Method for controlling a continuously variable transmission and associated transmission

Abstract

Method (300) for controlling a continuously variable transmission (CVT) (140), the method comprising: determining an actual speed ratio (303), a desired speed ratio (302), and a commanded speed ratio (301); determining a rate of change (325) of the overall speed ratio based on the actual speed ratio (303), the desired speed ratio (302), and the commanded speed ratio (301); determining a commanded speed ratio path (341) based on the desired speed ratio (302) and the commanded speed ratio (301); determining a coefficient (351) of ratio change and a factor (352) of force ratio (KpKs) based on the commanded speed ratio path (341); and determining a commanded shift force (335) based on the rate of change (325) of the overall speed ratio and the Coefficient (351) of the change in ratio;and controlling a primary pulley force and a secondary pulley force for the CVT (140) based on the commanded shift force (335) and the force ratio factor (352) (KpKs); wherein determining the rate of change (325) of the overall speed ratio, based on the actual speed ratio (303), the desired speed ratio (302) and the commanded speed ratio (301), includes: determining a feedback ratio (311) based on the difference between the commanded speed ratio (301) and the actual speed ratio (303); determining a feed-forward ratio (321) based on the difference between the commanded speed ratio (301) and the desired speed ratio (302); and combining the feedback ratio (311) and the feed-forward ratio (321).;

Description

TECHNICAL FIELDThis disclosure relates to a continuously variable transmission for a vehicle powertrain, and a corresponding method and control routine.BACKGROUNDVehicle engines with an internal combustion engine coupled to a continuously variable or infinite variable transmission (CVT) may be used to provide tractive effort in vehicles. A CVT is capable of varying an input / output speed ratio over a range between a minimum (down) and a maximum (up) ratio to allow an infinitely variable selection of engine operation that achieves a desired balance of fuel consumption and engine performance in response to an output torque request.Known chain type continuously variable transmissions include two pulleys each having two pulleys. A chain runs between the two pulleys, wherein the two pulleys of the pulleys surround the chain in a clamping manner. By frictional engagement between the pulleys of the pulleys and the chain, the chain is connected to each of the pulleys for transmitting torques from one pulley to the other. One of the pulleys may act as a driving pulley and the other as a driven pulley. The gear ratio is the ratio between the torque of the driven pulley and the torque of the drive pulley. The gear ratio can be varied by compressing the two pulleys of one pulley and forcing the two pulleys of the other pulley apart, causing the chain to move higher or lower on the respective pulley.EP 1 499 900 B1 discloses a method for determining a speed of a component and for controlling a continuously variable transmission, in which a drive speed of the continuously variable transmission is calculated using a measured wheel speed and the transmission ratio of the continuously variable transmission in order to avoid possible oscillations in the drive speed, and the control of the continuously variable transmission is carried out either with a feed-forward control or with a feedback control.The object of the invention is to improve the control of a continuously variable transmission.This object is achieved by the subject matters of the independent claims. Advantageous refinements of the invention are described in the subroutines.SUMMARYA powertrain system including an internal combustion engine rotatably connected to a continuously variable transmission (CVT) variator is described herein. A method of controlling the CVT includes determining an actual speed ratio, a desired speed ratio, and a commanded speed ratio. A rate of change of the total speed ratio is determined based on the actual speed ratio, the desired speed ratio, and the commanded speed ratio, and a commanded speed ratio trajectory is determined based on the desired speed ratio and the commanded speed ratio. A ratio change coefficient and a ratio change factor are determined based on the commanded speed ratio trajectory, and a shift force is determined based on the rate of change of the total speed ratio and the ratio change coefficient. A primary pulley force and a secondary pulley force for the CVT are controlled based on the shift force and the factor of the power ratio. Determining the rate of change of the total speed ratio based on the actual speed ratio, the desired speed ratio and the commanded speed ratio thereby comprises determining a feedback transmission ratio rate based on the difference between the commanded speed ratio and the actual speed ratio, determining a feed-forward transmission ratio rate based on the difference between the commanded speed ratio and the desired speed ratio, and combining the feedback transmission ratio rate and the feed-forward transmission ratio rate.The foregoing features and advantages, as well as other features and advantages of the present disclosure, will be apparent from the following detailed description of some of the best modes and other embodiments of the present disclosure with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGSOne or more embodiments will now be described by way of example with reference to the accompanying 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 housing, in accordance with the disclosure; FIG. 2 schematically illustrates