Transmission fluid control method for continuously variable transmissions

Abstract

Transmission fluid control system for a vehicle, comprising the following: the selective actuation of a switching valve (120) of a continuously variable transmission (CVT) (14) either: (i) from a closed to an open position; or (ii) from the open to the closed position, wherein the switching valve (120), when the switching valve (120) is in the closed position, prevents transmission oil from flowing through a flow path between a transmission oil pump (104) and a pressure regulating valve (116) of the CVT (14); and directs the transmission oil flow back into the transmission oil pump (104) and wherein the switching valve (120) allows transmission oil to flow through the flow path when the switching valve (120) is in the open position; determining a pressure setting (268) when the switching valve (120) (i) changes from the closed to the open position; or (ii) changes from the open to the closed position; determining a target line pressure (264) by a second target pressure module (272); Determining a set target pressure (256) based on the pressure setting (268) and the target line pressure (264); and controlling the opening of the pressure regulating valve (116) based on the set target pressure (256).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to vehicle transmissions and, more particularly, to a transmission fluid control method for a vehicle for regulating transmission oil pressure within a continuously variable transmission.

[0002] For background information, reference is made to the documents EP 0 161 824 A1, US 2015 / 0 148 157 A1 and US 2013 / 0 109 516 A1, which describe conventional transmission fluid control methods. BACKGROUND

[0003] An engine generates torque, which is delivered to a transmission. A vehicle's automatic transmission may include a variety of fluid-controlled friction devices, such as clutches. A control module may engage and disengage one or more of the clutches to establish various gear ratios (also called speed ratios) within the transmission.

[0004] The transmission contains a transmission oil pump. The transmission oil pump supplies transmission oil to operate the transmission clutches, lubricate the transmission components, and cool the transmission components. Some transmission oil pumps are mechanically driven, e.g., by the engine. Other transmission oil pumps are electrically driven.

[0005] The invention is based on the object of providing a new transmission fluid control method for a vehicle which operates particularly reliably. SUMMARY

[0006] This object is achieved with a transmission fluid control method for a vehicle, which is characterized by the features of claim 1.

[0007] Further described is a transmission fluid control system of a vehicle. A shift valve control module selectively actuates a shift valve of a continuously variable transmission (CVT) from either: (i) a closed position to an open position; or (ii) from the open position to the closed position. The shift valve prevents transmission fluid flow through a flow path between a transmission fluid pump and a pressure control valve of the CVT when the shift valve is in the closed position. The shift valve also routes the transmission fluid back to the transmission fluid pump when the shift valve is in the closed position. The shift valve allows transmission fluid flow through the flow path when the shift valve is in the open position.A setting determination module determines a pressure setting when the switching valve is switched (i) from the closed position to the open position; or (ii) from the open position to the closed position. A setpoint pressure module determines a setpoint line pressure, also referred to herein as the setpoint pressure, output by the pressure control valve. An adjustment module determines an adjusted setpoint pressure based on the pressure setting and the setpoint pressure. A control valve control module controls the opening of the pressure control valve based on the adjusted setpoint pressure.

[0008] In further features, the transmission oil pump pumps the transmission oil via a second flow path (i) to the pressure control valve when the switching valve is in the open position and (ii) when the switching valve is in the closed position.

[0009] In further features, the setting module sets the set target pressure based on one of the following factors: (i) a product of the target pressure and the pressure setting; and (ii) a sum of the target pressure and the pressure setting.

[0010] In further features, the setting determination module sets the pressure setting to a predetermined value when the switching valve control module maintains the switching valve in the closed position and when the switching valve control module maintains the switching valve in the open position. The setting module sets the adjusted target pressure to the target pressure when the pressure setting corresponds to the predetermined value.

[0011] In further features, the setting determination module increases the pressure setting relative to the predetermined value when the switching valve control module switches the switching valve (i) from the closed position to the open position; or (ii) from the open position to the closed position.

[0012] In further features, a second desired pressure module determines a first desired pressure of transmission oil applied to a first pulley actuator and determines a second desired pressure of transmission oil applied to a second pulley actuator. The first pulley actuator is coupled to an input shaft of the CVT and expands and contracts based on a first pressure of transmission oil applied to the first pulley actuator. The second pulley actuator is connected to the output shaft of the CVT and expands and contracts based on a second pressure of transmission oil applied to the second pulley actuator. An (i) belt and a (ii) chain surround the first and second pulley actuators. The setting determination module determines the pressure setting based on a greater of a first or second desired pressure.

