MXPA99009754A - Continuously variable hydrostatic transmission ratio controller capable of generating amplified stroking forces - Google Patents

Abstract

To control transmission ratio of a continuously variable hydrostatic transmission including an input shaft (14), an output shaft (16), a hydraulic pump unit (18) driven by the input shaft (14), a grounded hydraulic motor unit (20), and a wedge-shaped swashplate (22) drivingly, pivotally connected to the output shaft (16) and positioned to accommodate pumped hydraulic fluid exchanges between the pump and motor units (18, 20). A ratio controller is provided having a pair of hydraulically actuated, differentially sized pistons (58, 68) coupled by a linkage mechanism to pivot the swashplate (22) in opposite transmission ratio-changing directions. The smaller piston (58) is incorporated internally of the output shaft (16), while the larger piston (68), of an annular shape, coaxially surrounds the output shaft (16). The linkage mechanism has a geometry effective to translate axial forces exerted by the pistons (58, 68) into amplified ratio-changing moments exerted on the swashplate (22). The ratio controller also includes a control valve (78) selectively positioned to change the hydraulic fluid pressure acting on the larger piston (68), such as to set a transmission ratio and also to determine the ratio-changing direction of swashplate pivotal motion.

Description

CONTROLLER OF THE PROPORTION OF THE HYDROSTATIC TRANSMISSION CONTINUOUSLY VARIABLE CAPABLE TO GENERATE AMPLIFIED RACE FORCES REFERENCE TO THE RELATED PATENTS The present invention relates to an improved ratio controller having a particular application in continuously variable transmissions of the type described in the Patents of the United States of North America Numbers: 5,423,183; 5,486,142; 5,524,437; 5,535,589; and 5,678,405. The descriptions of these patents are incorporated herein by reference. Technical Field The present invention relates to hydraulic machines, and more particularly, to hydrostatic transmissions capable of transmitting the energy of a primary motor to a load with continuously (infinitely) variable transmission ratios. BACKGROUND OF THE INVENTION In the cited patents, a hydrostatic transmission is disclosed which includes a hydraulic pump unit and a hydraulic motor unit positioned in axially aligned, opposite relation, on opposite sides of a wedge-shaped swashplate. The pump unit is connected to an input shaft driven by a primary motor, while the motor unit is grounded in the stationary transmission housing. An output arrow, coaxial with the input shaft and coupled in a driving manner to a load, is connected to the oscillating plate in coupling relationship at torque. When the pump unit is driven by the primary motor, hydraulic fluid is pumped back and forth between the pump and the motor unit through ports on the swashplate. As a result, three torque components are exerted, acting in the same direction, on the swash plate to produce an output torque on the output shaft to drive the load. Two of these torque components are a mechanical component exerted on the swashplate by the rotation pump unit and a hydromechanical component exerted on the swashplate by the motor unit. The third component is a purely hydrostatic component resulting from the differential forces created by the hydraulic pressures acting on the circumferentially opposite end surfaces of the swashplate ports, which have different surface areas due to the wedge shape of the swashplate. The torque-coupled connection of the wedge-shaped swash plate with the output shaft is such that the angular orientation of the swash plate can be varied with respect to the axis of the output shaft. When the input face of the oscillating plate juxtaposed with the pump unit is perpendicular to the axis of the output shaft, the proportion of the transmission, that is, the speed ratio, is set to 0: 1 (neutral). On the other hand, when the output face of the oscillating plate, juxtaposed with the motor unit and angularly offset from the input surface, is perpendicular to the axis of the output shaft, the transmission is set at 1: 1. Since the swashplate can be pivoted (reversed) in any angular orientation between the 1: 0 and 1: 1 ratio positions to set any intermediate ratio, the speed ratio of the transmission is continuously (infinitely) variable. In the hydrostatic transmissions described in the mentioned patents. Various modes of controllers are described for striking a wedge-shaped swashplate to vary the proportion of the transmission. These proportional controller modes use either a single double-acting piston or a pair of opposed pistons driven in opposite axial directions by pressurized hydraulic fluid carried from the oscillating plate ports to exert stroke forces (impetus) on the oscillating platen to vary the angular orientation of the oscillating plate and thus increase (upward stroke) or decrease (downward stroke) the proportion of the transmission. The running force exerted by these actuator pistons is solely the product of the hydraulic fluid pressure and the area of the piston surface exposed to hydraulic fluid pressure. Unfortunately, the force (s) generated by the piston (s) to set a proportion of the transmission and the necessary stroke force to change the proportion of the transmission vary according to the orientation of the swashplate. For example, at approximately the ratio position of 0.5: 1, when the angles of the input and output surfaces of the swash plate relative to the output shaft axis are equal, the opposite forces of the pumped hydraulic fluid acting on the surfaces of the oscillating plate are essentially the same. Thus the required force (s) exerted on the oscillating plate by the actuator piston (s) to fix the position of the 0.5: 1 ratio must increase disproportionately with the increase in the pressure of the hydraulic fluid available from the oscillating plate ports. Consequently, the piston (s) must have large surface areas in order to generate the forces required both to vary and to set the proportions of the transmission over the range of available proportions, which may include reverse angle beyond the 0: 1 ratio position and a limited overshoot range beyond the 1: 1 ratio position. A large actuator piston (s) adds size and weight to the transmission.

