JPS62223417A - Supercharging control device for diesel engine - Google Patents

Abstract

PURPOSE:To enable the engine in the caption to be started even when the compression ratio thereof is reduced by coupling a mechanical supercharger with the engine power shaft and closing a by-pass valve at the starting time of the engine. CONSTITUTION:When an electromagnetic clutch 24 is made to be in the coupling condition and a mechanical supercharger 15 is driven by a diesel engine 1, a bypass valve 17 is closed. On the other hand, when the electromagnetic clutch 24 is made to be in the uncoupling condition and the operation of the mechanical supercharger 15 is stopped, the by-pass value 17 is opened. At the starting time of the engine when an engine speed is lower than a fixed engine speed, the mechanical supercharger 15 is operated, and the by-pass value 17 is closed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a supercharging control device for a diesel engine.

[Conventional technology]

The biggest advantage of diesel engines is that in some countries such as Japan, the fuel itself is not only cheaper than gasoline, but also has a lower fuel consumption rate than gasoline engines. Therefore, in order to increase the merits of a diesel engine, it is necessary to keep the fuel consumption rate as low as possible.By the way, the fuel consumption rate and output after warming up of a diesel engine with a swirl chamber or a diesel engine with a pre-combustion chamber are shown in Figure 5. The geometric compression ratio ε (hereinafter referred to as compression ratio) is as shown in
It can be seen that for many engines, the best fuel consumption rate is achieved when the compression ratio ε is around 16 to 18. Therefore, in such a diesel engine, the compression ratio ε is set to 16
It can be seen that it is preferable to set the value to about 18.

However, in order to ignite and burn the injected fuel in a diesel engine, the compressed air temperature must be higher than the ignition temperature of the fuel near compression top dead center. However, as mentioned above, if the compression ratio is set to about 16 to 18, the compressed air temperature will be higher than the fuel ignition temperature after warm-up is completed, but under certain operating conditions such as when starting the engine cold, the compressed air temperature will be higher than the fuel ignition temperature. The temperature does not rise above the ignition temperature, so the engine cannot be operated. Additionally, when the amount of fuel injected is small and the calorific value is low, such as during idling or extremely light load operation, the compressed air temperature will rise above the ignition temperature of the fuel, but it will not become high enough, resulting in incomplete combustion and a misfire. This causes white smoke to be generated more easily. Furthermore, when a vehicle is operated in a place where the atmospheric pressure is low, such as at a high altitude, there is a wider operating range in which the compressed air temperature does not exceed the ignition temperature of the fuel. Therefore, the compression ratio has conventionally been set at about 20 to 23 so that the compressed air temperature is equal to or higher than the ignition temperature of the fuel even when the engine is cold started or when the vehicle is operated at a high altitude. However, when the compression ratio is set to about 20 to 23, the fuel consumption rate after warm-up is increased as shown in FIG. 5, and the merits of the diesel engine are reduced accordingly.

On the other hand, diesel engines equipped with an exhaust turbocharger in order to obtain higher output are conventionally known.

However, since the exhaust turbocharger is operated by exhaust energy, there is insufficient exhaust energy in low speed rotation ranges or light load ranges, and the rotation does not increase sufficiently, so supercharging is rarely performed. Therefore, even if the engine is equipped with an exhaust turbocharger, if the compression ratio is set to around 16 to 18, the compressed air temperature will not rise above the fuel ignition temperature when the engine is cold started. I have no choice but to set the ratio from 20 to 23.

On the other hand, diesel engines equipped with a mechanical supercharger driven by the engine are conventionally known.

In this diesel engine, the supercharger is operated even when the engine is started, so the compressed air temperature rises due to the supercharging action. Therefore, in such a diesel engine, the compression ratio is set to 1.
Even if the compression ratio is set to about 6 to 18, the compressed air temperature will be higher than the fuel ignition temperature when the engine starts, and thus, in this diesel engine, the compression ratio can be set to about 16 to 18, improving the fuel consumption rate. be able to. However, in this diesel engine, the supercharger is constantly operated, and therefore supercharging is performed even during engine medium load operation when there is no need for supercharging. There is a problem in that a drive loss occurs for driving the machine, and thus the fuel consumption rate worsens.

