Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2000-10-04
2002-08-06
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C477S050000, C474S028000
Reexamination Certificate
active
06428445
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a transmission, specifically an automatic, continuously variable transmission. Known transmissions of the kind discussed hereinafter have an rpm-converter means for converting an input rate of rotation (input rpm rate) to an output rpm rate, a transmission-control system for the rpm-converter means, as well as a supply circuit for the rpm-converter means into which a working fluid is fed by a fluid-conveyor device. The supply circuit carries the working fluid supplied by the pump by way of the transmission-control system to the rpm-converter means for setting different rpm-conversion ratios. A return circuit carries return fluid out of the rpm-converter means and/or the control system, e.g., to a reservoir tank for the working fluid. At least one branch conduit runs from the return circuit to provide at least one cooled and/or lubricated element of the transmission with working fluid. The transmission is further equipped with a flow-regulating device in the supply circuit, e.g., downstream of the fluid-conveyor device. The flow-regulating device has a run-off circuit to carry away the run-off portion of pressure that occurs as a result of the regulating function. The run-off circuit can lead to the reservoir tank or to the intake of the fluid-conveyor device to recharge the latter with working fluid. A transmission of this kind is shown, e.g., in DE 198 26 747 Al. A switching valve is arranged in the return circuit, whereby the working fluid flowing back from the rpm-converter means can either be directed to the intake of the fluid-conveyor device or supplied as a coolant to a clutch. The transmission described in DE 198 26 747 Al is preferably configured as a continuously variable transmission. Another continuously variable transmission is known, e.g. from DE 195 46 293 Al.
In automatic transmissions as described above, it is necessary to limit by means of the flow-regulating device the maximum rate at which working fluid flows to the transmission-control system and is made available to be directed to the rpm-converter means. The purpose of this regulation is to avoid excessive levels of backup pressure and losses in the conduits. In addition, the regulation allows the valves, particularly those of the transmission-control system, to be designed for a low flow rate, whereby the regulating performance is improved. As mentioned above, the run-off portion of the working fluid that occurs as a result of the regulating process can be used to charge the intake of the fluid-conveyor device, whereby the noise-generating properties of the fluid-conveyor device are improved. Thus, the flow-regulating device divides the total volume flow from the fluid-conveyor device into the regulated portion that is directed to the rpm-converter means and the run-off portion that is directed back to the reservoir tank or to the intake of the fluid-conveyor device. The working fluid returning from the high-pressure circuit (transmission-control system and rpm-converter means) is tapped off from the return circuit to be used with first priority for cooling and lubricating. Thus, the amount of fluid available as lubricant and coolant consists only of the remainder of the regulated portion after subtracting the control-system leakage and the dynamic flow-rate requirement of the rpm-converter means.
This creates a conflict between design objectives in transmissions of the known state of the art. On one hand, a sufficient amount of lubricant/coolant medium has to be available in order to avoid thermal instabilities in the thermal balance of the transmission even under worst-case conditions. This requires large quantities of fluid. On the other hand, there are also the objectives of keeping the pressure losses small and using compact dimensions in the transmission control system and its components, which requires relatively small quantities of fluid. Consequently, this causes a conflict because the control of the transmission requires a smaller amount of fluid than the lubricating and cooling functions.
OBJECT OF THE INVENTION
It is therefore the object of the present invention to provide an automatic transmission that belongs to the kind of transmissions described above but does not have the disadvantage of the aforementioned design conflict.
SUMMARY OF THE INVENTION
The invention meets the foregoing objective in an automatic transmission with an rpm-converter means, a control system for the rpm-converter means, and a supply circuit leading to the rpm-converter means. A pump feeds working fluid to the supply circuit, and a return circuit carries spent working fluid back from the rpm-converter means and/or the control system. The transmission also has at least one cooled and/or lubricated element that is supplied by the return circuit. A flow-regulating device is arranged in the supply circuit, and a run-off circuit removes the run-off portion of working fluid from the flow-regulating device. In a transmission according to the invention, the return circuit coming from the rpm-converter means and/or the transmission-control system and the run-off circuit carrying the run-off fluid from the flow-regulating device merge at a circuit junction. After the confluence at the circuit junction, the united streams from the return and run-off circuits continue in a combined flow-back circuit. As a result of this arrangement, the regulated portion of the working fluid that is returned from the high-pressure domain and the run-off portion that is removed by the flow-regulating device are reunited. Thus, in addition to the remainder of the regulated portion after subtracting the control-system leakage and other usages of fluid, the run-off portion itself, which has been removed by the flow-regulating device, becomes available to be supplied to components that need lubricating and/or cooling. The total flow-rate of the flow-back circuit depends, as a first approximation, on the rpm rate of the engine to which the automatic transmission is connected. In power-transmitting elements, e.g., in the rpm-converter means, the required lubricant/coolant quantity, likewise, depends on the engine rpm rate, because the maximum amount of power to be transmitted increases in nearly linear proportion with the engine rpm rate. Thus, the available amount of working fluid is harmonically matched to the fluid requirement for lubricating and cooling, so that the heat that is being generated can be carried away by the lubricant/coolant medium even at high engine-rpm rates. In other words, although a constant rate of fluid flow can be made available for the transmission control system as well as the rpm-converter means over the entire rpm range of the engine, the lubricated and/or cooled elements can be supplied with a larger volume of working fluid depending on the engine rpm rate, as the fluid-conveyor device is driven at the rpm-rate of the engine and therefore recirculates increased amounts of fluid at higher engine-rpm rates, with the excess flow being directed to the run-off circuit at the flow-regulating device.
A preferred embodiment of the invention has a charging circuit that leads from the flow-back circuit to the intake portion of the pump. Thus, the flow-back circuit, which carries the working medium coming from the high-pressure area as well as the run-off from the flow-regulating device, also supplies the intake portion of the fluid-conveyor pump in addition to the cooled and/or lubricated element(s), so that the intake portion can be charged, whereby the noise-generating properties of the fluid-conveyor device are improved.
It is further preferred according to the invention to have at least one lubricant/coolant circuit branching off from the flow-back circuit and leading to the at least one cooled and/or lubricated element. Thus, both the at least one cooled and/or lubricated element and the intake portion of the fluid-conveyor device are supplied with working fluid from the flow-back circuit.
An especially preferred embodiment has a cooler and/or converter arranged in the r
Agner Ivo
Friedmann Oswald
Darby & Darby
Lewis Tisha D.
LuK Lamellen und Kupplungsbau GmbH
Marmor Charles A
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