DE102015115512B4 - Control device for a diesel engine - Google Patents

Abstract

A control device for performing combustion control of a fuel in a diesel engine (10), the control device comprising:means (33) for detecting the kinematic viscosity of the fuel; andmeans (40) for switching the combustion control of the fuel from a predetermined control to a soot suppression control for suppressing the amount of soot discharged upon combustion of the fuel in the diesel engine when the kinematic viscosity of the fuel detected by the kinematic viscosity detecting means viscosity is detected is lower than a first threshold or higher than a second threshold, the second threshold being higher than the first threshold, the predetermined control being predetermined on the assumption that the fuel has predetermined properties.

Description

background

1. Technical field

The present invention relates to a control device that controls combustion of a fuel in a diesel engine.

2. Description of the Prior Art

Fuels for diesel engines that are commercially available in the market vary greatly in properties from each other. Therefore, the combustion states of the fuels vary greatly according to the properties of the fuels; thus, exhaust emission may deteriorate and misfire may occur.

In order to solve the above problem, Japanese Patent Publication No. discloses JP 2006 - 226 188 A discloses a device that detects the cetane number of a fuel based on the combustion state of the fuel injected by a pilot injection.

However, even if the cetane number of the fuel is detected and the combustion of the fuel is controlled only according to the cetane number of the fuel, it may still be impossible to prevent the exhaust emission from being deteriorated. For example, the inventors of the present application have found that in the case where the number of aromatic components and side chain components contained in the fuel is relatively high, it is difficult for the fuel to be burned, resulting in a Increase in the amount of soot discharged results.

The DE 10 2008 025 350 A1 discloses a method for determining the deviation of the quality of a fuel from a reference quality and the resulting change in exhaust gas emissions by evaluating pressure waves in the fuel. It is provided that the internal combustion engine is or will be equipped with discontinuous fuel delivery and/or fuel extraction and that during operation the pressure fluctuations that form in the fuel system are detected with the aid of a sensor and, by analyzing this pressure curve in an electronic control unit, the deviation from a Fuel reference quality and/or the type of fuel are determined and from this deviations of the raw emissions from the raw emissions when using the reference fuel and/or influences on the behavior of an aftertreatment system downstream of the internal combustion engine, which has changed compared to operation with reference fuel, are determined and/or when a deviation from the Reference fuel quality, the service intervals and/or the engine oil change intervals are changed.

The DE 10 2004 042 010 A1 discloses a method for determining the ignition delay after a fuel injection signal in a self-igniting internal combustion engine by evaluating an ion current signal. To compensate for different ignition delays with different fuels, the fuel injection signal is shifted in time or angle according to the time difference or angle difference between the respectively detected ion current signal and a definable standard ion current signal or a time or angle signal corresponding thereto. As part of a regulation, this automatically adapts to fuels of different quality and composition.

The JP 2009 - 127 529 A discloses an apparatus for controlling the fuel injection amount, wherein a kinematic viscosity sensor detects the kinematic viscosity of fuel, and an EUC controls the fuel injection amount of a fuel injector to maintain a target air-fuel ratio, and the target air-fuel ratio based on of the kinematic viscosity of the fuel detected by the kinematic viscosity sensor when the engine operating state is in a transient state.

According to the DE 10 2011 079 064 A1 provide methods and systems for controlling exhaust emissions by adjusting fuel injection into an engine cylinder from multiple fuel injectors based on the fuel type of the injected fuel and further based on the soot load of the engine. Soot produced by direct fuel injection is reduced by reducing an amount of direct injection into a cylinder as engine soot load increases.

The DE 10 2011 083 909 A1 describes a regeneration method for a soot particle filter permeated with an exhaust gas flow, in which a combustion strategy to be used for regenerating the soot particle filter is selected as a function of a determined fuel type and/or proportion of biofuel, the selection of the combustion strategy being carried out by specifying a characteristic combustion temperature for the determined fuel type and/or proportion of biofuel.

short version

The present invention was made in view of the above-mentioned problems. It is therefore a primary object of the present invention to provide a control device for a diesel engine which can prevent exhaust emission from being deteriorated by controlling combustion of a fuel in the engine in accordance with properties of the fuel.

