-switching shaft  50  in the transmission housing  31 . An apex end portion of the arm  46  is engaged with the groove notched on a midway portion of the clutch fork shaft  48 . The speed-changing lever (not shown), which is interlocked with the switching lever  19  provided beside the operator&#39;s seat  2  of vehicle, is fixed onto an external-of-housing end portion of the direction-switching shaft  50 . 
     In the above structure, the clutch slider  47  can be slidden among a forward-driving position, a backward-driving position and a neutral position according to operation of the switching lever  19 . 
     A detent mechanism  66  is provided with the clutch fork shaft  48  to keep its operating positions. The detent mechanism  66  comprises three grooves  48   a  notched on the clutch fork shaft  48  in correspondence to the above-mentioned three operating positions (the forward-driving position, the backward-driving position and the neutral position), and a detent ball  67  biased by spring so as to engage with one of the three grooves  48   a.    
     An electrical switch  68  is provided with the clutch fork shaft  48  so as to detect its neutral position. The switch  68  is electrically connected with a circuit for starting a cell motor of the engine  3 , thereby allowing the engine  3  to start only when the clutch fork shaft  48  is located in its neutral position. 
     Next, description will be given on a differential  32 ′. The differential  32 ′ is constructed almost similarly with the differential  32  of above-mentioned embodiment, except that a differential locking mechanism  33  is provided. 
     The differential locking mechanism  33  is provided for locking the differential  32 ′. As shown in  FIG. 8 , a differential locking slider  57  is axially slidably provided around the right rear axle  8  on the opposite side to the differential casing  52  with the ring gear  53  between. A dog clutch portion  58  is formed on the surface of the differential locking slider  57  facing the ring gear  53 . An engaging portion  59  is formed at a boss of the ring gear  53  so as to engage with the dog clutch portion  58 . 
     In this structure, the differential locking mechanism  33  can be selected among the differential-locked mode wherein the dog clutch portion  58  is engaged with the engaging portion  59  and the differential casing  52  is connected integrally with the left and right rear axles  8 , and the differential-unlocked mode wherein the dog clutch portion  58  is disengaged from the engaging portion  59  and the differential  32 ′ connects the rear axles  8  in a differential manner. 
     As shown in  FIGS. 9 and 13 , a differential control shaft  63  is rotatably and vertically supported by the right housing member  31 R. A differential shift arm  64 , the apex end of which is engaged with the differential locking slider  57 , is fixed onto one end of the differential control shaft  63  which projects in an inward direction of the transmission housing  31 . 
     A differential locking control arm  65  is fixed onto one end of the differential control shaft  63  which projects in an outward direction of the transmission housing  31 . The differential locking control arm  65  is connected to the differential-locking operating tool (not shown) provided beside the operator&#39;s seat  2  through a linkage etc., thereby allowing operating to bring the differential  32 ′ into either a locked mode or an unlocked mode. 
     Next, the brake devices  22 ′ in this embodiment will be described. 
     As shown in  FIG. 8 , the boss of the ring gear  53  is supported by the side wall of the right housing member  31 R, and a boss of the differential casing  52  is by the side wall of the left housing member  31 L. Both of the side walls project cylindrically in an outward direction, thereby forming above-mentioned flanged portions  31 La and  31 Ra. The cylindrically flanged portions  31 La and  31 Ra, formed for mounting the axle housing  80 , forms its internal space into empty space (hereafter referred to as ‘jointing space’). 
     Besides, in above-mentioned ‘jointing space’, left and right outer walls of the housing members  31 L and  31 R project cylindrically in a laterally outward direction, thereby forming guide portions  31 Lb and  31 Rb. A pair of left and right pressure members  93  are fitted around the guide portions  31 Lb and  31 Rb respectively, and supported relatively rotatably and axially slidably. Each of the pressure members  93  has a ring-shape as shown in  FIG. 16 , and its internal diameter is equal to an external diameter of the guide portions  31 Lb and  31 Rb. Two hooks  93   a  are formed on the external periphery of each of the pressure members  93 . 
