Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Fluid controlled mechanical clutch or brake
Reexamination Certificate
2000-09-18
2002-06-04
Bonck, Rodney H. (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Fluid controlled mechanical clutch or brake
C475S116000, C477S906000
Reexamination Certificate
active
06398684
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control device of an automatic transmission for vehicles.
2. Description of the Prior Art
An example of conventional automatic transmission comprises a main transmission arranged coaxially with a torque converter and having planetary gear mechanisms, and a sub transmission arranged in parallel with the main transmission. The control device of the automatic transmission achieves a plurality of gear positions by engaging and disengaging friction elements such as clutches, brakes and one-way clutches.
In this type of control device, an automatic transmission control unit (hereinafter referred to as an ATCU) determines a gear position suitable for driving conditions, and on-off controls solenoid valves in the control device. The gear positions are changed by supplying and releasing an oil pressure supplied through the solenoid valves to and from friction elements by an oil pressure circuit comprised of shift valves and the like.
In the control device that is constructed in the above-mentioned manner, if there is a problem in the ATCU or the like, it is impossible to control the solenoid valves for determining the gear positions, and therefore, the gear position may be fixed at a specific gear position.
To address this problem, the oil pressure circuit in the conventional control device of the automatic transmission is constructed in such a manner that the gear position shifts to an intermediate gear position or a low speed gear position in order to insure a driving performance after the problem occurs.
In recent years, however, the number of gear positions have been increased so as to control a driving characteristic in a more refined manner in order to reduce energy consumption and the like. An automatic transmission with five gear positions has already been developed, and an automatic transmission with six gear positions is now being studied.
Accordingly, while a vehicle is driven at the high speed gear position such as the sixth speed gear position or the fifth speed gear position, if a problem occurs and the high speed gear position is shifted to an intermediate gear position such as the third speed gear position or a low speed gear position such as the second speed gear position, the abrupt down-shift may cause deterioration of the driving performance.
In order to prevent the gear position from shifting to the intermediate gear position or the low speed gear position, the control device may be constructed in such a manner that the gear position is shifted up to a highest speed gear position irrespective of the present gear position when there occurs a problem, In this case, however, the driving performance may deteriorate if the gear position is abruptly shifted up to the highest gear speed while a vehicle is driven at the low speed gear position.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a control device of an automatic transmission, which prevents the deterioration of driving performance even if there is a problem during driving.
According to the first aspect of the present invention, the control device of the automatic transmission, which comprises a plurality of gear position selecting signal pressure generating means that supplies and releases signal pressure for controlling engagement and disengagement of a plurality of friction elements, and shift control means that controls the gear position selecting signal pressure generating means according to gear positions selected by an automatic shift or a manual shift in order to achieve a plurality of forward driving gear positions by engagement and disengagement of the plurality of friction elements, is characterized in that:
the plurality of forward driving gear positions comprises at least a low speed gear position group composed of multiple forward driving gear positions including a lowest speed gear position and a high speed gear position group composed of multiple forward driving gear positions with higher speeds than the low speed gear position group;
the plurality of gear position selecting signal pressure generating means generates signal pressure to be supplied to friction elements, which are engaged at a predetermined gear position in the low speed gear position group, when the shift control means stops functioning; and
the control device of the automatic transmission comprises:
high speed gear position signal pressure generating means that generates signal pressure to be supplied to friction elements, which are engaged at a predetermined gear position in the high speed gear position group;
low speed gear position failsafe means that supplies the friction elements which are engaged at the predetermined gear position in the low speed gear position group with the signal pressure generated by the gear position selecting signal pressure generating means if the shift control means stops functioning when the shift control means selects a gear position in the low speed gear position group; and
high speed gear position failsafe means that supplies the friction elements which are engaged at the predetermined gear position in the high speed gear position group with the signal pressure generated by the high speed gear position signal pressure generating means if the shift control means stops functioning when the shift control means selects a gear position in the high speed gear position group.
Accordingly, if the shift control means stops functioning while a vehicle is driven at a gear position in a low speed gear position group, the low speed gear position failsafe means supplies the friction elements with the signal pressure outputted from the gear position selecting signal pressure generating means. When the shift control means stops functioning, the gear position selecting signal pressure generating means generates the signal pressure to be supplied to the friction elements that are engaged at a predetermined gear position in the low speed gear position group. Thus, a predetermined gear position in the low speed gear position group is engaged.
If the shift control means stops functioning while the vehicle is driven at a gear position in the high speed gear position group, the high speed gear position failsafe means supplies the friction elements with the signal pressure outputted from the high speed gear position signal pressure generating means. When the shift control means stops functioning, the high speed gear position signal pressure generating means generates the signal pressure to be supplied to the friction elements that are engaged at a predetermined gear position in the high speed gear position group. Thus, a predetermined gear position in the high speed gear position group is engaged.
Therefore, when the shift control means stops functioning, the gear position is fixed at the gear position at which the vehicle has been driven, or is switched to and fixed at a gear position in the same gear position group whether the vehicle is driven at a low speed gear position or a high speed gear position. This prevents the down-shift from the high speed gear position group to the low speed gear position group, or the up-shift from the low speed gear position group to the high speed gear position group, thereby preventing the deterioration of the driving performance.
According to the second aspect of the present invention, the control device of an automatic transmission, which comprises a plurality of gear position selecting signal pressure generating means that supplies and releases signal pressure for controlling engagement and disengagement of a plurality of friction elements, and shift control means that controls the gear position selecting signal pressure generating means according to gear positions selected by an automatic shift or a manual shift in order to achieve a plurality of forward driving gear positions by engagement and disengagement of the plurality of friction elements, is characterized in that:
the plurality of forward driving gear positions comprises at least a low speed gea
Bonck Rodney H.
Jatco Transtechnology Ltd.
Parekh Ankur
Rossi & Associates
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