According to exemplary embodiments, a control device for performing combustion control of a fuel in a diesel engine is provided. The control device includes: means for detecting the kinematic viscosity of the fuel; and means for changing over the combustion control of the fuel from a predetermined control to a soot suppression control for suppressing the amount of soot discharged upon combustion of the fuel in the diesel engine when the kinematic viscosity of the fuel determined by the Kinematic viscosity detector is detected is lower than a first threshold or higher than a second threshold. The second threshold is higher than the first threshold. The predetermined control is predetermined on the assumption that the fuel has predetermined properties.

With the above configuration, it is possible to switch the combustion control of the fuel from the predetermined control to the soot suppression control, thereby preventing the exhaust emission from being deteriorated when the kinematic viscosity of the fuel, detected by the kinematic viscosity detecting means is lower than the first threshold or higher than the second threshold, and thus the fuel is difficult to be burned.

In an exemplary embodiment, the first threshold is less than the kinematic viscosity of a reference fuel having the predetermined properties. The first threshold is set to such a kinematic viscosity that the amount of soot emitted when the fuel is burned in the diesel engine is greater than a predetermined amount. In addition, the second threshold is set to such a kinematic viscosity that is higher than the kinematic viscosity of the reference fuel that the amount of soot discharged when the fuel is burned in the diesel engine is larger than the predetermined amount.

In a further exemplary embodiment, the control device further comprises: a device for detecting the cetane number of the fuel; means for detecting fuel density; means for estimating the kinematic viscosity of the fuel based on the cetane number of the fuel detected by the cetane number detecting means and the density of the fuel detected by the density detecting means; and means for setting the second threshold in a manner to be higher by a predetermined value than the kinematic viscosity of the fuel estimated by the kinematic viscosity estimating means.

In still another exemplary embodiment, the controller further includes means for setting the first threshold to be lower by a predetermined value than the kinematic viscosity of the fuel estimated by the kinematic viscosity estimating means.

The predetermined control is preferably predetermined on the assumption that the fuel has the predetermined properties to make the combustion state of the fuel in the diesel engine optimal.

Preferably, when the kinematic viscosity of the fuel detected by the kinematic viscosity detecting means is lower than the first threshold, in addition to the soot suppressing control, the changing means further performs misfire suppressing control for suppressing the occurrence of misfire in the diesel engine.

The misfire suppression control may include control for increasing the injection amount of fuel in a pilot injection.

The misfire suppression control may also include control for retarding the timing of a pilot injection in a compression stroke of the diesel engine.

The soot suppression control may include control for increasing the amount of oxygen used for combustion of the fuel in the diesel engine.

The soot suppression control can also control a fuel injector include to the extent that this carries out a post-injection after a main injection of the fuel.

character list

The present invention will be more fully understood from the detailed description given below and the accompanying drawings of exemplary embodiments, which, however, should not be construed as limiting the invention to the specific embodiments, but are presented for purposes of explanation and understanding only.

• 1 eine schematische Ansicht, welche eine Dieselmaschine und deren periphere Konfiguration darstellt;
• 2 eine Ansicht bzw. ein Kennfeld, welches die Beziehung zwischen Kraftstoffdichte, Cetanzahl und kinematischer Viskosität darstellt;
• 3 ein Flussdiagramm, welches einen Vorgang einer ECU zum Durchführen einer Verbrennungssteuerung gemäß einer ersten Ausführungsform darstellt; und
• 4 ein Flussdiagramm, welches einen Vorgang der ECU zum Durchführen einer Verbrennungssteuerung gemäß einer zweiten Ausführungsform darstellt.

In the attached figures are:

• 1 Fig. 12 is a schematic view showing a diesel engine and its peripheral configuration;
• 2 a view or a map showing the relationship between fuel density, cetane number and kinematic viscosity;
• 3 12 is a flowchart showing a process of an ECU for performing combustion control according to a first embodiment; and
• 4 14 is a flowchart showing a process of the ECU for performing combustion control according to a second embodiment.

Description of Embodiments

[First embodiment]

This embodiment presents a control device applied to a diesel engine 10 of a motor vehicle to control combustion of a fuel injected into cylinders 11a of the diesel engine 10 through fuel injectors 17 .

