Transmission Engagement Control System

Abstract

The present invention discloses a transmission engagement control system. The transmission parking mechanism is hydraulically actuated. Specifically, the controller releases the parking pawl by controlling the engagement of a specific shift element under increased line pressure. The process of converting from the parking gear state to the forward gear or reverse gear state may include multiple sequential steps. In order to reduce the delay between the forward gear or reverse gear selected by the driver and the completion of the engagement, it is beneficial to increase the line pressure in response to the depression of the brake pedal before the shift lever moves. In order to limit the negative impact of the increased line pressure on fuel economy, if the driver does not move the shift lever immediately after the brake pedal is depressed, the line pressure is reduced again.

Description

Technical Field

[0001] The present disclosure relates to the field of control systems for motor vehicle automatic transmissions. In particular, the present disclosure relates to improving control strategies for engaging a forward gear or a reverse gear from a parking state. Background Art

[0002] Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse motion. However, certain types of engines can only operate efficiently over a narrow speed range. Therefore, a transmission that can effectively transfer power at multiple gear ratios is often used. When the vehicle speed is low, the transmission is usually operated at a high gear ratio, so that the engine torque is multiplied to improve acceleration. When the vehicle speed is high, running the transmission at a low gear ratio associates the engine speed with quiet, fuel-efficient cruising. Typically, the transmission has a housing mounted to the vehicle structure, an input shaft driven by the engine crankshaft, and an output shaft that drives the wheels, usually via a differential assembly, which allows the left and right wheels to rotate at slightly different speeds when the vehicle turns.

[0003] Discrete ratio transmissions are capable of transmitting power via multiple power flow paths, each associated with a different gear ratio. A specific power flow path is established by engaging a specific shift element, such as a clutch or brake. The transition from one gear ratio to another involves a change in the engaged shift element. In many transmissions, the torque capacity of each shift element is controlled by directing fluid to the shift element at a controlled pressure. A controller regulates the pressure by sending an electrical signal to a valve body.

[0004] When the vehicle is parked, the transmission may engage a park pawl that holds the transmission shaft stationary to prevent the vehicle from rolling away. The parking system is designed to remain engaged during extended unattended periods without consuming any energy. Typically, the park pawl engages in response to the driver selecting park and disengages in response to the driver selecting any other range such as reverse, neutral, drive, or low. However, there are some situations where the transmission may override the driver's selection. Summary of the invention

[0005] A transmission includes a parking pawl, a hydraulic control system, a pump, and a controller. The parking pawl is engageable to hold an output shaft stationary. The hydraulic control system includes a line pressure circuit. The hydraulic system may also include multiple clutch application circuits. To establish a gear ratio, the controller allows fluid to flow from the line pressure circuit to a first subset of the clutch application circuits. To release the parking pawl, the controller pressurizes a second subset of the clutch application circuits. The pump supplies pressurized fluid to the line pressure circuit. The controller is configured to increase pressure in the line pressure circuit in response to a brake pedal being depressed when the parking pawl is engaged to reduce the time required to engage the gear ratio. If the brake pedal is depressed for a period of time greater than a threshold while the shift lever is held in the park position or in response to the release of the brake pedal, the controller may reduce pressure in the line pressure circuit.

[0006] According to one embodiment of the present disclosure, the controller is further configured to reduce the pressure in the line pressure circuit in response to the release of the brake pedal.

[0007] According to one embodiment of the present disclosure, the controller is further configured to: inhibit increasing the line pressure in response to detecting a clutch fault.

[0008] A vehicle includes a parking mechanism, a transmission pump, and a controller. The parking mechanism selectively holds the vehicle stationary. The transmission pump supplies pressurized fluid to a line pressure circuit and selectively to a plurality of clutch application circuits. To engage a gear ratio, the controller engages a first subset of the shift elements by fluidly connecting a corresponding clutch application circuit to the line pressure circuit. To release the parking mechanism, the controller engages a second subset of the shift elements by fluidly connecting a corresponding clutch application circuit to the line pressure circuit. The controller is configured to increase pressure in the line pressure circuit in response to a brake pedal being depressed while the parking mechanism is engaged to reduce a time required to engage a transmission gear ratio. The controller may reduce pressure in the line pressure circuit if the brake pedal is depressed for a time greater than a threshold or if the brake pedal is released.

[0009] According to one embodiment of the present disclosure, the controller is further configured to: inhibit increasing the line pressure in response to detecting a clutch fault.

