Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on... – Fluid pressure actuator for adjustment of member
Reexamination Certificate
2000-10-06
2002-10-15
Hannon, Thomas R. (Department: 3682)
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
Fluid pressure actuator for adjustment of member
Reexamination Certificate
active
06464603
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus that are used to regulate by way of a regulating device the hydraulic fluid pressure that is applied through a control valve to one or more piston/cylinder units of a continuously variable cone-pulley transmission in order to set or change the transmission ratio.
A continuously variable cone-pulley transmission of the kind that the invention relates to has two adjustable pulleys, i.e., a first pulley mounted on a first shaft (input shaft) and a second pulley mounted on a second shaft (output shaft), and an endless flexible element such as a chain or belt (subsequently referred to as a chain-belt) to transmit torque between the pulleys. Each pulley is essentially a pair of conically tapered discs. In each pulley, one disc is rigidly connected to the respective shaft, while the other disc is constrained to the shaft only in the rotational sense but movable in the axial sense of the shaft.
The gripping pressure to hold the chain-belt between the discs is applied through actuating members that are arranged at the movable discs. The actuating members are pressurized by a torque sensor that is responsive to the magnitude of the torque to be transmitted. At least one of the disc pairs has a second actuating member configured as a ratio-controlling piston/cylinder unit that can be hydraulically pressurized to a pressure level (subsequently called the ratio-controlling pressure) that varies depending on the rpm-ratio (subsequently called the transmission ratio) that is to be set between the input shaft and the output shaft of the continuously variable transmission. The pressurized working fluid is delivered to the ratio-controlling piston/cylinder unit by way of a transmission-ratio valve.
The ratio-controlling pressure can be influenced by a pressure valve that supplies the transmission-ratio valve with an adequate amount of pressure for a rapid shifting of the axial positions of the movable discs and thus a rapid change of the D transmission ratio. For example, if the driver of a vehicle equipped with this type of transmission depresses the gas pedal to increase the speed of the vehicle, the immediate consequence is an increase in the amount of power that the engine delivers to the cone-pulley transmission. To translate the power increase into an acceleration of the vehicle requires an appropriate change of the transmission ratio, which requires a change in the ratio-controlling pressure that is delivered to the ratio-controlling piston/cylinder unit.
The transmission-ratio valve can be a pilot-controlled pressure-reducing valve whose pilot pressure is variable under the control of a proportional valve. The proportional valve, by generating appropriate changes of the pilot pressure, causes the transmission-ratio valve to open or to further increase the opening of a hydraulic passage to the piston/cylinder unit. The change of the pilot pressure delivered to the transmission-ratio valve occurs as a result of a change in the controlling electric current of the proportional valve. The controlling current of the proportional valve therefore has to be tied into a servo loop in which the actual current value is compared to a given target value, so that a deviation of the actual value from the target value can be corrected by the regulating servo. The same applies also in case where the transmission-ratio valve is controlled directly by an electric current to effect variations in the ratio-controlling pressure delivered to the piston/cylinder unit.
The vehicle power plant consisting of the continuously variable transmission and the combustion engine is exposed to significant variations of its operating conditions. For example, there may be large variations in the fluid temperature of the hydraulic circuit. As another example, a change of the transmission ratio will also cause changes in the behavior of the piston/cylinder unit and in the regulating behavior of the transmission-ratio valve. These are only two examples of factors that have an influence on the behavior of the hydraulic control of the transmission ratio.
OBJECT OF THE INVENTION
It is therefore the object of the present invention to provide a method and apparatus for controlling the ratio-controlling pressure of a working fluid by means of a regulating device, wherein variations in the regulating behavior of the transmission-ratio valve under different operating conditions are taken into account.
SUMMARY OF THE INVENTION
The invention meets the foregoing objective by introducing a method of regulating by way of a regulating device the ratio-controlling pressure that is applied through a transmission-ratio valve to one or more piston/cylinder units of a continuously variable cone-pulley transmission in order to set or change the transmission ratio. According to the invention, the ratio-controlling pressure is regulated in such a way that certain operating parameters of the regulating device (that will be referred to as control parameters) are adjusted depending on the amounts of ratio-controlling pressure to be applied and that the regulation is performed by using the adjusted control parameters.
Thus, the inventive method takes into account that with changing operating conditions, the transmission-ratio valve can in some cases have significantly different response times when there is a change in a control variable or an abrupt change in an extraneous interference quantity. In other words, the transfer function of the transmission-ratio valve is subject to change under different operating conditions. When the amount of current is changed in the proportional valve that generates the pilot pressure for the transmission-ratio valve, or also when the amount of current is changed in a current-controlled transmission-ratio valve in order to change the position of the valve piston in the piston bore, the reaction times for moving the piston to a different position will vary, i.e., the settling times for transient oscillations will be of different length. If the regulation is performed, e.g., by means of a regulating device configured as a P/I servo with proportional and integrating components and constant control parameters, it is possible that certain deviations or excursions of a quantity to be regulated can no longer be brought under control because the stability limit of the servo circuit has been reached and the aforementioned oscillations would no longer settle down.
In a continuously variable cone-pulley transmission of a kind where both of the disc pairs on the input shaft and the output shaft, respectively, are equipped with a piston/cylinder unit for setting or changing the transmission ratio, there is a change-over in the pressure between the piston/cylinder units and in the transmission-ratio valve, so that the characteristic curve of the transmission-ratio valve (pressure vs. current) has an inversion point or area (zero-pressure range) where the transmission-ratio valve is pressure-free. Therefore, if the regulation were performed with constant control parameters throughout the entire range of the characteristic curve of the transmission-ratio valve, the regulating device would reach its stability limit when operating in the zero-pressure range, and the response would no longer be a transient oscillation settling in at the new target pressure. If the control parameters were adapted only according to a limited range in the vicinity of the inversion point, then the regulating device would have a markedly sluggish reaction when operating outside of the zero-pressure range. On the other hand, if the control parameters were dimensioned to work for a regulation outside of the zero-pressure range, the regulation would be unstable when operating inside the zero-pressure range, i.e., the regulating servo circuit would suffer from instabilities.
The invention solves the foregoing problem by introducing the concept of adapting the control parameters in the regulating device to the targeted ratio-controlling pressure and performing the regulation proce
Holtmann Ludger
Reuschel Michael
Darby & Darby
Hannon Thomas R.
LuK Lamellen und Kupplungsbau Beteiligungs KG
McAnulty Timothy
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