     The differential locking slider  57  is placed in the guide portions  31 Rb of the right housing member  31 R. 
     As shown in  FIGS. 8 ,  9 ,  13 , and  17 , a pair of brake control shafts  96  are rotatably supported above the pressure members  93  in parallel with the rear axles  8 . An inner end portion of each of brake control shafts  96  is supported by a boss  17  formed on the side wall of each of left and right housing members  31 L and  31 R. An outer end portion of each of the brake control shafts  96  is supported by each of the axle housings  80  and projects outward. The above-mentioned brake control arm  23  is fixed onto the outward projecting portion of the brake control shaft  96 . 
     As shown in  FIG. 13 , a midway portion of the brake control shaft  96 , which faces one of the two hooks  93   a  of the pressure member  93 , is formed into a cam having a D-shape. In this structure, when the brake control arm  23  is operated and the brake control shaft  96  are rotated, the cam pushes the hook  93   a , thereby the pressure member  93  is rotated around the guide portion  31 Lb ( 31 Rb). 
     As shown in  FIG. 8 , a plurality of depressions, each of which is formed into a hemispherical shape, are arranged at regular intervals in circumference on the side wall of the left housing member  31 L at the outside of the guide portion  31 Lb. And, as shown in  FIGS. 8 and 13 , a plurality of ball retaining portions  70  project from the side wall of the right housing member  31 R in correspondence to above-mentioned depressions. A depression, having a hemispherical shape, is formed on each of the ball retaining portions  70 . 
     In correspondence to the position of the depressions, a plurality of depressions  93   b  are formed and arranged at regular intervals in circumference on one side face as shown in  FIG. 16 . Each of the depressions  93   b  looks like a lozenge in a side view and like a cone in a sectional view, such that the depth of the depression  93   b  is the greatest at a center portion in circumference. 
     A steel ball  94  is supported by each of the hemispherical depressions of the housing member  31 L ( 31 R), and the pressure member  93  is fitted around the guide portion  31 Lb ( 31 Rb) such that each of the steel balls  94  is fitted into each of the depressions  93   b . The each of above-mentioned friction discs  91  and  92  are disposed between the other side face of the pressure member  93  and the inner side face of the axle housing  80 . 
     In this structure, when the pressure member  93  is rotated along an outer peripheral surface of the guide portion  31 Lb ( 31 Rb) by the operation of brake control arm  23 , the pressure member  93 , onto which the cam action of the steel balls  94  is applied, gets thrust (greater as its rotational degree increases) and is slidden outward, thereby pressuring the friction discs  91  and  92  and braking the rear axles  8 . 
     A projection  92   a  is formed at a portion of each disc of the second multi friction discs  92 . Each of these projections  92   a  is engaged with a recess formed on inner surface of the axle housing  80 . As shown in  FIGS. 8 and 9 , a holding hook  107  is fixed in the vicinity of the recess. An apex end of the holding hook  107  holds the projection  92   a  of an innermost disc of the second friction discs  92 . 
     In above structure, when manufacturing of the transmission  4 , each of the brake devices  22 ′ can be installed in the each of the axle housings  80 , and the holding hook  107  can prevent the friction discs  91  and  92  from being detached from the axle housing  80 , thereby forming an assemblage of axle housing  80  and brake device  22 ′ as shown in  FIG. 9 . Therefore, the transmission  4 ′ can be simply assembled by mounting left and right such assemblages on the transmission housing  30 . 
     Instead of the holding hook  107 , the structure that an elastic wire having a U-like shape is fitted into two holes formed on the axle housing  80  such that the wire strides the projection  92   a , is available. This structure is applied on the above-mentioned electric motor type as shown in  FIGS. 10 and 11 . 
     In this electric motor type, a distance between the two holes  109  formed on the axle housing  80  is a little shorter than a distance between both ends of the wire  108 . Thus, when the wire  108  is fitted into two holes  109 , the wire transforms such that its both ends approach each other. A friction force is generated between the fitted wire  108  and the two holes  109  by an elasticity of the wire  108  such that the wire  108  does not detach from the axle housing  80  and can hold the friction discs  91  and  92  of the brake device  22 ′. 
     The guide portion  31 Rb is formed wider than the guide portion  31 Lb, and the external diameter of the differential locking slider  57  is smaller than the internal diameter of the guide portion  31 Rb (namely, smaller than the internal diameter of the pressure member  93 ). The differential locking slider  57  is provided at the inner space of the guide portion  31 Rb, and is overlapped with the pressure member  93  in a longitudinal direction of the rear axles  8 . 
     In this structure, the pressure member  93  and the differential locking slider  57  are provided in the above-mentioned ‘jointing space’. And, because each of the guide portions  31 Lb and  31 Rb is cylindrically formed coaxially with a rotational axis of the rear axles  8 , the rotational axis of the pressure member  93  is substantially coaxial with an axis of the differential locking slider  57  provided on the rear axle  8 . 
     Thus, the differential locking slider  57  and the pressure member  93  can be disposed in a compact mass, thereby enhancing the transmission  4 ′ in its compactness. 
     As shown in  FIGS. 8 and 13 , the differential locking slider  57  is disposed at inner space of the guide portion  31 Rb of the right housing member  31 R. As shown in  FIGS. 9 and 13 , the guide portion  31 Rb is formed such that its cylindrical wall is partly notched, thereby forming an opening portion  15 . The differential shift arm  64  is inserted through the opening portion  15 , and an apex portion of the differential shift arm  64  is engaged with the differential locking slider  57 . 
     As shown in  FIG. 13 , the differential control shaft  63 , onto which the differential shift arm  64  is fixed, is disposed at a position which is offset from a virtual plane P containing the rotational axis of the pressure member  93 . Therefore, the rotational axis of the differential control shaft  63  and the rotational axis of the differential shift arm  64  are disposed in skewed direction with each other and do not cross. 
     Thus, the differential locking slider  57  can be slidden through the rotation of the differential control shaft  63  and the differential shift arm  64 . The only small space needed for rotation of the differential shift arm  64  is sufficient for operating the differential locking slider  57  in the transmission housing  31 . 
     On the other hand, in the structure that the differential locking slider  57  is engaged with a shift fork which is slidden straightly, a large space is needed for shifting the shift fork, thereby inhibiting miniaturization of the transmission. The structure of this embodiment solves this issue. 
     In this embodiment, the brake control shaft  96  is placed on the opposite side to the differential control shaft  63  with the virtual plane P between. By this layout, a differential-locking operating system and a brake operating system can be disposed in a compact mass, and also can avoid interruptions with each other. 
     As shown in  FIG. 8 , the cylindrical flanged portion  31 Ra and the guide portion  31 Rb of the right housing member  31 R are formed wider than the portions  31 La and  31 Lb of the left housing member  31 L, because the differential locking slider  57  is disposed in the guide portion  31 Rb. As shown in  FIGS. 9 and 13 , the electrical switch  68 , the differential control shaft  63 , and a breather cap  16  for bleeding of air are disposed at the widely-formed cylindrical flanged portion  31 Ra, thereby achieving the rational layout for miniaturization of the transmission  4 ′. 
     In this embodiment, each of the axle housings  80  is formed symmetrically with respect to the virtual vertical plane which includes the axis of the rear axles  8 . Thus, two members of uniform shape can be used for both of left and right axle housings  80 , thereby reducing their manufacturing costs. 
     Furthermore, a pair of front and rear holes, formed on side walls of the respective axle housings  80 , are arranged symmetrically with respect to above-mentioned virtual vertical plane. And, in the structure that axle housings  80  are disposed left and right, each of the front holes supports each of left and right brake control shafts  96 , and each of the rear holes is covered by a cap  86  as shown in  FIG. 9 . Thus, the left and right brake control shafts  96  can be coaxially disposed, and left and right brake systems can be rationally symmetrically arranged. 
     Furthermore, two hooks  93   a , formed on each of the pressure members  93 , are arranged symmetrically as shown in  FIG. 16 . Thus, two members of uniform shape can be used for both of left and right pressure members  93 , thereby reducing their manufacturing costs. 
     Next, the structure for lubrication of the transmission  4 ′ will be described. 
     The transmission housing  31  is filled with lubricating oil in established amount, and an oil level OL is determined as shown in  FIG. 14 . In this state, when the transmission  4 ′ is driven and the ring gear  53  and a forward follower gear  43  rotate in the direction designating as a bold arrow in  FIG. 14 , the oil is splashed on the input shaft  5 ′ and the output shaft  37 , which are disposed at upward slant position of the ring gear  53 . 
     As shown in  FIGS. 14 and 18 , a trough portion  24 , having a V-shape in an interior side view, is formed on an inner face of side wall of the right housing member  31 R. An oil leading hole  76  is formed in a horizontal direction on the portion of the right housing member  31 R which faces a base of the trough portion  24 . The oil leading hole  76  communicates with a connecting hole  77 , which is formed vertically in the side wall of the right housing member  31 R. The connecting hole  77  is connected with a groove  78 , which is formed in a boss of the right housing member  31 R for supporting an end of the output shaft  37 ′. 
     In this structure, a part of the splashes of oil by rotation of the ring gear  53  etc. reaches above the trough portion  24 , and flows along the oil leading hole  76  and the connecting hole  77  and is led to the groove  78 , thereby lubricating a bearing which supports the output shaft  37 ′. And, a part of the oil flows along an oil path (designated as a reference numeral  87  in  FIG. 12 ), and lubricates the peripheral surface of the output shaft  37 ′ for rotatably supporting the follower gears  43  and  44 , and a engaging portion of the clutch slider  47 . 
     As shown in  FIGS. 14 and 18 , a lubricating inlet  82  is disposed just above the trough portion  24 . Therefore, when a cap  20  is taken off and lubricating oil is run in through the lubricating inlet  82 , all the lubricating oil falls into the trough portion  24 . A part amount of the lubricating oil can surely reach the groove  78  through the oil leading hole  76  and the connecting hole  77  and can lubricate the bearing supporting the output shaft  37 ′ and so on. 
     In this structure, even if components (e.g. the bearing for supporting the output shaft  37 , the follower gears  43  and  44 , the clutch slider  47 ) are not spread with the lubricating oil in advance of assembling the transmission  4 ′, these components are surely lubricated by only running the oil in through the lubricating inlet  82  after assembling the transmission  4 ′. Therefore, the number of man-hours for manufacturing can be reduced. 
     A hole  27  is formed at the bottom of side wall of the right housing member  31 R as shown in  FIG. 13 . An inner space of the transmission housing  31  and an inner space of the right axle housing  80  communicate with each other through the hole  27  such that the oil with which both the inner space are filled can circulate between. 
     Furthermore, two holes  25  and  26  are formed at the top of side wall of the right housing member  31 R. An inner space of the transmission housing  31  and an inner space of the right axle housing  80  also communicates with each other through the two holes  25  and  26  such that the air in both the inner space can circulate between. Thus, the air in the right axle housing  80  can be exhaled from the breather cap  16  disposed on the transmission housing  31 . 
     Similarly, holes are formed on the side wall of the left housing member  31 L (not shown). Therefore, the oil and air can circulate between the inner space of the transmission housing  31  and an inner space of the left axle housing  80 . 
     As shown in  FIG. 13 , the breather cap  16  is disposed at the ceiling portion of the right housing member  31 R. An opening portion  83  for installing the breather cap  16  is separated off by an inner wall  84  from the inner space of the transmission housing  31 , and a small hole  85  is formed on the inner wall  84 . 
     In this structure, the air in the transmission housing  31  can communicate with the atmosphere through the small hole  85  and the breather cap  16 . And, even if the oil filled with the transmission housing  31  is stirred and splashed around, a splash of the oil is blocked by the inner wall  84  before reaching the breather cap  16 , thereby preventing oil-leak from the breather cap  16 . 
     Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form may be changed in the details of construction, and the combination and arrangement of parts may be changed or altered without departing from the spirit and the scope of the invention as hereinafter claimed.