Vehicle control device

Abstract

To suppress a clutch of an automatic transmission from being burnt.SOLUTION: A vehicular control apparatus includes an automatic transmission for selecting a shift position by switching a clutch between an engaged state and a released state by hydraulic pressure, and switching between an output transmission state for transmitting an engine output to a drive wheel and an output shutoff state for shutting off a transmission of the engine output to the drive wheel. Further, the apparatus includes: a shift position determination part for determining a shift position of a shift operation part; a counter part for measuring an elapsed time from a start of the engine; and a torque limit part for limiting torque to be generated by the engine in a case where the shift position determination part determines that the shift position is in an output shutoff range in which the automatic transmission is in an output shutoff state, with the elapsed time measured by the counter part being shorter than a predetermined torque-limiting period.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a vehicle control device. [Background technology]

[0002] Conventionally, automatic transmissions equipped with multiple clutches and brakes have been used as part of a vehicle's power transmission mechanism. Automatic transmissions switch between a power transmission state in which engine power is transmitted to the drive wheels and a power interruption state in which engine power is interrupted from the drive wheels by combining the engaged and disengaged states of the clutch and the engaged and disengaged states of the brake. Furthermore, automatic transmissions achieve a desired gear position in the power transmission state by combining the engaged and disengaged states of the clutch and the engaged and disengaged states of the brake. In such automatic transmissions, the clutch engages when a piston moves when the hydraulic pressure in a hydraulic chamber increases. Therefore, automatic transmissions sometimes have a canceller chamber adjacent to the hydraulic chamber across the piston to prevent the clutch from unintentionally engaging due to centrifugal hydraulic pressure generated by high-speed rotation of oil remaining in the hydraulic chamber. The hydraulic pressure in the canceller chamber increases when filled with oil, thereby canceling out the centrifugal hydraulic pressure generated in the clutch's hydraulic chamber and preventing the clutch from unintentionally engaging. An automatic transmission equipped with such a canceller chamber is disclosed in Patent Document 1, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-211685 Summary of the Invention [Problem to be solved by the invention]

[0004] When the shift lever is in the neutral or parking position, clutch slippage is normally avoided even if the accelerator pedal is depressed during racing. This is because the automatic transmission is controlled to an output-shutoff state, and the centrifugal hydraulic pressure generated in the hydraulic chamber is offset by the hydraulic pressure in the canceller chamber, maintaining the clutch in a disengaged state. However, if the time since engine start is short and the canceller chamber is not sufficiently filled with oil, the hydraulic pressure in the canceller chamber may not rise sufficiently, causing clutch slippage and possibly clutch burn.

[0005] Therefore, an object of the vehicle control device disclosed in this specification is to suppress clutch burn in an automatic transmission. [Means for solving the problem]

[0006] The vehicle control device disclosed in this specification is a control device for a vehicle equipped with an automatic transmission that selects a gear stage by hydraulically switching between an engaged state and a disengaged state of the clutch, and switches between an output transmission state in which the engine output is transmitted to the drive wheels and an output cut-off state in which the transmission of the engine output to the drive wheels is cut off, and is equipped with a shift position determination unit that determines the shift position of a shift operating unit, a counter unit that measures the elapsed time since the engine was started, and a torque limiting unit that limits the torque generated by the engine when the shift position determination unit determines that the shift position is in an output cut-off range that puts the automatic transmission into an output cut-off state and the elapsed time measured by the counter unit is shorter than a predetermined torque limiting implementation period.

