JP2004251233A - Egr valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR valve capable of reducing the number of parts, pressure loss of the valve, and leak from a seat, facilitating assembly work, corresponding to mechanical failure such as fixation of a motor, and controlling reflux amount of exhaust gas steplessly. <P>SOLUTION: This EGR valve 1 has a main cylinder chamber 19 formed in a body 12 on a valve rod 7 side of a valve box 2, a main piston 21 fitted slidably in the main cylinder chamber 19 in the direction of shaft axis, a sub-cylinder chamber 23 formed on an extension line of a valve rod 7 of the main piston 21, a sub-piston 24 fitted slidably into the sub-cylinder chamber 23 in the direction of shaft axis to engage with the valve rod 7, a communicating hole 26 communicating the main cylinder chamber 19 with the sub-cylinder chamber 23, a supply and discharge passage 28 communicated with the main cylinder chamber 19 to supply and discharge fluid, and an operation rod 35 engaging with the main piston 21 and reciprocated in the axial direction by rotation of a motor 33. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an EGR (Exhaust Gas Recirculation) valve.
[0002]
[Prior art]
An EGR method is one of the methods for reducing exhaust gas, especially NOx, of an automobile diesel engine. In the EGR method, a part of the exhaust gas of an engine is returned to an intake system, mixed with fresh air (intake air), and sent to a combustion chamber, thereby reducing the amount of oxygen, lowering the combustion temperature, and suppressing the generation of NOx. ,. Since the EGR method reduces the pumping loss of the engine (the work of the piston sucking the intake air), the mechanical efficiency of the engine can be improved accordingly. On the other hand, the thermal efficiency will be reduced by the amount of oxygen. Further, when the amount of oxygen decreases, incomplete combustion occurs, and PM (particulate matter) increases contrary to the reduction of NOx. Therefore, in order to appropriately reduce NOx without lowering the efficiency of the engine and to suppress the contradictory increase in PM, the flow rate of the exhaust gas returned to the engine is determined according to the operating conditions (load, rotation speed) of the engine. Fine control is required by the EGR valve.
[0003]
As a conventional EGR valve for finely controlling the flow rate of exhaust gas returned to an engine, there is a conventional EGR valve in which an opening degree of an EGR valve is adjusted in multiple stages by a multi-stage positioning actuator (for example, see Patent Document 1).
[0004]
However, controlling the flow rate of exhaust gas returned to the engine stepwise has a limit in reducing NOx without lowering the efficiency of the engine and suppressing the contradictory increase in PM. Accordingly, development of an EGR valve for continuously controlling the flow rate of exhaust gas returned to the engine has been demanded. As a conventional EGR valve for continuously controlling the flow rate of exhaust gas returned to the engine, a first valve for opening and closing a first valve port and a second valve for opening and closing a second valve port are connected to an exhaust gas recirculation passage. Fixed to a valve shaft that is inserted into and retracted from a valve housing that can be moved forward and backward, and the lift position of the valve shaft is continuously adjusted by a shaft that is moved up and down by a stepping motor. (For example, see Patent Document 2).
[0005]
[Patent Document 1]
Japanese Utility Model Publication No. 7-41008 [Patent Document 2]
WO 99/61775 Pamphlet [0006]
[Problems to be solved by the invention]
However, in the EGR valve in which the position of the valve shaft equipped with the pair of valves is steplessly adjusted by the stepping motor to control the flow rate of the exhaust gas steplessly, since the pair of valves is used, There are the following problems. Since the number of parts is large and the assembling work is complicated, the manufacturing cost is increased. Since the pressure loss is large, a large amount of exhaust gas cannot flow. In addition, it is difficult to adjust the seating of the pair of valves at the same time, and the spring force for urging the valves cannot be increased. The fail-safe can cope with a failure in which power supply to the motor is stopped due to disconnection or the like, but cannot cope with a mechanical failure such as sticking of the motor.
[0007]
It is an object of the present invention to reduce the number of parts, facilitate assembly work, reduce valve pressure loss, reduce seat leakage, and respond to mechanical failures such as motor sticking. To provide an EGR valve capable of stepless control.
