JP2007100564A - Control device of variable valve train - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a variable valve train for improving a control responsiveness by generating proper braking torque by preventing flow of an excessive electric current when starting speed reduction or reversal control of a motor controlled by an H-bridge circuit in a switching system. <P>SOLUTION: When switching the motor to a reverse rotation state D from a normal rotation state A, when counter electromotive voltage EM generated by inertial rotation of the motor is larger (B) than target voltage VM just after starting switching control of reversing the target voltage VM, both upstream side FET 1 and 2 of the H bridge circuit are turned off, and downstream side one FET 3 is controlled in PMW (the other FET 4 is turned off), and a carrying electric current of the motor is controlled in a valve corresponding to the target VM by using only the counter electromotive voltage EM, and a speed is reduced by the proper braking torque. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for a variable valve mechanism that makes an opening characteristic of an engine valve variable by driving control of a motor by an H bridge circuit.

Patent Document 1 discloses a variable valve mechanism that makes a lift of an engine valve variable with an operating angle by rotationally driving a control shaft by a motor.
Patent Document 2 discloses motor drive control by an H-bridge circuit.
JP 2001-003773 A JP-A-9-9691

By the way, in the variable valve mechanism, a counter electromotive voltage is generated by the rotation of the motor. Therefore, in order to accurately control the motor current by PWM control, the switching duty ratio is set in consideration of the counter electromotive voltage. It is desirable to decide.
The counter electromotive voltage can be estimated from the rotational angular velocity of the motor.
Here, in order to decelerate or reverse the rotation of the motor, when the energization direction of the motor is switched to generate a reverse driving torque, immediately after the switching, the voltage remains on the switched motor and the inertial rotation of the motor. The counter electromotive voltage is in the same direction.

At this time, the current due to the counter electromotive voltage flows unintentionally through the path of the body diode of the upstream FET (switching element) turned off in the H → bridge circuit → the FET turned on on the upstream side → the motor. .
Here, immediately after switching, when the motor rotates at a high speed due to inertia and a large counter electromotive voltage is generated, the current flowing through the above path is large, so even if the downstream FET in the H bridge circuit is turned OFF, the target There is a problem that excessive current exceeding the current flows, braking torque more than necessary is generated, and the control angle of the rotation angle of the motor and thus the lift of the engine valve is lowered.

In particular, when control is performed using a motor with low inertia as a variable valve mechanism, deterioration of servo performance becomes obvious (see FIG. 6).
The present invention has been made in view of the above problems, and provides a control apparatus for a variable valve mechanism that can obtain a good control response by performing PWM control in consideration of a counter electromotive voltage of a motor. With the goal.

Therefore, in the present invention, the control of the variable valve mechanism that makes the opening characteristic of the engine valve variable by driving the motor so that the forward / reverse rotation direction can be switched by the H bridge circuit composed of four switching elements. A device,
When the driving torque generated by the motor and the motor rotation direction are opposite and the counter electromotive voltage of the motor exceeds the target voltage, the two upstream-side switching elements in the H-bridge circuit are both turned OFF, One of the downstream switching elements is turned OFF, and the other switching element is PWM-controlled to control the energization current.

  According to the above configuration, when the motor is decelerated and further reversed, if the drive torque generated by the motor and the motor rotation direction are opposite and the counter electromotive voltage of the motor exceeds the target voltage, only the counter electromotive voltage is used. Then, by performing PWM control of the downstream switching element, a desired energization current corresponding to the target voltage can be supplied to the motor, and the lift of the engine valve can be converged to the target value with good response.

Embodiments of the present invention will be described below.
FIG. 1 is a diagram illustrating a variable valve mechanism in the embodiment.
A variable valve mechanism 1 shown in FIG. 1 is a mechanism that changes the lift of an engine valve together with the operating angle, as disclosed in, for example, Japanese Patent Application Laid-Open No. 11-107725. In this embodiment, the variable valve mechanism 1 is applied to an intake valve. An example is shown.

  The variable valve mechanism 1 includes an intake valve 11 slidably provided on a cylinder head (not shown) and a drive shaft 2 rotatably supported by a cam bracket (not shown) on the cylinder head. A drive eccentric cam 3 fixed to the drive shaft 2 by press-fitting or the like, and a control that is rotatably supported by the same cam bracket at a position above the drive shaft 2 and arranged in parallel with the drive shaft 2 A shaft 12, a rocker arm 6 as an intermediate member swingably supported by the control eccentric cam 18 of the control shaft 12, and a swing cam 9 that contacts the tappet 10 disposed at the upper end of the intake valve 11; It has.

The drive eccentric cam 3 and the rocker arm 6 are linked by a link arm 4, and the rocker arm 6 and the swing cam 9 are linked by a link member 8.
The drive shaft 2 is driven by a crankshaft of an internal combustion engine via a timing chain or a timing belt.
The drive eccentric cam 3 has a circular outer peripheral surface, the center of the outer peripheral surface is offset from the axis of the drive shaft 2 by a predetermined amount, and the annular portion of the link arm 4 is rotatable on the outer peripheral surface. Is fitted.

The rocker arm 6 has a substantially central portion supported by the control eccentric cam 18 so as to be swingable, and an arm portion of the link arm 4 is linked to one end of the rocker arm 6 via a connecting pin 5. The upper end portion of the link member 8 is linked to the end portion via the connecting pin 7.
The control eccentric cam 18 is eccentric from the axis of the control shaft 12, whereby the rocking center of the rocker arm 6 changes according to the angular position of the control shaft 12.

The rocking cam 9 is fitted to the outer periphery of the drive shaft 2 and is rotatably supported, and a lower end portion of the link member 8 is linked to an end portion extending laterally via a connecting pin 17. ing.
On the lower surface of the swing cam 9, a base circle surface concentric with the drive shaft 2 and a cam surface extending in a predetermined curve from the base circle surface are continuously formed. These base circle surface and cam surface come into contact with the upper surface of the tappet 10 according to the swing position of the swing cam 9.

That is, the base circle surface is a section where the lift amount of the intake valve 11 becomes 0 as a base circle section. When the swing cam 9 swings and the cam surface contacts the tappet 10, the intake valve 11 gradually moves. It will lift.
A slight ramp section is provided between the base circle section and the lift section.

As shown in FIG. 1, the control shaft 12 is configured to rotate within a predetermined angle range by a DC servo motor 13 which is a lift / operation angle control actuator provided at one end.
The DC servo motor 13 is controlled by a control signal from the controller 50 and rotationally drives the control shaft 12 via the worm gear 15.

Here, the rotation angle of the control shaft 12 is detected by an angle sensor 14 composed of, for example, a potentiometer, and the DC servo motor 13 is closed-loop controlled based on the detected actual control state.
The operation of the variable valve mechanism 1 will be described. When the drive shaft 2 rotates, the link arm 4 moves up and down by the cam action of the drive eccentric cam 3, and the rocker arm 6 swings accordingly.

The swing of the rocker arm 6 is transmitted to the swing cam 9 via the link member 8, and the swing cam 9 swings.
The tappet 10 is pressed by the cam action of the swing cam 9, and the intake valve 11 is lifted.
Here, when the angle of the control shaft 12 is changed by being rotationally driven by the DC servo motor 13, the center position of the rocker movement of the rocker arm 6 is moved to change the initial position of the rocker arm 6. The initial swing position of the is changed.

For example, if the control eccentric cam 18 is positioned upward in the figure, the rocker arm 6 is positioned upward as a whole, and the end of the swing cam 9 on the side of the connecting pin 17 is relatively lifted upward. Become.
That is, the initial position of the swing cam 9 is inclined in a direction in which the cam surface is separated from the tappet 10.
Therefore, when the swing cam 9 swings as the drive shaft 2 rotates, the base circle surface is kept in contact with the tappet 10 for a long time, and the period during which the cam surface is in contact with the tappet 10 is short.

Accordingly, the lift amount of the intake valve 11 is reduced as a whole, and the angle range from the opening timing to the closing timing of the intake valve 11, that is, the operating angle is also reduced.
Conversely, assuming that the control eccentric cam 18 is positioned downward in the figure, the rocker arm 6 is positioned downward as a whole, and the end of the swing cam 9 on the side of the connecting pin 17 is relatively pushed downward. It becomes a state.

That is, the initial position of the swing cam 9 is inclined in a direction in which the cam surface approaches the tappet 10.
Therefore, when the swing cam 9 swings as the drive shaft 2 rotates, the portion that contacts the tappet 10 immediately shifts from the base circle surface to the cam surface.
Accordingly, the lift amount of the intake valve 11 increases as a whole, and the operating angle of the intake valve 11 also increases.

The initial position of the control eccentric cam 18 continuously changes according to the rotation angle of the control shaft 12, and accordingly, the lift characteristics of the intake valve 11 change continuously.
That is, the lift and the operating angle can be continuously expanded and contracted simultaneously.
Here, the configuration of the controller 50 will be described with reference to a control block diagram shown in FIG.

A detection signal (output voltage) from the angle sensor 14 is input to an angle signal input unit 501, and the angle signal input unit 501 converts the detection signal (output voltage) into rotation angle data of the control shaft 12. Output.
The rotation angle data of the control shaft 12 is input to the motor current command generation unit 502.
The motor current command generation unit 502 receives an angle command (target angle) of the control shaft 12 that is separately calculated based on the engine operating state, and the angle command and the actual angle detected by the angle sensor 14. Based on the motor current command (target motor current) is calculated and output.

  In the drive signal calculation unit 503, the motor current command is input, and the drive signal of each switching element of the switching circuit 505, which will be described later (ON of the upstream side element, is set) so that the current flowing through the DC servo motor 13 becomes the command value. OFF and downstream element duty ratio) are calculated and output. Here, the duty ratio is determined based on the voltage VB of the drive power source 506 and the counter electromotive voltage EM generated with the rotation of the DC servo motor 13 in order to flow the current according to the motor current command with high accuracy.

  In the switching circuit 505, as shown in FIG. 3, a switching element (FET) 1 and a switching element (FET) 3 are connected in series, and a switching element (FET) 2 and a switching element (FET) 4 are connected in series. These are connected in parallel to the drive power source 506, and the DC servo motor 13 is connected between the connection point between the switching element FET1 and the switching element FET3 and the connection point between the switching element FET2 and the switching element FET4. It is composed of an H bridge circuit.

  The upstream side FETs 1 and 2 are directly ON / OFF controlled by inputting the drive signal from the drive signal calculation unit 503, and the downstream side FETs 3 and 4 are converted to the drive signal from the drive signal calculation unit 503. Based on this, a switching pulse (PWM pulse) generated by the PWM signal generation circuit 504 is input, and the power supply to the DC servo motor 13 is switched ON / OFF to perform PWM control.

Here, the upstream side FETs 1 and 2 are selectively controlled to be ON and the other is OFF as the basic operation mode, and the energization direction of the DC servo motor 13 is switched. When a predetermined condition is satisfied such as during deceleration or reversal of the motor, both are turned off and PWM control using only the back electromotive force is performed.
The voltage of the driving power source 506 is detected by a driving voltage detector 507 and output to the driving signal calculator 503.

The counter electromotive voltage EM generated with the rotation of the DC servo motor 13 is calculated by the counter electromotive voltage calculation unit 508 based on the rotation angular velocity of the DC servo motor 13 and is output to the drive signal calculation unit 503.
The back electromotive voltage calculation unit 508 receives the rotational angular velocity data obtained by the rotational speed calculation unit 509, and the back electromotive voltage calculation unit 508 multiplies the rotational angular velocity data by a constant stored in advance. Thus, the counter electromotive voltage is obtained, and this is output to the drive signal calculation unit 503.

The rotational speed calculation unit 509 obtains rotational angular velocity data by differentiating the rotational angle data of the control shaft 12 output from the angle signal input unit 501.
Note that the rotation speed calculation unit 509 calculates the difference between the latest rotation angle and the rotation angle before a certain time (for example, 10 ms) as data indicating the rotation angular speed.
Here, between the angle signal input unit 501 and the rotation speed calculation unit 509, a hysteresis processing unit 510 that performs a hysteresis process for removing noise from the rotation angle data is provided.

