Motor vehicles – Power – Including traction motor of kind driven by noncompressible...
Reexamination Certificate
1999-10-25
2001-07-17
Johnson, Brian L. (Department: 3618)
Motor vehicles
Power
Including traction motor of kind driven by noncompressible...
C060S442000, C060S483000
Reexamination Certificate
active
06260653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydrostatic motor unit, comprising at least two hydraulic motors, at-least one of which has a variable capacity, whereby the hydraulic motors can be switched hydraulically in parallel, and can have output rotors that are coupled with each other.
2. Background Information
Such a motor unit designed to be used as the central propulsion unit of a work machine is described in DE 42 35 710 A1. This prior art motor unit consists of a high-speed axial piston motor with a variable capacity and, located axially parallel to it, an internally pressurized low-speed radial piston motor with a constant capacity. The output shaft of the axial piston motor has a gear wheel engaged with gear teeth attached to the outer periphery of the rotationally mounted housing of the radial piston motor. The speed difference between the higher-speed motor and the lower-speed motor is equalized by a step-down transmission between the gear wheel and the gear teeth.
When the two motors are switched in parallel, the two hydraulic motors, depending on their individual capacity, each have an output moment. The two output moments are output together as the total output moment. The radial piston motor can be disconnected by separation from the hydraulic circuit and pressurization of the piston toward the internal top dead center position. The hydraulic fluid released is available for the axial piston motor. The axial piston motor, immediately before the deactivation of the radial piston motor, is set to the minimum capacity. When the radial piston motor is deactivated, the axial piston motor must be very quickly reset to the maximum capacity, to be able to absorb the additional hydraulic fluid from the radial piston motor without a switching pulse (which corresponds to synchronization). By a subsequent reduction of the capacity, and at a reduced total output moment of the motor unit, the output speed of rotation of the motor unit can be increased further with respect to the hydraulic parallel operation of the two hydraulic motors, and the conversion range of the motor unit can be increased.
The drive system experiences an interruption in the traction produced at the moment of the deactivation of the radial piston motor and the reduction of the axial piston motor. This interruption is undesirable in certain applications. For example, such applications include traction drive systems for work machines such as fork lift trucks, etc. Due to the potential resulting interruption in the braking force, a motor unit of the prior art cannot be used in traction drive systems that operate in a closed circuit and which are also used for operating brakes.
On account of their large size and the effort and expense involved in their construction, the motor unit described above is also unsuitable for applications where space is limited, e.g., in wheel drive systems. In most such cases, variable high-speed axial piston motors are used, downstream of which a step-down gear train is located.
The prior art also discloses the use of low-speed radial piston motors as wheel drives (direct drive). Radial piston motors, however, do not have a variable capacity with a multiple-stroke construction, which significantly limits the types of potential applications. In a single-stroke form, of course, the capacity can be varied. Although in that case, such drive systems represent high-speed motors, which require a subsequent stepping down, if the objective is to have low output speeds with a high output moment.
The object of this invention is to make available a hydrostatic motor unit of the type described above that is easy to manufacture, compact and can be used in a wide variety of applications.
SUMMARY OF THE INVENTION
The invention provides that the output rotors are oriented coaxially with one another and are connected to each other in rotational synchronization. Such a motor unit can, on one hand, be made small enough that it can be used as a wheel drive, for example, and it does not require any downstream gear train, and can also be used as a variable low-speed motor, i.e., it can be used at low output speeds for a high transmission of power.
The hydrostatic motor unit of the invention makes it possible to achieve an “internal” division of the output. When switched to operate hydraulically in parallel, the variable motor is thereby initially set to the maximum capacity. As a function of the ratio of the maximum capacity of the constant motor and the variable 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 there are defined output moments of the hydraulic motors which in this mode of operation are added to each other. Then, if the speed of a vehicle equipped with the motor unit of the invention is to be increased, the capacity of the variable motor is reduced continuously and without any interruption in traction. Accordingly, additional hydraulic fluid flows to the constant motor as a result of which the speed of rotation of the motor unit increases—as the output moment decreases.
The output rotors of the motor unit of the invention can be bolted to each other, for example, or they can be rotationally synchronized with each other in another manner. One method that is particularly easy in terms of fabrication and assembly is to have the output rotors be part of a one-piece rotor block that contains the work chambers of both hydraulic motors.
With regard to the compact size of the motor unit of the invention, at least one of the hydraulic motors may be a radial piston motor, in particular, an internally pressurized radial piston motor.
If the radial piston motor is a multiple-stroke unit, it has an advantageous effect on the power density of the motor unit. At low output speeds, as a result of the large capacity achieved by the multiple-stroke capability, the motor unit can produce a high output moment.
In one refinement of the invention, the radial piston motor can be shutdown partly or completely. The quantity of hydraulic fluid that is released by the partial or total shutdown of the radial piston motor is available to the other motor for a further increase of the output speed of the motor unit, which is a requirement for certain applications (e.g., for vehicles that are designed to operate at higher speeds).
In an additional embodiment of the invention, at least one of the hydraulic motors is an axial piston motor utilizing the swash plate design. Because axial piston machines are reliable and easily operated motors in terms of the variability of the capacity, in one configuration of the invention, the capacity of the axial piston motor is also variable. The axial piston motor can also be shutdown partly or completely.
The variable hydraulic motor may be reversible. In the reversed status, the direction of rotation of the output rotor remains the same, and the direction of flow of the hydraulic fluid in the variable motor is reversed. Consequently, additional hydraulic fluid can be supplied to the hydraulic motor which has a constant capacity, i.e., the variable motor operating in reverse acts as the pump driven by the output rotor of the constant motor, the “delivery volume” of which further increases the output speed of the motor unit. Consequently, in this operating mode, the conversion range, i.e. the range of speeds of the motor unit of the invention, is significantly expanded.
In one embodiment of the motor unit of the invention, which is advantageous in terms of ease of fabrication and assembly, the motor unit consists of an internally pressurized, multiple-stroke radial piston motor with a constant capacity, and an axial piston motor with a variable capacity that utilizes the swash plate design.
For certain types of applications, such as in connection with the use of the motor unit in vehicles that are designed to travel at higher speeds, the radial piston motor may have multiple banks, i.e. in two banks.
Consequently, in spite of the large capaci
Johnson Brian L.
Linde Aktiengesellschaft
Luby Matthew
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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