[0008]
[Means for Solving the Problems]
An EGR valve according to claim 1 of the present invention includes a valve box interposed in an exhaust gas recirculation path, a valve seat formed in a valve passage of the valve box, and a valve body detachably seated on the valve seat. An EGR valve having a valve spring for urging the valve body in a seating direction and a valve rod for moving the valve body back and forth.
A main cylinder chamber formed in the body on the valve stem side of the valve box; a main piston slidably fitted in the main cylinder chamber in the axial direction; and a center line of the valve stem of the main piston. A sub-cylinder chamber formed on an extension line, a sub-piston fitted slidably in the axial direction into the sub-cylinder chamber and abutting on the valve stem, and communicating the main cylinder chamber and the sub-cylinder chamber. A communication hole, a supply / discharge passage communicating with the main cylinder chamber to supply / discharge a fluid, and an operation rod abutting on the main piston and reciprocating in an axial direction by rotation of a motor are provided.
[0009]
In the above-described EGR valve, when the exhaust gas is not recirculated to the engine, the valve body is seated on the valve seat and the valve port is closed. When returning the flow rate of the exhaust gas according to the operating conditions of the engine to the engine, the fluid is supplied from the supply / discharge passage to the main cylinder chamber. Offset through. When the operation rod is stroked by a predetermined amount by rotation of the motor in a state where the resilience of the valve spring is reduced, the valve rod is stroked via the main piston against the resilience of the valve spring. At this time, since the resilience of the valve spring is reduced, the valve rod can be stroked against the resilience of the valve spring even with a small pressing force on the operating rod by the motor. Since the valve body is separated from the valve seat by the stroke amount of the operation rod via the valve rod, the sub piston and the main piston, the opening of the EGR valve is steplessly controlled by rotation by the motor. . When the opening of the EGR valve is reduced by the reverse rotation of the motor, the valve rod is pushed back by the resilient force of the valve spring, so that the main piston moves the main cylinder chamber to the return stroke of the operation rod accompanying the reverse rotation of the motor. It is pushed back following. At this time, since the sub-cylinder chamber is in a state of being filled with the fluid, the sub-piston maintains the state fixed to the sub-cylinder chamber.
[0010]
According to a second aspect of the present invention, in addition to the EGR valve of the first aspect, a first breather hole is provided between a stroke substitute chamber of the body and a spring installation chamber, and the valve box is provided with a first breather hole. It is characterized in that two breather holes are provided.
[0011]
Even if the volume of the body's stroke chamber and the spring installation chamber changes due to the operation of the motor, since the air is communicated to the atmosphere through the first breather hole and the second breather hole, resistance occurs in driving the motor. There is no.
[0012]
In the EGR valve according to claim 3 of the present invention, in addition to the EGR valve according to claim 1 or 2, a pressure reducing valve is interposed between the air source and the supply / discharge port of the supply / discharge passage. It is characterized by the following.
[0013]
Normally, the pressure of the air source of the vehicle fluctuates between 637 and 931 kPa due to repeated consumption of air by use of a brake and replenishment of air by an air compressor. It will act on the valve as it is. However, by interposing the pressure reducing valve, the fluctuation of the pressure acting on the EGR valve can be suppressed to a small value, thereby making it possible to reduce the capacity of the motor such as driving torque and power consumption.
[0014]
In the EGR valve according to a fourth aspect of the present invention, on the premise of the first to third aspects, a piston spring seat is projected from an upper end portion of the main piston. A spring is interposed between the body and the body.
[0015]
When the electromagnetic switching valve (30) is turned off and the supply / discharge passage (28) is released to the atmosphere, there is no force to push the main piston (21) to the valve body (6) via the sub piston (24). Therefore, the force for positioning the main piston (21) disappears. Therefore, the main piston (21) can freely move in the main cylinder chamber (19), and is easily vibrated. By interposing the main piston spring (40) between the piston spring seat (38) and the body (12), the vibration of the main piston (21) can be prevented.
[0016]
An EGR valve according to a fifth aspect of the present invention is based on the premise of the fourth aspect, wherein a spring is interposed between an upper end of the sub cylinder chamber and the sub piston.