elements of a variator of a chain-type CVT, in accordance with the disclosure; and FIG. 3 schematically illustrates a block diagram of a speed ratio control program that may be used to control a speed ratio of a variator in a CVT, in accordance with the disclosure.DETAILED DESCRIPTIONReferring to the drawings, wherein the illustrations are intended to illustrate certain exemplary embodiments and not limit the same purposes, FIG. 1 schematically illustrates elements of a powertrain system 100 including an internal combustion engine (engine) 110 rotatably connected to a continuously variable transmission (CVT) 140 via a torque converter 120 and a transmission housing 130. The powertrain system 100 is connected via a propulsion system 150 to a vehicle tire 160 for providing tractive force when applied in a vehicle. Operation of the powertrain system 100 is monitored and controlled by a control system 10 in response to driver commands and other factors.Engine 110 may be any suitable internal combustion engine capable of converting hydrocarbon fuel into mechanical energy for generating torque in response to the control commands from control system 10. Torque converter 120 is a device that provides a fluid clutch between its input and output members for transferring torque, and preferably includes a pump 122 connected to engine 110, a turbine 124 connected via the output member to transmission housing 130, and a torque converter clutch 126 that detects the rotation of pump 122 and turbine 124, which is controllable by control system 10. The output member of the torque converter 120 is rotatably coupled to the transmission housing 130, which includes toothed gears or other suitable transmission mechanisms that provide for down-gearing between the torque converter 120 and the CVT 140. Alternatively, the transmission housing 130 may be another suitable transmission configuration for providing gearing between the engine 110, the torque converter 120, and the CVT 140, including, but not limited to, for example, a chain drive transmission configuration or a planetary gear configuration. In alternative embodiments, either or both of the torque converter 120 and the transmission housing 130 may be omitted.The transmission housing 130 includes an output member rotatably connected to the CVT 140 via an input member 51. An embodiment of the CVT 140 will be 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, half shaft, or other suitable torque transmitting member. The propulsion system 150 may include a differential gear set, a chain-drive gear set, or other suitable arrangement of transmissions for transmitting torque with one or more vehicle wheels 160.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 turbine speed sensor of the torque converter 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 rotational position / speed measurement device, such as a Hall-effect sensor. Each of the speed sensors mentioned communicates with the control system 10. As used herein, the term "position" and similar terms refer to a rotational or angular position of a rotating element, unless expressly stated otherwise.The control system 10 preferably includes one or more controllers 12 and a user interface 14. The controller 12 may include a plurality of control devices, wherein each controller 12 is related to monitoring and controlling a single system. This may include an engine control unit (ECM) to control the engine 110 and a transmission control unit (TCM) to control the CVT 140 and to monitor and control a single subsystem, such as a torque converter clutch. The controller 12 preferably includes a storage device 11 containing executable instruction sets. The user interface 14 communicates with and monitors operator input devices including, for example, an accelerator pedal 15, a brake pedal 16, and a transmission gear selector 17. the user interface 14 determines an operator torque request based on the mentioned operator inputs. In one embodiment, the transmission gear selector 17 includes an up-tap / down-tap function whereby a driver can manually select a transmission ratio and thus disable transmission control. A high tap command results in a command to the CVT 140 to increase its gear ratio achieved by increasing a speed ratio in the CVT 140. A down-tap command results in a command to the CVT 140 to reduce the transmission ratio by reducing the speed ratio in the CVT 140.The terms controller, control module, module, controller, processor, and the like refer to one or more combinations of an application specific integrated circuit(s) (ASIC), electronic circuit(s), central processing unit(s) such as microprocessor(s), and non-transitory memory components connected thereto in the form of memories and memory devices (read only memory, programmable read only memory, random access memory, hard disk drive, 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 that can be accessed by one or more processors to provide described functionality. (Input / output circuit(s) and devices include analog / digital converters and related devices that monitor inputs from sensors, such inputs being monitored at a predetermined sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control programs, code, algorithms, and similar terms refer to any controller-executable instruction sets such as calibrations and look-up tables. Each controller executes a program or programs to provide the desired functions, including monitoring inputs from sensing devices and other networked controllers and executing control and diagnostic instructions to control operation of actuators. The programs may be executed at regular intervals, such as during running operation every 100 microseconds. Alternatively, programs