METHOD FOR CONTROLLING A CONTINUOUSLY VARIABLE TRANSMISSION AND ASSOCIATED TRANSMISSION

Abstract

Method for controlling a continuously variable transmission (CVT) (140), wherein the method comprises the following: a determination of a first rate of change of velocity ratio (321) based on a desired velocity ratio (302) and an instructed velocity ratio (301); a determination of an instructed velocity ratio trajectory (341) based on the first velocity ratio rate of change (321), an actual velocity ratio (303) and an instructed velocity ratio (301); characterized by the fact that the procedure further comprises: a determination of a translation change coefficient (351) and a force ratio factor (352) based on the instructed velocity ratio trajectory (341); a determination of a shifting force (335) based on the transmission change coefficient (351) and an overall speed ratio change rate (325); a control, via a control, a primary pulley force and a secondary pulley force for the CVT (140) based on the shift force (335) and the force ratio factor (352), and a control of a primary pulley pressure and a secondary pulley pressure for the CVT (140) based on the shift force (335), the force ratio factor (352), a minimum pulley clamping force (356), a centrifugal force (355) and a spring force (354) for the CVT (140).

Description

TECHNICAL FIELD

[0001] This disclosure relates to a method for controlling a continuously variable transmission and an associated transmission. BACKGROUND

[0002] Internal combustion engine powertrains coupled with a continuously variable transmission (CVT) can be used to provide traction power in vehicles. A CVT is capable of varying an output / drive speed ratio across a range between a minimum (down) and a maximum (overdrive) ratio, allowing an infinitely variable selection of engine operation that achieves a desired balance of fuel consumption and engine power in response to an output torque demand.

[0003] Common chain-type continuously variable transmissions (CVTs) consist of two pulleys, each with two grooved pulleys. A chain runs between the two pulleys, with the two grooved pulleys surrounding the chain like a sandwich. Through continuous friction roller engagement between the grooved pulleys and the chain ring, the chain is coupled to each pulley to transmit torque from one pulley to the other. One of the pulleys can act as the drive or input pulley, and the other as the driven or output pulley. The gear ratio is the ratio of the torque of the driven pulley to the torque of the drive pulley.The gear ratio can be changed by moving the two pulleys of one of the pulleys closer together and moving the two pulleys of the other pulley further apart, causing the chain ring to ride higher or lower on the respective pulley.

[0004] DE 197 33 677 B4 discloses a device for controlling a continuously variable transmission. DE 197 21 027 A1 teaches a hydraulic emergency control for setting a constant clamping ratio in a continuously variable belt transmission. SUMMARY

[0005] An object underlying the invention is to provide an improved method for controlling a continuously variable transmission and a corresponding continuously variable transmission.

[0006] This problem is solved by the subject matter of the independent claims.

[0007] A powertrain system is described that includes an internal combustion engine rotatably coupled to a variator located within a continuously variable transmission (CVT). A method for controlling the CVT includes determining a first speed ratio change rate based on a desired and a commanded speed ratio, and determining a commanded speed ratio trajectory based on the first speed ratio change rate, an actual speed ratio, and a commanded speed ratio. A gear change coefficient and a force ratio factor are determined based on the commanded speed ratio trajectory. A shift force is determined based on the gear change coefficient and an overall speed ratio change rate.The method is characterized in that the force of the primary and secondary pulleys for the CVT is controlled based on the shift force and the force ratio factor, and that a primary pulley pressure and a secondary pulley pressure for the CVT are controlled based on the shift force, the force ratio factor, a minimum pulley clamping force, a centrifugal force, and a spring force for the CVT.

[0008] The above features and advantages, as well as other features and advantages of the present teachings, will become more apparent from the following detailed description of some of the best modes and other embodiments of the present teachings with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the following, one or more embodiments are described by way of example with reference to the attached drawings, in which: Fig. 1 schematically illustrates elements of a powertrain system including an internal combustion engine rotatably connected to a continuously variable transmission (CVT) via a torque converter and a transmission, according to the disclosure; Fig. 2 schematically illustrates elements of a variator of a chain-type CVT according to the disclosure; and Fig. 3 and Fig. 4 schematically illustrate block diagrams of a gear ratio control routine that may be used to control a variator speed ratio in a CVT, in accordance with the disclosure. DETAILED DESCRIPTION

[0010] Referring to the drawings, wherein the representations are intended to illustrate certain exemplary embodiments and not to limit these purposes, wherein Fig. 1 schematically illustrates elements of a drive system 100 including an internal combustion engine (motor) 110 rotatably connected to a continuously variable transmission (CVT) 140 via a torque converter 120 and a transmission 130. The drive system 100 is connected to a vehicle tire 160 via a drive system 150 to provide traction when used in a vehicle. The operation of the drive system 100 is monitored and controlled by a control system 10 in response to driver commands and other factors.

