METHOD AND DEVICE FOR CONTROLLING A CONTINUOUSLY VARIABLE TRANSMISSION

Abstract

Method (300) for controlling the operation of a continuously variable transmission (CVT) (140) including a hydraulically controlled variator (30), the method (300) comprising: the detection of a non-stationary event that causes an instruction to change a translation ratio of the variator (30); deactivating the feedback control of the hydraulic pressure to the variator (30) during the unsteady event; determining a target pressure to achieve the instructed change in the translation ratio of the variator (30); Determining a print path based on the target pressure; and the execution (310) of the feed-forward control of the hydraulic pressure to the variator (30) in response to the pressure path during the unsteady event.

Description

TECHNICAL FIELD

[0001] This disclosure relates to a continuously variable transmission for a vehicle powertrain and a corresponding method and control routine. BACKGROUND

[0002] Internal combustion engine powertrains coupled with a continuously variable or infinitely variable transmission (CVT) can be used to provide traction power in vehicles. A CVT can operate with input / output ratios that are infinitely variable between a minimum (underdrive) and a maximum (overdrive) ratio, thereby offering a choice of engine operation that allows a preferred balance of fuel consumption and engine power in response to a driver's torque demand. The ability to provide continuously variable input / output ratios distinguishes a CVT from a stepped transmission, which has a variety of fixed ratios that can be selected in steps in response to a torque demand.

[0003] Common chain-type CVT transmissions have two pulley units, each with two pulleys. A chain runs between the two pulley units, with the two pulleys of each pulley unit clamping the chain. The frictional engagement between the pulleys of each pulley unit and the chain couples the chain to each pulley unit, thus transferring torque from one pulley unit to the other. One pulley unit can act as the drive or input pulley unit, while the other can act as the driven or output pulley unit. The gear ratio is the ratio of the output pulley unit torque to the input pulley unit torque.The gear ratio can be changed by moving the two pulleys of one unit closer together and the two pulleys of the other unit further apart, thereby pushing the chainring on the respective unit further outward or further inward. The movement of the pulleys of the pulley units can be achieved by the action of controlled hydraulic pressure. Hydraulic pressure control routines can be underdamped, resulting in overshoots, or they can be overdamped, resulting in undershoots; both can cause system instability and power loss.

[0004] US Pat. No. 4,670,843 A discloses detecting a transient state of a continuously variable transmission by calculating a difference between a target gear ratio and an actual gear ratio. If the difference exceeds a threshold value, a transient state exists, whereupon the feedback control is deactivated and the feedforward control is activated.

[0005] The document DE 103 16 439 A1 discloses a continuously variable transmission in which the detection of slippage or sliding between the pulleys of the variator is carried out using a gear ratio gradient or an adjustment speed of the gear ratio.

[0006] The object of the invention is to control a hydraulic pressure for a variator in a continuously variable transmission in such a way that pressure overshoots and pressure undershoots are minimized or prevented.

[0007] This object is achieved by the features of the independent claims. Advantageous developments of the invention are described in the subclaims. SUMMARY

[0008] A continuously variable transmission (CVT) with a hydraulically controlled variator is described. A method for controlling the CVT includes detecting a transient event that causes a commanded change in a variator gear ratio and disabling control of hydraulic pressure to the variator during the transient event. A target pressure to achieve the commanded change in the variator gear ratio is determined and a pressure trajectory is determined based on the target pressure. Feedforward control of the hydraulic pressure to the variator is performed in response to the pressure trajectory during the transient event.

[0009] 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

[0010] In the following, one or more embodiments are described by way of example with reference to the accompanying drawings, in which: Fig. 1 schematically shows a drive system with an internal combustion engine rotatably connected to a continuously variable transmission (CVT) within the scope of the disclosure via a torque converter and a gearbox; Fig. 2 is a schematic cross-sectional illustration of the elements of a variator in a chain-type CVT in accordance with the disclosure; Fig.3 shows, in accordance with the disclosure, a schematic block diagram of a control routine 300 for the hydraulic pressure in a CVT, which is advantageous for controlling the hydraulic pressure while avoiding or minimizing the overshoot or undershoot in one embodiment of the variator of the CVT with reference to the Fig. 1 and Fig. 2 can be used; and Fig. 4 graphically shows hydraulic pressure, a closed-loop integrator state, and a controller state versus time during a transient event involving a commanded increase in hydraulic pressure, in accordance with the disclosure. DETAILED DESCRIPTION

[0011] Referring to the drawings, in which the representations are for illustrating certain exemplary embodiments and not for the purpose of limiting the same, 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 housing 130. The drive system 100 is connected to a vehicle wheel 160 by a driveline 150 to provide traction power when used in a vehicle. The operation of the drive system 100 is regulated by a control system 10 in response to driver inputs and other factors.

