JPH0250299B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention includes an exhaust turbo supercharger for supercharging intake air, and the diameter of the exhaust gas introduction passage to the turbine of the exhaust turbo supercharger is This invention relates to an engine equipped with a diameter variable means that varies the diameter according to engine operating conditions.

[Prior art] Conventionally, the diameter of the exhaust passage upstream of the turbine is switched between large and small depending on engine operating conditions such as engine speed and load, and when the engine is operating at low speed, the passage diameter is set to the "small" side. and set it to
Turbocharging improves the engine's output performance in the low speed range by narrowing down the exhaust gas and increasing the speed at which the exhaust gas flows into the turbine, causing the turbine to rotate at high speed to quickly increase boost pressure. The attached engine is publicly known (Utility Model No. 56-161139)
(see publication).

In an engine having such a structure, the turbocharging efficiency can be improved by improving the turbine output in a low speed range, and accordingly, the output performance of the engine can be improved to some extent.

However, in a low speed range, the diameter of the exhaust gas introduction passage is narrowed down to a small diameter, so as the engine speed increases, the exhaust pressure on the upstream side of the turbine increases rapidly. Such an increase in exhaust pressure becomes a major factor that inhibits engine combustibility, such as an increase in the amount of internal EGR (the amount of exhaust gas that remains in the combustion chamber).

In particular, the diameter of the exhaust gas introduction passage is “small”.
When the exhaust pressure is changed from ``high'' to ``large'', the exhaust pressure gradually decreases as the passage diameter increases, and the combustibility of the engine is improved at once. As a result, engine output performance will improve step by step. In other words, because the required control amount of the control device that governs engine combustion is different, it may not be possible to effectively extract the engine output, or the engine output performance may not change continuously before and after switching the passage diameter. changes discontinuously,
There is a problem in that there is a large difference in engine output before and after switching.

[Object of the Invention] The object of the present invention is to improve the exhaust pressure characteristics that occur before and after switching the passage diameter in a turbocharged engine equipped with means for varying the passage diameter of the exhaust gas introduction passage to the turbine as described above. An object of the present invention is to provide a control device for a turbocharged engine that can effectively respond to changes in the engine speed.

[Structure of the Invention] Therefore, in the present invention, the characteristics of the control amount for the engine operating state of the combustion state control means that governs the combustion state of the engine are changed in synchronization with the change in the diameter of the exhaust gas introduction passage. The basic feature is that a control amount changing means is provided for changing the combustion state so as to suppress changes in the combustion state due to switching.

In other words, in the present invention, the diameter of the exhaust gas introduction passage to the turbine can be changed from "small" to "large" or "large".
Before and after switching from "small" to "small", the so-called engine set is switched in a direction to suppress changes in the combustion state due to switching from large to small diameter. In this case, the elements included in the engine set that govern the combustion state are the amount of advance of the ignition timing,
These include various factors such as EGR characteristics and fuel amount, and the combustion characteristics of these various factors are optimally controlled according to changes in exhaust pressure variation characteristics.

[Effects of the Invention] According to the present invention, it is possible to set an engine set that matches changes in the combustion state due to fluctuations in exhaust pressure, and it is possible to effectively prevent output fluctuations, abnormal combustion, etc.

[Examples] Examples of the present invention will be described in detail below.

As shown in FIG. 1, an engine 1 includes a turbo supercharger installed across an intake passage 5 and an exhaust passage 6, which are opened and closed with respect to a combustion chamber 4 by an intake valve 2 and an exhaust valve 3, respectively. 7, and an exhaust passage 6
When the turbine 9 is driven by the exhaust gas flowing down, the blower 10 is driven in conjunction with this.
It has a basic structure in which so-called intake air supercharging is performed by supplying intake air whose pressure has been increased by a blower 10 to the combustion chamber 4.

An air cleaner 11 is installed on the upstream side of the blower 10 in the intake passage 5, and an air flow meter 12 for measuring the amount of intake air from moment to moment is interposed downstream thereof. In addition, the blower 10 of the intake passage 5
A throttle valve 13, which is opened and closed according to the load of the engine 1, is provided downstream of the throttle valve 13, and a fuel injection valve 14 is provided downstream of the throttle valve 13.

On the other hand, the exhaust passage 6 is partitioned into a low-speed exhaust gas introduction passage 16 and a high-speed exhaust gas introduction passage 17 by a partition wall 15 at the exhaust gas introduction port of the turbine 9. The upstream side of the valve 17 is opened and closed on and off by a switching valve 18, which serves as a diameter variable means according to the present invention. Furthermore, a catalytic exhaust gas purification device 19 is interposed in the exhaust passage 6 downstream of the turbine 9.

The low-speed exhaust gas introduction passage 16 includes an exhaust passage 6 downstream of the turbine 9 that bypasses the turbine 9.
A waste gate passage 20 is opened to bypass a part of the exhaust gas, and by opening and closing the passage 20 with a waste gate valve 21, the supercharging pressure is set in advance as described below. Control the boost pressure so that it does not exceed the maximum boost pressure.