[0011] The engine 110 may be any suitable internal combustion engine capable of converting hydrocarbon fuel into mechanical power to produce torque in response to control commands for the control system 10. The torque converter 120 is a device that provides fluid communication between its input and output members for transmitting torque, and preferably includes a pump 122 connected to the engine 110, a turbine 124 connected via the output member to the transmission 130, and a torque converter clutch 126 that determines rotation of the pump 122 and the turbine 124 and is controllable by the control system 10. The output member of the torque converter 120 rotatably connects to the transmission 130, which includes meshed gears or other suitable gearing mechanisms that provide downlink between the torque converter 120 and the CVT 140.Alternatively, the transmission 130 may be any other suitable gear configuration for providing meshing between the engine 110, the torque converter 120, and the CVT 140, including, but not limited to, a chain drive configuration or a planetary gear configuration, for example. In alternative embodiments, either both or one of the torque converter 120 and the transmission 130 may be omitted.

[0012] The transmission 130 includes an output member rotatably connected to the CVT 140 via an input member 51. An embodiment of the CVT 140 is described with reference to Fig. 2. An output member 61 of the CVT 140 is rotatably connected to the drive system 150, which is rotatably connected to the vehicle wheels 160 via an axle, halfshaft, or other suitable torque-transmitting member. The drive system 150 may include a differential gear set, a chain-drive gear set, or other suitable gear arrangement for transmitting torque to one or more vehicle wheels 160.

[0013] The powertrain system 100 preferably includes one or more sensor devices for monitoring speeds of various devices, including, for example, an engine speed sensor 112, a torque converter turbine speed sensor 125, a CVT variator input speed sensor 32, a CVT variator output speed sensor 34, and a wheel speed sensor 162. Each of the aforementioned speed sensors may be any suitable position / device for measuring speed, such as a Hall-effect sensor. Each of the aforementioned speed sensors communicates with the control system 10. As used herein, the term 'speed' and similar terms refer to a rotational speed of a rotating element unless expressly stated otherwise.As used herein, the term 'position' and similar terms refer to a rotational or angular position of a rotating element, unless expressly stated otherwise.

[0014] The control system 10 preferably includes one or a plurality of control modules 12 and a user interface 14. A single controller 12 is shown for ease of illustration. The controller 12 may include a plurality of control devices, wherein each of the controllers 12 is dedicated to monitoring and controlling a single system. This may include an engine control module (ECM) for controlling the engine 110 and a transmission control module (TCM) for controlling the CVT 140 and for monitoring and controlling a single subsystem, such as a torque converter clutch. The controller 12 preferably includes a storage device 11 containing executable sets of instructions. The user interface 14 communicates with and monitors user input devices, including, for example, an accelerator pedal 15, a brake pedal 16, and a gear selector in the transmission 17.The user interface 14 determines an operator torque request based on the aforementioned operator inputs. In one embodiment, the gear selector in the transmission 17 includes a tap-up / tap-down function, allowing a driver to manually select a gear ratio, thus overriding the transmission controls. A tap-up command results in a command to the CVT 140 to increase its gear ratio by increasing a speed ratio in the CVT 140. A tap-down command results in a command to the CVT 140 to decrease the gear ratio by decreasing the speed ratio in the CVT 140.