[0013] In further features, the second target pressure module determines the first and second target pressures based on a target rotational ratio of the input shaft to the rotation of the output shaft.

[0014] In further features, the switching valve control module switches the switching valve from the closed position to the open position when a rate of change of the target ratio is greater than a first predetermined value, and switches the switching valve from the open position to the closed position when the rate of change of the target ratio is less than a second predetermined value.

[0015] In further features, the switching valve control module determines a transition rate based on the greater of the first and second desired pressures and, based on the transition rate, switches the switching valve (i) from the closed position to the open position or (ii) from the open position to the closed position.

[0016] In further features, a first pulley valve control module controls the opening of a first valve based on the first desired pressure, the first valve receiving transmission fluid from the pressure regulating valve and regulating transmission fluid flow to the first pulley actuator. A second pulley valve control module controls the opening of a second valve based on the second desired pressure, the second valve receiving transmission fluid from the pressure regulating valve and regulating transmission fluid flow to the second pulley actuator.

[0017] In the method according to the invention, the transmission oil pump pumps transmission oil further to the pressure control valve via a second flow path (i) when the switching valve is in the open position and (ii) when the switching valve is in the closed position.

[0018] In further features, determining the adjusted target pressure includes setting the adjusted target pressure based on one of the following factors: (i) a product of the target pressure and the pressure setting; and (ii) a sum of the target pressure and the pressure setting.

[0019] In further features, determining the pressure setting includes setting the pressure setting to a predetermined value when the switching valve is maintained in the closed position and when the switching valve is maintained in the open position; while determining the adjusted target pressure includes setting the adjusted target pressure to the target pressure when the pressure setting is equal to the predetermined value.

[0020] In further features, determining the pressure setting includes setting the pressure setting to a value greater than the predetermined value when the switching valve is switched (i) from the closed position to the open position; or (ii) from the open position to the closed position.

[0021] In further features, the transmission oil regulation method further includes: determining a first target pressure of transmission oil applied to a first pulley actuator; determining a second target pressure of transmission oil applied to a second pulley actuator, wherein the first pulley actuator is coupled to an input shaft of the CVT and expands and contracts based on a first pressure of transmission oil applied to the first pulley actuator, wherein the second pulley actuator is coupled to an output shaft of the CVT and expands and contracts based on a second pressure of transmission oil applied to the second pulley actuator, wherein either (i) a belt or (ii) a chain surrounds the first and second pulley actuators;and wherein determining the pressure setting includes determining the pressure setting based on a greater of the first and second desired pressures.;

[0022] In further features, determining the first and second target pressures includes determining the first and second target pressures based on a target rotational ratio of the input shaft to the rotation of the output shaft.

[0023] In further features, actuating the switching valve includes: switching the switching valve from the closed position to the open position when a rate of change of the target ratio is greater than a first predetermined value; and switching the switching valve from the open position to the closed position when the rate of change of the target ratio is less than a second predetermined value.

[0024] In further features, the transmission fluid control method further includes: determining a transition rate based on the greater of the first target pressure, second target pressure, or target line pressure; and based on the transition rate, switching the switching valve from (i) the closed position to the open position or (ii) the open position to the closed position.

[0025] In further features, the transmission oil regulation method further includes: controlling the opening of a first valve based on the first target pressure, wherein the first valve receives transmission oil from the pressure regulating valve and regulates the transmission oil flow to the first pulley actuator; and controlling the opening of a second valve based on the second target pressure, wherein the second valve receives the transmission oil from the pressure regulating valve and regulates the transmission oil flow to the second pulley actuator.

[0026] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are provided for purposes of illustration only. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present disclosure will become more fully understood with reference to the detailed description and the accompanying drawings, in which: Fig. 1A-1B show a functional block diagram of an exemplary vehicle system; Fig. 2 shows a functional block diagram of an exemplary continuously variable transmission (CVT) system; Fig. 3 shows a functional block diagram of an exemplary transmission oil regulation system; Fig. 4 shows a flowchart illustrating an exemplary method for controlling valves of a CVT for a transition of a shift valve from a closed position to an open position or from the closed position to the open position.