[0010] A method of controlling a transmission includes: controlling pressure in a line pressure circuit to a first level with the transmission in a park position and a brake pedal released; and then, in response to depression of the brake pedal, increasing the pressure to a second level. If the brake pedal remains depressed for a period greater than a threshold time with the transmission in a park position, the pressure may be reduced to the first level. In response to a shift lever moving from a park position, a first shift element engages to release a park pawl. Then, at least one shift element, which may include the first shift element, may be released. Then, a second shift element may engage to establish a power flow path from a transmission input shaft to a transmission output shaft. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the transmission system.

[0012] Figure 2 Is applicable to Figure 1 A schematic diagram of the transmission gear transmission device of the gearbox of a transmission system.

[0013] Figure 3 yes Figure 1 Schematic diagram of the parking subsystem of the transmission's hydraulic control system.

[0014] Figure 4 Is used for operation Figure 1 Flowchart of the transmission. DETAILED DESCRIPTION

[0015] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and other embodiments may take various alternative forms. The drawings need not be drawn to scale; some features may be exaggerated or reduced to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as being restrictive, but merely as a representative basis for teaching those skilled in the art to utilize the present invention in a variety of ways. It will be understood by those of ordinary skill in the art that the various features shown and described with reference to any of the figures may be combined with the features shown in one or more other figures to produce embodiments that are not explicitly shown or described. The combination of features shown provides representative embodiments for typical applications. However, various combinations and variations of features consistent with the teachings of the present disclosure may be expected for specific applications or implementations.

[0016] Figure 1A vehicle transmission is schematically shown. The thick solid line represents a mechanical power flow connection. The thin solid line represents the flow of hydraulic fluid. The dotted line represents the flow of information signals. The power is usually supplied from the crankshaft of the internal combustion engine at the input shaft 10. The fluid coupling 12 includes a pump wheel drivably connected to the input shaft 10 and a turbine drivably connected to the turbine shaft 14. Whenever the pump wheel rotates faster than the turbine, power is transmitted from the pump wheel to the turbine through the moving fluid. The fluid coupling 12 can be a torque converter that also includes a guide wheel, which redirects the fluid when the pump wheel rotates substantially faster than the turbine, so that the turbine torque is several times the pump wheel torque. The gearbox 16 includes gear transmission elements and shift elements configured to establish various power flow paths between the turbine shaft 14 and the output 18. The output 18 is preferably drivably connected to the vehicle drive wheel via a differential that allows a slight speed difference when the vehicle turns. Each power flow path can be established by engaging a related subset of the shift elements. At low vehicle speeds, a power flow path providing torque multiplication and speed reduction between the turbine shaft and the output shaft can be established to optimize vehicle performance. At high vehicle speeds, a power flow path providing speed multiplication can be established to minimize fuel consumption.

[0017] The shift elements within the gearbox 16 are engaged by supplying hydraulic fluid to the clutch application chamber at an elevated pressure. Each shift element may include a clutch pack that interleaves friction plates splined to one component with release plates splined to a different component. The fluid forces the piston to squeeze the clutch pack so that the friction between the friction plates and the release plates combines the components. The torque capacity of each shift element varies in proportion to the change in fluid pressure. The pump 20 is driven by the input shaft 10, draws fluid from the oil pan 22 and delivers it to the valve body 24 at an elevated pressure (referred to as line pressure). In some transmission hydraulic control systems, there may be multiple hydraulic circuits that transport pressurized fluid from the pump to other circuits. For example, some transmissions may have a separate hydraulic circuit that also delivers fluid from an electric pump or accumulator to a subset of other circuits when the engine is not running to drive the main pump. In this article, any circuit that delivers fluid from a main pressure source at an adjusted input pressure is referred to as a line pressure circuit. The valve body 24 delivers fluid to the clutch application chamber at a pressure controlled by a signal from a powertrain controller 26. The powertrain controller 26 utilizes a plurality of input signals including signals from an accelerator pedal 28, a brake pedal 30, and a shift lever 32. The shift lever 32 allows the driver to select among at least park, reverse, neutral, and drive operating modes. In addition to providing fluid to the clutch apply chamber, the valve body also provides fluid for lubrication and provides fluid to the torque converter 12. The fluid ultimately drains from the gearbox 18 back to the sump 22 at ambient pressure.

[0018] Figure 2An exemplary transmission is schematically shown in FIG. The transmission utilizes two simple planetary gear sets 40 and 50 and a stepped pinion gear set 60. The simple planetary gear set 40 includes a gear carrier 42 supporting a plurality of planetary gears 44. The planetary gears 44 mesh with a ring gear 46 and a sun gear 48. The simple planetary gear set 50 includes a gear carrier 52 supporting a plurality of planetary gears 54. The planetary gears 54 mesh with a ring gear 56 and a sun gear 58. The stepped pinion gear set 60 includes a gear carrier 62 supporting a plurality of stepped planetary gears 64. One set of teeth of each stepped planetary gear 64 meshes with a ring gear 66 and a sun gear 68. Another set of teeth of each stepped planetary gear 64 meshes with a sun gear 70.