1 12 illustrates the diesel engine 10 and its peripheral configuration. The diesel engine 10 is, for example, an in-line four-cylinder diesel engine. For the sake of simplicity, in 1 however, only one of the four cylinders 11a of the diesel engine 10 is shown.

As in 1 is shown, the diesel engine 10 comprises a cylinder block 11, pistons 12, of which in 1 only one is shown, a cylinder head 13, an intake port 14, an exhaust port 15, intake valves 16, of which Fig 1 only one is shown, the fuel injectors 17, of which 1 only one is shown, outlet valves 18, of which in 1 only one is shown, a VVT (variable valve timing) device 21 and an EGR (exhaust gas recirculation) device 26.

In the cylinder block 11, the four cylinders 11a are formed. Further, in each of the cylinders 11a, a corresponding one of the pistons 12 is reciprocably received. In addition, the cylinder head 13 is mounted on the cylinder block 11 . Accordingly, in the diesel engine 10, four combustion chambers each defined by a corresponding one of the cylinders 11a, a corresponding one of the pistons 12, and the cylinder head 13 are formed.

The intake passage 14 is connected to the cylinder block 11 . Specifically, the intake passage 14 is connected to each of the cylinders 11a via an intake manifold and a corresponding cylinder head inner passage 14a formed in the cylinder head 13 . In operation, with the rotation of a crankshaft (not shown) of the diesel engine 10, camshafts 19A and 19B of the diesel engine 10 also rotate. Further, with rotation of the camshaft 19A, each of the intake valves 16 is actuated to open and close the corresponding cylinder head inner passage 14a close. In addition, the VVT device 21 varies the opening and closing timings of the intake valves 16 by adjusting the difference in rotational phase between the crankshaft and the camshaft 19A.

The exhaust port 15 is also connected to the cylinder block 11 . Specifically, the exhaust port 15 is connected to each of the cylinders 11a via an exhaust manifold and a corresponding cylinder head internal port 15a formed in the cylinder head 13 . In operation, with rotation of the camshaft 19B, each of the exhaust valves 18 is actuated to open and close the corresponding cylinder head internal passage 15a.

The fuel is pressurized by a fuel pump (not shown) and supplied to a common rail 20 . The common rail (or accumulator) 20 accumulates the fuel therein at a high pressure. Each of the fuel injectors 17 injects the fuel received in the common rail 20 into a corresponding one of the cylinders 11a.

The EGR device 26 includes an EGR passage 27 and an EGR valve 28. The EGR passage 27 connects the outlet passage 15 with the inlet passage 14. The EGR valve 28 is arranged in the EGR passage 27 to Opening and closing passage 27 . In operation, according to the opening degree of the EGR valve 28, a part of the flow in the exhaust passage 15 flowing exhaust gas is returned to (or introduced into) the intake passage 14 .

In an intake stroke of the diesel engine 10, air is drawn into the cylinders 11a via the intake passage 14. Then, in a compression stroke of the diesel engine 10, the air in the cylinders 11a is compressed by the respective pistons 12. Further, when the respective pistons 12 have moved toward the vicinity of the top dead centers of the cylinders 11a, the fuel is injected through the respective fuel injectors 17 into the cylinders 11a. Then, in a combustion stroke (or power stroke) of the diesel engine 10, the fuel is auto-ignited and burned in the cylinders 11a. Thereafter, in an exhaust stroke of the diesel engine 10, the exhaust gas is discharged from the cylinders 11a by the respective pistons 12 via the exhaust passage 15. In addition, part of the exhaust gas flowing in the exhaust passage 15 is recirculated to the intake passage 14 by the EGR device 26 .

In the diesel engine 10, in-cylinder pressure sensors 31 and a fuel density sensor 32 are provided. Each of the in-cylinder pressure sensors 31 is configured to sense the pressure in a corresponding one of the cylinders 11a. The fuel density sensor 32 is configured in such a way that it records or detects the density of the fuel fed to the fuel injectors 17 . The fuel density sensor 32 is configured in particular in such a way that it records or detects the density of the fuel, for example using a natural vibration phase measurement method.

Furthermore, in a fuel tank (not shown) of the diesel engine 10, a kinematic viscosity sensor 33 and a fuel amount sensor 34 are provided. The kinematic viscosity sensor 33 is configured to sense the kinematic viscosity of the fuel in the fuel tank. The kinematic viscosity sensor 33 can be implemented by, for example, a capillary tube viscometer or a kinematic viscometer based on a hot-wire method. The fuel amount sensor 34 is configured to sense the amount of fuel in the fuel tank.