[0028] In the drawings, the same reference numerals are used for similar and / or identical elements. DETAILED DESCRIPTION

[0029] An engine generates drive torque for a vehicle. A continuously variable transmission (CVT) transfers the torque to one or more of the vehicle's wheels. A transmission oil pump pumps transmission oil through one transmission flow path to a line pressure control valve. The transmission oil pump also pumps transmission oil to a switching valve located in a second transmission flow path between the transmission oil pump and the line pressure control valve. The switching valve can open to provide a first transmission oil flow rate to the line pressure control valve and can be closed to provide a portion (e.g., one-half) of the first transmission oil flow rate to the line pressure control valve while returning the other portion to the transmission pump suction. An increase in fuel consumption can be realized when the switching valve is closed because the transmission oil pump imposes a lower load.

[0030] The CVT includes a primary pulley and a secondary pulley. The primary pulley is coupled to an input shaft, while the secondary pulley is coupled to an output shaft. Torque is transferred to one or more of the vehicle's wheels via the output shaft. A belt or chain encircles the primary and secondary pulleys.

[0031] The primary pulley includes a primary pulley actuator that expands and contracts based on transmission oil pressure applied to the primary pulley actuator and centrifugal force. The secondary pulley includes a secondary pulley actuator that expands and contracts based on transmission oil pressure applied to the secondary pulley actuator, centrifugal force, and a spring force. The primary and secondary pulley actuators vary the speed ratio between the CVT's input and output shafts via expansion and contraction.

[0032] The line pressure control valve supplies transmission fluid to various actuators / functions of the CVT. For example, the line pressure control valve supplies transmission fluid to the primary and secondary pulley actuators based on a desired drive ratio and various transmission outputs.

[0033] Some conditions, such as a shift valve transition from the closed to the open position or from the open to the closed position, can cause a reduction in the line pressure control valve output pressure and a decrease in the transmission fluid pressure applied to one or more of the pulley actuators. This can cause the belt or chain to slip.

[0034] According to the present disclosure, a valve control module opens the line pressure control valve to increase the output pressure (relative to a desired output pressure) before, during, and for a predetermined period of time after the shift valve transitions from the closed to the open position or from the open to the closed position. The valve control module may also have a set speed at which the shift valve transitions from the closed to the open position or from the open to the closed position. This may minimize or prevent pressure fluctuations in the line pressure control valve output pressure and / or the transmission fluid pressure exerted on one or more of the pulley actuators during the transition.

[0035] Fig. 1A and Fig. 1B include functional block diagrams of an exemplary vehicle system. An internal combustion engine 12 drives a transmission 14 via a torque converter 16. Engine 12 may, for example, be a gasoline engine, a diesel engine, or another suitable engine type. A vehicle may further include one or more electric motors and / or motor-generator units (MGUs), such as MGU 18.

[0036] The engine 12 transmits torque to the torque converter 16 via an engine output shaft 20, such as a crankshaft. The torque converter 16 delivers torque to the transmission 14 via a transmission input shaft 22. In some cases, the torque converter 16 may be omitted. The electric motor(s) and / or MGU(s) may also transmit torque to the transmission input shaft 22 to supplement or replace the engine torque output. An MGU may convert mechanical energy to electrical energy under certain circumstances, such as to recharge one or more batteries and / or to provide power to electronic components of the vehicle.

[0037] The transmission 14 transmits torque between the transmission input shaft 22 and a transmission output shaft 24. The drive ratio may refer to or be based on the ratio between the speed of the transmission input shaft 22 and the speed of the transmission output shaft 24. The transmission output shaft 24 drives a drive system 26, while the drive system 26 transmits torque to the wheels (not shown) of the vehicle. A range selector control 28 allows a user to select a transmission operating mode 14. The mode may include, for example, a park mode, a reverse mode, a neutral mode, or one or more forward drive modes.

[0038] The transmission 14 is a continuously variable transmission (CVT). A primary pulley 30 is coupled to and rotates with the transmission input shaft 22. A secondary pulley 32 is coupled to and rotates with the transmission output shaft 24. The primary pulley 30 includes a primary pulley actuator 34 that expands and contracts based on transmission oil pressure applied to the primary pulley actuator 34. The secondary pulley 32 includes a secondary pulley actuator 36 that expands and contracts based on transmission oil pressure applied to the secondary pulley actuator 36.While the example of the primary pulley 30 is provided directly coupled to the transmission input shaft 22, the primary pulley 30 may be indirectly coupled to the transmission input shaft 22 via one or more torque-transmitting devices. Likewise, while the example of the secondary pulley 32 is provided directly coupled to the transmission output shaft 24, the secondary pulley 32 may be indirectly coupled to the transmission output shaft 24 via one or more torque-transmitting devices.

