Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Patent
1999-06-01
2000-06-27
Wright, Dirk
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
477 47, F16H 5942
Patent
active
060800801
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an arrangement and a method for adjusting the transmission ratio of a continuously variable transmission.
BACKGROUND OF THE INVENTION
Continuously variable vehicle transmissions are generally identified by "CVT" and are, for example, known from EP,A1,0,451,887. Such CVT transmissions permit driving at low engine rpms. The adjustment of the transmission ratio generally takes place hydraulically and the required hydraulic pressure is supplied by a hydraulic pump driven by the vehicle engine. However, a sudden and very intense braking can lead to the situation that the CVT transmission still has a relatively low transmission ratio in some circumstances for a vehicle standstill because the volumetric displacement of the pump at low engine rpms is insufficient in the short braking time which is available in order to adjust the transmission to a high start transmission ratio. If the vehicle is at standstill, then the transmission cannot be adjusted so that the objective must be to always reach the start transmission ratio shortly before the vehicle comes to standstill.
In order to adjust the start transmission ratio at the end of the braking operation, the transmission can be adjusted as rapidly as possible to large transmission ratios when an intense deceleration is recognized. A torque converter is generally mounted between the vehicle engine and the CVT transmission and this torque converter can be bridged by a converter bridging clutch. For this reason, the rpm of the engine drops to the idle rpm at the instant at which the converter bridge clutch opens. At the very latest, it can be that the displacement volume of tine hydraulic pump is no longer adequate in order to adjust the transmission so that the vehicle comes to standstill with transmission ratios which are less than the start transmission ratio.
One possibility of solving this problem comprises driving the engine at an increased idle rpm during braking. However, this can remain only a very limited intervention because, during deceleration of the vehicle, in no case can a propulsion torque be effective on the wheels because of increased engine rpm.
SUMMARY OF THE INVENTION
The object of the present invention is to reliably reach the start transmission ratio at the end of braking without extending the actual braking operation.
As already described, the invention proceeds from a transmission which is mounted between the vehicle engine and the drive wheels of a vehicle and is designed with respect to its transmission ratio so as to be continuously adjustable. This CVT transmission has a primary end and a secondary end. At least first sensor means are provided for detecting the rpm of the primary end.
The essence of the invention is that a deceleration state of the vehicle of a pregiven or pregivable extent is determined. The output rpm of the vehicle engine is adjusted in dependence upon the detected rpm of the primary end in response to the determination of this deceleration state. It is especially provided that additional sensor means for detecting the output rpm of the vehicle engine are provided and the output rpm of the vehicle engine is adjusted in the sense of a control to the detected rpm of the primary end.
The invention proceeds from the condition that during a braking operation by the vehicle engine, such an accelerated torque can be effective which is just so high that no propulsion power is transmitted via the converter which opposes braking. Here, it is provided that a torque converter having a converter bridge clutch is mounted between the vehicle engine and the transmission. The converter bridge clutch is opened in response to the determination of the deceleration state.
A hydrodynamic converter transmits no power precisely when the output rpm and the input rpm are equal, that is, the converter slip is zero. Accordingly, the converter input rpm, that is, the engine output rpm, is so controlled during the deceleration operation (braking operation) that it is equal to the converter out
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patent: 5199399 (1993-04-01), Shibuya
patent: 5435795 (1995-07-01), Mochizuki et al.
Bolz Martin-Peter
Hulser Holger
Luh Joachim
Ottesen Walter
Robert & Bosch GmbH
Wright Dirk
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