Reversible hydrostatic transmission with dump valve

Abstract: A hydrostatic transmission is disclosed comprising a radial ball pump (11) and a radial ball motor (13) wherein the normal journal member (33) may be replaced by an alternative or modified journal member (33'), such that even with a reverse direction of actuation of the displacement control (49), the HST still operates in the forward direction, with no other changes required. The present invention also includes a simplified dump valve member (107) comprising a single, unitary member which may be merely inserted to its assembled position in which a pair of retention portions (123, 135) retain the dump valve, and permit it to pivot about the retention portions from an unactuated position (FIG. 1) to an actuated position (FIG. 8).

Description: Background of the Disclosure The present invention relates to hydrostatic transmissions (HSTs), and more particularly, to such transmissions which are used in connection with the propulsion of vehicles such as lawn and garden tractors. A typical hydrostatic transmission includes a pair of fluid displacement mechanisms, one of which functions as a pump and the other of which functions as a motor. Conventionally, the pump comprises a variable displacement hydrostatic unit, while the motor comprises a fixed displacement hydrostatic unit. Therefore, there are typically various controls associated with the pump, such as some form of displacement control, and perhaps other controls as well. Although the present invention may be used advantageously with hydrostatic transmissions including various types of fluid displacement mechanisms, it is especially advantageous when the fluid displacement mechanisms comprise radial piston devices, and the invention will be described in connection therewith. As used herein, the term "radial piston" will be understood to include devices in which the piston is either a true cylindrical piston which reciprocates in a cylinder, or a ball member which reciprocates in a cylinder. A hydrostatic transmission known from US-A-5 234 321 comprises a housing assembly, a variable displacement radial piston pump and a fluid pressure operated motor disposed in the housing assembly. The radial piston pump includes displacement varying means operable to vary the displacement of the pump, including reversible control means operable to move the displacement varying means in first and second opposite directions, in response to movement of the control means in first and second opposite directions from a neutral position. The motor defines a fluid inlet and a fluid outlet, and the housing assembly defines high and low pressure passages in fluid communication with the fluid inlet and the fluid outlet, respectively. The pump comprises a rotor assembly rotatably mounted on a journal member disposed within a journal bore defined by the housing assembly, the journal bore providing open fluid communication with both of the high and low pressure passages. The journal member defines high and low pressure pump slots in fluid communication with contracting and expanding chambers, respectively, of the pump. The journal member further defines first and second axial bores, and first and second passages interconnect the pump slots and the high and low pressure passages. The hydrostatic transmission operates in a forward direction in response to movement of the control means in the first direction from the neutral position in the presence of a journal member disposed in the journal bore wherein the first axial bore is in fluid communication with the low pressure pump slot and the first passage is in fluid communication with the first axial bore and with the low pressure passage, and the second axial bore is in fluid communication with the high pressure pump slot and the second passage is in fluid communication with the second axial bore and with the high pressure passage. One of the problems associated with providing hydrostatic transmissions to vehicle original equipment manufacturers (OEMs) is that each OEM normally has its own preferred linkage arrangement designed into its vehicle. For example, one OEM may utilize a pump displacement control in which depressing a foot pedal pushes or pulls a linkage member "forward" for the purpose of increasing pump displacement in a forward direction. Another vehicle OEM may have a pump displacement control in which depressing a foot pedal shifts a linkage member "rearward" to increase pump displacement in the forward direction. Typically, the manufacturers of HSTs have provided the pumps of their transmissions with pump displacement controls which move one direction to increase pump displacement moving forward and move in the opposite direction to increase pump displacement moving in reverse. If the potential OEM customer already has its control linkage set up for movement corresponding to what is already available on the HST, there are no linkage changes required. If, on the other