[0007] In the vehicle control device having the above configuration, the torque limiting unit can be configured to gradually release the torque limit after a torque limit release start time set at a timing before the end of the torque limit implementation period has elapsed, thereby bringing the engine torque closer to the target torque. [Effects of the Invention]

[0008] According to the vehicle control device disclosed in this specification, it is possible to suppress clutch burn in an automatic transmission. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of a vehicle in which a vehicle control device according to an embodiment is incorporated. [Figure 2] FIG. 2 is a cross-sectional view showing a part of an automatic transmission mounted on a vehicle in which the vehicle control device of the embodiment is incorporated. [Figure 3] FIG. 3 is a flowchart showing an example of torque limit control executed by the vehicle control device according to the embodiment. [Figure 4] FIG. 4 is a time chart showing an example of torque limit control executed by the vehicle control device according to the embodiment. [Figure 5] FIG. 5 is an example of a map that is referenced in the torque limit control executed by the vehicle control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions and proportions of the various parts in the drawings may not be exactly the same as those in reality. In addition, some details may be omitted in the drawings.

[0011] (Embodiment) <Vehicle> First, a vehicle 1 equipped with an ECU (Electronic Control Unit) 50 corresponding to a vehicle control device of the embodiment will be described with reference to Fig. 1. The vehicle 1 includes an engine 2, a torque converter 3, an automatic transmission 4, axles 5, drive wheels 6, an actuation gear mechanism 11, the ECU 50, a shift operation unit 58, and a hydraulic control circuit 60.

[0012] The engine 2 is an internal combustion engine and is provided with a throttle valve 2a that adjusts the amount of intake air that is mixed with fuel to create an air-fuel mixture. In this embodiment, the throttle valve 2a is an electronic throttle valve, but it may be another type of throttle valve.

[0013] The output (torque) generated by the engine 2 is transmitted to left and right drive wheels 6 via a torque converter 3, an automatic transmission 4, a differential gear mechanism 11, and left and right axles 5. The configurations of the engine 2 and the torque converter 3 are well known, and therefore a detailed description thereof will be omitted here.

[0014] <Automatic Transmission> The automatic transmission 4 includes various rotating members (not shown) that form a planetary gear mechanism therein, as well as a first clutch C1, a second clutch C2, a first brake B1, and a second brake B2. The first brake B1 and the second brake B2 are provided in a transmission case 4a of the automatic transmission 4. The automatic transmission 4 changes the combination of the engaged and disengaged states of the first clutch C1 and the second clutch C2 and the engaged and disengaged states of the first brake B1 and the second brake B2. By changing these combinations, the automatic transmission 4 switches between an output transmission state in which the torque of the engine 2 is transmitted to the drive wheels 6 and an output interruption state in which the transmission of the torque of the engine 2 to the drive wheels 6 is interrupted. The automatic transmission 4 also shifts to a desired gear in the output transmission state. The combination of the engaged and disengaged states of the first clutch C1, the second clutch C2, the first brake B1, and the second brake B2 required to set the automatic transmission 4 in a desired state varies depending on the configuration of the planetary gear mechanism built into the automatic transmission 4. The ECU 50 controls the switching between engagement and release of the first clutch C1, second clutch C2, first brake B1 and second brake B2 in the automatic transmission 4, that is, the shift control of the automatic transmission 4, via the hydraulic control circuit 60.

[0015] Now, with reference to FIG. 2, the internal structure of the automatic transmission 4 of this embodiment, in particular the structure around the first clutch C1 and the second clutch C2, will be described.

[0016] The first clutch C1 and the second clutch C2 are both disposed around the rotation axis C. The first clutch C1 is provided so as to be able to connect and disconnect the first rotating member 12 and the second rotating member 14. The second clutch C2 is provided so as to be able to connect and disconnect the second rotating member 14 and the third rotating member 40.

[0017] The first clutch C1 includes friction plates 15, 16 disposed between the first rotating member 12 and the second rotating member 14 in the radial direction, and a first piston 18 for pressing the friction plates 15, 16. The first clutch C1 also includes a first spring 20a that biases the first piston 18 in a direction along the rotation axis C (hereinafter referred to as the axial direction) away from the friction plates 15, 16, and a first partition wall 22 that holds the first spring 20a.

[0018] The first rotating member 12 is formed in a cylindrical shape with a bottom and an open end, and is disposed so as to be rotatable about a rotation axis C. The first rotating member 12 has a cylindrical portion 12a located on the radially outer side, and a bottom portion 12b connected to one axial end of the cylindrical portion 12a and extending radially inward. A friction plate 15 is provided on the inner peripheral side of the cylindrical portion 12a.