[0015] The terms controller, control module, module, controller, control unit, processor, and the like refer to one or more combinations of application-specific integrated circuits (ASICs), electronic circuit(s), central processing unit(s), such as microprocessor(s), and associated non-transitory memory components in the form of memory and storage devices (read-only memory, programmable read-only memory, random access memory, hard disk, etc.). The non-transitory memory component is capable of storing machine-readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuit(s), input / output circuit(s) and devices, signal conditioning and buffer circuits, and other components accessible by one or more processors to provide described functionality.Input / output circuitry and devices include analog-to-digital converters and related devices that monitor inputs from sensors, where such inputs are monitored at a predetermined sampling frequency or in response to a trigger event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms refer to any set of instructions executable by a controller, such as calibrations and lookup tables. Each controller executes a control routine or routines to provide desired functions, which include monitoring inputs from sensing devices and other networked controllers and executing control and diagnostic instructions to control the operation of actuators. The routines may be executed at regular intervals, such as every 100 microseconds during operation.Alternatively, routines may be executed in response to a trigger event. Communication between controllers and between controllers, actuators, and / or sensors may be accomplished via direct wiring, a networked communications bus connection, a wireless connection, or any other suitable communications link. Communication involves the exchange of data signals in any suitable form, including, for example, electrical signals propagated over a conductive medium, electromagnetic signals over air, optical signals over fiber optic cables, and the like. Data signals may include signals representing inputs from sensors, signals representing actuator commands, and communication signals between controllers.The term "model" refers to processor-based or processor-executable code and associated calibration that simulates the physical existence of a device or physical process. As used herein, the term "dynamic" describes steps or processes that execute in real time and are characterized by monitoring or otherwise determining parameter status and regularly or periodically updating parameter status during the execution of a routine or between iterations of the routine.

[0016] Fig. Figure 2 schematically illustrates elements of one embodiment of a variator 30 of a chain-type continuously variable transmission (CVT) 140, which is advantageously controlled by a controller 12. The variator 30 transmits torque between the first rotating element 51 and the second rotating element 61. The first rotating element 51 is referred to herein as the input member 51, and the second rotating element 61 is referred to herein as the output member 61. In one embodiment, a hydraulic pump 70 fluidly connects to elements of the variator 30 to provide pressurized hydraulic fluid via a hydraulic circuit 71.

[0017] The variator 30 includes a first or primary pulley 36, a second or secondary pulley 38, and a flexible continuous rotatable device 40 rotatably connected to the first and second pulleys 36, 38 for transmitting torque therebetween. The first pulley 36 is rotatably connected to the drive member 51, and the second pulley 38 is rotatably connected to the driven member 61. The rotatable device 40 is adapted to transmit torque between the first and second pulleys 36, 38, and thus between the drive and driven members 51, 61. The first pulley 36 and drive member 51 rotate about a first axis 48, and the second pulley 38 and driven member 61 rotate about a second axis 46. The continuous rotatable device 40 may be a belt, a chain, or other suitable flexible continuous device.The input speed sensor 32 may be mounted near the input member 51 for generating a CVT input speed 33 related to a speed of the first input pulley 36. The output speed sensor 34 may be mounted near the output member 61 for generating a CVT output speed 35 related to a speed of the second output pulley 38. One of the first and second pulleys 36, 38 acts as a ratio-forming pulley to establish a speed ratio, and the other of the first and second pulleys 36, 38 acts as a clamp pulley to generate sufficient clamping force to transmit torque therebetween. As used herein, the term 'speed ratio' refers to a variator speed ratio, which is the ratio of a CVT output speed and a CVT input speed.The CVT input speed may be determined based on the signal input from one of the engine speed sensors 112, the torque converter turbine speed sensor 125, or the input speed sensor 32, as described herein, or another suitable speed / position sensor. The CVT output speed may be determined based on a signal input from the output speed sensor 34 or the wheel speed sensor 162, as described herein, or another suitable speed / position sensor. The speed ratio parameters are determined based on the CVT input speed and the CVT output speed.

[0018] The first pulley 36 is sectioned perpendicular to the first axis 48 to define a first annular groove 50 formed between a movable pulley 52 and a fixed pulley 54. The movable pulley 52 moves or translates along the first axis 48, which is relative to the fixed pulley 54. The movable first pulley 52 may, for example, be connected to a drive member 51 via a spline connection, thereby enabling axial movement of the movable first pulley 52 along the first axis 48. The fixed first pulley 54 is disposed opposite the movable first pulley 52. ​​The fixed first pulley 54 is axially attached to the drive member 51 along the first axis 48. As such, the fixed first pulley 54 does not move in the axial direction of the first axis 48.The movable first pulley 52 and the fixed first pulley 54 each include a first groove surface 56. The first groove surfaces 56 of the movable first pulley 52 and the fixed first pulley 54 are disposed opposite one another to define the annular first groove 50 therebetween. The opposed first groove surfaces 56 preferably form an inverted frustoconical shape such that movement of the movable first pulley 52 toward the fixed first pulley 54 expands an outer pulley diameter of the annular first groove 50. An actuator 55 is arranged such that the first pulley 36 controls an axial position of the movable first pulley 52 in response to a drive signal 53, which includes urging the movable first pulley 52 toward the fixed first pulley 54. In one embodiment, the actuator 55 is a hydraulically controlled device, e.g.a valve that fluidly connects to the hydraulic circuit 71, and the control signal 53 is a hydraulic pressure signal.