hand, the HST manufacturer has its pump displacement control set up to move in a direction opposite to that of the linkage being used by the vehicle OEM, it is necessary for the HST manufacturer to request the vehicle OEM to redesign and reverse the vehicle linkage to accommodate the HST linkage. Accordingly, it is an object of the present invention to provide an improved hydrostatic transmission which can be used on a vehicle having either forward-moving linkage or rearward-moving linkage, without any substantial redesign or revision of the hydrostatic transmissions, and which eliminates the need for the vehicle OEM to redesign or reverse its linkage. The above and other objects of the invention are accomplished by the provision of an improved hydrostatic transmission as defined in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an axial cross-section of a hydrostatic transmission of the type with which the present invention may be utilized. FIG. 2 is a transverse cross-section, taken on line 2-2 of FIG. 1 , and on the same scale. FIG. 3 is an axial cross-section, taken on line 3-3 of FIG. 1 , and on the same scale. FIG. 4 is a fragmentary transverse cross-section, similar to FIG. 2 , but on a larger scale, illustrating one aspect of the present invention. FIG. 5 is a fragmentary axial cross-section, similar to FIG. 3 , but on the same scale as FIG. 4 , further illustrating the one aspect of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, which are not intended to limit the invention, FIG. 1 is an axial cross-section of a hydrostatic transmission of the type with which the present invention may be utilized. The hydrostatic transmission may be generally of the type known from US-A-5,234,321. A hydrostatic transmission comprises a hydrostatic pump, generally designated 11, and a hydrostatic motor, generally designated 13. The pump 11 includes a pump cover 15, while the motor 13 includes a motor cover 17, and the pump 11 and motor 13 share a common manifold body 19. The pump cover 15, motor cover 17, and manifold body 19 are joined together by a plurality of bolts, to comprise a housing assembly, and to define therein a hydrostatic transmission case 21 (also referred to hereinafter as a "case chamber"). Preferably, the hydrostatic transmission, as shown in FIG. 1, comprises a self-contained, stand alone unit. Referring now to FIG. 2, in conjunction with FIG. 1, the pump cover 15 defines an input hub portion 23, within which is disposed an input shaft 25, rotatably supported within the hub portion 23 by means of a bearing set 27. Typically, the input shaft 25 has an input pulley (not shown in FIG. 1) keyed to the input shaft, or attached in some other suitable means, by means of which engine torque is transmitted to the hydrostatic pump 11. At its inner end (bottom end in FIG. 1), the input shaft 25 includes a terminal portion 29 through which a drive pin (not shown in FIG. 1) extends, transverse to the axis of rotation of the input shaft 25, the function of the drive pin being to engage a cut out portion of a pump rotor 31. Therefore, rotation of the input shaft 25 drives the pump rotor 31. The pump rotor 31 is disposed about a cylindrical support member 33 (also referred to hereinafter as a journal member), which is press-fit into a cylindrical journal bore 34 in the manifold body 19. The support member 33 defines a pair of axially-extending bores 35 and 37 (see also FIG. 2). The bore 35 comprises a low pressure inlet passage, and the bore 37 comprises a high pressure outlet passage, assuming rotation of the pump rotor 31 in a clockwise direction as viewed in FIG. 2. As is well known to those skilled in the art, if the direction of rotation of the pump rotor 31 were reversed, the bore 35 would be the high-pressure outlet passage, and the bore 37 would be the low pressure inlet passage. The pump rotor 31 defines a plurality of cylinder bores 39, and disposed within each bore 39 is a piston or ball 41, it being understood that the present invention is equally applicable to a radial piston or a radial ball type of device. The balls 41 are in engagement with, and restrained in their radial travel, by a concave surface on a race member 43, which is disposed within a cam ring 45. The cam ring 45 is disposed to pivot about the axis of a cam pivot pin 47 (shown only in FIG. 2), the pin 47 being received within a pair of aligned bores defined by the pump cover 15 and the manifold body 19. As is generally well-known to those skilled in the art, pivotal movement of the cam ring 45 varies the displacement and output fluid flow of the pump 11, for any given input speed. Pivotal movement of the cam ring 45 about the axis of the pivot pin 47 is accomplished by means of a displacement control assembly, generally designated 49 (shown only in FIG. 2). Such displacement controls are well known to those skilled in the art, are not an essential feature of the invention, and therefore, will be described only briefly herein. The displacement control assembly 49 includes a control shaft 51, which extends through the pump cover 15 for connection to a linkage arrangement (not shown herein). Appropriate movement of the linkage rotates the control shaft 51 about its axis of rotation, thereby causing angular displacement of a pin 53 which is received in an opening 55 defined by the cam ring 45. Thus, rotation of the control shaft 51 results in pivotal movement of the cam ring 45 about the cam pivot pin 47 in a known manner, to vary the displacement of the pump 11 from its neutral (zero displacement) position shown in FIG. 2. Assuming the control shaft 51 is rotated clockwise (thus pivoting the cam ring 45 counter-clockwise about the pivot pin 47), the operation of the pump 11 will now be described. As the input shaft 25 rotates, the pump rotor 31 rotates, with some of the balls 41 moving radially outward in their respective cylinder bores 39, drawing inlet fluid from the axial bore 35. At the same time, certain of the balls 41 are being displaced radially inwardly, thus pumping pressurized fluid from their respective cylinder bores 39 into the axial bore 37. Fluid communication from the axial bore 35 to the outwardly moving balls 41 is by means of a pump slot 57 defined by the journal member 33. Similarly, communication of pressurized fluid from the inwardly moving balls 41 to the axial bores 37 is by means of a pump slot 59, defined by the journal member 33. Referring now to FIG. 3, in conjunction with FIG. 1, the hydrostatic motor 13 is a fixed-displacement motor, but is otherwise of the same general construction as the pump 11. Thus, the motor 13 includes a cylindrical support member 61 (also referred to hereinafter as a journal member), which is press-fit into a cylindrical journal bore 62 defined by the manifold body 19. The support member 61 defines a pair of axially extending bores 63 and 65, and a pair of housing slots 64 and 66 (labelled only in FIG. 6) communicating with the axial bores 63 and 65, respectively. As is well known to those skilled in the art, the construction of the motor support member 61 may be substantially the same as that of the pump support member 33. Rotatably supported on the support member 61 is a motor rotor 67 which defines a plurality of cylinder bores 69, with a piston or ball 71 being disposed reciprocally within each of the bores 69. The balls 71 are restrained in their radial travel by a concave surface of a race member 73, the race member 73 being seated within a recess in the manifold body 19, and restrained axially therein by the motor cover 17. The motor rotor 67 includes an output portion 75, by means of which the rotor 67 can drive an output shaft 77 (shown in FIG. 3, but omitted from FIG. 1) by any suitable means, which is well known to those skilled in the art and will not be illustrated or described herein. Referring still primarily to FIGS. 1 and 3, the lower portion of the journal member 33 defines a housing slot 79 in open communication with the axial bore 35, and a housing slot 81 in open communication with the axial bore 37. The housing slots 79 and 81 could also be referred to as "motor slots" but are not so referenced herein because they are not in direct communication with the motor 13. By means of the opposite ends of a cross bore 83, which is plugged at its upper end in FIG. 3 by means of a threaded plug 85, the bore 35 and housing slot 79 are in communication with a passage 87, while the axial bore 37 and housing slot 81 are in fluid communication with a passage 89. The passage 87 is in fluid communication with the axial bore 63 of the support member 61 by means of a vertical bore 91, and similarly, the passage 89 is in fluid communication with the axial bore 65 by means of a vertical bore 93. Thus, with the input shaft 29 rotating clockwise, as was described previously, pressurized fluid is communicated through the axial bore 37, then through the cross bore 83, the passage 89, the vertical bore 93, then through the axial bore 65 to those cylinders 69 of the motor 15 in which the ball 71 is moving radially outward, as is well known to those skilled in the art. At the same time, in the case of those cylinders 69 in which the ball 71 is moving radially inward, low pressure exhaust fluid is being communicated through the axial bore 63, then through the vertical bore 91, through the passage 87, then through the cross bore 83, the housing slot 79, and through the axial bore 35 to the inlet of the pump 11, also in a manner well known to those skilled in the art. As a result, the output shaft 77 of the motor 13 is driven in what will be considered hereinafter the "forward" direction. Referring again primarily to FIGS. 2 and 3, it should be noted that the axial bores 35 and 37 are "straight" (as illustrated in FIG. 1), and that the bores 35 and 37 are oriented at approximately a 45° angle, i.e., a plane interconnecting the axes of the bores 35 and 37 would be oriented at approximately 45° to a