Next, details of processing in the drive signal calculation unit 503 and, in turn, details of motor control will be described with reference to the flowchart of FIG.
In step S1, it is determined whether the target voltage VM of the motor is zero. Here, the target voltage VM is a voltage desired to be applied to the motor in order to obtain the motor target current ICMD (a positive or negative value corresponding to the energization direction) calculated by the motor current command generator 502, and the target current VM Calculated by multiplying ICMD by the DC resistance value RM of the motor.

When it is determined in step S1 that the target voltage VM of the motor is not 0, that is, there is a motor drive request, the process proceeds to step S2.
In step S2, it is determined whether the target voltage VM is positive (eg, positive when a voltage is applied in the direction of the arrow of VM in FIG. 3).
If it is determined in step S2 that the target voltage VM is positive, the process proceeds to step S3.

In step S3, it is determined whether the back electromotive voltage EM of the motor is positive. Here, it is assumed that the back electromotive force EM is applied in the direction of motor rotation when the target voltage VM is maintained positive (for example, the direction of the arrow EM in FIG. 3).
When it is determined in step S3 that the back electromotive voltage EM is positive, the process proceeds to step S4.
In step S4, the FETs 1 to 4 of the switching circuit 505 are controlled as follows.

FET1 = ON
FET2 = OFF
FET3 duty ratio = 0 (substantially OFF)
Duty ratio of FET4 = | VM | / (VB− | EM |)
Here, VB is a power supply voltage, and (VB− | EM |) represents an effective voltage VA that can be used for driving the motor.

If it is determined in step S2 that the target voltage VM is negative, the process proceeds to step S5.
In step S5, it is determined whether the back electromotive voltage EM is negative.
If it is determined in step S5 that the back electromotive voltage EM is negative, the process proceeds to step S6.
In step S6, the FETs 1 to 4 of the switching circuit 505 are controlled as follows.

FET1 = OFF
FET2 = ON
Duty ratio of FET3 = | VM | / (VB− | EM |)
FET4 duty ratio = 0
As described above, in steps S4 and S6 in which the direction of the target voltage VM is maintained to be positive or negative, the PWM control according to the target voltage VM is performed using the voltage obtained by subtracting the back electromotive voltage EM from the power supply voltage VB as an effective voltage. As a result, a current corresponding to the target voltage VM is supplied to the motor (see FIGS. 5A and 5D).

Further, when the back electromotive voltage EM is determined to be negative in step S3, or when the back electromotive voltage EM is determined to be positive in step S5, the process proceeds to step S7.
In step S7, the target voltage VM (absolute value) and the back electromotive voltage EM (absolute value) are compared in magnitude.
When it is determined in step S7 that | VM | <| EM |, that is, when the motor inertia rotation immediately after the positive / negative of the target voltage VM is switched, the counter electromotive voltage EM exceeds the target voltage VM. The process proceeds to step S8.

In step S8, whether the VM is positive or negative is determined.
If it is determined in step S8 that VM is negative, the process proceeds to step S9.
In step S9, the FETs 1 to 4 of the switching circuit 505 are controlled as follows.
FET1 = OFF
FET2 = OFF
Duty ratio of FET3 = | VM | / | EM |
FET4 duty ratio = 0
Then, the current due to the back electromotive voltage flows through the path of motor → PWM controlled FET3 → FET4 body diode → motor (see FIG. 5B).

If it is determined in step S8 that the VM is positive, the process proceeds to step S10.
In step S10, the FETs 1 to 4 of the switching circuit 505 are controlled as follows.
FET1 = OFF
FET2 = OFF
FET3 duty ratio = 0
Duty ratio of FET4 = | VM | / | EM |
Then, a current due to the counter electromotive voltage flows through a path of motor → PWM controlled FET 4 → FET 3 body diode → motor.

As described above, in steps S9 and S10 immediately after the target voltage VM is switched between positive and negative, only the counter electromotive voltage EM is generated in the motor, and PWM control is performed using the counter electromotive voltage EM as the effective voltage VA. An appropriate braking torque can be applied by supplying a current corresponding to the target voltage VM without flowing a current.
Further, when it is determined in step S7 that | VM |> | EM |, that is, as the inertial rotation of the motor to which the braking torque is applied by the above control decreases, the counter electromotive voltage EM decreases, and the target If it falls below the voltage VM, the process proceeds to step S11.

