Method and apparatus for ratio control for a continuously variable transmission

An apparatus for ratio control of a continuously variable transmission includes a driver commanded ratio unit outputting a signal defining a commanded ratio. A clamp control portion is in communication with the driver commanded ratio unit. The clamp control portion includes: a ratio limits and override ring selecting a ratio matching the commanded ratio from an executable functions having stored ratio code data; a screening monitor continuously receiving output from the executable functions and using an input from a vehicle speed signal to compute minimum and maximum ratio limits for the ratio selected by the ratio limits and override ring; and a ratio control execution ring in communication with the screening monitor. The ratio control execution ring calculates a range of pressures allowed for operation of both primary and secondary pulleys of the continuously variable transmission.

INTRODUCTION

The present disclosure relates to continuously variable transmissions (CVTs) and ratio control systems for a continuously variable transmission.

Continuously variable transmissions (CVTs) change hydraulic pressure on an input pulley set and an output pulley set connected by a belt or chain to change an effective diameter of the pulley sets thereby allowing a continuous variation of a transmission ratio. Ratio control systems are provided using computer control systems including engine control modules (ECM's) and transmission control modules (TCM's) to monitor and change the hydraulic pressure to provide driver commanded torque changes, to incorporate engine data, and to incorporate environmental inputs.

An unintended deceleration (UD) or an unintended acceleration (UA) may be possible if the ratio control system's computer controls receive hazardous (corrupt) inputs from the ECM's algorithm, software, or calibrations, or if the TCM's algorithm, software, or calibrations are themselves corrupted. Corrupted inputs are possible due to environmental conditions such as ultraviolet light, electromagnetic pulses in areas where the vehicle is operating, temperature variations, corrupted calibration data, AEPP (accelerator effective pedal position) input error, ratio selection error, ratio command computation error, possibly resulting in a UD or UA hazard metric violation.

Current CVTs may default to a safe mode wherein power from the prime mover is significantly reduced or a severely limited transmission output if corrupted inputs are received which would cause a UD or UA event or an unintended acceleration. It is undesirable in many situations to default to the shutdown condition if the condition can be attributed primarily to corrupted data.

Thus, while current CVT ratio control systems achieve their intended purpose, there is a need for a new and improved system and method for monitoring and controlling CVT ratio.

SUMMARY

According to several aspects, an apparatus for ratio control of a continuously variable transmission includes a driver commanded ratio unit. The driver commanded ratio unit outputs a signal defining a commanded ratio. A ratio selection and ratio control clamp control portion is in communication with the driver commanded ratio unit. The ratio selection and ratio control clamp control portion includes a ratio limits and override ring selecting a ratio matching the commanded ratio from a ratio limits and override ring executable functions having stored ratio code data. A ratio limits and override ring screening monitor continuously receives output from the ratio limits and override ring executable functions and uses an input from a vehicle speed signal to compute minimum and maximum ratio limits for the ratio selected by the ratio limits and override ring. A ratio control execution ring is in communication with the ratio limits and override ring screening monitor. The ratio control execution ring calculates a range of pressures allowed for operation of both primary and secondary pulleys of the continuously variable transmission.

In another aspect of the present disclosure, the ratio control execution ring includes a ratio control execution ring executable functions having a range of pressures to achieve the commanded ratio from stored data related to multiple different commanded ratios.

In another aspect of the present disclosure, the ratio control execution ring includes a ratio control execution ring screening monitor continuously receiving pressure signal data from the ratio control execution ring executable functions and measuring commanded primary and secondary pulley pressures.

In another aspect of the present disclosure, a vehicle acceleration signal derived from speed sensor information is included, the ratio control execution ring screening monitor applying vehicle acceleration data received from the vehicle speed sensor to identify if commanded pressure delta is leading or lagging a sudden change in vehicle deceleration.

In another aspect of the present disclosure, a transmission solenoid control ring is included. The ratio control execution ring screening monitor forwards a clamping signal to the transmission solenoid control ring to establish commanded pressures to the primary pulley and the secondary pulley.

In another aspect of the present disclosure, the ratio selection and ratio control clamp control portion further includes a variator desired ratio ring directly receiving the commanded ratio from the driver commanded ratio unit and communicating the commanded ratio to the ratio limits and override ring.

In another aspect of the present disclosure, an engine controller is in communication with the desired ratio ring, wherein the desired ratio ring selects which of the commanded ratio or an engine commanded ratio from the engine controller to forward to the ratio limits and override ring.

