Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Fluid pump and motor in one of plural paths to or from...
Patent
1999-07-07
2000-08-22
Bonck, Rodney H.
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Fluid pump and motor in one of plural paths to or from...
475 72, 747321, F16H 4704
Patent
active
061064270
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a continuously variable transmission having the features stated in the preamble of claim 1.
BACKGROUND OF THE INVENTION
Patent EP 0 429 517 B1 has disclosed a continuously variable transmission with one hydrostatic and one mechanical power branch. In such transmissions, a summarizing transmission adds up the power of both power branches and optionally guides it via a mechanical transmission to a vehicle drive. If the mechanical power branch is interrupted by a clutch, the hydraulic power branch transmits the whole power. If the hydrostat is set to zero, the mechanical power branch transmits the whole power. Between said two operating points, the power distribution is determined by the control of the hydrostat.
The hydrostat comprises one pump and one hydrostatic motor of which at least one unit is regulatable. Pressure and flow rate or capacity in the time unit determine the power of the hydrostatic power branch. The ratio of the flow rate of the pump to the capacity of the hydrostatic motor yields the reduction ratio or conversion of the hydrostat.
The higher the power and the greater the conversion range, the larger the hydrostat must be. Although the hydrostats, especially large hydrostats, are good to regulate continuously, they have a poorer effectiveness and require a higher construction cost in comparison with mechanical transmissions. To keep the hydrostats small, the whole reduction ratio range of the transmission is divided by a multi-stage transmission into several forward and reverse drive ranges. In each drive range, the hydrostat passes through its whole adjustment range from maximum to minimum and vice versa. In the end positions, the shift elements to be engaged in the transmission attain synchronizer speed so that it is possible to shift smoothly. To this end as a rule are used force-locking, multi-disc clutches which can be shifted by the hydraulic actuation devices.
The hydrostat further reaches or passes through once in each range the zero position in which the whole power is mechanically transmitted with the best effectiveness. Therefore, transmissions are designed so that operating points in which the transmission is very often operated be in speed ranges of the transmission having a high mechanical transmission portion of power. By said steps and by numerous drive ranges, transmissions with favorable degrees of effectiveness are obtained. With the number of drive ranges and transmission stages, the number of clutch shift processes, of course, increases. Response or reaction and adjusting times of the hydraulic actuation devices result in long shift processes and in losses whereby the effectiveness is deteriorated.
With this background, the problem to be solved by the invention consists in altogether optimizing, especially abbreviating, the shift processes.
SUMMARY OF THE INVENTION
According to the invention, the problem is solved by the features of claim 1, while advantageous embodiments and developments of the invention can be understood from the subclaims.
Shift signals are usually triggered when a shift or synchronizer speed is attained, thereafter elapse a response or reaction time and an adjusting time until the shift elements are engaged. Therefore, a time interval exists between the triggering of the shift signals upon reaching the synchronizer speed and the actual shifting point whereby the shift process is unnecessarily prolonged and the whole effectiveness deteriorates.
According to the invention, the time interval between the triggering of the shift signals and the actual shift point is compensated by a control unit. The control unit triggers the shift signal around the time before the shift or synchronizer speed is reached so that the actual shift point preferably falls directly on the moment at which the synchronizer speed is attained. Thereby the shift process is shortened and the total effectiveness improved.
According to the invention, the reduction ratio or the moment when the shift signal must be triggered is dete
REFERENCES:
patent: 4170153 (1979-10-01), Mizuno et al.
patent: 4852429 (1989-08-01), Kunzer et al.
patent: 5376056 (1994-12-01), Wakahara et al.
patent: 5529546 (1996-06-01), Ishino et al.
patent: 5560203 (1996-10-01), Pollman
patent: 5624339 (1997-04-01), Coutant et al.
patent: 5888162 (1999-03-01), Moeller et al.
patent: 5980411 (1999-11-01), Wontner
Nikolaus Heinrich
Paton Robert
Bonck Rodney H.
Waddell Tisha D.
ZF Friedrichshafen AG
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