[0019] The second pulley 38 is sectioned perpendicular to the second axis 46 to define a second annular groove 62 therebetween. The annular second groove 62 is arranged perpendicular to the second axis 46. The second pulley 38 includes a movable pulley 64 and a fixed pulley 66. The movable pulley 64 moves toward an axis or translates along the second axis 46 that is relative to the fixed pulley 66. The movable second pulley 64 can, for example, be connected to the output member 61 via a spline connection, thereby enabling axial movement of the movable second pulley 64 along the second axis 46. The fixed second pulley 66 is arranged opposite the movable second pulley 64. The fixed second pulley 66 is axially connected to the output member 61 along the second axis 46.As such, the fixed second pulley 66 does not move toward the second axis 46. The movable second pulley 64 and the fixed second pulley 66 each include a second groove surface 68. The second groove surfaces 68 of the movable second pulley 64 and the fixed second pulley 66 are disposed opposite one another to define the annular second groove 62 therebetween. The opposed second groove surfaces 68 preferably form an inverted frustoconical shape such that movement of the movable second pulley 64 toward the fixed second pulley 66 expands a diameter of the outer pulley of the annular second groove 62.An actuator 65 is arranged to control, with the second pulley 38, an axial position of the movable second pulley 64 in response to a drive signal 63, which includes the forced actuation of the movable second pulley 64 toward the stationary second pulley 66. In one embodiment, the actuator 65 is a hydraulically controlled device, e.g., a valve, fluidly connected to the hydraulic circuit 71, and the drive signal 63 is a hydraulic pressure signal. A ratio between the diameter of the outer pulley of the first pulley 36 and the diameter of the outer pulley of the second pulley 38 defines a transmission torque ratio. Other elements, such as coupling assemblies in the form of selectable one-way clutches and the like, may be interposed between the variator 30 and other drivetrain and driveline components and systems.

[0020] Control routines for embodiments of powertrain system 100, including engine 110 and CVT 140, when deployed in a vehicle, may be implemented to provide traction. One purpose of a control routine may be to track commanded operating conditions with zero or minimal steady-state tracking errors and with rapid, smooth response to output torque requests. This includes sensing and controlling system operation, including engine torque control, system capabilities such as transmission hydraulic line pressures, system and component temperatures, sensor measurement capabilities, and other factors.

[0021] Fig. 3 and Fig. 4 schematically illustrate a block diagram of a speed ratio control routine (routine) 300 advantageously used to control a CVT speed ratio in one embodiment of the CVT 140 with reference to the Fig. 1 and Fig. 2 can be used.

[0022] The CVT speed ratio can be controlled by controlling the force applied to the primary pulley 36, e.g., a primary pulley pressure command, and by controlling the force applied to the secondary pulley 38, which is calculated or otherwise determined based on a minimum pulley clamp force, a shift force, and an IDE model as described herein. Speed ​​ratio parameters of routine 300 include a commanded speed ratio 301, a desired speed ratio 302, and an actual speed ratio 303.

[0023] The actual speed ratio 303 indicates an actual measured value for the speed ratio and is determined from a ratio of the measured input and output speeds, e.g., the CVT input speed 33 measured by the input speed sensor 32 and the CVT output speed 35 measured by the output speed sensor 34.

[0024] Desired speed ratio 302 is a preferred speed ratio for operation of the CVT 140 in powertrain system 100, responsive to operator torque requests and balancing or otherwise demonstrating factors related to drivability, fuel economy, emissions, and other operating conditions that may be monitored or estimated and related to an output power command, vehicle speed, and engine torque. Commanded speed ratio 301 is a speed ratio commanded by the controller for implementation during execution of a next iteration of routine 300, or it is an achievable target ratio.As described herein, the controller 12 controls the CVT 140 to achieve the desired speed ratio by controlling pressure from one or both of the primary pulleys 36 and the secondary pulley 38 of the CVT 140. Pressure control of one or both of the primary pulleys 36 and the secondary pulley 38 of the CVT 140 may be achieved by controlling the drive signals and command signals 53, 63 to apply the required pressures to the first and second actuators 55, 65 for the desired speed ratio, wherein the required pressures are preferably in the form of a primary and a secondary pressure command.