On the other hand, a bypass passage is provided to bypass the mechanical supercharger, and when the exhaust temperature is below a predetermined temperature or the engine load is below a predetermined load, the operation of the supercharger is stopped and the bypass passage is closed. Air is supplied into the engine cylinder from
A diesel engine is known in which a supercharger is activated to perform supercharging when the exhaust gas temperature is above a predetermined temperature or when the engine load is above a predetermined load (Japanese Utility Model Publication No. 47-37939). No. Publication and Actual Publication 1977-
(See Publication No. 15442).

Additionally, a bypass passage is provided to bypass the mechanical turbocharger, and a bypass valve is installed in this bypass passage, and the bypass valve is opened so that the intake temperature downstream of the turbocharger reaches the target intake temperature during steady partial load operation. The applicant has already filed an application for a diesel engine that controls the amount
43475).

[Problem that the invention seeks to solve]

However, when the engine starts, the exhaust temperature is low and the load is small.
Therefore, in the diesel engine described in the above-mentioned Japanese Utility Model Publication No. 47-37937 or Japanese Utility Model Publication No. 49-15442, the supercharger is not operated when the engine is started. Therefore, these diesel engines cannot have a compression ratio of about 16 to 18. Also, Jitsugan Sho 59-1434
In the diesel engine described in No. 75, the turbocharger is considered to be activated even when the engine is started, but the turbocharger is also activated during medium-load operation after warm-up, and thus the fuel consumption rate is reduced. The problem is that it increases.

[Means for Solving the Problems] In order to solve the above problems, according to the present invention, a mechanical supercharger is disposed in the intake passage of a diesel engine, and the mechanical supercharger is connected via a connection/disconnection device. The bypass passage is connected to the output shaft of the engine, the bypass passage is branched from the intake passage upstream of the mechanical supercharger, the bypass passage is connected to the intake passage downstream of the mechanical supercharger, and a bypass valve is disposed within the bypass passage. When the engine starts, the mechanical supercharger is connected to the engine output shaft and the bypass valve is closed, and the connection between the mechanical supercharger and the engine output shaft is cut off in a predetermined operating range other than when the engine is started. At the same time, the bypass valve is opened.

〔Example〕

Referring to FIG. 1, ■ is a diesel engine, 2 is a cylinder block, 3 is a piston that reciprocates within the cylinder block, 4 is a cylinder head, 5 is a combustion chamber formed between the cylinder head 4 and the piston 3, 6 7 is an intake valve, 7 is an intake boat, 8 is a swirl chamber, 9 is a fuel injection valve disposed in the swirl chamber 8, and 10 is a nozzle port that communicates the swirl chamber 8 with the combustion chamber 5, respectively.

In the embodiment shown in FIG. 1, the compression ratio of the diesel engine l is 1.
It is set to about 6 to 18. Thermal theory, the invention can also be applied to diesel engines without a swirl chamber 8 or a pre-combustion chamber. The compression ratio of such diesel engines is usually 16
However, when the present invention is applied to these diesel engines, the compression ratio is set to about 12 to 14.

Although not shown in the drawings, an exhaust valve is attached to the cylinder head 4, and the combustion chamber 5 is connected to an exhaust manifold 11 via this exhaust valve. On the other hand, the intake boat 7 has an intake branch pipe 12
The surge tank 13 is connected to a common surge tank 13 through an air intake duct 14, and the surge tank 13 is connected to an air cleaner (not shown) through an intake duct 14. A mechanical supercharger 15 is arranged within this intake duct 14 . A bypass passage 1G is branched from the intake duct 14 upstream of the mechanical supercharger 15, and this bypass passage 16 is connected to the inside of the surge tank 13. A bypass valve 17 is arranged within the bypass passage 16 . The bypass valve 17 is controlled to open and close by a negative pressure diaphragm device, and a negative pressure chamber 18 of the negative pressure diaphragm device is connected to a negative pressure tank 20 via a switching valve 19 that can communicate with the atmosphere.