In step S11, whether the VM is positive or negative is determined.
If it is determined in step S11 that VM is negative, the process proceeds to step S12.
In step S12, the FETs 1 to 4 of the switching circuit 505 are controlled as follows.
FET1 = OFF
FET2 = ON
Duty ratio of FET3 = (| VM |-| EM |) / VB
FET4 duty ratio = 0
If it is determined in step S11 that the VM is positive, the process proceeds to step S13.

In step S13, the FETs 1 to 4 of the switching circuit 505 are controlled as follows.
FET1 = ON
FET2 = OFF
FET3 duty ratio = 0
Duty ratio of FET4 = (| VM |-| EM |) / VB
As described above, when the target voltage VM becomes larger than the back electromotive voltage EM, the current flowing in the closed circuit formed between the motor and the upstream FET by the back electromotive voltage EM and the duty by the power supply voltage VB. By adding the shortage current flowing to the downstream FET to be controlled, a current corresponding to the target voltage VM can be supplied to give an appropriate braking torque (see FIG. 5C).

If the motor target voltage VM is 0 in step S1, that is, if a motor stop request is generated, the process proceeds to step S14, and the FETs 1 to 4 of the switching circuit 505 are controlled as follows. To stop.
FET1 = OFF
FET2 = OFF
FET3 duty ratio = 0
FET4 duty ratio = 0
5A to 5D show a process of switching the motor in the normal rotation state to the reverse rotation state through the switching control according to the present invention.

FIG. 6 shows a state change during the same control as in the prior art.
The structure of the variable valve mechanism 1 is not limited to that shown in FIG. 1, and the engine valve whose open characteristic is variable by the variable valve mechanism 1 is not limited to the intake valve. The opening characteristics of the variable engine valve are not limited to the lift and the operating angle.

The perspective view which shows the variable valve mechanism in embodiment. The block diagram which shows the control function of the controller in embodiment. The figure which shows the detail of the switching circuit in embodiment. The flowchart which shows the control function of the controller in embodiment. The figure which shows the process in which the rotation direction of the motor in embodiment is switched. The figure which shows the mode of the state change at the time of control in embodiment compared with the past.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Variable valve mechanism, 11 ... Intake valve, 12 ... Control shaft, 13 ... DC servo motor, 14 ... Angle sensor, 501 ... Angle signal input part, 502 ... Motor current command generation part, 503 ... Drive signal calculation part, 504... PWM signal generation circuit, 505... Switching circuit, 506... Drive power supply, 507... Drive voltage detector, 508 .. counter electromotive voltage calculator, 509.

Claims (5)

A control device for a variable valve mechanism that varies the opening characteristics of an engine valve by driving a motor so that the forward / reverse rotation direction can be switched by an H bridge circuit composed of four switching elements,
When the driving torque generated by the motor and the motor rotation direction are opposite and the counter electromotive voltage of the motor exceeds the target voltage, the two upstream-side switching elements in the H-bridge circuit are both turned OFF, A control device for a variable valve mechanism, wherein one of the downstream switching elements is turned off, and the other switching element is PWM controlled to control the energization current.   The control apparatus for a variable valve mechanism according to claim 1, wherein the counter electromotive voltage is calculated based on a rotation speed of a motor.   When the target voltage of the motor is VM and the counter electromotive voltage is EM, the energization duty ratio DUTY in the downstream PWM-controlled switching element is set to DUTY = | VM | / | EM | The control apparatus for a variable valve mechanism according to claim 1 or 2.   The motor drive control device according to any one of claims 1 to 3, wherein the variable valve mechanism makes the lift of the engine valve variable according to a rotation angle of the motor.   The variable valve mechanism is rotationally driven by a crankshaft of an engine, a drive shaft having a drive cam fixed on the outer periphery thereof, a rocker arm that swings by rotation of the drive cam linked to one end, and the other end of the rocker arm 5. A rocking cam that opens the engine valve in linkage with the portion, and the rocking arm swinging fulcrum is changed by drive control of the motor. 6. The motor drive control apparatus according to 1.

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