Another feature of the ratio controllers described in the aforementioned patents is that the swashplate is mounted on a fixed pivot bolt on the output shaft to establish an oscillating swivel pivot axis that intersects the shaft of the output shaft at a right angle. Then, axially directed stroke forces are exerted on the oscillating plate at radially offset locations of the shaft of the output shaft to generate the necessary moments to vary and fix proportions of the transmission. Unfortunately, these moments exert bending forces on the output shaft, which place high loads on bearings and support structure and can cause deflection of the output shaft. Consequently, the output shaft and its supporting components must be adapted to the size of compliance to withstand those bending moments. This is added to the size and cost, as well as the cost, of the transmission.

Description of the Invention An object of the present invention is to provide an improved continuously variable hydrostatic transmission. Another objective of the present invention is to provide improvements in the provisions for controlling the proportion of the transmission in continuously variable hydrostatic transmissions.

Yet another object of the present invention is to provide a proportion controller for continuously variable hydrostatic transmissions of the type described in the cited United States patents. Still another objective is to provide an improved ratio controller for continuously variable hydrostatic transmissions that grants packaging advantages that contribute to reductions in the size, weight and cost of the transmission. To achieve these objectives, the continuously variable hydrostatic transmission of the present invention comprises a housing; an entry arrow locked in the housing; a output shaft which is muted in the housing and having an axis, a hydraulic pump unit driven by the input shaft, a hydraulic motor unit fixed to the housing, a wedge-shaped oscillating plate placed between the hydraulic pump units and motor and including ports to accommodate the pumped flow of hydraulic fluid between the hydraulic pump and motor units; and a connector pivotally connecting the swashplate to the output arrow in torque coupling relationship. The transmission further comprises a ratio controller that includes a first coupled chamber for the pressurized hydraulic fluid received, a first piston having a first surface area of the face exposed to the hydraulic fluid pressurized in the first chamber, a second chamber coupled to the fluid pressurized received, a second piston having a second face surface area, and a link mechanism connected to the oscillating platen and acting on the first piston driven in a first direction by the hydraulic fluid pressurized in the first chamber to produce a first impetus which pivots the oscillating plate in a first direction of change of the proportion of the transmission and which acts on the second piston driven in a second direction opposite the first direction by the pressurized hydraulic fluid in the second chamber to produce a second pivoting momentum to the oscillating plate in a second direction change of the proportion of the transmission. According to a feature of the present invention, the link mechanism has an effective geometry for axially translating the forces exerted on the link mechanism by the first and second pistons, when driven in their respective first and second directions, towards first and second amplified impulses for pivoting the oscillating plate in the first and second directions of change of the transmission ratio, respectively. Additional features and advantages of the invention will be presented in the description that follows, and, in part, will be apparent from the description, or will be known from the practice of the invention. The objects and advantages of the invention will be known and achieved by the apparatuses particularly indicated in the following description in writing and in the appended claims, as well as the accompanying drawings. It will be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. The accompanying drawings are intended to provide a further understanding of the invention, and are incorporated into and constitute a part of the specification to illustrate one embodiment of the invention, and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a fragmentary longitudinal sectional view of a variable hydrostatic transmission incorporating a controller of the improved ratio according to an embodiment of the present invention; and Figure 2 is a fragmentary, enlarged sectional view of a control valve used in the improved ratio controller of Figure 1. Like reference numerals refer to corresponding parts in all different views of the drawings.