When the negative pressure chamber 18 is connected to the negative pressure tank 20 by the switching action of the switching valve 19, the bypass valve 17 opens, and the negative pressure chamber I
8 is opened to the atmosphere, the bypass valve 17 is closed. This switching valve 19 is controlled based on an output signal from an electronic control unit 7) 30. The electronic control unit 30 consists of a digital computer, and includes a ROM (read-on memory) 32, a RAM (
random access memory) 33, CPU (microprocessor)-34, input port 35 and output port 3
6. The switching valve 19 is connected to the output port 36 via a drive circuit 38 .

A driving pulley 21 is attached to the crankshaft of the engine, and a driven pulley 23 is driven by this driving boob IJ21 via a belt 22. This driven pulley 23 is connected to the mechanical supercharger 15 via an electromagnetic clutch 24 that constitutes a connection/disconnection device. When the electromagnetic clutch 24 is in the engaged state, the mechanical supercharger a15 is driven by the diesel engine 1, and when the electric ζft clutch 24 is in the disengaged state, the operation of the mechanical supercharger 15 is stopped. The electromagnetic clutch 24 is connected to the output port 36 via the drive circuit 39, and therefore the electromagnetic clutch 24 is connected to the electronic control unit 3.
It is controlled based on the output signal of 0.

A crank angle sensor 25 that generates an output pulse every time the engine crankshaft rotates by a predetermined crank angle is disposed on the drive pulley 21, and the crank angle sensor 25 is connected to the input port 35.

The engine speed is calculated from the output pulse of the crank angle sensor 25. A water temperature sensor 26 for detecting the engine cooling water temperature is attached to the cylinder block 2, and the water temperature sensor 26 is connected to an input port 35 via an AD converter 40. Water temperature sensor 26 generates an output voltage proportional to the engine cooling water temperature. The accelerator pedal 27a is connected to a load sensor 27 that detects the amount of depression of the accelerator pedal 27a, and this load sensor 27 is connected to the input port 35 via the AD converter 41. The load sensor 27 generates an output voltage proportional to the amount of depression of the accelerator pedal 27a, that is, the engine load. Further, the atmospheric pressure sensor 28 is connected to the AD converter 4
2 to the input capo I.35. This atmospheric pressure sensor 28 generates an output voltage proportional to atmospheric pressure. Furthermore, a starter switch 29 is connected to the input port 35. This starter switch 29 is turned on when the starter motor is operated to start the engine.
Therefore, it can be determined from the output signal of the starter inch 29 whether or not the starter motor is operated.

In the present invention, when the electromagnetic clutch 24 is in the engaged state and the engine-type supercharger 15 is driven by the diesel engine 1, the bypass valve 17 is closed, and the electromagnetic clutch 24 is in the engaged state and the bypass valve 17 is closed.
4 is in the uncoupled state and the operation of the mechanical supercharger 15 is stopped, the bypass valve 17 is opened.

FIG. 2 shows control of the mechanical supercharger 15 and bypass valve 17 according to engine cooling water temperature and atmospheric pressure. In addition, in Figure 2, (8), (B), (C),
(D) shows control in the following states.

(8) If the vehicle is operated in a low area before warm-up is completed (B) If the vehicle is operated in a low area after warm-up is completed (C) If the vehicle is operated in a high area before warm-up is completed When the vehicle is operated (D) When the vehicle is operated at a high altitude after completion of warm-up In Fig. 2, hatched areas P and Q indicate mechanical supercharger 1.
5 indicates a region where the bypass valve 17 is closed, and other regions indicate a region where the mechanical supercharger 15 is stopped and the bypass valve 17 is open. In addition, Fig. 2 (A) and (B).

In (C) and (D), the vertical axis shows the mechanical load,
The horizontal axis NE shows the engine speed. Next, each (8) to (D)
Mechanical supercharger 15 and bypass valve 1 in each state of
The control of No. 7 will be explained in order.

