METHOD FOR CONTROLLING A GEARBOX CLUTCH AND GEARBOX WITH A GEARBOX CLUTCH

Abstract

Methods for controlling a transmission clutch, comprising: Guiding fluid at a controlled pressure to an application chamber (106) of the coupling; as a response to reducing a clutch slip speed at a constant rate, reducing the controlled pressure; and as a reaction to reducing the rate of reduction of the clutch slip speed, increasing the controlled pressure.

Description

TECHNICAL FIELD

[0001] This disclosure relates to a method for controlling an automatic transmission clutch and a transmission with an automatic transmission clutch. In particular, the disclosure relates to a method for controlling a starting clutch during an inertia phase of a shift to improve shift quality at the end of the shift, and to a transmission with a controller implementing the method. GENERAL STATE OF THE ART

[0002] Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse motion. However, some engine types are only capable of operating efficiently within a narrow speed range. Consequently, transmissions capable of efficiently transferring power at a wide range of speed ratios are widely used. A transmission speed ratio is the ratio of an input shaft speed to an output shaft speed. When the vehicle is traveling at low speeds, the transmission is typically operated at a high speed ratio so that it multiplies the engine torque for improved acceleration. At high vehicle speeds, operating the transmission at a low speed ratio allows an engine speed consistent with smooth, fuel-efficient driving.

[0003] Many automatic transmissions employ a discrete number of different gear ratios, with each ratio established by the engagement of a specific subset of clutches. A clutch that selectively holds a gear member against rotation may be referred to as a brake. Some clutches may be actively controlled, such as by hydraulic actuation. Other clutches may be passive devices, such as one-way clutches. To shift from one speed ratio to another, one clutch is engaged and another clutch is disengaged. The process of shifting from one speed ratio to another can produce torque disturbances in the transmission output. If these torque disturbances are excessive, they may be unpleasant to vehicle occupants.

[0004] DE 10 2014 204 106 A1 discloses a method for controlling a transmission clutch, comprising: calculating an open-loop pressure command based on a clutch slip speed such that the open-loop pressure command decreases as the slip speed decreases; calculating a closed-loop pressure command based on input shaft acceleration, input shaft speed, or slip speed; and commanding a clutch application pressure corresponding to a sum of the open-loop pressure command and the closed-loop pressure command.

[0005] According to DE 690 18 418 T2, the slip for an engaging clutch is controlled during an inertia phase of an upshift. SUMMARY OF REVELATION

[0006] An example method for controlling a transmission includes calculating an open-loop and closed-loop pressure command and commanding a clutch application pressure equal to the sum of the open-loop and closed-loop pressure commands. The calculating and commanding may occur during an upshift inertia phase for which the clutch is an on-going element. The open-loop pressure command is calculated based on a clutch slip speed such that the open-loop pressure command decreases as the slip speed decreases. The open-loop pressure command may also be based on transmission input torque. The closed-loop pressure command is calculated based on a rate of change of the clutch slip speed.For example, slip speed can be calculated using output data and turbine shaft speed sensors.

[0007] A method of controlling a transmission clutch according to the invention is shown in claim 1. Accordingly, the method includes directing fluid at a controlled pressure to a clutch apply chamber and adjusting the controlled pressure in response to a clutch slip speed. The controlled pressure may be a sum of an open-loop term and a closed-loop term. In response to decreasing a clutch speed at a constant rate, the controlled pressure is reduced. This may occur, for example, because the open-loop term decreases as clutch slip decreases. In response to decreasing a rate of decrease in clutch speed, the controlled pressure is increased. This may occur, for example, as a result of increasing the closed-loop term.

[0008] A transmission according to the invention is described in claim 7. Accordingly, the transmission includes a clutch, a valve body, and a controller. The valve body directs fluid at a controlled pressure to an application chamber of the clutch. The controller reduces the controlled pressure in response to a clutch slip speed decreasing at a constant rate. The controller increases the controlled pressure in response to a clutch speed decreasing rate.

[0009] Advantageous further developments of the invention are described in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic representation of a vehicle powertrain suitable for use with the disclosed method. Fig.2 is a schematic representation of an exemplary transmission gear assembly suitable for use with the disclosed method. Fig. 3 is a cross-sectional view of a transmission clutch in a fully open position. Fig. Figure 4 is a diagram of commanded clutch pressures during a synchronous upshift. Fig. Figure 5 is a diagram of clutch slip speeds during a synchronous upshift. Fig. Figure 6 is a diagram showing an example calibration function for an open loop print command. Fig. 7 is a flowchart illustrating the disclosed method. DETAILED DESCRIPTION

[0010] A drive train of a vehicle 10 is in Fig.1 is illustrated schematically. Solid lines indicate mechanical connections. Dashed lines indicate the flow of signals. Double lines indicate the flow of fluid. An engine 12 provides power to rotate a crankshaft 14. A transmission 16 transfers power from the crankshaft 14 to a driveshaft 18, while potentially modifying the speed and torque to better match the vehicle's current requirements. A differential 20 distributes power to a left wheel 22 and a right wheel 24, while allowing slight speed differences between the wheels, such as when the vehicle is cornering.