[0039] As in Fig. 1B, a belt or chain 38 surrounds the primary and secondary pulleys 30 and 32 for rotating the transmission input shaft 22 and the transmission output shaft 24. The expansion and contraction of the primary and secondary pulley actuators 34 and 36 vary the rotational ratio between the transmission input shaft 22 and the transmission output shaft 24.

[0040] The engine control module (ECM) 60 controls the operation of the engine 12. The ECM 60 or another control module (not shown) may control the operation of one or more electric motors and / or MGUs in various applications. A transmission control module (TCM) 70 controls the operation of the transmission 14. While the TCM 70 is shown as being implemented within the transmission 14, the TCM 70 may be implemented external to the transmission 14 in various applications. The ECM 60 and the TCM 70 may share data.

[0041] With reference to Fig. Figure 2 presents a functional block diagram of an exemplary use of the CVT system. The CVT 14 includes a transmission oil pump 104 that draws transmission oil from a reservoir 112 or other suitable transmission oil source. The transmission oil pump 104 is mechanically driven by the engine 12, such as by rotation of the crankshaft 20 or the transmission input shaft 22.

[0042] The transmission oil pump 104 transfers the transmission oil to a pressure control valve 116 via a first flow path. The transmission oil pump 104 also transfers the transmission oil to a switching valve 120 via a second flow path. When the switching valve 120 is open, the transmission oil flows from the transmission oil pump 104 through the switching valve 120 to the pressure control valve 116. In various applications, the switching valve 120 can be integrated within the transmission oil pump 104. When the switching valve 120 is closed, the second flow path is reconnected to the pump suction.

[0043] The pressure regulating valve 116 regulates the flow and / or pressure of transmission fluid to a primary pulley valve 124, a secondary pulley valve 128, and / or one or more other actuators / functions 132. The pressure regulating valve also regulates the flow and / or pressure of transmission fluid to other actuators / functions 134 via a separate flow path. The other actuators and / or functions 132 and 134 may include, for example, the torque converter 16 (e.g., clutch), forward / reverse clutches, one or more variable bleed solenoid (VBS) or variable force solenoid (VFS) valves that regulate the flow and pressure of transmission fluid to the various valves and components, cooling the CVT 14, and / or lubrication of components of the CVT 14. An output pressure of the pressure regulating valve 116 may be referred to as line pressure 122.

[0044] The primary pulley valve 124 regulates the flow (and pressure) of transmission fluid to the primary pulley actuator 34. For example, the primary pulley valve 124 may be opened to increase the flow or pressure of transmission fluid at the primary pulley actuator 34, expanding the primary pulley actuator 34. The primary pulley valve 124 may be closed to decrease the flow or pressure of transmission fluid at the primary pulley actuator 34, contracting the primary pulley actuator 34. An output pressure of the primary pulley valve 124 may be referred to as primary pulley pressure 126.

[0045] The secondary pulley valve 128 regulates the flow (and pressure) of transmission fluid to the secondary pulley actuator 36. For example, the secondary pulley valve 128 may be opened to increase the flow of transmission fluid to the secondary pulley actuator 36, expanding the secondary pulley actuator 36. The secondary pulley valve 128 may be closed to decrease the flow of transmission fluid to the secondary pulley actuator 36, contracting the secondary pulley actuator 36. An output pressure of the secondary pulley valve 128 may be referred to as secondary pulley pressure 136. Corresponding VBS or VFS valves (not shown), for example, may be used to regulate the flow / pressure of transmission fluid from the shift valve 120, the primary and secondary pulley valves 124 and 128, and the pressure regulator valve 116.

[0046] A fluid control module 150 controls the actuation of the switching valve 120, the pressure control valve 116, the primary pulley valve 124, and the secondary pulley valve 128. Generally, the fluid control module 150 actuates the switching valve 120 to one of two discrete positions at a given time: an open position; or a closed position. The fluid control module 150 causes the switching valve 120 to transition between the two discrete positions under certain circumstances.

[0047] When the switching valve 120 is in the closed position, the transmission oil pump 104 operates in partial mode (e.g., half-open). The switching valve 120 blocks the transmission oil flow of the second flow path in the closed position, so that the transmission oil pump 104 pumps transmission oil only through the first flow path to the pressure control valve 116. Because the transmission oil pump 104 is driven by the engine 12, a fuel efficiency improvement (i.e., a fuel consumption reduction) of the engine 12 (compared to full-mode operation) can be realized during partial mode operation because the transmission oil pump 104 imposes a lower torque load on the engine 12.