In another aspect of the present disclosure, the ratio selection and ratio control clamp control portion further includes: a CVT commanded ratio trajectory ring, the commanded ratio trajectory ring generating a commanded CVT ratio meeting the minimum and maximum ratio limits; and a clamping pressure determination ring identifying a minimum pressure or force required for operation of either the primary or the secondary pulley, the minimum pressure communicated to the ratio control execution ring.

In another aspect of the present disclosure, the data saved in the ratio limits and override ring executable functions includes predetermined ratio ranges individually applicable to operational conditions including uphill, downhill, braking, and panic stop.

In another aspect of the present disclosure, the ratio limits and override ring executable functions selects a ratio achieving conditions of the commanded ratio given vehicle operating conditions.

According to several aspects, an apparatus for ratio control of a continuously variable transmission includes a driver commanded ratio unit outputting a signal defining a commanded ratio. A ratio selection and ratio control clamp control portion is in communication with the driver commanded ratio unit. The ratio selection and ratio control clamp control portion includes a ratio limits and override ring selecting a ratio matching the commanded ratio from an ratio limits and override ring executable functions having stored ratio code data. A ratio control execution ring is in communication with the ratio limits and override ring, the ratio control execution ring calculating a range of pressures allowed for operation of both a primary pulley and a secondary pulley of the continuously variable transmission. The ratio control execution ring includes: a ratio control execution ring executable functions having stored data related to multiple different commanded ratios; and a ratio control execution ring screening monitor continuously receiving pressure signal data from the ratio control execution ring executable functions and measuring commanded primary and secondary pulley pressures. The ratio control execution ring screening monitor applies vehicle acceleration data to identify if commanded pressure is leading or lagging a sudden change in vehicle acceleration. The ratio control execution ring monitor also takes into account vehicle speed and current vehicle operating condition.

In another aspect of the present disclosure, a ratio limits and override ring screening monitor continuously receives output from the ratio limits and override ring executable functions.

In another aspect of the present disclosure, a vehicle speed signal is included, the ratio limits and override ring screening monitor using the vehicle speed signal to compute minimum and maximum ratio limits for the ratio selected by the ratio limits and override ring.

In another aspect of the present disclosure, the ratio selection and ratio control clamp control portion further includes a CVT commanded ratio, the commanded ratio trajectory ring generating a CVT commanded ratio meeting the minimum and maximum ratio limits.

In another aspect of the present disclosure, the ratio selection and ratio control clamp control portion further includes a clamping pressure determination ring identifying a minimum pressure or force required for operation of either the primary pulley or the secondary pulley.

In another aspect of the present disclosure, each of the CVT commanded ratio and the minimum pressure is independently communicated to the ratio control execution ring.

In another aspect of the present disclosure, a transmission solenoid control ring is included. The ratio control execution ring screening monitor forwards a clamping signal to the transmission solenoid control ring to establish commanded pressures to the primary pulley and the secondary pulley. A clutch control module is in communication with the transmission solenoid control ring.

According to several aspects, an apparatus for ratio control of a continuously variable transmission includes a driver commanded ratio unit outputting a signal defining a commanded ratio. A ratio selection and ratio control clamp control portion is in communication with the driver commanded ratio unit. The ratio selection and ratio control clamp control portion includes: a ratio limits and override ring selecting a ratio matching the commanded ratio from an ratio limits and override ring executable functions having stored ratio code data; a ratio limits and override ring screening monitor continuously receiving output from the ratio limits and override ring executable functions and using an input from a vehicle speed signal to compute minimum and maximum ratio limits for the ratio selected by the ratio limits and override ring; a ratio control execution ring in communication with the ratio limits and override ring screening monitor, the ratio control execution ring calculating a range of pressures allowed for operation of both primary and secondary pulleys of the continuously variable transmission. The ratio control execution ring includes: a ratio control execution ring executable functions having a range of pressures to achieve the commanded ratio from stored data related to multiple different commanded ratios; and a ratio control execution ring screening monitor continuously receiving pressure signal data from the ratio control execution ring executable functions and measuring commanded primary and secondary pulley pressures, the ratio control execution ring screening monitor applying vehicle acceleration data received to identify if commanded pressure is leading or lagging a sudden change in vehicle deceleration.

In another aspect of the present disclosure, a clutch control monitoring ring is provided external to the ratio selection and ratio control clamp control portion. The clutch control monitoring ring continuously monitors an accelerator pedal, a brake pedal, and pressures of the primary pulley and the secondary pulley pressures.

