JP2658365B2 - Control method of stepper motor driven exhaust gas recirculation control valve - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an exhaust gas recirculation control valve used in an exhaust gas recirculation control device of an internal combustion engine, and more particularly to a stepper motor driven exhaust gas. The present invention relates to a control method relating to a stepper motor initialization process in a recirculation control valve.

[Related Art] An exhaust gas recirculation control valve used in an exhaust gas recirculation control device of an internal combustion engine is configured such that opening and closing and control of the valve opening amount are electrically performed by a stepper motor. Control valves have already been proposed, which are disclosed, for example, in JP-A-57-193751 and JP-A-62-136680.

In the exhaust gas recirculation control valve, it is preferable that the valve element is pressed against the valve seat with a predetermined valve closing force so that the exhaust gas recirculation is reliably stopped when the valve is closed. In view of this, the valve drive rod and the valve shaft, which are reciprocated in the axial direction by the stepper motor, are not directly and rigidly connected to each other, and are connected with a compression-type elastic member such as a compression coil spring or a rubber-like elastic member. In the fully opened state, it is considered that a valve element provided on the valve shaft is pressed against the valve shaft by a compression elastic deformation of the compression elastic member so that a predetermined valve closing force is obtained. I have.

[Problems to be Solved by the Invention] In a stepper motor drive type exhaust gas recirculation control valve, unless an additional measuring device such as a potentiometer is provided, the drive position of the valve element (from the number of steps given to the stepper motor) (Absolute value) cannot be known, so that it is necessary to bring the valve element to the fully open position by the stepper motor when the internal combustion engine is started, and to perform an initialization process for detecting the drive position of the valve element from the number of steps at this time.

In the initialization process, it is necessary for the stepping motor to perform a valve closing drive at a required output so that the compression type elastic member is compressed elastically deformed by a predetermined amount and the valve element is closed with a predetermined valve closing force. However, at extremely low temperatures, the effective output of the stepper motor decreases due to the high viscosity of the oil in the bearings and threaded portions of the rotating parts of the stepper motor, so that the stepper motor has a predetermined valve closing valve element. It may not be possible to close the valve until the valve is closed with force. In this case, the normal initialization process is not performed, and in this initialization process, the relationship between the actual position of the valve element and the number of steps is disturbed, and the valve element is driven more to the valve opening side accordingly. As a result, exhaust gas recirculation is performed at a flow rate higher than the appropriate flow rate, and the operability of the internal combustion engine deteriorates.

An object of the present invention is to provide a control method of a stepper motor driven exhaust gas recirculation control valve in which an appropriate initialization process is performed even when the engine is started at an extremely low temperature.

Means for Solving the Problems According to the present invention, as described above, an axial movement of a valve drive rod reciprocated in an axial direction by a stepper motor is transmitted to a valve shaft via a compression elastic member. In a fully closed state, a valve element provided on the valve shaft is pressed against a valve seat by a compression elastic deformation of the compression elastic member to obtain a valve closing force, so that a stepper motor drive type is provided. In the control method of the exhaust gas recirculation control valve, the valve element is brought to a fully closed position by a stepper motor when the engine temperature becomes equal to or higher than a predetermined value after the start of the internal combustion engine, and the number of steps of the stepper motor and the valve element This is achieved by a control method characterized by initializing the relationship with the position.

[Operation and Effect of the Invention] When the engine temperature becomes equal to or higher than a predetermined value after the start of the internal combustion engine, the oil present in each rotating part of the stepper motor is also warmed up and has an appropriate viscosity. The motor outputs the required effective output,
Thus, in the initialization process performed at this time, the valve element is driven to a predetermined fully closed position where the valve element is pressed against the valve seat with a predetermined valve closing force under the compression elastic deformation of the compression elastic member. Become. Thereby, the initialization process of the relationship between the number of steps of the stepper motor and the position of the valve element is appropriately performed.

[Example] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

First, an example of a stepper motor drive type exhaust gas recirculation control valve used for carrying out the control method according to the present invention will be described with reference to FIG.