[0048] When the switching valve 120 is in the open position, the transmission oil pump 104 operates in full-mode operation. The switching valve 120 activates the transmission oil flow of the second flow path in the open position, so that the transmission oil pump 104 pumps transmission oil through the first and second flow paths to the pressure control valve 116.

[0049] The fluid control module 150 can cause the switching valve 120 to transition from the closed to the open position or from the open to the closed position under various circumstances. For example, only the fluid control module 150 can cause the switching valve 120 to transition from the closed to the open position when a change in the desired gear ratio between the input and output shafts 22 and 24 is greater than a predetermined value. The fluid control module 150 can cause the switching valve 120 to transition from the open to the closed position when a change in the desired gear ratio between the input and output shafts 22 and 24 is less than a predetermined value.

[0050] With reference to Fig. Figure 3 shows a functional block diagram of an exemplary transmission fluid control system. The fluid control module 150 can be implemented independently within the TCM 70 or within other suitable modules.

[0051] A desired gear ratio module 204 determines a desired gear ratio (between the input and output shafts 22 and 24), as well as a desired rate of change 208 of the desired gear ratio achieved using the primary and secondary pulley actuators 34 and 36. The desired gear ratio module 204 may determine the desired gear ratio and the desired rate of change 208 of the desired gear ratio, for example, based on an accelerator pedal position (APP) 212, a vehicle speed 216, and / or one or more other suitable parameters. The desired gear ratio module 204 may determine the desired gear ratio and the desired rate of change 208 of the desired gear ratio, for example, using one or more lookups or functions relating the APP 212 and the vehicle speed 216 to the desired gear ratio and the desired rate of change 208 of the desired gear ratio.

[0052] A target pressure module 220 determines a primary pulley target pressure 224 and a secondary pulley target pressure 228 based on the target ratio change rate 208. The primary pulley target pressure 224 corresponds to a primary pulley pressure target value 126. The secondary pulley target pressure 228 corresponds to a secondary pulley pressure target value 136. The first target pressure module 220 may determine the primary pulley target pressure 224 and the secondary pulley target pressure 228, for example, using one or more lookups or functions that relate the target ratio and / or the target ratio change rate 208 to the primary pulley target pressure 224 and the secondary pulley target pressure 228.

[0053] A primary valve control module 232 controls the opening of the primary pulley valve 124 based on the primary pulley target pressure 224. The primary valve control module 232 may, for example, control the opening of the primary pulley valve 124 in a closed-loop manner based on the difference between the primary pulley target pressure 224 and a measured or estimated value of the primary pulley pressure 126. For example, the primary valve control module 232 may open the primary pulley valve 124 while the primary pulley target pressure 224 increases, and may also do the opposite.

[0054] A secondary valve control module 236 controls the opening of the secondary pulley valve 128 based on the secondary pulley target pressure 228. The secondary valve control module 236 may, for example, control the opening of the secondary pulley valve 128 in a closed-loop manner based on the difference between the secondary pulley target pressure 228 and a measured or estimated value of the secondary pulley pressure 136. For example, the secondary valve control module 236 may open the secondary pulley valve 128 while the secondary pulley target pressure 228 increases, and may also do the opposite.

[0055] A switching valve control module 240 controls the actuation of the switching valve 120. As mentioned above, the switching valve 120 is operated in either the open or closed position. The switching valve control module 240 selectively causes the switching valve 120 to transition from the open to the closed position and from the closed to the open position.

[0056] For example, the switching valve control module 240 may cause the switching valve 120 to transition from the closed to the open position when a transition signal 244 is generated. A transition module 248 may generate the transition signal 244 to transition from the closed position to the open position, for example, when the desired ratio change rate 208 is greater than a predetermined amount and / or when one or more other predetermined conditions are met. The switching valve control module 240 may also cause the switching valve 120 to transition from the open to the closed position when the transition signal 244 is generated.The transition module 248 may also generate the transition signal 244 for transitioning from the open to the closed position, for example, when the desired rate of change 208 of the desired ratio is less than a predetermined amount and / or when one or more other predetermined conditions are met.

[0057] A control valve control module 252 controls the opening of the pressure control valve 116 based on a set desired line pressure 256. The set desired line pressure 256 corresponds to a setpoint of the line pressure 122. For example, the control valve control module 252 can open the pressure control valve 116 when the set desired line pressure 256 increases and, under certain circumstances, can also have the opposite effect.