[0019] Sun gear 58 is fixedly coupled to turbine shaft 14. Carrier 42 and ring gear 66 are fixedly coupled to output shaft 18. Carrier 52 is fixedly coupled to ring gear 46. Carrier 62 and ring gear 56 are fixedly coupled to each other and selectively coupled to turbine shaft 14 via clutch 72. Sun gear 68 is selectively coupled to turbine shaft 14 via clutch 74 and selectively held against rotation by brake 76. Sun gear 70 is selectively held against rotation by brake 78. Sun gear 48 is selectively held against rotation by brake 80. One-way clutch 82 passively holds carrier 62 against rotation in one direction. One-way clutch 84 holds carrier 62 against rotation in the other direction when brake 86 is engaged. One-way clutch 82 and one-way clutch 84 and brake 86 may be implemented as selectable one-way clutches that always prevent rotation in one direction and prevent rotation in the other direction when activated.

[0020] Table 1 lists the recommended pitch diameter ratios for each planetary gear set.

[0021] Table 1

[0022] Ring gear 46 / sun gear 48 2.24 Ring gear 56 / sun gear 58 2.24 Ring gear 66 / sun gear 68 2.96 Ring gear 66 / sun gear 70 1.61

[0023] As shown in Table 2, engaging the clutch and brake in two combinations establishes eight forward speed ratios and one reverse speed ratio between the turbine shaft 14 and the output 18. X indicates that the clutch is required to establish the speed ratio. When the gear set has a pitch diameter ratio as shown in Table 1, the speed ratio has the value indicated in Table 2.

[0024] Table 2

[0025] 72 74 76 78 80 82 / 84 / 86 ratio Step Reverse gear X X -2.96 1st gear X X 4.69 2nd Gear X X 3.30 1.42 3rd Gear X X 3.01 1.10 4th Gear X X 1.92 1.57 5th Gear X X 1.45 1.33 6th Gear X X 1.00 1.45 Gear 7 X X 0.75 1.34 8th Gear X X 0.62 1.21

[0026] The park mechanism 88 selectively couples the output 18 to the transmission housing to prevent vehicle movement when the vehicle is parked. The park mechanism 88 is designed to remain engaged once engaged without requiring any external power.

[0027] Figure 3 The parking control subsystem of the hydraulic control system is schematically shown. The valve core of the parking valve 100 is mechanically connected to the parking mechanism 88 so that movement in one direction engages the parking mechanism and movement in the other direction disengages the parking mechanism. The spring inside the parking mechanism biases the system toward engagement. The hydraulic control system includes a line pressure circuit 102 that supplies pressurized fluid to other hydraulic circuits in the hydraulic control system. The fluid pressure in the line pressure circuit 102 is controlled using a regulating valve and in some cases by controlling the displacement of the pump. The line pressure biases the parking valve toward the parking position. The hydraulic control system also includes a group of clutch application circuits that are directed to the application chamber of each hydraulically controlled shift element. The fluid pressure in the clutch application circuit is controlled to a level between zero and the pressure in the line pressure circuit 102. These clutch application circuits include circuits 104 and circuits 106 that engage the shift element 76 and the shift element 78, respectively. Park valve 100 fluidly connects exit-park circuit 108 to line pressure circuit 102 when park is disengaged and exhausts exit-park circuit 108 when park is engaged. Hydraulic circuits 110 and 112 bias the park valve toward the disengaged position. Check valve 114 fluidly connects circuit 110 to the clutch 76 application circuit 104 or the exit-park circuit 108, whichever has a higher pressure. Similarly, check valve 116 fluidly connects circuit 112 to the clutch 78 application circuit 106 or the exit-park circuit 108, whichever has a higher pressure.

[0028] When the parking mechanism is engaged, the parking mechanism itself and the line pressure tend to hold the parking valve 100 in the engaged position. To disengage the parking mechanism, brake 76 and brake 78 are engaged by controlling the pressure to be equal to the line pressure of the application circuits 104 and 106. Check valve 144 and check valve 116 fluidly connect these clutch application circuits to circuit 110 and circuit 112, respectively. The pressure in circuit 110 and circuit 112 forces the parking valve into the disengaged position. Once in the disengaged position, the parking valve 100 will exit the parking circuit 108 fluidly connected to the line pressure circuit 102. As a result, the parking valve tends to remain in the disengaged position even if brakes 76 and brakes 78 are released. To reengage the parking mechanism, the pressure in the line pressure circuit 102 is reduced to a level at which the parking mechanism spring forces the parking valve to the engaged position.

