JP2012013051A - Device for control of vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an engine from being stopped before an actual VCT phase (actual valve timing) returns to a predetermined start time position (for example, a most retarded position) due to an engine stall caused by braking operation, in a system provided with a variable valve timing device.SOLUTION: When the actual VCT phase is not returned to a start time position during braking operation, whether an engine stall will occur is predicted depending on whether an engine rotation speed Ne has sharply decreased in a low rotation speed range. When the occurrence of engine stall is predicted, a speed change mechanism 17 of an automatic transmission 12 is switched from a non-neutral state (power transmittable state) to a neutral state (non-power transmitting state) at that point. Thereby, even if a wheel 15 assumes a locked state by braking, transmission of torque in a rotation stop direction from the wheel 15 side to the engine 11 side is avoided or inhibited, thus preventing the engine stall.

Description

  The present invention relates to a vehicle control device including a variable valve timing device that changes a valve timing of an engine (internal combustion engine).

  In recent years, some engines mounted on vehicles have adopted variable valve timing devices that change the valve timing (open / close timing) of intake valves and exhaust valves for the purpose of improving output, reducing fuel consumption, and reducing exhaust emissions. . A variable valve timing device that is currently in practical use changes the valve timing of an intake valve or an exhaust valve that is opened and closed by the camshaft by changing the rotational phase (VCT phase) of the camshaft with respect to the crankshaft. There are a lot of things.

  In general, a hydraulically driven variable valve timing device can normally control the VCT phase (valve timing) only after the engine rotational speed (that is, the rotational speed of the oil pump) has increased and the hydraulic pressure has increased to some extent. Therefore, in order to ensure engine startability, it is preferable to change the actual VCT phase to a position suitable for starting in advance when the engine is stopped and lock it with a lock pin or the like.

  Therefore, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2008-75484) and Patent Document 2 (Japanese Patent Laid-Open No. 2009-156217), an IG switch (ignition switch) is turned off and an engine stop command is issued. In some cases, the variable valve timing device is controlled so that the actual VCT phase is changed to a position suitable for starting (lock position) within a period until the rotation of the engine stops. At that time, in Patent Document 1, the engine rotational speed is maintained at a predetermined rotational speed or higher until the deviation between the actual VCT phase and the target VCT phase (position suitable for starting) becomes a predetermined value or lower. Further, in Patent Document 2, engine stop is delayed until a predetermined delay time elapses after the engine stop command is generated.

JP 2008-75484 A JP 2009-156217 A

  By the way, when a wheel is locked (rotation stopped) by panic braking (rapid braking) or braking on a low friction road surface, the load applied to the engine (torque in the rotation stopping direction transmitted from the wheel side to the engine side) suddenly increases. Since the engine speed increases, the engine rotation speed may suddenly decrease and engine stall (so-called engine stall) may occur. In such a case, since the engine stops in a very short time, there is a possibility that the engine stops before the actual VCT phase returns to a predetermined starting position (for example, a position suitable for starting). If the engine is stopped before the phase returns to the starting position, problems such as poor startability or abnormal noise occur at the next engine start.

  The techniques of Patent Document 1 and Patent Document 2 described above are all from when an engine stop command is generated to when engine rotation stops at the time of normal engine stop (that is, when the engine is stopped according to the engine stop command). It is a technology that changes the actual VCT phase to a predetermined start position within a period, and solves the above-described problem when an engine stall occurs due to a brake operation (that is, when the engine suddenly stops without an engine stop command). Can not.

  Therefore, the problem to be solved by the present invention is to provide a vehicle control device that can prevent the engine from stopping before the actual VCT phase returns to a predetermined starting position due to engine stall caused by brake operation. There is to do.

  In order to solve the above-mentioned problems, the invention according to claim 1 includes a variable valve timing device that changes the valve timing by changing the rotational phase of the camshaft (hereinafter referred to as “VCT phase”) with respect to the crankshaft of the engine. In the vehicle control device, when the engine stall occurs due to the engine stall prediction means for predicting whether or not the engine stall will occur and the actual VCT phase is not at the predetermined starting position during the braking operation of the vehicle. The engine is provided with an engine stall prevention means for controlling the power transmission system of the engine so as to prevent the engine stall when predicted.

  In this configuration, when it is predicted that an engine stall will occur when the actual VCT phase is not at a predetermined starting position (for example, a position suitable for starting) during a brake operation, the engine power is prevented so as to prevent the engine stall. By controlling the transmission system (for example, a speed change mechanism, a torque converter, etc.), it is possible to prevent the engine from being stopped before the actual VCT phase returns to a predetermined start position due to engine stall due to brake operation. Deterioration of startability and generation of abnormal noise can be prevented.