In addition, the fuel density sensor 32 and the kinematic viscosity sensor 33 are provided with a heater, and these respectively detect the density of the fuel and the kinematic viscosity of the fuel upon heating the fuel to a predetermined temperature by the heater.

The ECU (Electronic Control Unit) 40 consists of a microcomputer of a known type, which includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and I/O (Input/Output) interfaces. The ECU 40 controls the fuel injectors 17, the VVT device 21 and the EGR device 26 based on the received values from various sensors including a crank angle sensor (not shown), a cooling water temperature sensor (not shown), an accelerator pedal position sensor ( not shown) which include in-cylinder pressure sensors 31, fuel density sensor 32, kinematic viscosity sensor 33 and fuel quantity sensor 34.

Specifically, in the present embodiment, the fuel injectors 17, the VVT device 21 and the EGR device 26 each have adjusted control states adjusted in advance on the assumption that the fuel has reference properties according to the operating state of the diesel engine 10 by one To make combustion state of the fuel in the diesel engine 10 optimal. Based on the sensed values of the various sensors, the ECU 40 controls the fuel injectors 17, the VVT device 21 and the EGR device 26 in order to bring them into their adjusted control states, respectively. In other words, the ECU 40 performs normally-adapted combustion control, which is predetermined on the assumption that the fuel has the reference properties, based on the sensed values of the various sensors. For example, the ECU 40 controls the fuel injectors 17 to perform pilot and main injections.

2 represents the relationship between fuel density, cetane number and kinematic viscosity. In addition, in 2 the solid circles represent fuel with different properties.

In general, when the straight chains of the molecules contained in the fuel become short and hence the number, the number of side chain components becomes relatively large and therefore the number of hydrogen atoms becomes relatively small, making it difficult to burn the fuel of carbon atoms becomes low. The smaller the number of carbon atoms in the molecules contained in the fuel, the lower the kinematic viscosity of the fuel. In addition, when the number of polycyclic aromatic components contained in the fuel becomes high, it becomes difficult to burn the fuel. The higher the The number of polycyclic aromatic components contained in the fuel is, the higher the kinematic viscosity of the fuel is. Therefore, the inventors of the present application paid attention to the fact that the amount of soot discharged upon combustion of the fuel increases in a low kinematic viscosity region and a high kinematic viscosity region. In the low kinematic viscosity range, the kinematic viscosity of the fuel is lower than a first threshold. In the high kinematic viscosity region, the kinematic viscosity of the fuel is higher than a second threshold that is higher than the first threshold.

How out 2 As can be seen, the relationship between fuel density and kinematic viscosity is as follows: the lower the fuel density, the lower the kinematic viscosity; and the higher the fuel density, the higher the kinematic viscosity. In addition, the relationship between cetane number and kinematic viscosity is as follows: the lower the cetane number, the lower the kinematic viscosity; and the higher the cetane number, the higher the kinematic viscosity. Therefore, the kinematic viscosity in the map decreases from 2 , wherein horizontal and vertical axes represent fuel density and cetane number, respectively, in a direction indicated by a double-headed arrow. Moreover, the low kinematic viscosity area is located at a left lower part of the map, whereas the high kinematic viscosity area is located at a right upper part of the map.

In addition, the map of 2 obtained by experimentally determining in advance the relationship between fuel density, cetane number and kinematic viscosity for fuels commercially available on the market.

In the present embodiment, when the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is greater than or equal to the first threshold and less than or equal to the second threshold, the ECU 40 performs the normally-adapted combustion control. On the other hand, when the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is lower than the first threshold or higher than the second threshold, the ECU 40 performs soot suppression control for suppressing that emitted when the fuel in the diesel engine 10 is burned amount of soot. In other words, when the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is lower than the first threshold or higher than the second threshold, the ECU 40 switches combustion control of the fuel in the diesel engine 10 based on the normally adjusted combustion control to the soot suppression control.

3 12 shows a process of the ECU 40 for performing the combustion control of the fuel in the diesel engine 10 according to the present embodiment. This process is repeated by the ECU 40 in a predetermined cycle (for example, each time the fuel injectors 17 inject the fuel into the corresponding cylinders 11a of the diesel engine 10).

