Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1991-02-13
1992-04-28
Wright, Dirk
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
3644241, F16H 6142
Patent
active
051077221
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an arrangement and a method of operating a variable drive unit for a motor vehicle, particularly for agricultural and construction machinery., with a controllable internal combustion engine and a hydrostatic-mechanical power split transmission with continuously variable transmission ratio according to the introductory part of claim 1.
From the patent specification (DE 35 12 523) a continuously variable power split compound load-shifting transmission with group shifting is known. The transmission consists of two gear subgroups. One of them is a continuously variable power split linkage with several shafts. The other gear subgroup is a gear-shift mechanism with one speed group and several auxiliary gears which act upon the main driven shaft. The two linkage shafts alternately actuate the gear-shift mechanism. The gear shifts occur free of load at synchronous rotational speeds and without interruptions of traction power. The transmission works like a continuous transmission with a large range of controller output and makes possible to operate the internal combustion engine of a vehicle along a characteristic curve for minimal fuel consumption, this way achieving fuel economy.
From the laid open FR-A 21 43 154 a continuously variable hydromechanical load-shifting transmission is known, which can be adjusted in such a manner that in all operational states the driving internal combustion engine is operated in its best performance range. In order to avoid skidding of the vehicle tiers when the engine develops its full power, in the transmission for instance a pressure-control valve is provided in the hydrostatic transmission branch, in order to limit the transmittable maximum torque. This hydromechanical load-shifting transmission is purely hydrostatically operated for the start and reverse drive.
Drive units with hydrostatic-mechanical power split transmissions for motor vehicles usually register very high losses under certain operational conditions of the vehicle, e.g. at start or while traveling with very low speeds under high load. When the vehicle is standing and shifted into the first speed range, the primary unit built like an adjusting pump reaches its maximum delivery volume already in idling at the nominal speed of the internal combustion engine, whereby high hydrostatic idling losses result. With increasing load at the start, the delivery volume of the adjusting pump decreases, however, due to the load-dependent pressure increase, the hydraulic losses remain considerable, so that in this operational range the general efficiency remains low. Further, the large delivery volumes of the adjusting pump at high pressures in correlation with the high rotational speeds transmitted to the hydrostat by an internal combustion engine at nominal speeds leads to premature wear and to high noise emissions of the transmission.
For motor vehicles which start frequently from stillstand and/or permanently operate under conditions of very low speeds and high loads, such as agricultural and construction equipment, the operation of hydrostatic-mechanical power split transmissions is particularly problematic.
It is the object of the invention to improve on an arrangement and a method for operating a variable drive unit with a controllable internal combustion engine and a hydrostatic-mechanical power split transmission so that the motor vehicles which have to start frequently and/or travel at very low speeds under high load, can be operated with increased efficiency of the transmission and with reduced wear, reduced noise emission and lower speed (rpm) of the internal combustion engine.
The problem is solved according to the invention in that a common control device for the internal combustion engine and the power split transmission is provided, device which in a first phase of a starting operation under full load sets the speed n.sub.mot of the internal combustion engine to a lower value than the nominal rotational speed, resets the adjusting pump to a maximal delivery volume and engages the clutch f
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Arain Abdul
Nikolaus Heinrich W.
Paton Robert
Dubno Herbert
Wright Dirk
Zahnradfabrik Friedrichshafen AG
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