Prime-mover dynamo plants – Electric control – Engine control
Reexamination Certificate
1999-06-04
2001-01-30
Enad, Elvin (Department: 2834)
Prime-mover dynamo plants
Electric control
Engine control
C290S04000F, C290S04000F, C290S04000F, C290S04000F, C477S043000, C477S047000
Reexamination Certificate
active
06181020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic driving-torque control system for an automotive vehicle with a continuously variable automatic transmission, often abbreviated to “CVT”, in which a required driving torque to be applied to axle driveshafts or drive wheels is determined as a combination of the engine power output and the transmission ratio of the CVT, and specifically to a system capable of providing the enhanced accuracy of driving-torque control in a low-speed range as well as in mid- and high-speed ranges.
2. Description of the Prior Art
In continuously variable automatic transmissions such as a belt type continuously variable automatic transmission, a toroidal type continuously variable automatic transmission, or the like, a desired transmission ratio of the continuously variable automatic transmission (CVT) is first derived or determined depending on both vehicle speed and engine load, for automatic shifting control. Feedback control is then executed so that an actual transmission ratio is adjusted to the desired transmission ratio. During acceleration where the required engine load increases with the driver's accelerator pedal depression, an automatic downshifting operation is executed, so that the actual transmission ratio is adjusted toward near the lowest speed-change ratio with the desired transmission ratio automatically increasing. During driving at low engine loads with the accelerator pedal released, an automatic upshifting operation is executed, so that the actual transmission ratio is adjusted toward near the highest speed-change ratio with the desired transmission ratio automatically decreasing. Japanese Patent Provisional Publication No. 7-172217 discloses techniques for deriving a required driving torque value (a positive wheel torque value) based on both the vehicle speed and the accelerator-pedal depression amount. In recent years, the driving-torque control is often combined with the automatic shifting control as previously discussed, in order to enhance the accuracy of driving-torque control, accounting for better fuel economy. The integrated driving-torque control, in which the electronic engine power output control is integrated into the automatic shifting control, has been disclosed in Japanese Patent Provisional Publication No. 62-110536.
SUMMARY OF THE INVENTION
In case of the integrated driving-torque control disclosed in the Japanese Patent Provisional Publication No. 62-110536, a required driving torque value is arithmetically calculated on the basis of both the vehicle speed and the accelerator pedal depression amount. For the automatic shifting control, an optimal fuel-consumption (an optimal fuel efficiency) dependent desired transmission ratio is arithmetically calculated on the basis of both the required driving torque value arithmetically calculated and the vehicle speed detected, so as to produce the required driving torque while attaining the lowest possible fuel consumption. On the other hand, for the electronic engine power output control, a desired engine power output value or a desired engine output torque value is arithmetically calculated on the basis of both the required driving torque value and an actual transmission ratio, and then a desired throttle opening is arithmetically calculated on the basis of the desired engine power output value and engine speed. As seen in
FIG. 3
, a rate of change of the required axle-driveshaft driving torque T
o
* with respect to the vehicle speed VSP is usually preset or predetermined to become greater in the low-speed range rather than in the mid- and high-speed ranges, at any accelerator pedal depression amount APS, thus insuring driveability of the vehicle. In presence of errors in detection of the vehicle speed VSP during driving at low speeds, there would be great fluctuations of the required driving torque T
o
* owing to the increased rate of change of required driving torque T
o
* with respect to the vehicle speed VSP in the low speed ranges. The presence of an error in detection of the vehicle speed in the low speed range reduces the accuracy in calculation of the required driving torque T
o
*. Additionally, in the low speed range, a releasable coupling device such as a torque converter is often conditioned in a transient state, thus producing an increased error in calculation or derivation of a desired engine power output value (a desired engine output torque value) from the required driving torque T
o
*. It is desirable to enhance the accuracy of driving-torque control in a low-speed range as well as in mid- and high-speed ranges in automotive vehicles with a continuously variable automatic transmission.
Accordingly, it is an object of the invention to provide a driving-torque control system for automotive vehicles with a continuously variable automatic transmission, which avoids the aforementioned disadvantages of the prior art.
It is another object of the invention to provide a driving-torque control system for an automotive vehicle combined with a continuously variable automatic transmission, which is capable of enhancing the accuracy of driving-torque control even in a low speed range as well as mid- and high-speed ranges.
In order to accomplish the aforementioned and other objects of the present invention, an integrated driving-torque control system for an automotive vehicle with a continuously variable automatic transmission and an electronically-controlled engine whose power output is changeable irrespective of depression of an accelerator pedal, comprises a desired transmission ratio arithmetic-calculation circuitry calculating a required axle-driveshaft driving torque from a depression amount of the accelerator pedal and a vehicle speed, and retrieving a desired transmission ratio on the basis of the required axle-driveshaft driving torque and the vehicle speed, an automatic shifting control section executing automatic shifting control for the continuously variable automatic transmission so that an actual transmission ratio is adjusted to the desired transmission ratio, a first arithmetic-calculation circuitry calculating a first desired engine output torque corresponding to the required axle-driveshaft driving torque, a second arithmetic-calculation circuitry calculating a second desired engine output torque corresponding to the depression amount of the accelerator pedal, a selector selecting the first desired engine output torque as a desired engine output torque when the vehicle speed is equal to or greater than a predetermined vehicle speed threshold, and selecting the second desired engine output torque as the desired engine output torque when the vehicle speed is less than the predetermined vehicle speed threshold, and an engine power output control section executing engine power output control for the electronically-controlled engine in response to the desired engine output torque selected by the selector.
According to another aspect of the invention, an integrated driving-torque control system for an automotive vehicle with a continuously variable automatic transmission and an electronically-controlled engine whose power output is changeable irrespective of depression of an accelerator pedal, comprises means for retrieving a required axle-driveshaft driving torque on the basis of a depression amount of the accelerator pedal and a vehicle speed, from a predetermined required axle-driveshaft driving-torque characteristic map, means for calculating a desired transmission ratio on the basis of the required axle-driveshaft driving torque and the vehicle speed by reference to a predetermined desired transmission ratio characteristic map, automatic shifting control means for executing automatic shifting control for the continuously variable automatic transmission so that an actual transmission ratio is adjusted to the desired transmission ratio, first arithmetic-calculation means for calculating a first desired engine output torque corresponding to the required axle-driveshaft driving torque, second arithm
Katakura Shusaku
Uchida Masaaki
Yasuoka Masayuki
Enad Elvin
Foley & Lardner
Nissan Motor Co,. Ltd.
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