may be executed in response to a trigger operation. Communication may be accomplished between the controllers and between controllers, actuators, and / or sensors via direct cabling, a networked communication bus connection, a wireless connection, or any other suitable network communication line connection. Communication involves the exchange of data signals in any suitable form including, for example, electrical signals passed over a conductive medium, electromagnetic signals over the air, optical signals over optical fibers, and the like. Data signals may include signals representing inputs from sensors, signals representing commands from actuators, 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 process. As used herein, the term "dynamic" describes steps or processes that are executed in real-time and are characterized by monitoring or otherwise determining parameter states and periodically or periodically updating parameter states when executing a program or between iterations when executing the program.FIG. 2 schematically illustrates elements of a variator 30 of a chain-type continuously variable transmission (CVT) 140 that is advantageously controlled by a controller 12.The variator 30 transfers torque between the first rotary element 51 and the second rotary element 61, the first rotary element 51 is hereinafter referred to as the input member 51, and the second rotary element 61 is hereinafter referred to as the output member 61.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 to transmit torque therebetween. The first pulley 36 is rotatably mounted on the input member 51 and the second pulley 38 is rotatably mounted on the output member 61, and the rotatable device 40 is adapted to transfer torque between the first and second pulleys 36, 38 and thus between the input and output members 51, 61. The first pulley 36 and the input member 51 rotate about a first axis 48, and the second pulley 38 and the output member 61 rotate about a second axis 46. The input speed sensor 32 may be mounted near the input member 51 for generating a CVT input speed 33 that is related to a speed of the first input pulley 36, and the output speed sensor 34 may be mounted near the output member 61 for generating a CVT output speed 35 that is 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 clamping pulley to generate sufficient clamping force to transfer torque therebetween. As used herein, the term "speed ratio" refers to a variator speed ratio that is a ratio between a CVT output speed and a CVT input speed. The CVT input speed may be determined based on the signal input from the engine speed sensor 112 or the turbine speed sensor of the torque converter 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.The first pulley 36 is divided perpendicular to the first axis of rotation 48 to define a first annular groove 50 formed between a movable disc 52 and a stationary disc 54. The movable sheave 52 moves or is displaced along the first axis 48 relative to the stationary sheave 54. For example, the first movable plate 52 may be splined to the drive member 51 thereby permitting axial movement of the first movable plate 52 along the first axis 48. The first fixed plate 54 is disposed opposite to the first movable plate 52. The first stationary plate 54 is connected in the axial direction to the drive element 51 along the first axis 48. As such, the first stationary plate 54 does not move in the axial direction on the first axis 48. the first movable plate 52 and the first stationary plate 54 each include a first groove surface 56. the first groove surfaces 56 of the first movable plate 52 and the first stationary plate 54 are oppositely disposed to define the first annular groove 50 therebetween. The opposing first groove surfaces 56 preferably form an inverted frustoconical shape such that movement of the first movable disc 52 toward the first stationary disc 54 increases an outer pulley diameter of the first annular groove 50. An actuator 55 is disposed together with the first pulley 36 to control an axial position of the first movable disc 52 in response to a control signal 53, including urging the first movable disc 52 toward the first fixed disc 54. In one embodiment, the actuator 55 is a hydraulically controlled device and the control signal 53 is a hydraulic pressure signal.The second pulley 38 is split perpendicular to the second axis 46 to define a second annular groove 62 therebetween. The second annular groove 62 is disposed perpendicular to the second axis 46. The second pulley 38 includes a movable disc 64 and a stationary disc 66. the movable disc 64 moves in the axial direction or is displaced along the second axis 46 relative to the stationary disc 66. For example, the second movable plate 64 may be splined to the output member 61 thereby permitting axial movement of the second movable plate 64 along the second axis 46. The second fixed plate 66 is disposed opposite to the second movable plate 64. The second stationary plate 66 is axially fixed to the output member 61 along the second axis 46. As such, the second stationary plate 66 does not move in the direction of the second axis 46. the second movable plate 64 and the second stationary plate 66 each include a second groove surface 68. the second groove surfaces 68 of the second movable plate 64 and the second stationary plate 66 are oppositely disposed and the second annular groove 62 is interposed therebetween. the second opposing groove surfaces 68 preferably form an inverted frustoconical shape such that movement of the second movable plate 64 toward the second stationary plate 66 increases an outer pulley diameter of the second annular groove 62. An