Patent Publication Number: US-2002007633-A1

Title: Hydrostatic continuously variable transmission

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a hydrostatic continuously variable transmission having a distributor valve in which a holding structure is simplified.  
       [0003] 2. Description of Background Art  
       [0004] A hydrostatic continuously variable transmission has been known as a continuously variable transmission for a motorcycle or an automobile. Such a continuously variable transmission is disclosed in Japanese Examined Patent Publication No. 7-56340 and Japanese Unexamined Patent Publication No. 4-203553. Its schematic configuration is illustrated in FIG. 8.  
       [0005] As shown in FIG. 8, this hydrostatic continuously variable transmission has a fixed displacement type swash plate hydraulic pump P connected to the crank shaft side of an engine and a variable displacement type swash plate hydraulic motor M connected to a speed reduction gear side. The hydraulic pump P and the hydraulic motor M are connected to each other to constitute a hydraulic closed circuit via an inside oil passage (low pressure passage)  52  which is a low pressure passage in a normal load operation but is a high pressure passage in a speed reducing operation, that is, in a reverse load operation and an outside oil passage (high pressure passage)  53  which is a high pressure passage in a normal load operation but is a low pressure passage in a reverse load operation. An oil supply passage  47  connected to an oil supply pump  88  sucking oil from an oil reservoir  87  is connected to the inside oil passage  52  via a first check valve  95  and is connected to the outside oil passage  53  via the second check valve  96 .  
       [0006] The hydraulic pump P and the hydraulic motor M both include cylinder bores formed in the same circumference and plungers (pistons) reciprocating in the cylinder bores. Valve bores for connecting the cylinder bores to the low pressure oil passage and the high pressure oil passage are radially positioned and distributor valves are mounted into the respective valve bores and are reciprocated in a radial direction to switch the cylinder bores between the high pressure oil passage and the low pressure oil passage.  
       [0007] The distributor valves of the hydraulic pump side are driven by a first eccentric ring to which power is transmitted from a driving side and the distributor valves of the hydraulic motor side are driven by a second eccentric ring of a casing side. A slip ring (or ball bearing) is disposed inside each eccentric ring and the tops of the distributor valves are in sliding contact with the inside of the slip ring. The distributor valves of the hydraulic pump side and the hydraulic motor side are combined with respective expansion rings at their top sides.  
       [0008] The conventional combination structure of the distributor valves with the expansion ring is disclosed in Japanese Examined Patent Publication No. 6-89831. In this structure, an expansion ring includes a plurality of elongated holes having two holes of different diameters as compared to the number of distributor valves and the top of each distributor valve is passed through the hole of a large diameter and is shifted to the hole of a small diameter and then the hole of a large diameter side is closed with a plug. Further, in another structure the top of each distributor valve is enlarged and sandwiched by the expansion ring and the slip ring.  
       [0009] The conventional structure described in the former, however, complicates the shape of the hole of the expansion ring and hence increases manufacturing costs. Further, it needs a plug for clogging the hole. Still further, in the conventional structure, the distributor valve regulates the motion of the expansion ring and hence the plug collides with the distributor valve to apply an impact load to the plug. In this case, it is thought that an iron-base material having resistance to an impact is used as the material of the plug but the iron-base material increases the weight of the plug, which results in an increase in the inertia mass of the expansion ring and a decrease in the action thereof. In the structure described in the latter, if the top of the distributor valve, whose peripheral surface is finished by grinding, is enlarged in size, the distributor valve can not be through-ground, which makes it difficult to ensure accuracy and increases manufacturing costs.  
       SUMMARY AND OBJECTS OF THE INVENTION  
       [0010] In view of such circumstances, the present invention has been made and it is an object of the present invention is to provide a simple combination structure of distributor valves with an expansion ring which can reduce weight and costs.  
       [0011] A hydrostatic continuously variable transmission includes a hydraulic closed circuit in which a swash plate hydraulic pump is connected to a swash plate hydraulic motor with a low pressure oil passage and a high pressure oil passage concentric with the low pressure oil passage. The swash plate hydraulic pump includes valve bores each of which is radially formed to connect the cylinder bore of the hydraulic pump to the low pressure oil passage and the high pressure oil passage. The swash plate hydraulic motor includes valve bores each of which is radially positioned to connect the cylinder bore of the hydraulic motor to the low pressure oil passage and the high pressure oil passage. Distributor valves are provided and are disposed in individual valve bores and are moved in a radial direction to switch the cylinder bore of the hydraulic pump and the cylinder bore of the hydraulic motor between the low pressure oil passage and the high pressure oil passage and are combined with an expansion ring. The configuration of the present invention to solve the problem described above is characterized in that the head portion of the distributor valve is inserted into an elongated hole made in the expansion ring and that a clip is engaged with a groove made on the head portion of the distributor valve projecting outside from the expansion ring to combine the distributor valve with the expansion ring.  
