Method for controlling a powertrain system

Abstract

To reduce fuel consumption, when the vehicle is stopped in drive mode, the transmission is shifted to a neutral state, referred to as neutral idle. During the transition from the neutral idle state to the engaged state, the engine torque is controlled to avoid excessive shift energy and mitigate acceleration drops. In particular, the engine torque is set to a level equal to the sum of the transmission torque capacity and an offset, the offset being a function of the accelerator pedal position. The transmission torque capacity is calculated based on the engaged shift element torque capacity and the torque ratio associated with the kinematics and the torque converter. To accommodate noise factors, such as changes over time, the offset function is adapted in response to measured clutch energy and acceleration drops.

Description

Technical Field

[0001] The present disclosure relates to the field of control systems for vehicles having automatic transmissions. More particularly, the present disclosure relates to a control strategy for controlling an engine when transitioning from a neutral idle state to a drive state. Background Art

[0002] Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse motion. However, some types of engines can only operate efficiently within a narrow range of speeds. Therefore, a transmission that can effectively transfer power at a variety of gear ratios is often used. When the vehicle is at low speeds, the transmission is usually operated at a high gear ratio so that the transmission multiplies the engine torque to improve acceleration. At high vehicle speeds, operating the transmission at a low gear ratio allows engine speeds associated with quiet, fuel-efficient cruising. Typically, the transmission has a housing that is mounted to the vehicle structure; an input shaft that is driven by the engine crankshaft; and an output shaft that drives the wheels, usually via a differential assembly that 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 a variety of 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. Shifting 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 delivering fluid to the shift element under a controlled pressure. A controller adjusts the pressure by sending an electrical signal to a valve body. Summary of the invention

[0004] A method for controlling a vehicle powertrain system includes disengaging a shift element to place a transmission in a neutral idle state, thereby commanding the torque capacity of the shift element to increase to transition back to an engaged state. The rate of increase of the torque capacity of the shift element can be based on the accelerator pedal position. The transition to the neutral idle state occurs in response to the vehicle being stopped in a drive mode. The transition back to the engaged state occurs in response to the release of the brake pedal. During the transition to the engaged state, the engine torque is commanded to be equal to the sum of the transmission torque capacity and an offset, wherein the offset is a function of the accelerator pedal position. The torque capacity can be calculated by multiplying the torque capacity of the shift element by the torque multiplication ratio of the torque converter and also by the torque ratio between the shift element and the turbine shaft.

[0005] The method may also include adapting the offset for future neutral idle events. In particular, in response to the clutch energy during the transition exceeding a threshold, the offset may be reduced such that a lower engine torque is commanded during a subsequent transition from a neutral state to an engaged state at the same accelerator pedal position. In response to the clutch energy during the transition not exceeding a threshold, the offset may be increased such that a higher engine torque is commanded during a subsequent transition from a neutral state to an engaged state at the same accelerator pedal position. The amount of the increase may be proportional to the acceleration drop during the transition. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a schematic diagram of the vehicle powertrain.

[0007] Figure 2 is a schematic diagram of a planetary transmission gearbox.

[0008] Figure 3 is a flow chart illustrating a method of transitioning from a neutral idle state to an engaged state.

[0009] Figure 4 It shows the adaptation Figure 3 A flowchart of the method for the functions used in the method. DETAILED DESCRIPTION

[0010] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are only examples, and other embodiments may take multiple and alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show the details of specific components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as being restrictive, but only as a representative basis for teaching those skilled in the art to adopt the present invention in various ways. As will be understood by those of ordinary skill in the art, the various features shown and described with reference to any one of the accompanying drawings may be combined with the features shown in one or more other drawings to produce embodiments that are not explicitly shown or described. The combination of the features shown provides a representative embodiment of a typical application. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be desirable for specific applications or implementations.

[0011] Figure 1An example vehicle powertrain is schematically shown in FIG. Mechanical power flow is indicated by thick solid lines. Thin solid lines indicate fluid flow. Dashed lines indicate information signal flow. Power is provided by an internal combustion engine 10 that drives a transmission input shaft 12. The transmission includes a torque converter 14 and a gearbox 16. The torque converter 14 includes a pump wheel fixed to the transmission input shaft 12 and a turbine fixed to a turbine shaft 18. When the transmission input shaft 12 rotates faster than the turbine shaft 18, the torque converter applies positive torque to the turbine shaft 18 and negative torque to the shaft 12, thereby resisting engine rotation. When the shaft 12 rotates significantly faster than the shaft 18, the torque converter multiplies the torque so that the torque applied to the turbine shaft 18 is higher than the torque generated by the engine. The torque converter 14 also includes a lock-up clutch that transmits torque without relative rotational speed.