(8) When the vehicle is operated in a lowland area before warm-up is completed. In this case, as shown in area Q, the engine speed NE is lower than a certain speed, for example, 600r, p, m. During operation, that is, when the engine is started, the mechanical supercharger 15 is activated and the bypass valve 17 is closed. In this way, by operating the mechanical supercharger 15 to supercharge the engine when starting the engine, it is possible to increase the air pressure in the combustion chamber 5 at the time of starting compression. Therefore, even if the compression ratio is set to about 16 to 18, the compressed air temperature at the end of the compression stroke can be made equal to or higher than the ignition temperature of the fuel, and the engine can thus be started easily. Further, before the warm-up is completed, the engine load is low, and when the engine load is higher than that, the mechanical supercharger 15 is activated. Also, depending on the engine, the compressed air temperature in the combustion chamber 5 may not rise sufficiently during low-speed, low-load operation before completion of warm-up; In some cases, the compressed air temperature may not rise sufficiently. In such a case, the broken line area S in Fig. 2 (Δ)
Alternatively, even in R, the mechanical supercharging [15] may be activated.

(B) If the vehicle is operated at a low altitude after warm-up has been completed.In this case, apart from when the engine is restarted after warm-up has been completed, the mechanical The supercharger 15 is operated (Si region P), and during partial load operation where the engine load is lower than Ll, the operation of the mechanical supercharger 15 is stopped and the bypass valve 17 is opened.

Therefore, during partial load operation, the intake air is supplied into the surge tank 13 via the bypass passage 16 without being pressurized. In the present invention, the compression ratio is set to about 16 to 18, but in this case, even without supercharging, the compressed air temperature in the combustion chamber 5 can be raised above the ignition temperature of the fuel after warm-up is completed. In this way, stable combustion can be ensured. Also, in this way the compression ratio is increased from 16 to 18.
By setting it to a certain degree, the compression work can be reduced, so the fuel consumption rate can be reduced accordingly, and furthermore, since there is no driving loss for driving the mechanical supercharger 15, the fuel consumption rate can be further reduced. do. That is, the fuel consumption rate can be minimized during partial load operation by lowering the compression ratio compared to the prior art and by stopping the operation of the mechanical supercharger 15. Also, depending on the engine, when the engine is idling, operating at extremely low load, or going down a slope while supplying fuel, the engine temperature may drop and the compressed air temperature may not rise sufficiently, resulting in a misfire. White smoke may occur. In such an engine, it is desirable to operate the mechanical supercharger 15 even in the region T shown by the broken line in FIG. 4(B).

(C) If the vehicle is operated at a high altitude before warm-up is completed When the vehicle is operated at a high altitude, the compressed air temperature is lower than that at a low altitude because the density of the air decreases. The operating range in which the temperature does not exceed the ignition temperature of the fuel is expanded. Therefore, before warm-up is completed, the mechanical supercharger 15 is operated not only when the engine is started, but also during partial load operation at low to medium speeds. In addition, depending on the institution, Figure 2 (C)
There are cases where it is necessary to operate the mechanical supercharger 15 even in the region indicated by the broken line U, and in this case, the mechanical supercharger a15 is operated in all operating conditions.

(D) When the vehicle is operated at a high altitude after warm-up is completed. In this case, mechanical supercharging [15] is activated when the engine load is equal to or higher than the constant load L2 (area P). The mechanical supercharger 15 is also operated during low speed and low load, low speed and medium load, and medium speed and low load operations. The load L2 at which supercharging is started is lower than the load in the lowland area, and the area Q is the fourth
It is wider than the region 'F in FIG. Note that depending on the engine, it may be necessary to operate the mechanical supercharger 15 even in the area indicated by the broken line ■ in FIG. It will be done. The operating region, the operating stop region, and the bypass valve 1 of the mechanical supercharger 15 shown in FIG. 2 (A) to (D), respectively.
The valve opening area and valve closing area of No. 7 are stored in advance in the form of a map at a predetermined address of 120M32.

FIG. 3 shows a flowchart for controlling the mechanical supercharger 15 and bypass valve 17 shown in FIG.

Referring to FIG. 3, first, in step 50, it is determined whether the starter switch 29 is on, that is, whether the starter motor is operated. If the starter switch 29 is on, the process proceeds to step 51, where the electromagnetic clutch 24 is engaged to operate the mechanical supercharger 15, and at the same time, the bypass valve 17 is closed. Next, in step 52, the elapsed time T0 from when the starter switch 29 was turned off is set based on the engine cooling water temperature.