Best Way to Carry Out the Invention As seen in Figure 1, a continuously variable hydrostatic transmission, generally indicated at 10, comprises, as basic components, a housing, fragmentarily indicated at 12, in which an input arrow is muted 14 and an output arrow 16 generally related end-to-end, coaxial. The end of the input shaft external to the housing is suitably adapted for pulse connection with a primary motor (not shown), while the end of the output shaft external to the input shaft 14 drives a hydraulic pump unit, generally indicated at 20, is grounded in the housing 12 in axially opposite relation to the pump unit 18. A wedge-shaped oscillating plate, generally indicated at 22, is impulsively connected to the output shaft at a position between the pump and motor units and is carried to provide pumped exchanges of hydraulic fluid between the pump and motor units. A ratio controller, generally indicated at 24 and structured according to one embodiment of the present invention, is linked to the oscillating plate for the purpose of pivotally adjusting the angular orientation of the oscillating plate with respect to the axis of the output shaft 25, fixing by this the ratio of the transmission of the speed of the output arrow to the speed of the input arrow. Now, referring to Figure 1, in greater detail, the cylindrical inner end of the input shaft 14 is joined to the radially extended carrier 26 which mounts a plurality of axially spaced, angularly spaced posts 28, rotatingly mounting each a pump piston 30 reciprocating respectively in a separate cylinder 32 of a cylinder block of the annular pump 34. A cylindrical extension of the piston holder 26 mounts an annular spherical bearing 36 which serves to mount the pump cylinder block 34 for progressing with precession movement as the pump unit 18 is driven in rotation by the inlet arrow 14. The hydraulic motor unit 20 is essentially equivalent to the hydraulic pump unit 18. However, an annular motor piston carrier 38, equivalent to a rotary pump piston carrier 26, is grounded in the housing 12 by an annular array of posts 40, which also serve to pivotally mount the motor pistons 42 at their free ends. These reciprocating motor pistons and respective cylinders 43 are provided in a motor cylinder block 44, which is rotatably mounted on the motor piston carrier via an annular spherical bearing 46. Since the motor unit 20 is grounded in the housing 12, the motor pistons 42 and the motor cylinder block 44 do not rotate. However, the spherical assemblies of the motor pistons to the posts 40 and the motor cylinder block to the carrier 38 accommodate nutation, precession movement of the motor cylinder block in the same manner as to the pump cylinder block. Reference can be made to the aforementioned patents for a more detailed description of the hydraulic pump unit 18 and the hydraulic motor unit 20. As also described in these patents, the opposite faces of the engine cylinder blocks are pressed. in sliding interfacial contact with the inlet faces 22a and outlet 22b of the oscillating plate 22. The inlet and outlet faces of the oscillating plate 22 are angularly oriented at an acute angle to provide the wedge shape of the oscillating plate. The ports 23, which extend between the inlet and outlet faces of the swash plate, communicate with the openings 25 in the cylinders of the pump and motor, such that hydraulic fluid is pumped back and forth between the pump and motor units. to generate torque of hydrostatic output in the oscillating plate. Still referring to Figure 1, the portion of the outlet arrow 16 that extends through the central openings in the hydraulic pump units 18 and motor 20 and the oscillating plate 22 is formed as a hollow cylinder section 16A. The roller bearings 50 serve to mute the output shaft section 16A for rotation in coaxial relationship within the input shaft 14. The open interior of the output shaft section 16A is closed at its internal termination by a plug 52 and is grooved, as indicated at 53, at its outer end to drive the connection with the inner end of the solid output shaft 16. A pivot pin 54 extends transversely through the section of the output shaft 16 and serves to mount an oscillating plate 22 for pivotal movement that changes the ratio with respect to a pivot axis that intersects the axis of the output shaft 25 at a right angle. The axial recess of the arrow section 16A adjacent to its internal termination provides a cylinder 56 to slidably receive a drive piston 58 to the left side of the pivot pin 54. The left end face 59 of the drive piston 58, the cylinder 56, and plug 52 define a chamber 60 which is coupled only on the high pressure side of the swash plate via a hydraulic fluid circuit diagrammatically indicated at 63. Examples of how this fluid circuit can be set to carry pressurized hydraulic fluid from the side high-pressure oscillating plate 22 are described in the reference patents Numbers: 5,423,183 and 5,535,589. While the hydraulic circuit 150 in the patent No. 5,535,589 is structured to be coupled only on the low pressure side of the oscillating plate, to be coupled only on the high pressure side of the oscillating plate, in accordance with the present invention, it is only necessary to reversing the flow direction of the check valve 154 in the 5,535,589 patent. The fluid circuit 63 herein includes this check valve, as indicated at 63a. As indicated at 62, piston rings are provided to prevent the leakage of hydraulic fluid from the chamber 60 past the actuator piston 58. On the outlet side (right) of the pivot pin 54, a sleeve 64 of cross section in the form of L is fitted within the central opening of the stationary motor piston carrier 38 to provide an annular cylinder 66 for slidably receiving an annular actuator piston 68. An annular chamber 70 is thus defined between the right end face of the piston 68 and an annular piston 68. radial wall 69 of sleeve 64 which closes the right end of cylinder 66. According to a feature of the present invention, the area of the right end face 67 of the actuator piston 68 is larger than the area of the left end face 59 of the drive piston 58. The left end of the actuator piston 68 has notches to accept the outer ring of a thrust bearing 72, the inner ring of which is received in a complete