JP2000018064A - Common rail type fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a common rail type fuel injection system, capable of seeking an accurate fuel injection quantity reflected on the properties of fuel ranging from a common rail to an injector by means of operation used with a bulk modulis to be sought on the basis of a pressure propagation velocity. SOLUTION: Owing to a zero cross point in the common rail pressure of differential value to be sought by a detection signal out of a pressure sensor installed in a common rail, a period t of pulsation in the common rail pressure due to a pressure wave reflecting between the common rail and an injector, is sought. Moreover, a bulk modulus K (=πa2+ΔP) is sought by a pressure propagation velocity (a) of fuel sought from a pressure propagation distance and this period Δt, a pressure dropping quantity ΔP and fuel density ρof the common rail pressure on the basis of fuel injection. If common rail capacity is set to be Vc, a fuel supply quantity Q is found out by operation of Vc×ΔP/K.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common rail type fuel injection device for injecting fuel into a combustion chamber of an engine based on a pressure action of fuel supplied from a common rail.

[0002]

2. Description of the Related Art Conventionally, as a fuel injection device for an engine,
The fuel stored in the common rail is supplied to a plurality of injectors, a part of the fuel is used as a working fluid to operate the injectors, and the fuel supplied from the common rail is formed at the tip of the injector by the operation of each injector. There is known a common rail type fuel injection device of a type in which an injection hole is injected into a combustion chamber of an engine.

FIG. 3 schematically shows an example of the above common rail type fuel injection device. The fuel sucked up from the fuel tank 4 via the filter 5 by the feed pump 6 and pressurized to a predetermined suction pressure is sent to the high-pressure fuel pump 8 through the fuel pipe 7. The high-pressure fuel pump 8
For example, the fuel supply pump is a so-called plunger type fuel supply pump driven by an engine. The fuel supply pump boosts the fuel to a high pressure determined based on an operation state and the like, and supplies the fuel to the common rail 2 through the fuel pipe 9. . Fuel stored in the common rail 2 at a predetermined pressure is supplied from the common rail 2 to the plurality of injectors 1 through the fuel supply pipe 3. In the illustrated example, the engine is a six-cylinder engine, and injectors 1 for injecting fuel into combustion chambers formed therein are arranged in six cylinders (not shown). It is clear that the engine is not limited to the illustrated six cylinders but may be four cylinders.

The fuel relieved from the high-pressure fuel pump 8 is returned to the fuel tank 4 through a return pipe 10. Further, of the fuel supplied from the fuel supply pipe 9 to the injector 1, the fuel not consumed for injection into the combustion chamber is returned to the fuel tank 4 through the return pipe 11. The controller 12 includes various sensors such as a crank angle sensor for detecting the engine speed, an accelerator opening sensor for detecting the accelerator opening, and a fuel temperature sensor for detecting the temperature of the high-pressure fuel. Is input. Other sensors for detecting the operating state of the engine include an intake pipe pressure sensor for detecting an intake pipe pressure, a water temperature sensor for detecting a coolant temperature, and the like. Further, a detection signal of the fuel pressure in the common rail 8 (hereinafter, referred to as common rail pressure) detected by the pressure sensor 13 provided on the common rail 2 is sent to the controller 12.

[0005] Based on these signals, the controller 13 controls the combustion so that the fuel can be optimally adjusted to the operating state of the engine, for example, by the fuel corresponding to the optimal injection timing with the optimal fuel injection amount. The mode of fuel injection by the injector 1 including the fuel injection timing and injection amount is controlled so as to be injected into the chamber. The injection pressure of the fuel injected from the injector 1 is substantially equal to the common rail pressure. The magnitude of the injection pressure that determines the fuel injection amount together with the injection period is controlled by controlling the flow control valve 14 to control the amount of high-pressure fuel supplied to the common rail 2. When the fuel in the common rail 2 is consumed by the injection of the fuel from the injector 1 or when the fuel injection amount is changed, the controller 12 controls the flow control valve 14 so that the common rail pressure becomes a predetermined fuel pressure. This controls the amount of fuel discharged from the high-pressure fuel pump 8 to the common rail 2. The common rail fuel injection device itself is conventionally known, and further detailed description is omitted.