[0058] An adjustment module 260 sets a desired line pressure 264 based on a pressure setting 268 to generate the adjusted desired line pressure 256. For example, the adjustment module 260 may adjust the adjusted desired line pressure 256 equal to or based on a sum or product of (a) the desired line pressure 264 and (b) the pressure setting 268.

[0059] A second desired pressure module 272 determines the desired line pressure 264. For example, the second desired pressure module 272 may receive one or more desired line pressure requests 276 and set the desired line pressure 264 equal to or based on a largest (maximum) of the desired line pressure requests 276. Desired line pressure requests may be generated for various reasons and for various actuators. For example, a desired line pressure request may be generated to achieve the desired gear ratio, to control the torque converter clutch, or for lubrication and / or cooling.

[0060] A setting determination module 280 determines the pressure setting 268. The setting determination module 280 may set the pressure setting 268 to a predetermined value when the transition signal 244 is not generated. The setting module 260 sets the set desired line pressure 256 equal to the desired line pressure 264 when the pressure setting 268 is set to the predetermined value. For example, in the example of the setting module 260 setting the set desired line pressure 256 equal to a sum of the desired line pressure 264 and the pressure setting 268, the predetermined value may be 0.0. In the example of the setting module 260 setting the set desired line pressure 256 equal to a product of the desired line pressure 264 and the pressure setting 268, the predetermined value may be 1.0.

[0061] When the transition signal 244 is generated, the setting determination module 280 determines the pressure setting 268 based on a maximum target pressure 284. More specifically, when the transition signal 244 is generated and a state signal 288 is in a first state, the setting determination module 280 determines the pressure setting 268 based on the maximum target pressure 284 using a first lookup table. The first lookup table establishes the relationship between the respective maximum target pressure and the pressure settings. When the transition signal 244 is generated and the state signal 288 is in a second state, the setting determination module 280 determines the pressure setting 268 based on the maximum target pressure 284 using a second lookup table. The second lookup table establishes the relationship between the respective maximum target pressure and the pressure settings.

[0062] The pressure settings of the second table of values ​​may be greater than the pressure settings of the first table of values ​​corresponding to the respective predetermined maximum target pressure. Thus, for a given maximum target pressure 284, the pressure setting 268 may be greater when the status signal 288 is in the second state than when the status signal 288 is in the first state.

[0063] A maximum module 292 determines a maximum target pressure 284 based on the primary pulley target pressure 224, the secondary pulley target pressure 228, and the target line pressure 264. For example, the maximum module 292 may set the maximum target pressure 284 equal to or based on the largest (maximum) of the primary pulley target pressure 224, the secondary pulley target pressure 228, and the target line pressure 264.

[0064] A state module 296 generates the state signal 288. The state module 296 sets the state signal 288 to the first state when the transmission oil pump 104 is delivering (via the pressure regulating valve 116) a maximum amount of transmission oil for lubrication under the current operating conditions (e.g., above 134). In this state, the line pressure regulating valve 116 also directs excess flow back to the transmission oil pump 104. The state module 296 may set the state signal 288 to the second state when the pressure regulating valve 116 is limiting (i.e., providing less than the maximum) flow for lubrication under the current operating conditions. In this case, the pressure regulating valve 116 does not direct excess flow back to the transmission oil sump 112.While the example of two states based on whether the maximum amount of fluid is delivered occurs in different implementations, there can be multiple states for situations between the extremes.

[0065] The current operating conditions may, for example, be an indicator 308 of whether the switching valve 120 is in the open or closed position, or an indicator of a speed 312 of the transmission oil pump 104 and / or one or more other operating conditions. In the case that the transmission oil pump 104 is a variable displacement pump that switches between two effective displacements, the current operating conditions may also include a displacement of the transmission oil pump 104. The maximum pressure module 304 may determine the maximum line pressure 300, for example, using one or more functions and / or value tables that establish the relationship between the current operating conditions and the respective maximum line pressure.

[0066] As mentioned above, the switching valve control module 240 causes the switching valve 120 to transition from the closed to the open position or from the open to the closed position when the transition signal 244 is generated. The switching valve control module 240 determines a speed at which the switching valve 120 transitions from the closed to the open position or from the open to the closed position 284 based on the maximum target pressure. More specifically, when the transition signal 244 is generated and the state signal 288 is in the first state, the switching valve control module 240 determines the speed at which the transition of the switching valve 120 occurs based on the maximum target pressure 284 using a third lookup table. The third lookup table relates the respective maximum target pressure to the transition speeds.In various implementations, a third lookup table may be used to transition from closed to open positions and another third lookup table may be used to transition from open to closed positions. When the transition signal 244 is generated and the state signal 288 is in the second state, the switching valve control module 240 determines the speed at which the transition of the switching valve 120 occurs based on the maximum target pressure 284 using a fourth lookup table. The fourth lookup table relates the respective maximum target pressure to the transition speeds. In various implementations, a fourth lookup table may be used to transition from closed to open positions and another fourth lookup table may be used to transition from open to closed positions.