[0019] The second rotating member 14 is formed in a cylindrical shape with one end open and one end closed, and is arranged to be rotatable around a rotation axis C. A friction plate 16 is arranged on the outer circumferential side of a cylindrical portion 14a located radially outward of the second rotating member 14.

[0020] The friction plate 15 is spline-fitted to the inner circumferential surface of the cylindrical portion 12a of the first rotating member 12 so as to be non-rotatable relative to the first rotating member 12 but movable in the axial direction. The friction plate 16 is spline-fitted to the outer circumferential surface of the cylindrical portion 14a of the second rotating member 14 so as to be non-rotatable relative to the first rotating member 12 but movable in the axial direction. A plurality of friction plates 15 and a plurality of friction plates 16 are provided, stacked alternately in the axial direction. A first snap ring 28a is provided on the inner circumferential surface of the cylindrical portion 12a of the first rotating member 12 so as to prevent movement in the axial direction. The first snap ring 28a is disposed on the side away from the first piston 18 in the axial direction and is provided to restrict movement of the friction plates 15, 16 in one direction in the axial direction.

[0021] The first piston 18 includes a large diameter portion 18a and a small diameter portion 18b that are connected together in the axial direction. The small diameter portion 18b of the first piston 18 is slidably fitted between the inner and outer inner circumferential surfaces of an annular groove 30 formed in the bottom portion 12b of the first rotating member 12. In addition, the large diameter portion 18a of the first piston 18 is formed with a pressing portion 18a1 that presses the friction plates 15, 16.

[0022] An oil-tight first hydraulic chamber 32 is formed by the first piston 18 and the annular groove 30 of the first rotating member 12. When oil is supplied into this first hydraulic chamber 32, the first piston 18 is moved axially in a direction pressing against the friction plates 15, 16, and the first clutch C1 is engaged. Oil is supplied to the first hydraulic chamber 32 from a hydraulic control circuit 60 (see FIG. 1). The oil is supplied via a first oil passage 34a formed in the rotating shaft 34, a fourth oil passage 36a formed in the cylindrical member 36, and an eighth oil passage 12c formed in the first rotating member 12. The rotating shaft 34 is arranged to be rotatable about the rotation axis C. The cylindrical member 36 is connected to the inner peripheral end of the second rotating member 14.

[0023] The first partition wall 22 is formed in a disk shape, and its inner peripheral end is fixed to the first rotating member 12 by a snap ring so as to be immovable in the axial direction, and its outer peripheral end is in sliding contact with the inner peripheral surface of the large diameter portion 18a of the first piston 18. A first spring 20a is interposed between this first partition wall 22 and the first piston 18, and biases the first piston 18 in the axial direction in a direction away from the friction plates 15, 16. Therefore, when oil is not supplied to the first hydraulic chamber 32, the biasing force of the first spring 20a moves the first piston 18 to a position where it does not press the friction plates 15, 16.

[0024] A first canceller chamber 38 is formed in an area of the first hydraulic chamber 32 adjacent to the first piston 18 in the axial direction. The first canceller chamber 38 is formed as an oil-tight space surrounded by the first partition wall 22, the first piston 18, and the bottom 12b of the first rotating member 12. Oil is supplied to the first canceller chamber 38 via a ninth oil passage 12d formed in the first rotating member 12 and a fifth oil passage 36b formed in the cylindrical member 36. The oil supplied to the first canceller chamber 38 is a portion of the oil discharged from an oil pump (not shown) driven by the engine 2 (see FIG. 2). When the oil pump is driven for a predetermined time or longer, a sufficient amount of oil is filled in the first canceller chamber 38.