notch. It is provided in a collar 74 which is slidably mounted on the section of the exit arrow 16A. The annular chamber 70 is coupled as a fluid by a fluid circuit, diagrammatically indicated at 76, with a control valve, generally indicated at 78 and described in greater detail in Figure 2. As seen further in Figure 1, a crank arm 80 is provided at an upper apex with a hole 80a through which the pivot pin 54 is received in tight fitting relationship, so as to pivotally mount the crank arm at a central location within the the output arrow 16A generally aligned with the axis of the output arrow. The crank arm depends through an axially elongated groove 79 in the section of the output shaft 16A and serves to mount a bolt 80b in a second vertex to the left of the pivot pin 54 and a bolt 80c in a third vertex a the right of the pivot pin. An axially elongated pulse arm 82, located in diametrically opposite relation to the crank arm 80, carries a bolt 82a at its left end and a bolt 82b at its right end. The upper edge of the pulse arm 82 is formed with a notch 82c for receiving a radially inwardly extending tongue 83 formed on the oscillating plate 22, thereby connecting the pulse arm with the oscillating plate. The pulse arm 82 is received through an axially elongated slot 81 in the section of the outlet arrow 16A and has a curved lower edge conformed to the rounded upper apex of the crank arm 80, on which the arm of the crank is supported. impulse. A pair of links 84 is pivotally interconnected by the bolt 85 to provide a ball joint 86, while its free ends are opened to respectively receive the pin 82a carried by the pulse arm 82 and the pin 80b carried by the crank arm 80. A second pair of arcuate joints 88 is interconnected by a bolt 89 to provide a ball joint 90, and its free ends are opened to respectively receive the pulse arm bolt 82b and the crank arm bolt 80c. The arcuate shape of the joints 88 allows them to extend along the periphery of the section of the exit arrow 16A in a closely spaced relationship. As seen in Figure 1, the ball joint 86 of the joints 84 is positioned to fit on the right side 61 of the drive piston 58, and the joint 90 of the links 88 is positioned to fit on the left edge of the collar 74 which is connected to the actuator piston 68 by the thrust washer 72. As will be seen from the description that follows, the geometry of the pivotally interconnected crank arm 80, the thrust arm 82, and the hinge pairs 84 and 88 provide a mechanism capable of transferring axial forces produced by actuator pistons 68 and 58 in amplified impulses exerted on the oscillating plate 22 of sufficient force to strike the oscillating plate 22 at angular positions of the infinitely variable transmission ratio regardless of the orientation of the oscillating plate. returning to the enlargement of Figure 2, the control valve 78 includes a valve body 92 fixed to the housing of the transmission 12 and having a recess 94 for slidably receiving a valve sleeve 96. An upper annular cavity 98 and a lower annular cavity 100 are machined on the surface of the recess 94. The outer termination of the fluid circuit 102 is in fluid communication with the cavity 98 to supply this cavity with hydraulic fluid carried on the high pressure side of the oscillating plate 22. An example of how this fluid circuit can be provided is described in the aforementioned United States of America Patent Number: 5,486,142. The cavity 100 is engaged in the actuator chamber 70 by the circuit 76 provided by a passage formed in the valve body 92 and the motor piston holder 38. A port 104, punched through the wall of the valve sleeve 96 provides fluid communication between the annular cavity 98 and the interior of the valve sleeve 97. A port 106 is also pierced through the wall of the valve sleeve 96 to provide fluid communication between the inside of the valve sleeve and the annular cavity 100 in the valve body recess 94. A crank 110 is pivotally mounted at its upper end to the valve body 92 by a bolt 111. A link 112 is pivotally connected to a lower end of the crank 110 by a bolt. 113, while the free end of this joint carries a pin 114 for pivotally mounting the upper end of a pin 116. The lower end of this pin is captured in a hole 117 drilled in the actuator piston 68. The crank 110 also includes a bifurcated projection that provides a slot 118 for receiving a transverse pin 119 carried at the lower end of the sleeve 96. As seen from this description, the actuator piston 68 is bonded to the valve sleeve 96, so that this movement and the position of this actuator piston is effective to move and position the valve sleeve within the valve recess 94. Concluding the structural description of the valve 78, slidably mounted within the valve sleeve 96 is a valve spool 120 having a cylindrical flat part 122 at its lower end, and a cylindrical flat part 124 at its upper end. The flat part 122 serves to open and close the port 106 in the valve sleeve 96, while the flat part 124 only serves as a bearing surface to ensure the continuous and slidable movement of the valve spool 120 coaxially inside the valve sleeve. 96. To vary the axial position of the valve spool 120 within the valve sleeve 96, the upper end of the valve spool is connected to a front screw 126, which is driven by a stepped motor 128 mounted on the upper end of the valve spool. valve body 92. From the description of the control valve 78, it is seen that when the valve spool 120 is advanced downwardly through the valve sleeve 96, the flat part 122 opens the port 106 in fluid communication with the port 104, so that the high pressure hydraulic fluid that exists in the annular cavity 98 can flow into the cavity 100 and through the circuit 76 to pressurize the chamber to 70 is located at the atmospheric pressure existing at the lower end of the valve sleeve 96 below the flat part 122. As noted above, the actuator chamber 60 in Figure 1 is continuously pressurized via the fluid circuit 62 to the hydraulic fluid pressure existing on the high pressure side of the oscillating plate 22. Thus, when the actuating chamber 70 is ventilated to atmospheric pressure by the valve 78, the high fluid pressure in the chamber 60 exerts sufficient force on the face 59 of the actuator piston 58 to drive the piston to the right.

