Hydrostatic motor unit

Details Hydrostatic motor unit Hydrostatic motor unit

2000-01-27

2001-06-19

Estremsky, Sherry (Department: 3681)

Planetary gear transmission systems or components

Fluid drive or control of planetary gearing

Pump and motor in series with planetary gearing

C180S308000

Reexamination Certificate

active

06248037

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to hydrostatic motors and, more particularly, to a hydrostatic motor unit having at least two hydraulic motors that can be connected in parallel, at least one of which has a variable absorption volume, in which the hydraulic motors are coupled to each other on the output side with the interposition of a transmission.
2. Description of the Currently Available Technology
A known motor unit used as the central drive system of a work machine is described in DE 42 35 710 A1. This motor unit consists of a high-speed axial piston motor that has a variable absorption volume and, located axially parallel to it, an internally pressurized radial piston motor that has a constant absorption volume and is used as a low-speed motor. The output shaft of the axial piston motor is provided with a gear wheel which is engaged with gearing that is located on the outside periphery of the rotationally mounted housing of the radial piston motor. The difference in speed between the high-speed motor and the low-speed motor is equalized by a gear ratio reduction in the transmission formed by the gear wheel and the gearing.
When connected hydraulically in parallel, the two hydraulic motors—as a function of their individual absorption volume—each generates an output moment. The two output moments are measured together (summed) to define the total output moment. The radial piston motor can be deactivated by isolating it from the hydraulic circuit and by pressurizing the pistons toward their inner dead center position. The hydraulic fluid released (freed) is thereby available to the axial piston motor. The axial piston motor is set to the minimum absorption volume immediately before the radial piston motor is shut off. When the radial piston motor is shut off, the axial piston motor is very quickly returned to maximum absorption volume, so that it can absorb the additional hydraulic fluid from the radial piston motor without any shifting jolts. This process corresponds to a synchronization. By the subsequent reduction of the absorption volume of the axial piston motor—with a reduced total output moment of the motor unit—the output speed of the motor unit can be further increased compared to the hydraulic parallel operation of the two hydraulic motors, and the possible range of speeds at which the motor unit can be used can be increased.
On account of its large size and the cost and complexity of its construction, the motor unit described above is unsuitable for use in restricted spaces, such as wheel drives. In most cases, such applications require high-speed variable axial piston motors, downstream of which a step-down transmission is connected.
The known art also includes the use of low-speed radial piston motors as wheel drives (direct drive). Radial piston motors, however, do not have a variable absorption volume in a multiple-stroke configuration, which significantly restricts the range of potential applications. In a single-stroke configuration, of course, the absorption volume can be adjusted, but in that case such drive mechanisms represent high-speed motors which require a subsequent reduction in the gear ratio if low output speeds and a high output moment are required.
Therefore, it is an object of this invention to provide a hydrostatic motor unit which is simple, compact and can be used over a wide range of applications.
SUMMARY OF THE INVENTION
The invention provides a hydrostatic motor unit in which the hydraulic motors are arranged coaxial to each other. On one hand, such a motor unit can be configured small enough that it can be used as a wheel drive, and on the other hand it can be used as a variable low-speed engine, i.e. for low output speeds and high power transmission.
In one preferred configuration of the motor unit of the invention that is advantageous in terms of achieving a design that is simple to manufacture and assemble as well as compact, the invention teaches that the motor unit comprises a radial piston motor that has a constant absorption volume (and preferably is internally pressurized and has multiple stroke capability) and an axial piston of swash plate design that is axially next to the radial piston motor and has a variable absorption volume.
The multiple-stroke capability of the radial piston motor results in the maximum power density of the motor unit. The motor unit is able to output a high output moment at low output speeds as a result of the large absorption volume that can be achieved by the multiple-stroke capability. In terms of the ability to vary their absorption volume, axial piston motors represent reliable and easily controlled propulsion mechanisms.
With the hydrostatic motor unit of the invention, an “internal” power distribution is achieved. In hydraulically parallel operation, therefore, the adjustable axial piston motor is first set to maximum absorption volume. As a function of the ratio of the maximum absorption volumes of the constant radial piston motor and the adjustable axial piston motor, and as a function of the output-side load of the motor unit, at a constant output power of a hydraulic pump that pressurizes the hydraulic motors at a determined output speed there are definite output moments of the hydraulic motors, which under these operating conditions are cumulative. If the speed of a vehicle equipped with the motor unit of the invention is to be increased, the absorption volume of the variable axial piston motor can be reduced continuously and without interruption of the traction force. Accordingly, additional hydraulic fluid flows to the constant radial piston motor, as a result of which the speed of the motor unit is increased, as the output moment is reduced.
In one appropriate refinement of the invention, the radial piston motor can be shut down partly and/or completely. The quantity of hydraulic fluid released when the radial piston motor is shut down partly or completely is then available to the axial piston motor to further increase the output speed of the motor unit, which is a requirement for certain applications (e.g. for vehicles that are designed and equipped to operate at high speeds).
For the applications described above, it is advantageous if the radial piston motor is a multiple-row motor, e.g. with two rows. In spite of the large absorption volume, the dimensions in the radial direction can thereby be kept small.
Moreover, if it is possible to shut down at least one motor row of the multiple-row radial piston motor partly (e.g. with respect to individual pistons) and/or entirely, on one hand the axial piston motor can be configured smaller, and on the other hand—depending on the shifting capability of the radial piston motor—there are a number of shifting capabilities that can be realized, in which case the axial piston motor can be used to regulate the different shifting positions.
If the maximum absorption volume of the axial piston motor is less than the absorption volume of the radial piston motor, there are advantages with regard to the dimensions of the axial piston motor and its dynamic response (rapid variation capability of the swash plate because of low inertial forces).
It is particularly advantageous if the axial piston motor is reversible. In the reversed state, and if the direction of rotation of the output rotor of the radial piston motor and the cylinder drum of the axial piston motor remain the same, the direction of flow of the hydraulic fluid in the axial piston motor is reversed. Additional hydraulic fluid can thus be fed to the radial piston motor, which has a constant absorption volume, i.e. in the reversed position, the variable axial piston drive system acts as a pump that is driven by the output rotor of the radial piston motor, and the “delivery volume” of the pump further increases the output speed of the motor unit. In this operating state, consequently, the conversion range, i.e. the speed range of the motor unit of the invention, can be expanded significantly.
In one advantageous refinement of the invention,

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