JPH084601A - Exhaust gas recirculation system for diesel engine - Google Patents

Abstract

(57) [Abstract] [Purpose] In a diesel engine, the intake throttle valve is driven mechanically and non-linearly with respect to the engine load, and it is inexpensive, highly reliable and highly accurate without changing the EGR rate in the light load region. To EG
Secure R amount. [Structure] A mechanical cam 25 is used in an exhaust gas recirculation system of a diesel engine in which an intake throttle valve 15 is provided in an intake passage 14 and an EGR control valve 8 which is controlled to be fully opened / closed is provided midway in an exhaust gas recirculation pipe 7. Then, the intake throttle valve 15 is driven, and the intake throttle valve 15 is kept open at a predetermined opening until the diesel engine reaches a predetermined load.When the engine exceeds a predetermined load, the load is increased. The intake throttle valve 15 is gradually opened according to the shape of the cam surface of the cam 25. Further, the intake throttle valve 15 is provided with an actuator 26 for controlling the opening of the intake throttle valve 15 regardless of the load on the engine when the EGR is cut.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for a diesel engine, and more particularly to a diesel engine exhaust gas recirculation system provided with an intake throttle valve in an intake passage.

[0002]

2. Description of the Related Art In order to reduce NOx in exhaust gas,
An EGR device is known in which exhaust gas flowing in an exhaust passage is recirculated into an intake passage through an exhaust gas recirculation (hereinafter referred to as EGR) passage. In such an EGR device, an EGR control valve is usually provided in the EGR pipe, and the EGR gas amount to be supplied into the intake passage is controlled by the opening degree of the EGR control valve. Such an EGR device is used not only in gasoline engines but also in diesel engines.

By the way, NOx in a diesel engine
When EGR is performed in order to reduce the EGR, since the air-fuel ratio of the engine is operated lean in the low load range of the engine, the EGR
I want to increase the amount. That is, since the exhaust gas discharged when the engine is in a light load state contains a large amount of oxygen, the effect is small unless a large amount of EGR is performed, and smoke is generated even if a large amount of EGR is performed. Hard to occur.

On the other hand, in the high load region of the diesel engine, the amount of oxygen in the exhaust gas is small, and even if a small amount of EGR is performed, NO
It is effective in reducing x. Then, if a large amount of EGR is performed in the high load region of the engine, smoke is likely to occur, so it is desirable to keep the amount of EGR in the high load region small. Japanese Patent Application Laid-Open No. 55-17659 discloses a diesel engine having an intake throttle valve provided in an intake passage for performing such EGR control. In the device proposed in this publication, the negative pressure generated in the intake throttle valve is guided to a negative pressure actuator, and E
The opening of the GR control valve is increased.

However, in the device of this publication, since the opening degree of the EGR control valve is controlled by the negative pressure generated in the intake throttle valve, there is a problem that the degree of freedom is small and it is difficult to supply the required EGR amount. is there. Therefore, in recent years, a system has been proposed in which the opening degree of the intake throttle valve and the opening degree of the EGR control valve provided in the middle of the EGR pipe are independently controlled, and the required EGR amount can be accurately supplied. Some of such systems keep the intake throttle valve fully closed until a predetermined load is reached (Japanese Patent Laid-Open No. 55-1097).
No. 54).

[0006]

However, in the device described in JP-A-55-109754, it is necessary to perform EGR even in the light load range to reduce NOx. The EGR control valve must be controlled to open in the fully closed state, and in this case, there is a risk that the variation in the EGR rate will increase due to the variation in the opening of the intake throttle valve.

Therefore, according to the present invention, the EGR control valve is fully open / closed control, and the intake throttle valve is mechanically driven with a characteristic that it opens nonlinearly with respect to the load of the engine, so that the EGR in the light load range is performed. It is an object of the present invention to provide an exhaust gas recirculation device for a diesel engine, which has a small fluctuation in the rate.

[0008]

According to the present invention to achieve the above object, in a diesel engine having an intake throttle valve provided in an intake passage, an exhaust gas recirculation in which a part of exhaust gas flowing through the exhaust passage is returned to the intake passage. An exhaust gas recirculation device for a diesel engine provided with a passage, wherein the intake throttle valve is kept open at a predetermined opening until the diesel engine reaches a predetermined load, and when the load exceeds a predetermined load, the load is increased. And an EGR control valve provided in the middle of the exhaust gas recirculation passage, and an opening / closing means for opening / closing the EGR control valve. Is characterized by.

The opening adjusting means of the intake throttle valve is
When the EGR control valve is fully closed and the first opening adjusting means for adjusting the opening degree of the intake throttle valve according to the depression amount of the accelerator pedal, the above-mentioned regardless of the depression amount of the accelerator pedal. It is desirable that the intake throttle valve is constituted by second opening degree adjusting means for controlling the opening of the intake throttle valve.

