Continuously variable transmission and control method thereof

1. A continuously variable transmission installed in a vehicle, which shifts an output rotation of a power source and transmits a shifted rotation to drive wheels, comprising:

a variator which is a belt type continuously variable speed change mechanism capable of varying a speed ratio continuously;

a subtransmission mechanism provided in series with the variator and having a first gear position and a second gear position, the second gear position having a smaller speed ratio than the first gear position, as forward gear positions;

a destination through speed ratio setting unit which sets, on a basis of an operating condition of the vehicle, a through speed ratio which is an overall speed ratio of the variator and the subtransmission mechanism to be realized in accordance with the operating condition as a destination through speed ratio;

a shift control unit which controls at least one of the speed ratio of the variator and a gear position of the subtransmission mechanism such that an actual through speed ratio which is an actual value of the through speed ratio becomes the destination through speed ratio;

a coordinated shifting unit which changes the gear position of the subtransmission mechanism and varies the speed ratio of the variator in an opposite direction to a speed ratio variation direction of the subtransmission mechanism when the actual through speed ratio passes a predetermined mode switch line;

a shift response improvement requirement determining unit which determines, on the basis of the operating condition of the vehicle, whether or not an improvement in a shift response of the continuously variable transmission is required; and

a shift speed varying unit which increases a shift speed of the subtransmission mechanism compared with a normal coordinated shift when the improvement in the shift response of the continuously variable transmission is determined to be required and the actual through speed ratio passes the predetermined mode switch line from a Low side to a High side, the normal coordinated shift being a coordinated shift which is performed when the improvement in the shift response of the continuously variable transmission is not determined to be required and the actual through speed ratio passes the predetermined mode switch line.

2. The continuously variable transmission as defined in claim 1 , wherein the shift speed varying unit modifies the destination through speed ratio to the High side and increases the shift speed of the subtransmission mechanism compared with the normal coordinated shift when the improvement in the shift response of the continuously variable transmission is determined to be required and the actual through speed ratio passes the predetermined mode switch line from the Low side to the High side.

3. The continuously variable transmission as defined in claim 1 , wherein the shift response improvement requirement determining unit determines that the improvement in the shift response of the continuously variable transmission is required when an opening of an accelerator pedal of the power source is greater than a predetermined opening.

4. The continuously variable transmission as defined in claim 1 , wherein the shift response improvement requirement determining unit determines that the improvement in the shift response of the continuously variable transmission is required when the vehicle is traveling uphill.

5. The continuously variable transmission as defined in claim 1 , wherein the shift response improvement requirement determining unit determines that the improvement in the shift response of the continuously variable transmission is required when an oil temperature of the continuously variable transmission or a temperature of a frictional engagement element constituting the subtransmission mechanism is higher than a predetermined temperature.

6. A control method for a continuously variable transmission installed in a vehicle so as to shift an output rotation of a power source and transmit a shifted rotation to drive wheels, including a variator which is a belt type continuously variable speed change mechanism capable of varying a speed ratio continuously, and a subtransmission mechanism in series with the variator and having a first gear position and a second gear position, the second gear position having a smaller speed ratio than the first gear position, as forward gear positions, the method comprising:

a destination through speed ratio setting step for setting, on a basis of an operating condition of the vehicle, a through speed ratio which is an overall speed ratio of the variator and the subtransmission mechanism to be realized in accordance with the operating condition as a destination through speed ratio;

a shift control step for controlling at least one of the speed ratio of the variator and a gear position of the subtransmission mechanism such that an actual through speed ratio which is an actual value of the through speed ratio becomes the destination through speed ratio;

a coordinated shifting step for changing the gear position of the subtransmission mechanism and varies the speed ratio of the variator in an opposite direction to a speed ratio variation direction of the subtransmission mechanism when the actual through speed ratio passes a predetermined mode switch line;

a shift response improvement requirement determining step for determining, on the basis of the operating condition of the vehicle, whether or not an improvement in a shift response of the continuously variable transmission is required; and

a shift speed varying step for increasing a shift speed of the subtransmission mechanism compared with a normal coordinated shift when the improvement in the shift response of the continuously variable transmission is determined to be required and the actual through speed ratio passes the predetermined mode switch line from a Low side to a High side, the normal coordinated shift being a coordinated shift which is performed when the improvement in the shift response of the continuously variable transmission is not determined to be required and the actual through speed ratio passes the predetermined mode switch line.