In another aspect of the present disclosure, the clutch control monitoring ring is in communication with an acceleration-deceleration module containing multiple acceleration-deceleration data rings, the clutch control monitoring ring generating an open-input-clutch signal to open a vehicle input clutch.

DETAILED DESCRIPTION

Referring toFIG. 1, a vehicle power transmitting system10according to one aspect of the present disclosure includes a power source12such as an internal combustion engine or electrical motor. Output from the power source12is transmitted via an input shaft14from the power source12and via a torque converter16, providing a fluid coupling, to a chain or belt-driven continuously variable transmission18, and a reduction gear device20, after which it is distributed to at least one driven wheel22.

The continuously variable transmission18includes a primary or an input side variable pulley24, a secondary or an output side variable pulley26, and a transmission chain or belt, hereinafter belt28. The input side variable pulley24provided on the input shaft14defines an input side member with a variable effective diameter30. The output side variable pulley26, provided on an output shaft32, is an output side member that has a variable diameter34. The belt28serves as a power transmission member that is positioned around and in frictional contact with the variable pulleys24and26such that power is transmitted via frictional force between the belt28and the variable pulleys24and26.

The input side variable pulley24includes a conical faced fixed sheave36, a conical faced movable sheave38, and an input hydraulic chamber40. Similarly, the output side variable pulley26includes a conical faced fixed sheave42, a conical faced movable sheave44, and an output hydraulic chamber46. The fixed sheave36is fixed to the input shaft14and the fixed sheave42is fixed to the output shaft32. The movable sheave38is axially slidable on the input shaft14to move in an axial direction of the input shaft14, while being prevented from rotating around the axis of the input shaft14. Similarly, the movable sheave44is axially slidable on the output shaft32to move in an axial direction of the output shaft32, while being prevented from rotating around the axis of the output shaft32.

The input hydraulic chamber40receives pressurized hydraulic fluid and generates axial thrust by displacing the movable sheave38to vary a V-shaped groove width formed between the fixed sheave36and the movable sheave38. Similarly, the output hydraulic chamber46receives pressurized hydraulic fluid and generates an oppositely directed axial thrust with respect to the movable sheave38by displacing the movable sheave44to vary a V-shaped groove width formed between the fixed sheave42and the movable sheave44. An input shaft14to output shaft32speed ratio can be continuously changed by changing the V-shaped groove widths defined by of each of the movable sheaves38and44. Changing the V-shaped groove widths varies a winding diameter or effective diameter of the belt28around the pulleys, which is done by controlling one or both of the hydraulic pressure in the input hydraulic chamber40of the primary or input side variable pulley24and the hydraulic pressure in the output hydraulic chamber46of the secondary or output side variable pulley26. Sensor input data and actuator output data, and commands for controlling the continuously variable transmission18such as from a driver controlled accelerator pedal47are provided to and by a transmission control module (TCM)48. The TCM48communicates with the accelerator pedal47, a brake pedal49, and the primary and secondary input side variable pulleys24,26.

Referring toFIG. 2and again toFIG. 1, a backbone of the control system defining the TCM48is presented. The TCM48includes a driver commanded ratio unit50having multiple data rings. The driver commanded ratio unit50outputs a signal defining a desired or commanded driver torque or ratio, generated for example by driver displacement of an accelerator pedal, which is communicated to a CVT desired ratio ring52. The desired ratio ring52is included in a ratio selection and ratio control clamp control portion54of the TCM48. The driver commanded ratio unit50also communicates with code rings of an executive shift determination section56including for example a shift point ring58which provide shift decisions to a CVT mode shift control and garage shift control section60which is provided in a clutch control module62. The clutch control module62controls operation of clutches for example to achieve forward or reverse operation, garage shift, torque converter lockup, and the like, and also receives data from a clutch control adapt ring64. The CVT mode shift control and garage shift control section60outputs data to a clutch control output arbitration ring66. Output from the clutch control output arbitration ring66is forwarded to a solenoid command arbitration ring68. The solenoid command arbitration ring68also receives input from a solenoid override ring70which filters solenoid command signals.

The TCM48also includes a transmission commanded pressure72which receives pressure signals from at least one hydraulic pressure sensor74. Output commands from the solenoid command arbitration ring68of the clutch control module62are forwarded to a transmission solenoid control ring76which generates electrical control signals to provide electrical current for operation of the various solenoids which distribute hydraulic pressure to the input hydraulic chamber40and the output hydraulic chamber46. According to several aspects, in addition to or in lieu of utilizing the driver intended torque from the driver commanded ratio unit50, the desired ratio ring52can also receive command input directly from an engine control module78. Ratio input from the engine control module78may be used for example to help improve fuel economy when engine operating conditions can be used to override the driver commanded ratio.