At step S11, the ECU 40 determines whether a condition for detecting the properties of the fuel is satisfied.

In this step, based on the amount of fuel in the fuel tank detected by the fuel amount sensor 34, the ECU 40 first determines, in particular, whether fuel has been supplied. If the determination is "Yes" (ie, fuel has been supplied), then the ECU 40 judges that the condition for detecting the properties of the fuel is satisfied.

In addition, at this step, when the amount of fuel detected by the fuel amount sensor 34 has been increased, the ECU 40 judges only once that fuel has been supplied.

If the determination at step S11 is "No", the process proceeds directly to step S18 and skips steps S12 to S17.

On the contrary, if the determination at step S11 results in "Yes", the process proceeds to step S12.

At step S12, the ECU 40 causes the kinematic viscosity sensor 33 to pick up the kinematic viscosity of the fuel in the fuel tank.

At step S13, the ECU 40 determines whether the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is lower than the first threshold.

In addition, the first threshold is lower than the kinematic viscosity of a reference fuel that has the reference properties. The first threshold is based on such a kinematic vis kosity is set so that the amount of soot emitted when the fuel is burned in the diesel engine 10 is greater than a predetermined amount.

If the determination at step S13 returns "Yes", the process proceeds to step S14.

At step S14, the ECU 40 switches the combustion control of the fuel in the diesel engine 10 from the normally adjusted combustion control to the soot suppression control.

Specifically, as the soot suppression control, the ECU 40 increases the amount of oxygen used for combustion of the fuel in the diesel engine 10 . Specifically, the ECU 40 performs at least one of the following operations: (1) reducing the opening degree of the EGR valve 28 of the EGR device 26; (2) increasing the fuel pressure in the common rail 20 (or the pressure of the fuel injected by the fuel injectors 17) by the fuel pump; and (3) increasing the intake pressure by the VVT device 21 compared to the normally adjusted combustion control. In addition, as the soot suppression controller, the ECU 40 can control each of the fuel injectors 17 to perform post injection after main injection.

At step S<b>15 , the ECU 40 performs misfire suppression control for suppressing the occurrence of a misfire in the diesel engine 10 .

Specifically, as the misfire suppression control, the ECU 40 performs at least one of the following operations: (1) increasing the injection amount of fuel in each of the pilot injections by the fuel injectors 17; and (2) retarding the timing of each of the pilot injections in the compression stroke of the diesel engine 10 compared to the normally adjusted combustion control. Then the process ends.

In addition, the soot suppression control at step S14 and the misfire suppression control at step S15 are continued until the next switching of the combustion control to the normally adjusted combustion control.

On the other hand, if the determination at step S13 results in "No", the process proceeds to step S16.

At step S16, the ECU 40 further determines whether the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is higher than the second threshold.

In addition, the second threshold is set to such a kinematic viscosity, which is higher than the kinematic viscosity of the reference fuel, that the amount of soot discharged when the fuel is burned in the diesel engine 10 is larger than the predetermined amount.

If the determination at step S16 returns "Yes", the process proceeds to step S17.

At step S17, the ECU 40 switches or changes the combustion control of the fuel in the diesel engine 10 from the normally adjusted combustion control to the soot suppression control. Then the process ends.

In addition, the soot suppression control at step S17 is continued until the next switching of the combustion control to the normally adjusted combustion control.

On the other hand, if the determination at step S16 is "No", the process proceeds to step S18.

At step S18, the ECU 40 performs the normally-adapted combustion control.

In particular, in this step, the ECU 40 controls the fuel injectors 17, the VVT device 21 and the EGR device 26 based on the received values of the various sensors in order to bring them into their respective adjusted control states. Then this process ends.

According to the present embodiment, it is possible to obtain the following advantageous effects.

In the present embodiment, the ECU 40 switches the combustion control of the fuel in the diesel engine 10 from the normally adjusted combustion control to the soot suppression control for suppressing the amount of soot discharged when the fuel is burned in the diesel engine 10 when the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is lower than the first threshold or higher than the second threshold. The second threshold is higher than the first threshold. The normally adjusted combustion control (or predetermined combustion control) is presupposed is correct that the fuel has the reference properties (or predetermined properties).