In this common rail type fuel injection device, the injector 1 has an injector body 21 as shown in FIG. 4 and a needle valve slidable in a hollow hole 23 attached to the injector body 21 and formed therein. 24 having a nozzle 22. The fuel supplied from the common rail 2 to each injector 1 through the fuel supply pipe 3 is connected to the fuel supply pipe 3 via a fuel inlet joint 30 and is provided with fuel passages 31, 32 and a nozzle 22 formed inside the injector body 21. When the injection hole 25 formed at the tip of the nozzle 22 is opened by the lift of the needle valve 24 through the fuel reservoir 33 formed in the hollow hole 23 and the passage around the needle valve 24, It is injected into the combustion chamber. Excess fuel is returned to the common rail through the return pipe 11.

The injector 1 is provided with a pressure control chamber type needle valve lift mechanism for controlling the lift of the needle valve 24. That is, part of the high-pressure fuel supplied from the common rail 2 is also supplied to the pressure control chamber 40 formed inside the injector 1. The head of the injector 1 is provided with an electromagnetic valve 15 as an electronic device for controlling the inflow and outflow of the working fluid into and out of the pressure control chamber 40. The controller 12 controls the controller 12 according to the operating state of the engine. By controlling the operation of the solenoid valve 15, the pressure state of the working fluid in the pressure control chamber 40 is controlled to a high pressure state by the introduced high pressure fuel or a low pressure state in which the pressure in the pressure control chamber 40 is released. A drive current as a control signal from the controller 12 is sent to a solenoid 38 of the solenoid valve 15 through a signal line 37. When the solenoid 38 is excited, the armature 39 rises and the on-off valve 42 provided at the end of the fuel passage 41 as a leak passage opens, so that
By discharging the fuel supplied to the pressure control chamber 40 through the open on-off valve 42, the high fuel pressure in the pressure control chamber 40 is released.

In a central hollow hole 43 formed in the injector body 21 of the injector 1, a control piston 44 is provided so as to be able to move up and down. The taper surface 34 facing the fuel reservoir 33 and the needle valve 24 are less than the pressing force applied to the control piston 44 by the force based on the pressure in the pressure control chamber 40 reduced when the solenoid valve 15 is operated and the spring force of the return spring 45. The control piston 44 rises because the force for pushing up the control piston 44 is superior based on the fuel pressure acting on the tip of the control piston 44. As a result, the needle valve 24 is lifted, and fuel is injected from the injection hole 25. The fuel injection amount depends on the fuel pressure in the fuel passage and the needle valve 24.
(Lift amount, lift period).

In the above common rail type fuel injection device, the actual fuel injection amount of the injector 1 is calculated from the pressure drop amount of the common rail 2 before and after the fuel injection. The controller 12 controls the valve opening time of the fuel injection valve so that the actual fuel injection amount obtained in this manner becomes a target fuel injection amount according to the operating state of the engine. The calculation of the actual fuel injection amount is described in
There is one disclosed in Japanese Patent Publication No. -186034. The calculation of the actual fuel injection amount described in this publication is performed based on the pressure drop amount of the common rail, the common rail pressure before the drop, the capacity of the accumulator, and the fuel temperature.

A fuel injection rate measuring device has been proposed in which fuel is injected into a volume to detect a pressure increase ΔP in the volume, and a fuel injection amount is calculated based on ΔP and the bulk modulus. (See JP-A-64-63649).
According to the fuel injection rate measuring device, the bulk modulus is a function of the fuel temperature and the fuel pressure at that time, and the relationship is stored in the ROM of the controller as a map. When calculating the fuel injection amount, the bulk elastic modulus is obtained from the map according to the temperature and the pressure, and the calculation of the fuel injection amount is corrected by the obtained bulk elastic modulus.

