Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
1997-03-31
2001-04-17
Wright, Dirk (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
C477S107000
Reexamination Certificate
active
06217477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for a continuously variable automatic transmission such as a toroidal type continuously variable automatic transmission and a pulley type continuously variable automatic transmission.
2. Description of Related Art
This kind of automatic transmission control systems controls a rotational speed input to a continuously variable transmission gear mechanism to bring it into agreement with a target rotational speed. Such a continuously variable automatic transmission control system is known from, for example, Japanese Unexamined Patent Publication No. 61-146639.
In gear shift control for the continuously variable automatic transmission which controls the gear ratio so as to bring the engine speed into agreement with a target engine speed determined in accordance with vehicle speed and engine throttle opening, when operating the engine in a zone of low engine speeds and high engine loads to meet a demand for improved fuel efficiency, it is necessary in order to drop the engine speed for the same vehicle speed to perform control to bring the transmission into a high speed transmission ratio (which is equivalent to making the gear ratio lower).
When performing the high speed transmission ratio control, in a state where the automatic transmission is on the side of high speed ratios, the engine operates at a low speed and causes only a small decrease in speed when the engine throttle fully closes in the idle position. For this reason, in the case where a fuel-cut zone is established in order to interrupt fuel delivery to the engine while the engine speed is higher than a specified speed, when the engine throttle fully closes while the automatic transmission is at a high speed ratio, a time for which the engine speed stays in the fuel cut zone is shortened due to a small decrease in engine speed. As a result, it is hard to make the best use of the fuel cut zone, and hence aggravation of fuel efficiency is encountered.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an automatic transmission control system for controlling the gear ratio of an automatic transmission so as to change an engine speed toward a target engine speed established based on vehicle speed and engine throttle position in which an engine speed taken on when the engine throttle fully closes is kept to stay within the fuel cut zone as long as possible.
The above object of the invention is achieved by providing an automatic transmission control system which the target engine speed is increased with the result of causing an increase in gear ratio when the engine throttle opening becomes below a specified level, so that the engine speed remains in the fuel cut zone as long as possible.
The automatic transmission control system which controls a gear ratio of an automatic transmission to bring an engine speed of rotation to a target speed of rotation predetermined according to a vehicle speed and a throttle opening interrupts fuel delivery to the engine when the engine speed is higher than a specified speed while the throttle opening is smaller than a specified opening and increases the target engine speed to increase the gear ratio when the throttle opening is less the specified opening.
With the automatic transmission control system, even when the gear ratio is lowered to lower the engine speed for the purpose of a high transmission ratio, the target engine speed is increased when the engine throttle decrease its opening smaller than a specified opening. Accordingly, while the target engine speed falls afterward, a time for which the engine speed stays in the fuel cut zone is prolonged with an effect of improved fuel efficiency.
When a throttle opening increased above the specified opening after having once been decreased below the specified opening is detected, the gear ratio is controlled according to the increased target engine speed until the target engine speed at detection of the increased throttle opening becomes over the increased target engine speed. That is, when the vehicle is accelerated, the increased target engine speed is employed to control the gear ratio until the target engine speed at the detection of acceleration becomes higher than the increased target engine speed. As a result, it is prevented that the engine speeds falls in spite of an acceleration demand and consequently a feeling of acceleration is improved.
The control system may interrupt the control of gear ratio according to the increased target engine speed when the throttle opening is smaller than the specified opening after a predetermined period for which the throttle opening less than the specified opening is not detected. In other words, before the predetermined period of time passes from an occurrence of no detection of engine throttle opening less than the specified opening, or when the engine throttle opens greatly than the specified opening, the increased target engine speed is employed until it is exceeded by the target engine speed. However, when the predetermined period has passes while the engine throttle opens less than the specified opening, it is regarded that the vehicle is not under acceleration, then, the target engine speed is not increased. In this way, the target engine speed established according to vehicle speed and engine throttle opening is continuously employed with an effect of a smooth decrease in engine speed which improve a feeling of driving during ordinary traveling.
The control system may include a pumping loss control means to change pumping loss of the engine. The pumping loss control means causes a decrease in pumping loss of the engine when the throttle opening is less than the specified opening. Although there is an apprehension that the engine provides too strong braking effect following the fuel cut control when the target engine speed is increased with an effect of staying in the fuel cut zone as long as possible, the utilization of the pumping loss changing means prevents the engine from providing inappropriately strong braking force. The pumping loss changing means may cause a decrease in pumping loss of the engine when the vehicle speed is less than a specified speed while the throttle opening is less than the specified opening.
According to another embodiment of the invention, the control system interrupts fuel delivery to the engine when the engine speed is higher than the specified speed while the throttle opening is less than the specified opening. In this case, the target engine speed is established based on a vehicle speed and a throttle opening when a throttle opening less than the specified opening is detected, or based on a vehicle speed only when a throttle opening greater than the specified opening is detected. The later target engine speed is established so as to cause a raise in engine speed during deceleration. When the throttle opening is less than the specified opening, the target engine speed raises with en effect of increasing the gear ratio. Consequently, even in the case where the gear ratio is decreased to lower the engine speed for high speed transmission ratio, the target engine speed is increased immediately when the throttle opening falls below the specified opening. The gear ratio may be controlled according to the target engine speed established based on a vehicle speed only until target engine speed is exceeded by the target engine speed established based on both vehicle speed and throttle opening when the throttle opening increases above the specified opening after having once decreased below the specified opening, that is, when the vehicle is under acceleration. This prevents a decrease in engine speed occurring in spite of an acceleration demand, and consequently a feeling of acceleration is improved.
The control of gear ratio according to the target engine speed established based on a vehicle speed only is interrupted when the throttle opening is less than the specified opening still after a predetermined period for which no detection of throttle
Nobumoto Hidetoshi
Yoshida Hiromasa
Mazda Motor Corporation
Sixbey, Friedman, Leedom & Ferguson, PC
Studebaker Donald R.
Wright Dirk
LandOfFree
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