Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2000-07-20
2002-01-15
Marmor, Charles A. (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S048000
Reexamination Certificate
active
06338695
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a vehicular transmission which comprises a transmission capable of varying its speed change ratio and of transmitting the driving force output from the engine to the drive wheels of a vehicle.
BACKGROUND OF THE INVENTION
Such vehicular transmissions have been used for mechanical power transmission in vehicles. As speed change mechanisms incorporated in these transmissions, not only gear transmissions with a plurality of speed ratios but also continuously variable transmissions with a belt, etc. have been used for speed change control. Recently, a hybrid transmission which uses an electrical motor in addition to an engine has been introduced for fuel efficiency. The applicant of the present invention is also developing a hybrid transmission. This hybrid transmission comprises a continuously variable transmission with a metal V-belt which is disposed around the common output shaft of an engine a and an electrical motor arranged in series, and the output shaft of the continuously variable transmission is provided with a forward/reverse switching mechanism and a starting clutch (main clutch).
One purpose for developing this transmission is to improve fuel efficiency. Therefore, there is a consideration that the operation of the engine be controlled such that it stops when the vehicle has stopped (referred to as “idling elimination”). As such idling elimination control, there is a method to stop the engine when the engine comes into idling after the vehicle has stopped completely. However, when the vehicle is decelerated by releasing the accelerator pedal that has been depressed, an engine brake is effected. It is known that, during this deceleration, the fuel injection to the engine is terminated (or the supply of fuel is terminated). In this situation, there is a more desirable way to eliminate engine idling. When the vehicle is decelerated to a halt, the fuel injection is terminated, so this condition should be maintained to stop the engine. This method seems more favorable for improving the fuel efficiency.
When the engine is stopped to avoid engine idling, the transmission is set at a LOW ratio, and the supply of electricity to the electromagnetic valves (solenoid valves) which control the speed change operation may be stopped (or the electrical currents supplied are reduced almost to zero) because there is no need to perform any speed change. While the engine is not operated, preferably, the supply of electricity to such electromagnetic valves be terminated, and the charge in the battery be conserved for the time being. In this way, the charge in the battery can be used more advantageously to power the electrical motor in an effective way. Generally, the electromagnetic valves are disposed between a hydraulic pump which is driven by the engine and hydraulically operated actuators which systematically set the speed change ratio of the transmission. The spool of each of these valves is disposed in a fine balance of biasing forces which are generated by a resilient member such as spring, by the electromagnetism created by a current through the solenoid of the valve and by a back pressure fed back from the control pressure that controls the actuation of an actuator, and they are systematically controlled to change the control pressures which effect the speed change operation of the transmission.
If the operation of the engine is being terminated to avoid idling, and when the rotational speed of the engine decreases below the idling rotational speed of the engine, the output of the hydraulic pump, which is driven by the engine, attenuates. As the pressure of the hydraulic circuit of the transmission decreases, the back pressure acting on each electromagnetic valve also decreases. In this situation, once the pressure of the hydraulic circuit has begun decreasing, even though the electrical current necessary for maintaining the speed change ratio of the transmission at a LOW ratio is provided continuously, the spool of each electromagnetic valve starts to shift in the direction of the force generated the resilient member because the decreasing back pressure creates a change in the above described balance. As the spool comes close to the wall of the housing of the respective valve, it happens to cause a chattering, which is a displeasing vibration and a noise.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control system for a vehicular transmission which system is capable of preventing electromagnetic valves from chattering when the pressure of the hydraulic circuit of the transmission decreases as the operation of the engine is terminated to avoid engine idling.
In order to achieve this objective, the present invention provides a first embodiment of control system for a mechanical power transmission which is used for driving a vehicle. This control system comprises an engine, a speed change mechanism (for example, the continuously variable transmission CVT of the embodiment described in the following section), a hydraulic pump and an electromagnetic valve (for example, the drive-pulley electromagnetic valve
45
and the driven-pulley electromagnetic valve
46
of the following embodiment). The speed change mechanism transmits the driving force of the engine with speed change, and the hydraulic pump is driven by the engine to deliver hydraulic oil. The electromagnetic valve is disposed between a first oil passage (for example, the oil passage
103
a
and the oil passage
103
b
of the following embodiment) and a second oil passage (for example, the oil passage
107
and the oil passage
108
of the following embodiment). In this arrangement, the first oil passage leads to the pump while the second oil passage leads to a speed change actuator (for example, the variable width drive pulley
11
and the variable width driven pulley
16
of the following embodiment) of the speed change mechanism. The electromagnetic valve adjusts the pressure of the oil to control the speed change actuator in a balance of first, second and third biasing forces and delivers this control pressure into the second oil passage. Here, the first biasing force is generated by a resilient member, the second biasing force is generated electromagnetically, and the third biasing force is generated by the back pressure from the second oil passage. In this arrangement, the system according to the present invention controls the vehicular transmission in the following way. After the rotational speed of the engine has become below a reference rotational speed which is lower than an idling rotational speed and after the pressure of the first oil passage begins to decrease, for a predetermined time, the current to the electromagnetic valve is adjusted and supplied to generate the second biasing force in a magnitude that can supplement a decrease in the third biasing force, which decrease is caused from a decrease in the pressure of the first oil passage. Then, after the predetermined time has elapsed, the current supplied to the electromagnetic valve is set almost to zero. The above mentioned predetermined time corresponds, for example, to a time which takes, after the pressure of the first oil passage begins to decrease, for the spool of the electromagnetic valve to be pushed and shifted toward the wall of the housing of the valve by the resilient member as the third biasing force decreases, so as to result in a chattering with the wall.
In this first embodiment of control system according to the present invention, if the rotational speed of the engine decreases below the reference rotational speed, which is lower than the idling rotational speed of the engine, for example, in an engine idling elimination control, and when the pressure of the first oil passage begins to decrease, for the predetermined time, the current to the electromagnetic valve is adjusted and supplied to generate the second biasing force in a magnitude that can supplement the third biasing force which decreases in correspondence with the decreasing press
Aoki Akihira
Fukushima Yukihiko
Armstrong Westerman Hattori McLeland & Naughton LLP
Ho Ha
Honda Giken Kogyo Kabushiki Kaisha
Marmor Charles A.
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