[0017]
When the electromagnetic switching valve (30) is turned off and the supply / discharge passage (28) is released to the atmosphere, the pressure in the sub cylinder chamber (23) and the main cylinder chamber (19) becomes atmospheric pressure and the sub piston (24) is released. ) To the valve element (6), there is no force for positioning the sub-piston (24). Therefore, the sub-piston (24) can freely move in the sub-cylinder chamber (23), and easily vibrates. By interposing a sub piston spring (45) between the upper end of the sub cylinder chamber (23) and the sub piston (24), vibration of the sub piston (24) can be prevented.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0019]
As shown in FIG. 1, an EGR valve 1 according to the present embodiment is integrally assembled with a stepless positioning actuator 11, and the stepless positioning actuator 11 is a valve body 6 of the EGR valve 1. It is configured to control the opening of the steplessly. The EGR valve 1 is provided in the middle of an exhaust gas recirculation path (not shown) that connects an intake path and an exhaust path of a diesel engine (not shown). That is, the EGR valve 1 includes the valve box 2 in which the valve passage 3 is opened, and the valve passage 3 is provided in the middle of the exhaust gas circulation path. A valve port 4 is formed in the middle of the valve passage 3, and a valve seat 5 is formed around the valve port 4. The valve body 6 is mounted on the valve seat 5 so as to be detached and seated. The valve body 6 moves forward and backward along the center line of the valve seat 5 so that the opening degree of the valve port 4 can be increased or decreased. It has become. A valve rod 7 is formed integrally with the valve body 6, and the valve rod 7 is slidably supported by a guide 8 fixed to the valve box 2. A spring seat 10 is mounted on the tip of the valve stem 7, and a valve spring 9 is interposed between the spring seat 10 and the ceiling wall of the valve box 2 in a state of accumulation. That is, the valve rod 7 is constantly urged by the valve spring 9 in the direction in which the valve element 6 is seated on the valve seat 5.
[0020]
The stepless positioning actuator 11 has a body 12, which is assembled to the EGR valve 1 on the valve rod 7 side of the valve box 2 of the EGR valve 1 and is provided opposite to the body 12 and the valve box 2. Bolts are inserted into bolt insertion holes of three sets of flanges (not shown) and are fastened with nuts. A spring installation chamber 13 in which the valve spring 9 is installed is formed between the mating surfaces of the body 12 and the valve box 2, and a stroke substitute chamber 14 is formed at the upper end of the body 12. A first breather hole 15 is formed in a partition wall between the spring installation chamber 13 and the stroke room 14 of the body 12 so as to communicate the spring installation room 13 and the stroke room 14. A second breather hole 16 having a filter 17 is provided on the side wall on the side of the box 2 so as to communicate the spring installation chamber 13 with the atmosphere. By opening the first breather hole 15 and the second breather hole 16, even if the volumes of the stroke substitute chamber 14 and the spring installation chamber 13 change due to the operation of the motor 33, resistance is generated in driving the motor 33. Can be prevented.
[0021]
A cylinder portion 18 is formed at the center of the partition wall between the spring installation chamber 13 and the stroke allowance chamber 14 of the body 12, and a main cylinder chamber 19 is provided on an extension of the center line of the valve rod 7 of the cylinder portion 18, An insertion hole 20 smaller in diameter than the main cylinder chamber 19 is formed in series and concentrically. A main piston 21 is slidably fitted in the main cylinder chamber 19 in the axial direction, and a piston rod 22 connected to the upper surface of the main piston 21 is slidably inserted into the insertion hole 20. A sub-cylinder chamber 23 is formed concentrically on an extension of the center line of the valve stem 7 of the main piston 21, and a sub-piston 24 is slidably fitted in the sub-cylinder chamber 23 in the axial direction. . A stopper 25 is screwed on the outer periphery of the lower end of the main piston 21, and the upper end of the valve rod 7 abuts the center of the bottom of the sub-piston 24 in a state where the periphery of the bottom is in contact with the stopper 25. Is set to A communication hole 26 is formed at a connection portion of the piston rod 22 having a smaller diameter than the main piston 21 with the main piston 21 so as to communicate the main cylinder chamber 19 and the sub cylinder chamber 23. A supply / discharge port 27 is opened to communicate with the upper end of the main cylinder chamber 19. A supply / discharge passage 28 that supplies and discharges compressed air (hereinafter, referred to as air) as a pressure fluid is connected to the supply / discharge port 27, and the supply / discharge passage 28 is connected via a pressure reducing valve 29 and an electromagnetic switching valve 30. It is connected to an air source 31. The reason why the pressure reducing valve 29 is interposed is that, since the pressure of the air source fluctuates in the range of 637 to 931 kPa, the influence of the pressure fluctuation is avoided and the motor is downsized. If there is sufficient driving force of the motor, the pressure reducing valve 29 need not be provided. The electromagnetic switching valve 30 is configured to switch between supply and discharge of air to the supply / discharge port 27 according to a command from the controller 32.
