Continuously variable transmissions, synchronous shifting, twin countershafts and methods for control of same
Systems and methods for controlling transmissions having CVTs are disclosed with multiple modes and gearing arrangements for range enhancements, where embodiments include synchronous shifting to allow the transmission to achieve a continuous range of transmission ratios, while minimizing “empty” cycling of the CVT during mode shifts. Embodiments provide for wide ratio range and performance and efficiency flexibility, while maximizing CVT usage through synchronous shifting.
1. A transmission comprising:
a double planetary gearset for receiving rotary power from an input source;
a variator coupled to the double planetary gearset, the variator configured for stepless adjustment of a speed ratio over a range of speed ratios between a first maximum speed ratio and a second maximum speed ratio;
a first countershaft associated with a first gear;
a second countershaft associated with a second gear, wherein each of the first countershaft and the second countershaft is configured to receive power from the variator;
an output shaft configured to receive power from each of the first gear and the second gear; and
a control system comprising:
a first clutch corresponding to the first gear;
a second clutch corresponding to the second gear; and
a controller communicatively coupled to the variator, the first clutch, and the second clutch, wherein the control system is configured to adjust the speed ratio of the variator and selectively engage the first gear or the second gear, wherein in a first mode, the control system is configured to engage the first gear on the first countershaft and adjust the variator from the first maximum speed ratio to the second maximum speed ratio to increase the transmission ratio from a first transmission ratio to a second transmission ratio, wherein in a second mode, the control system is configured to engage the second gear on the second countershaft and adjust the variator from the second maximum speed ratio to the first maximum speed ratio to increase the transmission ratio from the second transmission ratio to a third transmission ratio, wherein changing from the first mode to the second mode comprises disengaging the first clutch from the first gear and engaging the second clutch to the second gear, wherein in the first mode power is transmitted through the double planetary gearset and the variator according to a first power path, wherein in the second mode power is transmitted through the double planetary gearset and the variator according to a second power path, wherein changing from the first mode to the second mode comprises controlling the double planetary gearset, wherein in the first mode power is transmitted from a first set of planetary gears to the variator, wherein in the second mode power is transmitted from a second set of planetary gears to the variator, and wherein changing from the first mode to the second mode comprises changing from the first set of planetary gears to the second set of planetary gears.
2. The transmission of claim 1 , wherein changing from the first mode to the second mode comprises changing a configuration of the variator.
3. The transmission of claim 2 , wherein the variator comprises a ball planetary continuously variable transmission comprising a plurality of traction planets, and wherein the control system is configured to change a tilt angle of the plurality of traction planets to adjust the speed ratio of the variator.
4. The transmission of claim 3 , wherein the variator comprises a first traction ring on a first side of the plurality of traction planets, a second traction ring on a second side of the plurality of traction planets, and a sun located radially inward of the plurality of traction planets, wherein in a first mode power is transferred from the first traction ring through the plurality of traction planets to one of the second traction ring or the traction sun, and wherein in a second mode power is transferred from the second traction ring through the plurality of traction planets to the first traction ring.
5. The transmission of claim 1 , wherein the input source comprises a prime mover, wherein the control system comprises a prime mover controller and a plurality of sensors associated with the prime mover and the transmission, and wherein the control system is further configured to:
receive an input signal associated with a target output power; and
adjust one or more parameters of the prime mover and the transmission to achieve the target output power.
6. The transmission of claim 5 , wherein the control system is further configured to operate according to one of a plurality of control algorithms, wherein in an efficiency control algorithm the prime mover and the transmission are controlled to operate the prime mover based on an efficiency map, and wherein in a power control algorithm the prime mover and the transmission are controlled to operate the prime mover based on a power map.
7. The transmission of claim 6 , wherein operating the control system in the efficiency control algorithm comprises maintaining the prime mover within an operating range for input power efficiency.
8. The transmission of claim 6 , wherein operating the control system in the power control algorithm comprises adjusting the prime mover over a range of power inputs for the target output power.
