JPH0751912B2 - Method of detecting combustion air for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for detecting combustion air used for calculating a fuel injection amount of an internal combustion engine and the like.

BACKGROUND ART In a so-called electronically controlled fuel injection device for an internal combustion engine, it is necessary to detect the intake air flow rate in order to determine the fuel injection amount. In the method previously proposed by the applicant of the present invention to detect the intake air flow rate, the intake air flow rate is detected based on the intake pressure and the throttle valve opening. This method has good responsiveness, and the intake air flow rate can be detected relatively accurately in response to opening / closing of the throttle valve.

However, in this prior art, it is premised that the pressure on the upstream side of the throttle valve is atmospheric pressure under 760 mmHg. Therefore, when the atmospheric pressure changes, for example, at high altitudes, an error necessarily occurs. In order to solve this problem, when the atmospheric pressure is detected, the following two methods can be considered.

(1) Measure the intake pressure immediately after the ignition key switch is turned on. That is, when the internal combustion engine is stopped, the pressure in the surge tank is equal to the atmospheric pressure, and therefore the pressure in the surge tank is detected before the starter motor is rotated by connecting the ignition key switch. Therefore, the atmospheric pressure can be detected.

(2) Detect the pressure in the surge tank when the throttle valve is fully opened. When the throttle valve is fully opened, the pressure in the surge tank is equal to the atmospheric pressure. Therefore, the atmospheric pressure can be detected by detecting the pressure in the surge tank.

Problems to be Solved by the Invention In the method (1), detection cannot be performed during normal operation. That is, once the internal combustion engine is started, it cannot be detected until it is stopped and restarted.
Further, in the above method (2), the throttle valve is rarely fully opened, so that it is difficult to perform frequent detection. Furthermore, both methods (1) and (2) above
It cannot be used in an internal combustion engine having an exhaust gas recirculation function. That is, the detected pressure in the surge tank also includes the pressure of the recirculated exhaust gas, and therefore it is not possible to accurately detect only the intake pressure.

In order to solve the above-mentioned problems, another prior art proposed by the applicant of the present application detects the intake air flow rate from the differential pressure between the upstream side and the downstream side of the throttle valve. In this method, a new pressure detector is additionally provided on the upstream side of the throttle valve in order to detect the atmospheric pressure, resulting in a high cost.

An object of the present invention is to provide a method for detecting combustion air of an internal combustion engine, which is capable of detecting the atmospheric pressure on the upstream side of the throttle valve at low cost.

Means for Solving Problems According to the present invention, an intake pressure Pm under a predetermined atmospheric pressure is obtained based on a rotation speed N of an internal combustion engine per unit time and a throttle valve opening θ, and a graph or It is stored in advance as a table, the actual intake pressure P2 of the internal combustion engine is detected, the actual rotational speed N1 of the internal combustion engine is detected, the actual throttle valve opening θ1 of the internal combustion engine is detected, and the graph or table From the above, the intake pressure P1 under the predetermined atmospheric pressure corresponding to the actual rotational speed N1 of the internal combustion engine and the throttle valve opening θ1 is determined, and the difference P between this intake pressure P1 and the intake pressure P2 is determined, Based on the predetermined atmospheric pressure and the difference P, the actual atmospheric pressure Pa
Is a method of detecting air for combustion in an internal combustion engine.

Operation According to the present invention, the intake pressure Pm corresponding to the rotation speed N of the internal combustion engine per unit time and the throttle valve opening θ is experimentally obtained under a predetermined atmospheric pressure of 760 mmHg, for example. And store it in memory as a graph or table.

During actual operation, the engine speed N1 per unit time
And the throttle valve opening θ1 and the intake pressure P2 are detected, and the intake pressure P1 corresponding to the rotational speed N1 and the throttle valve opening θ1 is obtained from the graph or table, and the intake pressure P1 and the intake pressure P2 are obtained. The difference P with is calculated.

By subtracting the difference P thus obtained from 760 mmHg, the actual atmospheric pressure Pa can be obtained. Therefore, the differential pressure between the upstream side and the downstream side of the throttle valve can be accurately detected from the actual atmospheric pressure Pa and the intake pressure P2, and the accurate fuel can be obtained without being affected by the change in the atmospheric pressure Pa. The injection amount can be calculated.

FIG. 1 is a block diagram of an embodiment of the present invention. A plurality of combustion chambers E1 to Em are formed in the internal combustion engine 13, and combustion air is supplied to the combustion chambers E1 to Em from an intake pipe 15.
A throttle valve 16 is interposed in the intake pipe 15. Combustion air passing through the throttle valve 16 is guided from the surge tank 14 to intake pipes A1 to Am individually provided for the combustion chambers E1 to Em, respectively. Combustion injection valves B1 to Bm are connected to the intake pipes A1 to Am, respectively.
Is provided, and in each explosion process in each of the combustion chambers E1 to Em, the fuel amount determined by the processing device 31 described later is injected. An intake valve C1 is provided in each combustion chamber E1 to Em.
~ Cm and exhaust valves D1 to Dm are provided. The internal combustion engine 13 is, for example, a 4-cycle spark ignition internal combustion engine having spark plugs G1 to Gm.

