Diagnostic system for a hydrostatic transmission or transaxle

[0001] This invention relates to hydrostatic transmissions and transaxles generally and, in particular, to diagnostic systems for use in such units.

[0002] This invention discloses an improved diagnostic system for use with a hydrostatic transmission or transaxle or a similar hydrostatic or hydraulic apparatus. This invention permits easier access to the hydraulic system for performing diagnostic tests on the unit without the need to open the unit. It is well-known that one will frequently need to test a unit such as a hydrostatic transmission or transaxle. This testing arises with field units when performance has decreased or if there is a question about the performance level of a unit. In known designs, a diagnostic unit may be created by penetrating the housing wall with hydraulic lines that are attached to the hydraulic porting of a center section located within the housing, or by penetrating the housing wall with porting formed in the center section. Penetrating the housing wall with porting formed in the center section also adds expense and complexity that is likely not required for most units.

[0003] In the present invention, a passage may be created in the housing wall and a fitting inserted therein to access porting within the center section. Such a passage may be machined after a unit is assembled, offering the opportunity to access center section porting only when needed. The ability to form the passage after assembly of the unit also means that the passage may be created in the field when needed versus having the expense of every unit being so configured.

[0004] The invention herein comprises an improved diagnostic apparatus which, in one embodiment, can be formed as part of the fastener holding a hydrostatic transmission center section to the housing. Other embodiments are possible within the scope of this invention. This diagnostic system can be connected to a test system external to the vehicle, such as in a laboratory, or it can be connected to an onboard system to provide the status information to the vehicle user.

[0005] This invention also discloses an improved relief valve that may also be used in conjunction with the other features of the invention or may be used on its own. The relief valve is formed as part of a fastener used to secure a center section to a housing element.

[0006] This invention is specifically described in connection with a zero turn apparatus vehicle similar to that shown in U.S. Application No. 60/572,163 commonly owned with this application and filed on May 18, 2004. The terms of that application are incorporated herein by reference. It will be understood, however, that this invention is not specific to any one transaxle or transmission design and that it can also be used with other transaxles or transmissions. Some of these are shown, e.g., in U.S. Pat. No. 5,314,387 and U.S. Pat. No. 6,185,936, which are commonly owned with this application and which are also incorporated herein by reference.

[0007] A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth illustrative embodiments that are indicative of the various ways in which the principles of the invention may be employed.

[0019] This invention is described herein with respect to exemplary vehicle 10, which is shown in FIG. 1 with one rear wheel and one driving unit removed for clarity. It will be understood that other transmissions, transaxles, vehicles and applications can be used in accordance with the present invention.

[0020] Hydrostatic transaxles are well-known in the art, and the internal functioning of the various components, such as the pump, motor, hydraulic porting and the like are described in U.S. Pat. Nos. 5,314,387 and 6,185,936. In the figures herein, center section 40 is attached to housing 21 by means of horizontal fasteners 49 which are parallel to the axle 24. In other designs, such as that shown in U.S. Pat. No. 5,314,387, the center section fasteners are shown as being vertical, i.e., perpendicular to the axles. The direction of the fasteners with respect to the axles or the split line of the housing elements is not critical to this invention.

[0021] In this embodiment, vehicle 10 includes a prime mover or engine 12 and a pair of transaxles 20 mounted on frame 14 and having a pair of driven wheels 18 driven by axles 24. Such vehicles generally include a driven apparatus such as mower deck 15, which is connected to transaxle 20 through a belt and pulley assembly 13. There generally will be two user controls 16 which are connected to the respective transaxles 20 to control the output speed and direction thereof. A console 17 may be located to be accessible to the driver. It will be understood that there will be additional linkages and the like, such as engine controls and brake linkages, which are not important to this invention. Only one transaxle 20 is shown in FIG. 1 for clarity, and each transaxle has an output axle 24. Other designs can include a pair of output axles linked through a differential in a single transaxle housing.