The face 61 of the drive piston 58 engages in a drive manner with the ball joint 86, causing the links 84 to straighten. A generally upward force is thus exerted on the bolt 82a, and a generally downward force is exerted on the bolt 82b. The crank arm 80 freely pivots on the pivot pin 54 in the counterclockwise direction, while the impulse arm 82 is rocked in the clockwise direction, causing the oscillating plate 22 to pivot in the clockwise direction. the clockwise direction to increase the proportion of the transmission. At the same time, a generally upward force is exerted on the pin of the pivot 80c as the crank arm 80 pivots in the counterclockwise direction, and a generally downward force is exerted on the pin 82c according to the driving arm 82 rocks in the clockwise direction. The joints 88 are caused to collapse, producing a force to the right on the ball joint 90, which, in turn, drives the actuator piston 68 in the clockwise direction via the collar 74 and the thrust bearing 72. Since the chamber 70 is ventilated at atmospheric pressure, the actuator piston 68 offers little resistance to the axial driving force of the actuator piston 58 in striking the oscillating platen 22 clockwise to increase the proportion of the transmission .

To decrease the proportion of the transmission, the valve spool 120 is moved downwards by the stepped motor 128 to open the port 106, so that the actuating chamber 70 is pressurized to the pressure of the hydraulic fluid existing on the high pressure side. of the oscillating plate via the fluid circuit 102, the cavity 98, and the port 104. Although the actuator chambers 60 and 70 are now pressurized to the same high fluid pressure, the leftward force exerted on the actuator piston 68 is greater that the force to the right exerted on the actuator piston 58, since the face 67 of the piston 68 is of greater area than the area of the face 59 of the actuator piston 58. In this way, the axial force exerted on the ball joint 90 of the links 88 by the actuator piston 68 is greater than the rightward force exerted on the ball joint 86 of the joints 84 exerted by the piston n actuator 58. As the ball joint 90 is driven to the left, the joints 88 are straightened to exert a generally upward on the bolt 82b and a downward force on the pin 80c. The crank arm 80 is rotated clockwise to exert a force generally upwardly on the bolt 80b, while the force generally exerted upwardly on the bolt 82b rocks the driving arm 82 in the opposite direction to the arms. clock hands to exert downward force on pin 82a. The hinges 84 collapse, driving the ball joint 86 in the leftward direction, which, in turn, drives the piston 58 to the left as the oscillating plate 22 is struck in the counterclockwise direction to decrease the proportion of the transmission. By virtue of the geometrical relationships of the pivotal interconnections of the joints 84 and 88 with each other and with the driving arm 82 and the crank arm 80, the axial forces generated by the actuating pistons 58 and 68 on the ball joints 86 and 90 They will produce vertical forces on the driving and crank arm equal to the tangent of the joint angles with the axis 25 of the output shaft. Thus, for example, if the angles of the joints 88 with the axis 25 are equal to 75 °, as shown roughly in Figure 1, the vertical forces exerted on the bolts 82b and 80c as the joints 88 are straightened are equal to the tangent of an angle of 75 ° multiplied by the axial force to the left exerted on the ball joint 90 by the actuator piston 68. Thus, the axial forces exerted by the actuator piston 68 move in vertical forces on the bolts 80c and 82b that are amplified by a factor of 3.732. This force amplification factor increases as the angle of the joints 88 with the axis of the output shaft 25 approaches 90 °. At the same time, the opposite, generally vertical, forces transferred to the bolts 80b and 82a by the crank arm 80 and the impulse arm 82 cause the joints 84 to collapse. An axial force (which is amplified as long as the angle of these articulations with the axis 25 is greater than 45 °) in the ball joint 86 drives the actuator piston 86 to the left. By virtue of this force amplification feature of the present invention and the larger face area of the actuator piston 68, the axial stroke force produced by this piston can be made sufficiently powerful to not only overpotentize the actuator piston 58, but also generate a stroke decrease impetus on the oscillating plate 22 to decrease the transmission ratio regardless of the angular orientation of the oscillating plate. It will be appreciated that, under certain operating conditions, the force exerted by the driving arm 80 which tends to collapse the joints 84 can produce a force generally downward on the pin 82a which supplements the downward stroke force by the driving arm 80 on the oscillating plate 22. As a further feature of the present invention, the axial travel forces generated by the actuator pistons 58 and 68 are moved in opposing, generally vertical, forces which, although amplified in magnitude, are canceled each other in the ball joint bolts 85 and 89. In this way, the stroke forces exerted on the swashplate 22 do not result in bending forces exerted on the output shaft. Returning to Figure 2, the axial position of the valve spool 120 within the valve sleeve 96 fixed by a vehicle operator control via a step motor 128 establishes a desired angular orientation (transmission ratio) of the oscillating plate 22. Any proportion of the particular transmission is fixed when the elements of the control valve 78 are in the position illustrated in Figure 2. It is seen that the flat part 122 blocks the port 106, and thus the flow of the hydraulic fluid inwardly is blocked. and out of the actuator chamber 70. The fluid pressure in the actuator chamber 68 which exactly balances the force exerted on the actuator piston 58 by the hydraulic fluid pressure in the actuator chamber 60. These balanced, opposite-directed forces produce opposing forces. , balanced on the oscillating plate 22 effective to sustain an angular orientation of fixation of the proportion n of the oscillating plate 22. Since the surface area of the piston face 67 is larger than the surface area of the piston face 59, the fluid pressure in the actuator chamber 70 necessary to maintain a reference value of the ratio will be less than the fluid pressure in the actuator chamber 60. When the stepper motor 128 is activated to drive the valve spool 120 downward in response to an order from the vehicle operator to decrease the transmission ratio (reduce vehicle speed ), the port 106 is opened by the flat part 122, so that the hydraulic fluid pressure in the actuator chamber 70 can be increased to the level existing on the high pressure side of the oscillating plate 22, ie equal to the pressure of fluid in the actuator chamber 60. By virtue of the larger surface area of the face of the actuator piston 68, the piston is driven to the left to strike down the piston. oscillating lato 22. Under the feedback path provided by articulation 112 and crank 110, the movement to the left of the actuator piston 68 moves in a downward movement of the valve sleeve 96. When the oscillating plate is struck downward to the setting position of the proportion commanded by the depressed position of the valve spool 120, the valve sleeve 96 is pulled down so that the port 106 is completely blocked by the flat part 122. The actuator chamber 70 is then isolated from the port 104 and the high pressure side of the oscillating plate 22, leaving the fluid pressure in the chamber 70 at a level sufficient to exert an axial force to the left on the actuator piston 68 to counterbalance the axial force to the right exerted on the actuator piston 58 by the pressure of the fluid in the actuator chamber 60. In this way Holds the fixation of the ratio of the diminished stroke of the swash plate ordered by the operator. Conversely, when the operator commands an increased speed, the stepped motor 128 pulls the valve spool 120 upwards to an elevated position. Flat surface 122 again unlocks port 106, but in this case, actuator chamber 70 is vented at atmospheric pressure through the open lower end of valve sleeve 96. Actuator piston 58 is energized by high pressure of the fluid in the actuator chamber 60 for the upward stroke of the oscillating plate 22 and driving the actuator piston 68 to the right. The valve sleeve 96 is urged upward via the feedback movements of the articulation 112 and the crank 110 until the surface 122 again completely blocks the port 106 to isolate the actuator chamber 70. The axial forces of the actuator pistons 58 and 68 again counterbalanced to hold the new position of the highest proportion of the oscillating plate ordered by the operator. From the above description, it is seen that the valve spool 120 is positioned in response to the operator's setting orders and the movement of the valve sleeve 96 tracks the movement of the oscillating plate 22 via the feedback mechanism supplied by the actuator piston 68, the articulation 112, and the crank 110 to indicate when the orders, of establishing the proportion, of the operator have been fulfilled. It will also be noted that the pressure of the fluid in only one chamber, the actuator chamber 70, is controlled in order to increase the stroke and decrease the stroke of the oscillating plate 22, as well as to sustain an establishment of the ratio of the oscillating plate. Since the actuator chamber 60 continuously engages in fluid with the high pressure side of the oscillating plate 22 and, together with the actuator piston 58, is contained with the output shaft section 16A, the fluid sealing considerations are relaxed. of high PV (pressure / velocity) imposed by the fluid circuit 62. Since the actuator chamber 70 is located on the side of the transmission motor unit where the components are stationary, the fluid seal for the fluid circuits 76 and 102, in the manner discussed in the joint, commonly assigned pending application, serial number No. 089 / 608,389, filed on February 28, 1996, is unimportant. It will be appreciated that the positioning of the valve spool by the stepped motor 128 can be controlled by electronic digital processing circuits that respond to operator inputs and various operating parameters of the transmission 10, such as hydraulic fluid pressure, speed of the input arrow, and speed of the output arrow. Each revolution or partial revolution (step) of the stepped motor 128 will cause a finite movement of the valve reel 96, which, in turn, produces a finite increase in the stroke of the swashplate. In this way, fixations of the proportions of the oscillating plate can be achieved with extreme precision. When the stepped motor is not stepped, the valve spool 120 is stationary, as well as the angular position of the fixation of the ratio of the oscillating plate 22. It will be apparent to those skilled in the art that various modifications and variations can be made in the continuously variable hydrostatic transmission of the present invention and the illustrated construction thereof without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention described herein. For example, both actuator pistons 58 and 68 could be provided internally of the output shaft section 16A or provided as annular components coaxially surrounding the output shaft section.