The surge tank 14 has a pressure detector for detecting the intake pressure.
19 are provided. The intake pipe 15 is provided with a temperature detecting element 27 for detecting the intake air temperature. The internal combustion engine 13 is provided with a crank angle detector 28 for detecting a crank angle,
A valve opening detector 30 is provided to detect the opening of the throttle valve 16.

An oxygen concentration detector 21 is provided in the middle of the exhaust pipe 20, and the exhaust gas is purified by the three-way catalyst 22 and discharged to the outside. Between the exhaust pipe 20 and the surge tank 14, a side passage 23 for recirculating a part of the exhaust gas is provided in order to reduce NOx. The side passage 23 controls the flow rate. Valve to do
24 are intervening.

Processing device reproduced by a micro computer
Reference numeral 31 is an input interface 32 and an analog / digital converter for converting an input analog signal into a digital signal.
33, a processing circuit 34, an output interface 35, and a memory
Including 36 and. The memory 36 includes read-only memory and random access memory. In the embodiment of the present invention, in response to the output from the detectors 19, 28, 30, etc., the fuel injection valve B1
Controls the fuel injection amount for each explosion process that is injected from ~ Bm.

On the other hand, an automobile manufacturer measures the intake pressure Pm corresponding to the rotation speed N of the internal combustion engine 13 per unit time and the throttle valve opening θ under a predetermined atmospheric pressure of 760 mmHg, for example. The measurement result is as shown in FIG. 2, for example, and the intake pressure Pm increases as the throttle valve opening θ increases and the rotational speed N of the internal combustion engine 13 decreases.
The measurement results shown in FIG. 2 are stored in the memory 36 as a graph or a table as shown in FIG.

With the experimental results stored in this manner, during actual operation of the internal combustion engine 13, the flow rate control valve 24 is closed and exhaust gas recirculation through the bypass 23 is not performed, and the pressure detector 19 is used. The actual pressure of the surge tank 14, that is, the intake air pressure P2 is detected, and the crank angle detector 28 is used to detect the internal combustion engine 13
The rotation speed N1 per unit time is detected, and the opening degree θ1 of the throttle valve 16 is detected by the valve opening detector 30. Based on the detected rotational speed N1 and the throttle valve opening θ1, the intake pressure P under the atmospheric pressure of 760 mmHg is obtained from the above-mentioned graph or table stored in the memory 36.
Ask for 1. From the difference P between the intake pressures P1 and P2 thus obtained, the first
The actual atmospheric pressure Pa can be calculated based on the equation.

Pa = 760- (P1-P2) = 76-P (1) When this atmospheric pressure Pa is stored in the memory 36, the flow control valve
24 is opened and exhaust gas recirculation is performed.

By the way, from Bernoulli's formula Where ρ is the specific gravity of air, v is the velocity of air,
P0 is the pressure of the intake air. When this second formula is applied to the throttle valve 1, Here, Q is the intake air flow rate per unit time passing through the throttle valve 16, A is a flow passage sectional view of the throttle valve 16, and P1 is the throttle valve 16 under the atmospheric pressure of 760 mmHg.
Is the pressure on the downstream side, that is, the intake pressure.

Here, the flow passage cross-sectional area A of the throttle valve 16 is A = K1 · f
(Θ1) (4) θ1 is the opening degree of the throttle valve 16, and K1 is a constant. Therefore, from the third and fourth equations However K2 is a constant. Here, if the atmospheric pressure Pa is almost constant,
It is understood that the intake air flow rate Q per unit time passing through the throttle valve 16 depends on the opening degree θ1 of the throttle valve 16 and the intake pressure P1. Therefore, when the opening degree θ1 of the throttle valve 16 is constant, the intake air flow rate Q changes to a parabolic shape with respect to the differential pressure ΔP between the atmospheric pressure Pa and the intake pressure P1, as shown in FIG. The intake air flow rate Q does not depend on the recirculation amount of the exhaust gas recirculated through the side passage 23. In this way, the intake air flow rate Q can be accurately obtained. The data of FIG. 4 is stored in the memory 36 as a graph or table.

In FIG. 4, the line l1 is the case where the opening θ of the throttle valve 16 is 1.7 °, the line l2 is 5 °, the line l3 is 10 °, the line l4 is 15 °, and the line l5. Is
20 °, line l6 is 25 °, line l7 is 30 °, line l8 is 35 °, line l9 is 40 °,
Line l10 is 45 ° and line l11 is 50 °.