[0010]

According to the exhaust gas recirculation system for an internal combustion engine of the present invention, the intake throttle valve is kept open at a predetermined opening by the opening adjusting means of the intake throttle valve until the diesel engine reaches a predetermined load. When the above is reached, the intake throttle valve is gradually opened as the load increases. An EGR control valve provided in the middle of the exhaust gas recirculation passage is provided.
The GR control valve is opened / closed by the opening / closing means. The intake throttle opening degree adjusting means adjusts the opening degree of the intake throttle valve according to the amount of depression of the accelerator pedal, and the EGR control valve is fully closed. It may be constituted by a second opening degree adjusting means for controlling the opening of the intake throttle valve regardless of the depression amount of the accelerator pedal.

[0011]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram showing the configuration of an embodiment of an exhaust gas recirculation device for a diesel engine with an exhaust brake of the present invention. In FIG. 1, 1 is a 4-cylinder diesel engine, 2
Is an intake manifold, 3 is an exhaust manifold, 4 is an exhaust pipe,
5 is an exhaust brake device provided with an exhaust control valve 51 provided in the middle of the exhaust pipe 4, 6 is a muffler, 7 is an exhaust gas recirculation pipe (EGR pipe) that guides exhaust gas from the exhaust manifold 3 to the intake manifold 2, and 8 is EGR control valve, 9 is a vacuum pump, 10 is a control circuit (ECU: engine control unit), and 11, 12 and 22 are control valves which are provided in the middle of the negative pressure introducing pipe 13 and whose opening and closing are controlled by the control circuit 10. , 14 are intake pipes connected to the intake manifold 2, 15
Is an intake throttle valve (intake control valve) provided in the intake pipe 14, 23 is an accelerator pedal, 25 is an accelerator pedal 2
3 is a cam connected to the accelerator wire 24 to drive the intake throttle valve 15, and 26 is an actuator capable of independently controlling the intake throttle valve 15.

The EGR control valve 8 is opened / closed by a signal from the control circuit 10. That is, when the control valve 12 is opened by the control circuit 10, the negative pressure from the vacuum pump 9 is guided to the EGR control valve 8 through the negative pressure introducing pipe 13 and opens. The EGR control valve 8 opens, and the exhaust gas flows from the exhaust manifold 3 through the EGR pipe 7 to the intake manifold 2
When it is recirculated to NOx, NOx in the exhaust gas is reduced.

The exhaust brake device 5 is valve-closed when the control circuit 10 detects the deceleration state of the vehicle. That is, when the deceleration state of the vehicle is detected by the control circuit 10, the control valve 11 is opened by the control circuit 10 and the negative pressure from the vacuum pump 9 is guided to the exhaust brake device 5. To be closed. When the exhaust control valve 51 is closed, the exhaust gas is confined in the exhaust pipe 4 and the EGR pipe 7, and the back pressure increases, so that the pumping friction of the piston increases and it functions as a brake.

In this embodiment, the intake throttle valve 15 has a cam 25 provided with an arm 151 provided at an end of a rotary shaft 150 thereof.
The valve opening is controlled by being pushed. Further, the cam 25 is connected to the accelerator pedal 2 via the accelerator wire 24.
3 is connected, and when the accelerator pedal 23 is depressed, it is pulled by the accelerator wire 24 and rotates. The cam 25 does not contact the arm 151 at first, but when the cam 25 rotates a predetermined opening degree, the cam 25 contacts the arm 151 of the intake throttle surface 15,
By the subsequent rotation, the arm 151 is pushed by the cam 25 to rotate, and the opening degree of the intake throttle valve 15 increases. The amount of depression of the accelerator pedal 23 and the opening characteristic of the intake throttle valve 15 depend on the shape of the cam surface on which the cam 25 pushes the arm 151.

The actuator 26 forcibly opens the intake throttle valve 15 to a predetermined opening regardless of the operation of the cam 25. That is, the actuator 26 forcibly opens the intake throttle valve 15 when the control circuit 10 opens the control valve 22 and the negative pressure from the vacuum pump 9 is guided to the actuator 26 via the negative pressure introducing pipe 13. Let me speak.

Although not shown, an accelerator opening sensor is attached to the rotary shaft 250 of the cam 25. 2 (a) is an EG of the internal combustion engine with the exhaust brake of FIG.
It is a configuration explanatory view including a sectional view showing details of configurations of an R control valve 8 and an exhaust valve 30 provided in the internal combustion engine 1. Figure 2
In (a), the same components as those in FIG. 1 are designated by the same reference numerals.

An intake port 16 is provided at a portion of the diesel engine 1 which is connected to the intake manifold 2, and the intake port is connected to a combustion chamber 17 via an intake valve 20. Inside the combustion chamber 17, there is a piston 18, and the exhaust gas burned in the combustion chamber 17 is discharged from the exhaust port 19 to the exhaust manifold 3 via the exhaust valve 30. The exhaust valve 30 includes a valve body 31 that opens and closes the exhaust port 19, a spring 32 that biases the valve body 31 toward the side that closes the exhaust port 19, and an exhaust cam that opens the valve body 31 against the spring 32. 33 is provided.