[0022] Transaxle 20 is shown in detail in FIGS. 2, 3 and 7. A main housing 21 is joined to side housing 22 along a split line perpendicular to output axle 24 to form an oil sump 25. FIG. 3 shows an internal view of transaxle 20. Center section 40 is mounted in sump 25 and is preferably secured to main housing 21 through a plurality of fasteners 49. As is known in the art, input shaft 34, which is driven by pulley 35, drives rotatable pump cylinder block 41, which includes a plurality of axial pistons (not shown). A fan 33 may be mounted on input shaft 34. Since axial piston pumps and motors are well known in the art, the pistons for pump cylinder block 41 are not shown in detail in these figures. As is known in the art, motor thrust bearing 73 can be supported entirely within housing 21 at a fixed angle, and motor pistons 72 abut fixed bearing 73.

[0023] The pump pistons (not shown) abut moveable swash plate 42, which is connected to control arm 31 through a trunnion shaft (not shown) to control the direction and output of the unit. Pump cylinder block 41 is connected to motor cylinder block 85 through hydraulic porting 70 located inside center section 40. Motor output shaft 44 is driven by motor cylinder block 85 and has a gear 43 engaged thereto. A gear train comprising gear 43, intermediate gears 47A and 47B and output gear 48 transfer rotational force from motor output shaft 44 to output axle shaft 24.

[0024] Center section 40 is shown most clearly in FIGS. 5 and 6. The stylized drawing of FIG. 6 depicts the hydraulic porting 70 formed in center section 40; this figure also shows plane 90 where the cross-sectional cut line 7—7 of FIG. 4 will be on center section 40 to assist in the understanding of the portions of hydraulic porting 70 shown in FIG. 7 and the other related figures. Center section 40 comprises a pump running surface 87 having a pair of pump kidneys 89A and 89B formed thereon and a motor running surface 86 having a pair of motor kidneys 88A and 88B formed thereon.

[0025] FIG. 7 shows a portion of center section 40 mounted in sump 25 and secured to housing 21 by at least one fastener 49. As noted previously, certain features shown in FIG. 7, such as cylinder block 85, bearing 73 and others are shown solid to assist with clarity. Due to the cross-sectional cut of FIG. 7, the pair of passages 71A and 71B is actually two portions of port 71, which is connected to motor kidney 88B. Another passage 74 is connected to the other motor kidney 88A. An additional passage 53 is bored into center section 40 and is connected to one of the passages 71A or 71B.

[0026] Fastener 49 passes through opening 57 formed in center section 40. It is threaded into opening 52 formed in housing member 21 by means of threads 51, thereby securing center section 40 to housing member 21. Fastener 49 is preferably a hex-head bolt as shown most clearly in FIGS. 9 and 10 and has a threaded portion 51 and head portion 59.

[0027] Fastener 49 is shown with a pair of cross passages 54 and 56, which may be drilled therein. When used with diagnostic elements 29, 63 or 64 that requires minimal flow, only one passage 54 or 56 may be necessary. Such passage may be formed from the exterior of fastener 49 to intersect with an interior passage 58 and may not be formed completely through fastener 49. In the figures shown herein passage 58 is drilled into fastener 49 longitudinally, so that passages 58, 54 and 56 all converge at a junction point and are open to one another. As can be seen in FIG. 7, a cylindrical cavity 60 is formed in opening 57 of center section 40 (i.e., between the walls of opening 57 and the outer surface of fastener 49 adjacent thereto). This space permits unrestricted oil flow from passage 53 into bore 58 regardless of the orientation of holes 54 and 56 when fastener 49 is screwed into position. This arrangement permits oil to flow from passage 71B through passage 53 to fastener 49. Bore 58 opens into opening 52, which is connected to fitting 61. Note that the opening into which fitting 61 is inserted may be machined after the unit is completely assembled, such as may be desirable in a field situation. Fitting 61 may then be inserted into that opening and connected to a diagnostic system.