FIG. 5 is a flow chart for explaining the operation. At step n1, the flow control valve 24 is closed to stop the exhaust gas recirculation through the side passage 23, and at step n2, the pressure sensor is detected.
The pressure in the surge tank 14, that is, the actual intake pressure P2 is detected by 19. Crank angle detector for step n3
28, the number of revolutions N1 of the internal combustion engine 13 per unit time is detected, and at step n4, the valve opening detector 30 detects the opening θ1 of the throttle valve 16.

In step n5, it is judged whether or not the flag indicating whether or not the atmospheric pressure detection mode is 1, and if so, that is, in the atmospheric pressure detection mode, step n6
Then, the intake pressure P1 under the atmospheric pressure of 760 mmHg is read from the graph or table stored in the memory 36 in correspondence with the rotation speed N1 and the throttle valve opening θ1.
At step n7, the actual atmospheric pressure Pa is calculated from the difference P between the intake pressures P1 and P2.
Is calculated and stored in the memory 36. At step n8, the flow control valve 24 is opened to perform normal exhaust gas recirculation, and then the process proceeds to step n9. When the flag is 0 in step n5, the process directly goes to step n9.

At step n9, the differential pressure ΔP between the actual atmospheric pressure Pa and the intake pressure P2
Is obtained, and at step n10, based on this differential pressure ΔP,
The intake air flow rate Q is read from the graph or table of FIG. 4 stored in the memory 36. At step n11, the fuel injection amount J corresponding to the intake air flow rate Q is obtained, and at step n12, fuel is injected from the fuel injection valves B1 to Bm.

In step n13, it is judged whether or not a predetermined time T has passed since the previous atmospheric pressure detection mode. If so, the process proceeds to step n14, where the flag 1 indicating the atmospheric pressure detection mode is set and step n1 is set. Return to. When the predetermined time T has not elapsed from the previous atmospheric pressure detection mode in step n13, the flag is reset to 0 in step n15 and the process returns to step n2.

As described above, in the present embodiment, it is possible to detect the actual intake pressure Pa at low cost without providing a new pressure detector or the like on the upstream side of the throttle valve 16. As a result, the pressure difference ΔP between the upstream side and the downstream side of the throttle valve 16 can be accurately detected, and the fuel injection amount J can be calculated with high accuracy.

As described above, according to the present invention, the intake pressure Pm corresponding to the rotational speed N of the internal combustion engine and the throttle valve opening θ is experimentally obtained under a predetermined atmospheric pressure of 760 mmHg.
From this intake pressure Pm, the actual rotational speed N1 and the throttle valve opening θ
Since the intake pressure P1 corresponding to 1 and the intake pressure P1 is calculated to determine the difference P between the intake pressure P1 and the actual intake pressure P2, by subtracting the difference P thus obtained from 760 mmHg It is possible to obtain the atmospheric pressure Pa, and thus it is possible to accurately detect the differential pressure between the upstream side and the downstream side of the throttle valve from the actual atmospheric pressure Pa and the intake pressure P2, and the influence of the change in the atmospheric pressure Pa. An accurate fuel injection amount can be calculated without being affected. Further, it is not necessary to newly install a pressure detector on the upstream side of the throttle valve for detecting the atmospheric pressure Pa, and therefore, the cost is not increased.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a graph showing the relationship between the rotational speed N of the internal combustion engine 13 and the intake pressure Pm at each throttle valve opening θ, and FIG. FIG. 4 is a graph showing the contents of the store, FIG. 4 is a graph showing the relationship between the differential pressure ΔP and the intake air flow rate Q at each throttle valve opening θ of the inventor's experimental results, and FIG. 5 is a flow for explaining the operation. It is a chart. 13 …… Internal combustion engine, 14 …… Surge tank, 15 …… Intake pipe,
16 ... Slot valve, 19 ... Pressure detector, 20 ... Exhaust pipe, 23 ... Side passage, 28 ... Crank angle detector, 30 ... Valve opening detector, 31 ... Processor, 36 ... … Memory, B1 to Bm ……
Fuel injection valve, E1 to Em ... Combustion chamber, G1 to Gm ... Spark plug

Claims (1)

[Claims] 1. An intake pressure Pm under a predetermined atmospheric pressure is calculated based on a rotation speed N of an internal combustion engine per unit time and a throttle valve opening .theta. And is stored in advance as a graph or a table. , The actual intake pressure P2 of the internal combustion engine is detected, the actual rotational speed N1 of the internal combustion engine is detected, the actual throttle valve opening θ1 of the internal combustion engine is detected, and the actual internal combustion engine The intake pressure P1 under the predetermined atmospheric pressure corresponding to the rotation speed N1 and the throttle valve opening θ1 is determined, and the difference P between the intake pressure P1 and the intake pressure P2 is determined to obtain the predetermined atmospheric pressure. From the difference P, the actual atmospheric pressure Pa
A method for detecting air for combustion in an internal combustion engine, characterized in that: