Shift control apparatus and method of continuously variable transmission
A shift control apparatus of a CVT installed in a non-ABS equipped vehicle is arranged to estimate a condition of a transmission ratio of the CVT, to prohibit a shift operation of varying the transmission ratio to a high-speed-side transmission ratio relative to a first predetermined transmission ratio when the driving-wheel acceleration is greater than or equal to a predetermined acceleration, and to cancel the prohibition of the shift operation when the transmission ratio is in a high speed side relative to a second transmission ratio under a condition that the driving-wheel acceleration becomes greater than or equal to the predetermined acceleration.
1. A shift control apparatus of a continuously variable transmission (CVT) which is installed in a vehicle equipped with a brake system except for an antilock brake system, the shift control apparatus comprising:
a controller arranged
(a) to obtain a driving-wheel acceleration,
(b) to estimate a condition of a transmission ratio of the CVT,
(c) when the driving-wheel acceleration is greater than or equal to a predetermined acceleration that is a spin determination acceleration value for determining wheel spin, to prohibit an upshift operation of varying the transmission ratio to a high speed side transmission ratio relative to a first predetermined transmission ratio, and
(d) when the transmission ratio is in a high speed side relative to a second predetermined transmission ratio that is a high-speed-side transmission ratio as compared with the first predetermined transmission ratio, under the condition that the driving-wheel acceleration is greater than or equal to the predetermined acceleration, to cancel the prohibition of the upshift operation.
2. The shift control apparatus as claimed in claim 1 , wherein the second predetermined transmission ratio is 1.0.
3. The shift control apparatus as claimed in claim 1 , wherein the CVT includes a belt-type CVT which comprises a primary pulley, a secondary pulley, a belt wound around the primary and secondary pulleys, and a stepping motor for varying widths of the respective primary and secondary pulleys, the controller being further arranged to estimate the condition of the transmission ratio on a basis of a step position of the stepping motor when the driving-wheel acceleration is greater than or equal to the predetermined acceleration.
4. The shift control apparatus as claimed in claim 1 , wherein the predetermined acceleration is a lower limit of an unachievable large acceleration region for the vehicle.
5. The shift control apparatus as claimed in claim 1 , wherein the first predetermined transmission ratio is a limit transmission ratio by which the vehicle is capable of starting on a travelable road in friction coefficient and gradient.
6. A method of executing a shift control of a continuously variable transmission (CVT) which is installed in a vehicle equipped with a brake system except for an antilock brake system, the shift control apparatus comprising the steps of:
obtaining a driving-wheel acceleration;
estimating a condition of a transmission ratio of the CVT;
prohibiting an upshift operation of varying the transmission ratio to a high speed side transmission ratio relative to a first predetermined transmission ratio when the driving-wheel acceleration is greater than or equal to a predetermined acceleration that is a spin determination acceleration value for determining wheel spin; and
canceling the prohibition of the upshift operation when the transmission ratio is in a high speed side relative to a second predetermined transmission ratio that is a high-speed-side transmission ratio as compared with the first predetermined transmission ratio, under the condition that the driving-wheel acceleration becomes greater than or equal to the predetermined acceleration.
7. The method as claimed in claim 6 , wherein the second predetermined transmission ratio is 1.0.
8. The method as claimed in claim 6 , wherein the CVT includes a belt-type CVT which comprises a primary pulley, a secondary pulley, a belt wound around the primary and secondary pulleys, and a stepping motor for varying widths of the respective primary and secondary pulleys, the controller being further arranged to estimate the transmission ratio on a basis of a step position of the stepping motor when the driving-wheel acceleration is greater than or equal to the predetermined acceleration.
9. The method as claimed in claim 6 , wherein the predetermined acceleration is a lower limit of an unachievable large acceleration region for the vehicle.
10. The method as claimed in claim 6 , wherein the first transmission ratio is a limit transmission ratio by which the vehicle is capable of starting on a travelable road in friction coefficient and gradient.
11. A shift control apparatus of a continuously variable transmission (CVT) which is installed in a vehicle equipped with a brake system except for an antilock brake system, the shift control apparatus comprising:
driving-wheel acceleration obtaining means for obtaining a driving-wheel acceleration;
transmission ratio estimating means for estimating a condition of a transmission ratio of the CVT;
prohibiting means for prohibiting an upshift operation of varying the transmission ratio to a high speed side transmission ratio relative to a first predetermined transmission ratio, when the driving-wheel acceleration is greater than or equal to a predetermined acceleration that is a spin determination acceleration value for determining wheel spin; and
canceling means for canceling the prohibition of the upshift operation when the transmission ratio is in a high speed side relative to a second predetermined transmission ratio that is a high-speed-side transmission ratio as compared with the first predetermined transmission ratio, under the condition that the driving-wheel acceleration is greater than or equal to the predetermined acceleration.