[0012] The gearbox 16 provides various gear ratios and torque multiplication factors between the turbine shaft 18 and the transmission output shaft 20. The transmission output shaft 20 is typically drivably connected to the wheels via a fixed ratio final reduction gear and a differential. The gearbox 16 selectively establishes at least one neutral state, at least one reverse gear ratio, and a plurality of forward gear ratios. The gearbox 16 includes a plurality of shifting elements, such as brakes and clutches, which are engaged to establish a power flow path associated with the reverse gear ratio and the forward gear ratio.

[0013] A pump 22 driven by the engine draws fluid from an oil pan 24 and delivers the fluid under high pressure to a valve body 26. In response to a signal from a controller 28, the valve body delivers pressurized fluid to the lockup clutch of the torque converter and the apply chambers of the shift elements within the gearbox 16. The controller 28 controls the torque capacity of the shift elements by varying the command pressure of the fluid delivered to the respective apply chambers. The controller 28 also sends a signal to the engine 10 to adjust the torque supplied to the transmission input shaft 12. The controller 28 utilizes signals from a plurality of sensors, including an accelerator pedal sensor 30, a brake pedal sensor 32, and a gear selector 34 operated by the driver.

[0014] Figure 2An example transmission gearbox 16 is exemplarily shown in FIG. By selectively engaging a designated subset of shift elements, the gearbox establishes ten forward speed ratios and one reverse speed ratio between the turbine shaft 18 and the output shaft 20. The transmission utilizes four simple planetary gear sets 40, 50, 60 and 70. Sun gear 46 is fixedly coupled to sun gear 56, carrier 42 is fixedly coupled to ring gear 78, ring gear 58 is fixedly coupled to sun gear 66, ring gear 68 is fixedly coupled to sun gear 76, turbine shaft 18 is fixedly coupled to carrier 52, and output shaft 20 is fixedly coupled to carrier 72. Ring gear 48 is selectively held against rotation via brake 80, and sun gears 46 and 56 are selectively held against rotation via brake 82. Turbine shaft 18 is selectively coupled to ring gear 68 and sun gear 76 via clutch 84. Intermediate shaft 36 is selectively coupled to carrier 62 via clutch 86, selectively coupled to carrier 42 and ring gear 78 via clutch 88, and selectively coupled to ring gear 58 and sun gear 66 via clutch 90. Recommended gear ratios for each planetary gear set are listed in Table 1.

[0015] Table 1

[0016] Ring gear 48 / center gear 46 2.20 Ring gear 58 / center gear 56 1.75 Ring gear 68 / center gear 66 1.60 Ring gear 78 / center gear 76 3.70

[0017] As shown in Table 2, engaging the clutches and brakes in four combinations establishes ten forward gear ratios and one reverse gear ratio between the turbine shaft 18 and the output shaft 20. An X indicates that a shift element is required to establish the gear ratio. (X) indicates that a shift element can be applied, but the shift element is not required to establish the power flow path. In 1st gear, instead of applying clutch 86, clutch 88 or clutch 90 can be applied without changing the gear ratio, or only brakes 80 and 82 and clutch 84 can be engaged. When the gear sets have the number of teeth shown in Table 1, the gear ratios have the values ​​shown in Table 2. The neutral state is established by engaging fewer shift elements than are required to establish the power flow path.

[0018] Table 2

[0019]

[0020] When the vehicle is stationary with the drive mode selected via the gear selector 34 and the brake pedal 32 depressed, the controller commands the engine 10 to produce sufficient torque to maintain the engine at a predetermined idle speed. The engine torque required to maintain the idle speed depends on the speed of the transmission input shaft 12 and the turbine shaft 18. In this case, since the driver does not want wheel torque, the controller can disengage the shift element to put the gearbox in a neutral state. For example, if the gearbox is in 1st gear when the vehicle slows to a stop, the controller can disengage one of the shift elements 80, 82 or 84 to put the gearbox in a neutral state. With the gearbox 16 in a neutral state, the turbine shaft 18 will accelerate to the same speed as the transmission input shaft 12, so that the torque converter 14 does not resist the rotation of the transmission input shaft 12. This reduces the load on the engine, thereby reducing fuel consumption.

[0021] When the driver releases the brake pedal 32 or presses the accelerator pedal 30, the controller reengages the shift element to reestablish the power flow path for 1st gear. The controller does this by commanding a gradual increase in pressure to the shift element apply chamber to gradually increase the torque capacity. As the torque capacity of the shift element increases, the speed of the turbine shaft 18 decreases, causing the torque converter 14 to once again transfer torque from the transmission input shaft 12 to the turbine shaft 18 and multiply the torque.

[0022] When the driver depresses the accelerator pedal 30, the controller 28 typically commands the engine 10 to produce a torque level as a function of the position of the accelerator pedal 30. This torque level is referred to as the driver command torque. The driver command torque may also be a function of other parameters, such as the speed of the transmission input shaft 12 and / or the speed of the transmission output shaft 20. However, if the driver depresses the accelerator pedal 30 before fully reestablishing the power flow path for 1st gear, the driver may wish to command a torque that is less than the driver command torque.

[0023] During the transition from neutral to 1st gear, the elements selectively coupled by the shift element rotate relative to each other. Heat is generated at the friction interface at a rate proportional to the shift element torque capacity and the relative speed. If the controller transitions from idle control to driver command control of engine torque during this transition, the engine speed will increase. The increase in engine speed tends to increase turbine speed and turbine torque. This increases the rate of heat generation in the upcoming shift element and increases the duration of the transition, thereby significantly increasing the total amount of heat that must be absorbed by the shift element. In some cases, the heat may exceed the ability of the shift element to store and dissipate the heat, causing the shift element to overheat.

[0024] On the other hand, setting the engine torque level too low during the transition period can also be problematic. If the engine torque is too low, the turbine will slow down as the engagement is completed. In this case, most of the input torque to the gearbox is actually due to the inertia of the turbine, rather than to the power transferred from the engine. After engagement, the turbine speed will be proportional to the increasing vehicle speed, so the effect of the turbine inertia on the gearbox input torque will disappear (and actually become slightly negative). This can cause a sudden drop in vehicle acceleration. Higher engine torque just before engagement avoids this situation by keeping the turbine at a constant or slightly increasing speed just before engagement is completed.

[0025] Figure 3 A process for controlling a powertrain system during a transition from a neutral idle state to a normal drive state is shown. The process begins in a neutral idle state 100. In the neutral idle state, the drive mode is selected using the gear selector 34, the brake pedal 32 is depressed, and the vehicle is stationary. In the neutral idle state, the controller controls the engine to maintain a predetermined target idle speed. A shift element required to establish a 1st gear power flow path is disengaged. This shift element is called a neutral idle (NI) clutch. The pressure in the application chamber of the NI clutch can be set to keep the stroke of the piston at a minimum torque capacity.

[0026] The process transitions out of the neutral idle state 100 in response to the release of the brake pedal. During the transition, the controller tracks how much energy is being dissipated into the NI clutch. This is initiated at 102. At 104, the command pressure of the apply chamber of the NI clutch is incremented. The size of the increment is greater than the size of the increment when the accelerator pedal is further depressed, resulting in a faster reengagement. At 106, the controller utilizes shaft 12 (N 泵轮 ) and 18(N 涡轮 ) measured speed and a table to estimate the torque converter torque ratio (k). At 108, the controller estimates the torque capacity of the NI clutch based on the command pressure from 104. At 110, the controller increments the NI clutch energy to account for the energy dissipated since the last cycle. At 112, the controller increments the T NI The transmission clutch (T capacity) is calculated by multiplying the torque ratio between the NI clutch and the turbine by , k, and any torque ratio between the NI clutch and the turbine. At 114, the controller looks up an offset in a table based on the accelerator pedal position. For low levels of accelerator pedal depression, the offset may be negative. For higher levels of accelerator pedal depression, the offset will generally increase. At 116, the controller commands the engine to produce a torque equal to the transmission torque capacity (i.e., T 容量) and the torque of the sum of the offset. At 118, the controller measures and records the acceleration of the output shaft and the pedal position. The acceleration can be measured, for example, by derivatizing the output shaft speed measurement or by directly reading the accelerometer. These measurements will be used in the adaptation steps described later. At 120, the controller checks whether the slip across the entire NI clutch is close to zero (within a threshold of about 5rpm). If it is not zero, the process is repeated starting from 104. Once the slip approaches zero at 120, the controller executes the adaptation function described below at 122 and proceeds to the normal driving state 124. In the normal driving state, the transmitter torque command is based on the normal driver demand function.