[0022]
A DC motor 33 is mounted on the upper end surface of the body 12. A female screw formed on the inner peripheral surface of the hollow rotary shaft of the DC motor 33 is prevented from rotating by the motor housing 34 and is slidable in the axial direction. A male screw portion 36 formed on the outer peripheral surface of the operation rod 35 supported by the shaft is screwed. A piston spring seat 38 is screwed into a screw hole 39 at an upper end portion of the piston rod 22, and a main piston spring 40 is interposed between the piston spring seat 38 and the cylinder portion 18 in a stored state. . A sub-piston spring 45 is interposed between the upper end of the sub-cylinder chamber 23 and the sub-piston 24. The reason for interposing the main piston spring 40 is as follows. When the supply / discharge passage 28 is exhausted by switching the electromagnetic switching valve 30, the pressure in the sub-cylinder chamber 23 and the main cylinder chamber 19 becomes atmospheric pressure, and there is no force to push down the main piston 21 via the sub-piston 24. The force for positioning the piston 21 disappears. Therefore, the main piston 21 can freely move in the main cylinder chamber 19, and is in a state of being easily vibrated. The main piston spring 40 prevents the vibration of the main piston 21. Similarly, the sub-piston spring 45 is for preventing the sub-piston 24 from freely vibrating due to the atmospheric pressure in the sub-cylinder chamber 23. The lower end of the operating rod 35 is set so as to abut the bottom surface of the screw hole 39 of the piston rod 22. The rotation of the DC motor 33 is controlled by the controller 32 so that the vertical stroke of the operation rod 35 is adjusted. Reference numeral 41 denotes a stem seal, and reference numerals 42, 43, and 44 denote O-rings.
[0023]
Next, functions and effects will be described.
[0024]
When the exhaust gas is not recirculated to the engine, as shown in FIG. 1, the EGR valve 1 is in a state where the valve body 6 is seated on the valve seat 5 and the valve port 4 is closed. At this time, the valve spring 6 strongly urges the valve rod 7 upward, so that the valve body 6 is strongly seated on the valve seat 5. When the pressure on the downstream side (engine side) becomes higher than the pressure on the upstream side (exhaust pipe side), the valve body 6 separates from the valve seat 5 and opens the valve port 4. Can be reliably prevented. Further, since the valve body 6 is strongly seated on the valve seat 5, seat leakage can be reduced.
[0025]
The controller 32 obtains the opening degree of the valve body 6 corresponding to the flow rate of the exhaust gas returned to the engine by the EGR valve 1 according to the operating conditions of the engine and a DC motor for moving the operation rod 35 corresponding to the opening degree. The rotation speed of the motor 33 is calculated, a switching signal is transmitted to the electromagnetic switching valve 30, and a predetermined control signal is transmitted to the DC motor 33. When the electromagnetic switching valve 30 is switched, the air from the air source 31 is supplied from the supply / discharge passage 28 to the supply / discharge port 27 via the electromagnetic switching valve 30 and the pressure reducing valve 29, so that the main piston chamber 19 Since a pressing force acts on the sub-cylinder 23 and a force pressing the sub-piston 24 against the stopper 25 acts on the sub-cylinder chamber 23, the valve rod 9 is pressed and contracted via the spring seat 10. Force acts. The force for compressing the valve spring 9 by the air pressure does not actually compress the valve spring 9, but reduces the resilience of the valve spring 9. For example, the initial spring force of 300N is reduced to 50N.