transverse plane passing through the axis of the support member 33. Such a plane would be oriented vertically in both FIGS. 2 and 3. In FIGS. 2 and 3, it may be seen that both the pump slots 57 and 59 and the housing slots 79 and 81 are oriented approximately perpendicular to the axial bores 35 and 37. In other words, the housing slot 79 includes a bottom surface 95 (see FIG. 3) and that bottom surface 95, as well as the bottom surfaces of the other slots 57, 59 and 81 are all oriented approximately perpendicular to the imaginary plane passing through the axial bores 35 and 37. The above-described relationship of the axial bores 35 and 37 and slots 57, 59, 79, and 81 is the conventional relationship which has been in use commercially and has the following result. With the input shaft 29 rotating clockwise in FIG. 2, rotation of the control shaft 51 in a clockwise direction will result in pivotal movement of the pin 53 as indicated by the arrow in FIG. 2, and fluid will flow as described previously, resulting in rotation of the output shaft 77 in the forward direction. As was discussed in the BACKGROUND OF THE DISCLOSURE, in certain vehicle applications, it is desirable for the control shaft 51 to be connected to a linkage which moves in a direction opposite to what is "normal", wherein the resulting rotation of the control shaft 51 in the counter-clockwise direction (as viewed in FIG. 2) will result in rotation of the output shaft 77 in the forward direction. In accordance with the present invention, such may be accomplished by "replacing" the support member 33, having the construction shown in FIGS. 2 and 3, with a modified support member or journal member 33' having the construction shown in the fragmentary views of FIGS. 4 and 5. As used herein, it will be understood that reference to the journal member 33 being "replaced" by the modified journal member 33' typically means that, during the assembly of hydrostatic transmissions to be used with the "opposite" linkage, the modified journal member 33' will be inserted in the manifold body 19, rather than the standard journal member 33. Referring now primarily to FIGS. 4 and 5, it should be noted that those figures are oriented the same as FIGS. 2 and 3, respectively, but are enlarged relative thereto. In FIG. 4 it may be seen that the modified journal member 33' defines pump slots 57' and 59', and by comparing FIG. 5 to FIG. 2, it may be seen that the slots 57' and 59' are oriented the same as were the slots 57 and 59 in FIG. 2. However, in the modified or "reverse" journal member 33' of FIGS. 4 and 5, the axial bores 35' and 37' are not perpendicular to the pump slots 57' and 59', as was the case with the journal member 33. Instead, the plane containing the axes of the bores 35' and 37' is oriented at an acute angle to the pump slots 57' and 59'. In the subject embodiment, the acute angle is approximately 45°. Referring now primarily to FIG. 5, the reverse journal member 33' defines housing slots 79' and 81', which are displaced about 90° from the position of the housing slots 79 and 81, as shown in FIG. 3. The housing slots 79' and 81' also define an acute angle relative to the plane containing the axes of the bores 35' and 37'. Viewing the reverse journal member 33', as shown in FIGS. 4 and 5 in the context of FIGS. 2 and 3, the operation of the present invention, including the reverse journal member 33' in place of the regular journal member 33, will be described. Assuming the control shaft 51 is rotated counterclockwise (thus pivoting the cam ring 45 clockwise about the pivot pin 47), the balls in the cylinders communicating with the pump slot 59' are now moving radially outwardly, drawing inlet fluid from the axial bore 37. At the same time, the remainder of the balls 41 are being displaced radially inwardly, thus pumping pressurized fluid from their respective cylinder bores 39 into the pump slot 57' and the axial bore 35'. The pressurized fluid flows from the axial bore 35' into the housing slot 79' , which is in fluid communication through the cross-bore 83, passage 91, etc., with the cylinders in the motor 13 in which the balls 71 are moving radially outward. At the same time, fluid is exhausted from those cylinders 69 in which the ball 71 is moving radially inward, with the low-pressure exhaust fluid flowing back through the passage 87, through the upper end of the cross-bore 83, and into the housing slot 81'. From there, low-pressure fluid flows through the axial bore 37' and back up to the pump slot 59', ready to enter the expanding cylinders of the pump 11. Thus, it may be seen that the motor 13 is still driven in the forward direction, even with the direction of input to the displacement control assembly 49 being reversed, simply by inserting the reverse journal member 33' in place of (instead of) the journal member 33. No other change or modification of any part of the hydrostatic transmission is required, in order to accommodate such reversed direction