In the drawing, reference numeral 10 denotes a body of an exhaust gas recirculation control valve, in which a valve port 12 is provided.
A valve seat 14 is formed around 12. A cone-shaped valve element 16 is engaged with the valve port 12, and the valve element 16 has a valve seat.
By seating on the valve 14, the valve port 12 is closed, and by moving upward in the figure, the effective opening area of the valve port 12 is increased away from the valve seat 14, that is, the valve opening amount is increased.

The valve element 16 is provided integrally with the valve shaft 18, and the valve element 18 is fitted in a support hole 20 provided in the body 10 and supported so as to be movable in the axial direction from the body 10, that is, in the vertical direction in the figure. Have been. A spring retainer 22 is fixed to a tip (upper end) of the valve shaft 18.

A stepper motor 30 is mounted on the upper part of the body 10. The stepper motor 30 has an annular stator 32 and a rotor 36 disposed inside the stator 32 and rotatably supported by the body 10 by a ball bearing 34. Rotor
36 has a screw hole 38 at the center thereof, and the screw portion 42 of the valve drive rod 40 is screwed into the screw hole 38. Valve drive rod
Numeral 40 is non-rotatably engaged with the body 10 by the rotation preventing member 44 so as to be non-rotatably movable only in the axial direction. It has become. The valve drive rod 40 and the valve shaft 18 are arranged on the same axis, and a spring retainer 46 is fixed to a distal end (lower end) of the valve rod 40. A compression coil spring 43 for removing backlash of the screw portion 42 is provided between the spring retainer 46 and the body 10.

A compression coil spring 48 is provided between the spring retainer 46 and the spring retainer 22 of the valve shaft 18. Compression coil spring 48
Is located between the spring retainers 22 and 46 and urges them both in the axial direction to separate them. A stepper member 50 is attached to the spring retainer 46.
Engages with the spring retainer 22 to define the maximum separation between the spring retainers 22 and 46.

Thus, when the valve drive rod 42 descends from the stepper motor 30, the movement of the valve drive rod 42 is
18 will be transmitted. When the valve element 16 is brought to the fully closed position by the stepper motor 30, the compression coil spring
Reference numeral 48 denotes a compression elastic deformation, and the valve element 16 has a predetermined valve shut-off force by the repulsive force of the compression elastic deformation.
To maintain airtightness when the valve is closed.

FIG. 2 shows the relationship between the number of steps of the stepper motor 30 and the lift amount of the valve shaft 18, that is, the valve opening amount. FIG. 3 shows the number of steps of the stepper motor and the valve closing force applied to the valve element 16. The relationship is shown.

FIG. 4 shows an embodiment of a control device used for carrying out the control method of the stepper motor driven type exhaust gas recirculation control valve according to the present invention. The control device 60 is of an electronic control type including a general microcomputer, the information about the intake pipe pressure of the internal combustion engine from the intake pipe pressure sensor 62, the information about the rotation speed of the internal combustion engine from the rotation speed sensor 64, Information about the temperature of the cooling water of the internal combustion engine is given from the temperature sensor 66, and information about whether the ignition switch of the internal combustion engine is on or off is given from the ignition switch 68, and the operation of the stepper motor 30 is performed according to the information. Controlling the exhaust gas recirculation flow rate.

FIG. 5 shows a main routine for implementing the control method of the stepper motor driven exhaust gas recirculation control valve according to the present invention. This main routine is started when the ignition switch is turned on at the time of starting the internal combustion engine.In the first step 10, when the cooling water temperature Tw of the internal combustion engine detected by the temperature sensor 66 is equal to or higher than a predetermined value Twset. A determination is made as to whether there is. The predetermined value Twset corresponds to an engine warm-up temperature at which exhaust gas recirculation is started, and Tw ≧ Tw
If it is set, go to step 20; otherwise, go to step 30.

In step 20, the EGR permission flag Fegr is set to 1.

In step 30, the EGR permission flag Fegr is set to 0.

After steps 20 and 30, proceed to step 40,
In 40, for the initialization process, the actual number of steps of the step motor 30 is set to 10, the target number of steps is set to 0, and the flag Fint indicating that the initialization is being performed is set to 1. Done. After step 40, the process proceeds to step 50.