[0029] Using a shift element to disengage the parking mechanism adds a step to the process of shifting from park to either drive or reverse. If this shift takes too long, the driver will be dissatisfied. Therefore, it is beneficial to minimize the time between the shift lever movement and the disengagement of the parking mechanism.

[0030] Figures 1 to 3 A method of controlling a transmission Figure 4 . The method begins in response to starting the engine with the shift lever in the park position, and at step 120, in preparation for disengagement from the park position, the controller may command the engagement of brakes 78 and 86. Since both brakes 76 and 78 must be engaged when the parking mechanism is released, engaging one of the brakes in advance reduces the time required for the driver to move the shift lever out of the park position. If the shift lever is moved to reverse, brake 86 will need to be engaged, and if the shift lever is moved to forward gear or neutral, brake 86 can be engaged, so the early engagement potentially reduces the number of steps that must be completed after the shift lever is moved. If a selected one-way clutch is utilized, it is important to ensure that the gear carrier 62 is stationary when the selectable one-way clutch is engaged. The engagement of brakes 78 and the parking mechanism ensures that the gear carrier 62 is stationary. Engaging only brakes 78 and brakes 86 does not limit the speed of the turbine shaft 14. Allowing the turbine shaft 14 to rotate at the same speed as the engine reduces engine torque and fuel consumption. At step 122, the controller 26 commands a relatively low line pressure (P_low) to minimize the torque required to drive the pump. The torque required to drive the pump at idle can significantly affect fuel economy. The controller enters state 124 while waiting for the driver to shift out of park.

[0031] The interlock mechanism prevents the driver from shifting out of the park gear until the brake pedal is depressed. Typically, the driver does not depress the brake pedal until they intend to shift from the park gear. Therefore, depressing the brake pedal while in the park gear is a strong indication that the driver will immediately shift from the park gear, but not a guarantee. Releasing the parking mechanism will require both engaging the clutch 76 and increasing the line pressure. In anticipation of an imminent shift from the park gear, at step 126, the controller 26 increases the line pressure (P_high) in response to the depression of the brake pedal. In this case, because the brake 76 has not yet been commanded to engage, increasing the line pressure does not cause the release of the parking mechanism. Although fuel consumption increases due to increased line pressure, it only increases for a short period of time. At step 128, a countdown timer is started that lasts about 10 seconds. If the timer expires before the driver moves the shift lever out of the park gear, the line pressure returns to a low level associated with the idle speed of the park gear. If the controller is operating in a fault mitigation mode due to a clutch fault being detected, the controller may return to state 124 without increasing the line pressure at step 125. In the event of a clutch failure, particularly if the failure occurs in an engaged state, increasing line pressure may place the transmission in an unsafe condition. If the brake pedal is released, then at step 128, the controller sets a countdown timer for approximately 1 to 2 seconds. In this manner, if the brake pedal is depressed and then quickly released, the target line pressure increases in a short period of time. In an alternative embodiment, control may instead proceed directly to step 122 in response to a brake release event.

[0032] In response to the movement of the shift lever out of the park gear, at step 130, the controller 26 commands the brake 76 to engage. If the line pressure returns to a low level, it increases again at step 132. After the clutch application circuit is connected to the line pressure circuit, fluid flows into the clutch application chamber. The pressure in the clutch application circuit may not increase to the commanded line pressure level until the clutch piston has travel. In fact, the pressure in the line pressure circuit may drop briefly when filling the clutch application chamber. When the initial line pressure is high, the delay between the command engagement and the increase in clutch application pressure is smaller. Once the pressure in the circuit 104 and the circuit 106 reaches a sufficient level, the parking mechanism will release. At step 134, the controller waits for the parking mechanism to release. Once the parking mechanism release is detected, at step 136, the brake 76 and the brake 78 are disengaged. Also at step 136, the target line pressure changes to a suitable value (P_shift) for the controlled engagement of the forward gear or reverse gear ratio, which may be lower than the value required to disengage the parking mechanism. If the shift lever is moved from park to drive, as determined at step 138, then at step 140 the brake 80 is subsequently engaged to establish a first gear power flow path and the controller moves to a drive state 142. If the shift lever is moved from park to reverse, as determined at step 144, then at step 146 the clutch 74 is engaged to establish a reverse power flow path and the controller moves to a reverse state 148. Establishing one of these power flow paths includes slowing the turbine shaft 14 to nearly a standstill. Changing turbine speed too quickly can create an unpleasant experience for vehicle occupants, so it is important to engage these shift elements in a controlled manner. If the shift lever is moved from park to neutral, the controller moves to a neutral state 150.