of input to the displacement control assembly 49. Furthermore, it has been determined in connection with the development of the present invention that the modified reverse journal member 33' does not detract in any way from the efficiency (either volumetric or mechanical) of the pump 11, or of the overall hydrostatic transmission. Although the present invention has been described in connection with a situation in which the vehicle OEM wishes to utilize a reversed input to the displacement control assembly 49, the reverse journal member 33' could also be used in a situation where the vehicle OEM wishes to use "normal" input to the displacement control assembly 49, but is utilizing a vehicle engine which provides an input to the input shaft 25 of the pump 11 which is "reversed" from what is normal. In other words, if the standard, commercially available engine provides a clockwise rotation of the input shaft 25 (looking down in FIG. 1), some vehicle OEM's may have an engine which provides a counterclockwise input. In that case, the reverse journal member 33' may be used in conjunction with the counterclockwise input to the pump 11, and the direction of rotation of the output shaft 77 will still correspond to what is considered the "normal" forward direction of operation. Therefore, references hereinafter and in the appended claims to a "forward input" or "reverse input" will be understood to refer to either the input to the displacement control assembly 49 or to the input shaft 25 of the pump 11. Also, although the present invention has been described in connection with replacing the journal member 33 of the pump 11, those skilled in the art will appreciate that the invention is not so limited, and that the journal member 61 of the motor 13 could be replaced by a reverse journal member (made generally in accordance with the teachings of FIGS. 4 and 5), and the functional result would be the same. In other words, by utilizing a normal pump journal 33 but a reverse motor journal, if either the input to the displacement control assembly 49 or the input drive to the input shaft 25 is reversed, the output shaft 77 will rotate in the "forward" direction. It will also be understood by those skilled in the art that if both inputs are reversed, then it is necessary to utilize both the normal pump journal and the normal motor journal in order for the output shaft 77 to operate in the forward direction.

Claims: A hydrostatic transmission comprising a housing assembly (15, 17, 19), a variable displacement radial piston pump (11) and a fluid pressure operated motor (13) disposed in said housing assembly; said radial piston pump (11) including displacement varying means (49) operable to vary the displacement of said pump, including reversible control means operable to move said displacement varying means (49) in first and second opposite directions, in response to movement of said control means in first and second opposite directions from a neutral position (FIG. 2); said motor (13) defining a fluid inlet (65) and a fluid outlet (63), and said housing assembly (15, 17, 19) defining high (89) and low (87) pressure passages in fluid communication with said fluid inlet (65) and said fluid outlet (63), respectively; said pump (11) comprising a rotor assembly (31) rotatably mounted on a journal member (33) disposed within a journal bore (34) defined by said housing assembly, said journal bore providing open fluid communication with both of said high (89) and low (87) pressure passages; said journal member (33) defining high and low pressure pump slots (57,59) in fluid communication with contracting and expanding chambers (39), respectively, of said pump, said journal member further defining first (35) and second (37) axial bores, and first (79) and second (81) passages interconnecting said pump slots and said high (89) and low (87) pressure passages; wherein said hydrostatic transmission operates in a forward direction in response to movement of said control means in said first direction from said neutral position (FIG. 2) in the presence of a first journal member (33) disposed in said journal bore (34) wherein said first axial bore (35) is in fluid communication with said low pressure pump slot (57) and said first passage (79) is in fluid communication with said first axial bore (35) and with said low pressure passage (87), and said second axial bore (37) is in fluid communication with said high pressure pump slot (59) and said second passage (81) is in fluid communication with said second axial bore (37) and with said high pressure passage (89); characterized in that said hydrostatic transmission operates in said forward direction in response to movement of said control means in said second direction from said neutral position in the presence of a second journal member (33') disposed in said journal bore (34), wherein said first axial bore (35') is in fluid communication with said high pressure pump slot (57') and said first