       [0012] According to the hydrostatic continuously variable transmission having the above-mentioned configuration, the distributor valve is supported with the expansion ring only by putting the clip in the groove of the head portion of the distributor valve and by passing the distributor valve in this state through a simple elongated hole made in the expansion hole. Hence, this can simplify the structure thereof and reduce the weight thereof.  
       [0013] Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
     [0015]FIG. 1 is a longitudinal cross-sectional view of a hydrostatic continuously variable transmission in accordance with one preferred embodiment in which the present invention is applied to the power unit of a vehicle;  
     [0016]FIG. 2 is a side view, partly in cross section, of a first or a second expansion ring;  
     [0017]FIG. 3 is a plan view of an expansion ring;  
     [0018]FIG. 4 is a plan view of a U-shaped clip;  
     [0019]FIG. 5 is a side view of a U-shaped clip;  
     [0020]FIG. 6 is a side view of a distributor valve;  
     [0021]FIG. 7 is an enlarged view of a switching portion of a distributor valve; and  
     [0022]FIG. 8 is a schematic configurational view of a hydrostatic continuously variable transmission.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0023] In FIG. 1, there is illustrated a longitudinal cross-sectional view of a hydrostatic continuously variable transmission in accordance with one preferred embodiment in which the present invention is applied to the power unit of a vehicle.  
     [0024] In FIG. 1, a swash plate hydraulic pump P includes an input cylindrical shaft  5  provided with an output gear  2   a  of a first speed reduction gear; a pump cylinder  7  relatively rotatably supported by the inside peripheral wall of the input cylindrical shaft  5  via a ball bearing  6 ; a plurality of cylinder bores  8  formed in the pump cylinder  7  in an annular arrangement such that they surround the rotary axis of the pump cylinder  7 ; a plurality of pump plungers  9  slidably fitted in the respective cylinder bores  8 ; a plate  10  whose front surface is engaged with and put into contact with the outside ends of the respective pump plungers  9 ; and a pump swash plate  12  for supporting the plate  10  via an angular contact bearing  13  and a radial bearing  14  so as to hold the plate  10  in a state tilted at a predetermined angle with respect to the axis of the pump cylinder  7  around an imaginary trunnion axis O 1  intersecting the axis of the pump cylinder  7  at right angles. The pump swash plate  12  is integrally formed with the input cylindrical shaft  5 .  
     [0025] When the input cylindrical shaft  5  is rotated, the pump swash plate  12  described above reciprocates the pump plungers  9  via the plate  10  and the bearings  13 ,  14  to make them repeat a suction stroke and a discharge stroke.  
     [0026] The hydraulic motor M includes a motor cylinder  17  integrally formed with the pump cylinder  7  described above and positioned at the right side in FIG. 1 on the same axis as the pump cylinder  7 ; a plurality of cylinder bores  18  formed in the motor cylinder  17  such that they surround the rotary axis of the motor cylinder  17 ; a plurality of motor plungers  19  slidably fitted in the respective cylinder bores  18 ; a plate  20  whose front surface is engaged with and put into contact with the outside ends of the respective pump plungers  19 ; a motor swash plate  22  for supporting the plate  20  via an angular contact bearing  27  and a radial bearing  28 ; and a motor swash plate anchor  23  for supporting the back surface of the motor swash plate  22 .  
     [0027] The opposed contact surfaces  22   a  and  23   a  of the motor swash plate  22  and the motor swash plate anchor  23  which are put into contact with each other are formed in a spherical surface having a center at an intersection of the axis of the motor cylinder  17  and a trunnion axis O 2 . Further, the motor swash plate  22  is supported by the motor swash plate anchor  23  such that it can relatively rotate around the trunnion axis O 2 .  
     [0028] A cylindrical cylinder holder  24  is connected to the motor cylinder side end of the motor swash plate anchor  23  and a ball bearing  25  is interposed between the cylinder holder  24  and the outer periphery of the motor cylinder  17 .  
