Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2000-05-17
2001-12-25
Estremsky, Sherry (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C477S044000, C477S115000
Reexamination Certificate
active
06332859
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for controlling a continuously variable transmission on the basis of parameters indicating an engine output torque.
2. Related Art
The continuously variable transmission to be mounted on an automobile is exemplified by a continuously variable transmission (as will be called the “CVT”) which is constructed by combining a metallic belt and a pair of (primary/secondary) pulleys having a variable groove width, for example.
In this CVT, the speed or RPM (Revolutions Per Minute) of an engine, as inputted from the primary pulley, is changed with the change in the winding diameter of the belt made to run between the two pulleys, and is transmitted from the secondary pulley to the differential and the drive wheels. Moreover, a gear ratio is controlled by adjusting the flow of oil fed to the primary pulley.
On the other hand, the torque, transmitted between the primary pulley and the secondary pulley, is determined by the force for pushing the belt between those pulleys. In the CVT, therefore, a line pressure control is made to push the belt sliplessly with the secondary pulley by using an oil pressure, for example. As this line pressure grows higher, the force to push the belt becomes the higher. If a pushing force higher than necessary is applied to the belt, however, the smooth movement of the belt is deteriorated. Therefore, the line pressure control is performed under a target value which is determined on the basis of the input torque inputted to the CVT (i.e., the torque outputted from the engine) and the gear ratio.
This line pressure control is made in the prior art on the basis of a torque information dictated by an average effective pressure (which is calculated by dividing the torque by the displacement of the engine and which indicates a parameter value of the engine output torque) calculated on the basis of a demanded value of an engine output demanded by the driver, by using a value estimated from the average effective pressure as the engine output torque.
Here, the torque information, obtained on the basis of the accelerator opening, is not the information of the torque which is generated from the engine by burning a fuel, but the preceding torque information which was intended to generate the power. Thus, the torque information has a quick output timing and an excellent responsiveness for a shift in which the torque abruptly changes. However, the torque information has a poor precision because it is estimated from the value demanded by the driver.
In a steady state with little torque change, therefore, because of a poor precision of the torque information, the frequency of generating an excessive belt pushing force is so high that the fuel economy (i.e., miles/gallon) of the automobile is adversely affected.
SUMMARY OF THE INVENTION
The invention has been conceived in view of the background thus far described and has an object to provide a control system for a continuously variable transmission, which can make compatible the belt slippage prevention based on the responsiveness of the continuously variable transmission at a shifting time of an abrupt torque change, and a control for suppressing an excessive belt pushing force in a steady state of the continuously variable transmission during little torque change.
According to a first aspect of the invention, there is provided a control system for a continuously variable transmission, comprising: a first element for determining a first parameter value indicating an engine output torque from the engine RPM and the value of an engine output demanded by the driver; a second element for determining a second parameter value indicating the engine output torque from a parameter value corresponding to a rate of fuel injection into the engine; a selection element for selecting one of the first parameter value and the second parameter value; and a control element for controlling the continuously variable transmission on the basis of the selected parameter value.
In the continuously variable transmission control system, the selection element may output, at a fuel cutting drive, a value, which is determined by adding a load on an accessory connected to the engine to the first parameter value, to the control element.
In the continuously variable transmission control system, the selection element may select the larger one of the first parameter value and the second parameter value, when the torque abruptly rises, and the second parameter value when the torque does not abruptly rise.
In the continuously variable transmission control system, the force to push the pulley of the continuously variable transmission may be controlled by a fluid pressure fed to the continuously variable transmission, and may comprise a gear ratio detecting element for detecting the gear ratio of the continuously variable transmission. The control element may calculate a target feed fluid pressure to be fed to the continuously variable transmission, from the engine output torque based on the selected parameter value and from the gear ratio, thereby to control an actual feed fluid pressure to the target feed fluid pressure.
In the continuously variable transmission control system, the first and second parameter values may be a target average effective pressure of the engine.
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Asayama Hiroki
Misaki Kenji
Nakamori Kenichi
Sato Hironobu
Takeda Atsushi
Estremsky Sherry
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Pang Roger
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