The EGR control valve 8 is divided into a valve portion 8A and a valve drive portion 8B. Inside the housing 80 of the valve portion 8A, a valve body 81 for opening and closing the EGR pipe 7 and a valve body 81 are attached. There is a valve stem 82. Further, the valve drive unit 8B has a housing 88 partitioned by a diaphragm 83 into an atmospheric pressure chamber 88A and a negative pressure chamber 88B.
Within B is a spring 84. The end of the valve shaft 82 is connected to the diaphragm 83 on the side of the atmospheric pressure chamber 88A, and the diaphragm 83 is urged by the spring 84 in the direction in which the valve body 81 closes the EGR pipe 7.

When the control valve 12 shown in FIG. 1 is opened and the negative pressure by the vacuum pump 9 is introduced into the negative pressure chamber 88B through the negative pressure introducing pipe 13, the diaphragm 83 is attached with the spring 84. Negative pressure chamber 88B against the power
Since it moves to the side, the valve body 81 opens and the exhaust gas
It is returned to the intake manifold 2 through the R pipe 7. In addition,
When the exhaust control valve 51 of the exhaust brake device 5 is closed, the back pressure in the exhaust pipe 4 and the EGR pipe 7 rises while pulsating as shown by the solid line B in FIG. 3 (a), and stabilizes at a constant pressure. . This pulsation occurs because the exhaust gas confined in the exhaust pipe 4 flows back into the cylinder when the valve body 31 of the exhaust valve 30 opens during the exhaust stroke, the pressure drops, and then the exhaust stroke proceeds. This is because when the piston 18 moves upward, the piston 18 is compressed and the pressure increases.

Further, the increase of the pressure stops as a whole with the passage of time because the back pressure is the spring 32 of the exhaust valve 30.
Exhaust valve 3 in the cylinder during the intake stroke
This is because the zero valve body 31 is pushed down by the back pressure and the exhaust gas escapes to the combustion chamber 17 during the intake stroke. If the spring 32 is strengthened in this state to raise the valve opening set pressure of the exhaust valve 30, the pressure at which this back pressure stabilizes is shown by the solid line A in FIG. 3 (a).
It becomes higher as shown in. Then, when the spring 32 of the exhaust valve 30 is further strengthened, the back pressure rises high as shown by the chain line C.

On the other hand, when the set opening pressure of the spring 84 of the EGR control valve 8 is lower than the set opening pressure of the spring 32 of the exhaust valve 30, the exhaust control valve 51 closes the exhaust pipe 4 and the back pressure rises. At times, the EGR control valve 8 opens earlier than the exhaust valve 30, lowering the back pressure and deteriorating the braking performance of the exhaust brake. Therefore, in this embodiment, as shown in FIG. 2 (b), the valve opening set pressure due to the back pressure of the exhaust valve 30 is made larger than the back pressure lower limit value at which the exhaust braking force can be secured,
The valve opening set pressure by the back pressure of the EGR control valve 8 is made larger than the valve opening set pressure of the exhaust valve. In this manner, the EGR control valve 8 is set with the set valve opening pressure of the exhaust valve 30 set to a value that can ensure the braking performance of the exhaust brake device 5.
By setting the valve-opening set pressure of the spring 84 of the exhaust valve 30 to be equal to or higher than the valve-opening set pressure of the spring 32 of the exhaust valve 30, deterioration of the exhaust brake performance by the EGR control valve 8 is prevented.

An example of calculation of the valve opening set pressure of the spring 32 of the exhaust valve 30 and the valve opening set pressure of the spring 84 of the EGR control valve 8 will be shown below. Where Dex is the area to which back pressure is applied in the direction of opening the valve body 31 of the exhaust valve 30, Pex is the back pressure required for operating the exhaust brake (varies depending on the vehicle), Degr
Is the area to which back pressure is applied in the direction in which the valve element 81 of the EGR control valve 8 is opened.

If the valve opening set pressure of the spring 32 of the exhaust valve 30 is Fex, Fex = [π × (Dex) ² × Pex] × 1/4 ... The valve opening set pressure of the spring 84 of the EGR control valve 8 is Feg.
If r, then Fegr ≧ [π × (Degr) ² × Pex] × 1/4 ... From this equation and the equation, the following equation holds.

(Fegr / Fex) ≧ (Degr / Dex) ² ... By modifying the equation, Fegr ≧ Fer × (Degr / Dex) ² ... Therefore, the EGR can be achieved so that the force obtained by the equation can be achieved.
The valve opening set pressure Fegr of the spring 84 of the control valve 8 may be set.

