Abstract:
The invention relates to a brake system for reducing the number of brake parts, a brake installing space and a vehicle width, and for facilitating an adjustment operation of equalizing the left and right braking forces. Rotary friction plates for braking a differential case and an axle are supported on the differential case and the axle respectively, while stationary friction plates are arranged axially and alternately with respect to the rotary friction plates and are supported non-rotatably on a gear case to brake the differential case and the axle at once by the operation of a single operating arm. A brake housing is integrally formed in an end wall of the gear case. The end wall, through which the axle passes, has an opening from which the brake members can be removed and inserted to improve assembly efficiency.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to a brake system for a vehicle, especially a small vehicle, such as an all-terrain vehicle or a utility vehicle, provided with a differential drive mechanism in a gear case in which a final reduction gear is housed. 
     2. Description of Related Art 
     Japanese Patent Laid-Open No. 59-130791/1984 discloses a conventional system as shown in FIG. 5, in which a gear case  101  is provided therein with a large final reduction gear  102 , a differential drive mechanism  104  and a wet type multiplate friction brake  105  for braking a differential case  106  alone. The friction brake  105  is provided with a plurality of rotary friction plates  113  spline-fitted in a hub  112 , which is fixed to the differential case  106 , in such a manner that the rotary friction plates  113  can be axially moved, and a plurality of stationary friction plates  114  spline-fitted in an inner circumferential surface of the gear case  101  so that the stationary friction plates  114  can be axially moved. 
     There is another conventional system for arranging drum brakes, which are adapted to brake left and right axles independently, on the left and right sides of a gear case. In this system, levers of the respective brakes are combined together into a single operating mechanism, and both the left and right drum brakes are actuated by a single operation. 
     When a braking operation is carried out in the former conventional system while a vehicle travels straight, the skidding (revolution without load) of one side wheel does not occur since the differential drive mechanism is not operated. However, when a braking operation is carried out while the vehicle turns, the differential drive mechanism is operated to cause a floated wheel to skid (revolve without load) in some cases. 
     In the latter conventional system, in which drum brakes are arranged on the left and right sides of a gear case, two sets of brake parts, such as drums, shoes and levers, are required. Accordingly the number of parts increase, and a double brake installing space is required. Moreover, it is necessary to adjust the brakes so that balanced left and right braking forces are put forth. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to reduce the number of brake parts, a brake installing space and a vehicle width and to facilitate an adjustment operation for equalizing left and right braking forces, by enabling a differential case and one axle to be braked at once with one set of wet type multiplates. 
     According to one aspect of the invention, there is provided a brake system for vehicles having a gear case wherein a final reduction gear and a differential case of the differential drive mechanism is housed. The brake system includes a first rotary friction plate supported on the differential case, and a second rotary friction plate supported on an axle. The brake system also includes a plurality of stationary friction plates arranged axially alternately with respect to the rotary friction plates. The stationary friction plates are supported non-rotatably on the gear case. The stationary friction plates and the rotary friction plates are pressed at once in a single braking operation to brake the differential case and the axle. It becomes possible to brake both the differential case and one axle at once by a single braking operation, brake the rotation of a differential gear, and brake wheels by equal left and right braking forces without causing one wheel to skid (revolve without load) even while the vehicle is turned. 
     According to another aspect of the invention, a brake housing is integrally formed with an end wall of the gear case, and the end wall, through which the axle passes, has an opening from which the rotary friction plates and the stationary friction plates are removed and inserted. Various brake parts, such as rotary friction plates, can be set in the brake housing through the opening in a side portion of the gear case, so that assembly and disassembly of the brake system can be carried out simply. 
     According to another aspect of the invention, the number of the first rotary friction plates is set larger than the number of the second rotary friction plates so that a differential case braking force is larger than an axle braking force. The braking force for the differential case which substantially works to brake the vehicle is set large, and that for the axle which works to prevent the differential gear from rotating idly is set small, so that the braking force can be efficiently used. 
     These objects as well as other objects, features and advantages of the invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of a power transmission mechanism for a small vehicle to which this invention is applied; 
     FIG. 2 is an enlarged horizontal sectional view of a gear case; 
     FIG. 3 is a sectional view taken along the line III—III in FIG. 2; 
     FIG. 4 is an enlarged sectional view taken along the line IV—IV in FIG. 3; and 
     FIG. 5 is a horizontal sectional view of a conventional system. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a diagram of a power transmission mechanism for a small vehicle, such as an all-terrain vehicle or a utility vehicle, provided with a brake system according to the invention. A rear gear case  2 , in which a differential drive mechanism  7 , a large final reduction gear  9  and left and right rear axles  12 ,  13  are housed, is integrally formed with transmission cases  1 ,  2  and each of the two cases  1 ,  2  have left-and-right-divided structures with a mating face H therebetween. An axial left end wall of the gear case  2  is provided with a partition wall  34  for a brake and a brake housing  50  thereon so that the wall  34  and the housing  50  are integral therewith, and has a large opening  49  therein from which brake parts can be inserted and removed. The opening  49  is provided with a detachable left cover  3 . In a right end wall of the gear case  2 , an opening  38  is formed for inserting a diff-lock member  46  therethrough, and a right cover  4  is detachably mounted over the opening  38 . 
     The transmission case  1  is provided therein with a transmission input shaft  17  operatively connected to a prime mover (not shown in the drawings) via a belt type non-stage transmission, intermediate shafts  18 ,  19  and a transmission output shaft  20 . The shafts  17 ,  18 ,  19 ,  20  are provided thereon with a plurality of groups of speed change gears G and an advancing-backing change clutch  21 . The power inputted by the transmission input shaft  17  is transmitted to the output shaft  20  via a suitable group of gears G having a desired gear ratio, and the resultant power is transmitted from a small final reduction gear  8  mounted fixedly on the transmission output shaft  20  to the large final reduction gear  9 . 
     A wet type multiplate braking system  6  is arranged at a left side portion of the gear case  2  with the large final reduction gear  9  and the differential drive mechanism  7 , and the diff-lock member  46  is arranged at a right side portion thereof. Left and right rear axles  12 ,  13  are inserted from the left and right sides of the gear case  2  and are supported thereby. 
     The differential drive mechanism  7 , of which the basic structure is well known, includes a differential case  23  with which the large final reduction gear  9  is combined firmly, left and right large differential gears  24  provided in the differential case  23 , and a pair of small differential gears  25  meshed with the two large differential gears  24  at right angles thereto. The large differential gears  24  are fixed by spline-fitting to inner end portions of the left and right rear axles  12 ,  13 , and the small differential gears  25  are supported rotatably in a right-angled posture with respect to the axes of the rear axles  12 ,  13  on a support shaft  39  fixed to the differential case  23 . 
     A boss  33  is integrally formed with the differential case  23  at a left end portion thereof and extends from the end wall  23   a  of the differential case  23  to the left. A large front wheel driving power take-off gear  28  is fixed to the differential case  23  at a right end portion thereof. The differential case  23  is rotatably supported on the gear case  2  via a bearing  37  fitted in an outer circumferential portion of a boss portion  28   a  of the large gear  28 , and a bearing  36  fitted in an outer circumferential portion of the left boss  33 . The large front wheel driving power take-off gear  28  is meshed with a small front wheel driving power take-off gear  30  mounted fixedly on a front wheel driving power take-off shaft  29 . 
     FIG. 2 shows an enlarged horizontal section of the gear case  2 . The left rear axle  12  is inserted in a seal  41  and a bearing  42  which are fitted in the left cover  3 , passes through the interior of the boss  33 , projects into the interior of the differential case  23 , and is spline-fitted into the left large differential gear  24  as described above. The right rear axle  13  is inserted in a seal  43  and a bearing  44  which are fitted in the right cover  4 , passes through the boss portion  28   a  of the large front wheel driving power take-off gear  28 , projects into the interior of the differential case  23 , and is spline-fitted into the right large differential gear  24  as described above. 
