Continuously variable automatic transmission and transmission system and method for controlling high-torque events

Abstract

Method for controlling a continuously variable transmission (CVT) (140) for a vehicle including a variator arrangement (30) for a motor vehicle, the method comprising: specifying an initial minimum clamping pressure to be applied to the variator arrangement (30) in order to achieve a desired torque capacity; Determining at least one vehicle operating parameter; Determining a vehicle state based on at least one vehicle operating parameter, wherein the vehicle state can be selected from at least one basic state, an elevated state and a high state; Selecting a compensation strategy based on the vehicle state, wherein the compensation strategy can be selected from at least one basic compensation strategy, an enhanced compensation strategy and a high compensation strategy, wherein the basic compensation strategy is selected when the basic state has been determined, wherein the enhanced compensation strategy is selected when the enhanced state has been determined and the high compensation strategy is selected when the high state has been determined; the instruction of an increased clamping pressure to be applied to the variator arrangement (30) when the increased compensation strategy has been selected and a predetermined condition has been met; the instruction of a high clamping pressure to be applied to the variator arrangement (30) when the high compensation strategy has been selected; characterized by the fact that furthermore, the vehicle state can be selected from a severe state and an unreliable road state, and the compensation strategy can further be selected from a severe compensation strategy and a compensation strategy for an unreliable road, wherein the severe compensation strategy is selected when the severe state has been determined, and wherein the compensation strategy for an unreliable road is selected when the unreliable road state has been determined; the procedure further includes: instructing a heavy clamping pressure of the variator and instructing a reduction to a maximum possible engine torque when the heavy compensation strategy has been selected; and instructing the variator arrangement (30) to apply a clamping pressure for an unreliable road when the compensation strategy for an unreliable road has been selected, wherein the step of determining the at least one vehicle operating parameter includes determining the wheel slip magnitude, wherein the method includes determining whether the wheel slip magnitude exceeds an initial wheel slip magnitude threshold for at least one rebound time duration, wherein the method includes selecting one of the enhanced compensation strategy, the unreliable road compensation strategy, the high compensation strategy, and the severe compensation strategy if the wheel slip magnitude exceeds the initial wheel slip magnitude threshold for at least the rebound time duration, wherein the method further includes lowering the initial wheel slip magnitude threshold to a reduced wheel slip threshold when instructed to apply one of the following clamping pressures to the variator arrangement (30): the unreliable road clamping pressure, the enhanced clamping pressure,the high clamping pressure and the heavy clamping pressure, wherein the heavy condition includes wheel slip exceeding a heavy threshold, the heavy threshold being greater than the initial wheel slip size threshold, . wherein the unreliable road condition includes at least one of the following: a predetermined number of irregularities within a roughness threshold timeframe; that the wheel slip magnitude exceeds the initial wheel slip magnitude threshold for longer than a holding timeframe; and a predetermined number of wheel slip detections within a timeframe for an unreliable road, wherein the wheel slip detections are instances where the wheel slip magnitude exceeds the initial wheel slip magnitude threshold and where the clamping pressure for an unreliable road is lower than the increased clamping pressure, and where the clamping pressure for an unreliable road is determined based on at least the following criteria: wheel slip magnitude, vehicle speed, drive torque, accelerator pedal input and vehicle acceleration.