[0012] The engine 110 may be any suitable internal combustion engine capable of converting hydrocarbon-based fuels into mechanical energy to generate torque in response to demand from the control system 10. The torque converter 120 is a device having a fluid coupling between the input and output for transmitting torque and typically includes a pump 122 connected to the engine 110, a turbine 124 connected via an output member to the transmission housing 130, and a torque converter clutch 126 that connects the rotation of the pump 122 and the turbine 124 and is controlled by the control system 10. The output member of the torque converter 120 is rotatably connected to the transmission housing 130, where a gear set or other suitable gear mechanism acts as a reduction gear between the torque converter 120 and the CVT 140.Alternatively, the transmission housing 130 may include another suitable gear configuration to perform the transmission function between the engine 110, the torque converter 120, and the CVT 140, including, by way of non-limiting example, a chain ring gear or a planetary gear set. In alternative embodiments, the torque converter 120 and the transmission housing 130 may be omitted individually or together.

[0013] 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 is described with reference to Fig.2. An output member 61 of the CVT 140 is rotatably connected to the driveline 150, which in turn is rotatably connected to the vehicle wheels 160 via an axle, a half-shaft, or other suitable form of torque transmission. The driveline 150 may include a differential gear set, a chain and sprocket set, or other suitable transmission configuration for transmitting torque to one or more vehicle wheels 160.

[0014] The drive 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, which preferably monitors vehicle speed (Vss). Any suitable device capable of sensing rotational positions and speeds may be one of the aforementioned speed sensors, including, for example, a Hall-effect sensor. Each of the aforementioned speed sensors communicates with the control system 10.

[0015] The control system 10 preferably includes a controller 12 and a user interface 14. The controller 12 may include a plurality of control devices, each device dedicated to monitoring and controlling a single system. This may include an engine control module (ECM) for controlling the engine 110, a transmission control module (TCM) for controlling the CVT 140, and for monitoring and controlling a single subsystem such as the torque converter clutch 126. The controller 12 preferably includes a non-volatile memory device 11 with executable instruction sets and a cache memory 13. The user interface 14 communicates with user input devices including, for example, an accelerator pedal 15, a brake pedal 16, and a gear selector lever 17 for retrieving output torque.In some embodiments, the gear selector lever 17 has a tap-up / tap-down function that allows the driver to manually select a gear ratio and override the automatic operation of the CVT 140. A tap-up command to the CVT 140 to lower the gear ratio is implemented by increasing the gear ratio on the variator. A tap-down command to the CVT 140 to increase the gear ratio is implemented by decreasing the gear ratio on the variator.

[0016] 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 circuits, central processing units such as microprocessors and associated non-volatile memory components in the form of memory and storage devices (read only memory, programmable read only memory, random access memory, hard disk, etc.) including the cache memory 13. The cache memory 13 is preferably designed as non-volatile memory with programmable read / write capabilities, which supports the storage of data arrays for the retrieval of power on / off cycles such as those encountered in vehicles and key-off / key-on events.The non-volatile memory component may store machine-readable instructions in the form of one or more software or firmware programs, routines, combinational logic circuits, input / output circuits and devices, signal conditioning and buffer circuits, and other components accessible by one or more processors to provide described functionality. Input / output devices and circuits include analog-to-digital converter-related devices that monitor sensor inputs at a predetermined polling frequency or in response to a trigger event. Software, firmware, programs, instructions, control programs, code, algorithms, and similar terms refer to any set of instructions executable by a controller, such as calibrations and lookup tables.Each controller executes control routine(s) for the desired functions, including monitoring inputs from sensor devices and other networked controllers, and executing control and diagnostic routines to control the operation of actuators. The routines can be executed at regular intervals, such as every 100 microseconds during operation. Alternatively, routines can be executed in response to a trigger event. Communication between controllers and between controllers, actuators, and / or sensors can be established using a direct wired connection, a networked communication bus, a wireless connection, or another suitable communication link.Communication involves the exchange of data signals by any suitable means, including, as examples, electrical signals over a conductive medium, electromagnetic signals through air, optical signals over fiber optics, and the like. Data signals may include signals representing inputs from sensors and actuator commands, as well as communication signals between controllers. The term "model" refers to processor-based or processor-executable code and associated calibration used to simulate the physical existence of a device or physical process. As used, the term "dynamic" describes steps or processes that are executed in real time and are characterized by monitoring, otherwise determining, and periodically updating parameters during execution of a routine or between iterations of that execution.

