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Europaisches Patentamt J» European Patent Office Si) Publication number: 0213564 B1 Office europeen des brevets EUROPEAN PATENT SPECIFICATION Date of publication of the patent specification: © intci.- B60K 17/14, F16H 39/40 19.12.90 Application number: 86111601.0 Date of filing: 21 .08.86 Hydrostatic transaxle and locking differentiation and brake therefor. Priority: 26.08.85 US 769033 Proprietor: EATON CORPORATION, Eaton Center, 1111 Superior Avenue, Cleveland Ohio44114(US) Date of publication of application: 11.03.87 Bulletin 87/11 Inventor: Giere, David Warren, 110934 von Hertzen Circle, Chaska Minnesota 5531 8(US) Publication of the grant of the patent: 19.12.90 Bulletin 90/51 Representative: Schwan, Gerhard, Dipl.-lng., Elfenstrasse 32, D-8000 Munchen 83(DE) Designated Contracting States: DEFRGBITSE References cited: CH-A-281 003 CH-A-287435 DE-A- 1816183 DE-A- 1945439 FR-A- 1487 479 FR-A-2478766 GB-A-853197 US-A-2874790 10 CO CM Q Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned ft statement. It shall not be deemed to have been filed until the opposition fee has been paid (Art. 99(1) European patent Jf! convention). ACTORUM AG EP 0 213 564 B1 Description prevent spinout of one drive wheel relative to the other during loss of traction situations. Although a BACKGROUND OF THE DISCLOSURE transaxle assembly of the type described above has provided generally satisfactory performance, The present invention relates to hydrostatic 5 the excessive weight, size, and cost of such units transaxle assemblies, and more particularly, to such make them commercially less desirable. assemblies which have the capability for the opera- In a known hydrostatic transaxle assembly (GB-A tor to select from among various operating modes. 853 197) for use on a vehicle having a of Certain source mo- vehicles, such as lawn and garden trac- tive power, a fluid pump driven by the source of tors, have used hydrostatic transaxle assemblies 10 power, and a pair of driven wheels, the transaxle for transmitting engine torque to a pair of ground- assembly comprises first and second motor drive wheels assem- engaging to propel the vehicle. A typi- blies each including a rotary fluid pressure actuat- cal transaxle assembly which has been used com- ed device, fluid communication means for communi- includes mercially a variable displacement hydraulic cating pressurized fluid from the fluid pump to the such that the ratio pump, of pump output flow to 15 fluid pressure activated device to the fluid pump, a pump input speed (engine speed) could be infinitely gear section, and axle means; the gear section be- varied the vehicle by operator. This ability to infi- ing operably disposed between the fluid pressure nitely vary the output-input ratio, without interrupt- actuated device and the axle means to transmit the ing torque transmission, makes transaxle assem- rotary output of the fluid pressure actuated device blies greatly preferred over conventional clutch 20 to the axle means, and the axle means being and oper- gear transmission arrangements for vehicles able to transmit the rotary output of the motor as- of the type referred to above. sembly to the respective driven wheel; each of the Vehicles which utilize transaxle assemblies fre- gear sections including a gear member having a quently encounter operating conditions in which one speed of rotation representative of the of of the speed ro- drive wheels has less traction than the other 25 tation of the respective motor assembly; the drive wheel. It has long been recognized by the man- transaxle assembly further being provided with in- ufacturers of such vehicles that it is desirable to terwheel differentiation means comprising means provide the operator of the vehicle with some type selectively permitting or preventing differentiation of control arrangement for effectively dealing with action revolution of said driven wheels. In this prior such loss of traction situations. At the same time, 30 transaxle assembly the fluid communication means it however, is recognized that under most operating are defined by pipes interconnecting the pump and conditions, the vehicle must be able to have "normal the first and second motor assemblies, the latter differentiation" between the two drive whels, i.e., it being axial piston motors which, in the same manner must be for possible the two drive wheels to be driv- as the pump, are of the swash plate type. The gear en at substantially different speeds, such as during 35 section includes a pair of toothed wheels which are a sharp turn. fixed on a countershaft of the swash plate of the re- In addition to dealing with the loss of traction situ- spective motor and which are in meshing there engage- ation, are various other operating conditions ment with a toothed wheel attached to the respec- which occur with such vehicles. For example, it is tive axle shaft. The means selectively