[0025] The third rotating member 40 is disposed between the cylindrical member 36 and the second rotating member 14 in the radial direction. A second clutch C2 is disposed between the third rotating member 40 and the second rotating member 14. The second clutch C2 includes friction plates 24, 25 disposed between the second rotating member 14 and the third rotating member 40 in the radial direction, and a second piston 44 for pressing the friction plates 24, 25. The second clutch C2 also includes a second spring 20b that biases the second piston 44 in a direction along the rotation axis C (hereinafter referred to as the axial direction) away from the friction plates 24, 25, and a second partition wall 42 that holds the second spring 20b.

[0026] The third rotating member 40 is formed in a cylindrical shape with a bottom and an open end, and is arranged to be rotatable about a rotation axis C. The third rotating member 40 has a cylindrical portion 40a located on the radially outer side, and a bottom portion 40b connected to one axial end of the cylindrical portion 40a and extending radially inward. A friction plate 25 is provided on the outer circumferential side of the cylindrical portion 40a of the third rotating member 40.

[0027] The second rotating member 14 is formed in a cylindrical shape with one end open and one end closed, and is disposed so as to be rotatable about a rotation axis C. Friction plates 16 of the first clutch C1 are disposed on the outer periphery of a cylindrical portion 14a located radially outward of the second rotating member 14. Friction plates 24 of the second clutch C2 are disposed on the inner periphery of the cylindrical portion 14a.

[0028] The friction plate 24 is spline-fitted to the inner peripheral surface of the cylindrical portion 14a of the second rotating member 14 so as to be non-rotatable relative to the friction plate 24 but movable in the axial direction. The friction plate 25 is spline-fitted to the outer peripheral surface of the cylindrical portion 40a of the third rotating member 40 so as to be non-rotatable relative to the friction plate 24 but movable in the axial direction. A plurality of friction plates 24 and a plurality of friction plates 25 are provided, and are stacked alternately in the axial direction. A second snap ring 28b is provided on the outer peripheral surface of the cylindrical portion 40a of the third rotating member 40 so as to prevent movement in the axial direction. The second snap ring 28b is disposed on the side away from the second piston 44 in the axial direction and is provided to restrict movement of the friction plates 24, 25 in one direction in the axial direction.

[0029] The second piston 44 is slidably fitted between the inner circumferential surface of the cylindrical portion 40a of the third rotating member 40 and the cylindrical member 36. The second piston 44 is formed with a pressing portion 44a for pressing the friction plates 24, 25.

[0030] The second partition wall 42 is formed in a disk shape, and its inner peripheral end is fixed to the cylindrical member 36 by a snap ring so as to be immovable in the axial direction, and its outer peripheral end is in sliding contact with the second piston 44.

[0031] An oil-tight second hydraulic chamber 46 is formed by the second piston 44 and the second partition wall 42. When oil is supplied into this second hydraulic chamber 46, the second piston 44 is moved axially in a direction pressing against the friction plates 24, 25, and the second clutch C2 is brought into an engaged state. Oil is supplied to the second hydraulic chamber 46 from a hydraulic control circuit 60 (see FIG. 1). The oil is supplied via a second oil passage 34b formed in the rotating shaft 34 and a sixth oil passage 36c formed in the cylindrical member 36.

[0032] A second spring 20b is interposed between the third rotating member 40 and the second piston 44, and urges the second piston 44 in the axial direction away from the friction plates 24, 25. Therefore, when oil is not supplied to the second hydraulic chamber 46, the urging force of the second spring 20b moves the second piston 44 to a position where it does not press the friction plates 24, 25.

[0033] A second canceller chamber 48 is formed in an area of the second hydraulic chamber 46 adjacent to the second hydraulic chamber 46 in the axial direction, separated by the second piston 44. The second canceller chamber 48 is formed as an oil-tight space surrounded by the third rotating member 40, the second piston 44, and the cylindrical member 36. Oil is supplied to the second canceller chamber 48 via a third oil passage 34c formed in the rotating shaft 34 and a seventh oil passage 36d formed in the cylindrical member 36. The oil supplied to the second canceller chamber 48 is a portion of the oil discharged from an oil pump (not shown) driven by the engine 2 (see FIG. 1). When the oil pump is driven for a predetermined time or longer, a sufficient amount of oil is filled in the second canceller chamber 48.