In this way, when the exhaust brake device 5 operates, the exhaust valve 30 opens before the EGR control valve 8, so the back pressure can be controlled so that the exhaust brake force can be secured. By devising the valve opening set pressure of the exhaust valve 30 that originally exists in the diesel engine, a strong drive source for increasing the valve opening force of the EGR control valve 8, a negative pressure switching device, etc. are unnecessary. .

Next, the operation of the intake throttle valve 15 constructed as shown in FIG. 1 will be described with reference to FIGS. 3 (b) and 4 (a)-(d). The accelerator pedal 23 and the cam 25 are connected via an accelerator wire 24, and when the accelerator pedal 23 is stepped on, the cam 25 rotates about a rotation shaft 250. An arm 151 provided at the end of the rotary shaft 150 of the cam 25 and the intake throttle valve 15.
As shown in FIG. 4 (a), means that the accelerator pedal 23 is not in contact in the idle state. In this idle state, the intake throttle valve 25 does not open and is in a relatively small predetermined opening state that is not fully closed. This idle state corresponds to point a in the characteristic diagram of FIG. 3 (b).

From this idle state, the accelerator pedal 23
Even if the vehicle is stepped on gradually, the cam 25 keeps the arm 15 until the stepped amount of the accelerator pedal 23 reaches a predetermined value.
1, the intake throttle valve 25 is not fully closed, and a relatively small predetermined opening state is maintained. That is, as shown in FIG. 3 (b), the intake throttle valve 25 is maintained in the initial state in a light load state in which the accelerator opening is from point a to point b.

FIG. 4B shows a state in which the accelerator pedal 23 is further depressed and the outer peripheral surface of the cam 25 contacts the arm 151 of the intake throttle valve 15. The state where the outer peripheral surface of the cam 25 contacts the arm 151 of the intake throttle valve 15 corresponds to point b in the characteristic diagram of FIG. 3 (b). In this way, after the cam 25 and the arm 151 of the intake throttle valve 15 contact each other, the arm 151 is pushed by the cam 25 and rotates in accordance with the depression amount of the accelerator pedal 23.

When the accelerator pedal 23 is further depressed from the point b in the characteristic diagram shown in FIG. 3 (b), the intake throttle valve 1
The opening degree of No. 5 is large due to the non-linear characteristic corresponding to the shape of the outer peripheral surface of the cam 25. C in the characteristic diagram shown in FIG. 3 (b)
The points indicate the medium load state of the engine, and the states of the accelerator pedal 23, the cam 25, and the intake throttle valve 15 in this state are shown in FIG. 4 (c). After that, when the accelerator pedal 23 is further depressed, the opening degree of the intake throttle valve 15 further increases. Point d in the characteristic diagram shown in FIG. 3 (b) shows a high load state of the engine, and the states of the accelerator pedal 23, the cam 25, and the intake throttle valve 15 in this state are shown in FIG. 4 (d). Be done.

On the other hand, the EGR rate, where Ga is the intake air amount and Ge is the EGR gas flow rate, Ge / (Ga + G
What is represented by e) is EGR as shown in FIG.
When the size (diameter) of the control valve is determined, when the EGR control valve is in the fully closed / fully opened control, it corresponds uniquely to the opening degree of the intake throttle valve. According to the study of the present inventor, the basic equation of this EGR rate is shown by the following equation in the case of a non-supercharged engine. However,
Aeg is the effective area of the EGR control valve (cm ² ), Aex is the effective area of the exhaust pipe (cm ² ), Ath is the effective area of the intake throttle valve (cm ² ), γg is the exhaust gas density, and γo is the air density. . EGR rate = 1 / {1+ [1 / [√ (Aeg / Aex) ² + (Aeg / Ath) ² × (γg / γo)]]} (where √ is √ (Aeg / Aex) ² + ( Aeg / Ath) ² × (γg / γo)
That is, according to the formula, the EGR rate is the EGR passage area Ae.
g, passage area Aex of exhaust pipe, passage area Ath of intake throttle valve
And becomes a function of only the exhaust gas density γg and the air density γo. Here, it can be considered that the air density γo of the atmosphere is a constant and the passage area Aex of the exhaust pipe is also a constant. Further, the passage area Aeg of the EGR control valve can be regarded as a constant because the valve opening position is fixed when the EGR control valve is fully opened.

On the other hand, the exhaust gas density γg changes depending on the operating conditions of the diesel engine, but it is a function of the air amount, and is a function of the area Ath of the intake throttle valve that controls the air amount. Therefore, when the EGR control valve is fully closed / fully opened, the EGR rate expressed by the equation is
It is a function of the area Ath of the intake throttle valve, that is, a function of only the opening degree of the intake throttle valve. From this, it can be seen that as the number of each term on the right side of the expression becomes smaller, the EGR rate becomes smaller, that is, as the opening degree of the intake throttle valve becomes larger, the EGR rate becomes smaller and becomes a constant value. . Therefore, EG
The R ratio is as shown in FIG. 5 (a) with respect to the opening of the intake throttle valve.