  In this case, the engine stall prevention means may prevent the engine stall by setting the speed change mechanism provided in the power transmission system to a neutral state (a state where no power is transmitted). In this way, even when the wheels are locked due to panic braking (rapid braking) or braking on a low friction road surface, the rotation is stopped from the wheel side to the engine side by setting the speed change mechanism to the neutral state. Transmission of torque in the direction can be avoided or suppressed, and engine stall can be prevented.

  According to a third aspect of the present invention, the engine stall prevention means may prevent engine stall by bringing a lock-up clutch of a torque converter provided in the power transmission system into a released state (disengaged state). In this way, even if the wheel is locked due to panic braking (rapid braking), braking on a low friction road surface, etc., the engine is started from the wheel side by releasing the torque converter lock-up clutch. Transmission of torque in the rotation stop direction to the side can be avoided or suppressed, and engine stall can be prevented.

  According to a fourth aspect of the present invention, the engine stall prediction means may predict whether or not an engine stall will occur based on at least one of a brake operation state, an engine rotation speed, and a vehicle speed. For example, if the engine speed or vehicle speed suddenly decreases during a brake operation, or if the amount of brake operation increases rapidly, an engine stall may occur, so the brake operation state, engine speed, vehicle speed, etc. Can be predicted whether or not an engine stall will occur.

FIG. 1 is a diagram showing a schematic configuration of a vehicle drive system in an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of the variable valve timing control system. FIG. 3 is a time chart for explaining a problem when an engine stall occurs. FIG. 4 is a time chart for explaining an execution example of engine stall prevention control according to this embodiment. FIG. 5 is a flowchart for explaining the processing flow of the engine stall prevention control routine.

Hereinafter, an embodiment embodying a mode for carrying out the present invention will be described.
First, a schematic configuration of the vehicle drive system will be described with reference to FIG.
The power of the output shaft of the engine 11, which is an internal combustion engine, is transmitted to the automatic transmission 12, and the power of the output shaft of the automatic transmission 12 is transmitted to the wheels 15 via the differential gear mechanism 13, the axle 14, and the like. The automatic transmission 12 is constituted by a torque converter 16 and a transmission mechanism 17, and may be a stepped transmission that switches a gear step from a plurality of gear steps in a stepwise manner, or a CVT that changes continuously (nothing). A step transmission). The torque converter 16 is provided with a lockup clutch 18 for engaging or disengaging between the input shaft side and the output shaft side.

  The accelerator sensor 19 detects the accelerator opening (the amount of operation of the accelerator pedal), and the brake switch 20 detects the brake operation. Further, the vehicle speed is detected by the vehicle speed sensor 21, and the operation position of the shift lever is detected by the shift switch 22.

Next, a schematic configuration of the variable valve timing control system will be described based on FIG.
In the engine 11, power from the crankshaft 23 is transmitted to the intake side camshaft 27 and the exhaust side camshaft 28 via the sprockets 25 and 26 by the timing chain 24. The intake side camshaft 27 is provided with a hydraulically driven variable valve timing device 29, and the variable valve timing device 29 changes the rotation phase (VCT phase) of the intake side camshaft 27 with respect to the crankshaft 23. The valve timing of an intake valve (not shown) that is driven to open and close by the intake side camshaft 27 is changed.

  Further, hydraulic oil (oil) in the oil pan 31 is pumped up by the oil pump 30 driven by the power of the engine 11 and supplied to the hydraulic control valve 32, and the hydraulic control valve 32 advances the variable valve timing device 29. The oil pressure (oil amount) supplied to the angle port and the retard port is controlled. A check valve 33 is provided on the inlet port side of the hydraulic control valve 32 to prevent oil backflow.

  A cam angle sensor 34 that outputs a cam angle signal pulse at a specific cam angle for cylinder discrimination is installed on the outer peripheral side of the intake side cam shaft 27, while a predetermined crank angle is provided on the outer peripheral side of the crank shaft 23. A crank angle sensor 35 is provided for outputting a crank angle signal pulse every time. The crank angle and the engine speed are detected based on the output signal of the crank angle sensor 35, and the actual valve timing (actual VCT phase) of the intake valve is detected based on the output signals of the cam angle sensor 34 and the crank angle sensor 35. The

  Outputs of the various sensors and switches described above are input to an electronic control circuit (hereinafter referred to as “ECU”) 36. The ECU 36 is mainly composed of a microcomputer, and controls the engine 11 and the automatic transmission 12 by executing various control programs stored in a built-in ROM (storage medium). The engine 11 and the automatic transmission 12 may be configured to be controlled by separate control circuits (for example, the engine 11 is controlled by the engine ECU and the automatic transmission 12 is controlled by the AT-ECU).

  At this time, the ECU 36 calculates a target valve timing (target VCT phase) according to the engine operating state, and a variable valve timing device so that the actual valve timing (actual VCT phase) matches the target valve timing (target VCT phase). The 29 hydraulic control valves 32 are feedback-controlled.