[0034] Here, the operation of the first clutch C1 and the second clutch C2 will be described.

[0035] When the first clutch C1 is engaged, oil is supplied to the first hydraulic chamber 32, causing the first piston 18 to move axially toward the friction plates 15, 16 against the biasing force of the first spring 20a and press against the friction plates 15, 16. This causes the friction plates 15, 16 to be frictionally engaged with each other, and the first clutch C1 is engaged. When the first clutch C1 is released, oil is discharged from the first hydraulic chamber 32. If the first canceller chamber 38 is filled with oil at this time, even if racing occurs and the oil remaining in the first hydraulic chamber 32 rotates at high speed, generating centrifugal oil pressure, this centrifugal oil pressure is offset by the oil pressure in the first canceller chamber 38.

[0036] When the second clutch C2 is engaged, oil is supplied to the second hydraulic chamber 46, causing the second piston 44 to move axially toward the friction plates 24, 25 against the biasing force of the second spring 20b and press against the friction plates 24, 25. This causes the friction plates 24, 25 to be frictionally engaged with each other. This causes the second clutch C2 to be engaged. When the second clutch C2 is released, oil is discharged from the second hydraulic chamber 46. If oil is filled in the second canceller chamber 48 at this time, even if racing occurs and the oil remaining in the second hydraulic chamber 46 rotates at high speed, generating centrifugal oil pressure, this centrifugal oil pressure is offset by the oil pressure in the second canceller chamber 48.

[0037] ECU Next, the ECU 50 will be described. The ECU 50 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), backup RAM, and other storage devices. The ECU 50 executes calculations and various controls based on programs and maps stored in the CPU, ROM, and other storage devices. The RAM is a memory that temporarily stores the results of calculations performed by the CPU and data input from various sensors, and the backup RAM is a non-volatile memory that stores data that should be saved when the engine 2 is stopped, for example.

[0038] The ECU 50 executes output control of the engine 2 and shift control of the automatic transmission 4. Referring again to FIG. 1, an accelerator operation amount signal indicating an accelerator position Acc, which is the amount of operation of an accelerator pedal 53, detected by an accelerator position sensor 52, is transmitted to and input into the ECU 50. A signal indicating an engine rotation speed Ne, which is the rotation speed of the engine 2, detected by an engine rotation speed sensor 54 is also transmitted to and input into the ECU 50. Furthermore, a throttle valve opening signal indicating an opening θth of the throttle valve 2a, detected by a throttle valve opening sensor 56, and a signal Psh indicating a shift position from a shift operation unit 58 are each transmitted to and input into the ECU 50.

[0039] On the other hand, the ECU 50 outputs a drive signal to a throttle actuator that operates the opening θth of the throttle valve 2a, and an ignition signal that commands the ignition timing of the engine 2. The ECU 50 also outputs an engine control signal Se that includes a fuel supply amount signal that controls the amount of fuel supplied to the engine 2 by a fuel injection device that supplies or stops fuel to the intake pipe or cylinders of the engine 2. The ECU 50 also outputs a gear change control signal Sc that controls a linear solenoid valve (not shown) in the hydraulic control circuit 60 to switch the gear positions of the automatic transmission 4.

[0040] The vehicle 1 employs a so-called shift-by-wire system (SBW system) in which the shift range is switched by electrically controlling various solenoids provided in the hydraulic control circuit 60 based on the shift position signal Psh from the shift operating unit 58.