As shown in Fig. 4, this elapsed time T0 corresponds to the engine cooling water'/
It decreases as HK increases. The relationship shown in FIG. 4 is previously stored in the ROM 32, and in step 52 the elapsed time T0 is determined from this stored relationship.

When the starter switch 29 is switched from on to off, the process proceeds from step 50 to step 53, where it is determined whether or not the elapsed time T has become T0 or more. If 'r<'ro, the processing cycle is completed. Therefore, the mechanical supercharger 15 is operated for a while after the engine is started, and this operating time becomes longer as the engine cooling water temperature K becomes lower. Engine cooling water temperature K
The lower the engine cooling water temperature K, the more likely misfires and white smoke will occur. Therefore, by increasing the operating time of the mechanical supercharger 15 as the engine cooling water temperature K becomes lower, it is possible to prevent misfires and white smoke from occurring immediately after the engine starts. .

If it is determined in step 53 that T > To, the process proceeds to step 54, where the engine cooling water temperature K is kept at a constant value K. It is determined whether or not the temperature is higher than , that is, whether or not warm-up has been completed. If K<KO, the process proceeds to step 55 where it is determined whether the atmospheric pressure P is higher than a constant value P0, that is, whether the vehicle is being driven in a lowland. If P>PG, the routine proceeds to step 56, where the mechanical supercharger 15 and bypass valve 17 are controlled according to the map shown in FIG. 2(A). If P<PO, that is, if the vehicle is being driven at a high altitude, proceed to step 57 and proceed to step 57 as shown in FIG. 2(C).
The mechanical supercharger 15 and bypass valve 17 are controlled according to the map shown in FIG. On the other hand, when K>Ko, that is, after the warm-up is completed, the process proceeds to the suttebu 58 where the atmospheric pressure P is kept at a constant value P.

It is determined whether or not it is higher than . If P>Po, the routine proceeds to step 59, where the mechanical supercharger 15 and bypass valve 17 are controlled according to the map shown in FIG. 2(B).

If P<PO, proceed to step 60 and proceed to Fig. 2 (D).
The mechanical supercharging [15] and the bypass valve 17 are controlled according to the map shown in FIG.

〔Effect of the invention〕

By activating the mechanical supercharger to supercharge the engine when starting the engine, the engine can be started even if the compression ratio of the engine is lowered. Therefore, since the compression ratio can be lowered, the fuel consumption rate can be reduced. On the other hand, the operation of the mechanical supercharger is stopped in a predetermined operating range other than when the engine is started, for example, during partial load operation after completion of warm-up. At this time, since the compression ratio is set low, the fuel consumption rate is reduced, and furthermore, the drive loss for operating the mechanical supercharger is eliminated, which further reduces the fuel consumption rate. Consumption rate can be minimized.

[Brief explanation of drawings]

Figure 1 is an overall diagram of the diesel engine, Figure 2 is a diagram showing the operating area of the mechanical supercharger, and the opening and closing of the bypass valve.
The figure is a flowchart i for performing supercharging control, FIG. 4 is a diagram showing the relationship between elapsed time T0 and cooling water temperature, and FIG. 5 is a diagram showing fuel consumption rate and engine output. 12...Intake branch pipe, 14...Intake duct, 1
5... Mechanical supercharger, 16... Bypass passage, 17
...Bypass valve, 27...Load sensor, 28...
・Atmospheric pressure sensor, 29...Start inch. (A) (B) (C) (D) Figure 2

Claims (1)

[Claims] A mechanical supercharger is placed inside the intake passage of a diesel engine,
The mechanical supercharger is connected to the output shaft of the engine via a connection/disconnection device, and a bypass passage is branched from the intake passage upstream of the mechanical supercharger, and the bypass passage is connected to the intake passage downstream of the mechanical supercharger. A bypass valve is connected to the passage and placed in the bypass passage, and when the engine is started, the mechanical supercharger is connected to the engine output shaft and the bypass valve is closed, so that a predetermined operating range other than when the engine is started is provided. This is a diesel engine supercharging control system that disconnects the mechanical supercharger from the engine output shaft and opens a bypass valve.