  Further, when an unillustrated IG switch (ignition switch) is turned off and an engine stop command is generated, the actual VCT phase can be changed to a predetermined start position within a period until the engine 11 stops rotating. The hydraulic control valve 32 of the valve timing device 29 is controlled. Here, the starting position is a position suitable for starting, and in the case of the variable valve timing device 29 of the intake valve, for example, is set to the most retarded position.

  By the way, as shown in FIG. 3, when the wheel 15 is locked (rotation stopped) by panic braking (rapid braking) or braking on a low friction road surface, the load applied to the engine 11 (from the wheel 15 side to the engine 11 side). Since the torque in the rotation stop direction (transmitted) increases rapidly, the engine rotation speed may decrease rapidly and engine stall (so-called engine stall) may occur. In such a case, since the engine 11 stops in a very short time, the engine 11 may stop before the actual VCT phase returns to a predetermined start position (for example, the most retarded position). If the engine is stopped before the VCT phase returns to the starting position, problems such as poor startability and abnormal noise occur at the next engine start.

  As a countermeasure against this, the ECU 36 executes an engine stall prevention control routine shown in FIG. 5 to be described later. When it is predicted that the engine will stall, the power transmission system of the engine 11 (for example, the transmission mechanism 17 of the automatic transmission 12) is controlled so as to prevent the engine stall.

  Specifically, as shown in FIG. 4, whether or not both of the following two conditions are satisfied when the actual VCT phase does not return to the starting position during the brake operation (when the brake signal is ON): Therefore, it is predicted whether or not an engine stall will occur.

(1) Engine speed Ne <judgment value K1
(2) Engine speed change ΔNe <judgment value K2
Here, for example, the determination value K1 is set to a slightly higher rotation speed than the idle rotation speed, and the determination value K2 is set to a negative value.

  If both of these conditions (1) and (2) are satisfied, it is determined that the engine stall may occur because the engine speed is suddenly decreasing in the low speed range during braking. Predict that an engine stall will occur.

  When it is predicted that an engine stall will occur, the transmission mechanism 17 of the automatic transmission 12 is switched from a non-neutral state (a state where power can be transmitted) to a neutral state (a state where power is not transmitted) at the time t1. Thus, even when the wheel 15 is locked by the brake, the torque in the rotation stop direction is prevented from being transmitted from the wheel 15 side to the engine 11 side to prevent or suppress the engine stall (engine rotation). Return the speed to idle speed).

The engine stall prevention control of the present embodiment described above is executed by the ECU 36 in accordance with the engine stall prevention control routine of FIG. The processing contents of this routine will be described below.
The engine stall prevention control routine shown in FIG. 5 is repeatedly executed at predetermined intervals while the ECU 36 is powered on. When this routine is started, first, in step 101, it is determined whether or not the brake is being operated (the brake signal is ON) based on the output signal of the brake switch 20, and it is determined that the brake is being operated. For example, the process proceeds to step 102, where it is determined whether or not the actual VCT phase is a predetermined starting position. Here, the starting position is a position suitable for starting, and in the case of the variable valve timing device 29 of the intake valve, for example, is set to the most retarded position.

  If it is determined in step 101 that the brake is not being operated, or if it is determined in step 102 that the actual VCT phase is the starting position, this routine is executed without executing the subsequent processing. finish.

On the other hand, if it is determined in step 101 that the brake is being operated, and if it is determined in step 102 that the actual VCT phase is not the starting position, the process proceeds to step 103 where the crank angle sensor 35 detects the actual VCT phase. After the engine speed Ne is read, the routine proceeds to step 104, where the difference between the current value Ne (i) of the engine speed and the previous value Ne (i-1) is calculated as the engine speed change amount ΔNe.
ΔNe = Ne (i) -Ne (i-1)

Thereafter, the process proceeds to step 105, where it is predicted whether or not an engine stall will occur depending on whether or not both of the following two conditions are satisfied.
(1) Engine speed Ne <judgment value K1
(2) Engine speed change ΔNe <judgment value K2
Here, for example, the determination value K1 is set to a slightly higher rotation speed than the idle rotation speed, and the determination value K2 is set to a negative value.

If both of these conditions (1) and (2) are satisfied, it is determined that the engine stall may occur because the engine speed is suddenly decreasing in the low speed range during braking. Predict that an engine stall will occur. The processing in step 105 serves as an engine stall predicting means in the claims.
If it is predicted in this step 105 that no engine stall will occur, this routine is terminated without executing the processing from step 106 onward.

