Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Pump and motor in series with planetary gearing
Patent
1997-01-02
1998-11-24
Ta, Khoi Q.
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Pump and motor in series with planetary gearing
475141, 192 4A, F16H 6112, F16H 4704
Patent
active
058399844
DESCRIPTION:
BRIEF SUMMARY
In a drive system of the above mentioned kind such as particularly used in construction machinery, for example, loaders, excavators, or crawlers, a prime mover, especially a diesel engine, drives a hydrostatic variable displacement pump. The variable displacement pump, together with a variable displacement motor, form a hydrostatic transmission whose reduction ratio is preferably adjusted by a speed-dependent control pressure (automotive drive regulation). Together with the hydrostatic transmission, a powershiftable gear (often a two-ratio planetary transmission) belongs to said drive system. The utilizable reduction range of the drive system can be increased with said powershiftable transmission.
A construction machine, such as a loader, drives its working cycle in the first gear. The cruising speed is changed by the variable speed of the diesel engine and by means of the hydrostatic transmission. The powershiftable transmission makes it possible to change the mechanical reduction even while traveling under load.
For construction machines which can travel quicker than a predetermined cruising speed such as 25 km/h, different legal injunctions or regulations are to be observed in relation to the brakes. In a single-circuit braking system, there has to be an auxiliary operating brake together with the normal operating brake. A locking or parking brake is also required. In EP-A 0 408 592 was disclosed a powershiftable two-ratio planetary transmission unit where two friction clutches (one clutch and one brake) can be actuated independently of each other. The friction clutch situated inside acts between the inner and outer central gears of the planetary transmission unit. Both central gears can thus be optionally braced with each other (variable displacement and/or auxiliary braking function). Pursuant to the above mentioned legal regulations, when the brake valve is actuated in order to introduce a dynamic emergency braking or in case of failure of the control pressure or of the power supply, a certain deceleration must be obtained. The brake torque needed for this is clearly less than the maximum design torque transmissible by the friction clutches. Said circumstance causes inadmissibly strong brakings or a blockage of the driving gears. In such a case the driver could no longer control the vehicle.
The problem on which this invention is based is to provide a drive system in which the braking action is adapted to the cruising speed and the vehicle weight both on the road and off-road.
The problem on which the invention is based is solved by the fact that the brake switching valve is connected by line sections with the gearshift valves, that in one switching position of the brake switching valve, a reservoir is filled with hydraulic fluid and that in another switching position of the brake switching valve, the reservoir is connected to a pressure chamber of a brake. The proposed solution is particularly advantageous since the reservoir in normal operation (brake switching valve open) is constantly filled with hydraulic fluid. In the operation of the brake the reservoir delivers the volume of fluid into a hydraulic-fluid line which discharges in the pressure chamber of the clutch or brake. In this manner an adjustable residual pressure always acts upon the brake. The brake is designed for dynamic decelerations. The deceleration always takes place in the higher gear and inadmissibly great decelerations values, which could constitute a possible source of danger, are reliably prevented.
The brake switching valve is advantageously front-mounted on the gearshift valves so that a connecting line leads from the feed pump to an input of the brake switching valve. The reservoir is attached by one line to the line section which follows the brake switching valve.
An advantageous design of the drive system consists in that the brake switching valve is attached by a line section to a hydraulic-fluid line which is connected, on one side, with a brake valve and, on the other, with the pressure chamber of the brake (or clutch
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Eymuller Helmut
Heilig Eduard
Legner Jurgen
Mann Egon
Ta Khoi Q.
ZF Friedrichshafen AG
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