[0028] In the embodiment described herein, console 17 is mounted on vehicle 10 and preferably includes an electric warning signal 63 and may include a hydraulic pressure gauge 64. This configuration provides an on-vehicle diagnostic system to provide the user feedback on the operational condition of the unit.

[0029] Hydraulic lines 66A and 66B connect fitting 61 to hydraulic gauge 64 through a tee-fitting 62. A pressure transducer 68 is also connected to tee-fitting 62 and is then connected to electric warning signal 63 through electric line 69.

[0030] In an alternative embodiment also depicted in FIG. 7, this diagnostic system could also be separate from the vehicle and only attached thereto on an as-needed basis for testing. Here, hydraulic lines 66A and 66B and the elements connected thereto are replaced with a single hydraulic line 66A′ connected to a separate diagnostic unit 29 having, for example, a hydraulic gauge 64′. This invention can easily be used with either style of diagnostic system, or with another type of system, and all that is required for such a change is the connection of a different hydraulic connection to fitting 61. It will be understood that the specifics of the diagnostic system, either on-board the vehicle or separate therefrom, are not critical to this invention. The various diagnostics described herein are preferably pressure related and require minimal fluid flow and thus will have minimal effect on the performance of transaxle 20. Further, if diagnostics are no longer required, fitting 61 may be capped or plugged to allow continued operation of the transaxle.

[0031] Fastener 49 may optionally include a relief valve 77 in its head portion. While relief valves are generally known, this invention eliminates the need for a separate relief valve and fastener by combining the two features into a single element. Specifically, this design permits the system to bleed off fluid from hydraulic porting 70 to sump 25 if pressure in porting 70 exceeds a desired maximum.

[0032] Relief valve 77 is shown most clearly in FIGS. 7 and 10. Ball 81 is mounted against seat 75 to close bore 58 from opening 80 formed in fastener head 59, and it is biased against seat 75 by spring 82, which is held in place by a pin 83. When pressure in passage 53 and thus bore 58 exceeds a selected level, ball 81 will unseat from seat 75 and permit hydraulic fluid to discharge to sump 25 by way of opening 80. The pressure at which valve 77 will open depends upon application needs and can be changed by selecting spring 82 having the proper spring constant.

[0033] FIG. 8 depicts an alternative embodiment of this invention where fastener 149 is not used to connect passage 53 to a diagnostic system, but rather performs the relief valve function only. Passage 158 is bored therein from the hex head 159 to the depth necessary to intersect bores 54 and 56. The relief valve feature of fastener 149 can be otherwise identical to that described above.

[0034] Another embodiment is shown in FIG. 11, where two separate fasteners 49 and 249 are depicted. Fastener 49 is depicted as being identical to that described above in FIG. 7. Hydraulic line 66 could be attached from fitting 61 to a diagnostic system of the user's choice as also described above. The second fastener 249 is hydraulically connected through passage 55 to port 74. As described above, port 74 would be connected to motor kidney 88A, while passages 71A and 71B are connected to motor kidney 88B. In this particular embodiment, fastener 249 includes the relief valve features, and does not include the diagnostic features, similar to that described above with respect to FIG. 8.

[0035] It will be understood that different combinations are possible within the scope and spirit of this invention. For example, while it is probably not needed for most applications, two fasteners 49 having the diagnostic connection capability could be used, with one connected to each motor kidney. One, both or neither could have the relief valve feature, as needed. Similarly, two fasteners similar to fastener 249 with relief valve capability could be used, with neither one having a diagnostic capability. In essence, this invention provides a wide range of alternatives to the user of the hydraulic system, and it can be easily tailored to meet various needs.

[0036] While this invention has been described in connection with bolts, it will be understood that the various passageways could be formed in structure that does not perform the securing function of a bolt or other fastener. If the center section is preferably secured to the housing by another means, then another member could be mounted in a manner similar to fastener 49 to perform the diagnostic functions only.

[0037] While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modification and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements of the embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalents thereof.