[0011] The transmission 16 includes a torque converter 24 and a gear case 26. The torque converter transfers power from the crankshaft 14 to a turbine shaft 28. The gear case 26 transfers power from the turbine shaft 28 to the input shaft 18. A controller 30 sends signals to a valve body 32, causing the valve body 32 to send pressurized fluid to clutches in the transmission case 26. The gear ratio of the transmission case 26 depends on which subset of clutches are supplied with pressurized fluid. The controller 30 uses many inputs to determine what commands to send to the valve body 32, including signals from an output speed sensor 34 and a turbine speed sensor 36.

[0012] An example gearbox is shown in Fig.2 is schematically illustrated. The proposed method can be applied to a wide variety of gearbox arrangements. The gearbox utilizes four simple planetary gear sets 40, 50, 60, and 70. The sun gear 42 is fixedly connected to the sun gear 52, the carrier 44 is fixedly connected to the ring gear 76, the ring gear 56 is fixedly connected to the sun gear 62 via the shaft 80, the ring gear 66 is fixedly connected to the sun gear 72, the turbine shaft 28 is fixedly connected to the carrier 54, and the input shaft 18 is fixedly connected to the carrier 74. The ring gear 46 is selectively held against rotation by the brake 88, and the sun gears 42 and 52 are selectively held against rotation by the brake 90. The turbine shaft 28 is selectively coupled to the ring gear 66 and the sun gear 72 by the clutch 92.The intermediate member 82 is selectively coupled to the carrier 64 by the clutch 94, selectively coupled to the carrier 44 and the ring gear 76 by the clutch 96, and selectively coupled to the shaft 80 by the clutch 98.

[0013] As shown in Table 1, by engaging the clutches and brakes in combinations of four each, ten forward speed ratios and one reverse speed ratio are established between the turbine shaft 28 and the drive shaft 18. An X indicates that the corresponding clutch is engaged to establish the speed ratio. TABLE 1 88 90 92 94 96 98 Relationship Step Back X X X X -4,79 102 % 1. X X X X 4,70 2. X X X X 2,99 1,57 3. X X X X 2,18 1,37 4. X X X X 1,80 1,21 5. X X X X 1,54 1,17 6. X X X X 1,29 1,19 7. X X X X 1,00 1,29 8. X X X X 0,85 1,17 9. X X X X 0,69 1,24 10. X X X X 0,64 1,08

[0014] All single-stage and two-stage shifts are accomplished by gradually engaging one clutch, called an on-coming element, while gradually releasing another clutch, called an off-going element. During each of these shifts, three clutches, called holding elements, are held fully engaged while one element is held fully disengaged. In other transmission arrangements, the number of holding elements may vary.

[0015] Fig. 3 shows a cross section of the coupling 98. The coupling housing 82, the intermediate element in Fig.2, is supported to rotate around the shaft 80, which in turn is supported to rotate around the turbine shaft 28. A set of separator plates 100 are splined to the housing 82 such that they rotate with the housing 82 but are free to slide axially. A lock washer 102 restricts axial movement to the right. A set of friction plates 104 are splined to the shaft 80 and interdigitated with the separator plates 100. The friction plates and separator plates may collectively be referred to as a clutch pack. When pressurized hydraulic fluid is directed to the application chamber 106, the piston 108 slides axially with respect to the housing 82. After the piston 108 moves into contact with the clutch plate, the force pushes the friction plates and separator plates together. Friction between the friction plates and separator plates transmits torque between the housing 82 and the shaft 80.The maximum amount of torque that can be transmitted at a given moment is referred to as the torque capacity of the clutch. When the pressure in the apply chamber 106 is released, the return spring 110 urges the piston 108 away from the clutch pack to disengage the clutch. As the clutch housing 82 rotates, centrifugal forces tend to increase the pressure of the fluid in the apply chamber 106, which tends to engage the clutch. To prevent inadvertent disengagement, non-pressurized fluid is directed into the balance chamber 112. The centrifugal force pressurizes the fluid in the balance chamber, thus counteracting the force created by the centrifugal force in the apply chamber.