[0017] Fig. Figure 2 schematically shows elements of a variator 30 in one embodiment of the CVT 140, which can be controlled by the TCM. 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 hereinafter as the input member 51, and the second rotating element 61 is referred to hereinafter as the output member 61.

[0018] The variator 30 includes a first, or primary unit 36, a second, or secondary unit 38, and a flexible, continuously rotatable device 40 connecting the first and second pulley units 36, 38 to transmit torque therebetween. The first pulley unit 36 ​​is rotatably mounted on the drive member 51, the second pulley unit 38 is rotatably mounted on the output member 61, and the rotatable device 40 is adapted to transmit torque between the first and second pulley units 36, 38 and, thus, between the drive and output members 51, 61. The first pulley unit 36 ​​and drive member 51 rotate about a first axis 48, and the second pulley unit 38 and output member 61 rotate about a second axis 46. The continuously rotatable device 40 may be a belt, a chain, or other suitable flexible, continuous device.The input speed sensor 32 may be mounted close to the input member 51 and generates a value for the CVT input speed 33, which depends on the speed of the first pulley unit 36, and the output speed sensor 34 may be mounted close to the output member 61 and generates a value for the CVT output speed 35, which depends on the speed of the second pulley unit 38. One of the pulley units 36, 38 functions as a ratio unit, establishing a speed ratio, and the other of the pulley units 36, 38 functions as a clamping unit, applying sufficient clamping force to transfer torque between the two. As used herein, the term 'speed ratio' refers to the speed ratio of the variator, which is a ratio of the speed of the output member 61 to the speed of the input member 51.The speed of the input member 51 can be determined from signal inputs of the engine speed sensor 112, the torque converter turbine speed sensor 125, or the input speed sensor 32 described herein, or from other suitable speed / position sensors. The speed of the output member 61 can be determined from signal inputs of the output speed sensor 34 or the wheel speed sensor 162 described herein, or from other suitable speed / position sensors. Regardless of the measurement system(s) used, the speed ratio parameters depend on the CVT input speed and the CVT output speed.

[0019] The first disk unit 36 ​​is divided perpendicular to the first rotation axis 48 into a first movable disk 52 and a first fixed disk 54, thus forming a first groove 50 between the two. The first movable disk 52 is moved or translated axially along the first axis 48 relative to the first fixed disk 54. For example, the first movable disk 52 can be connected to the drive member 51 by a spline, thus enabling the axial movement of the first movable disk 52 along the first axis 48. The first fixed disk 54 is mounted opposite the first movable disk 52. The first fixed disk 54 is axially fastened to the drive member 51 along the first axis 48. In this respect, the first fixed disk 54 is not movable in the axial direction of the first axis 48. The first movable disk 52 and the first fixed disk 54 each have a groove surface 56.The first surfaces 56 of the groove formed by the first movable disc 52 and the first fixed disc 54 face each other, thereby forming the circular first groove 50 therebetween. The opposing surfaces 56 of the first groove are preferably shaped like an inverted truncated cone, so that movement of the first movable disc 52 toward the first fixed disc 54 increases the outer diameter of the disc assembly within the circular first groove 50. A first actuator 55 is coupled to the first disc assembly 36 to regulate the axial position of the first movable disc 52 in response to a control signal 53, thereby moving the first movable disc 52 toward the first fixed disc 54. In certain embodiments, the first actuator 55 is a hydraulically controlled device, and the control signal 53 is a hydraulic pressure signal.