It is therefore intended that the specification and the drawings be considered as examples only, with the true scope and spirit of the invention indicated by the following claims.

Claims (19)

1. A continuously variable hydrostatic transmission comprising, in combination: a housing; an entry arrow locked in the housing; an output arrow that is muted in the housing and has an axis; a hydraulic pump unit driven by the input shaft, - a hydraulic motor unit fixed to the housing: a wedge-shaped oscillating plate placed between the hydraulic and motor pump units and including ports to accommodate the pumped fluid flow Hydraulic between the hydraulic and motor pump units; a connector that pivotally connects the oscillating plate to the output shaft in coupled relation by torque; and a proportion controller including, - a first chamber coupled to the pressurized hydraulic fluid received, a first piston having a first surface area of the face exposed to pressurized hydraulic fluid in the first chamber, a second chamber coupled to receive hydraulic fluid pressurized, a second piston having a second surface area of the face exposed to the hydraulic fluid pressurized in the second chamber, the second surface area of the face being greater than the first surface area of the face, and a joint mechanism connected to the oscillating plate and acting on the first piston driven in a first direction by hydraulic fluid pressurized in the first chamber to produce a first impetus that pivots the oscillating plate in a first direction of the transmission that changes the ratio and driven on the second piston driven in a second direction opposite the first dire The hydraulic fluid is pressurized in the second chamber to produce a second impetus that pivots the oscillating plate in a second direction of the transmission that changes the ratio.

2. The transmission defined in claim 1, wherein at least one of the first and second pistons is provided internally of the output shaft.

3. The transmission defined in claim 1, wherein at least one of the first and second pistons is provided as an annular component that coaxially surrounds the output shaft. The transmission defined in claim 1, wherein the first chamber and the first piston are provided internally of the exit shaft, and the second chamber and the second piston are provided as annular components that co-axially surround the exit shaft. The transmission defined in claim 1, wherein the first chamber engages exclusively in fluid with a high pressure side of hydraulic fluid of the swashplate, and wherein the proportion controller further includes a control valve that is operated to selectively control the hydraulic fluid pressure in the second chamber. The transmission defined in claim 5, wherein the control valve is selectively positioned to (1) close the second chamber so as to inhibit the driven movements of the first and second pistons in their respective first and second directions, to maintain a angular position of fixing the ratio of the oscillating plate transmission, (2) ventilating the second chamber, to allow the impulse movement of the first piston in the first direction to pivot the oscillating plate in the first direction of the shift transmission. the ratio, and (3) coupling the second chamber to the hydraulic pressure high-pressure side of the oscillating plate, to produce driven movement of the second piston in the second direction to pivot the oscillating plate in the second direction of the transmission. proportion. The transmission defined in claim 6, wherein the control valve includes: a valve body having an elongated recess and first and second axially elongated recesses formed in a recess surface at axially displaced locations, a first passage that the first cavity is coupled to the high-pressure side of the hydraulic fluid of the oscillating plate, and a second passage that couples the second cavity to the second chamber, an elongated valve sleeve disposed in the recess and having a first radial port open to the second chamber. first cavity and a second radial port open to the second cavity; and a valve spool received slidably in the valve sleeve and having a flat surface for opening and closing the second port. The transmission defined in claim 7, wherein the proportion controller further includes an actuator connected to adjust an axial position of the valve spool within the valve sleeve in accordance with a setting of the proportion of the transmission selected by an operator The transmission defined in claim 8, wherein the proportion controller further includes a feedback joint interconnecting the second piston and the valve sleeve to axially place the valve sleeve within the valve body in accordance with a position angular, of the fixation of the proportion of the transmission, of the oscillating plate. The transmission defined in claim 9, wherein the valve sleeve includes a vent opening to which the second port is placed in fluid communication by the valve spool when axially positioned by the actuator to produce pivotal movement of the valve. oscillating plate in the first direction of change of proportion. The transmission defined in claim 1, wherein the articulation mechanism has an effective geometry for transferring forces axially exerted on the articulation mechanism by the first and second pistons, when driven in their respective first and second directions, in first and second amplified impulses for pivoting the oscillating plate in the first and second directions of change of the transmission ratio, respectively. The transmission defined in claim 11, wherein the connector includes a transverse pivot pin attached to the output shaft and having a pivot axis that intersects the axis of the output shaft, and wherein the articulation mechanism includes, - an axially elongated boom arm having a connection to the swashplate at a radially offset location from the pivot shaft and first and second connection points offset in opposite axial directions relative to the pivot shaft, a pivotally mounted crank arm by the pivot pin in substantially diametrically opposite relation to the pulse arm and having first and second connection points offset in respective opposite axial directions of the pivot axis, a pair of first articulations elongated pivotally interconnected at the corresponding ends to produce a first ball joint and having free ends respectively pivotalmen connected to the first connection points of the driving arm and the crank arm, and a pair of elongated second articulations pivotally interconnected at the corresponding ends to produce a second ball joint and having free ends connected pivotally respectively to the second points of connection of the driving arm and the crank arm, whereby the axial force exerted on the first ball joint by the first piston, when driven in the first axial direction, reinforces the first joints and collapses the second joints to drive the second piston in the first axial direction and for exerting the first amplified impetus on the swashplate, and the axial force exerted on the second swivel joint by the second piston, when driven in the second axial direction, straightens the second articulations and collapses the first joints to boost r the first piston in the second axial direction and exert the second amplified impetus on the oscillating plate. The transmission defined in claim 12, wherein the first chamber and the first piston are provided internally of the exit shaft, and the second chamber and the second piston are provided as annular components coaxially surrounding the outlet shaft. 1