With the above configuration, it is possible to switch or change the combustion control of the fuel from the normally adjusted combustion control to the soot suppression control, thereby preventing the exhaust emission from being deteriorated when the emission detected by the sensor 33 kinematic viscosity of the fuel recorded for the kinematic viscosity is lower than the first threshold or higher than the second threshold and therefore it is difficult for the fuel to be burned.

In the present embodiment, the first threshold is lower than the kinematic viscosity of the reference fuel having the reference properties (or predetermined properties). The first threshold is set to such a kinematic viscosity that the amount of soot discharged when the fuel is burned in the diesel engine 10 is greater than the predetermined amount.

In setting the first threshold as set out above when the kinematic viscosity of the fuel falls in the low kinematic viscosity regions (see 2 ), by switching the combustion control of the fuel from the normal adjusted combustion control to the soot suppression control, it is still possible to suppress the amount of soot emitted when the fuel is burned in the diesel engine 10.

In the present embodiment, the second threshold is set to such a kinematic viscosity higher than the kinematic viscosity of the reference fuel that the amount of soot discharged when the fuel is burned in the diesel engine 10 is larger than the predetermined amount.

When setting the second threshold as set forth above, when the kinematic viscosity of the fuel falls within the high kinematic viscosity range (see 2 ), by switching the combustion control of the fuel from the normal adjusted combustion control to the soot suppression control, it is still possible to suppress the amount of soot emitted when the fuel is burned in the diesel engine 10.

In the present embodiment, the normally adjusted combustion control (or predetermined combustion control) is predetermined on the assumption that the fuel has the reference properties (or predetermined properties) to make the combustion state of the fuel in the diesel engine 10 optimal.

Therefore, when the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is greater than or equal to the first threshold and less than or equal to the second threshold, it is possible to obtain a good combustion state of the fuel in the diesel engine by performing the normally adjusted combustion control 10 ensure.

In general, with the fuel density held constant, the lower the cetane number of the fuel, the lower the kinematic viscosity of the fuel. In addition, when the cetane number of the fuel is low, the ignition quality of the fuel is poor and therefore misfire easily occurs. In view of the above, in the present embodiment, in addition to the soot suppression control, the ECU 40 further performs the misfire suppression control for suppressing the occurrence of a misfire in the diesel engine 10 when the detected by the kinematic viscosity sensor 33 kinematic viscosity of the fuel is lower than the first threshold.

Consequently, it is possible to suppress both the amount of soot discharged when the fuel is burned in the diesel engine 10 and the occurrence of a misfire in the diesel engine 10 .

In the present embodiment, the misfire suppression control includes control for increasing the injection amount of fuel at each of the pilot injections by the fuel injectors 17.

Consequently, it is possible to stabilize the combustion of the fuel injected by each of the pilot injections, thereby suppressing the occurrence of misfire in the diesel engine 10.

In the present embodiment, the misfire suppression control also includes control for retarding the timing of each of the pilot injections in the compression stroke of the diesel engine 10.

Consequently, it is possible to perform each of the pilot injections at a time when the pressure and temperature in the corresponding combustion chamber tion chamber have been increased sufficiently. Consequently, it is possible to stabilize the combustion of the fuel injected by each of the pilot injections, thereby suppressing the occurrence of misfire in the diesel engine 10.

In the present embodiment, the soot suppression control includes control for increasing the amount of oxygen used for burning the fuel in the diesel engine 10 .

Consequently, it is possible to facilitate combustion of the fuel in the diesel engine 10, thereby suppressing the amount of smoke emitted when the fuel in the diesel engine 10 is combusted.

In the present embodiment, the soot suppression control includes controlling each of the fuel injectors 17 to perform post injection after main injection.

Consequently, it is possible to burn the soot generated by the main injection by the post injection, thereby suppressing the amount of soot discharged when the fuel in the diesel engine 10 is combusted.

[Second embodiment]

The kinematic viscosity of the fuel can also be estimated or determined by a method described below. In some cases, however, the estimated kinematic viscosity may differ from the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 . In particular, when the in the vicinity of the high kinematic viscosity region (see 2 ) recorded kinematic viscosity is higher than the estimated kinematic viscosity, the actual amount of soot exhausted may be greater than the estimated amount of soot exhausted.