[0020] The hydraulic pressure can be monitored by a sensor in the first actuator 55, or at another location in a hydraulic circuit that supplies the first actuator 55 with pressurized hydraulic fluid.

[0021] The second disc unit 38 is split perpendicular to the second axis 46 to define a second circular groove 62. The second circular groove 62 is perpendicular to the second axis 46. The second disc unit 38 has a second movable disc 64 and a second fixed disc 66. The second movable disc 64 is moved or translated axially along the second axis 46 relative to the fixed disc 66. For example, the second movable disc 64 can be connected to the output member 61 by a spline, thus enabling the axial movement of the second movable disc 64 along the second axis 46. The second fixed disc 66 is mounted opposite the second movable disc 64. The second fixed disc 66 is axially attached to the output member 61 along the second axis 46. In this respect, the second fixed disc 66 is not movable in the axial direction of the second axis 46.The second movable disc 64 and the second fixed disc 66 each have a groove surface 68. The second groove surfaces 68 of the second movable disc 64 and the second fixed disc 66 face each other, thus forming the round second groove 62 therebetween. The opposing surfaces 68 of the second groove are preferably in the shape of an inverted truncated cone, so that movement of the second movable disc 64 toward the second fixed disc 66 increases the outer diameter of the disc unit in the round second groove 62. A second actuator 65 is arranged with the second disc unit 38 so that it can regulate the axial position of the second movable disc 64 in response to a control signal 63, thus also moving the second movable disc 64 toward the second fixed disc 66.In certain embodiments, the second actuator 65 is a hydraulically controlled device, and the control signal 63 is a hydraulic pressure signal. The hydraulic pressure may be monitored by a sensor in the second actuator 65, or elsewhere in a hydraulic circuit that supplies the first actuator 65 with pressurized hydraulic fluid. A ratio between the diameter of the outer disc unit of the first disc unit 36 ​​and the diameter of the outer disc unit of the second disc unit 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 components and systems of the drive system and powertrain.

[0022] The speed ratio can be described in terms of an actual and a desired speed ratio. An actual speed ratio is a present, measured value for the speed ratio and can be determined based on a ratio of the input speed signal 33 and the output speed signal 35. A desired speed ratio is a commanded, future value for the speed ratio determined based on monitored and estimated operating conditions related to an output power command, vehicle speed, engine torque, and other factors. The TCM uses control routines to control the CVT 140 to regulate the desired speed ratio by regulating pressure on one or both of the primary and secondary pulley assemblies 36 and 38 of the CVT 140.Pressure control for one or both of the primary and secondary pulley units of the CVT 140, 36 and 38, may be achieved by controlling the drive and actuating signals 53, 63 to apply the required pressure to the first and second actuators 55, 65 to change the desired speed ratio, preferably in the form of a primary and a secondary pressure command.

[0023] CVT operation involves controlling hydraulic pressure, which may require measuring hydraulic pressure and mapping it to the disc unit pressure. The accuracy of the measured disc unit pressure can vary depending on whether the CVT is performing a transient event or is in a steady-state operating condition. A transient event is typically caused by a change in the state of an operating parameter that affects the equilibrium of the system and represents a change in the state of an operating parameter. A transient event may be a change in a variator gear ratio in response to a change in output torque demand via a signal or otherwise authorized input from an accelerator pedal, brake pedal, or transmission status.

[0024] There may be a hydraulic restriction between the point where the pulley assembly pressure is measured and the point where pressure is applied to the moving pulley, causing the applied pressure to lag behind the measured pressure. The pressure offset may be magnified during a transient event due to high fluid flow. The effect of the offset between measured and applied hydraulic pressure may be greatest during rapid ratio changes, and the associated changes in commanded pressure may result in under- or over-shoots in the pressure at a pulley assembly, affecting CVT performance and stability. These pressure inaccuracies act as disturbances in the closed-loop pressure control routine and may result in an unwanted change in transmission output speed.The behavior of the hydraulic system under large pressure changes is explained by the dynamic behavior of its hydromechanical components. Therefore, the use of proportional and / or integral terms in closed-loop pressure control routines may be undesirable, as this can lead to potential buildup at the integrator related to pressure limitations and offset.