[0027] Figure 4 The process performed at 122 to adapt the offset function is shown. At 130, the controller uses Figure 3 The controller uses the value recorded in step 118 to calculate the average accelerator pedal position during the previous transition. At 132, the controller uses the value recorded in step 118 to calculate the average accelerator pedal position during the previous transition. Figure 3 The acceleration drop in the previous transition can be calculated based on the values ​​recorded in step 118. The acceleration drop can be calculated as follows. The peak acceleration value can be determined by taking the maximum value of the acceleration values ​​recorded within a certain time interval near the end of the transition (such as between 0.15 seconds before the end of the transition and 0.1 seconds after the end of the transition). The acceleration drop can be determined by taking the difference between the peak acceleration value and the minimum acceleration value between the peak time and the end of the interval. At 134, based on the acceleration drop and the acceleration drop in the previous transition, the acceleration drop can be calculated based on the acceleration drop and the acceleration drop in the previous transition. Figure 3 The correction factor is calculated based on the clutch energy associated with the previous transition calculated in step 110. The formula for calculating the correction factor includes two predetermined positive coefficients k 1 and k 2 The two predetermined positive coefficients determine the magnitude of the adjustment based on the acceleration drop and the clutch energy, respectively. The first term in the formula increases the offset for future events based on the acceleration drop, which tends to reduce the acceleration drop. The second term decreases the offset whenever the clutch energy exceeds the threshold, which tends to reduce the clutch energy in future events. If the acceleration drop and clutch energy are based on k 1 , k 2 and E 阈值 The selected values ​​are substantially in equilibrium, then the correction coefficient is close to zero. At 136, the table representing the offset function is updated. Various methods are known for updating the function represented by the table. For example, only the tabulated values ​​closest to Pos may be updated, or the tabulated values ​​on either side of Pos may be updated, or other values ​​close to Pos may also be updated in small amounts.

[0028] The result of the adaptation is a gradual modification of the offset function so that the commanded engine torque during the transition from neutral idle appropriately balances the acceleration drop with the clutch energy at each different accelerator pedal position. In particular, if the clutch energy is less than the target E 阈值 , then the commanded engine torque during the subsequent transition is higher. The rate of increase within a series of transitions is based on the magnitude of the acceleration drop. If the clutch energy substantially exceeds E 阈值 , then the commanded engine torque in the subsequent transition will be lower.

[0029] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms expected 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 other embodiments of the present invention that may not be explicitly described or illustrated. Although various embodiments may have been described as providing advantages or being more preferred than other embodiments or prior art implementations relative to one or more desired characteristics, a person of ordinary skill in the art recognizes that, in order to achieve the desired overall system properties, one or more features or characteristics may be compromised, depending on the specific application and implementation. Therefore, embodiments described as being less ideal than other embodiments or prior art implementations relative to one or more characteristics are within the scope of the present disclosure and may be desirable for specific applications.

[0030] According to the present invention, a method for controlling a vehicle powertrain system is provided, the method comprising: disengaging a shift element in response to the vehicle being stopped in a drive mode to place the transmission in a neutral state; commanding the torque capacity of the shift element to increase to transition from the neutral state to the engaged state in response to the release of a brake pedal or the depression of an accelerator pedal; and during the transition from the neutral state to the engaged state, commanding the engine torque to be equal to the sum of the transmission torque capacity and an offset, wherein the offset is a function of the accelerator pedal position.

[0031] According to an embodiment, the above method is further characterized in that the transmission torque capacity is calculated by multiplying the torque capacity of the shift element by the torque multiplication ratio of the torque converter.

[0032] According to an embodiment, the above method is further characterized in that calculating the transmission torque capacity further comprises multiplying a torque ratio between the shift element and the turbine shaft.

[0033] According to an embodiment, the rate at which the torque capacity of the shift element is increased during the transition is based on the accelerator pedal position.

[0034] According to an embodiment, the above method is further characterized by reducing the offset in response to the clutch energy during the transition exceeding the threshold value so that during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position, a lower engine torque is commanded.

[0035] According to an embodiment, the above method is further characterized by: in response to the clutch energy during the transition not exceeding the threshold, increasing the offset so that during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position, a higher engine torque is commanded.

[0036] According to an embodiment, the offset is increased by an amount proportional to the drop in acceleration during the transition.

[0037] According to the present invention, a powertrain control method is provided, the method comprising: when a drive mode is selected, transitioning from a neutral state to an engaged state by increasing the torque capacity of a shift element; and during the transition, commanding the engine torque to be equal to the sum of the transmission torque capacity and an offset, wherein the transmission torque capacity is a function of the torque capacity of the shift element, and the offset is a function of the accelerator pedal position.

[0038] According to an embodiment, the rate at which the shift element torque capacity is increased during the transition is based on the accelerator pedal position.

[0039] According to an embodiment, the above method is further characterized by reducing the offset in response to the clutch energy during the transition exceeding the threshold value so that during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position, a lower engine torque is commanded.