In view of the above, in the present embodiment, the second threshold is set higher than the estimated kinematic viscosity of the fuel by a predetermined value.

4 12 shows a process of the ECU 40 for performing the combustion control of the fuel in the diesel engine 10 according to the present embodiment. This process is repeated by the ECU 40 in a predetermined cycle (for example, each time the fuel injectors 17 inject the fuel into the corresponding cylinders 11a of the diesel engine 10).

At step S21, the ECU 40 determines whether the condition for detecting the properties of the fuel is satisfied.

If the determination at step S21 is "No", the process proceeds directly to step S32 and skips steps S22 to S31.

On the contrary, if the determination at step S21 results in "Yes", the process proceeds to step S22.

At step S22, the ECU 40 causes the kinematic viscosity sensor 33 to pick up the kinematic viscosity of the fuel in the fuel tank.

At step S23, the ECU 40 determines whether the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is lower than the first threshold.

If the determination at step S23 results in "Yes", the process proceeds to step S24.

At step S24, the ECU 40 switches or changes the combustion control of the fuel in the diesel engine 10 from the normally adjusted combustion control to the soot suppression control.

At step S25, the ECU 40 performs the misfire suppression control for suppressing the occurrence of a misfire in the diesel engine 10. FIG. Then the process ends.

On the other hand, if the determination at step S23 results in "No", the process proceeds to step S26.

At step S26, the ECU 40 causes the fuel density sensor 32 to sense the density of fuel fed to the fuel injectors 17.

At step S27, the ECU 40 detects the cetane number of the fuel.

In addition, the cetane number of the fuel can be detected by a known method such as that disclosed in Japanese Patent Publication No JP 2006-226188 A is revealed. Specifically, according to the method disclosed in the patent document, the ECU 40 can detect the cetane number of the fuel based on the combustion state of the fuel injected by pilot injection which is performed by one of the fuel injectors 17.

At step S28, the ECU 40 estimates the kinematic viscosity of the fuel based on the detected density and the cetane number of the fuel.

Specifically, the ECU 40 estimates using the map of FIG 2 the kinematic viscosity of the fuel, which corresponds to the recorded density and the cetane number of the fuel.

At step S29, the ECU 40 sets the second threshold based on the estimated kinematic viscosity of the fuel.

Specifically, in this embodiment, the ECU 40 sets the second threshold to the sum of the estimated kinematic viscosity of the fuel and the predetermined value. That is, the second threshold is set to be higher than the estimated kinematic viscosity of the fuel by the predetermined value.

In addition, the second threshold may also be set to the product of the estimated kinematic viscosity of the fuel and a predetermined coefficient.

At step S30, the ECU 40 further determines whether the kinematic viscosity of the fuel detected by the kinematic viscosity sensor 33 is higher than the second threshold.

If the determination at step S30 returns "Yes", the process proceeds to step S31.

At step S31, the ECU 40 switches or changes the combustion control of the fuel in the diesel engine 10 from the normally adjusted combustion control to the soot suppression control. Then the process ends.

On the other hand, if the determination at step S31 is "No", the process proceeds to step S32.

At step S32, the ECU 40 performs the normally-adapted combustion control. Then the process ends.

As described above, in the present embodiment, the second threshold is set to be higher than the estimated kinematic viscosity of the fuel by the predetermined value. Consequently, when there is a possibility that the actual amount of soot discharged is larger than the estimated amount of soot discharged, by performing the soot suppression control in a timely manner, it is possible to suppress the amount of soot discharged. Moreover, since the second threshold can be set flexibly, it is possible to suppress the amount of soot discharged not only when the amount of soot discharged is particularly large but also when the amount of soot discharged is slightly larger than expected is.

In addition, according to the present embodiment, it is also possible to obtain the same advantageous effects as described in the first embodiment.

While the foregoing particular embodiments have been shown and described, it will be apparent to those skilled in the art that various modifications, changes and improvements can be made without departing from the spirit of the present invention.