[0025] A first portion of routine 300 involves using feedforward and feedback control to determine an overall speed ratio change rate 325 based on the commanded speed ratio 301, the desired speed ratio 302, and the actual speed ratio 303. The feedback control employs a controller 310 that determines the feedback ratio rate 311 based on the difference between the commanded speed ratio 301 and the actual speed ratio 303. The controller 310 may include any suitable control device, including, by way of non-limiting examples, a proportional-integral-derivative (PID) controller, an optimal robust controller, or a model predictive control (MPC) device.The feedforward control uses a feedforward controller 320 that determines a feedforward speed ratio rate 321 based on the difference between the commanded speed ratio 301 and the desired speed ratio 302. The overall speed ratio change rate 325 can be determined by combining the feedback ratio rate 311 and the forward speed ratio rate 321, for example, by calculating an arithmetic sum thereof. The forward speed ratio rate 321 and the commanded speed ratio 301 are evaluated in a trajectory controller 340, which determines a commanded speed ratio trajectory 341 based thereon.

[0026] How best to Fig. 4, the feedforward controller 320 determines the rate of the forward speed ratio 321 based on a desired ratio error 305 and related factors 312. The desired ratio error 305 is a difference between the commanded speed ratio 301 and the desired speed ratio 302. The feedforward controller 320 considers vehicle operating conditions and operator inputs to the accelerator pedal 15, the brake pedal 16, and the transmission gear selector lever 17, including the up / down tip function. The related factors 312 include, by way of non-limiting examples, transmission temperature, input speed, and input torque, with a limit on available power based on the capability of the hydraulic pump and hydraulic system, line pressure, and an existing force of the secondary pulley 38.A first control flag 313 may be used to indicate whether or not the forward speed ratio rate 321 is used.

[0027] If a change in the desired speed ratio 302 is a ramp change, the feedforward controller 320 determines the rate of the forward speed ratio 321 as follows: Rate=(DsrdRatio−CmndRatio)*FeedFwdGain where: DsrdRatio is the desired speed ratio 302, CmndRatio is the commanded speed ratio 301 and FeedFwdGain is a calibratable gain factor.

[0028] If a change in the desired speed ratio 302 is a step change, the feedforward controller 320 determines the speed ratio change rate 321 as follows: Rate=−(Nr*AccelProf) / Ni2 wherein: Ni is the CVT drive speed 33, No is the CVT output speed 35, and

[0029] AccelProf is a commanded acceleration profile for the input member 51 of the CVT 140. In certain embodiments, the first speed ratio change rate 321 is a calibrated value that may be determined based on vehicle speed, input torque, the speed ratio, and a torque capacity ratio.

[0030] Operating conditions in which the desired speed ratio 302 is a step change include a response to an operator up-tap input to the transmission gear selector lever 17, or when an operator releases the accelerator pedal 15 to decelerate the vehicle.

[0031] When the operator's operation of the brake pedal 16 indicates an urgent request to slow the vehicle and stop the vehicle's forward movement, the forward controller 320 determines the rate of the forward speed ratio 321 as follows: Rate=PumpLimitedRdot wherein: PumpLimitedRdot is a maximum achievable time rate of change in the speed ratio, limited only by the fluid pressure capability of the hydraulic pump 70.

[0032] The first control flag 313 indicates whether to employ the forward speed ratio rate 321 based on monitored operating conditions. The feedforward controller 320 may choose not to determine the forward speed ratio rate 321 based on the desired ratio error 305 and the hardware limitations 312 of the variator 140. This may include conditions related to speed measurement uncertainty, such as during low-speed operating conditions when the speed of one of the first and second pulleys 36, 38 is less than a speed at which it can be accurately measured using the speed sensors 32, 34. This may also include conditions when the speed of one of the first and second pulleys 36, 38 is transitioning from the low-speed state to a non-low-speed state.When the first control flag 313 is set, i.e., equal to a logic 1, the forward speed ratio rate 321 is set equal to zero. When the first control flag 313 is reset, i.e., equal to a logic 0, the forward speed ratio rate 321 is set as described herein. Thus, when operating at low pulley speeds or during a transition of pulley speeds from a low-speed state to a non-low-speed state, the forward speed ratio rate 321 can be commanded to zero.

