Interrelated power delivery controls – including engine control – Clutch control – Condition responsive control
Reexamination Certificate
2001-11-30
2003-05-20
Bonck, Rodney H. (Department: 3681)
Interrelated power delivery controls, including engine control
Clutch control
Condition responsive control
Reexamination Certificate
active
06565483
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates in general to control systems for controlling a torque converter used with an automatic transmission and more particularly to control systems of a type that controls a relative rotation (or slip rotation) between input and output elements of the torque converter. More specifically, the present invention is concerned with a slip control system for converging the slip rotation of the torque converter to a target level.
2. Description of Related Art
The torque converter is a device that carries out a power transmission between input and output elements through a fluid. Thus, the torque converter is somewhat poor in having a satisfied power transmission efficiency although it exhibits a good torque fluctuation absorbing function and a good torque multiplying function.
Accordingly, nowadays, a so-called lock-up type torque converter has been widely used, which, under a vehicle running condition wherein the torque fluctuation absorbing and torque multiplying functions are not actually needed by the torque converter, establishes a locked engagement between the input and output elements of the torque converter using a lock-up clutch.
Some of the lock-up type torque converters are of an ON/OFF type which establishes either the lock-up mode or the torque converter mode depending on running condition of the vehicle. However, in this ON/OFF type, it is difficult to solve or minimize residual noises and shocks that are produced when the converter makes switching between ON and OFF conditions. In fact, for reducing such residual noises and shocks, a suitable slip rotation of the torque converter is needed at the switching. However, due to nature of the ON/OFF type, the torque converter has a limitation in a slip control range, and thus it is difficult to further improve the transmission efficiency of a torque converter with such ON/OFF type.
SUMMARY OF INVENTION
In order to solve the above-mentioned problem, various slip control systems for the torque converter have been hitherto proposed. One of them is of a system wherein a slip control range is so set that with the lock-up clutch being left in a so-called half-engaged condition (viz., slip control condition), the slip rotation of the torque converter is so controlled or restricted as to assure the minimum torque fluctuation absorbing and toque multiplying functions. With this, the slip rotation control can be effected at a much lower vehicle speed range.
In general, in the above-mentioned slip control system, a target slip rotation speed is determined in accordance with vehicle operation factors, such as engine throttle opening, vehicle speed, temperature of hydraulic fluid of the transmission, etc., and the engaging force of the lock-up clutch is so controlled that, in the above-mentioned slip control range, the real slip rotation speed is finally controlled or converged to the target slip rotation speed. According to the above-mentioned slip control system, from a theoretical point of view, the slip rotation control can be extended to much lower speed range without suffering from residual noises and shocks and thus improvement in fuel consumption is achieved avoiding deterioration of drivability of the vehicle.
However, in fact, since the engaging force of the lock-up clutch for controlling the slip rotation speed can not be theoretically controlled, shocks and residual noises tend to be produced due to a temporary engagement of the lock-up clutch.
In order to solve such problem, the same applicants have hitherto proposed slip control systems which are shown in Laid-open Japanese Patent Application (Tokkai Hei) 11-82726 and Laid-open Japanese Patent Application (Tokkai Hei) 11-141677. However, as will be described hereinafter, even the slip control systems of these publications have failed to exhibit a satisfied performance in the slip rotation control.
It is therefore an object of the present invention to provide a slip control system of a torque converter, which is thought out by taking the measures disclosed by the publications into consideration.
According to a first aspect of the present invention, there is provided a slip control system of a torque converter with a lock-up clutch, the slip control system controlling a slip rotation speed between input and output elements of the torque converter by controlling an engaging condition of the lock-up clutch, the slip control system comprises a sensor that detects a speed difference between the input and output elements of the torque converter; a sensor that detects an operation condition of a throttle valve of the engine; a sensor that detects an output torque of the engine; an actuator that controls the engaging condition of the lock-up clutch in accordance with an instruction signal applied thereto; and a controller which is configured to carry out calculating a target slip rotation speed of the torque converter based on a vehicle speed and an open degree of the throttle valve; calculating a running condition of the vehicle based on the operation condition of the throttle valve, the running condition including a drive condition wherein the speed of the input element of the torque converter is higher than that of the output element and a coast condition wherein the speed of the input element is lower than that of the output element; calculating a torque converter characteristic with reference to a speed of the output element of the torque converter and the running condition of the vehicle, the torque converter characteristic being represented by a relation between a converter torque to be transmitted by the torque converter and a slip rotation of the torque converter; calculating a target converter torque based on the torque converter characteristic, the target converter torque being a converter torque provided when the torque converter carries out a slip rotation at the target slip rotation speed; calculating a target lock-up clutch engaging torque based on the target converter torque and the engine torque; and outputting an instruction signal to the actuator to provide the lock-up clutch with the target lock-up clutch engaging torque.
According to a second aspect of the present invention, there is provided a method of controlling a slip control apparatus of a torque converter with a lock-up clutch, the slip control apparatus controlling a slip rotation speed between input and output elements of the torque converter by controlling an engaging condition of the lock-up clutch, the slip control apparatus including a sensor that detects a speed difference between the input and output elements of the torque converter; a sensor that detects an operation condition of a throttle valve of the engine; a sensor that detects an output torque of the engine; and an actuator that controls the engaging condition of the lock-up clutch in accordance with an instruction signal applied thereto. The method comprises calculating a target slip rotation speed of the torque converter based on a vehicle speed and an open degree of the throttle valve; calculating a running condition of the vehicle based on the operation condition of the throttle valve, the running condition including a drive condition wherein the speed of the input element of the torque converter is higher than that of the output element and a coast condition wherein the speed of the input element is lower than that of the output element; calculating a torque converter characteristic with reference to a speed of the output element of the torque converter and the running condition of the vehicle, the torque converter characteristic being represented by a relation between a converter torque to be transmitted by the torque converter and a slip rotation of the torque converter; calculating a target converter torque based on the torque converter characteristic, the target converter torque being a converter torque provided when the torque converter carries out a slip rotation at the target slip rotation speed; calculating a target lock-up clutch engaging torque based on th
Adachi Kazutaka
Segawa Satoshi
Bonck Rodney H.
Nissan Motor Co,. Ltd.
Pang Roger
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