Interrelated power delivery controls – including engine control – Transmission control – With clutch control
Reexamination Certificate
2003-04-16
2004-08-10
Wright, Dirk (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
With clutch control
Reexamination Certificate
active
06773372
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2002-124952 filed on Apr. 25, 2002, including the specification, drawings and abstract are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a vehicle drive control apparatus and, more particularly, to a vehicle drive control executed in a coast state of the vehicle where a throttle valve is fully closed.
2. Description of Related Art
There is a known vehicle drive control apparatus including (a) an engine that generates power through combustion of fuel, (b) a fluid power transmission device having a lock-up clutch for transmitting the power through fluid, (c) a unit for executing a fuel cut control that stops supply of the fuel upon establishment of a fuel cut condition including that a vehicle is in a coast state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than an engine speed at release of the fuel cut operation (hereinafter referred to as F/C release engine speed), and (d) a unit for engaging the lock-up clutch upon establishment of a lock-up clutch engagement condition including that the vehicle is in the coast state. For example, in an apparatus disclosed in JP-A-9-53718, the lock-up clutch is slip engaged in the coast state such that the engine speed is increased and the fuel cut range (vehicle speed range) is expanded, thus improving the fuel efficiency.
In the above-described vehicle drive control apparatus, a reverse input of the driving wheels causes the engine speed to be increased, generating the engine braking force. Upon downshifting in the automatic transmission as decrease in the vehicle speed, an inertia caused by the change in the engine speed considerably varies the engine braking force, which may cause the occupant of the vehicle to feel a certain shock. If the vehicle speed in the coast state at downshifting is reduced as low as possible, the range of the change in the engine speed can be decreased, thus reducing the shock. In the aforementioned case, however, the engine speed may become lower than the F/C release engine speed at rapid deceleration of the vehicle such that the fuel supply is resumed, thus deteriorating the fuel efficiency. As the coast down vehicle speed is set to be relatively higher in order to continue the fuel cut operation (interruption of the fuel supply), the shock resulting from shifting is likely to occur. Reducing the shock by decreasing the shifting speed, however, may lower the engine speed below the F/C release engine speed during shifting.
In the case where the lock-up clutch is not slip controlled for a certain reason (for example, the temperature of the work fluid is low), the engine speed is decreased and thus the fuel cut is not operated. When downshifting is performed at the same speed as that of the aforementioned state, the rotational speed of the input shaft considerably changes to cause the shock owing to the change in the engine speed even if the lock-up clutch is in an OFF state.
In the case where the idling speed of the engine is increased to be higher upon actuation of an accessory such as an air conditioning unit, assuming that the F/C release engine speed is set to a constant value, the engine speed changes at release of the fuel cut operation, resulting in the shock. If the F/C release engine speed is increased to cope with the change in the idling speed, the engine speed may become lower than the F/C release engine speed such that the fuel supply is resumed, deteriorating the fuel efficiency.
Generally the slip control of the lock-up clutch is executed through a feedback control such that the slip amount of the lock-up clutch approaches a predetermined target slip amount. The feedback control is stopped at downshifting operation where the engine speed changes sharply because of low response. The slip control is executed through a feed-forward control (at a constant engagement torque) only. If the engagement torque of the lock-up clutch is set to a lower value, the engine speed is decreased to be lower than the F/C release engine speed. As a result, the fuel supply is resumed, deteriorating the fuel efficiency. On the contrary, if the engagement torque is set to a higher value, the engine braking force changes sharply, the shock is likely to occur. If the feedback control is resumed after completion of shifting in the state there the deviation between the actual and the target slip amounts is large, the slip amount, that is, the engine speed may be changed in accordance with the deviation. The sharp change in the engine braking force, thus, may cause the vehicle occupant to feel the shock.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a technology that prevents generation of a shock owing to the sharp change in the engine braking force at downshifting, or deterioration in the fuel efficiency owing to resumption of the fuel supply caused by the engine speed lower than the F/C release engine speed in a coast state where the fuel cut control and the lock-up clutch engagement control are executed.
According to an embodiment of the invention, a vehicle drive control apparatus includes an engine that generates power through combustion of fuel, an automatic transmission that transmits a reverse input from a driving wheel to the engine and automatically performs a gear shifting among a plurality of forward gear stages each having a different gear ratio, a fluid power transmission device interposed between the automatic transmission and the engine for transmitting power through fluid, the fluid power transmission device having a lock-up clutch, and a controller. The controller executes a fuel cut control for stopping supply of the fuel to the engine upon establishment of a fuel cut condition including that a vehicle is in a coasting state where a throttle valve of the engine is fully closed, and an engine speed is equal to or higher than a predetermined value, executes a control for engaging the lock-up clutch upon establishment of a lock-up clutch engagement condition including that the vehicle is in the coasting state, and executes a control of the automatic transmission for downshifting at a coast down vehicle speed that changes in accordance with a state of the lock-up clutch under the control for engaging the lock-up clutch.
In the aforementioned embodiment, the controller sets the coast down vehicle speed at which the lock-up clutch is engaged to be higher than the coast down vehicle speed at which the lock-up clutch is disengaged.
In the vehicle drive control apparatus, the downshifting is performed by the automatic transmission at a coast down vehicle speed that is set depending on the engagement state of the lock-up clutch. If the coast down vehicle speed at which the lock-up clutch is engaged is set to the value higher than the coast down vehicle speed at which the lock-up clutch is disengaged, downshifting can be performed while continuing the fuel cut operation in the state where the lock-up clutch is engaged. This makes it possible to improve the fuel efficiency. Meanwhile, if there is a high possibility that the fuel cut operation is not executed because of decrease in the engine speed when the lock-up clutch is disengaged, the downshifting is performed at a low vehicle speed. Therefore, the change in the rotational speed of the related portions along with the downshifting performance may be reduced, thus preventing the downshifting shock.
In the embodiment, the controller sets the coast down vehicle speed at which the lock-up clutch is disengaged is higher than the coast down vehicle speed at which the lock-up clutch is engaged.
If the coast down vehicle speed at which the lock-up clutch is disengaged is set to the value higher than the coast down vehicle speed at which the lock-up clutch is engaged, downshifting can be performed while continuing the fuel cut operation in the state where the lock-up clutch is engaged. Even in the state where the lock-up clutch is disengaged, if t
Matsubara Tooru
Noumori Ayato
Tanaka Yoshikazu
Tomomatsu Hideo
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
Wright Dirk
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