Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2002-03-19
2004-08-31
Lewis, Tisha D (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C477S050000, C477S091000, C477S156000
Reexamination Certificate
active
06783479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for operating an automatic transmission as a function of, among other things, engine rotational speed. The invention also relates to an automatic transmission for a variable speed internal combustion engine, with a delivery system for a working medium with which at least one adjusting device is acted on by a first control device which, in turn, is controlled by a pilot pressure that can be accurately changed by a second control device to operate the adjusting device.
2. Description of the Related Art
A similar method and a similar automatic transmission are disclosed in German Patent Publication No. DE 195 46 293 A1, in which is disclosed a belt driven, conical pulley transmission with input side and output side pairs of conical disks. The power transmission between the two pairs of conical disks can be effected by a steel loop or band. Each pair of conical disks includes an axially movable disk and an axially fixed conical disk. The axially displaceable conical disk halves are arranged diagonally opposite each other. By an axial displacement of the movable conical disk halves, the effective lever arms of the pairs of conical disks become larger or smaller in opposite directions.
The axial displacement of the movable conical disk halves is achieved with an adjusting device. A first control device actuates the adjusting device. The first control device includes one or two hydraulic valves to which a pilot pressure is applied. The first control device is controlled by an electrically actuated second control device, for example a proportional valve. To adjust the transmission ratio of the belt driven, conical disk transmission, depending upon the demand, the pilot pressure is accurately changed by the second control device, for example by suitable software.
In the event of an electronic failure, the adjusting device can no longer be controlled by the first control device because of the failure of the electronically-operated second control device, and the automatic transmission will no longer function. Consequently, continued operation (limp home) of a motor vehicle with that type of automatic transmission is no longer possible by its own power, and it must therefore be towed away.
The object of the invention is to provide an appropriate method and an appropriate automatic transmission that enable continued operation by its own power when an electronic failure occurs and/or the second control device fails.
SUMMARY OF THE INVENTION
The object is attained with a method for operating an automatic transmission as a function of, among other things, the engine rotational speed, in that the transmission ratio is changed to a limp home condition of the automatic transmission after a starting procedure in order to maintain the engine rotational speed at a specific constant value. A transmission ratio of high speed results when the engine rotational speed increases, and a transmission ratio of low speed results when the engine rotational speed decreases. A constant engine rotational speed is maintained through the transmission ratio control in a limp home condition.
A preferred embodiment of the method is characterized in that the transmission ratio is adjusted to a high speed ratio, after the starting process, at increasing engine rotational speed, until the minimum possible transmission ratio condition is reached, which is then maintained during further increases in engine rotational speed. After reaching the minimum transmission ratio condition, the engine rotational speed can no longer be maintained constant, and it increases until the engine performance is in equilibrium with the running resistance.
Another preferred embodiment of the method is characterized in that the transmission ratio, after the starting process, is adjusted to a low speed ratio at decreasing engine rotational speed, until the largest possible transmission ratio condition is reached, which is then maintained during further decreases in engine rotational speed. After reaching the largest possible transmission ratio condition, the engine rotational speed can no longer be maintained constant and decreases.
A further preferred embodiment of the method is characterized in that, when the rotational speed is increased further, the transfer of torque from an input element to an output element is interrupted with the aid of a clutch or converter. The engine is thereby prevented from stalling.
A further preferred embodiment of the method is characterized in that the specific value at which the engine rotational speed is maintained constant is greater than the so-called stall speed. The maximum rotational speed at which a clutch or a converter can still slip is designated as the stall speed. The stall speed is therefore the rotational speed at which the converter or the clutch stops the engine with completely applied brakes and full throttle. A certain minimum difference between the stall speed and the transmission ratio control rotational speed is to be maintained for safety reasons.
The object is achieved in an automatic transmission for a variable rotational speed internal combustion engine, with a delivery system for a working medium, with which at least one adjusting device is actuated by a first control device, which, in turn, is controlled by a pilot pressure that can be specifically changed by a second control device in order to operate the adjusting device, in that in addition to the second control device a third control device is provided, which is actuated by a working medium transported by the delivery system, with the help of which the pilot pressure for controlling the first control device is changed as a function of the rotational speed of the internal combustion engine, when a switching device is switched from a normal position to a limp home position.
The automatic transmission in accordance with the invention is distinguished by an additional third control device, which is hydraulically or pneumatically operated by the working medium transported by the delivery system. As a result, the operation of the adjusting device is ensured even when the second control device fails. In that way an emergency operation of the automatic transmission is ensured, so that continued operation, for example to the nearest service station, is possible.
One embodiment of the automatic transmission is characterized in that the delivery system for the working medium is composed of a pump whose delivered volumetric flow depends upon the rotational speed of the internal combustion engine. That can be achieved, for example, by coupling the input of the pump with the camshaft or the crankshaft of the internal combustion engine. The volumetric flow of the pump, which is dependent upon the speed of the internal combustion engine, is utilized in a so-called limp home condition of the automatic transmission for controlling the transmission ratio of the transmission and/or a starting clutch.
A further embodiment of the automatic transmission is characterized in that the third control device has an axially-displaceable, spring-biased control plunger with a first and second working surface for the working medium delivered by the delivery system, as well as with a third working surface, which is contacted by the regulated pilot pressure, whereby the first and second working surfaces on the control plunger of the third control device, which are contacted by the working medium, are of the same size. In the normal condition of the transmission, the same working medium pressure acts on the first and second working surfaces on the control plunger of the third control device. The magnitude of the regulated pilot pressure can be adjusted by the spring bias acting on the control plunger. The spring-biased control plunger of the third control device functions as a pressure regulator that maintains the pilot pressure at a constant value. Two control edges can be formed on the control plunger, which ensure that the pilot pressure will decrease when it exceeds a speci
Lewis Tisha D
Luk Lamellen und Kupplungen Beteiligungs KG
Mangels Alfred J.
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