The actual fuel pressure in the reservoir tank for storing the high-pressure fuel delivered from the fuel supply pump is reduced by supplying the fuel to the fuel injection valve. However, the actual fuel pressure in the reservoir tank after the reduction is lower than the actual fuel pressure in the reservoir tank. From the pressure difference from the target fuel pressure according to the operating condition of the engine, the discharge rate of the fuel supply pump required to restore the actual fuel pressure of the reservoir tank to the target fuel pressure is determined using the bulk modulus. A fuel supply control method has been proposed (Japanese Patent No. 2658510).
Reference).

[0012]

When the common rail having the volume Vcr is filled with fuel, the amount of fuel flowing out of the common rail (that is, fuel consumption) Q
Is the variation ΔP of the common rail pressure before and after fuel injection.
It is obtained by the following equation based on and the bulk modulus K. Q = (Vcr / K) × ΔP Equation (1) Although the volume Vcr is constant, the volume elastic modulus K basically fluctuates according to temperature and pressure even if it is a physical property value. Of course, different values are shown depending on the properties of the fuel, that is, the specifications of the gas oil (JIS No. 2 gas oil and No. 3 gas oil are sold depending on the season and region). Therefore, if the parameters (temperature, pressure, etc.) are specified, the bulk modulus K can be stored in the ROM of the controller in advance as a map, but it is difficult to specify all the parameters, and it is difficult to specify all the parameters. Preparing a map in accordance with a combination of parameters increases the cost of the fuel injection device.

Therefore, even if the bulk modulus fluctuates, if the value can be obtained by calculation from another easily detectable physical quantity, a ROM having a large capacity as a map according to the number of enormous combinations of various kinds of parameters can be obtained. The amount of fuel supplied to each injector from the common rail using the bulk modulus obtained at a low cost and directly at the time of need, while eliminating the need to store the Has to be calculated accurately.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to detect the amount of a common rail pressure drop which drops based on fuel injection, and calculate the fuel consumption from the common rail pressure drop and the bulk modulus. An object of the present invention is to provide a common rail type fuel injection device which can calculate an elastic modulus by a calculation using a sound velocity and accurately calculate a fuel consumption amount even if a property of the fuel changes.

The present invention includes a common rail for storing fuel, an injector for injecting fuel supplied from the common rail into a combustion chamber, and a controller for controlling fuel injection from the injector in accordance with an operating state of the engine. The controller determines the fuel density, the amount of pressure drop as the difference between the fuel pressure of the common rail before and after the fuel is injected from the injector, and the pressure propagation speed of the fuel that varies according to the properties of the fuel. And calculating a fuel supply amount supplied from the common rail to the injector based on a bulk modulus of the fuel determined from the following.

[0016] The controller corrects the density of the fuel according to the temperature of the fuel. The correction by the temperature is obtained by, for example, a linear expression of a temperature having a coefficient obtained from a density and a linear expansion coefficient at a reference temperature.

[0017] The controller is configured to control the fuel by a predetermined propagation distance in which a pressure wave that repeats reflection between the common rail and the injector propagates, and a cycle of fuel pressure pulsation generated in the common rail by the pressure wave. Is calculated.

The common rail is provided with a pressure sensor for detecting a fuel pressure, and the controller obtains the pressure drop amount of the common rail fuel pressure based on a detection signal from the pressure sensor. And calculating the cycle of the pulsation of the fuel pressure as a time interval between successive maximum values or minimum values detected based on a differential value of a detection signal from the pressure sensor.

The controller determines a target fuel injection amount in accordance with an operation state of the engine, and calculates a target fuel injection amount based on a deviation between the target fuel supply amount and the calculated fuel supply amount.
The fuel injection from the injector is controlled so that the fuel injection amount matches the target fuel injection amount.