[0033] The trajectory controller 340 determines the commanded speed ratio trajectory 341 based on the forward speed ratio rate 321 and a commanded ratio error 304 determined based on the difference between the commanded speed ratio 301 and the actual speed ratio 303, as well as considering the hardware limitations 312 of the variator 140, e.g., hydraulic line pressure, and drivability concerns. Inputs to the trajectory controller 340 include the transmission temperature 345, the input speed 344, the input torque 343, and the desired speed ratio 302, as well as a second control flag 347 indicating a command to use the desired gear ratio 302 as the commanded speed ratio 301.When the speed ratio change rate is set to zero via command, the commanded speed ratio trajectory 341 remains at the previously commanded value based on the actual speed ratio 303, which was determined at the last calculated value before the pulley speed became low. This state remains active until the desired speed ratio 302 expires within a threshold difference from the measured speed ratio 303 or a timer.

[0034] The commanded speed ratio trajectory 341 is determined by integrating the rate of the forward speed ratio 321 with a variable coefficient determined based on the commanded speed ratio 301 and a speed ratio error equal to the difference between the actual speed ratio 303 and the commanded speed ratio 301.

[0035] The commanded speed ratio trajectory 341 can be limited by hardware to the minimum and maximum speed ratios. The integration can also be reset if the second control flag 347, which indicates a command to use the desired speed ratio 302 as the commanded speed ratio 301, is TRUE. The second control flag 347, which indicates the command to use the desired gear ratio 302 as the commanded speed ratio 301, can be set to TRUE if, during an upshift, the actual speed ratio 303 is greater than the desired speed ratio 302, and the desired speed ratio 302 is greater than the commanded speed ratio 301.The second control flag 347, which indicates the command to use the desired speed ratio 302 as the commanded speed ratio 301, may also be set to TRUE if, during the downshift, the actual speed ratio 303 is less than the desired speed ratio 302, and the desired speed ratio 302 is less than the commanded speed ratio 301. Under such conditions, the commanded speed ratio 301 is reset to the desired speed ratio 302.

[0036] The commanded speed ratio trajectory 341 may be configured as a function of the desired speed ratio, the currently commanded speed ratio, and the currently measured speed ratio. This includes calculating the commanded ratio trajectory, which takes line pressure and vehicle behavior into account. The commanded speed ratio trajectory, as defined herein, accommodates the input or execution of special gear changes, such as the response to incremental upshifts or downshifts. The commanded speed ratio trajectory considers the geometric hardware limits for the minimum and maximum ratio when calculating the trajectory. The commanded speed ratio trajectory may be changed if there is a likelihood of measurement uncertainty.

[0037] The commanded speed ratio trajectory 341 is an input to the ide model 350, which determines a gear ratio change coefficient 351 based on the commanded speed ratio trajectory 341 for an embodiment of the CVT 140, and a force ratio factor (KpKs) 352 for the relationship of primary and secondary pulley force. The ide model 350 includes processor-executable code and an associated calibration that simulates physical relationships associated with the operation of an embodiment of the CVT 140. ide models and their development and implementation are known and therefore will not be described in detail herein. The physical relationships can be reduced to the following executable relationship for a variator ratio derivative ṙ, wherein the variator ratio derivative ṙ corresponds to the commanded speed ratio trajectory 341, i.e.a time rate of change in the commanded speed ratio 301 is indicated. The variator ratio derivative ṙ can be represented as follows and combines a feedback ratio rate and a feedforward ratio rate:. r˙=k(VSR,ωp)∗Fshift

[0038] The switching force F shift can be determined as follows: Fshift=Fprim−KpKs(VSR,TCR)Fsec

[0039] The terms of equations 4 and 5 include the following: F prim is a force associated with the first or primary pulley 36, taking into account associated compressive and centrifugal forces; F sec is a force associated with the second or secondary pulley 38, taking into account associated compressive, centrifugal and spring forces; ω p is the CVT drive speed; k is a gear ratio change coefficient 351; KpKs is the force ratio factor 352; TCR is the torque capacity ratio 342 for the CVT 140 embodiment; and VSR is the desired speed ratio 302.