For example, when those in the vicinity of the low kinematic viscosity region (see 2 ) recorded kinematic viscosity is lower than the estimated kinematic viscosity, the actual amount of soot exhausted may be greater than the estimated amount of soot exhausted. To solve this problem, the process according to the first embodiment (see 3 ) may be modified to further comprise, prior to step S13, steps of setting the first threshold to be lower than the estimated kinematic viscosity of the fuel by a predetermined value. Similarly, the process according to the second embodiment (see 4 ) may be modified to include, prior to step S23, steps of setting the first threshold to be a predetermined value lower than the estimated kinematic viscosity of the fuel. With the above modifications, it is possible to suppress the amount of discharged soot by performing the soot suppression control in a timely manner when there is a possibility that the actual amount of discharged soot is larger than the estimated amount of discharged soot. Moreover, since the first threshold can be flexibly set, it is possible to suppress the amount of soot discharged not only when the amount of soot discharged is particularly large but also when the amount of soot discharged is slightly larger than expected can.

In addition, the process according to the first embodiment (see 3 ) may be modified so as to dispense with the misfire suppression control at step S15. Similarly, the process according to the second embodiment (see 4 ) may be modified so as to dispense with the misfire suppression control at step S25.

In the foregoing embodiments, when fuel has been supplied, the ECU 40 judges that the condition for detecting the properties of fuel is satisfied. However, the ECU 40 can judge that the condition for detecting the properties of the fuel is satisfied when the diesel engine 10 has been in operation for a predetermined period of time or when the vehicle has run a predetermined distance.

Claims (11)

A control device for performing combustion control of a fuel in a diesel engine (10), the control device comprising: means (33) for detecting the kinematic viscosity of the fuel; and means (40) for switching the combustion control of the fuel from a predetermined control to a soot suppression control for suppressing the amount of soot discharged upon combustion of the fuel in the diesel engine when the kinematic viscosity of the fuel detected by the kinematic viscosity detecting means viscosity is detected is lower than a first threshold or higher than a second threshold, the second threshold being higher than the first threshold, the predetermined control being predetermined on the assumption that the fuel has predetermined properties. control device claim 1 , wherein the first threshold is lower than the kinematic viscosity of a reference fuel having the predetermined properties and the first threshold is set to such a kinematic viscosity that the amount of soot emitted upon combustion of the fuel in the diesel engine is greater than one predetermined amount. control device claim 1 or 2 wherein the second threshold is set to such a kinematic viscosity that is higher than the kinematic viscosity of the reference fuel that the amount of soot emitted when the fuel is burned in the diesel engine is greater than the predetermined amount. control device claim 1 or 2 , further comprising: means (40, 17, 31) for detecting the cetane number of the fuel; means (32) for detecting fuel density; means (40) for estimating the kinematic viscosity of the fuel based on the cetane number of the fuel detected by the cetane number detecting means and the density of the fuel detected by the density detecting means; and means (40) for setting the second threshold in a manner to be higher by a predetermined value than the kinematic viscosity of the fuel estimated by the kinematic viscosity estimating means. control device claim 1 , further comprising: means for detecting the cetane number of the fuel; means for detecting fuel density; means for estimating the kinematic viscosity of the fuel based on the cetane number of the fuel detected by the cetane number detecting means and the density of the fuel detected by the density detecting means; and means (40) for setting the first threshold in a manner to be lower by a predetermined value than the kinematic viscosity of the fuel estimated by the kinematic viscosity estimating means. Control device according to one of Claims 1 until 5 , wherein the predetermined control is predetermined on the assumption that the fuel has the predetermined properties to make the combustion state of the fuel in the diesel engine optimal. Control device according to one of Claims 1 until 6 wherein, when the kinematic viscosity of the fuel detected by the kinematic viscosity detecting means is lower than the first threshold, the switching means further performs a misfire suppression control for suppressing occurrence of a misfire in the diesel engine in addition to the soot suppression control. control device claim 7 , wherein the misfire suppression control comprises a control for increasing the injection amount of the fuel in a pilot injection. control device claim 7 or 8th wherein the misfire suppression control includes control for retarding the timing of a pilot injection in a compression stroke of the diesel engine. Control device according to one of Claims 1 until 9 wherein the soot suppression control comprises a control for increasing the amount of oxygen used for combustion of the fuel in the diesel engine. Control device according to one of Claims 1 until 10 , wherein the soot suppression control comprises controlling a fuel injector to perform a post injection after a main injection of the fuel.

Images