Planetary gear transmission systems or components – With lubricaton
Reexamination Certificate
2000-02-02
2002-02-26
Marmor, Charles A (Department: 3681)
Planetary gear transmission systems or components
With lubricaton
C475S161000, C477S045000
Reexamination Certificate
active
06350215
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a hydraulic system for pressure actuation of a variator of an automatic transmission having an emergency running device.
To control modern automatic transmission in motor vehicles, it is known to use an electronic transmission control (EGS) with which criteria relevant to the user, such as driving comfort, driveability, and criteria relevant to safety are amply satisfied.
In the case of a defect of the electronic transmission control, emergency, programs are often provided which are designed in a manner, such that, in an emergency, a vehicle can be operated in the most extensive possible speed range. But, according to such emergency running systems, the cooling of the transmission in such a state of driving is problematic, since the heat onset in the emergency operation of the transmission must be eliminated by the cooling system of the vehicle and in the case of complete failure of the electronic transmission control, the transmission has no inherent possibility of positively acting upon the heat economy.
This particularly applies to CVT (continuously variable transmission) automatic transmissions which have a variator for continuous adjustment of a reduction ratio between a shortest possible speed ratio (LOW) and a longest possible speed ratio (overdrive, OD).
In “
ATZ Automobiltechnische Zeitschrift
”96 (1994) has been described such a CVT transmission, having one first cone pulley pair upon an input shaft as primary pulley set and a second cone pulley pair upon an output shaft as secondary pulley set. Each cone pulley pair consists of a first pulley axially stationary and a second pulley axially movable which provide the primary or secondary pulley as designated. Between the cone pulley pairs rotates a torque transmission member which constitutes, e.g. a link belt wound around the cone pulley pair. To adjust the primary or secondary pulley, it is actuated with a pressure medium from a pressure source, the pressure being adjusted with the aid or an electronic transmission control and of an electrohydraulic pressure-supply device.
DE 44 36 506 has disclosed a device for control of a CVT transmission in which an electronic control unit determines, via electromagnetic actuators and hydraulic valves, the pressure level of the pressure spaces of primary pulley and secondary pulley that, in particular, have not been dynamically balanced.
For a failure of the electronic control unit, an emergency device is provided, which has two pressure-regulating valves, two pressure-reducing valves and at least one emergency valve wherein a primary valve and a secondary valve provide a constant static pressure ratio or power ratio between primary pulley and secondary pulley under a constant static secondary pressure level.
From the magnitude of said static power ratio and of the dynamic forces on the pulleys in which the pressure has not been dynamically balanced, it is possible to established the magnitude of the speed ratio change of the CVT transmission from a normal operation to the emergency operation. The emergency operation is described here as a state of the CVT transmission in which have been interrupted a pressure regulation of the variator on the EGS side and a contact pressure regulation of the variator on the EGS side.
In this known device, the speed ratio of the CVT transmission changes, according to the issued torque of an internal combustion machine provided as input unit, the variable change of speed ratio in the emergency operation making a reliable start uphill and an improved driveability at high terminal speed possible.
As an input signal on an electronic control unit there are available, e.g. the signal of a load position of the input unit such as the throttle valve position in the case of an internal combustion engine, the rotational speed of the transmission input shaft, the rotational speed of the output shaft, or the temperature of the pressure medium. From the input signal, an operation point is determined and the corresponding rotational speed of the transmission input shaft or the speed ratio of the CVT transmission is adjusted. When an error occurs, the CVT transmission changes over to emergency operation in which there are no longer on the side of the EGS any rotational speed regulation and contact pressure regulation.
Even though the known solution offers an extensive possible adjustment range of the variator, it still is problematic that the contact pressure for the corresponding pulleys must be interpreted, according to the extreme corner points of the driveability range. One of said corner points is the guarantee of the maximum start up power in the lowest gear, i.e. in or near the LOW speed ratio. For the transmitting capacity of the variator, a higher contact pressure is required on the secondary pulley at the highest speed ratio and high input torque. Conditioned by the draft, the static force adjusted on the secondary pulley, the magnitude of which depends on the maximum input torque to be transmitted, is constant throughout the torque range. The speed ratio adjustment results from the draft of the constant static pressure ratio between primary pulley and secondary pulley combined with the dynamically, not balanced adjustment spaces.
In all states of operation, except during maximum output torque, however, the consequence of this is an excess of contact pressure which disadvantageously leads, during emergency operation to a high operating temperature in the variator with the consequence of an impairment of the durability of the automatic transmission with respect to the mechanics and of an electronic control unit, a blockage in the transmission oil sump (mechatronics), or a lowering of the oil quality. Other negative phenomena with increasing temperature of the variator and thus increaisng temperature of oil are increased internal leakages in the transmission and an idle power increase therewith. Thus results the problem of a requirement of a suitably dimensioned radiator.
The problem, which this invention is based, is to provide a hydraulic system for pressure actuation of a variator of a CVT automatic transmission having in the emergency operation a constant pressure ratio between primary and secondary pulleys, wherein the thermal load of the automatic transmission in emergency operation is easily and economically reduced so as to prevent damage in the automatic transmission due to heat effect during the emergency operation.
According to the invention, this problem is solved with a hydraulic system according to claim
1
.
SUMMARY OF THE INVENTION
A boost of the radiator through-flow by which is achieved a cooling of the lubricant that extensively eliminates thermally conditioned damages in the automatic transmission.
According to the inventive solution, the increased heat onset in the emergency operation can be advantageously removed, via the radiator, without the dimensions thereof, being larger than for the cooling power required in normal operation, provided that in the normal operation the radiator still has not been operated on the oil side to thermodynamic saturation. Therewith is eliminated the need of a larger or additional radiator with the associated consequences of a larger installation space being required and higher costs.
REFERENCES:
patent: 5089964 (1992-02-01), Morishige et al.
patent: 5273492 (1993-12-01), Kashiwase et al.
patent: 5890987 (1999-04-01), Lamers
patent: 5944626 (1999-08-01), Spiess et al.
patent: 5961408 (1999-10-01), Konig et al.
patent: 6015359 (2000-01-01), Kunii
patent: 44 36 506 (1996-04-01), None
patent: 0017054 (1984-01-01), None
patent: 0270255 (1988-11-01), None
Davis & Bujold PLLC
Ho Ha
Marmor Charles A
ZF Batavia L.L.C.
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