passage (79') is in fluid communication with said first axial bore (35') and with said high pressure passage (89), and said second axial bore (37') is in fluid communication with said low pressure pump slot (59') and said second passage (81') is in fluid communication with said second axial bore (37') and with said low pressure passage (87). A hydrostatic transmission as claimed in claim 1, characterized by, in said first journal member (33), said first (79) and second (81) passages comprise slots oriented generally parallel to each other, and generally perpendicular to said axial bores (35,37). A hydrostatic transmission as claimed in claim 1, characterized by, in said second journal member (33'), said first (79') and said second (81') passages comprise slots oriented generally parallel to each other, and oriented at an acute angle relative to said axial bores (35',37'). A hydrostatic transmission as claimed in claim 1, characterized in that said first (79, 79') and second (81, 81') passages comprise high and low pressure housing slots in fluid communication with said high (89) and low (87) pressure passages, respectively; said first (35) and second (37) axial bores of said first journal member (33) are oriented generally perpendicular to said pump slots (57, 59), and said housing slots (79, 81) of said first journal member (33) are oriented generally perpendicular to said axial bores (35, 37); and said first (35') and second (37') axial bores of said second journal member (33') are oriented at an acute angle to said pump slots (57', 59'), and said housing slots (79', 81') of said second journal member (33') are oriented at an acute angle to said axial bores (35', 37'). A hydrostatic transmission as claimed in claim 4, characterized by said acute angle of said axial bores (35', 37') relative to said pump slots (57', 59') comprises about forty-five degrees. A hydrostatic transmission as claimed in claim 4, characterized by said acute angle of said housing slots (79', 81') relative to said axial bores (35', 37') comprises about forty-five degrees. A hydrostatic pump (11) or motor (13) of the radial piston type comprising a housing assembly (15,17,19) defining high (89) and low (87) pressure passages; wherein said hydrostatic pump or motor comprises a rotor assembly (31;67) rotatably mounted on a journal member (33;61) disposed within a journal bore (34;62) defined by said housing assembly, said journal bore providing open fluid communication with both of said high (89) and low (87) pressure passages; said journal member (33;61) defining high and low pressure slots (57,59) in fluid communication with contracting and expanding chambers (39;69) of said pump or motor (11;13); said journal member (33;61) further defining first (35;63) and second (37;65) axial bores and first (79;64) and second (81;66) passages providing fluid communication between said first and second axial bores and said high and low pressure passages; wherein said pump or motor operates in a forward direction in response to a forward input in response to the presence of a first journal member (33;61) disposed in said journal bore (34;62) wherein said first axial bore (35;63) is in fluid communication with said low pressure slot (57) and said first passage (79;64) is in fluid communication with said low pressure passage (87), and said second axial bore (37;65) is in fluid communication with said high pressure slot (59) and said second passage (81;66) is in fluid communication with said high pressure passage (89); characterized in that aid pump or motor operates in a forward direction in response to a reverse input in response to the presence of a second journal member (33') disposed in said journal bore (34;62) wherein said first axial bore (35';63) is in fluid communication wit said high pressure slot (57') and said first passage (79';64) is in fluid communication with said high pressure passage (89), and said second axial bore (37';65) is in fluid communication with said low pressure slot (59') and said second passage (81';66) is in fluid communication with said low pressure passage (87). s A hydrostatic pump (11) or motor (13) as claimed in claim 7, characterized by, in said first journal member (33), said axial bores (35,37) are oriented generally perpendicular to said high and low pressure slots (57,59), and said first (79;64) and said second (81;66) passages comprise slots oriented generally perpendicular to said axial bores (35,37). A hydrostatic pump (11) or motor (13) as claimed in claim 7, characterized by, in said second journal member (33'), said axial bores are oriented at an acute angle relative to said high and low pressure slots, and said first and second passages comprise slots oriented at an acute angle relative to said axial bores.

Inventors: BYRD WILLIAM ALLAN, HAAG ARTHUR FRED, BYRD, WILLIAM ALLAN, HAAG, ARTHUR FRED
Applicants: EATON CORP, EATON CORPORATION
Application year: 1995
Main classification: F16H39
IPC codes: F16H39, B60K17