[0025] Fig.3 schematically shows a block diagram of a CVT hydraulic pressure control routine (routine) 300 that can be optimally used to regulate hydraulic pressure to minimize or prevent pressure overshoots or undershoots to the elements of the variator 30 of the CVT 140. This preferably includes good responsiveness to the effects of pressure control, since the characteristics of pressure control may vary under steady-state and transient conditions. The routine 300 incorporates the characteristics of the pressure control to achieve acceptable pressure control under both transient and steady-state operating conditions. This preferably also includes disabling closed-loop pressure control during transient events, preferably by appropriately tuning the proportional and integral terms for gain feedback and by resetting an integrator term to zero.The feed-forward control of the hydraulic pressure to the variator 30 includes determining a pressure path when there is an absolute difference between the desired hydraulic pressure and the actual hydraulic pressure that is greater than a minimum pressure threshold.

[0026] Routine 300 is preferably executed by the controller 12 communicating with and presiding over the operation of the TCM to control the hydraulic pressure in a clamping disc assembly of an embodiment of the variator 30 of the CVT 140 and drive system 100 described with reference to Fig. 1 and Fig. 2, to improve the CVT 140's response to changes in output torque demand. The Fig. The routine 300 shown in Figure 3 is described in conjunction with Table 1, which contains a breakdown with numerically labeled blocks and the corresponding functions and is explained below. Table 1 BLOCK BLOCK CONTENT 302 Monitoring an output torque request 304 Determine the target gear ratio for the CVT variator based on the output torque request 306 Determine whether the target gear ratio requires a transient or steady-state control of the hydraulic pressure to the variator 310 Execution of feed-forward control of the hydraulic pressure to the variator; Disable the proportional gain term for the proportional control of the variator's hydraulic pressure 312 The integral gain term for the integral control of the hydraulic pressure deactivate the variator 314 Activate the feed-forward control of the variator hydraulic pressure 320 Execution of feedback control of the hydraulic pressure to the variator; Activate the proportional gain term for the proportional control of the variator's hydraulic pressure 322 Activate the integral gain term for the integral control of the variator hydraulic pressure 324 Disable the feed-forward control of the variator hydraulic pressure 330 Control the hydraulic pressure to the variator, which responds to feed-forward and feedback control.

[0027] Routine 300 is executed periodically to supply hydraulic pressure to one or both of the primary pulley assembly 36 and the secondary pulley assembly 38 of the variator 30 to achieve a desired gear ratio. Pressure control for one or both of the primary and secondary pulley assemblies, 36 and 38, can be achieved by controlling the drive and actuation signals 53, 63 to apply the required pressure to the first and second actuators 55, 65 to change the desired speed ratio. Preferably, the required pressures are achieved in the form of a primary and a secondary pressure command.

[0028] Routine 300 includes monitoring an output torque request (302) and determining a desired speed ratio for the CVT based on the output torque request (304). The desired speed ratio is compared to a currently commanded speed ratio to determine whether hydraulic pressure control should be controlled with steady-state or transient pressure control.

[0029] A transient pressure control is ordered when a difference between the desired speed ratio and the currently commanded speed ratio is greater than a minimum threshold value. This minimum threshold value is associated with a change in hydraulic pressure to the variator 30 required to achieve the desired speed ratio (306)(0). A steady-state pressure control is ordered when a difference between the desired speed ratio and the currently commanded speed ratio is less than the minimum threshold value (306)(1). Therefore, in cases where the change in hydraulic pressure to achieve the desired speed ratio is less than the minimum threshold value, the steady-state pressure control is ordered. Likewise, in cases where the change in hydraulic pressure to achieve the desired speed ratio is greater than the minimum threshold value, the transient pressure control is ordered.

[0030] If transient pressure control is ordered (306)(0), a proportional gain term in the proportional feedback control of the hydraulic pressure of the variator 30 is set to a value that deactivates the proportional feedback control (310), and an integral gain term in the integral feedback control is set to a value that deactivates the integral feedback control (312). Alternatively, the proportional gain term in the proportional feedback control of the hydraulic pressure of the variator 30 is set to a value that limits the proportional feedback control to a transient-specific gain (310), and an integral gain term is set to a value that limits the integral feedback control to a transient-specific gain (312).Feed-forward control of the hydraulic pressure supplied to the variator 30 is enabled and preferably performed as described herein to minimize or eliminate overshoots or undershoots of the hydraulic pressure during transient events (314).