9. A transmission comprising:
a planetary gearset for receiving rotary power from an input source;
a variator coupled to the planetary gearset, the variator configured for stepless adjustment of a speed ratio over a range of speed ratios between a first maximum speed ratio and a second maximum speed ratio;
a first countershaft associated with a first gear;
a second countershaft associated with a second gear, wherein each of the first countershaft and the second countershaft is configured to receive power from the variator;
an output shaft configured to receive power from each of the first gear and the second gear;
a third gear associated with the first countershaft;
a third clutch corresponding to the third gear;
a fourth gear associated with the second countershaft;
a fourth clutch corresponding to the fourth gear; and
a control system comprising:
a first clutch corresponding to the first gear;
a second clutch corresponding to the second gear; and
a controller communicatively coupled to the variator, the first clutch, and the second clutch, wherein the control system is configured to adjust the speed ratio of the variator and selectively engage the first gear or the second gear, wherein in a first mode, the control system is configured to engage the first gear on the first countershaft and adjust the variator from the first maximum speed ratio to the second maximum speed ratio to increase the transmission ratio from a first transmission ratio to a second transmission ratio, wherein in a second mode, the control system is configured to engage the second gear on the second countershaft and adjust the variator from the second maximum speed ratio to the first maximum speed ratio to increase the transmission ratio from the second transmission ratio to a third transmission ratio, wherein changing from the first mode to the second mode comprises disengaging the first clutch from the first gear and engaging the second clutch to the second gear, wherein in a third mode the control system engages the third gear on the first countershaft and adjusts the variator from the first maximum speed ratio to the second maximum speed ratio to increase the transmission ratio from the third transmission ratio to a fourth transmission ratio, wherein in a fourth mode the control system engages the fourth gear on the second countershaft and adjusts the variator from the second maximum speed ratio to the first maximum speed ratio to increase the transmission ratio from the fourth transmission ratio to a fifth transmission ratio, wherein changing from the second mode to the third mode comprises disengaging the second clutch from the second gear and engaging the third clutch to the third gear, and wherein changing from the third mode to the fourth mode comprises disengaging the third clutch from the third gear and engaging the fourth clutch to the fourth gear.
10. The transmission of claim 9 , further comprising:
an infinitely variable transmission (IVT) clutch;
a IVT gear coupled to the first countershaft;
an output planetary gearset coupled to the output shaft; and
a forward clutch coupled to the output planetary gearset, wherein the control system is further configured to engage the forward clutch for the first mode or the second mode, wherein in an IVT mode the control system is further configured to engage the IVT clutch to the IVT gear and engage the fourth clutch to the fourth gear, and wherein the control system is further configured to adjust the speed ratio of the variator to one of a positive transmission ratio, a negative transmission ratio, and a powered zero transmission ratio.
11. A transmission comprising:
a planetary gearset for receiving rotary power from an input source;
a variator coupled to the planetary gearset, the variator configured for stepless adjustment of a speed ratio over a range of speed ratios between a first maximum speed ratio and a second maximum speed ratio;
a first countershaft associated with a first gear;
a second countershaft associated with a second gear, wherein each of the first countershaft and the second countershaft is configured to receive power from the variator;
an output shaft configured to receive power from each of the first gear and the second gear;
an infinitely variable transmission (IVT) clutch;
a IVT gear coupled to the second countershaft;
an output planetary gearset coupled to the output shaft;
a forward clutch coupled to the output planetary gearset; and
a control system comprising:
a first clutch corresponding to the first gear;
a second clutch corresponding to the second gear; and
a controller communicatively coupled to the variator, the first clutch, and the second clutch, wherein the control system is configured to adjust the speed ratio of the variator and selectively engage the first gear or the second gear, wherein in a first mode the control system is configured to engage the first gear on the first countershaft and adjust the variator from the first maximum speed ratio to the second maximum speed ratio to increase the transmission ratio from a first transmission ratio to a second transmission ratio, wherein in a second mode, the control system is configured to engage the second gear on the second countershaft and adjust the variator from the second maximum speed ratio to the first maximum speed ratio to increase the transmission ratio from the second transmission ratio to a third transmission ratio, wherein changing from the first mode to the second mode comprises disengaging the first clutch from the first gear and engaging the second clutch to the second gear, wherein the control system is further configured to engage the forward clutch for the first mode or the second mode, wherein in an IVT mode the control system is further configured to engage the IVT clutch to the IVT gear and engage the first clutch to the first gear, wherein the control system is further configured to adjust the speed ratio of the variator to one of a positive transmission ratio, a negative transmission ratio, and a powered zero transmission ratio, and wherein the control system is further configured to disengage the IVT clutch from the IVT gear and engage the forward clutch to change from the IVT mode to the first mode.