In addition, the turbine 9 and the catalytic exhaust gas purification device 1
The exhaust passage 9 between the exhaust passage 9 and the intake passage 5 downstream of the throttle valve 13 are referred to as exhaust gas recirculation passages (hereinafter simply referred to as exhaust gas recirculation passages).
It's called the EGR passage. ) 22, EGR
When the exhaust gas recirculation control valve (hereinafter referred to as FGR valve) 23 installed in the passage 22 is opened, part of the exhaust gas is recirculated to the intake side, and as is well known, an inert recirculation is performed. The generation of NOx is suppressed by suppressing an excessive rise in the maximum combustion temperature of the engine 1 due to exhaust gas.

Above waste gate valve 21, switching valve 1
8. Items that are directly or indirectly related to the combustibility of the engine 1, such as the spark plug 24 and fuel injection valve 14 installed in the combustion chamber 4, are controlled by the computer 25 installed in the vehicle, as detailed below. control.

This computer 25 is connected to the air flow meter 1.
2 detected by the intake air amount and rotation speed sensor 26
The engine speed is detected by the pressure sensor 2 installed in the intake passage 5 downstream of the throttle valve 13.
The following control is executed using the supercharging pressure detected by 7 and the exhaust pressure detected by the pressure sensor 28 installed in the exhaust passage 6 downstream of the turbine 9 as input data.

(B) Control over the switching valve 18 As shown in FIG. When the exhaust pressure Peo is below, the switching valve 18 is closed, and when the exhaust pressure exceeds the set exhaust pressure Peo, the switching valve 18 is opened.

The above-mentioned set exhaust pressure Peo is set to, for example, 200 mmHg, which corresponds to the exhaust pressure when the throttle valve 13 is fully open and the engine speed is 3000 rpm.

As shown in FIG. 1, a switching actuator 29 that opens and closes this switching valve 18 is located at a portion where the switching valve 18 is installed (upstream of the turbine 9).
The control valve 3 is a diaphragm device whose operation source is the exhaust pressure of
1 is opened by an opening command signal from the computer 25, the actuating rod 29b, one end of which is fixed to the diaphragm 29a, is pushed in the direction of arrow A against the spring force of the coil spring 29c, and an appropriate link mechanism 32 The switching valve 18 connected through the switch valve 18 is opened to open the high-speed exhaust gas introduction passage 17. In other words, until the set exhaust pressure Peo is reached, the exhaust gas from engine 1 is exclusively
The exhaust gas is introduced into the turbine 9 in a narrowed state by the low-speed exhaust gas introduction passage 16 (hereinafter, this state is referred to as a state with a small passage diameter A/R), and the exhaust pressure Pe increases beyond the set exhaust pressure Peo. Then, the switching valve 18 opens the high-speed exhaust gas introduction passage 17, and from then on, the exhaust gas is introduced into the turbine 9 through both the high-speed and high-speed exhaust gas introduction passages 16, 17. The passage diameter will be enlarged (hereinafter, this state will be referred to as a state where the passage diameter A/R is large).

Depending on the control of the switching valve 18, the exhaust pressure Pe becomes as shown by the solid line Pe in FIG.
In the low speed range, the exhaust pressure increases rapidly as the engine speed increases, drops by one step at the switching point SP, and then decreases again to increase as the engine speed increases. Note that the dotted line Pe' in the figure shows the exhaust pressure increase characteristic when the switching valve 18 is not provided (that is, when the passage diameter A/R is large).

(b) Control of supercharging pressure The control of supercharging pressure, especially the maximum supercharging pressure, is performed by controlling the opening and closing of the waste gate valve 21 described above.

For this waste gate valve 21,
A wastegate actuator 34 is provided on the discharge side of the blower 10 and is made of a diaphragm device whose operation source is the supercharging pressure introduced by the supercharging pressure introduction passage 33 having a pressure outlet. A relief passage 35 is provided which branches off from the middle and communicates with the intake passage 5 on the upstream side of the blower 10, and an electromagnetically actuated control valve 36 for opening and closing this relief passage 35 is provided.

The computer 25 determines that the supercharging pressure P detected by the pressure sensor 27 installed downstream of the intake passage 5 is the maximum supercharging pressure Pmax
When it reaches, an opening operation signal is output to the control valve 36 to open the relief passage 35 and relieve the supercharging pressure to the upstream side of the blower 10. As a result, supercharging pressure no longer acts on the wastegate actuator 34, and the wastegate valve 21, which had been kept closed, is opened, bypassing the turbine 9, and directing some of the exhaust gas to the turbine 9. lead directly downstream. As a result of such control, the boost pressure is controlled so that the boost pressure does not increase beyond the maximum boost pressure Pmax.

In this case, since the switching valve 18 is closed in the low speed range, the supercharging pressure P remains constant even in the low speed range.
As the engine speed increases, the pressure increases quickly and reaches the maximum supercharging pressure Pmax well before the switching point SP of the switching valve 18, so that supercharging can be effectively achieved in the low speed range.

For reference, in FIG. 3, the boost pressure increase characteristic when the switching valve 18 is not provided, that is, when the passage diameter A/R is large, is shown by a dotted line P'.

