Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1991-02-13
1992-09-15
Lorence, Richard
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
74880, 74872, F16H 4704
Patent
active
051468123
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an arrangement and a method for operating a continuously variable drive unit for motor vehicles with a controllable internal combustion engine and a hydrostatic mechanical power split transmission with continuously variable transmission ratio.
THE RELATED ART
From the patent document (DE 35 12 523) is known a continuously variable power split compound load-shifting transmission with group shifting. 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 a speed group and several auxiliary gears which act upon the main drive shaft. Both linkage shafts alternately actuate the gear-shift mechanism. The gear shifts occur free of load at synchronous rotational speeds and without interruption of the traction power. The transmission works like a continuous transmission with a large range of controller output and makes possible operation of an internal combustion engine of a vehicle along a characteristic curve for minimal fuel consumption thereby achieving fuel economy.
Such hydrostatic-mechanical power split transmissions for motor vehicles are impaired by high losses under certain operational circumstances, since the efficiency of the hydrostatic branch decreases in cases of high delivery volumes between primary unit and secondary unit. The high pressures occurring in the hydrostatic branch at large delivery volumes of the primary unit, combined with the high rotational speeds transmitted by the internal combustion engine to the primary unit, lead to high losses, early wear and to heavy noise emission of the transmission.
Since the output fraction of the hydrostatic branch at large delivery volumes of the primary unit is relatively large with respect to the total power flow through the power split transmission, the lowered efficiency of the hydrostatic branch has a very disadvantageous effect on the total output of the power split transmission.
During the gear-shift process over the entire speed range in the mechanical branch of a hydrostatic-mechanical power split transmission, there occurs as a rule in the hydrostatic branch a load combination with the large delivery volume of the primary unit and the high pressures. Also during the gear-shift process, the transmission output shaft is separated from one of the linkage shafts of the linkage gearing and is connected to another linkage shaft. This process takes places at synchronous rotational speeds of the involved linkage shafts. The linkage shafts are connected via clutches to the output shaft of the transmission, whereby overcutting occurs during the gear-change process, with a rigid transmission ratio existing between the hydrostatic and the mechanical transmission branches
The operation of the power split transmission under load leads to leakage losses in the hydrostatic branch. In order to compensate these losses, a modified delivery volume of the primary unit has to be preestablished, in order to reach a certain speed of the input shaft driven by the secondary unit. As a consequence, in order to reach a synchronous speed of the linkage shaft to be engaged, the angle of the swash plate of the primary unit in the hydrostatic branch has to be variably set, depending on the rotational speed existing at the moment at the output shaft of the transmission.
In the traction or thrust operation of the drive unit the swash plate of the primary unit has to be set at a larger or smaller angle, in order to bring the secondary unit to the rotational speed required for reaching the gear-shift point.
The alteration of the transmission ratio in the mechanical branch before and after the shifting process determines the torque difference which acts upon the hydrostatic branch before and after the shifting process. If the angle of the swash plate of the primary unit required for reaching a gear-shift point is maintained after the shifting process has taken place, the delivery volume of the primary
REFERENCES:
patent: 3298251 (1967-01-01), Moss
patent: 4481844 (1984-11-01), Ironside et al.
Nikolaus Heinrich
Paton Robert
Dubno Herbert
Lorence Richard
Trousdell William O.
Zahnradfabrik Friedrichshafen AG
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