The desired ratio ring52communicates with a ratio limits and override ring80which includes a ratio limits and override ring executable functions82having stored ratio code data. Data saved in the ratio limits and override ring executable functions82can include for example predetermined ratios or ratio ranges applicable to different operational conditions such as uphill, downhill, braking, panic stop, and the like. The ratio limits and override ring executable functions82receives the requested ratio from the desired ratio ring52and selects the most appropriate ratio to achieve the conditions of the requested ratio given vehicle operating conditions. To ensure that the ratio selected by the ratio limits and override ring executable functions82is not based on corrupted data or is outside of an allowable range of conditions for the ratio, a ratio limits and override ring screening monitor84continuously receives the ratio data output from the ratio limits and override ring executable functions82and using an input from a vehicle speed signal85computes minimum and maximum ratio limits86based on a vehicle speed for the commanded or ratio selected by the ratio limits and override ring executable functions82.

The computed minimum and maximum ratio limits86are applied to keep a screened ratio87output from the ratio limits and override ring screening monitor84within a safe range defined as a range which avoids an unintended deceleration or an unintended acceleration. This ensures any upstream data corruption, for example due either to a computation or from a controller area network (CAN) transmission, or the like, does not manifest itself as an engine over-speed condition due for example to a broad ratio step command. The screened ratio87output from the ratio limits and override ring screening monitor84modified as necessary by the computed minimum and maximum ratio limits86is forwarded to a CVT commanded ratio trajectory ring88. The ratio limits and override ring screening monitor84sends the screened ratio87modified by the minimum and maximum ratio limits86as commands to the commanded ratio trajectory ring88to protect against a bad ratio command from being commanded by the commanded ratio trajectory ring88. If either the minimum or maximum limits86are met, the monitor will not let the ratio exceed the limit, and a flag is set indicating the monitor has limited the ratio in the ratio limits and override ring80and the commanded ratio trajectory ring88.

Using the screened ratio87, the commanded ratio trajectory ring88generates a commanded CVT ratio89meeting the minimum and maximum ratio limits86which is communicated to a clamping force ring90. Given the commanded CVT ratio89, the clamping force ring90identifies a lowest or minimum pressure or force required for operation of either of the primary or the secondary pulleys. This minimum pressure signal is communicated to a ratio control execution ring92. The commanded CVT ratio89is also directly communicated to the ratio control execution ring92. Given the minimum pressure necessary for any one of the primary or the secondary pulleys the ratio control execution ring92then calculates a range of pressures allowed for operation of both the primary and the secondary input side variable pulleys24,26.

The ratio control execution ring92includes a ratio control execution ring executable functions94identifies an acceptable range of pressures to achieve each commanded ratio from stored data related to multiple different commanded ratios. The ratio control execution ring executable functions94communicates with a ratio control execution ring screening monitor98. Similar to the ratio limits and override ring screening monitor84, to ensure that the pressure range selected by the ratio control execution ring executable functions94is not based on corrupted data or is outside of an allowable pressure range for the commanded ratio, the ratio control execution ring screening monitor98continuously receives pressure signal data from the ratio control execution ring executable functions94and using vehicle speed data received from an output speed sensor TOSR100plus vehicle acceleration data, the ratio control execution ring screening monitor98measures the commanded primary and secondary pulley pressures and takes into account if commanded pressure is leading or lagging a sudden change in vehicle deceleration. The ratio control execution ring screening monitor98also takes into account vehicle speed and vehicle operating conditions. The ratio control execution ring screening monitor98forwards a clamping signal102to the transmission solenoid control ring76to establish commanded primary and secondary pulley pressures.

The ratio control execution ring screening monitor98can also modify the clamping signal102to clamp commanded primary and secondary pulley pressures as necessary to prevent a hazard. If an unexpected command is generated from the pressures that could lead to an unintended deceleration or unintended acceleration, a hazard condition is present. If a hazard condition is present the ratio control execution ring screening monitor98limits the clamping signal102defining the commanded primary and secondary pulley pressures to a safe level which will not lead to an unintended deceleration or an unintended acceleration.