actuator 65 is arranged to control, with the second pulley 38, an axial direction position of the second movable disc 64 in response to a control signal 63 including pressing the second movable disc 64 toward the second fixed disc 66. In one embodiment, the actuator 65 is a hydraulically controlled device and the control signal 63 is a hydraulic pressure signal. A ratio between the outer diameter of the first pulley 36 and the outer diameter of the second pulley 38 defines a transmission torque ratio. Other elements, such as clutch assemblies in the form of selectable one-way clutches and the like, may be employed between the variator 30 and other components and systems of the powertrain and drive system.FIG. 3 schematically shows a block diagram of a program for controlling a speed ratio (program) 300 that may be advantageously used for controlling a speed ratio of the CVT, including an embodiment of the CVT 140 with reference to FIGS. 1 and 2. In certain embodiments, the primary plate force and the secondary plate force are described with respect to a primary plate pressure and a secondary plate pressure, respectively.Speed ratio parameters of the program 300 include a commanded speed ratio 301, a desired speed ratio 302, and an actual speed ratio 303. The actual speed ratio 303 shows a present measured value for the speed ratio and is determined based on a ratio of the measured output and input speeds, for example, the CVT input speed 33 as measured by the input speed sensor 32 and the CVT output speed 35 as measured by the output speed sensor 34. The desired speed ratio 302 is a preferred speed ratio for operating the CVT 140 in the powertrain system 100 that responds to operator torque requests and compensates for or otherwise accounts for factors associated with drivability, fuel consumption, emissions, and other operating conditions that can be monitored or estimated and relate to an output power command, vehicle speed, and engine torque. The commanded speed ratio 301 is a speed ratio determined by the controller 12 and achievable with a zero steady state lane error as well as providing fast and smooth responsiveness. As described herein, the controller 12 controls the CVT 140 to achieve the desired speed ratio by controlling the pressure on the primary pulley 36 and / or the secondary pulley 38 of the CVT 140. Control of the pressure on the primary pulley 36 and / or the secondary pulley 38 of the CVT 140 may be achieved by controlling the drive and driven signals 33, 35 to apply the required pressure to the first and second actuators 55, 65 to effect the desired speed ratio, the required pressure preferably being in the form of a primary pressure command and a secondary pressure command.A first portion of the program 300 includes using feed-forward control and feedback control to determine a rate of change of the total speed ratio 325 based on the commanded speed ratio 301, the desired speed ratio 302, and the actual speed ratio 303. Feedback control uses the controller 310 that determines a feedback gear ratio 311 based on the difference between the commanded speed ratio 301 and the actual speed ratio 303. The controller 310 may be any suitable feedback control including, by way of example and not limitation, proportional-integral-derivative (PID) control, optimum robust control, or model-based predictive control (MPC). The feedforward controller uses a feedforward controller 320 that determines a feedforward transmission rate 321 based on the difference between the commanded speed ratio 301 and the desired speed ratio 302. The rate of change of the total speed ratio 325 may be determined by combining the feedback ratio rate 311 and the feed-forward ratio rate 321, for example, calculating an arithmetic sum thereof. The feed-forward gear ratio 321 and the commanded speed ratio 301 are evaluated in a path controller 340, which determines a commanded speed gear ratio path 341 based thereon. The commanded speed ratio trace 341 is a time rate of change in the commanded speed ratio 301. As such, the ratio control includes feedback and feedforward control for determining the rate of change of the total speed ratio 325, respectively, and use of the feedforward control for determining the commanded speed ratio trajectory 341. The rate of change of the total speed ratio 325 may be used by a shift force calculation program 330 to determine a commanded shift force (P-cmd) 335 as described herein. Mechanical constraints of the powertrain system 100 including the engine 110, torque converter 120, transmission housing 130, and CVT 140, each including hardware and hydraulic capabilities, are accounted for in determining the rate of change of the total speed ratio 325 based on the commanded speed ratio 301. Further, the rate of change of the total speed ratio 325 may vary when a step change in the commanded speed ratio 301 is commanded, and it may be necessary to determine whether changes in engine torque control and / or changes in engine speed requests are necessary for a fast and timely ratio response.The commanded speed ratio trajectory 341 is input to an IDE model 350 that determines a coefficient of ratio change 351 based on the commanded speed ratio trajectory 341 for an embodiment of the CVT 140 and a factor of power ratio (KpKs) 352 for the ratio of primary pulley force and secondary pulley force. The IDE model 350 includes processor-executable code and associated calibration that simulates the physical relationships 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. Variator ratio derivative ṙ may be represented as follows and is based on feedback ratio 311 and feed-forward ratio 321:The switching force P can be determined as follows:The