[0067] The transition rates of the fourth set of values ​​may be greater than the transition rates of the third set of values ​​corresponding to the respective predetermined maximum set pressure. Thus, for a given maximum set pressure 284, the transition rate used to cause the switching valve 120 to transition from the closed to the open position or from the open to the closed position may be greater (faster) when the state signal 288 is in the second state than when the state signal 288 is in the first state.

[0068] By increasing the desired line pressure 264 based on the pressure setting 268 and / or controlling the transition speed of the shift valve 120, changes (e.g., decreases) in the line pressure 122, the primary pulley pressure 126, and / or the secondary pulley pressure 136 due to the transition can be minimized. This can minimize or prevent slippage of the belt or chain 38, and minimize or prevent changes in the gear ratio achieved by the primary and secondary pulley actuators 34 and 36.

[0069] With reference to Fig. 4, a flowchart illustrating an exemplary method for controlling valves of the CVT 14 to transition the shift valve 120 from the closed to the open position or from the open to the closed position is shown. Control begins at 404 when the shift valve 120 is in either the closed or open position.

[0070] At 404, the second target pressure module 272 determines the target line pressure 264, while the target ratio module 204 determines the target ratio and the target rate of change 208 of the target ratio. The first target pressure module 220 determines the primary and secondary pulley target pressures 224 and 228 based on the target ratio and the target rate of change 208 of the target ratio. The state module 296 sets the state signal to either the first state or the second state at 404. The maximum module 292 also determines the maximum target pressure 284 at 404.

[0071] At 408, the transition module 248 determines whether the switching valve 120 should transition from the closed to the open position or from the open to the closed position. If 408 is false, the transition module 248 does not generate a transition signal 244, and control continues at 410. The switching valve control module 240 maintains the switching valve 120 in the closed or open position at 410. The setting determination module 280 may therefore set the pressure setting 268 equal to the predetermined value so that the set desired line pressure 256 is set equal to the desired line pressure 264.The control valve control module 252 controls the pressure control valve 116 based on the set desired line pressure 256, the primary valve control module 232 controls the primary pulley valve 124 based on the primary pulley pressure 224, and the secondary valve control module 236 controls the secondary pulley valve 128 based on the secondary pulley pressure 228. If 408 is true, the transition module 248 generates the transition signal 244, and control continues at 412. The transition module 248 may continue to generate the transition signal 244 until the switching valve 120 reaches the open or closed position.

[0072] The switching valve control module 240 and the setting determination module 280 determine whether the state signal 288 is in the first state at 412. If 412 is true, control continues to 416. The switching valve control module 240 determines the transition speed for transitioning the switching valve 120 from the closed to the open position or from the open to the closed position using the third lookup table based on the maximum target pressure 284 at 416. The setting determination module 280 determines the pressure setting 268 using the first lookup table based on the maximum target pressure 284 at 416. Control then continues to 424.

[0073] If 412 proves to be false, control continues to 420. The switching valve control module 240 determines the transition speed for transitioning the switching valve 120 from the closed to the open position or from the open to the closed position using the fourth lookup table based on the maximum target pressure 284 at 420. The setting determination module 280 determines the pressure setting 268 using the second lookup table based on the maximum target pressure 284 at 420. Control then continues to 424.

[0074] At 424, the adjustment module 260 increases the desired line pressure 264 based on the pressure setting 268 to create the set desired line pressure 256. At 428, the regulator valve control module 252 controls the pressure regulator valve 116 based on the set desired line pressure 256. The switching valve control module 240 causes the switching valve 120 to transition to the open or closed position at the transition rate at 428. Additionally, the primary valve control module 232 controls the primary pulley valve 124 based on the primary pulley pressure 224, while the secondary valve control module 236 controls the secondary pulley valve 128 based on the secondary pulley pressure 228.