When the volume of the common rail is Vc, the pressure drop amount of the fuel pressure of the common rail is ΔP, the density of the fuel is ρ, and the pressure propagation speed is a, the controller calculates The fuel supply amount Q is calculated. Q = Vc × ΔP / (ρ × a ² + ΔP)

According to the common rail fuel injection system of the present invention, the amount of fuel supplied from the common rail to the injector is determined by the difference between the fuel density and the fuel pressure of the common rail before and after the fuel is injected from the injector. In addition to the pressure drop amount as described above, the bulk elastic modulus of the fuel is determined in consideration of the pressure propagation velocity of the fuel, and is calculated by calculation based on the bulk elastic modulus. Therefore, the bulk modulus is obtained as a value corresponding to the property of the fuel, and as a result, an accurate fuel supply amount corresponding to the property of the fuel can be obtained. The actual fuel injection amount obtained by subtracting the dynamic leak amount leaking from the pressure control chamber from the fuel supply amount is actually injected from the injector. According to the present invention, the actual fuel injection amount is accurately obtained, and accordingly, the controller can perform accurate fuel injection control so as to obtain the target fuel injection amount.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a common rail fuel injection system for an engine according to the present invention will be described below with reference to the drawings. As the outline of the common rail type fuel injection device, the device shown in FIG. 3 can be used as it is, so that detailed description is omitted again. FIG. 1 shows a common rail type fuel injection device according to the present invention, which is used for a certain period (or crank angle) before a compression top dead center of a combustion cycle.
Command pulse for controlling supply or stop of a control current (voltage) to the solenoid valve 15 of the injector 1;
4 is a graph showing a fuel injection rate at which fuel is injected from a fuel cell into a combustion chamber, a fuel pressure (common rail pressure) Pc at a common rail 2, and a differential value thereof.

Let K be the bulk modulus of the fuel and the pressure change ΔP
Assuming that a volume change ΔV is generated when there is, the following equation is established from the definition of the bulk modulus. ΔV = (V / K) × ΔP Expression (2) Based on this expression, the fuel consumption supplied from the common rail to the injector (the fuel injection amount injected from the injection hole of the injector 1 into the combustion chamber; The sum of the dynamic leak amount leaked from the pressure control chamber of the injector 1)
At the time of fuel injection, there is no fuel supply from the high-pressure fuel pump 8 and there is virtually no change in the volume of the common rail 2. It can be considered that the volume of the fuel that changes depending on the amount of fuel flowing out of the common rail 2, that is, the supply of fuel from the common rail 2 to the injector.
Therefore, the fuel supply amount actually sent from the common rail 2 to the injector 1 can be obtained from the pressure change of the common rail 2 based on the fuel injection and the bulk modulus of the fuel at that time.

The bulk modulus K has a certain relational expression between density and sound velocity. That is, assuming that the density is ρ and the sound velocity is a, the following equation (3) holds. a ² = K / ρ Expression (3) The density ρ is generally expressed by the following expression (4) as a function of temperature. ρ = ρ ₀ (1−β (T−T ₀ )) Expression (4) Here, ρ ₀ is, for example, a representative temperature T ₀ = 20 ° (C)
Represents the density when β is a coefficient of linear expansion. β
May be a fixed value, but since it is a coefficient of volume change per 1 ° C., for example, the β correction map shown in FIG. 2 may be stored in the ROM in advance, read out according to the temperature, and used for the calculation. preferable.

The density is obtained by dividing the mass M of the fuel by the volume V. Assuming that the volume changes by ΔV (positive value) when the pressure fluctuation ΔP (positive value) acts on the fuel, the density ρ ₁ after the change is expressed by the following equation (5). . ρ ₁ = M / (V−ΔV) Expression (5) On the other hand, the bulk modulus K is given by Expression (2) from the definition, and therefore, from Expressions (2) and (5). , ΔV, equation (6) is obtained. ρ ₁ = M / V (1− (ΔP / K)) Expression (6) By substituting Expression (6) into Expression (2) and solving for K, the following Expression (7) is obtained. K = ρa ² + ΔP (7) where ρ is the density (M / V) at the reference pressure before the pressure fluctuation ΔP occurs.