  On the other hand, if it is predicted in step 105 that an engine stall will occur, the routine proceeds to step 106 where the hydraulic control of the variable valve timing device 29 is performed so that the actual VCT phase is changed to the starting position (for example, the most retarded position). The valve 32 is controlled (for example, the control duty of the hydraulic control valve 32 is set to 0%).

  Thereafter, the process proceeds to step 107, and the speed change mechanism 17 of the automatic transmission 12 is switched from the non-neutral state (state where power can be transmitted) to the neutral state (state where power is not transmitted). Thereby, even when the wheel is locked by the brake, the engine stall is prevented by avoiding or suppressing the torque in the rotation stop direction from being transmitted from the wheel 15 side to the engine 11 side (engine speed). To the idle speed). The processing in step 107 serves as an engine stall prevention means in the claims.

  In the present embodiment described above, when it is predicted that an engine stall will occur when the actual VCT phase is not at a predetermined starting position (for example, the most retarded position) during the brake operation, the engine stall is prevented. Since the power transmission system of the engine 11 (for example, the speed change mechanism 17 of the automatic transmission 12) is controlled, the engine 11 stops before the actual VCT phase returns to a predetermined start position due to engine stall due to brake operation. Can be prevented beforehand, and deterioration of startability and generation of abnormal noise can be prevented.

  In this embodiment, since the engine stall is prevented by setting the speed change mechanism 17 of the automatic transmission 12 to the neutral state, the wheel 15 is moved by a panic brake (rapid brake) or a brake on a low friction road surface. Even in the locked state, by setting the speed change mechanism 17 to the neutral state, transmission of torque in the rotation stop direction from the wheel 15 side to the engine 11 side can be avoided or suppressed, and engine stall can be prevented. It can be surely prevented.

  In the above embodiment, the engine stall is prevented by setting the speed change mechanism 17 of the automatic transmission 12 to the neutral state. However, the method for preventing the engine stall is not limited to this, and can be changed as appropriate. For example, the engine stall may be prevented by bringing the lock-up clutch 18 of the torque converter 16 of the automatic transmission 12 into a released state (disengaged state). In this way, even when the wheel 15 is locked due to panic braking (rapid braking), braking on a low friction road surface, or the like, the lock-up clutch 18 of the torque converter 16 is released, so that the wheel Transmission of torque in the rotation stop direction from the 15 side to the engine 11 side can be avoided or suppressed, and engine stall can be reliably prevented.

  Further, the engine stall may be prevented by setting the transmission mechanism 17 of the automatic transmission 12 to the neutral state and releasing the lockup clutch 18 of the torque converter 16. Alternatively, an engine stall may be prevented by providing a hydraulically or electromagnetically driven clutch in the power transmission system of the engine 11 and releasing the clutch (disengaged).

  Further, in the above embodiment, whether or not the engine stall occurs is predicted based on whether or not the engine speed is suddenly decreasing in the low rotation range during the brake operation. The method of predicting whether or not the engine is not limited to this may be changed as appropriate.For example, whether or not the engine stall occurs depending on whether or not the vehicle speed is rapidly decreasing in the low speed region during the brake operation. It may be predicted. Alternatively, it may be predicted whether or not an engine stall will occur depending on whether or not the brake operation amount has suddenly increased (that is, sudden braking).

  In addition, the present invention is not limited to the variable valve timing device for the intake valve, but may be applied to the variable valve timing device for the exhaust valve. In this case, the starting position is set to the most advanced position, for example.

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Automatic transmission, 15 ... Wheel, 16 ... Torque converter, 17 ... Transmission mechanism, 18 ... Lock-up clutch, 23 ... Crankshaft, 27 ... Intake side camshaft, 29 ... Variable valve Timing device, 30 ... oil pump, 32 ... hydraulic control valve, 34 ... cam angle sensor, 35 ... crank angle sensor, 36 ... ECU (engine stall predicting means, engine stall preventing means)

Claims (4)

In a vehicle control device including a variable valve timing device that changes a valve timing by changing a rotational phase of a cam shaft (hereinafter referred to as a “VCT phase”) with respect to an engine crankshaft,
Engine stall prediction means for predicting whether or not an engine stall will occur;
The engine power transmission system is controlled so as to prevent engine stall when the engine stall prediction means predicts that engine stall will occur when the actual VCT phase is not at a predetermined starting position during vehicle brake operation. A vehicle control device comprising: an engine stall prevention means.   2. The vehicle control device according to claim 1, wherein the engine stall prevention unit prevents the engine stall by setting a speed change mechanism provided in the power transmission system to a neutral state. 3.   3. The vehicle control device according to claim 1, wherein the engine stall prevention unit prevents the engine stall by releasing a lock-up clutch of a torque converter provided in the power transmission system. 4. .   The engine stall prediction means predicts whether or not the engine stall will occur based on at least one of a brake operation state, an engine rotation speed, and a vehicle speed. The vehicle control device described.

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