[0040] According to an embodiment, the above method is further characterized by: in response to the clutch energy during the transition not exceeding the threshold, increasing the offset so that during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position, a higher engine torque is commanded.

[0041] According to an embodiment, the offset is increased by an amount proportional to the drop in acceleration during the transition.

[0042] According to the present invention, a powertrain system is provided, the powertrain system having: an engine; a transmission; and a controller, the controller being programmed to shift the transmission from a neutral state to an engaged state by increasing the torque capacity of a shifting element to increase the transmission torque capacity, and during the shift, commanding the engine torque to be equal to the sum of the transmission torque capacity and an offset, wherein the offset is a function of an accelerator pedal position.

[0043] According to an embodiment, the controller is programmed to increase the torque capacity of the shift element at a certain ratio based on the accelerator pedal position during a gear shift.

[0044] According to an embodiment, the controller is further programmed to: in response to the clutch energy during the shift exceeding the threshold, command a lower engine torque during a subsequent shift from the neutral state to the engaged state at the same accelerator pedal position.

[0045] According to an embodiment, the controller is further programmed to: command a higher engine torque during a subsequent shift from a neutral state to an engaged state at the same accelerator pedal position in response to the clutch energy during the shift not exceeding a threshold.

[0046] According to an embodiment, the difference between the commanded engine torque during the subsequent gear shift and the commanded engine torque during the gear shift is proportional to the acceleration drop during the gear shift.

Claims

1. A method for controlling a vehicle powertrain system, the method comprising: disengaging the shift element to place the transmission in a neutral state in response to the vehicle being stopped in the drive mode; commanding an increase in torque capacity of the shift element to transition from the neutral state to an engaged state in response to a release of a brake pedal or depression of an accelerator pedal; as well as During a transition from the neutral state to the engaged state, an engine torque is commanded equal to a sum of a transmission torque capacity and an offset, wherein the offset is a function of an accelerator pedal position. 2 . The method of claim 1 , further comprising calculating the transmission torque capacity by multiplying the torque capacity of the shift element by a torque converter torque multiplication ratio. 3 . The method of claim 2 , wherein calculating the transmission torque capacity further comprises multiplying a torque ratio between the shift element and a turbine shaft. 4 . The method of claim 1 , wherein the rate at which the torque capacity of the shift element increases during the transition is based on the accelerator pedal position.

5. The method of claim 1, further comprising: In response to the clutch energy during the transition exceeding a threshold, the offset is reduced such that a lower engine torque is commanded during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position.

6. The method of claim 5, further comprising: In response to the clutch energy during the transition not exceeding the threshold, the offset is increased such that a higher engine torque is commanded during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position.

7. The method of claim 6, wherein the offset is increased by an amount proportional to the drop in acceleration during the transition.

8. A power transmission system control method, the method comprising: When a drive mode is selected, the shifting state is transitioned from the neutral state to the engaged state by increasing the torque capacity of the shift element; as well as During the transition, the commanded engine torque is equal to the sum of the transmission torque capacity and an offset, wherein the transmission torque capacity is a function of the shift element torque capacity and the offset is a function of the accelerator pedal position.

9. The power transmission system control method according to claim 8, further comprising: In response to the clutch energy during the transition exceeding a threshold, the offset is reduced such that a lower engine torque is commanded during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position.

10. The power transmission system control method according to claim 8, further comprising: In response to the clutch energy during the transition not exceeding a threshold, the offset is increased such that a higher engine torque is commanded during a subsequent transition from the neutral state to the engaged state at the same accelerator pedal position. 11 . The powertrain control method of claim 10 , wherein the offset amount is increased by an amount proportional to the acceleration drop during the transition period.

12. A power transmission system, comprising: engine; transmission; as well as A controller that is programmed to: shifting the transmission from a neutral state to an engaged state by increasing the torque capacity of a shift element to increase the transmission torque capacity, and During a gear shift, the engine torque is commanded to be equal to the sum of the transmission torque capacity and an offset, wherein the offset is a function of the accelerator pedal position.

13. The powertrain system of claim 12 wherein the controller is further programmed to: in response to clutch energy during the shift exceeding a threshold, command a lower engine torque during a subsequent shift from the neutral state to the engaged state at the same accelerator pedal position.

14. The powertrain system of claim 12 wherein the controller is further programmed to: in response to clutch energy during the shift not exceeding a threshold, command a higher engine torque during a subsequent shift from the neutral state to the engaged state at the same accelerator pedal position.

15. The powertrain system of claim 14, wherein the difference between the commanded engine torque during the subsequent gear shift and the commanded engine torque during the gear shift is proportional to the acceleration drop during the gear shift.

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