[0040] Under stationary operating conditions: KpKs=Fprim / Fsec and Fshift=0

[0041] The relationship for the variator ratio derivative ṙ, described with reference to Eqs. 4 and 5, can be developed for an embodiment of the CVT 140 by using empirical data collected and analyzed for a range of speeds, loads, and speed ratio conditions to determine the conditions for the various factors and coefficients. The force ratio factor KpKs 352 represents a ratio F prim and F secthat takes into account hydraulic pressure, centrifugal pressure forces, and spring force, and can be empirically derived using the commanded speed ratio 301 and a torque capacity ratio 342. The force ratio factor KpKs 352 is dependent on an input pulley torque 343, the CVT input speed 33, the CVT output speed 35, the transmission oil temperature 345, the transmission fluid quality, and other factors. The ratio change coefficient k 351 is a calibrated term determined using empirical data associated with the operation of an embodiment of the CVT 140.

[0042] The gear ratio change coefficient k 351 and the total speed ratio change rate 325 are used by the shift force calculation routine 330 to determine a commanded shift force Fshift-cmd 335. The commanded shift force Fshift-cmd 335 is an amount of additional force applied to the first pulley 36 or the second pulley 38 to change the speed ratio in response to a shift command.

[0043] A pulley pressure determination routine 360 ​​uses the commanded shift force Fshift-cmd 335 and the force ratio factor KpKs 352 to determine the primary and secondary pulley pressure commands for controlling the CVT 140, taking into account a minimum pulley clamp force 356, a centrifugal force 355, a spring force 354, and a torque force coefficient 353. The minimum pulley clamp force 356, the centrifugal force 355, the spring force 354, and the torque force coefficient 353 are application-specific parameters that can be determined based on empirical relationships. As such, the primary and secondary pulley pressure commands for controlling the CVT 140 are based on the desired forces (including clamp and feedback correction forces) and the hydraulic characteristics of the transmission under specific operating conditions.

[0044] The pulley pressure determination routine 360 ​​determines the primary pulley pressure command, e.g., the drive signal 53 for the variator 30, described with reference to Fig. 2, and also determines the secondary pulley pressure command, e.g., the control signal 63 for the variator 30, described with reference to Fig. 2, to control the actuators of the CVT 140 to adjust the speed ratio of the CVT 140.

[0045] The flowchart and block diagrams in the flowcharts illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, or portion of code that includes one or more executable instructions for implementing the specified logical function(s). It should also be understood that each block of the block diagrams and / or flowchart representations and combinations of blocks in the block diagrams and / or flowchart representations may be implemented by special-purpose hardware-based systems that perform the specified functions or operations, or combinations of special-purpose hardware and computer instructions.These computer program instructions may also be stored in a computer-readable medium that can direct a computer or other programmable data processing device to function in a particular manner such that the instructions stored in the computer-readable medium produce an article of manufacture, including instruction means for implementing the function or process depicted in the flowchart.

[0046] The detailed description and the drawings or figures support and describe the present teachings, but the scope of the present teachings is defined solely by the claims. While some of the best modes and other embodiments of the present teachings have been described in detail, various alternative designs and embodiments for practicing the present teachings are known in the appended claims.