[0041] The ECU 50 includes a shift position determination unit 50a, a counter unit 50b, and a torque limiting unit 50c. The shift position determination unit 50a determines the shift position based on a shift position signal Psh from a shift operation unit 58. Specifically, the shift position determination unit 50a determines whether the shift position is in the drive range (D range), which is an output transmission range, or in the neutral range (N range) or parking range (P range), which are output cutoff ranges. The counter unit 50b measures the elapsed time T from the start of the engine 2. The torque limiting unit 50c limits the torque generated by the engine 2 when the shift position determination unit 50a determines that the shift position is in the output cutoff range, i.e., the N range or the P range, and the elapsed time T measured by the counter unit 50b is shorter than a preset torque limiting implementation period tlim [sec] (see FIG. 4). Specifically, the torque limiting unit 50c narrows the opening θth of the throttle valve 2a to reduce the intake amount and thereby limits the torque generated by the engine 2.

[0042] Here, the reason why the torque limiting unit 50c performs such torque limiting will be explained. In this embodiment, when the shift position is in the N range or the P range, the first clutch C1, the second clutch C2, and the first brake B1 in the automatic transmission 4 shown in FIG. 1 are released, and only the second brake B2 is engaged.

[0043] However, immediately after the engine 2 starts, the first clutch C1 or the second clutch C2 may unintentionally attempt to transition to an engaged state. This occurs because insufficient oil is supplied to the first canceller chamber 38 or the second canceller chamber 48 immediately after the engine 2 starts. If the accelerator pedal 53 is depressed in this state, centrifugal hydraulic pressure is generated in the first hydraulic chamber 32 or the second hydraulic chamber 46, causing the first canceller chamber 38 or the second canceller chamber 48 to function improperly. This may result in slippage of the first clutch C1 or the second clutch C2. In particular, the automatic transmission 4 of this embodiment is not designed to have both the second brake B2 and the second clutch C2 engaged at any shift position. Therefore, if both the second brake B2 and the second clutch C2 are engaged in the automatic transmission 4, the force attempting to rotate the second clutch C2 within the automatic transmission 4 has nowhere to escape, potentially causing slippage of the second clutch C2. Therefore, if no measures are taken, there is a possibility that clutch burn will occur, particularly in the second clutch C2.

[0044] Therefore, in the vehicle 1 of this embodiment, torque limitation is implemented by the ECU 50 under predetermined conditions.

[0045] <Torque limit control> An example of torque limit control performed by the ECU 50 will be described below with reference to FIGS. 3 to 5. FIG. 4 is an example of a time chart of torque limit control, in which Psh indicates the shift position and θth indicates the opening of the throttle valve 2a (see FIG. 1). STARTflg is a flag indicating whether the engine 2 has started, TRQlim indicates the torque command value when torque limiting is being performed, and TRQtrg indicates the target torque. TRQflg is a flag indicating whether torque limiting is being performed. The target torque TRQtrg is determined based on the throttle opening θth. When torque limiting is being performed, the torque command value TRQlim is applied in priority to the target torque TRQtrg. In other words, when torque limiting is being performed, the torque of the engine 2 is controlled to be the torque command value TRQlim.

[0046] In this embodiment, tlim [sec] is set as the torque limit implementation period. One of the conditions for implementing torque limit is that the elapsed time T from the start of the engine 2 is shorter than the torque limit implementation period tlim [sec]. In this embodiment, the torque limit implementation period tlim [sec] is from time t0 to time t4 in FIG. 4. The torque limit implementation period tlim [sec] is set as the time during which a sufficient amount of oil is supplied so that the pressure in the second canceller chamber 48 reaches a value that can offset the centrifugal hydraulic pressure that may occur in the second hydraulic chamber 46.

[0047] In this embodiment, the torque limit release start time tlimre [sec] is set to a timing before the torque limit implementation period tlim [sec] ends. In this embodiment, time t1 is set as the torque limit release start time tlimre [sec].

[0048] In the following description, it is assumed that the engine 2 is started from a stopped state. Therefore, in the state before time t0 in FIG. 4, the shift position is in the N range, and the opening θth of the throttle valve 2a is 0%. Accordingly, the engine start flag STARTflg is set to OFF. Also, at this stage, torque limitation is not being implemented, so the torque limitation implementation flag TRQflg is set to OFF, and an invalid value is input as the torque command value TRQlim. Also, since the engine 2 has not been started, the target torque TRQtrg is set to the value TRQ when the opening θth is 0%. θth=0% The same applies when the shift position is in P range instead of N range.