conditions of Eq. 1 and 2 are as follows:ω p is the CVT input speed;VSR is the desired speed ratio 302;k is the coefficient of ratio change 351; andThe change rate of the total speed ratio is an arithmetic sum of the feedback ratio rate 311 and the feed-forward ratio rate 321.Thus, the force associated with the first or primary pulley 36 may be determined as follows: wherein:F prim is a force associated with the first or primary pulley 36 that takes into account associated compressive and centrifugal forces;F sek is a force associated with the second or secondary pulley 38 that takes into account associated compressive, centrifugal, and spring forces; andKpKs is the factor of the force transmission.Under steady state operating conditions, the factor of the power ratio may be determined as follows.The ratio for the variator ratio derivative ṙ is referred to with reference to Eq. 1 Eq. 1 and Gl. Referring to FIG. 2, it may be developed for an embodiment of the CVT 140 that uses the collected empirical data collected for a range of speeds, loads, and speed ratio conditions and analyzed to determine the states for the various factors and the coefficients. The force ratio factor KpKs 352 represents a ratio of F prim to F sek that takes into account the forces of hydraulic pressure, centrifugal pressure, and spring force, and may be derived empirically by using the IDE model 350 with the commanded speed ratio 301 and a torque capacity ratio 342. The factor of power ratio KpKs 352 is dependent on a drive pulley torque 343, a CVT input speed 33, a CVT output speed 35, a transmission fluid temperature 345, transmission fluid quality, and other factors, and may be determined empirically. The coefficient of ratio change k 351 is a calibrated term determined using empirical data relating to the operation of an embodiment of the CVT 140. The ratio change coefficient k 351 and the rate of change of the total speed ratio 325 are used by the shift force calculation program 330 to determine the commanded shift force P-cmd 335. The commanded shift force P-cmd 335 is a magnitude of additional force applied to the first pulley 36 or the second pulley 38 for changing the speed ratio in response to a commanded shift.A pulley pressure determination program 360 uses the commanded shift force P-cmd 335 and the force ratio factor KpKs 352 to determine the primary and secondary pulley pressure commands to control the CVT 140, considering the minimum pulley clamping forces 356, centrifugal forces 355, spring forces 354, and torque force coefficients 353. The minimum pulley clamping forces 356, centrifugal forces 355, spring forces 354, and torque force coefficients 353 are application specific parameters that can be determined based on empirical relationships. As such, the primary and secondary sheave pressure commands for controlling the CVT 140 are based on the desired forces, including clamping and feedback correction forces, and the hydraulic characteristics of the transmission under certain operating conditions.The pulley pressure determination program 360 determines the primary pulley pressure command, e.g., the control signal 53 for the variator 30 described with reference to FIG. 2, and also determines a secondary pulley pressure command, e.g., the control signal 63 for the variator 30 described with reference to FIG. 2, for controlling the actuators of the CVT 140 to adjust the speed ratio of the CVT 140.The speed ratio control program 300 enables tracking of the commanded speed ratio to achieve a zero steady state track error with fast and uniform responsiveness. This includes determining a commanded ratio trajectory and a commanded ratio rate of change based on the desired speed ratio and the actual speed ratio using the feedback and feed-forward control programs. Hardware performance constraints are taken into account in determining the commanded ratio, for example, when line pressure or flowability is not large enough to meet the task. When commanded to change a step ratio, it is important to determine whether engine torque control and / or engine speed requests are needed for a fast and smooth ratio response. The factor of the power ratio KpKs 352 is used for ratio control to determine the ratio between the primary pulley force and the secondary pulley force. Such operation enables the calculation of the force on the gear forming pulley with respect to the minimum pulley clamping force 356 and the factor of the force gear KpKs 352. Such operation also enables selection of either the first pulley 36 or the second pulley 38 as a pinch pulley based on the desired forces, including pinch and feedback correction forces and the hydraulic characteristics of the transmission under the respective operating conditions.The flowchart and block diagram 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 is also noted that each block of the block diagrams and / or flowchart illustrations, and combinations of blocks in the block diagrams and / or flowchart illustrations, may be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. These computer program instructions may also be stored in a computer readable medium that can control a computer or other programmable data processing apparatus 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 operation depicted in the flowchart.The detailed description and the drawings or figures aid in and describe the present disclosure, but the scope of the present disclosure is defined solely by the claims. While a few of the best modes and other embodiments of the present disclosure have been described in detail, various alternative constructions and embodiments exist for practicing the present disclosure in the appended claims.