     [0029] The motor swash plate  22  is moved between a vertical position at right angles and a maximum tilt position tilted at a predetermined angle with respect to the axis of the motor cylinder  17  when the motor swash plate  22  is rotated around the trunnion axis O 2  by a ball screw mechanism  79  connected to a motor  80 , and when it is tilted, it can reciprocate the motor plungers  19  to make them repeat a suction stroke and a discharge stroke as the motor cylinder  17  is rotated.  
     [0030] The pump cylinder  7  and the motor cylinder  17  are integrally combined with each other to form a cylinder block B which is integrally formed with an output shaft  31 .  
     [0031] One side of the output shaft  31  extends beyond the boundary of the cylinder block B and passes through the plate  10  and the pump swash plate  12  to support the end portion of the pump swash plate  12  via the angular contact ball bearing  33 . Further, a ball bearing  35  is disposed between the pump swash plate  12  and the casing  4 .  
     [0032] The other side of the output shaft  31  extends beyond the boundary of the cylinder block B and passes through the plate  20 , the motor swash plate  22 , and the motor swash plate anchor  23 . The motor swash plate anchor  23  is supported by the output shaft  31  at end side of the output shaft  31  (at the right end side in FIG. 1) via an angular contact ball bearing  41 . The motor swash plate anchor  23  is integrally formed with the casing  4 . An input gear  3   a  of a second speed reduction gear is mounted on the outer periphery of the output shaft  31  at the outside in the axial direction of the output shaft  31 .  
     [0033] The inside of the hollow output shaft  31  integral with the cylinder block B forms an oil supply passage  47 . The oil supply passage  47  is connected to an oil reservoir  87  at one end of the output shaft  31  (at the left end side in FIG. 1) via an oil filter  89  and an oil supply pump  88 . At the other end of the output shaft  31 , the oil supply passage  47  is closed with a plug  48  or is opened with a restrictor.  
     [0034] An annular groove is formed on the outer peripheral surface of the output shaft  31  between the group of cylinder bores  8  of the pump cylinder  7  and the group of cylinder bores  18  of the motor cylinder  17  to form an annular inside oil passage  52  between the outer peripheral surface of the output shaft  31  and the inner peripheral surface of the cylinder block B integrally fitted on the output shaft  31 . Further, an annular groove is formed on the outer peripheral surface of the cylinder block B to form an annular outside oil passage  53  between the outer peripheral surface of the cylinder block B and the inner peripheral surface of a ring body  56  integrally fitted on the outer peripheral surface of the cylinder block B.  
     [0035] First valve bores  57  are radially made in the annular partition wall between the inside oil passage  52  and the outside oil passage  53  of the cylinder block B, at the group of the cylinder bores  8  side, between the group of cylinder bores  8  of the pump cylinder  7  and the group of cylinder bores  18  of the motor cylinder  17  and in the outer peripheral wall of the outside oil passage  53 , that is, in the ring body  56 , wherein the number of the first valve bores are equal to that of the cylinder bores  8 . Also, second valve bores  58  are radially made in the annular partition wall between the inside oil passage  52  and the outside oil passage  53  of the cylinder block B, at the group of the cylinder bores  18  side, between the group of cylinder bores  8  of the pump cylinder  7  and the group of cylinder bores  18  of the motor cylinder  17  and in the outer peripheral wall of the outside oil passage  53 , that is, in the ring body  56 , wherein the number of the second valve bores are equal to that of the cylinder bores  18 . The respective cylinder bores  8  communicate with the respective first valve bores  57  through respective pump ports  59  and the respective cylinder bores  18  communicate with the respective second valve bores  58  through respective motor ports  60 .  
     [0036] Spool type first distributor valves  61  are slidably fitted in the respective first valve bores  57  and spool type second distributor valves  62  are slidably fitted in the second valve bores  58 . Then, a first eccentric ring (eccentric cam)  63  surrounding the first distributor valves  61  is engaged with the outside ends of the first distributor valves  61  via a slip ring (or a ball bearing)  65  and a second eccentric ring (eccentric cam)  64  surrounding the second distributor valves  62  is engaged with the outside ends of the second distributor valves  62  via a slip ring (or a ball bearing)  66 .  
     [0037] The outside ends of the first distributor valves  61  are combined with each other by a first expansion ring  67  concentric with the first eccentric ring  63  and the outside ends of the second distributor valves  62  are combined with each other by a second expansion ring  68  concentric with the second eccentric ring  64 .  