Using the temperature corrected by equation (4), the bulk modulus K can be determined by equation (7). K = ρ ₀ × (1−β (T−T ₀ )) × a ² + ΔP (8) Here, the fuel temperature T can be obtained by a temperature sensor arranged on the common rail, and the pressure drop ΔP Can be determined by sampling the common rail pressure. Further, the sound speed a can be calculated from the pulsation obtained by sampling the common rail pressure. Further, the fuel consumption amount Q can be obtained by substituting K obtained by Expression (8) into K of Expression (1). Q = Vcr × ΔP / [ρ ₀ (1-β (T−T ₀ )) × a ² + ΔP] (9)

The sampling of the common rail pressure and the determination of the sound velocity of the fuel from the sampling will be described with reference to the graph shown in FIG. The horizontal axis in FIG. 1 is time (or crank angle), and indicates a certain period before the top dead center (TDC) of the piston reciprocating in each cylinder. The vertical axis indicates, in order from the top, a command pulse for supplying an exciting current for operating the solenoid valve 15 of each injector 1 from the controller 12, a fuel injection rate of fuel injected from the injector 1, and a common rail pressure ( P
c) and its differential value.

At time t ₀ , when a command pulse is sent from the controller 12, an exciting current is supplied to the solenoid valve 15 provided in the injector 1 in response thereto, and the pressure of the working fluid in the pressure control chamber 40 in the injector 1 is reduced. When released, the needle valve 24 is lifted, and fuel is injected from an injection hole 25 formed at the tip of the injector 1. Fuel injection is started with a slight delay from time t _0, in accordance with the pulse width Pw of the command pulse, fuel is injected over a predetermined fuel injection period. The common rail pressure Pc starts to decrease with a further time delay after the fuel injection is started, and gradually decreases as the fuel injection proceeds.

A closer look at the change in the common rail pressure Pc reveals that the common rail pressure Pc shows a pulsation as it descends with fuel injection. When the high-pressure fuel is introduced into the injector 1 from the common rail 2, a pressure reflected wave is generated according to the shape of the fuel passage. The pressure reflected wave returns to the common rail 2, and the reflected wave reciprocates on the propagation path between the common rail 2 and the injector 1. The pressure sensor 13 detects the reflected pressure wave at this time as a pulsation of the common rail pressure Pc. The common rail pressure Pc by the pressure sensor 13 is sequentially detected by sampling at a constant cycle. The fluctuation of the common rail pressure Pc at each sampling time is smoothed by an appropriate averaging means, and when a differential value is obtained based on the smoothed common rail pressure Pc, the zero-cross timing from negative to positive (or If there is no zero-cross point, the zero-cross point of the approximate straight line) is obtained as the time at which the common rail pressure Pc shows the minimum value. By calculating the time between adjacent zero-cross times of the common rail pressure (time interval at which a minimum value is obtained), the pulsation period Δt can be calculated. It is needless to say that, instead of the time when the minimum value is taken, the time when the maximum value is taken may be detected.

The common rail 2 (specifically, the pressure sensor 1
Since the propagation distance L between 3) and each injector 1 can be measured and known in advance, the pulsation cycle (time interval between local minimum values) Δt of the common rail pressure Pc obtained by the above method is used. , The pressure propagation velocity of the fuel (that is, the sound velocity a) can be calculated by the following equation (10). a = 2L / Δt Expression (10) By using the fuel pressure propagation velocity (sound speed a) obtained by Expression (10) in Expressions (8) and (9), if the pressure drop amount ΔP is known, The bulk modulus K and the fuel consumption Q can be calculated.

[0031]