[0031] The feed-forward control of the hydraulic pressure supplied to the variator 30 is carried out with reference to Fig. 4, graphically depicts parameter states associated with the operation of an embodiment of the drive system 100 including the CVT 140 and variator 30. Curve 400 consists of parameter states including the confluence of hydraulic pressure 410, closed-loop integrator status 420, and feedback gain PIDgx 430 versus time on the horizontal axis during a transient event including a commanded increase in hydraulic pressure. The curve 400 shown with reference to Fig.The data shown in Figure 4 is associated with a portion of the feedforward control of the hydraulic pressure supplied to the variator during a transient event, including a commanded increase in hydraulic pressure in response to a command to change the gear ratio of the variator 30 during operation. The hydraulic pressure 410 includes an initial pressure 412 and a desired pressure 414, the initial pressure 412 being associated with a currently commanded speed ratio, and the desired pressure 414 being associated with a desired speed ratio. As shown, prior to time t1 402, steady-state operation is used in controlling the hydraulic pressure, while a sensed pressure 411 tracks the desired pressure 413 in response to a pressure command 415. The closed-loop integrator term 422 varies in response to the sensed pressure 411, and a feedback incremental state 432 is active.

[0032] A transient event begins at time t1 402, at which the closed-loop integrator term 422 and the feedback gain state 432 are reset to zero. The feedforward control of the hydraulic pressure operates based on the initial pressure 412 and the setpoint pressure 414, including determining the measured pressure 411 and the setpoint pressure 413 in response to a pressure command 415 as follows: The feed-forward control of the hydraulic pressure supplied to the variator during a transient event preferably includes determining a path between pressure commands whose difference, either indicated or as an absolute value, is greater than a pressure threshold, P SchwellenwertThe magnitude of the pressure threshold can depend on the pump, the speed of the drive variator pulley, the gearbox or variator drive torque, the temperature of the variator or fluid, the flow rate, and other factors. The path for the next pressure command, P n+1 , from the current print command, P n , to print target, P Ziel , can be defined by the following relationships according to equations 1 and 2 as follows. Pn+1=Pn−(CGAIN*(Pn−Ptarget)) and |Ptarget−Pn| <PSchwellenwert, dann Pn+1=PZiel oder Pn+1=Pniedrig wherein: CGAIN is a constant that controls how fast the trajectory travels to P Ziel converges, P n is the initial pressure, and P niedrig is a constant pressure term.

[0033] The purpose of defining the trajectory with reference to equations 1 and 2 in as much detail as possible is to first have a relatively large pressure change as the initial response of the hydraulic system and then to have smaller differences between the waypoints when approaching the target P Ziel . The relationship described with reference to equation 1 is preferably used to control the CVT 140 during the portion of its operation between times t1 402 and t2 404 after Fig. 4, the relationship described with reference to equation 2 is used to control the CVT 140 during the part of its operation between times t2 404 and t3 406 according to

[0034] Fig.4. This is used to reduce the pressure change rate to achieve a soft landing at the pressure target while minimizing or avoiding under- or over-pressure. Alternatively, the desired pressure path can be achieved through other means, including splines, cubic functions, filters, etc.

[0035] How to continue in Fig.As shown in Figure 4, the measured pressure 411 lags behind the commanded pressure 415 due to hydraulic constraints, transport delays, system communication latencies, and other factors. Feedforward control allows the commanded pressure to be increased to counteract the hydraulic clamping delay of the actual disk unit pressure. Overshoot is thus minimized at the end of the transient event, for example, at time t3 406, because the closed-loop control system is deactivated. The feedback gain state 432 becomes active starting at time t2 404, and the closed-loop integrator term 422 becomes active starting at time t3 406 in this example.

[0036] Again with reference to Fig.3, if steady-state pressure control is commanded (306)(1), a proportional gain term in the proportional feedback control of the variator hydraulic pressure is set to a value that enables the proportional feedback control (320), and an integral gain term in the integral feedback control is set to a value that enables the integral feedback control (322). The feedforward control of the variator hydraulic pressure is deactivated (324). Routine 300 controls the hydraulic pressure to the variator 30, which responds to feedforward and / or feedback control as described (330).