(C) Control of Advance Amount Ignition advance control for the spark plug 24 is basically performed according to the control characteristics shown in FIG. 4.

The feature of this ignition advance control is that, as shown in Fig. 4, in the low speed range before the switching point SP, the passage diameter A/
The aim is to control with a lead angle characteristic Tθ having a slightly smaller slope than the lead angle characteristic Tθ′ in the case of large R. This is because when the switching valve 18 is provided to reduce the diameter of the exhaust gas introduction passages 16 and 17 in the low speed range, the exhaust pressure Pe increases as explained in FIG. This is to prevent knocking by suppressing the amount of advance since the internal pressure in the engine increases and knocking becomes more likely to occur.

Then, at the switching point SP, the ignition advance amount is increased by one step, and from then on, the ignition advance amount is increased by a characteristic line with a slope larger than the previous one, and the ignition advance amount is increased according to the increase in engine speed. Shift to angle control.

(d) EGR control The EGR characteristics by EGR control are shown in Figure 5.
As is clear from Fig. 5, the EGR amount is variably controlled according to the engine speed and load, but in the low speed range (passage diameter A/R small) before the switching point SP,
The EGR characteristics are set to be one step lower than the high speed range (large passage diameter A/R) after switching point SP.
This is because the earlier the exhaust pressure upstream of the turbine 9 rises in the low speed range, the more the internal pressure in the low speed range increases.
Since the amount of EGR (that is, the amount of exhaust gas that remains without being exhausted from the combustion chamber 4) increases,
This is because if EGR control is performed in the same way as during normal exhaust pressure without the switching valve 18, the absolute amount of EGR will become excessive and the combustibility of the engine 1 will be extremely deteriorated.

The above EGR control is performed by controlling the drive of the EGR valve 23 by the computer 25.

(E) Fuel control The computer 25 controls the fuel injection valve 14 using, for example, the intake air amount detected by the air flow meter 12 and the engine rotation speed detected by the rotation speed sensor 26 as basic input information. This is done by map control as shown in FIG.

As shown in Fig. 6, the entire operating range includes an idle zone ID, a deceleration zone below the load line RL (fuel cut range), and an F/F/200 range that performs feedback control of the air-fuel ratio to a set air-fuel ratio near the stoichiometric air-fuel ratio. It is divided into six zones in total: zone B, low rotation increase zone C, increase zone A in the medium and high load ranges before switching point SP, and increase zone B in the high load range after switching point SP.

The fuel increase rate in the low-speed increase zone C is set to a value that can compensate for poor combustibility at low speeds, while in the increase zone B in the high-load range, high output of the engine 1 is guaranteed. Set the rate of increase that is possible.

The characteristics of the fuel control in this embodiment are as follows:
This is due to the expansion of zone A in the medium and high load range before SP to the medium load range. The enlarged area is shown as A' in FIG.

This expansion of the increase zone A toward the medium load side was done in consideration of the sudden increase in exhaust pressure Pe before the switching point SP mentioned above. In other words, under relatively high exhaust pressure conditions, there are factors that inhibit combustibility, such as an increase in internal EGR, making it difficult to secure the necessary output performance in the medium load range. be.

In the above embodiment, the exhaust gas introduction passage to the engine 9 is divided into two exhaust gas introduction passages 16 and 17 for low speed and high speed, and the high speed exhaust gas introduction passage 17 is controlled by the switching valve 18. Although the passage diameter is changed by opening and closing, the present invention provides a low-speed turbo supercharger having a relatively small-diameter exhaust gas introduction passage and a high-speed turbo supercharger having a relatively large-diameter exhaust gas introduction passage. A type of engine equipped with a turbo supercharger, in which the low speed turbo supercharger is used exclusively at low speeds, and the high speed turbo supercharger is dedicated or both turbo superchargers are used at high speeds. Needless to say, it can also be applied to

Further, for example, the fuel control method is not limited to the so-called map control method described with reference to FIG.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram of an engine according to an embodiment of the present invention, Fig. 2 is a graph showing the switching valve opening/closing control method, and Fig. 3 shows both the control characteristics of boost pressure and the change characteristics of exhaust pressure. Graphs shown in Figures 4 and 5
6 are graphs showing the control characteristics of the advance angle amount, EGR amount, and fuel amount, respectively. 1...Engine, 5...Intake passage, 6...Exhaust passage,
7...Turbocharger, 9...Turbine, 10...Blower, 14...Fuel injection valve, 16, 17...Low speed, high speed exhaust gas introduction passage, 18...Switching valve, 23
...EGR valve, 24...spark plug, 25...computer.

Claims (1)

[Claims] 1. An exhaust turbo supercharger for supercharging intake air, and a diameter that allows the diameter of the exhaust gas introduction passage to the turbine of the exhaust turbo supercharger to be varied according to engine operating conditions. In an engine provided with a variable means, the characteristic of the control amount for the engine operating state of the combustion state control means that governs the combustion state of the air-fuel mixture supplied to the engine is switched to change the size of the diameter by the diameter variable means. 1. A control device for an engine with an exhaust turbo supercharger, characterized in that a control amount changing means is provided for changing the combustion state so as to suppress a change in combustion state due to switching.