The ratio limits and override ring80and the ratio control execution ring92of the ratio selection and ratio control clamp control portion54are relied on to set a ratio, and to control clamping pressures to prevent unintended deceleration (UD) or unintended acceleration without requiring default to a safe mode even if the ratio control system's computer controls receive hazardous (corrupt) inputs from the ECM's algorithm, software, or calibrations, or if the TCM48algorithm, software, or calibrations are themselves corrupted.

A clutch control monitoring ring104is provided outside of the ratio selection and ratio control clamp control portion54. Via an input106, the clutch control monitoring ring104continuously monitors the accelerator pedal, the brake pedal, and primary and secondary pulley pressures. An acceleration-deceleration module108containing multiple acceleration-deceleration data rings receives input from throughout the vehicle. The acceleration-deceleration module108generates an acceleration-deceleration signal110forwarded to the clutch control monitoring ring104. If a predetermined vehicle acceleration per unit time or a predetermined vehicle deceleration per unit time outside of the limitations monitored by the ratio selection and ratio control clamp control portion54occurs which indicates an unintended acceleration or deceleration is present, thereby indicating a hazard is present, default to a safe mode may be interdicted. According to several aspects an unintended acceleration may be an acceleration exceeding 0.2 g in a period of 0.2 sec, and an unintended deceleration may be a deceleration exceeding 0.5 g in a time period of 0.5 sec. These values are exemplary and can vary within the scope of the present disclosure.

Accelerator pedal and brake pedal sensors assist in identifying when accelerator pedal or brake pedal actuation indicate a vehicle acceleration or deceleration are intended. A primary or secondary pulley pressure increase occurring together with a rapid vehicle deceleration without operation of the brake pedal may for example indicate an unintended deceleration.

In one example the clutch control monitoring ring104computes a hazard by evaluating a rate of change of transmission output speed occurring together with a large pulley pressure change before or after a large vehicle acceleration or deceleration. If a large acceleration or deceleration is present after a large change in pulley pressure, and with an accelerator or brake pedal input that does not exceed a calibratable input threshold, the clutch control monitoring ring104enables and evaluates if a deceleration hazard has occurred. A pressure diagnostic will also run when the clutch control monitoring ring104is tripped which diagnoses the reason or reasons for the hazard. When a hazard has occurred, an open-input-clutch signal112is generated which opens the vehicle input clutch, disconnecting power flow from the engine.

Referring toFIG. 3and again toFIGS. 1 and 2, a graph114presents exemplary data of ratio monitoring functions116over time118. A first curve120depicts a ratio minimum limit and a second curve122depicts a ratio maximum limit. A commanded ratio124curve presents a region126where the commanded ratio exceeds the second curve122ratio maximum limit when a vehicle speed depicted by a vehicle speed curve128indicates the vehicle is accelerating. A ratio clip Boolean130is applied in the region126to clip or limit the commanded ratio124to the maximum allowed ratio indicated by the second curve122ratio maximum limit.

As previously noted, to ensure that the ratio selected by the ratio limits and override ring executable functions82is not based on corrupted data or is outside of an allowable range of conditions for the ratio, the ratio limits and override ring screening monitor84continuously receives the ratio data output from the ratio limits and override ring executable functions82and using the vehicle speed input from the vehicle speed signal85computes minimum and maximum ratio limits86for the ratio selected by the ratio limits and override ring executable functions82. The computed minimum and maximum ratio limits86are applied as the ratio clip Boolean130to keep the screened ratio87output from the ratio limits and override ring screening monitor84within the safe range defined as a range which avoids an unintended deceleration or an unintended acceleration.

Referring toFIG. 4and again toFIGS. 1 through 3, a graph132presents exemplary data of pressure functions134over time136. A first curve138depicts a pressure of the clamping pulley and a second curve140depicts a pressure of the ratio pulley. A difference or delta limit142for the ratio pressure is predetermined. A deceleration curve144is depicted dropping below a deceleration threshold146during a time period when an increasing pressure delta148exceeds a pressure delta threshold150. At a time of a sharp change152occurs in the pressure delta148, a ratio clip Boolean154is applied to clip the system pressure to avoid an unintended deceleration or an unintended acceleration.

A method and apparatus for ratio control of a continuously variable transmission of the present disclosure offers several advantages. These include providing protection for transmission controls ratio control system from hazardous engine control inputs, including accelerator effective pedal position inputs. Protection is also provided against corrupted transmission controls including ratio selection, ratio command computation, and UD/UA metric violations. A two level algorithm is provided having as a first level calibration and computation corruption protection, and as a second level a fault monitor.