Claims

[1] Method for controlling a continuously variable automatic transmission (CVT) (140) for a vehicle including a variator arrangement (30) for a motor vehicle, the method comprising: commanding an initial minimum clamping pressure to be applied to the variator assembly (30) to achieve a desired torque capacity; determining at least one vehicle operating parameter; determining a vehicle state based on the at least one vehicle operating parameter, wherein the vehicle state is selectable from at least a base state, an elevated state, and a high state; selecting a compensation strategy based on the vehicle condition, wherein the compensation strategy is selectable from at least a base compensation strategy, an enhanced compensation strategy, and a high compensation strategy, wherein the base compensation strategy is selected when the base condition has been determined, the enhanced compensation strategy is selected when the enhanced condition has been determined, and the high compensation strategy is selected when the high condition has been determined; commanding an increased clamping pressure to be applied to the variator assembly (30) when the increased compensation strategy has been selected and a predetermined condition has been met; commanding a high clamping pressure to be applied to the variator assembly (30) when the high compensation strategy has been selected; characterized by , that the vehicle condition is further selectable from a severe condition and an unreliable road condition, and the compensation strategy is further selectable from a severe compensation strategy and an unreliable road compensation strategy, wherein the severe compensation strategy is selected when the severe condition has been determined, and wherein the unreliable road compensation strategy is selected when the unreliable road condition has been determined; the method further comprising: commanding a heavy clamping pressure of the variator and commanding a reduction to a maximum possible engine torque if the heavy compensation strategy has been selected; and instructing the application of an unreliable road clamping pressure to the variator arrangement (30) when the unreliable road compensation strategy has been selected, wherein the step of determining the at least one vehicle operating parameter includes determining the wheel slip magnitude, the method including determining whether the wheel slip magnitude exceeds an initial wheel slip magnitude threshold for at least one rebound period, the method including selecting one of the enhanced compensation strategy, the unreliable road compensation strategy, the high compensation strategy, and the severe compensation strategy if the wheel slip magnitude exceeds the initial wheel slip magnitude threshold for at least the rebound period, the method further including lowering the initial wheel slip magnitude threshold to a lowered wheel slip threshold when the application of one of the following clamping pressures to the variator assembly (30) is commanded: the unreliable road clamping pressure, the enhanced clamping pressure,the high clamping pressure and the severe clamping pressure, wherein the severe condition includes wheel slip exceeding a severe threshold, the severe threshold being greater than the initial wheel slip magnitude threshold, wherein the unreliable road condition includes at least one of the following: a predetermined number of bumps in a bump threshold time frame; the wheel slip magnitude exceeding the initial wheel slip magnitude threshold for longer than a hold time frame; and a predetermined number of wheel slip detections in an unreliable road time frame, the wheel slip detections being cases where the wheel slip magnitude exceeds the initial wheel slip magnitude threshold and where the unreliable road clamping pressure is lower than the increased clamping pressure, and wherein the clamping pressure for an unreliable road is determined based on at least the following criteria: wheel slip magnitude, vehicle speed, drive torque, accelerator pedal input, and vehicle acceleration. [2] The method of claim 1, further comprising commanding the initial minimum clamping pressure to be applied to the variator assembly (30) when the base compensation strategy has been selected. [3] The method of claim 2, further comprising activating a timer when the elevated condition is determined, wherein in the elevated compensation strategy, the predetermined condition for commanding the elevated clamping pressure includes determining that the timer has reached a predetermined threshold. [4] The method of claim 3, wherein the vehicle condition is further selectable from the severe condition and the unreliable road condition, wherein the compensation strategy is further selectable from the severe compensation strategy and the unreliable road compensation strategy, wherein the severe compensation strategy is selected when the severe condition has been determined and the unreliable road compensation strategy is selected when the unreliable road condition has been determined; if the heavy compensation strategy has been selected, commanding the application of a heavy clamping pressure to the variator arrangement (30) and commanding a reduction to a maximum possible engine torque; and if the unreliable road compensation strategy has been selected, instructing the application of an unreliable road clamping pressure to the variator arrangement (30), wherein the step of determining the at least one vehicle operating parameter includes determining at least one of wheel slip magnitude, wheel slip acceleration, transmission output acceleration, longitudinal acceleration, lateral acceleration, and engine speed. [5] Transmission control system (10) for controlling a continuously variable automatic transmission (CVT) (140) having a variator arrangement (30), the transmission control system (10) comprising an instruction set executable for carrying out the method according to claim 1. [6] The transmission control system (10) of claim 5, wherein the transmission control system (10) is configured to command the application of the initial minimum clamping force to the variator assembly (30) when the base compensation strategy has been selected, the transmission control system (10) further comprising a timer, the transmission control system (10) is configured to activate the timer when the elevated condition is determined, wherein in the elevated compensation strategy the transmission control system (10) is configured to command the elevated clamping pressure when the timer has reached a predetermined threshold. [7] Continuously variable automatic transmission (CVT) (140) for a motor vehicle, comprising: a variator assembly (30) having a first pulley (36) and a second pulley (38), the first and second pulleys (36, 38) being rotatably connected by a continuously rotatable device (40), the first pulley (36) being rotatably connected to a drive member (51) and the second pulley (38) being rotatably connected to an output member (61); the first pulley (36) including a first movable sheave (52) that moves along a first axis (48) relative to a first fixed sheave (54) in response to movement of a first actuator (55); the second pulley (38) having a movable sheave (64) that moves along a second axis (46) relative to a fixed sheave (66) in response to movement of a second actuator (65); and a control system (10) having at least one controller (12) and one or more sensors in communication with the controller (12), wherein the control system (10) includes a set of instructions executable to carry out the method according to claim 1.

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