In step 50, it is determined whether or not the flag Fint is 0. When Fint = 0, it means that the initialization process is not being performed. At this time, the process proceeds to step 60. Otherwise, that is, when the initialization process is being performed, the process proceeds to step 110 so that the normal exhaust gas recirculation control is not performed. move on.

In step 60, it is determined whether or not the flag Fegr is 1. If Fegr = 1, proceed to step 70; otherwise, proceed to step 80.

In step 70, the target step number TSt to be given to the stepper motor 30 to perform the exhaust gas recirculation at a predetermined flow rate determined according to the intake pipe pressure, the engine speed, the engine cooling water temperature and the like is determined. Is done. After step 70, the process proceeds to step 110.

In step 80, the target step number TSt of the stepper motor 30 is set to zero. As a result, the valve element 16 is continuously driven toward the fully closed position until the cooling water temperature Tw reaches the predetermined value Twset and the exhaust gas recirculation is started. After step 80, the process proceeds to step 90.

In step 90, it is determined whether or not the cooling water temperature Tw of the internal combustion engine detected by the temperature sensor 66 is equal to or higher than a predetermined value Twset. When Tw ≧ Twset, the engine temperature has become equal to or higher than a predetermined value after the engine is started. At this time, the process proceeds to step 100 to execute the initialization process, and otherwise, the process proceeds to step 110.

In step 100, for the initialization process,
The current actual step St of the step motor 30 is set to 10, the target step number TSt is set to 0, and the flag Fint indicating that the initialization process is being performed is set to 1. After step 100, the process proceeds to step 110.

In step 110, it is determined whether or not the ignition switch is off. When the ignition switch is off, there is a time when the engine should be stopped. In this case, the process proceeds to step 120, and when not, that is, when the engine is operating, the process returns to step 50.

Step 120 is executed when the engine is stopped. In step 120, for the initialization process, the current actual step number St of the stepper motor is corrected by a predetermined step number, for example, 5 step numbers, and the target step TSt is set to 0, Then, the flag Fint is set to 1 again. Step 12
After 0, the process proceeds to step 130.

In step 130, it is determined whether or not the flag Fint is 0. When Fint = 0, it is the initialization processing at the time of engine stop, in other words, when the valve-closing drive ends, and the process proceeds to step 140 at this time.

In step 140, the power of the stepper motor 30 and the like is turned off.

FIG. 6 shows a time interruption routine. In step 200, it is determined whether or not the target step number TSt is equal to the current actual step number St. If TSt = St, proceed to step 260 to maintain the current number of steps,
If not = St, go to step 210.

In step 210, it is determined whether or not the target step number TSt is larger than the current practical step number St. TS
When t> St, that is, when the current actual step number is smaller than the target step number TSt, the process proceeds to step 220. When not, that is, when the current actual step number St is larger than the target step TSt, the process proceeds to step 230.

In step 220, the stepper motor 30 is driven by one step in the valve opening direction. As a result, the valve drive rod 40 rises, and this drive is transmitted to the valve shaft 18 via the stopper member 50, and the valve opening amount of the valve element 16 increases.
After step 220, proceed to 240, and in step 240,
The current actual step number St is increased by one.

In step 230, the stepper motor 30 is driven by one step in the valve opening direction. As a result, the valve drive rod 40 descends, and its moving force is transmitted to the valve shaft 18 via the compression coil spring 48, so that the valve opening amount of the valve element 16 is reduced. After step 230, the process proceeds to step 250, in which the current actual number of steps St is reduced by one.

In both cases after step 240 and step 250, the process proceeds to step 260. In step 260, it is determined whether or not the flag Fint is 1. When Fint = 1, the initialization process is in progress, and the process proceeds to step 270 at this time.

In step 270, it is determined whether the target step number TSt is equal to the current actual step number St. TSt
When = St, the initialization process, that is, when the fully-closed drive is completed, the process proceeds to step 280.

In step 280, the flag Fint is set to 0.

According to the flowchart as described above, the stepper motor 30
Is controlled, the valve element 16 is driven to the fully closed position at the time of engine termination and at the time of restart, respectively. Later, when the cooling water temperature becomes equal to or higher than the predetermined value, the valve element 16 is driven again to the fully closed position by the stepper motor 30 for the initialization process. Thus, the correct initialization process is always performed immediately before the actual start of the exhaust gas recirculation.

