Power plants – Pressure fluid source and motor – With means purging – cleaning or separating undesirables from...
Reexamination Certificate
2001-08-21
2003-11-18
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
With means purging, cleaning or separating undesirables from...
C060S487000
Reexamination Certificate
active
06647720
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The invention concerns the hydrostatic unit for a hydro-mechanical torque division transmission for an agricultural or industrial utility vehicle, with a mounting frame in which the shafts arranged parallel to one another of at least two hydrostatic devices are supported by bearing units such that they can be rotated, and on which the adjusting devices of the hydrostatic devices are supported. The hydrostatic devices consist of a hydraulic motor and a variable-displacement pump, which are hydraulically connected.
The use of torque division transmissions is advantageous with stepless drive systems for utility vehicles, since they are able to meet the demanding requirements with regard to reasonable power loss. With torque division transmissions, a portion of the power of the internal combustion engine is passed through a stepless transmission branch and the other portion of the power is passed through a constant-speed mechanical transmission branch. After passing through the transmission branches, the two power flows are superimposed and combined once again, and then passed further via mechanical drive elements to the wheels.
The stepless transmission branch is normally implemented with a hydrostatic transmission, the hydrostatic devices of which are a variable-displacement hydraulic pump and a constant-displacement motor. In some cases, instead of the constant-displacement motor, a variable-displacement unit is used.
With most known hydro-mechanical torque division transmissions for utility vehicles, commercially available and mass-produced hydrostatic pumps and motors are used, with these being arranged such that their respective sides opposite to the shaft outlet are placed back-to-back, and normally being located inside a common housing together with an epicyclic gear-set (DE 40 21 686 A1). The epicyclic gear-set may consist of a planetary drum. This consists of a summation gearbox and a number of additional epicyclic gear-sets, which are activated one after the other, and the components of which for shifting between different transmission ratios can be linked together by clutches and brakes.
EP 0 465 752 A1 describes several stepless gear-changing mechanisms each with a hydrostatic transmission having a hydraulic pump and a hydraulic motor. The hydraulic motor and the variable-displacement pump are connected together via a hydraulic circuit. They may be installed separately from one another or in a common housing, and are flange-mounted on a transmission housing. Their two shafts are arranged parallel to one another, and extend into the transmission housing, where they are connected to a mechanical summation gearbox and a conventional speed-changing gearbox. For every gear-changing mechanism represented, a specifically adapted hydrostatic transmission is provided.
DE-A-36 24 989 describes a transmission with hydraulic and mechanical components for providing propulsion to vehicles, in which the hydrostatic devices are connected together rigidly as a pre-assemblable unit with a control and connection block. This pre-assemblable unit is disposed into a common housing with an epicyclic gear-set, various clutches and an intermediate shaft, the hydrostatic devices being disposed within the installation length of the epicyclic gear-set and axially parallel to it, with the intention of keeping size and noise level low.
In hydro-mechanical torque division transmissions, the hydrostatic components-the variable-displacement pump and the constant-displacement motor-account for a large portion of the value created. Generally, the gear-maker for torque division transmissions is not also a maker of hydrostatic components. In order for the total costs of a hydro-mechanical transmission to remain comparable with those of power-shift stepped drives or full-power stepped transmissions, the transmission manufacturer attempts to select hydrostatic units of as low a size as possible, which are thus of low power. As a result, however, it may become necessary to increase the number of components in the mechanical part of the transmission, which in turn leads to increased costs.
The arrangement and selection of the hydrostatic devices has to be matched to the mechanical branch in question (planetary drum). Here, it is of particular importance whether the torque division takes place at the beginning of the mechanical branch (“torque split”) or at the end of the mechanical branch (“speed split)”) or whether the mechanical branch is located between the two hydrostatic devices (“compound”). Additionally, it would be desirable to isolate the oil circuit for the hydrostatic devices from the lubrication oil circuit, but this entails considerable design effort. Furthermore, noise insulation with respect to the transmission housing can be implemented only with difficulty and at major expense.
The task on which the invention is based may be considered to consist in creating a hydrostatic unit of the type described earlier in such a manner that the problems listed earlier are resolved. In particular, a hydrostatic unit is to be provided which is usable in multiple applications and can therefore be manufactured in large numbers at low cost. It should be possible to provide a specific hydraulic circuit only for the hydrostatic devices and to keep noise transfer to the transmission housing at a low level.
The hydrostatic unit in accordance with the invention contains a mounting frame, on which the shafts of at least two hydrostatic devices are supported by bearing units such that they can rotate. The hydraulic circuits are also attached to the mounting frame, including a yoke, hydraulic hoses, valves and so on, as are the adjusting devices for the hydrostatic devices. The hydrostatic devices to do not have to have a specific housing of their own. At least one hydrostatic device, in the form of an adjustable-displacement pump, is mounted on the mounting frame such that it can be swivelled, while another hydrostatic device, in the form of a constant-displacement motor, can be mounted rigidly on the mounting frame. In place of a constant-displacement motor, however, a variable-displacement motor can also be used, being mounted such that it is movable.
An input shaft of the hydrostatic unit is also supported on the mounting frame by at least one bearing unit, having a driver/driven connection with the variable-displacement pump. At least two output shafts arranged parallel to one another and supported by at least one bearing unit each on the mounting frame are provided. At least one output shaft is driven mechanically by the input shaft, either directly or indirectly (e.g. via a gear-set or a mating connection), and at least one other output shaft is driven hydraulically, either directly or indirectly (e.g. via a gear-set or a mating connection) by the variable-displacement pump.
The mounting frame thus serves for the attachment of the hydrostatic devices and to support the input shaft and the output shafts. Together with the hydrostatic devices, the related hydraulic circuits and adjusting units, as well as the input shaft, the output shafts and the bearing units, it forms an autonomously functioning hydrostatic sub-assembly which can be pre-assembled and which can be tested independently of other transmission units.
The arrangement of the input shaft, the constant-displacement motor shaft, the variable-displacement pump shaft and the output shafts on a mounting frame make it possible for a hydrostatic unit formed in accordance with the invention to be used in a multiplicity of applications as a transmission module in vehicle drive trains to create stepless hydro-mechanical torque division drive designs. The hydrostatic unit delivers hydrostatic or mechanical power at various output shafts, to be passed on to the mechanical transmission branch of the overall transmission system, in particular into a planetary drum. It also supplies mechanical power to be passed on to mechanical power-consuming components such as power take-off shafts, air pumps, oil pumps and generators. Ev
Deere & Company
Leslie Michael
Look Edward K.
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