[0075] The pressure setting 268, the maximum target pressure 284, the transition speed, the primary pulley target pressure 224, the secondary pulley target pressure 228 and the target ratio, the target rate of change 208 of the target ratio, the target line pressure 264, and / or one or more other parameters may be updated / determined on one or more occasions while the switching valve control module 240 is causing the switching valve 120 to transition from the closed to the open position or from the open to the closed position. The pressure regulating valve 116, the primary pulley valve 124, the secondary pulley valve 128 may be adjusted accordingly in one or more occasions while the switching valve control module 240 is causing the transition of the switching valve 120. Control exits after 428 or 410, as appropriate. While the example of Fig.4 represents the completion of the process, control can return to 404.

Claims

[1] A transmission fluid control method for a vehicle, comprising: selectively actuating a shift valve (120) of a continuously variable transmission (CVT) (14) either: (i) from a closed to an open position; or (ii) from the open to the closed position, wherein the switching valve (120), when the switching valve (120) is in the closed position, prevents a transmission oil from flowing through a flow path between a transmission oil pump (104) and a pressure control valve (116) of the CVT (14); and redirects the transmission oil flow back into the transmission oil pump (104) and wherein the switching valve (120) allows transmission oil to flow through the flow path when the switching valve (120) is in the open position; determining a pressure setting (268) when the switching valve (120) (i) transitions from the closed to the open position; or (ii) from the open to the closed position; determining a desired line pressure (264) by a second desired pressure module (272); determining a set target pressure (256) based on the pressure setting (268) and the target line pressure (264); and controlling the opening of the pressure control valve (116) based on the set target pressure (256). [2] The transmission fluid control method of claim 1, wherein the transmission oil pump (104) further pumps transmission oil to the pressure regulating valve (116) via a second flow path (i) both when the switching valve (120) is in the open position and (ii) when the switching valve (120) is in the closed position. [3] The transmission fluid control method of claim 1, wherein determining the set desired pressure (256) includes setting the set desired pressure (256) based on one of the following: (i) a product of the desired line pressure (264) and the pressure setting (268); and (ii) a sum of the desired line pressure (264) and the pressure setting (268). [4] The transmission fluid control method of claim 1, wherein: determining the pressure setting (268) includes setting the pressure setting (268) to a predetermined value when the switching valve (120) is held in the closed position and when the switching valve (120) is held in the open position; and determining the set target pressure (256) includes setting the set target pressure (256) equal to the target line pressure (264) when the pressure setting (268) equals the predetermined value. [5] The transmission fluid control method of claim 4, wherein determining the pressure setting (268) includes setting the pressure setting (268) to a value greater than the predetermined value when the switching valve (120) transitions (i) from the closed to the open position; or (ii) from the open to the closed position. [6] A transmission fluid control method according to claim 1, comprising: determining a first desired pressure (224) of the transmission oil applied to a first pulley actuator (34); determining a second target pressure (228) of the transmission oil applied to a second pulley actuator (36), wherein the first pulley actuator (34) is coupled to a drive shaft (22) of the CVT (14) and expands and contracts based on a first pressure of the transmission oil applied to the first pulley actuator (34), wherein the second pulley actuator (36) is coupled to an output shaft (24) of the CVT (14) and expands and contracts based on a second pressure of the transmission oil applied to the second pulley actuator (36); and wherein either (i) a belt or (ii) a chain (38) surrounds the first and second pulley actuators (34, 36); and wherein determining the pressure setting (268) includes determining the pressure setting (268) based on a respective greater first or second desired pressure. [7] The transmission fluid control method of claim 6, wherein determining the first and second desired pressures includes determining the first and second desired pressures based on a desired ratio of rotation of the input shaft (22) to rotation of the output shaft (24). [8] A transmission fluid control method according to claim 7, wherein the switching valve (120) is actuated, comprising: actuating the switching valve (120) from the closed to the open position when a desired rate of change of the desired gear ratio is greater than a first predetermined value; and actuating the switching valve (120) from the open to the closed position when the desired rate of change of the desired gear ratio is less than a second predetermined value. [9] The transmission fluid control method of claim 6, further comprising: determining a transition speed based on the greater of the first target pressure, the second target pressure, and the target line pressure (264); and, actuating, based on the transition speed, the switching valve (120) (i) from the closed to the open position or (ii) from the open to the closed position. [10] The transmission fluid control method of claim 6, further comprising: controlling the opening of a first valve (124) based on the first desired pressure, the first valve receiving transmission oil from the pressure regulating valve (116) and regulating the transmission oil flow to the first pulley actuator (34); and controlling the opening of a second valve (128) based on the second desired pressure, the second valve receiving transmission oil from the pressure regulating valve (116) and regulating the transmission oil flow to the second pulley actuator (36).

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