[0026]
When the operation rod 35 is lowered by the rotation of the DC motor 33 as shown in FIG. 2 in a state where the resilience of the valve spring 9 is reduced, the valve rod 7 is moved through the main piston 21 to the valve stem 7. The spring 9 is pushed down against the elastic force. At this time, since the resilience of the valve spring 9 is sufficiently reduced, the valve rod 7 can resist the resilience of the valve spring 9 even with a small pressing force of the operation rod 35 by the DC motor 33. Can be pushed down. In other words, even if the initial spring force of the valve spring 9 is set large, the operation of pushing down the valve rod 7 by the small pushing force of the operation rod 35 by the DC motor 33 can be achieved. That is, the valve body 6 can be reliably seated on the valve seat 5 by the strong elastic force of the valve spring 9, and the valve body 6 is separated from the valve seat 5 by the small pushing-down force of the operating rod 35 by the DC motor 33. Can sit.
[0027]
FIG. 2 shows a case where the operation rod 35 has full stroke, that is, a case where the EGR valve 1 is fully opened. However, the opening degree of the EGR valve 1 is adjusted by adjusting the stroke amount of the operation rod 35 by the rotation of the DC motor 33. It can be controlled steplessly. That is, since the valve element 6 is separated from the valve seat 5 by the stroke of the operation rod 35 via the valve rod 7, the sub piston 24 and the main piston 21, the opening of the EGR valve 1 is controlled by the DC motor 33. The rotation is controlled steplessly. Since the flow rate of the exhaust gas returned to the engine can be finely controlled steplessly in accordance with the stepless control of the opening of the EGR valve 1, the engine can be precisely controlled in accordance with the operating conditions. NOx can be appropriately reduced without lowering the efficiency of the engine.
[0028]
When the DC motor 33 is rotated in the reverse direction and the opening of the EGR valve 1 is reduced, the valve rod 7 is pushed up by the resilient force of the valve spring 9, so that the main piston 21 moves the main cylinder chamber 19 into the DC motor 33. Is pushed up following the rise of the operating rod 35 due to the reverse rotation of. Also at this time, since the sub-cylinder chamber 23 is in a state of being filled with air, the sub-piston 24 is kept pressed against the stopper 25.
[0029]
By the way, if the DC motor 33 breaks down and locks while the valve body 6 is separated from the valve seat 5, the EGR valve 1 remains open and exhaust gas is supplied to the engine under operating conditions. However, since the heat is recirculated irrespective of the temperature, not only the thermal efficiency of the engine is reduced, but also a problem that black smoke blows out from the exhaust pipe may occur.
[0030]
In the EGR valve 1 according to the present embodiment, even if the DC motor 33 is locked due to a failure or the like while the valve body 6 is separated from the valve seat 5, as shown in FIG. When the switching valve 30 returns from the switching position to the normal position, the air in the sub cylinder chamber 23 passes through the communication hole 26, the main cylinder chamber 19, the supply / discharge port 27, the supply / discharge passage 28, the pressure reducing valve 29, and the electromagnetic switching valve 30. The valve rod 7 pushes up the sub-piston 24 against the sub-cylinder chamber 23 by the resilience of the valve spring 9, thereby causing the valve element 6 to move the valve body 6 to the valve seat 5. Can be seated. In this manner, even if the DC motor 33 is locked, it is possible to prevent the exhaust gas from flowing back to the engine by the EGR valve 1, so that the thermal efficiency of the engine is reduced and the black smoke is blown from the exhaust pipe. Can be prevented.
[0031]
According to the present embodiment described above, the opening degree of the EGR valve can be controlled in a stepless manner. Therefore, the exhaust gas recirculation amount is finely and optimally controlled according to the operating condition, so that the diesel engine The NOx amount can be reduced extremely effectively without impairing the performance of the diesel engine.
[0032]
Since the degree of opening of the EGR valve is controlled steplessly by a single valve element, the number of parts and the number of assembly steps can be reduced, and the manufacturing cost of the EGR valve and thus the diesel engine can be reduced. Further, since the valve passage has a simple configuration, the pressure loss of the EGR valve can be suppressed to a small value, and the flow rate of the exhaust gas returned to the engine can be set large.