     [0038] In FIG. 2 is illustrated a side view, partly in cross section, of the first or second expansion ring  67  or  68 , and in FIG. 3 is shown a plan view thereof, and in FIG. 4 and FIG. 5 are shown the plan view and the side view of a U-shaped clip. The shape of the first expansion ring  67  is almost the same as that of the second expansion ring  68 . Thus, the shape of the first expansion ring  67  will be described as follows.  
     [0039] The first expansion ring  67  is shaped like a ring and includes a sleeve portion  67   a  and flange portions  67   b ,  67   c  formed at both ends thereof with a groove shaped like a letter C in cross section. In the sleeve portion  67   a , at equal intervals, are formed as many elongated holes  151  as there are the first distributor valves  61 . The elongated hole  151  has a simple shape in which two semicircular portions of the same diameter are connected with straight portions.  
     [0040] On the other hand, the first distributor valve  61  which is shaped like a spool, as shown in FIG. 6, includes a switching portion  61   a  for switching the cylinder bore  8  between the low pressure oil passage  52  side and the high pressure oil passage  53  side, a small diameter portion  61   b  is connected to the switching portion  61   a  to form an oil passage for introducing hydraulic oil, and a guide portion  61   c  is connected to the small diameter portion  61   b . The tip of the guide portion  61   c  is a head portion on which an annular groove (cutaway portion)  61   d  is formed. The switching portion  61   a  and the guide portion  61   c  are slidably fitted in the first valve bore  57 .  
     [0041] In the groove  61   d  made on the head portion of the first distributor valve  61  is fitted a U-shaped clip  152  shown in FIG. 4 and FIG. 5 and the first distributor valve  61  is inserted in this state into the elongated hole  151  of the expansion ring  67 . Needless to say, the switching portion  61   a , the small-diameter portion  61   b , the guide portion  61   c  of the first distributor valve  61  are inserted into the first valve bore  57  of the cylinder block B. When the first distributor valves  61  with clips are inserted into all the elongated holes  151  and the first valve bores  57 , they are covered with a slip ring  65  on the outsides thereof and are set in this state inside the first eccentric ring  63  to bring about a state shown in FIG. 1, that is, a state in which the U-shaped clip  152  is engaged with the surface of the sleeve portion  67   a  of the expansion ring  67  and at the same time the top head surface  61   e  of the first distributor valve  61  is in contact with the inner peripheral surface  65   a  of the slip ring  65 . Therefore, the first distributor valve  61  is pulled up by the expansion ring  67  via the U-shaped clip  152  and the head portion thereof is pressed down by the slip ring  65 .  
     [0042] The second distributor valve  62  and the second expansion ring  68  for holding it have the same structure as the first distributor valve  61  and the first expansion ring  67  and are assembled inside the second eccentric ring  64  in the same way.  
     [0043] The first eccentric ring  63  is integrally formed with the input cylindrical shaft  5  and is positioned eccentrically by a predetermined distance ε 1  from the center of the cylinder block B along the tilt center (imaginary trunnion axis O 1 ) of the pump swash plate  12 . Also, the second eccentric ring  64  is connected to the cylinder holder  24  and is positioned eccentrically by a predetermined distance ε 2  from the center of the cylinder block B along the tilt center (imaginary trunnion axis O 2 ) of the motor swash plate  20 .  
     [0044] Here, describing the action of the first distributor valve  61 , when a relative rotation is produced between the input cylindrical shaft  5  and the pump cylinder  7 , that is, the cylinder block B, the respective first distributor valves  61  are reciprocated by the first eccentric ring  63  between the inside positions and the outside positions in the radial direction of the pump cylinder  7  with a stroke of two times the amount of eccentricity ε 1  in the first valve bore  57 . In the discharge region of the hydraulic pump P, the first distributor valve  61  is moved to the inside position to make the corresponding pump port  59  communicate with the outside oil passage  53  and to shut the communication between the pump port  59  and the inside oil passage  52 , whereby the hydraulic oil is pressure-fed to the outside oil passage  53  from the cylinder bore  8  by the pump plunger  9  in a discharge stroke.  
     [0045] Also, in the suction region of the hydraulic pump P, the first distributor valve  61  is moved to the outside position side to make the corresponding pump port  59  communicate with the inside oil passage  52  and to shut the communication between the pump port  59  and the outside oil passage  53 , whereby the hydraulic oil is sucked into the cylinder bore  8  from the inside oil passage  52  by the pump plunger  9  in a suction stroke.  
