Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Clutch control
Reexamination Certificate
1998-09-30
2001-11-06
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Clutch control
C701S064000, C477S063000, C477S070000, C477S077000, C477S079000, C192S003280, C192S003310
Reexamination Certificate
active
06314357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to lock-up control devices that control lock-up clutches provided in power transmission systems of cars equipped with automatic gears. This application is based on Patent Application No. Hei 9-269060 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
The power transmission system of the car uses both of a torque converter and a lock-up clutch so as to improve power transmission efficiency. The conventional lock-up control device, provided for the power transmission system of the car, is designed to use torque amplification effect of the torque converter (or deceleration effect) by adjusting engagement force of the lock-up clutch in response to situation in revolutions of the engine. In addition, the paper of Japanese Patent Application, Publication No. Hei 9-32915 discloses an example of the lock-up control device, which is designed as follows:
Based on depression of an accelerator pedal, a decision is made as to whether a driver has an intention to accelerate the car or not. If the driver has such an intention to accelerate the car, the lock-up control device releases an engaged state of the lock-up clutch, so that the power transmission system is placed in a power transmission state using the torque converter. Thus, the lock-up control device is capable of using torque amplification effect of the torque converter for acceleration of the car.
The above lock-up control device uses the torque amplification effect of the torque converter according to needs to improve acceleration performance of the car. In addition, the lock-up control device is capable of further improving the acceleration performance by adjusting deceleration ratio (or torque amplification ratio) of the torque converter based on variation ratio of engine load such that the engine can demonstrate the maximum driving force.
In general, it is preferable to obtain good fuel efficiency by employing an efficient way for transmission of the driving force of the engine. In order to do so, it is necessary to maintain the lock-up clutch as tightly as possible, in other words, it is necessary to place the lock-up clutch in an engaged state, so that utilization of the torque amplification effect of the torque converter is made minimal, wherein the torque amplification effect is utilized by releasing the engaging of the lock-up clutch.
In some case, a driver demands the car to make a high degree of acceleration corresponding to a high level of torque, which exceeds an amount of torque that is obtained by using the aforementioned torque amplification effect of the torque converter. In order to obtain such a high level of torque that is demanded by the driver, it is necessary to perform shift-down operation. Herein, acceleration performance of the car is greatly influenced by a manner to perform the shift-down operation. In general, the shift-down operation is performed in response to two stages of decisions, which are adequately made in different procedures. According to a first procedure, the device makes a decision such that the shift-down operation is performed in accordance with a shift map, which shows optimum shift positions on the basis of the relationship between the throttle opening and car velocity. According to a second procedure, a difference is detected between target torque and maximum torque corresponding to the above shift position, so if the engine does not have a room to increase engine torque thereof, the device makes a decision to perform the shift-down operation. Incidentally, the aforementioned two stages of decisions will be referred to as a first decision using the shift map and a second decision based on excessive engine torque, for example. By the way, gear-change boundary lines are drawn on the shift map to indicate events that gear-shift operations are performed. In other words, the shift-down operation is not performed unless the present point on the map representing the present relationship between the throttle opening and car velocity crosses a certain gear-change boundary line. For this reason, if the aforementioned first decision using the shift map is given a great weight, the shift-down operation does not follow up with accelerator pedal operation. As a result, drivability will be deteriorated. In contrast, if the second decision based on the excessive engine torque is given a great weight, the shift-down operation should be performed even in the case of the instantaneous shortage of the engine torque. In addition, the excessive engine torque occurs due to the shift-down operation, so shift-up operation is performed. Thus, the shift-up and shift-down operations are repeated, which is called a shift busy phenomenon.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a lock-up control device which is capable of demonstrating good acceleration performance by using torque amplification effect of the torque converter as maximally as possible and which is capable of providing good fuel efficiency by activating release of the engaging of the lock-up clutch as minimally as possible.
It is another object of the invention to provide a lock-up control device that if shortage of torque is not cleared by utilization of the torque amplification effect of the torque converter, is capable of certainly performing shift-down operation to demonstrate good drivability without causing shift busy phenomenon.
A lock-up control device is provided to control the engaging and release of a lock-up clutch, which is arranged in parallel with a torque converter to transmit driving force of an engine of a car. Herein, target driving force is calculated based on accelerator pedal opening and car velocity. A present shift position is detected using a shift map based on accelerator pedal opening, car velocity and engine speed. Target engine torque is calculated based on the target driving force and present shift position as well as a torque amplification ratio, which is detected when the torque converter is placed in a torque amplification state. A lock-up release instruction is issued under conditions that the torque converter is placed in the torque amplification state while the target engine torque is greater than a preset value, which is determined in advance based on a torque characteristic of the engine. Therefore, it is possible to provide the engine torque as maximally as possible while maintaining the present shift position. Thus, it is possible to obtain good fuel efficiency by limiting control in release of the engaging of the lock-up clutch as minimally as possible.
In addition, under the condition that the engaging of the lock-up clutch is released, the device makes a decision as to whether a shift-down operation is performed or not. Therefore, in the case where the car is short of the engine torque even when the amplification effect of the torque converter is used, the device instructs the car to automatically perform the shift-down operation. Thus, it is possible to demonstrate good drivability.
In the above decision, accumulation is performed on the accelerator pedal opening under the condition that the target engine torque is greater than the preset value. So, a shift-down instruction is issued under the condition that an accumulated value of the accelerator pedal opening exceeds a threshold value in accumulation of the accelerator pedal opening. Using the accumulation of the accelerator pedal opening, it is possible to certainly acknowledge an event that the driver continues his or her intention to accelerate the car. Only when the driver truly has the acceleration intention, the device instructs the car to perform the shift-down operation. Thus, it is possible to certainly avoid occurrence of the shift busy phenomenon.
REFERENCES:
patent: 4526557 (1985-07-01), Tanaka et al.
patent: 4543855 (1985-10-01), Oetting et al.
patent: 4714145 (1987-12-01), Kurihara et al.
patent: 4725951 (1988-02-01), Niikura
patent: 5035308 (1991-07-01), Baba et al.
patent: 50
Kon Takanori
Saito Yoshiharu
Armstrong Westerman Hattori McLeland & Naughton LLP
Broadhead Brian J.
Honda Giken Kogyo Kabushiki Kaisha
Louis-Jacques Jacques H.
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