[0033]
The initial spring force of the valve spring for seating the valve body of the EGR valve on the valve seat can be set large, so that the seat leakage can be reduced and the pressure on the engine side of the valve passage becomes the pressure on the exhaust pipe side. Even if it becomes larger, it is possible to prevent the valve body from being separated from the valve seat.
[0034]
Even if the DC motor locks, it is possible to prevent the exhaust gas from being recirculated to the engine by the EGR valve, so that it is possible to prevent a reduction in the thermal efficiency of the engine and the occurrence of black smoke from the exhaust pipe. it can.
[0035]
Note that the present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the gist of the present invention.
[0036]
For example, as the pressure fluid, not only compressed air (air) but also hydraulic pressure may be used. The motor is not limited to the DC motor, but may be a stepping motor or another motor.
[0037]
【The invention's effect】
As described above, according to the present invention, since the flow rate of the exhaust gas returned to the intake system of the engine can be continuously controlled, the recirculation amount of the exhaust gas can be finely and optimally controlled according to the operating conditions. Thus, the NOx amount of the diesel engine can be extremely effectively reduced without impairing the performance of the diesel engine.
[Brief description of the drawings]
FIG. 1 is a front sectional view showing an EGR valve according to an embodiment of the present invention.
FIG. 2 is a front sectional view showing the operation at the time of opening the valve.
FIG. 3 is a front sectional view showing the operation of the DC motor when an abnormality occurs.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... EGR valve, 2 ... valve box, 3 ... valve passage, 4 ... valve port, 5 ... valve seat, 6 ... valve body, 7 ... valve rod, 8 ... guide, 9 ... valve spring, 10 ... spring seat, 11 ... stepless positioning actuator, 12 ... body, 13 ... spring installation chamber, 14 ... stroke room, 15 ... first breather hole, 16 ... second breather hole, 17 ... filter, 18 ... cylinder part, 19 ... main cylinder Chamber, 20: insertion hole, 21: main piston, 22: piston rod, 23: sub cylinder chamber, 24: sub piston, 25: stopper, 26: communication hole, 27: supply / discharge port, 28: supply / discharge passage, 29 ... pressure reducing valve, 30 ... electromagnetic switching valve, 31 ... air source, 32 ... controller, 33 ... DC motor, 34 ... motor housing, 35 ... operation rod, 36 ... male thread, 38 ... piston spring Sheet, 39 ... screw hole, 40 ... main piston spring 41 ... stem seal, 42, 43, 44 ... O-ring, 45 ... sub-piston spring.

Claims (5)

A valve box provided in the exhaust gas recirculation path, a valve seat formed in a valve passage of the valve box, a valve element which is detachably seated on the valve seat, and biases the valve element in a seating direction. An EGR valve having a valve spring and a valve stem for moving the valve body forward and backward,
A main cylinder chamber formed in the body on the valve stem side of the valve box; a main piston slidably fitted in the main cylinder chamber in the axial direction; and a center line of the valve stem of the main piston. A sub-cylinder chamber formed on an extension line, a sub-piston fitted slidably in the axial direction into the sub-cylinder chamber and abutting on the valve stem, and communicating the main cylinder chamber and the sub-cylinder chamber. An EGR valve, comprising: a communication hole, a supply / discharge passage communicating with the main cylinder chamber to supply / discharge a fluid, and an operating rod abutting on the main piston and reciprocating in an axial direction by rotation of a motor. . The first breather hole is opened between a stroke substitute room of the body and a spring installation room, and a second breather hole is opened in the valve box. EGR valve. 3. The EGR valve according to claim 1, wherein a pressure reducing valve is interposed between the air source and the supply / discharge port of the supply / discharge passage. 4. The piston spring seat protrudes from the upper end of the main piston, and a spring is interposed between the piston spring seat and the body. 2. The EGR valve according to claim 1. The EGR valve according to claim 4, wherein a spring is interposed between an upper end portion of the sub cylinder chamber and the sub piston.

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