Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2000-03-20
2001-10-09
Marmor, Charles A. (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C474S028000
Reexamination Certificate
active
06299564
ABSTRACT:
BACKGROUND OF THE INVENTION
The instant invention concerns a system for control of a CVT driven by an input unit.
Continuously variable automatic transmissions, also called CVT, for motor vehicles are usually comprised of a start-up unit, a forward/reverse drive unit, a variator, an intermediate shaft, a differential and a hydraulic and electronic control unit. The CVT is driven by an internal combustion engine, via an input shaft, particularly the crankshaft. A start-up unit serves either a start-up clutch or a hydrodynamic converter. The forward/reverse drive unit serves for reversal of direction of rotation for forward or reverse drive and usually consists of a planetary reversing gear.
The variator consists of two bevel pulley pairs and a belt-type organ, each bevel pulley pair having a first bevel pulley axially stationary and a second bevel pulley axially movable. Hereinafter the bevel pulleys disposed on the input will be designated as primary pulley and the bevel pulleys disposed on the output as secondary pulley. Between the two pairs of bevel pulleys rotates the belt-type organ such as a sliding link conveyor.
The running radius of the belt-type organ and therewith the ratio of the CVT change by adjustment of the bevel pulleys. The second bevel pulley pair is non-rotatably connected with one output shaft which transmits the torque to an intermediate shaft via a pair of gears. The intermediate shaft serves for reversal of direction of rotation and adaptation of torque and rotational speed. The torque of the intermediate shaft is transmitted to the differential via one other pair of gears.
The control or regulation of the CVT is carried out by the electronic control unit via the hydraulic control unit. The hydraulic control unit contains electromagnetic actuators and hydraulic valves. A pump conveys the pressure medium from the lubricant sump to the hydraulic control unit and to the consumers of the CVT.
EP-A 0 634 590 has disclosed a system for hydraulic control of a CVT. The primary pulley and the secondary pulley are each adjusted via a hydraulic valve. The first valve controls the primary pulley and the second valve controls the secondary pulley. Both the first and second valves are pre-controlled by an electromagnetic pressure regulator. The second valve is here supplied with pressure medium by a pump, the pressure supply of the first valve being adjusted via a control edge of the second valve. The pressure level of the supply line for the first valve is thus identical with the pressure level delivered by the pump. The disadvantage resulting from this arrangement is that the pressure level of the secondary pulley cannot be adjusted below the minimal pressure level provided by the pump so that an overpressure between the secondary pulley and a belt-type organ results in a reduction in efficiency.
To overcome said disadvantage, the applicant's patent application 195 33 976.2 has already proposed a hydraulic system for a CVT preferably driven by an internal combustion engine having a common central first hydraulic branch in which a first pressure level prevails and which is fed by a pump from which a specific pressure supply branches off from the first hydraulic branch to each consumer; the consumers are here the primary pulley, the secondary pulley, the clutch or brake of the forward-reverse drive unit, the start-up unit and the lubrication points of the CVT. In each pressure feed to a consumer are located both a hydraulic valve and an electromagnetic pressure-control valve associated therewith in a manner such that the electronic pressure-control valve determines via the hydraulic valve the pressure level in the pressure feed of the consumer. The electromagnetic valves are, in this case, situated in a second hydraulic branch.
From the applicant's DE-P 44 36 506.3 is known a system for control of a CVT driven by an input unit which has a so-called emergency device, with two emergency valves, which is activated in case of failure of the electronic control unit and which provides a constant pressure ratio or power ratio between primary pulley and secondary pulley, the pressure level of an adjusting chamber of the secondary pulley then being constant. The first emergency valve is connected with the primary valve for the primary pulley and the secondary emergency valve with the secondary valve for the secondary pulley; the shift positions of both emergency valves are determined by an electromagnetic pressure-control valve in a manner such that in a first position of both emergency valves a first pressure-control valve acts upon the primary valve pre-controlling it and a second pressure-control valve acts upon the secondary valve pre-controlling it while in a second position of both emergency valves the pressure level of a pressure-reducing valve acts upon the primary valve and the secondary valve pre-controlling them.
The problem to be solved by the present invention is to propose a system for control of a CVT which offers the same advantages and reliability as the systems already known but, at the same time, simplifies construction and thus more economical production.
SUMMARY OF THE INVENTION
The invention provides that the main pressure valve and the hydraulic secondary valve for the secondary pulley be connected with a common electromagnetically controlled pressure-control valve and that geometry and spring tension of main pressure valve and secondary valve be designed so that the two valves have different characteristic lines.
The valve characteristic lines are, at the same time, defined so that in the range of high ratio of the transmission (overdrive) the primary pressure in the primary valve is higher than the secondary pressure in the secondary valve, but that in the remaining ratio ranges of the transmission, it is lower than the secondary pressure.
A pressure sensor is preferably located in the line between the secondary valve and the secondary pulley.
In order that the control pressure, provided by the common pressure-control valve, is ensured, even in case of leakages, on the active diameters of the main pressure valve and the secondary valve, it is advantageous that, on the pressure-control valve, a volume reinforcing valve is rear-mounted.
In another advantageous embodiment, the electromagnetic pressure-control valve acts only upon the main pressure valve, while the secondary valve is designed as a pressure-reducing valve in which a secondary pressure is set to a constant value which is lower than the main pressure.
Hence, the inventive system makes it possible to omit a pressure regulator, since the main pressure is coupled with the contact pressure whereby lowering to zero bar of the contact pressure is possible. The required variation between main pressure and contact pressure is obtained here by different characteristic line curves of the two valves. Unlike the systems known from the prior art, the main pressure is not directly connected with the contact pressure. Subject to a corresponding aspect ratio of primary and secondary pulleys, in all driving states needed the marginal conditions are kept as needed, since the contact pressure is lower than the main pressure. The main pressure valve and the secondary valve are, therefore, controlled either via a common pressure regulator, wherein it is possible to implement two different characteristic lines by spring characteristic and valve ratio, or by direct attachment of the secondary valve to the main pressure valve, the secondary valve being a pressure-reducing valve.
It is, therefore, possible with the inventive system to implement low contact pressures combined with high adjustment gradients.
REFERENCES:
patent: 4601680 (1986-07-01), Tokoro et al.
patent: 5888168 (1999-03-01), Niiyama et al.
patent: 6117045 (2000-09-01), Hopper
patent: 6224509 (2001-05-01), Gierling
patent: 44 36 506 A1 (1996-04-01), None
patent: 195 33 976 A1 (1997-03-01), None
patent: 0 634 590 A1 (1995-01-01), None
patent: 9-105457 (1997-04-01), None
Fessler Bernd
Gessler Klaus
Konig Hubert
Sommer Stefan
Davis & Bujold P.L.L.C.
Marmor Charles A.
Parekh Ankur
ZF Batavia L.L.C.
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