7. The continuously variable transmission as defined in claim 6 , wherein the shift speed varying step modifies the destination through speed ratio to the High side and increases the shift speed of the subtransmission mechanism compared with the normal coordinated shift when the improvement in the shift response of the continuously variable transmission is determined to be required and the actual through speed ratio passes the predetermined mode switch line from the Low side to the High side.

8. The continuously variable transmission as defined in claim 6 , wherein the shift response improvement requirement determining step determines that the improvement in the shift response of the continuously variable transmission is required when an opening of an accelerator pedal of the power source is greater than a predetermined opening.

9. The continuously variable transmission as defined in claim 6 , wherein the shift response improvement requirement determining step determines that the improvement in the shift response of the continuously variable transmission is required when the vehicle is traveling uphill.

10. The continuously variable transmission as defined in claim 6 , wherein the shift response improvement requirement determining step determines that the improvement in the shift response of the continuously variable transmission is required when an oil temperature of the continuously variable transmission or a temperature of a frictional engagement element constituting the subtransmission mechanism is higher than a predetermined temperature.

11. A continuously variable transmission installed in a vehicle, which shifts an output rotation of a power source and transmits a shifted rotation to drive wheels, comprising:

a variator which is a belt type continuously variable speed change mechanism capable of varying a speed ratio continuously;

a subtransmission mechanism in series with the variator and having a first gear position and a second gear position, the second gear position having a smaller speed ratio than the first gear position, as forward gear positions;

destination through speed ratio setting means for setting, on a basis of an operating condition of the vehicle, a through speed ratio which is an overall speed ratio of the variator and the subtransmission mechanism to be realized in accordance with the operating condition as a destination through speed ratio;

shift control means for controlling at least one of the speed ratio of the variator and a gear position of the subtransmission mechanism such that an actual through speed ratio which is an actual value of the through speed ratio becomes the destination through speed ratio;

coordinated shifting means for changing the gear position of the subtransmission mechanism and varies the speed ratio of the variator in an opposite direction to a speed ratio variation direction of the subtransmission mechanism when the actual through speed ratio passes a predetermined mode switch line;

shift response improvement requirement determining means for determining, on the basis of the operating condition of the vehicle, whether or not an improvement in a shift response of the continuously variable transmission is required; and

shift speed varying means for increasing a shift speed of the subtransmission mechanism compared with a normal coordinated shift when the improvement in the shift response of the continuously variable transmission is determined to be required and the actual through speed ratio passes the predetermined mode switch line from a Low side to a High side, the normal coordinated shift being a coordinated shift which is performed when the improvement in the shift response of the continuously variable transmission is not determined to be required and the actual through speed ratio passes the predetermined mode switch line.

12. The continuously variable transmission as defined in claim 11 , wherein the shift speed varying means modifies the destination through speed ratio to the High side and increases the shift speed of the subtransmission mechanism compared with the normal coordinated shift when the improvement in the shift response of the continuously variable transmission is determined to be required and the actual through speed ratio passes the predetermined mode switch line from the Low side to the High side.

13. The continuously variable transmission as defined in claim 11 , wherein the shift response improvement requirement determining means determines that the improvement in the shift response of the continuously variable transmission is required when an opening of an accelerator pedal of the power source is greater than a predetermined opening.

14. The continuously variable transmission as defined in claim 11 , wherein the shift response improvement requirement determining means determines that the improvement in the shift response of the continuously variable transmission is required when the vehicle is traveling uphill.

15. The continuously variable transmission as defined in claim 11 , wherein the shift response improvement requirement determining means determines that the improvement in the shift response of the continuously variable transmission is required when an oil temperature of the continuously variable transmission or a temperature of a frictional engagement element constituting the subtransmission mechanism is higher than a predetermined temperature.