By the way, in a diesel engine, as shown in FIG. 5B, the fuel injection amount is generally injected in proportion to the accelerator opening. Therefore, if the opening characteristic of the intake throttle valve that gives a predetermined EGR rate with respect to the accelerator opening is given, the predetermined EGR amount with respect to the fuel flow rate and the engine speed as shown in FIG. Can be supplied. On the other hand, the smoke generation limit when the EGR is executed mainly depends on the fuel flow rate. That is, if the fuel flow rate is large, smoke is likely to occur with a small EGR.

Therefore, the EGR is accurately performed with respect to the fuel flow rate.
However, in this embodiment, for example, as described in FIG. 3 (b), the opening of the intake throttle valve is set to a-b-c-d with respect to the accelerator opening. By changing to, it becomes stable with respect to the operating conditions of the engine shown by the solid line in FIG. 5 (c), and it becomes possible to control the EGR rate to be lowered arbitrarily arbitrarily and as the fuel flow rate increases. .

Using the above system, EGR
The control valve only needs to be fully opened at the time of operation, and an accurate flow rate can be secured. Further, the intake throttle valve 1 of FIG.
The accuracy of the profile of the cam 25 that opens the valve 5 is mechanically determined, and there is no problem that the control response is deteriorated.
Further, when the EGR control valve 8 that operates at a negative pressure as described in FIG. 2 is used, the negative pressure when the negative pressure is introduced into the negative pressure chamber 88B and the valve body 81 is opened. The relationship between the negative pressure in the chamber 88B and the lift amount of the valve body 81 is as shown in FIG. 5 (d). As can be seen from FIG. 5 (d), the characteristic when the negative pressure is introduced to open the EGR control valve 8 is indicated by the symbol e.
And the characteristic when the valve is closed is indicated by the symbol f.
As described above, the opening / closing characteristic of the EGR control valve 8 has a hysteresis characteristic with respect to the magnitude of the negative pressure. However, the lift amount of the valve element 81 at the fully open position of the EGR control valve 8 indicated by the symbol g in FIG. 5D is always stable and constant. Therefore, when the EGR control valve 8 is fully opened as in this embodiment, it is more accurate and a stable flow rate can be secured. On the other hand, when the valve body 81 of the EGR control valve 8 is used at the intermediate lift position in pressure feedback control of the EGR control valve 8 or the like, the lift position of the valve body 81 is accurate unless detected by a sensor and controlled. Since it cannot be controlled, an expensive lift sensor becomes necessary.

Next, the actuator 26 shown in FIG.
To the intake throttle valve 15 regardless of the operation of the cam 25.
The reason why the valve is opened to a predetermined opening will be described. Figure 6 (a) shows a diesel engine with an intake throttle valve,
It shows the intake pipe negative pressure characteristic with respect to the engine speed,
The line indicated by the symbol h is the intake pipe negative pressure characteristic of the present invention when the EGR is not executed, the line indicated by the symbol i is the conventional intake pipe negative pressure characteristic when the EGR is not executed, and the line indicated by the symbol j is the EGR executed. It shows the intake pipe characteristics in the case of. Also, the solid line in FIG. 6 (b) shows the opening of the intake throttle valve with respect to the accelerator opening of the diesel engine of the present invention, and the alternate long and short dash line shows the opening of the intake throttle valve with respect to the accelerator opening of the conventional diesel engine. Shows.

When EGR is performed, the intake pipe is EG
Since the exhaust gas flows through the R pipe, the intake pipe negative pressure does not increase even when the intake throttle valve is closed. On the other hand, EGR
If is not executed, the intake air amount is limited by the intake throttle valve, so even if the accelerator pedal 23 is depressed, that is, the engine speed is already increased, as in the above-described embodiment, If the throttle valve does not open, the negative pressure in the intake pipe downstream of the intake throttle valve increases, and pumping loss increases in an engine whose rotational speed is increased, which deteriorates fuel efficiency. Moreover, since the amount of air is small, the swirl in the combustion chamber of the engine is insufficient, and combustion is likely to deteriorate.

Therefore, in this embodiment, when the EGR is not executed, the actuator 26 shown in FIG. 1 is operated to force the intake throttle valve 1 regardless of the operation of the cam 25.
By opening valve 5 to a predetermined opening, deterioration of fuel consumption and combustion of the engine are prevented. Note that the actuator 26 does not need to open the intake throttle valve 15 to the fully open position when the EGR is not executed, and may be a predetermined opening from the initial position, for example, about half the fully open position of the intake throttle valve 15. The non-execution conditions of EGR include running at high altitude (when EGR is performed at this time, smoke is likely to occur), after cold start of the engine (when EGR is performed at this time, abnormal wear of the engine is likely to occur), etc. Is.