     [0046] Here, describing the action of the second distributor valve  62 , when the motor cylinder  17 , that is, the cylinder block B is rotated, the respective second distributor valves  62  are reciprocated by the second eccentric ring  64  between the inside positions and the outside positions in the radial direction of the cylinder block B with a stroke of two times the amount of eccentricity ε 2  in the second valve bore  58 . In the expansion region of the hydraulic motor M, the second distributor valve  62  is moved to the inside position to make the corresponding motor port  60  communicate with the outside oil passage  53  and to shut the communication between the motor port  60  and the inside oil passage  52 , whereby the high pressure hydraulic oil is supplied to the cylinder bore  18  of the motor plunger  19  in an expansion stroke from the outside oil passage  53 .  
     [0047] Also, in the contraction region of the hydraulic motor M, the second distributor valve  62  is moved to the outside position side to make the corresponding motor port  60  communicate with the inside oil passage  52  and to shut the communication between the motor port  60  and the outside oil passage  53 , whereby the hydraulic oil is discharged into the inside oil passage  52  from the cylinder bore  18  of the motor plunger  19  in a contraction stroke.  
     [0048] In this way, the cylinder block B is rotated by the sum of a reactive torque which is applied to the pump cylinder  7  by the pump swash plate  12  via the pump plunger  9  in the discharge stroke and a reactive torque which is applied to the motor cylinder  17  by the motor swash plate  22  via the motor plunger  19  in the expansion stroke and the rotational torque is transmitted to the second speed reduction gear by the output shaft  31 . In this case, the speed change ratio of the output shaft  31  to the input cylindrical shaft  5  is given by the following equation,  
       Speed change ratio = 1+( displacement of hydraulic motor M/ displacement of hydraulic pump P )  
     [0049] Therefore, if the displacement of the hydraulic motor M is changed to a certain value from zero, the speed change ratio can be changed from 1 to a certain necessary value. Further, since the displacement of the hydraulic motor M is determined by the stroke of the motor plunger  19 , the speed change ratio can variably be controlled from 1 to a certain value by tilting the motor swash plate  22  from a vertical position to a certain tilt position.  
     [0050] In the present preferred embodiment, as shown in FIG. 7, tapered portions  153 ,  154  are formed on both the side ends of the switching portion  61   a  of the first distributor valve  61 . The switching portion  61   a  is a portion for making the pump port  60  communicate with the inside oil passage  52  or the outside oil passage  53  or for shutting the communication between them, and since the communication of the pump port  60  with both the inside oil passage  52  and the outside oil passage  53  results in a reduction in efficiency, the switching portion  61   a  is required to be longer than the diameter of the pump port  60 . When the switching portion  61   a  communicates with the low pressure oil passage  52  or the high pressure oil passage  53 , a rapid change in opening area produces a large change in pressure. Therefore, a change in the opening area can be reduced by forming the tapered portions  153 ,  154 , which can reduce a change in pressure and hence can reduce vibrations and noises. Also, when the first distributor valve  61  slides, it can smoothly move by the guidance of the tapered portions  153 ,  154 . The second distribution valve  62  has the same structure as the first distributor valve  61 .  
     [0051] According to the hydrostatic continuously variable transmission in accordance with the present invention, in the hydrostatic continuously variable transmission includes a hydraulic closed circuit in which a swash plate hydraulic pump is connected to a swash plate hydraulic motor with a low pressure oil passage and a high pressure oil passage concentric with the low pressure oil passage. The swash plate hydraulic pump includes valve bores each of which is radially formed to connect the cylinder bore of the hydraulic pump to the low pressure oil passage and the high pressure oil passage. The swash plate hydraulic motor includes valve bores each of which is radially made to connect the cylinder bore of the hydraulic motor to the low pressure oil passage and the high pressure oil passage. Distributor valves are disposed in the valve bores and are moved in a radial direction to switch the cylinder bore of the hydraulic pump and the cylinder bore of the hydraulic motor between the low pressure oil passage and the high pressure oil passage. Expansion rings are provided and the head portion of the distributor valve is inserted into an elongated hole made in the expansion ring and a clip is engaged with a groove made in the head portion of the distributor valve projecting outside from the expansion ring to combine the distributor valve with the expansion ring. Therefore, this can simplify the structure thereof and reduce the weight thereof and does not impair the action of the expansion ring and can reduce manufacturing costs. Further, since the distributor valves have the same diameter, they can be finished by center-through-grinding, which results in ensuring high accuracy and cost reduction.  
     [0052] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.