[0016] The controller 30 regulates the current (or pulse width) to a solenoid in the valve body 32 such that the pressure in a particular channel within the valve body is regulated to a commanded pressure. The fluid then flows from the valve body to the application chamber through passage 114. Passage 114 extends through the stationary front support 116, through the turbine shaft 28, through the shaft 80, and into the housing 82. Since these components rotate at different speeds, seals 118 are used to direct the fluid from one component to another. Similarly, the unpressurized fluid is directed through passage 120 to the balance chamber 112.

[0017] The torque capacity of the clutch at any point in time can be given by the following formula: T=2∗(A∗(PApplication−PAdjustment)−F0)∗N∗μ∗r where A is the area of ​​the piston at the application and release chambers, P Anwendung the fluid pressure in the application chamber 106 is P Ausgleich is the fluid pressure in the compensation chamber 112, F0 is the force of the return spring, N is the number of friction plates, µ is the friction coefficient between the friction plates and the separator plates, and r is the mean radius of the friction plates. P Anwendung and P Ausgleichare set by the controller 30. A, N, and r are constant geometric properties. F0 does not vary substantially. The friction coefficient µ is subject to variation based on a number of factors, some of which are impractical to predict. For example, the inventors have observed that µ can sometimes vary with respect to the clutch slip speed (the difference between the rotational speeds of the shaft 80 and the housing 82). In particular, the inventors have observed that µ sometimes increases as the slip speed decreases. The fact that this does not occur in all cases makes compensation for this variation particularly challenging.

[0018] Fig.Figure 4 illustrates commanded pressure profiles for the oncoming clutch (ONC) and off-going clutch (OFG) during a synchronous upshift. (An upshift is synchronous when the off-going clutch is actively controlled and asynchronous when the off-going clutch is a one-way clutch.) Fig. Figure 5 illustrates the slip speed across the two clutches.

[0019] After the shift schedule algorithm or a driver command indicates that an upshift should be performed, the controller raises the on-coming clutch during a preparation phase. At 130, the pressure to the on-coming clutch is increased to a boost level for a boost duration. The purpose of the boost duration is to move the clutch piston from the disengaged position to the raised position as quickly as possible. The boost duration is generally selected such that the boost phase ends just before the piston is raised. At 132, a holding pressure is then commanded. At 134, the commanded pressure is then gradually increased to gently move the piston to the fully raised position. The slip across the on-coming clutch is based on the initial gear ratio and does not change during the preparation phase, as at 136 in Fig.5. The preparation phase ends when the oncoming clutch piston is fully raised at 138. During this time, the commanded pressure for the offgoing clutch can be reduced, as shown at 140, such that the torque capacity nearly matches the torque actually transmitted by the offgoing clutch. Because the offgoing clutch remains fully engaged during the preparation phase, slip across the offgoing clutch is zero. Throughout the entire preparation period, neither the torque ratio nor the speed ratio changes.

[0020] Once the preparation phase is complete, the torque transfer phase is executed by gradually reducing the commanded pressure to the off-going clutch, as shown at 142, and gradually increasing the commanded pressure to the on-coming clutch, as shown at 144. During this phase, the torque ratio gradually decreases to the upshifted value. Ideally, the speed ratio and slip remain constant across each clutch, although it may increase if the off-going clutch is disengaged too quickly compared to the rate at which the on-going clutch is engaged. Once the torque capacity of the off-going clutch reaches zero at 146, the inertia phase begins.

[0021] During the inertia phase, the on-coming clutch serves to slow the input, gradually reducing the transmission speed ratio to the upshifted value. The on-coming clutch pressure is set at 148 to create a torque capacity slightly greater than required to transmit turbine torque. The excess capacity serves to reduce the speed of the turbine (and indirectly the engine crankshaft) at 150. The inertia phase ends at 152 when the on-coming clutch no longer slips. At this point, the speed ratio equals the speed ratio of the upshifted gear. Once the clutch no longer slips, the transmitted torque drops to the level required to transmit turbine torque.The pressure can be further increased to provide a greater margin between the torque capacity and the transmitted torque to prevent the clutch from being allowed to slip again.

[0022] If the friction coefficient µ increases as the clutch slip speed decreases, the clutch torque capacity will also increase, even though a constant application pressure is commanded throughout the majority of the inertia phase. This will cause the rate of change of the slip speed to increase, as shown by the dotted lines at 154. In this scenario, the output torque increases during the final phase of the inertia phase and then abruptly decreases as the inertia phase ends. The resulting sudden change in output torque can be uncomfortable for vehicle occupants and may trigger audible vibrations in the driveline.