Claims

A method (300) of controlling a continuously variable transmission (CVT) (140), the method comprising: determining an actual speed ratio (303), a desired speed ratio (302), and a commanded speed ratio (301); determining a rate of change (325) of the total speed ratio based on the actual speed ratio (303), the desired speed ratio (302), and the commanded speed ratio (301); determining a commanded speed ratio trajectory (341) based on the desired speed ratio (302) and the commanded speed ratio (301); determining a coefficient (351) of the ratio change and a factor (352) of the force ratio (KpKs) based on the commanded speed ratio trajectory (341); determining a commanded shift force (335) based on the rate of change (325) of the total speed ratio and the coefficient (351) of the ratio change; and controlling a primary pulley force and a secondary pulley force for the CVT (140) based on the commanded shift force (335) and the factor (352) of the force ratio (KpKs); wherein determining the rate of change (325) of the total speed ratio based on the actual speed ratio (303), the desired speed ratio (302), and the commanded speed ratio (301) comprises: determining a feedback speed ratio (311) based on the difference between the commanded speed ratio (301) and the actual speed ratio (303); determining a feed forward gear ratio (321) based on the difference between the commanded speed ratio (301) and the desired speed ratio (302); and combining the feed forward gear ratio (311) and the feed forward gear ratio (321).The method (300) of claim 1, wherein controlling the primary pulley force for the CVT (140) based on the commanded shift force (335) and the factor (352) of the power ratio (KpKs) comprises controlling a primary command (53) for driving an actuator (55) of a movable sheave (52) of the primary pulley (36) of a variator (30) of the CVT (140) in response to the commanded shift force (335) and the factor (352) of the power ratio (KpKs).The method (300) of claim 1, wherein controlling the secondary pulley pressure for the CVT (140) based on the commanded shift force (335) and the factor (352) of the power ratio (KpKs) comprises controlling a secondary command (63) to drive an actuator (65) of a movable sheave (64) of the secondary pulley (38) of a variator (30) of the CVT (140) in response to the commanded shift force (335) and the factor (352) of the power ratio (KpKs).The method (300) of claim 1, wherein the actual speed ratio (303) comprises a measured value determined based on a ratio of a CVT input speed (33) and a CVT output speed (35).The method (300) of claim 1, wherein the desired speed ratio (302) comprises a speed ratio for operating the CVT (140) responsive to an operator torque request and the speed.The method (300) of claim 1, wherein the commanded speed ratio (301) comprises a speed ratio achievable with a zero steady state lane error.A continuously variable transmission (140) comprising: a variator (30) including a first pulley (36) and a second pulley (38), the first (36) and second (38) pulleys being rotatably connected by a flexible continuously rotatable device (40), wherein the first pulley (36) is rotatably connected to an input member (51) and the second pulley (38) is rotatably connected to an output member (61); wherein the first pulley (36) includes a movable sheave (52) that is displaced along a first axis (48) relative to a stationary sheave (54) in response to pressing a first actuator (55); wherein the second pulley (38) includes a movable sheave (64) that is displaced along a second axis (46) relative to a stationary sheave (66) in response to pressing a second actuator (65); a controller (12) in communication with a first sensor (32) configured to monitor a first speed (33) associated with the first pulley (36) and a second sensor (34) configured to monitor a second speed (35) associated with the second pulley (38) and operatively connected to the first (55) and second (65) actuators; wherein the controller (12) includes an instruction set executable to: determine an actual speed ratio (303), a desired speed ratio (302), and a commanded speed ratio (301); determine a rate of change (325) of the total speed ratio based on the actual speed ratio (303), the desired speed ratio (302), and the commanded speed ratio (301), determining a commanded speed ratio trajectory (341) based on the desired speed ratio (302) and the commanded speed ratio (301); determining a ratio change coefficient (351) and a force ratio factor (352) (KpKs) based on the commanded speed ratio trajectory (341); determining a commanded shift force (335) based on the total speed ratio change rate (325) and the ratio change coefficient (351); and controlling the first actuator (55) and the second actuator (65) based on the commanded shift force (335) and the force ratio factor (352) (KpKs); wherein determining the rate of change (325) of the total speed ratio based on the actual speed ratio (303), the desired speed ratio (302), and the commanded speed ratio (301) 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 feed forward ratio 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 feed forward ratio rate (321).

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