According to the common rail fuel injection system of the present invention, the fuel density and the pressure drop amount as the difference between the fuel pressure of the common rail before and after the injection of the fuel from the injector are increased. The bulk elastic modulus of the fuel is calculated in consideration of the pressure propagation velocity of the fuel, and the fuel supply amount supplied from the common rail to the injector is calculated based on the bulk elastic modulus. The properties of the fuel, that is, the bulk modulus that shows different values depending on the gas oil specifications (JIS No. 2 gas oil and No. 3 gas oil are sold depending on the season and region) are the pressure propagation that reflects the fuel properties. Since the fuel supply amount is obtained by the calculation using the speed, the fuel supply amount can be accurately obtained according to the property of the fuel. Therefore, it is not necessary to store the bulk modulus as a map in the ROM of the controller in advance, and a pressure sensor disposed on a common rail conventionally used for fuel injection control can be used as a sensor. It is possible to suppress an increase in cost as an injection device. In addition, since the fluctuation of the bulk modulus due to the temperature is reflected by the temperature change of the density, the temperature of the bulk modulus can be corrected by calculating using the fuel density corrected by the detected fuel temperature. . The actual fuel injection amount obtained by reducing the dynamic leak amount leaking from the pressure control chamber in the fuel supply amount is actually injected from the injector. According to the present invention, the actual fuel injection amount is accurately obtained, and accordingly, the controller can perform accurate fuel injection control so as to obtain the target fuel injection amount.

[Brief description of the drawings]

FIG. 1 is a graph showing changes in a command pulse, a fuel injection rate, a common rail pressure, and a differential value thereof before a top dead center.

FIG. 2 is a graph showing a temperature change of a linear expansion coefficient of a fuel density.

FIG. 3 is a schematic diagram showing the whole of a conventional common rail fuel injection device.

FIG. 4 is a sectional view showing an example of an injector used in the common rail fuel injection device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injector 2 Common rail 3 Fuel supply path 8 High pressure fuel pump 12 Controller 13 Pressure sensor 15 Solenoid valve ρ Fuel density Pc Common rail pressure ΔP Common rail pressure drop a Sound velocity (pressure propagation velocity) of fuel K Bulk modulus Q Fuel supply T Fuel temperature Δt Pulsation cycle L Pressure propagation distance Vc Common rail volume

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G084 AA01 BA13 CA04 CA06 DA06 EB12 EC03 FA10 FA11 FA33 FA39 3G301 HA02 JA11 JA18 KA11 LB11 LB13 LC01 MA13 MA18 NA01 NA05 NA09 NC02 ND02 NE03 NE08 PA07Z PB01Z PB03Z

Claims (6)

[Claims] 1. A fuel cell system comprising: a common rail for storing fuel, an injector for injecting fuel supplied from the common rail into a combustion chamber, and a controller for controlling fuel injection from the injector according to an operation state of an engine. The controller calculates a fuel density, a pressure drop amount as a difference between a fuel pressure of the common rail before and after the fuel is injected from the injector, and a fuel pressure propagation speed that changes according to a property of the fuel. A common rail fuel injection device comprising calculating a fuel supply amount supplied from the common rail to the injector based on a determined bulk modulus of fuel. 2. The common rail fuel injection device according to claim 1, wherein the controller corrects the density of the fuel according to a temperature of the fuel. 3. The controller according to claim 1, wherein a predetermined propagation distance in which a pressure wave repeating reflection between the common rail and the injector propagates, and a cycle of fuel pressure pulsation generated in the common rail by the pressure wave. 3. The common rail fuel injection device according to claim 1, wherein the pressure propagation speed of the fuel is calculated. 4. The common rail is provided with a pressure sensor for detecting fuel pressure, and the controller obtains the pressure drop amount of the common rail fuel pressure based on a detection signal from the pressure sensor. And
4. The method according to claim 3, further comprising calculating the cycle of the fuel pressure pulsation as a time interval between successive maximum values or minimum values detected based on a differential value of a detection signal from the pressure sensor. Common rail fuel injector. 5. The controller according to claim 1, wherein the controller calculates a target fuel injection amount according to an operation state of the engine, and calculates the target fuel injection amount based on a deviation between the target fuel supply amount and the calculated fuel supply amount. The common rail type fuel injection device according to any one of claims 1 to 4, comprising controlling fuel injection from the injector so as to match the target fuel injection amount. 6. The controller according to claim 1, wherein when the volume of the common rail is Vc, the pressure drop amount of the fuel pressure of the common rail is ΔP, the density of the fuel is ρ, and the pressure propagation speed is a, The fuel supply amount Q
The common rail type fuel injection device according to any one of claims 1 to 5, comprising: Q = Vc × ΔP / (ρ × a ² + ΔP)