[0037] Steady-state conditions do not require as high a flow rate as transient conditions. Because steady-state conditions do not require high flow rate, the measured pressure more accurately reflects the pressure at the disc unit. Improved accuracy of the measured pressure at the disc unit minimizes the need for any form of feedforward pressure control. Furthermore, with improved measurement accuracy, there is less urgency to disable or adjust closed-loop gains to ensure stable system operation.

[0038] The flowchart and block diagrams in the flowcharts illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer programs 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.

[0039] 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 exist in the appended claims.

Claims

[1] A method (300) for controlling the operation of a continuously variable transmission (CVT) (140) including a hydraulically controllable variator (30), the method (300) comprising: detecting a transient event causing an instruction to change a gear ratio of the variator (30); deactivating the feedback control of the hydraulic pressure to the variator (30) during the transient event; determining a target pressure to achieve the commanded change in the gear ratio of the variator (30); determining a print path based on the target pressure; and performing (310) feed-forward control of hydraulic pressure to the variator (30) in response to the pressure trajectory during the transient event. [2] Method (300) according to claim 1, further comprising: detecting a stationary event related to the operation of the variator (30); deactivating (324) the feed-forward control of the hydraulic pressure to the variator (30); and performing (320) only the feedback control of the hydraulic pressure to the variator (30) responsive to a commanded hydraulic pressure during the steady-state event. [3] The method (300) of claim 1, wherein disabling the feedback control of the hydraulic pressure to the variator (30) during the transient pressure event means resetting an integrator term (312) and a proportional term (310) of the feedback control to zero. [4] The method (300) of claim 1, wherein the transient event includes detecting a transient pressure control event with an associated commanded change in the gear ratio of the variator (30). [5] The method (300) of claim 1, further comprising determining the print path based on the difference between the target pressure and a current print command. [6] The method (300) of claim 1, comprising performing (310) feed-forward control of hydraulic pressure to the variator (30) responsive to the pressure path during the transient event to drive an actuator (55, 65) of a movable pulley (52, 64) of a pulley unit (36, 38) of the variator (30). [7] A method (300) for controlling the operation of a continuously variable transmission (CVT) (140) including a hydraulically controllable variator (30), the method (300) comprising: performing (310) only the feed-forward control of the hydraulic pressure to the variator (30) in response to a pressure trajectory during a transient event; and performing (320) only the feedback control of the hydraulic pressure to the variator (30) in response to the steady-state operation. [8] The method (300) of claim 7, wherein performing (310) only the feed-forward control of the hydraulic pressure to the variator (30) in response to a pressure trajectory during a transient event comprises: monitoring a commanded speed ratio of the variator (30); determining a commanded change in the gear ratio of the variator (30); determining a target pressure to achieve the commanded change in the gear ratio of the variator (30) based on the commanded speed ratio of the variator (30); and determining the pressure path in connection with the feed-forward control of the hydraulic pressure to the variator (30) based on the target pressure. [9] Continuously variable transmission (CVT) (140), comprising: a variator (30) having a first pulley unit (36) and a second pulley unit (38), the first (36) and second (38) pulley units being rotatably coupled by a flexible continuously rotatable device (40), the first pulley unit (36) being rotatably coupled to an input member (51) and the second pulley unit (38) being rotatably coupled to an output member (61); the first disc unit (36) having a movable disc (52) that moves along a first axis (48) relative to a fixed disc (54) in response to movement of a first actuator (55); the second disc unit (38) having a movable disc (64) that moves along a second axis (46) relative to a fixed disc (66) in response to the movement of a second actuator (65); and a controller (10) with an instruction set, the instruction set executable for: Detecting a transient event that causes an instruction to change a gear ratio of the variator (30), Deactivating the feedback control of the hydraulic pressure to the variator (30) during the transient event, Determining a target pressure to achieve the commanded change in the gear ratio of the variator (30), Determining a print path based on the target pressure, and Executing (310) the feed-forward control of the hydraulic pressure to the variator (30) responsive to the pressure trajectory during the transient event. [10] The CVT (140) of claim 9, further executable with the instruction set to: Detection of a stationary event related to the operation of the variator (30), Deactivating (324) the feed-forward control of the hydraulic pressure to the variator (30); and Performing (320) only the feedback control of the hydraulic pressure to the variator (30) responsive to a commanded hydraulic pressure during the steady state event.

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