Motor vehicles – Power – Including traction motor of kind driven by noncompressible...
Reexamination Certificate
1999-03-08
2001-02-13
Mar, Michael (Department: 3619)
Motor vehicles
Power
Including traction motor of kind driven by noncompressible...
C188S082900, C188S170000, C180S370000, C475S900000
Reexamination Certificate
active
06186262
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a hydrostatic mechanical wheel drive.
Hydrostatic mechanical wheel drives are used in movable construction machinery and in vehicles for special functions such as dumping, heavy transport, fire fighting, etc. both for wheel and full-track vehicles. They actuate individual wheels or sprocket wheels for driving a caterpillar. The wheels are screwed on a flange of a wheel hub.
The radial space available for the individual wheel drive as a rule is limited by the inner wheel diameter or a pitch circle diameter for fixing bolts. The wheel diameters and pitch circle diameters cannot be enlarged at will, since otherwise the wheels would no longer fit in the vehicle and the expense for added parts would increase, for example, for the tracks, supports, etc., and in the steered wheels the angle of lock would be substantially limited. Within this radial limitation has to be housed, the wheel drive with its mechanical transmission gearing in the form of a planetary gear, with a wheel bearing, a hydraulic lifting piston motor, a cover for a hydraulic connection and with a brake of short axial length and low weight.
DE-A1 27 44 977 shows a wheel drive with an axial piston motor of the swash plate type which has a constant displacement capacity. A highly reducing toothed wheel gearing in the form of a two-step planetary gear makes possible small radial dimensions and a heavy load capacity by the use of tapered roller bearings. The latter are situated between the wheel hub and a wheel hub support in which the hydromotor is accommodated and are rigidly connected with the planet carrier. The length of course is considerable.
To increase the speed range of the vehicle for driving on the road, the wheel drives have a clutch by which individual wheel drives can be disconnected when driving on the road. The reduced total displacement capacity of the remaining wheel drives produces, with the delivery rate of the pump remaining the same, an increased driving speed, but with reduced torque. In addition, the clutch increases the weight considerably, the construction expense and the length of the wheel drive.
As a drive unit can be provided any kind of hydromotor including, for example, a radial-piston motor. Although their construction is axially short, these require more radial space. In addition, in the wheel drive known the drive shaft can extend through on the vehicle inner side in order to mount a brake thereon, and this would further increase the weight and length.
Also known is a wheel drive for a full-track vehicle (Prospectus F 43421/RT 3391-383f of Zahnradfabrik Passau GmbH of the year 1991) in which an axial-piston motor according of the swash plate type is situated in a housing designed as wheel hub support. The swash plate is tiltably supported in a swivel frame and its inclination to the axis of rotation of the axial-piston motor can be adjusted by a lever mechanism and a hydraulic piston whereby changes the displacement capacity and thus the speed of rotation of the axial-piston motor can be achieved. The swash plate can be infinitely varied, there sufficing for many applications two adjusting steps, namely, for a maximum and minimum displacement capacity. This is even advantageous when it is necessary during operation quickly to change between two speed ranges.
Between the housing and the swivel frame, axially offset relative to the axial-piston motor, is a parking brake of multiple disc design with automatic actuation to be closed by a plate spring and hydraulically opened. The brake is thus between the axial-piston motor and a toothed wheel gearing. Thereby, accessibility and cooling are impaired. In addition, the space available is so narrow that the brake cannot with sufficient reliability hold heavy vehicles on slopes.
The invention is based on the problem of providing a compact hydrostatic mechanical wheel drive with a quickly responsive control for a radial-piston motor and a brake which is also suitable for heavy vehicles.
SUMMARY OF THE INVENTION
In the wheel drive, according to the invention, a short axial length is obtained by using a radial-piston motor. Slow running radial-piston motors having a high torque are very smooth running. Additionally, the valves required for control are integrated in the cover for a hydraulic connection thus saving space. Thereby are obtained short connecting lines to the brake and to the radial-piston motor whereby response characteristics are improved.
The brake opens automatically when the pressure in a brake line exceeds a preset value, conveniently 10 at, and closes by spring tension when the pressure falls below said value in coordination with a brake valve which opens the feed lines to the radial-piston motor as soon as the brake has opened and closes the feed lines before the brake closes. In order that the brake cannot be overloaded, there is provided in the brake line a pressure-reducing valve which limits the maximum pressure to a value such as 20 at.
It is advantageous that the brake opens more quickly than it closes. For this purpose serves a first throttle check valve in the brake line which opens during an increasing pressure. Thereby the brake is quickly loaded by the checking function while the pressure during discharge drops more slowly via the throttle.
The brake as a rule serves as a parking brake. It can be designed as multi-disc brake or positive brake. The positive fit parking brake requires only a small space both in axial and in radial directions, since the retaining forces are applied by the positive locking. This is possible by selecting adequate materials of long service life and strength in a small space even for heavy vehicles. The spring for closing the brake and the hydraulic devices such as the brake piston have to be designed for engaging and disengaging forces only and not for stronger retaining forces.
The parts of the brake with the positive fit components are conveniently in a pressure chamber wherein the axially movable second part sits upon a brake piston which lies coaxially relative to an axis of rotation of the wheel drive. The brake piston is guided by the spring loaded end out from the pressure chamber directly or via a cylinder housing of the radial-piston motor which positively connects the second part with the sun gear shaft. The brake piston and the spring can be dimensioned so that they are housed within the control cover.
According to another proposal, the spring supports itself on a bearing for support of the radial-piston motor on the wheel hub support. Thereby the expense and space for the support can be reduced.
In addition to the mechanically acting brake, the wheel drive has a hydraulic braking function by means of a brake valve locking the return flow from the radial piston motor as soon as the pressure drops below the preset pressure, for example, 10 at. If the pressure increases in a supply line above said value, the brake valve is adjusted by a second throttle check valve to a position which again releases the return flow and thus switches off the braking function. Pressure-limiting valves protect the supply lines against overpressure. They are conveniently connected between the brake valve and the radial-piston motor.
In order to be able to drive the wheel motor in several speed ranges with different torques, a displacement change-over valve is provided which shuts off a feed line for some cylinders of the radial piston motor and can connect that feed line with a return flow line. The small displacement capacity of the radial-piston motor produced thereby results, while the displacement of the hydraulic pump remains the same, a higher speed of rotation with reduced torque.
Numerous features are shown and described in combination in the specification and in the claims. The expert will conveniently regard the combined features in accordance with the problems to be solved and combine them to form added combinations.
REFERENCES:
patent: 4114737 (1978-09-01), Fukui
patent: 4213514 (1980-07-01), Ehrlinger et al.
patent: 4245724 (1981-01-01
Gebhard Wolfgang
Mann Egon
Davis and Bujold
Mar Michael
ZF Friedrichshafen AG
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