Further, as described with reference to FIG. 4, even if the accelerator is depressed during execution of EGR, it is necessary to prevent the intake throttle valve 15 from being opened until the accelerator opening becomes large to some extent, as shown in FIG. 6 (c). Will be explained. A curve h shown in FIG. 6 (c) shows the EGR rate with respect to the opening degree of the intake throttle valve 15 in the state where the EGR control valve is held in the fully opened state. In an operating state in which the engine is operated in the light load region and a high EGR rate is required, the EGR rate greatly changes with respect to the opening area of the intake throttle valve 15, as can be seen from the above equation. For example, the required value of the EGR rate is n in FIG. 6 (c).
Even if the opening degree of the intake throttle valve 15 is O point at the point, the opening degree of the intake throttle valve 15 slightly moves from the O point to the P point due to vibration or the like, so that the EGR rate deviates from the n point to the m point. Will end up. Therefore, in such a region where the EGR rate is sensitive, the outer peripheral surface (cam profile) of the cam 25 is the intake throttle valve 15.
If the arm 151 provided on the rotating shaft 150 is not contacted, an accurate predetermined EGR rate can be obtained by setting the initial opening degree of the intake throttle valve 15 with high accuracy.

In the exhaust gas recirculation control device for a diesel engine constructed as described above, the intake throttle valve is fixed at a predetermined opening in a light load range until the engine reaches a predetermined load, so that the opening area of the intake throttle valve is increased. The EGR rate does not change in the light load range of the engine, and the opening of the intake throttle valve is controlled by the cam. Even when the EGR rate fluctuates, it is not at the time when the intake throttle valve in which the amount of change in the EGR rate is the largest is not fully closed and is at a relatively small predetermined opening degree, so the amount of EGR variation can be made small. Further, when the EGR is not executed, the intake throttle valve is opened by the actuator regardless of the accelerator opening, so that pumping loss can be prevented.

FIG. 7 illustrates a specific structure of the intake throttle valve 15 of the exhaust gas recirculation control device for a diesel engine constructed as described above. FIG. 7 (a) shows an intake pipe attached to an intake pipe. FIG. 7B is a side view of the throttle valve unit 100, and FIG. 7B is a bottom view of FIG. 7A. In this specific example, the same components as those described with reference to FIG. 1 are designated by the same reference numerals for easy understanding.

In the intake throttle valve 15 of this embodiment, two arms are attached to one end of a rotary shaft 150 with the rotary shaft 150 sandwiched therebetween. One arm 151 has a rotary shaft 1
A roller 152 that engages with a cam 25, which will be described later, is attached to the tip of the roller 50 to drive the roller 50. The other arm 153 is connected to the intake throttle valve 15
It is a positioning arm for setting the initial position of the intake air throttle valve unit 100 and comes into contact with a stopper 27 provided at a predetermined position of the intake throttle valve unit 100. Also, the rotating shaft 1
A diaphragm actuator 26 is attached to the other end of the valve 50 to forcibly open the intake throttle valve 15 to a predetermined opening. This actuator 26
The negative pressure chamber of the vacuum pump 9 via the negative pressure introducing pipe 13.
And a control valve 22 that is driven to open and close by a control circuit (ECU) 10 in the middle of this negative pressure introduction 13.
Is provided. Then, the control valve 22 is opened by the control circuit 10, and when the negative pressure from the vacuum pump 9 is introduced into the negative pressure chamber of the actuator 26 via the negative pressure introducing pipe 13, the actuator 26 operates and the rotating shaft 150.
Rotates, and the intake throttle valve 15 is forcibly opened to a predetermined opening degree.

The cam 25 rotatably attached to one end of the rotary shaft 250 is provided with a lever 251 connected to an accelerator wire (not shown). Also, the cam 25
The cam surface (cam profile) 252 that engages with the above-mentioned roller 152 does not come into contact with the roller 152 until the cam 25 rotates to a predetermined angle. Furthermore,
Outside the profile 252 of the cam 25, there is a guard 28 integrally formed with the cam 25. This guard 28
Serves to protect the cam profile 252 from external forces. Roller 152 provided at the tip of arm 151
Is located in a space surrounded by the cam profile 252 and the guard 28. In addition, the rotary shaft 2 of the cam 25
An accelerator opening sensor 29 is attached to the other end of 50.

In the embodiment configured as described above, when the accelerator pedal (not shown) is depressed, the lever 251 is rotated by being pulled by the accelerator wire, so that the cam 25
Rotates about the rotation axis 251. The cam 25 is not in contact with the roller 152 at the tip of the arm 151 at first, but as shown in FIG. 8 (a), when the lever 251 rotates a predetermined angle from the initial position indicated by the chain double-dashed line, the cam 25
Also rotates a predetermined angle, and its profile 252 comes into contact with the roller 152 for rotating the intake throttle valve 15. When the lever 251 is pulled by the accelerator wire and further rotated from this position, the roller 152 moves on the profile 252 of the cam 25, and the arm 151 of the intake throttle valve 15 is pushed by the cam profile 252 to rotate, As shown in FIG. 8 (b), the opening degree of the intake throttle valve 15 increases.