     The diff-lock member  46  has dog teeth  47  on the left end thereof, and is spline-fitted around an outer circumference of the right rear axle  13  so that the diff-lock member  46  can be axially moved. The dog teeth  47  are axially opposed to dog teeth  48  formed on the boss portion  28   a  of the large front wheel driving power take-off gear  28 . When the diff-lock member  46  is moved to the left, the dog teeth  47 ,  48  are meshed with each other, so that the differential drive mechanism is locked. 
     Regarding the structure of the brake system  6 , the boss  33  of the differential case  23  is supported on an inner circumferential end portion of a brake supporting partition wall  34 , which is integral with the gear case  2 , via the left bearing  36 . The boss  33  projects into the interior of the brake housing  50 , and spline teeth  33   a  are formed on an outer circumferential surface of the portion of the boss  33  which projects thereinto. A plurality of rotary friction plates  51  for the differential case  23  are spline-fitted onto the spline teeth  33   a  so that the rotary friction plates  51  can only be moved axially. An outer circumferential surface of an inner end portion of the left rear axle  12  is provided with outer circumferential spline teeth  12   a  extending from an inner end of the same axle to the left cover  3 . Rotary friction plates  52  for the rear axles are spline-fitted with the spline teeth  12   a  between the left end surface of the boss  33  and the left cover  3 , so that the rotary friction plates  52  can only be moved axially. The number of the friction plates  51  for the differential case  23  is larger than that of the friction plates  52  for the rear axles. For example, the number of the rotary friction plates  51  for the differential case is set to five, while the number of the rotary friction plates  52  for the rear axles is set to two in this embodiment. Accordingly, the braking force for the differential case  23  becomes larger than that for the rear axles. 
     Stationary friction plates  53  are arranged between the rotary friction plates  51 ,  52  and at both outsides of the sets of the rotary friction plates  51 ,  52 , and have a plurality of circumferentially spaced, outwardly extending projections  54  integral therewith. As shown in FIG. 3, the projections  54  are engaged with axial grooves  56  formed in an inner circumferential surface of the brake housing  50  so that the projections  54  can only be moved axially. The stationary friction plate  53  at the extreme right position is oppositely disposed to the brake supporting partition wall  34 , and the stationary friction plate  53  at the extreme left position is oppositely disposed to a pressure cam ring  60 . The cam ring  60  is fitted in an outer circumferential surface of the boss portion  3   a  formed on the left cover  3  so that the cam ring  60  can be turned and be axially moved, the cam ring  60  being engaged with a left fixing ring  64  via steel balls  61  for the cam. The fixing ring  64  is fixed to the left cover  3 . 
     FIG. 4 is a sectioned development (enlarged sectional view taken along the line IV—IV in FIG. 3) showing the cam ring  60  and the fixing ring  64  cut in the circumferential direction. The cam ring  60  has a movable cam groove  62  in a left end surface thereof, and the fixing ring  64  has a fixed groove  65  in a right end surface thereof. A steel ball  61  is held between the grooves  62 , 65  so that the steel ball  61  can be rolled. The depth of the movable cam groove  62  of the cam ring  60  decreases in the direction opposite to the direction of an arrow R, while the depth of the fixed cam groove  65  of the fixing ring  64  decreases in the direction of the arrow R. When the cam ring  60  is turned in the direction of the arrow R with respect to the fixing ring  64 , the cam ring  60  is moved to the right via the steel ball  61  to press all stationary friction plates  53  and all rotary friction plates  51 ,  52  between the brake supporting partition wall  34  and cam ring  60 . Namely, the differential case  23  and left rear axle  12  are braked simultaneously via the rotary friction plates  51 ,  52 . 