[0049] First, in step S1, the ECU 50 determines whether the engine 2 has started. Whether the engine 2 has started is determined based on whether the rotation speed of the engine 2 acquired by the engine rotation speed sensor 54 (see FIG. 1) is equal to or greater than a predetermined value. In the time chart shown in FIG. 4, the engine 2 starts at time t0, and the engine start flag STARTflg is switched from OFF to ON. Whether the engine 2 has started may also be determined by other conventionally known methods, for example, based on whether an explosion in the engine 2 is detected.

[0050] If the determination in step S1 is affirmative (Yes determination), the process proceeds to step S2. On the other hand, if the determination in step S1 is negative (No determination), the process in step S1 is repeated until the determination in step S1 is affirmative.

[0051] In step S2, the counter unit 50b starts counting the time that has elapsed since the start of the engine 2. In step S3 that follows step S2, the torque limiting unit 50c determines whether or not a predetermined time has elapsed since the start of the engine 2, that is, whether or not time t4 has arrived and the torque limiting implementation period tlim [sec] has elapsed.

[0052] If the torque limiting unit 50c makes a negative determination in step S3, the ECU 50 proceeds to step S4. On the other hand, if the torque limiting unit 50c makes a positive determination in step S3, the process returns, and the ECU 50 repeats the process from step S1.

[0053] In step S4, the shift position determination unit 50a determines the shift position based on the shift position signal Psh from the shift operation unit 58. Specifically, the shift position determination unit 50a determines whether the shift position is in the P range or the N range. If the shift position determination unit 50a makes a positive determination in step S4, the ECU 50 proceeds to step S5. On the other hand, if the shift position determination unit 50a makes a negative determination in step S4, the process returns, and the ECU 50 repeats the process from step S1.

[0054] Referring to the time chart shown in FIG. 4, the shift position signal Psh indicates the N range from time t0 to time t2. Furthermore, after time t0, the engine 2 starts, and the engine start flag STARTflg changes from OFF to ON. Therefore, torque limitation is implemented from time t0 to time t2, the torque limitation implementation flag TRQflg is turned ON, and the ECU 50 executes the processing from step S5 onwards. In contrast, the shift position is changed from time t2 to time t3, and the shift position signal Psh indicates the D range. In this case, the torque limitation implementation flag TRQflg is turned OFF. This is because when the shift position signal Psh is in the D range, one of the conditions for implementing torque limitation is not satisfied.

[0055] In step S5, the limit execution torque TRQlimex is acquired. The limit execution torque TRQlimex is acquired based on the torque limit map shown in FIG. 5. Referring to FIG. 5, in this embodiment, the limit execution torque TRQlimex is acquired as the torque command value TRQlim until the time elapsed since the start of the engine 2 reaches the torque limit release start time tlimre [sec]. The limit execution torque TRQlimex is set to a value that can prevent clutch burn in the second clutch C2 even when oil is not sufficiently supplied to the second canceller chamber 48 (FIG. 2) and the hydraulic pressure increase is insufficient.

[0056] In step S6, which follows step S5, the limit execution torque TRQlimex obtained in step S5 is set in place of the target torque TRQtrg. If the original target torque TRQtrg continues to be used as shown in FIG. 4, for example, when the accelerator pedal 53 is depressed so that the opening θth becomes 50%, the target torque TRQtrg becomes TRQ θth=50% After the engine 2 is started, the torque limiting period tlim [sec] has not elapsed, and the hydraulic pressure in the second canceller chamber 48 (see FIG. 2) is not sufficiently increased, and the TRQ θth=50%When the torque limiting torque TRQ is output, the second clutch C2 may burn. In contrast, in this embodiment, torque limiting is performed and the value of the torque output by the engine 2 is set to the limiting torque TRQlimex, thereby making it possible to suppress clutch burn in the second clutch C2.