The amount of depression of the accelerator pedal and the opening characteristic of the intake throttle valve 15 depend on the shape of the cam profile 252 that pushes the roller 152 provided at the tip of the arm 151. The profile 252 of this cam 25 is shown in FIG. 9 (b).
When the shape is as shown by the solid line in Fig. 9, the opening of the intake throttle valve 15 with respect to the accelerator opening becomes as shown by the solid line in Fig. 9 (a). That is, in the light load region of the diesel engine, even if the accelerator pedal is depressed, the intake throttle valve opening does not change as indicated by points a and b in the characteristic diagram of FIG. 9 (a),
When the engine shifts to medium load operation, the intake throttle valve opening becomes as shown by point c in the characteristic diagram of Fig. 9 (b), and when the engine shifts to high load operation, ) The intake throttle valve opening is as indicated by point d in the characteristic diagram.

On the other hand, the profile 252 of this cam 25
9B has a shape shown by a broken line in FIG. 9B, the opening of the intake throttle valve 15 with respect to the accelerator opening is shown by a broken line ab'-c'-d 'in FIG. 9A. Like That is, the opening degree of the intake throttle valve, which does not change the opening degree of the intake throttle valve in the light load range of the diesel engine, becomes narrow, and the opening degree of the intake throttle valve in the middle and high load ranges is large. As described above, the opening characteristic of the intake throttle valve 15 with respect to the accelerator opening can be adjusted simply by changing the profile of the cam 25.

FIG. 10 is an overall constitutional view showing the constitution of another embodiment of the exhaust gas recirculation system for a diesel engine with an exhaust brake of the present invention, and the same reference numerals are given to the same constituent members as the embodiment shown in FIG. It is attached. Therefore, 1 is a 4-cylinder diesel engine, 2 is an intake manifold, 3 is an exhaust manifold, 4
Is an exhaust pipe, 5 is an exhaust brake device, 6 is a muffler, and 7 is E.
GR pipe, 8 EGR control valve, 9 vacuum pump, 1
0 is a control circuit (ECU), 11, 12, 22 are control valves,
13 is a negative pressure introducing pipe, 14 is an intake pipe, 15 is an intake throttle valve,
23 is an accelerator pedal, 24 is an accelerator wire, 25 is a cam, 26 is an actuator, 51 is an exhaust control valve, 15
0 is the rotary shaft of the intake throttle valve 15, 151 is an arm, 250
Is a rotating shaft of the cam 25.

The exhaust gas recirculation system of the diesel engine with an exhaust brake of this embodiment differs from the system of FIG. 1 in that two large and small EGR control valves 8L and 8S are provided in parallel in the middle of the EGR pipe 7. is there. Two EGR control valves 8L, 8
A negative pressure introducing pipe 13 is branched in the middle of S to connect a negative pressure introducing pipe 13L for the EGR control valve 8L and a negative pressure introducing pipe 13S for the EGR control valve 8S to S. The pipes 13L and 13S are provided with control valves 12L and 12S that are controlled to open and close independently by the control circuit 10.

As described with reference to FIG. 5 (a), the intake throttle valve 1
The EGR rate for the opening degree of 5 depends on the diameter of the EGR control valve, and when a large EGR rate is required, the EGR control valve 8
It is necessary to increase the diameter of. However, the big EGR
If the EGR control valve 8 is simply enlarged in order to obtain the rate, this diaphragm device also becomes large and the EGR control valve 8
However, the weight and outer shape of the product become large, which is disadvantageous in terms of space.
Therefore, when a large EGR rate is required, two EGR control valves 8L and 8S are provided in parallel as in this embodiment,
The diameter of the EGR control valve is increased by equalization.

As described above, since the EGR control valve is used in the fully open / fully closed control, the two EGR control valves 8L,
If the size of 8S is made different, the EGR rate for the same intake throttle opening can be finely controlled (in this embodiment, the diameter of the EGR control valve 8L is smaller than the diameter of the EGR control valve 8S. It has been enlarged). That is, two large and small E
If the full open / full close control of the GR control valves 8L and 8S is performed as described below, four stages of EGR rates can be realized with the same intake throttle valve opening.

EGR rate EGR control valve 8L (large valve diameter) EGR control valve 8S (small valve diameter) Stage 1 (Large) Full open Full open Stage 2 (Medium) Full open Full closed Stage 3 (Small) Full closed Full open Stage 4 (0 ) Fully closed Fully closed

[0051]

As described above, according to the present invention,
Since the intake throttle valve is kept open at a predetermined opening when the load is lighter than it does not reach the predetermined opening, the fluctuation of the EGR rate at a light load is reduced compared to the technique of fully closing the intake throttle valve at a light load. Can be made smaller.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a configuration of an embodiment of an exhaust gas recirculation device in a diesel engine with an exhaust brake of the present invention.