[0033] Alternative embodiments may differ from the embodiments described above. Specifically, while the embodiments described above release the parking mechanism in response to the engagement of two shift elements with an increased pressure, other embodiments may release the parking mechanism in response to the engagement of only one shift element or in response to the engagement of more than two shift elements. Although the embodiments described above establish a first gear power flow path and a reverse gear power flow path by engaging two shift elements, other embodiments may require less than two or more than two shift elements to establish these power flow paths. In the described embodiments, the subset of shift elements required to establish the first gear power flow path does not intersect with the subset of shift elements used to separate the parking mechanism. Similarly, the subset of shift elements required to establish the reverse gear power flow path does not intersect with the subset of shift elements used to separate the parking mechanism. In other embodiments, there may be an intersection of these subsets.

[0034] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments can be combined to form further embodiments of the present invention that may not be explicitly described or shown. Although various embodiments have been described as providing advantages over other embodiments or prior art implementations or being superior to other embodiments or prior art implementations for one or more desired characteristics, it will be appreciated by those of ordinary skill in the art that one or more features or characteristics can be compromised to achieve the desired overall system properties, depending on the specific application and implementation. Thus, embodiments described as being less desirable than other embodiments or prior art implementations in one or more characteristics are not outside the scope of the present disclosure and can be expected to be used for specific applications.

Claims

1. A transmission, comprising: a parking pawl that can be engaged to hold the output shaft stationary; A hydraulic control system having a line pressure circuit; a pump configured to supply pressurized fluid to the line pressure circuit; and A controller is configured to increase pressure in the line pressure circuit in response to depression of the brake pedal when the parking pawl is engaged to engage one of the shift elements for releasing the parking pawl before releasing the parking pawl, thereby reducing a time required to engage a gear ratio.

2. The transmission according to claim 1, wherein: The hydraulic control system further includes a plurality of clutch apply circuits, and wherein engaging the gear ratio includes allowing fluid to flow from the line pressure circuit to a first subset of the clutch apply circuits.

3. The transmission according to claim 2, wherein: The hydraulic control system is configured to release the park pawl in response to fluid pressure in a second subset of the clutch apply circuits.

4. The transmission according to claim 1, wherein: The controller is further configured to reduce pressure in the line pressure circuit if the brake pedal is depressed for greater than a threshold time while the shift lever is held in the park position.

5. A vehicle comprising: a parking mechanism configured to selectively hold the vehicle stationary; a transmission pump configured to supply pressurized fluid to a line pressure circuit; as well as A controller is configured to, in response to depression of the brake pedal while the parking mechanism is engaged, increase pressure in the line pressure circuit to engage one of the shift elements for releasing the parking mechanism before releasing the parking mechanism, thereby reducing a time required to engage a transmission gear ratio.

6. The vehicle of claim 5, further comprising a plurality of shift elements, and wherein: Engaging the transmission gear ratio includes engaging a first subset of the plurality of shift elements.

7. The vehicle according to claim 6, wherein: Engaging the transmission gear ratio further includes engaging a second subset of the plurality of shift elements to release the park mechanism.

8. The vehicle according to claim 5, wherein: The controller is further configured to reduce pressure in the line pressure circuit if the brake pedal is depressed for greater than a threshold time while the shift lever is held in the park position.

9. The vehicle according to claim 5, wherein: The controller is also configured to reduce pressure in the line pressure circuit in response to a release of the brake pedal.

10. A method for controlling a transmission, comprising: controlling the pressure in the line pressure circuit to a first pressure level when the transmission is in park by engagement of the parking pawl and the brake pedal is released; as well as In response to depression of the brake pedal with the transmission in a park gear, pressure in the line pressure circuit is increased to a second pressure level to engage a first of the shift elements for releasing the parking pawl before releasing the parking pawl.

11. The method according to claim 10, further comprising: In response to a brake pedal being depressed for a threshold time with the transmission in park, pressure in the line pressure circuit is reduced to the first pressure level.

12. The method according to claim 10, further comprising: In response to the shift lever being moved from the park position, a second one of the shift elements for releasing the parking pawl is engaged to release the parking pawl in the transmission.

13. The method according to claim 12, further comprising: After releasing the park pawl, a third shift element is engaged to establish a power flow path between the transmission input shaft and the transmission output shaft.

14. The method according to claim 13, further comprising: After releasing the parking pawl and before engaging the third shift element, the line pressure is reduced and at least one of the first shift element and the second shift element is released.

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