Interrelated power delivery controls – including engine control – Transmission control – With brake control
Reexamination Certificate
2001-04-30
2002-09-24
Wright, Dirk (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
With brake control
Reexamination Certificate
active
06454677
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vehicular automatic transmission (including a continuously variable transmission) which is constructed to perform an automatic control for establishing speed change ratios in response to changes in the driving condition while the driver manipulates the shift lever to select drive ranges.
BACKGROUND OF THE INVENTION
A vehicular automatic transmission comprises a speed change mechanism which includes a plurality of mechanical power transmission paths and is connected to an engine through, for example, a torque converter. Selection of or switching to an appropriate power transmission path, i.e., an appropriate speed change ratio, is automatically performed on the basis of, for example, the accelerator opening and the vehicle speed. Generally, a vehicle with an automatic transmission is equipped with a shift lever, which is operated by a driver. When the driver manipulates the shift lever, a range of speed change ratios or a drive range (for example, a reverse drive range, a neutral range, a forward drive range) is selected in response to the manipulation of the shift lever, and the speed change ratio is automatically adjusted or controlled within the selected drive range (usually in a forward drive range).
When a vehicle equipped with such an automatic transmission is stopped while the transmission is set in the forward drive range, a so-called creeping phenomenon occurs because the driving force from the engine which is idling is transmitted to the transmission through the torque converter and then to the wheels. This creeping phenomenon is beneficial for smooth starting under a certain condition, for example, when the vehicle stops and then starts on an upward slope, but not welcome when the vehicle should be kept stationary. At present, to keep the vehicle stationary, the brake must be operated against the creeping force, which is generated by the engine, so this brake operation reduces the mileage allowance or the fuel efficiency of the vehicle.
To solve this problem, a method to improve the fuel efficiency of such an automatic transmission is proposed. In this method, while the vehicle is kept stationary with the brake pedal being stepped or pressed for brake operation and the accelerator being substantially closed, the transmission is set into a neutral condition although the selection of the drive range is kept unchanged (for example, Japanese Laid-Open Patent Publication Nos. H11-193866, H11-230329, etc.).
In such a transmission which is set in a neutral condition while the brake pedal is pressed for keeping the vehicle stationary, the brake operation is monitored by a brake switch which is turned on while the brake pedal is pressed by the driver. More specifically, the brake switch turns on at the beginning of the brake actuation. However, the response of the brake switch is somewhat delayed when the brake pedal is released because a certain distance in the operational stroke of the brake pedal, which distance depends on how deep the pedal is pressed, must be cleared before the brake switch is actually turned off.
This characteristic property of the brake switch presents a following problem. After the vehicle has come into a halt with the brake pedal being pressed while the transmission is set in a drive range, if the brake pedal is released gradually or the brake pedal is released and kept half way in the operational stroke, then there is a possibility that while the brake operation itself terminates, the brake switch is kept being turned on. If this condition occurs, though the transmission itself is in a neutral, the control system detects that the brake is still being actuated. This condition results in a delayed response in the starting control of the vehicle.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control system for a vehicular automatic transmission, which system can establish a neutral condition for the transmission set in a forward drive range while the vehicle is stationary with the brake being operated, and which system thereafter enables the vehicle to start smoothly without any control delay when the brake pedal is released for starting the vehicle.
To realize the above objective, the present invention provides a control system (for example, the control valve CV and the electronic control unit ECU described as a preferred embodiment in the following section) for a vehicular automatic transmission (for example, the automatic transmission TM described in the following section, and also a continuously variable transmission). The control system according to the present invention performs an automatic control for selecting and establishing a speed ratio (speed change gear ratio) in response to the condition of the vehicle set in a drive range, and the control system creates a neutral condition if the vehicle is stationary with the brake of the vehicle being actuated and the accelerator for the engine being turned off (i.e., the accelerator pedal is released to turn off the accelerator, but the engine is kept idling) while the transmission is set in the drive range. This control system further comprises a brake operation detector (for example, the brake switch
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described in the following section), which detects the operational condition of the brake of the vehicle, and an output rotation detector (for example, the output rotation sensor
40
described in the following section), which detects the rotational speed of the output member of the transmission. With this arrangement, the control system terminates the neutral condition and sets a predetermined speed ratio (any of the speed ratios in the drive range) if the rotation of the output member is detected by the output rotation detector, even though the operation of the brake is still detected by the brake operation detector.
According to the present invention, if the operation of the brake is terminated while the transmission is in the neutral condition, then the termination of the actual brake operation is detected accurately by the output rotation detector. For example, when the vehicle is on a bumpy road or on a sloped road, the wheels of the vehicle tend to rotate at least a little. This minute rotation of the wheels can be detected by the output rotation detector, and the control system can control the transmission accordingly and appropriately. In a case where the brake pedal is released gradually or the brake pedal is released and kept half way in the operational stroke (in this case, even though the brake operation detector, i.e., the brake switch, has not detected the release of the brake pedal), the actual termination of the brake operation is detected by the output rotation detector, so the control system immediately shifts the transmission from the neutral condition to a predetermined speed ratio (for example, the LOW speed ratio) in the forward drive range. As a result, there is little delay in the control that terminates the neutral condition and starts the vehicle smoothly.
When the vehicle is on a road which descends forwardly, no control delay is experienced. Therefore, if the control system detects that the vehicle is on a descending road by an inclination sensor (for example, the inclination sensor
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described in the following section), which detects the inclination of the vehicle in the traveling direction, the control system may maintain the neutral condition even though the output rotation detector detects that the output member is rotating, and the control system may terminate the neutral condition when the brake operation detector detects that the brake is released. In this way, the fuel efficiency of the vehicle is improved by keeping the neutral condition a little longer.
On the other hand, when the vehicle is on an ascending road, the control system should expect a delay in the control for starting the vehicle. Therefore, if the control system detects by the inclination sensor that the vehicle is on an ascending road whose inclination is equal to or greater than a predetermined incl
Godai Shirou
Nakauchi Norio
Saito Yoshiharu
Takagi Kazumi
Armstrong Westerman & Hattori, LLP
Honda Giken Kogyo Kabushiki Kaisha
Wright Dirk
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