     Referring to FIG. 3, is a sectional view taken along the line III—III in FIG. 2, an outwardly extending projection  70  is formed on the cam ring  60 , and an operating arm  71  is engaged with the projection  70  in the direction opposite to the arrow R. The operating arm  71  is fixedly mounted on a brake shaft  75 , which is supported by a boss  73  formed on the brake supporting partition wall  34  and by a support hole  74  of the left cover  3  so that the brake shaft  75  can be turned, and which projects to the outside of the left cover  3  with a brake arm  77  fixedly mounted on an outer end portion thereof, as shown in FIG.  2 . An operating wire or rod  72  is joined to the brake arm  77  as shown in FIG. 3, and to a brake operator, such as a brake pedal, and urged backward by a return spring. Namely, when the brake arm  77  is turned forward against the return spring by the operating wire  72  (leftward in FIG.  3 ), the cam ring  60  is turned in the direction of the arrow R via the brake shaft  75 , operating arm  71  and projection  70 . 
     The brake housing  50  stores an oil up to, for example, a level L so that the friction brake is of the wet type. An engine oil is used as the oil, which is stored in a space from the interior of the transmission case  1  to the entire interior of the gear case  2  of FIG.  1 . 
     The operation of the differential drive mechanism  7  is well known. Referring to FIG. 1, the large final reduction gear  9  and differential case  23  are rotated together via the small final reduction gear  8 , and also the left and right rear axles  12 ,  13  are rotated at the same time via the support shaft  39 , small differential gears  25  and large differential gears  24 . When the loads on the left and right rear wheels are approximately equal, the left and right wheels are rotated at an equal speed, and when a difference between the left and right loads is large, for example during a turning movement of the vehicle, a differential motion is made by the rotation of the small differential gears  25  around their axis. 
     In order to brake the rear wheels, a brake operator such as a brake pedal, is operated to cause the cam ring  60  to be turned in the direction of the arrow R via the operating wire  72 , the brake arm  77 , the brake shaft  75 , the operating arm  71  and the projection  70 , which are shown in FIG. 3, and the cam ring  60  is then moved to the right, as shown in FIG. 4, by cam actions of the cam grooves  62 ,  65  and the steel balls  61 . Consequently, the friction plates  51 ,  52 ,  53  are pressed between the cam ring  60  and the brake supporting partition wall  34  to brake the differential case  23  and left rear axle  12  at the same time. Namely, the left rear axle  12  is braked with respect to the gear case  2  and also with respect to the differential case  23 , so that the rotation of the small differential gears  25  around their axis, i.e. around the support shaft  39  is restricted, whereby the right rear axle  13  is also braked via the small differential gears  25 . 
     Accordingly, the two rear axles  12 ,  13  can be braked without operating the differential drive mechanism  7  even while the vehicle turns, not to mention the case when the vehicle travels straight. 
     In order to assemble the brake system, the rotary friction plates  51 ,  52  and the stationary friction plates  53  are inserted from the left end opening  49  of the gear case  2  into the interior of the brake housing  50  before fixing the left cover  3 , shown in FIG.  2 . The left cover  3  on which the fixing ring  64 , the cam ring  60  and the brake shaft  74  are mounted in advance, is then fixed to the left end opening  49  of the brake housing  50 . 
     In the embodiment of FIG. 2, the ratio of the numbers of the rotary friction plates  51 ,  52  mounted on the differential case  23  and the rear axle  12  is set to 5:2, however the ratio is not limited to the value. Although the number of the rotary friction plates  51  on the differential case  23  is preferably larger than that of the rotary friction plates  52  on the rear axle  12 , it can be set equal to the number of the friction plates on the rear axle  12 . This invention can also be used as a brake system for front wheels. 
     Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, the description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and/or function may be varied substantially without departing from the spirit of the invention and all modifications which come within the scope of the appended claims are reserved.