Claims

[1] A method for controlling a continuously variable transmission (CVT) (140), the method comprising: determining a first speed ratio change rate (321) based on a desired speed ratio (302) and a commanded speed ratio (301); determining a commanded speed ratio trajectory (341) based on the first speed ratio change rate (321), an actual speed ratio (303), and a commanded speed ratio (301); characterized by that the method further comprises: determining a gear change coefficient (351) and a power ratio factor (352) based on the commanded speed ratio trajectory (341); determining a shift force (335) based on the gear ratio change coefficient (351) and an overall speed ratio change rate (325); controlling, via a controller, a primary pulley force and a secondary pulley force for the CVT (140) based on the shift force (335) and the force ratio factor (352), and controlling a primary pulley pressure and a secondary pulley pressure for the CVT (140) based on the shift force (335), the force ratio factor (352), a minimum pulley clamp force (356), a centrifugal force (355), and a spring force (354) for the CVT (140). [2] The method of claim 1, wherein determining the first speed ratio change rate (321) based on the desired speed ratio (302) and the commanded speed ratio (301) comprises determining the first speed ratio change rate (321) based on the difference between the desired speed ratio (302) and the commanded speed ratio (301) multiplied by a feedforward gain factor when a change in the desired speed ratio (302) is a ramp change. [3] The method of claim 1, wherein determining the first speed ratio change rate (321) based on the desired speed ratio (302) and the commanded speed ratio (301) comprises determining the first speed ratio change rate (321) in accordance with: Rate=−(No*AccelProf) / Ni2 wherein: Rate is the first speed ratio change rate (321), Ni is a CVT drive speed (33), No is a CVT output speed (35), and AccelProf is a commanded acceleration profile of a drive member (51) of the CVT (140) when a change in the desired speed ratio (302) is a step change. [4] The method of claim 1, wherein determining the first speed ratio change rate (321) based on the desired speed ratio (302) and the commanded speed ratio (301) comprises determining the first speed ratio change rate (321) as a maximum achievable time rate of change in speed ratio that is limited only by a fluid pressure capability of a hydraulic pump (70) that provides pressurized hydraulic fluid to the CVT (140). [5] The method of claim 1, wherein determining the commanded speed ratio trajectory (341) comprises integrating the first speed ratio change rate (321) employing a variable coefficient based on the difference between the actual speed ratio (303) and the commanded speed ratio (301). [6] The method of claim 1, wherein the overall speed ratio change rate (325) is determined based on the actual speed ratio (303), the desired speed ratio (302), and the commanded speed ratio (301), and comprises: Determining a feedback ratio rate (311) based on the difference between the commanded speed ratio (301) and the actual speed ratio (303); Determining a gear change rate (321) based on the difference between the commanded speed ratio (301) and the desired speed ratio (302); and Combining the feedback ratio rate (311) and the gear ratio change rate (321). [7] The method of claim 1, wherein determining the ratio change coefficient (351) based on the commanded speed ratio trajectory (341) comprises analyzing empirical data to develop a relationship for a variator ratio derivative ṙ according to the following equations: r˙=k(VSR,ωp)∗Fshift Fshift=Fprim−KpKs(VSR,TCR)Fsec wherein: k is the ratio change coefficient (351), VSR is the desired speed ratio (302), F prim is a force associated with a primary pulley (36) of a variator of the VSR, F secis a force assigned to a secondary pulley (38) of the variator of the VSR, F shift the switching force (335) is, ω p the CVT drive speed is KpKs is the force ratio factor (352), and TCR is a torque capacity ratio (342) for the CVT (140); and wherein the variator ratio derivative ṙ corresponds to the commanded speed ratio trajectory (341). [8] The method of claim 1, wherein determining a force ratio factor (352) based on the commanded speed ratio trajectory (341) comprises analyzing empirical data to develop a relationship for a variator ratio derivative ṙ according to the following equation: r˙=k(VSR,ωp)∗[Fprim−kpks(VSR,TCR)Fsec] wherein: VSR is the desired speed ratio (302), F primis a force associated with a primary pulley (36) of a variator of the VSR, F sec is a force assigned to a secondary pulley (38) of the variator of the VSR, ω p the CVT drive speed is, k is the gear ratio change coefficient (351) which is based on a ratio of F prim and F sec , is determined, KpKs is the force ratio factor (352), and TCR is a torque capacity ratio (342) for the CVT (140). [9] Continuously variable transmission (CVT) (140), comprising: a variator (30) having a first pulley (36) and a second pulley (38), the first and second pulleys (36, 38) being rotatably connected by a flexible, 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) comprises a movable pulley (52) that translates along a first axis (48) relative to a fixed pulley (54) in response to urging by a first actuator (55); the second pulley (38) comprises a movable pulley (64) that translates along a second axis (46) relative to a fixed pulley (66) in response to a second actuator (65); a controller configured in communication with a first sensor (32) to monitor a first speed associated with the first pulley (36) and configured in communication with a second sensor (34) to monitor a second speed associated with the second pulley (38), and operatively connected to the first and second actuators (55, 65); wherein the controller contains an instruction set executable to: Determining a first speed ratio change rate (321) based on a desired speed ratio (302) and a commanded speed ratio (301), Determining a commanded speed ratio trajectory (341) based on the first speed ratio change rate (321), an actual speed ratio (303) and the commanded speed ratio (301), characterized bythat the instruction set is further executable to: Determining a gear ratio change coefficient (351) and a force ratio factor (352) based on the commanded speed ratio trajectory (341), Determining a shift force (335) based on the gear ratio change coefficient (351) and an overall speed ratio change rate (325); Controlling a primary pulley pressure and a secondary pulley pressure for the CVT (140) based on the shift force (335), a minimum pulley clamp force (356) and the force ratio factor (352), and a centrifugal force (355) and a spring force (354) for the CVT (140).

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