FIG. 7 shows the change over time of the actual number of steps of the stepper motor when the initialization process is performed by the control method according to the present invention as described above. As is apparent from this time chart, the effective output of the stepper motor 30 is insufficient due to the low temperature state, despite the initialization processing for bringing the valve element 16 to the fully closed position at the time of engine start. For this reason, even if the valve element 16 is not brought to the normal fully closed position, when the engine is warmed up and the exhaust gas recirculation starts after startup, the initialization process for bringing the valve element 16 to the fully closed position again is performed. Is executed. At this time, since the temperature of the stepper motor 30 has also risen, the effective output of the stepper motor 30 does not become insufficient for performing the normal initialization process, whereby the valve element 16 is moved to the normal fully closed position. And the correct initialization process is performed.

In the above-described embodiment, the stepper motor 30 is continuously driven in the valve closing direction to reduce the actual number of steps to 0 until the coolant temperature reaches a predetermined value. When the predetermined value is reached, the temperature of the oil in each rotating part of the stepper motor 30 also rises, and these viscosities are always at appropriate values. As a result, the initialization process when the cooling water temperature becomes equal to or higher than the predetermined value is performed more reliably.

In the above-described embodiment, the valve element 16 can be operated even when the engine is stopped.
Is driven fully closed. Thereafter, if the power supply to the stepper motor 30 is stopped by turning off the power, the compression coil spring
The repulsive force of 48 causes the valve drive rod 40 to rise, which causes the rotor 36 to rotate in the valve opening direction and the actual number of steps of the stepper motor 30 to be Sset. Since the stepper motor 30 may be driven until the actual step number becomes 0 from the time when the number is the predetermined value Sset, the time required for driving the stepper motor 30 is short, and during this time, the valve element 16 is already in the valve seat. 14, the exhaust gas recirculation is not substantially performed, and the engine startability may be degraded due to the exhaust gas recirculation control valve being opened when the engine is started. Be avoided.

In the above, the present invention has been described in detail with respect to a specific embodiment. However, the present invention is not limited to this, and various embodiments can be made within the scope of the present invention. It will be clear to those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a stepper motor drive type exhaust gas recirculation control valve used for carrying out the control method according to the present invention, and FIG. 2 is a relationship between the number of stepper motors and the valve opening amount of the stepper motors. FIG. 3 is a graph showing the relationship between the number of steps of the stepper motor and the valve closing force applied to the valve element. FIG. 4 shows one embodiment of the control device used for implementing the control method according to the present invention. 5 and 6 are flowcharts each showing an embodiment of the control method according to the present invention. FIG. 7 is a flowchart showing the actual number of steps of the stepper motor when the initialization process is performed by the control method according to the present invention. It is a time chart which shows a temporal change. 10 ... Body, 12 ... Valve port, 14 ... Valve seat, 16 ... Valve element, 18 ... Valve shaft, 20 ... Support hole, 22 ... Spring retainer, 30 ...
… Stepper motor, 32 …… stator, 34 …… ball bearing, 36
…… Rotor, 38 …… Screw hole, 40 …… Valve drive rod, 42 ……
Screw part, 43 ... Compression coil spring, 44 ... Detent member, 46
… Spring retainer, 48… Compression coil spring, 50… Stopper member, 60… Control device, 62… Intake pipe pressure sensor, 64…
… Rotation speed sensor, 66 …… Temperature sensor, 68 …… Ignition switch

Claims (1)

(57) [Claims] An axial movement of a valve driving rod reciprocated in an axial direction by a stepper motor is transmitted to a valve shaft via a compression elastic member, and in a fully closed state, the compression movement of the compression elastic member is reduced. In a control method of a stepper motor-driven exhaust gas recirculation control valve configured such that a valve element provided on the valve shaft is pressed against a valve seat by elastic deformation to obtain a valve closing force, A control method characterized in that the valve element is brought to a fully closed position by a stepper motor when the engine temperature becomes equal to or higher than a predetermined value after starting, and a relationship between the number of steps of the stepper motor and the position of the valve element is initialized.