2 (a) is a configuration explanatory view including a cross-sectional view showing details of the configurations of an EGR control valve and an exhaust valve of the diesel engine engine with an exhaust brake of FIG. 1, and (b) is an opening of the EGR control valve and the exhaust valve. It is a characteristic view which compares the magnitude of valve setting pressure and shows.

FIG. 3 (a) is a diagram for explaining the characteristics of change in back pressure during operation of the exhaust brake according to the magnitude of the open valve set pressure of the exhaust brake valve, and FIG. 3 (b) is the accelerator of the intake throttle valve of FIG. It is a diagram which shows an example of the opening degree characteristic with respect to an opening degree.

4 (a) to (d) are points a in the characteristic diagram shown in FIG. 3 (b),
It is explanatory drawing explaining the amount of depression of an accelerator pedal, the movement of a cam, and the opening degree of an intake throttle valve at point b, point c, and point d.

FIG. 5 (a) is a diagram showing the relationship between the intake throttle valve opening and the EGR rate depending on the size of the EGR control valve, and FIG. 5 (b) shows the relationship between the accelerator opening and the fuel flow depending on the engine speed. A diagram showing the relationship, (c) a diagram showing the relationship between the engine speed and the fuel flow rate on the EGR contour line, and (d) showing the negative pressure in the negative pressure chamber of the EGR control valve and the lift amount of the EGR control valve. It is a diagram explaining a relationship.

FIG. 6 (a) is a diagram showing the relationship between the engine speed and the intake pipe negative pressure with respect to the presence or absence of EGR, comparing the present invention and the conventional device, and (b) is the accelerator opening degree in the present invention and the conventional device. Is a diagram showing a comparison of the intake throttle valve opening degree with respect to, and (c) is a diagram for explaining the relationship between the intake throttle valve opening degree and the EGR rate when the EGR control valve is fully opened.

7 shows a specific configuration of the exhaust throttle valve of FIG. 1, (a) is a side view of the intake throttle valve unit, and (b) is a bottom view of (a).

8A and 8B show the operation of the intake throttle valve unit shown in FIG. 7, where FIG. 8A is a diagram showing a state when a cam and a roller provided on an arm of the intake throttle valve are in contact with each other, and FIG. FIG. 6 is a diagram showing a state where an intake throttle valve is opened by a cam.

9 (a) is a diagram for explaining the intake throttle valve opening with respect to the accelerator opening when the cam profile of FIG. 7 is changed, and (b) is the intake throttle valve opening of (a). It is explanatory drawing explaining the difference of the profile of the cam for making it.

FIG. 10 is an overall configuration diagram showing the configuration of another embodiment of the exhaust gas recirculation device in the diesel engine with an exhaust brake of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diesel engine 2 ... Intake manifold 3 ... Exhaust manifold 4 ... Exhaust pipe 5 ... Exhaust brake device 7 ... Exhaust gas recirculation pipe (EGR pipe) 8 ... EGR control valve 9 ... Vacuum pump 10 ... Control circuit (ECU) 11, 12, 22 ... Control valve 13 ... Negative pressure introducing pipe 14 ... Intake pipe 15 ... Intake throttle valve 32 ... Spring 23 ... Accelerator pedal 24 ... Accelerator wire 25 ... Cam 26 ... Actuator 27 ... Stopper 28 ... Guard 29 ... Accelerator opening sensor 51 ... Exhaust control valve 81 ... Valve body 83 ... Diaphragm 84 ... Spring 88A ... Atmospheric pressure chamber 88B ... Negative pressure chamber 100 ... Intake throttle valve unit 150, 250 ... Rotating shaft 151 ... Arm 152 ... Roller 153 ... Positioning arm 251 ... Lever 252 ... Cam surface (profile)

Claims (2)

[Claims] 1. An exhaust gas recirculation system for a diesel engine, wherein an intake throttle valve is provided in an intake passage, and an exhaust gas recirculation passage is provided for returning a part of exhaust gas flowing through the exhaust passage to the intake passage. The intake throttle valve is kept open at a predetermined opening until the diesel engine reaches a predetermined load, and when the load is more than a predetermined load, the intake throttle valve is opened gradually as the load increases. An exhaust gas recirculation system for a diesel engine, comprising: an opening degree adjusting means for an intake throttle valve; an EGR control valve provided midway in the exhaust gas recirculation passage; and an opening / closing means for opening and closing the EGR control valve. 2. An opening degree adjusting means of the intake throttle valve adjusts an opening degree of the intake throttle valve according to a depression amount of an accelerator pedal, and the EGR control valve is fully closed. The second opening degree adjusting means for controlling the opening of the intake throttle valve regardless of the depression amount of the accelerator pedal, the diesel engine according to claim 1. Exhaust recirculation system.