[0057] In step S7, which follows step S6, the torque limiting unit 50c determines whether or not the torque limit release start time tlimre [sec] has elapsed since the start of the engine 2.

[0058] If the torque limiting unit 50c makes an affirmative determination in step S7, the ECU 50 proceeds to step S8. On the other hand, if the torque limiting unit 50c makes a negative determination in step S7, the ECU 50 repeats the process from step S6.

[0059] In step S8, the torque limiting unit 50c gradually changes the torque value of the engine 2, which has been set to the restriction execution torque TRQlimex, to the target torque TRQtrg. Specifically, after time t1 in FIG. 4 has elapsed, the torque control unit 50c gradually changes the torque value from the restriction execution torque TRQlimex at that time to the target torque TRQtrg at that time, TRQ θth=50% This makes it possible to return the torque value to the target torque TRQtrg corresponding to the depression amount of the accelerator pedal 53 while suppressing the occurrence of a torque step.

[0060] In step S9, which follows step S8, the torque limiting unit 50c again determines, as in step S3, whether a predetermined time has passed since the start of the engine 2, i.e., time t4, and whether the torque limiting implementation period tlim [sec] has elapsed.

[0061] If the torque limiting unit 50c makes a positive determination in step S9, the ECU 50 proceeds to step S10. On the other hand, if the torque limiting unit 50c makes a negative determination in step S9, the ECU 50 repeats the process of step S9 until a positive determination is made in step S9.

[0062] In step S10, the torque limiting unit 50c ends the torque limit. Then, the ECU 50 proceeds to step S11. In step S11, the ECU 50 determines whether the engine 2 has stopped. If the ECU 50 makes a negative determination in step S11, the ECU 50 repeats the processing of step S11 until a positive determination is made in step S11. On the other hand, if the ECU 50 makes a positive determination in step S11, the ECU 50 switches the engine start flag STARTflg to OFF and repeats the processing from step S1. In other words, the ECU 50 prepares for the next start of the engine 2.

[0063] According to this embodiment, when the shift position is in the N range or P range, which are output cut-off ranges, and the time elapsed since the start of the engine 2 is shorter than the torque limitation implementation period, the torque generated by the engine 2 is limited. This makes it possible to suppress clutch burn in the automatic transmission 4.

[0064] Furthermore, according to this embodiment, the torque limit is gradually released after the torque limit release start time has elapsed, allowing the engine torque to approach the target torque, thereby suppressing the occurrence of torque steps and restoring the torque value to the target torque TRQtrg.

[0065] The above-described embodiments are merely examples for implementing the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention. Furthermore, it is obvious from the above description that various other embodiments are possible within the scope of the present invention. [Explanation of symbols]

[0066] 1 vehicle 2 engines 3 Torque converter 4 Automatic transmission 5 axles 6 drive wheels 32 First hydraulic chamber 38 First canceller chamber 46 Second hydraulic chamber 48 Second canceller chamber 50 ECU (control unit) 50a Shift position determination unit 50b Counter section 50c Torque limiting section C1 First clutch C2 Second clutch B1 First brake B2 Second brake

Claims

[Claim 1] A control device for a vehicle equipped with an automatic transmission that selects a gear stage by hydraulically switching between an engaged state and a released state of a clutch, and switches between an output transmission state in which engine output is transmitted to drive wheels and an output interruption state in which transmission of engine output to the drive wheels is interrupted, a shift position determination unit that determines the shift position of the shift operation unit; a counter unit that measures the elapsed time from the start of the engine; a torque limiting unit that limits the torque generated by the engine when the shift position determining unit determines that the shift position is in an output cut-off range that puts the automatic transmission into an output cut-off state and when the elapsed time measured by the counter unit is shorter than a preset torque limiting implementation period, A vehicle control device in which the torque limiting unit gradually releases the torque limit after a torque limit release start time set before the end of the torque limit implementation period has elapsed, thereby bringing the engine torque closer to a target torque.

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