permitting or normally desirable for vehicles of this type to have 40 preventing differentiation action include a disc cou- some sort of parking brake to be applied only when pling having inner and outer discs. A carrier for the the vehicle is at a standstill, and it is especially de- inner discs is formed as an extension of the coun- sirable to incorporate such a parking brake into the tershaft of the swash plate of one of the motors or transaxle assembly to be used to propel such a vehi- is connected to said countershaft. A housing acting cle. 45 as a carrier for the outer discs is mounted on an ex- tension of the countershaft of the swash plate of Prior Art the other motor. In normal running the coupling is disengaged. If the differential action revolution of Prior to the time of the present invention, the the axle shafts is to be prevented, the coupling is commercially used transaxle assemblies have in- 50 engaged, e.g. by means of oil pressure, whereby eluded a hydrostatic transmission (HST) and a me- the two swash plates are rigidly interconnected and chanical axle assembly. The HST would typically be the torque of both motors may be applied to one of a light-duty HST such as the Model 1 1 sold by Eaton the driven wheels. Corporation and comprising a variable displace- An assembly comprising a hydrostatic transmis- ment, radial ball pump and a fixed displacement radi- 55 sion and a copperating multistep change speed gear al ball motor. The HST would transmit engine torque mechanism is known from DE-A 1 945 439. In this to the input of the mechanical axle assembly, which assembly a fluid pump is in communication, via con- would include a spur and/or bevel gear reduction duits, with first and second fluid motors. The output unit and a pair of output axles for connection to the shafts of the fluid motors are connected to the in- drive wheels. 60 puts of first and second planetary gear mecha- The mechanical axle assembly would typically in- nisms, respectively. Individual ones of the rotating clude some sort of differential to permit normal dif- parts of each of the planetary gear mechanisms are ferentiation between the left and right drive wheels. adapted for being selectively braked. The outputs On such axle assemblies, it is known to provide an of the planetary gear mechanisms are connected to automotive-type limited slip or locking differential to 65 the driven rear wheels of a four wheel vehicle. If EP 0 213 564 B1 the front wheels of the vehicle likewise are to be - a housing for the fluid pressure actuated devic- driven, the output gears of the first and second es of both said first and second motor assem- planetary gear mechanisms each are in meshing en- blies, as well as as gagement with a toothed gear, said gears being - passages forming said fluid communication fixed to the remote ends of a first and a second half- 5 means between sait fluid pump and said fluid pres- shaft, respectively. The adjacent ends of these sure actuated devices; and in that said inter- half-shafts are connected to first and second in- wheel differentiations means includes puts, respectively, of a lockable differential the ro- - first and second lock gear members which are tatabie cage of which is drivingly connected, separate from said gear sections and are in toothed through a gear set and a torque limiter coupling, to 10 engagement with said gear members of said first the input of a further differential having first and and second motor assemblies, respectively; second outputs which are connected to the driven - engagement means operably associated with front wheels. said first and second lock gear members; and - actuation means operably associated with said SUMMARY OF THE INVENTION 15 engagement means and selectively operable to move said engagement means between Accordingly, it is an object of the present inven- (i) a first position in which said gear members of tion to provide a hydrostatic transaxle assembly said first and second motor assemblies are free which overcomes the problems associated with the to rotate relative to each other, thus permitting prior art transaxle and vehicle propel systems de- 20 normal differentiation between said first and sec- scribed above, and at the same time, includes the ond motor assemblies and the speeds of the driv- capability of dealing effectively with loss of traction en wheels; and situations. (ii) a second position in which said gear members It is a more specific object of the present inven- of said first and second motor assemblies are tion to provide a hydrostatic transaxle assembly of 25 fixed relative to each other, thus preventing said the type which achieves the above-stated objects, normal differentiation between said first and sec- while providing the operator with the capability of ond motor assemblies and the speeds of the driv- selecting between a normal differentiating mode of en wheels.

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