Interrelated power delivery controls – including engine control – Transmission control – Continuously variable friction transmission
Reexamination Certificate
2001-12-19
2003-05-20
Wrigth, Dirk (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Continuously variable friction transmission
Reexamination Certificate
active
06565480
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control apparatus for a drive system, in which a torque transmission element such as a belt type continuously variable transmission or a traction type continuously variable transmission is connected to the output side of a power source activated to output a torque when fed with an energy such as a fuel.
2. Related Art
A continuously variable transmission, as adopted in a vehicle or a variety of power transmission mechanisms, is constructed to change the speed of a mating side, to which a torque is to be transmitted, by changing the radii of torque transmitting portions between rotary members. Specifically, the belt type continuously variable transmission is constructed to change the groove widths of an input side pulley and an output side pulley, on which a belt is made to run, so that the pulley radii at the portions gripping the belt, i.e., effective radii can be continuously changed by reducing the groove width of one pulley while increasing the groove width of the other pulley. Thus, the continuously variable transmission is constructed to change the ratio of the speeds between the input side pulley and the output side pulley, i.e., the gear ratio continuously.
On the other hand, the traction type continuously variable transmission, as also called the toroidal type continuously variable transmission, is constructed by gripping a power roller or a transmission member between a pair of discs having toroidal faces on their confronting faces and by tilting the power roller with respect to the center axis of rotations of the discs so that the gear ratio may be continuously changed by changing the radii of the contact position of the power roller with the input disc through an oil film and the contact position of the power roller with the output disc through an oil film from the center axis of rotations.
For the continuously variable transmission of this kind, therefore, it is necessary to form the portions, at which the torque is transmitted, into continuously smooth faces. Moreover, the transmission of the torque is effected by a frictional force (containing the shearing forces of the oil films) so that the contact pressure between the belt and the individual pulleys or the contact pressure between the discs and the power roller has to be raised according to the torque to be transmitted. Moreover, the torque transmitting faces of the pulleys or the discs are demanded to have a high surface hardness and a facial precision for enhancing a wear resistance to the flake wear or for smoothing the torque transmission.
When the belt is firmly gripped to increase its tension or when the power roller is firmly clamped by the individual discs, on the other hand, the motive power to be consumed for enhancing the gripping power and the clamping power and the power loss to be inevitably caused according to the torque transmission are increased to cause a deterioration in the fuel economy of the vehicle. Generally in the prior art, therefore, the gripping force of the belt or the clamping force of the power roller is controlled as low as possible within such a range as to cause neither slippage between the pulleys and the belt nor slippage between the discs and the power roller. When the continuously variable transmission is employed as a transmission of the vehicle, for example, the oil pressure for establishing the gripping force of the belt or the clamping force of the power roller is controlled on the basis of the load on the power source, as represented by the throttle opening.
There is a correlation between the load on the power source such as the throttle opening and the input torque to the continuously variable transmission connected to the output side of the power source. When the oil pressure is controlled according to the load on the power source, therefore, the torque demanded can be transmitted without causing the slippage in the continuously variable transmission. This is because the so-called “contact pressure” between the rotary members such as the pulleys or the discs and the transmission member such as the belt or the power roller matches the torque to be transmitted. When the torque to be transmitted abruptly rises, therefore, the frictional force to be established between the rotary members and the transmission member and the shearing force of the oil films may become relatively short to cause the slippage between the rotary members and the transmission member.
This slippage is exemplified by an engine stall while the vehicle is running. Specifically, during the running, a torque for keeping the vehicle speed at that time or an accelerating/decelerating torque is input to the continuously variable transmission. If the engine (or the power source) abruptly stops in that state, however, there is established the so-called “engine braking state”, in which the engine is forcibly turned by the running inertial force owned by the vehicle. In this case, the engine has a high inertial force, and a pumping loss is cased by feeding/discharging the air. On the continuously variable transmission disposed in the drive system to the drive wheels or the engine, therefore, there acts a considerably high torque (or a negative torque) than that during the ordinary running.
The oil pressure at that time, i.e., the gripping force (or the clamping force) of the transmission member is the pressure which is set on the basis of the engine load just before the engine stall occurs, so that the torque to be transmitted becomes relatively excessive. As a result, when the engine stall occurs during the running, the transmission torque capacity set in the continuously variable transmission becomes relatively short to cause the slippage between the rotary members and the transmission member. Accordingly, the torque transmission faces of the rotary members such as the pulleys or the discs are worn to cause fatal damages against the continuously variable transmission.
This situation has a tendency to become serious in a hybrid vehicle. Specifically, this hybrid vehicle has a power generator mounted in parallel with an engine, and the electric power may be generated by driving the power generator with the motive power of the engine while the vehicle is run with the output of the engine. When the engine stall occurs in such running state, a braking force (or the negative torque) is established in both the engine and the power generator. This may increase the torque to act on the continuously variable transmission to a higher level.
As a countermeasure for a gas exhaustion in the vehicle, there have been made a variety of proposals. In Japanese Patent Laid-Open No. 2000-60193 (JPA 2000-60193), for example, there is disclosed an apparatus for suppressing the fuel consumption rate by lowering the torque to be employed for the power generation when detected that the fuel became little. The apparatus disclosed has an object to elongate the distance to be traveled with the residual fuel. Therefore, this apparatus can avoid the engine stall in advance but cannot prevent the mechanical damages at the time when the engine stall occurs.
SUMMARY OF THE INVENTION
A main object of the present invention is to prevent or suppress the mechanical damages of a torque transmission element of a continuously variable transmission or the like even when a power source connected to the torque transmission element stops abruptly or suddenly.
In order to achieve this object, the invention is characterized by comprising means for controlling the transmission torque capacity of the torque transmission element to a level matching the so-called “negative torque” at the time when the power source stops, if it is predicted or decided that the power source stops suddenly.
In this invention, therefore, when it is predicted that the power source stops due to the exhaustion of energy, there is increased the transmission torque capacity in the torque transmission element connected to the output side of the power source. Even if the power source stops due
Endo Hiroatsu
Hoshiya Kazumi
Kinugasa Yukio
Ozeki Tatsuya
Toyota Jidosha & Kabushiki Kaisha
Wrigth Dirk
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