[0023] The use of feedback control is useful in addressing unpredictable noise factors. For example, the controller can adjust the pressure to maintain a target rate of change in slip speed during the inertia phase. A feedback control algorithm can calculate the commanded application pressure as a sum of an open-loop term and a closed-loop term. The open-loop term (sometimes referred to as a feedforward term) is a prediction of the pressure needed to achieve the desired rate of change in slip speed, neglecting unpredictable noise factors. The closed-loop term uses a measured signal to compensate for noise factors. An error signal is calculated, which corresponds to a difference between a desired rate of change in slip speed and the measured rate of change in slip speed.The closed-loop term may include subterms proportional to this error signal (a P subterm), proportional to a derivative of the error signal (a D subterm), and proportional to an integral of the error signal (an I subterm). The inventors found that when µ increases late in the inertia phase, the closed-loop term does not respond quickly enough to prevent degradation of shift quality.

[0024] The inventors have determined that it is preferable to decrease the open loop term as the slip speed decreases. Fig.Figure 6 shows example plots of the open-loop pressure term as a function of clutch slip speed. Plot 160 represents the open-loop term at low input torque, plot 162 represents the open-loop term at moderate input torque, and plot 164 represents the open-loop term at high input torque. The controller can interpolate between these plots for other values ​​of input torque. The data in Fig. 6 can be represented in the control system as a lookup table. During gear shifts, where µ increases, the rate of change of the slip speed remains constant, as shown by line 150 in Fig.5. During shifts where µ remains constant, the rate of change of slip speed decreases, as shown at 156. This lengthens the inertia phase, allowing the closed-loop term time to compensate by increasing the pressure command.

[0025] Fig.Figure 7 is a flowchart illustrating the control of the on-coming clutch. The procedure is executed at regular intervals throughout the inertia phase. At 170, the controller calculates the clutch slip. This may be achieved using two speed sensors, such as an output and turbine speed sensor, and known speed relationships among transmission elements. At 172, the controller calculates the open-loop term based on the input torque and the clutch slip. At 174, the controller calculates a rate of change of the slip speed. This may be accomplished by comparing the slip speeds calculated at previous time intervals. Then, at 176, the controller calculates an error term by subtracting the calculated rate of change of the slip speed from a target slip speed.At 178, the controller calculates the closed-loop pressure command term based on the error term and the P, D, and I subterms, as discussed above. At 180, the pressure command is calculated by summing the open-loop and closed-loop terms calculated at 172 and 178. Finally, at 182, a command is issued to the valve body to implement this pressure.

Claims

[1] A method for controlling a transmission clutch, comprising: Directing fluid at a controlled pressure to an application chamber (106) of the clutch; in response to reducing a clutch slip speed at a constant rate, reducing the controlled pressure; and in response to decreasing a rate of reduction of the clutch slip speed, increasing the controlled pressure. [2] The method of claim 1, further comprising calculating the controlled pressure as a sum of an open loop term and a closed loop term. [3] The method of claim 2, wherein the open loop term decreases as the clutch slip speed decreases, causing the reduction of the controlled pressure in response to the clutch slip speed decreasing at a constant rate. [4] The method of claim 3, wherein the open loop term is further based on a transmission input torque. [5] The method of claim 2, wherein the closed loop term is based on a difference between the rate of decrease in clutch slip speed and a target rate of decrease in clutch slip speed, causing the increase in the controlled pressure in response to the decrease in the rate of decrease in clutch slip speed. [6] The method of claim 1, wherein the transmission clutch is a starting clutch for a transmission upshift and the reducing and increasing occur during an inertia phase of the transmission upshift. [7] Transmission, comprising: a transmission clutch; a valve body (32); and a controller (30), wherein the valve body (32) directs fluid at a controlled pressure to an application chamber (106) of the clutch; the controller (30) reduces the controlled pressure in response to a clutch slip speed decreasing at a constant rate; and the controller (30) increases the controlled pressure in response to the rate of reduction of the clutch slip speed decreasing. [8] The transmission of claim 7, further comprising two speed sensors, wherein the controller (30) calculates the clutch slip speed based on data from the two speed sensors. [9] The transmission of claim 8, wherein the two speed sensors comprise an output speed sensor (34) and a turbine speed sensor (36). [10] A transmission according to claim 7, wherein the transmission clutch is a starting clutch for a transmission upshift and the reducing and increasing take place during an inertia phase of the transmission upshift.

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