4. The transmission defined in claim 13, wherein the first chamber is coupled exclusively by fluid to a high pressure hydraulic fluid side of the oscillating plate, and wherein the proportion controller further includes a control valve that acts to selectively control the hydraulic fluid pressure in the second camera. The transmission defined in claim 14, wherein the control valve is selectively positioned to (1) close the second chamber so as to inhibit the impulse movements of the first and second pistons in their respective first and second directions, so as to maintaining an angular position of fixing the ratio of the oscillating plate transmission, (2) ventilating the second chamber, to allow the impulse movement of the first piston in the first direction to pivot the oscillating plate in the first direction of the transmission of changing the ratio, and (3) coupling the second chamber to the high pressure hydraulic fluid side of the oscillating plate, to produce driven movement of the second piston in the second direction to pivot the oscillating plate in the second direction of the shift transmission of the proportion. The transmission defined in claim 15, wherein the control valve includes: a valve body having an elongated hollow and a first and second axially elongated cavities formed in a hollow surface at axially displaced locations, a first passage that coupling the first cavity to the high-pressure side of the hydraulic fluid of the oscillating plate, and a second passage that couples the second cavity to the second chamber, an elongated valve sleeve disposed in the recess having a first radial port open to the first cavity and a second radial port open to the second cavity; and a valve spool slidably received in the valve sleeve and having a flat surface for opening and closing the second port. The transmission defined in claim 16, wherein the proportion controller further includes an actuator connected to adjust an axial position of the valve spool within the valve sleeve in accordance with a setting of the proportion of the transmission selected by an operator The transmission defined in claim 17, wherein the proportion controller further includes a feedback joint that interconnects the second piston and the valve sleeve to axially place the valve sleeve within the valve body in accordance with a position of the angular transmission, of setting the ratio, of the oscillating plate. The transmission defined in claim 18, wherein the valve sleeve includes a vent opening to which the second port is placed in fluid communication by the valve spool when axially positioned by the actuator to produce pivotal movement of the valve. oscillating plate in the first direction of change of proportion. SUMMARY To control the transmission ratio of a continuously variable hydrostatic transmission inclu an input shaft (14), an output shaft (16), a hydraulic pump unit (18) driven by the input shaft (14), a grounded hydraulic motor unit (20), and a wedge-shaped oscillating plate (22) pivotally connected, urged, with the output shaft (16) and positioned to accommodate exchanges of hydraulic fluid pumped between the pump units and of engine (18,20). A proportion controller having a pair of hydraulically actuated pistons of different sizes (58, 68) coupled by an articulation mechanism for pivoting the oscillating platen (22) in directions of change of proportion of the transmission is provided. The smaller piston (58) is incorporated internally of the output shaft (16), while the larger piston (68), of an annular shape, coaxially surrounds the output shaft (16). The articulation mechanism has an effective geometry to translate the axial forces exerted by the pistons (58, 68) in amplified momentum of change of proportion exerted on the oscillating plate (22) The proportion controller also includes a control valve (78) which is selectively positioned to change the pressure of the hydraulic fluid acting on the larger piston (68), so that it fixes a proportion of the transmission and also determines the direction of the Change of proportion of the pivotal movement of the oscillating plate.