JP2011241731A - Fuel injection control device of engine with selective reduction catalyst device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device of an engine with a selective reduction catalyst device which can improve fuel consumption while preventing the deterioration of purifying capability.SOLUTION: The fuel injection control device includes an SCR device 4 disposed on an exhaust pipe 3 of the engine 2, an upstream-side NOx sensor 5 which detects an NOx concentration on the upstream side to the SCR device 4, a downstream-side NOx sensor 6 which detects an NOx concentration on the downstream side to the SCR device 4, a purification rate calculating unit 7 which calculates a purification rate E at the SCR device 4 based on an NOx concentration detected by the upstream-side NOx sensor 5 and an NOx concentration detected by the downstream-side NOx sensor 6, and a fuel injection time control unit 8 which controls fuel injection time of the engine 2 to a standard fuel injection time when the purification rate E at the SCR device 4 is fine while controlling the fuel injection time of the engine 2 to a fuel injection time at which exhaust gas is more clear than exhaust gas at the standard fuel injection time when the purification rate E at the SCR device 4 is deteriorated.

Description

  The present invention relates to a fuel injection control device for an engine with a selective reduction catalyst device that controls fuel injection timing in an engine having an exhaust pipe provided with a selective reduction catalyst device, and to improve fuel efficiency while preventing deterioration in purification performance. The present invention relates to a fuel injection control device for an engine with a selective reduction catalyst device.

  In the engine control of a diesel engine, the fuel injection timing is obtained by referring to an injection timing map with engine parameters such as accelerator opening and engine speed.

  Conventionally, the injection timing map has been set with the highest priority on reducing the amount of pollutants such as NOx contained in the exhaust gas. If the injection timing is determined with reference to this injection timing map, clean exhaust gas is produced. Optimized to be discharged. Also, the cooling water temperature indicating the engine temperature, the atmospheric temperature that is the temperature of the outside air to be sucked in, and the atmospheric pressure that differs between the flatland and the highland affect the exhaust gas components, so the injection timing is also corrected with these factors. It has been broken.

  On the other hand, in recent years, an SCR (Selective Catalytic Reduction) device for purifying NOx in exhaust gas is being developed at the rear stage of the engine. In the SCR device, urea water injected upstream becomes ammonia by the heat of the exhaust gas, and ammonia and NOx are neutralized by the action of the selective reduction catalyst. In the urea water injection control (SCR control), the NOx amount in the exhaust gas is estimated from the engine parameters and the exhaust gas temperature, and the urea water injection amount is determined. NOx sensors are installed upstream and downstream of the SCR device, and NOx concentrations upstream and downstream of the SCR device are fed back to the SCR control.

Japanese Patent Laid-Open No. 9-125938 JP 2000-303826 A

  By the way, it was found that the SCR control and the engine control are not sufficiently linked in order to move the SCR device from the research and development stage to the practical stage where it is actually mounted on the vehicle.

  In other words, at present, since SCR control and engine control are independent of each other, for example, even when the performance of NOx purification in the SCR device deteriorates for some reason, NOx emission is suppressed on the engine control side. It is not designed to perform control.

  As shown in FIG. 4, at the peak where the NOx concentration upstream of the SCR device (line 41) increases, if the purification performance of the SCR device is good, the NOx concentration downstream of the SCR device (line 42). Does not increase. However, if the purification performance of the SCR device is deteriorated, the NOx concentration (line 43) downstream of the SCR device increases with an increase in the NOx concentration upstream.

  Conversely, when the purification performance of the SCR device is good, NOx emission may be suppressed by increasing the EGR rate even in engine control. However, at this time, the engine control may give priority to cleaning the exhaust gas and sacrifice the fuel consumption. For this reason, improvement in fuel consumption is hindered.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fuel injection control device for an engine with a selective reduction catalyst device that can improve the fuel efficiency while solving the above-described problems and preventing deterioration in purification performance.

  In order to achieve the above object, the present invention provides an SCR (Selective Reduction Catalyst) device installed in an exhaust pipe of an engine, an upstream NOx sensor for detecting NOx concentration upstream of the SCR device, and an SCR device. A downstream NOx sensor that detects the NOx concentration on the downstream side, a purification that calculates the purification rate in the SCR device based on the NOx concentration detected by the upstream NOx sensor and the NOx concentration detected by the downstream NOx sensor When the purification rate in the rate calculation unit and the SCR device is good, the fuel injection timing of the engine is controlled to a standard fuel injection timing, and when the purification rate in the SCR device is deteriorated, the fuel injection timing of the engine is set to the standard fuel injection timing. And a fuel injection timing control unit that controls the fuel injection timing so that the exhaust gas becomes cleaner than the fuel injection timing.

  The fuel injection timing control unit calculates a purification rate deterioration amount calculation unit that calculates a purification rate deterioration amount as a purification rate deterioration amount by calculating a difference of the purification rate calculated by the purification rate calculation unit with respect to a theoretical purification rate in the SCR device set in advance. There may be provided an injection timing determining section for determining the fuel injection timing between the standard fuel injection timing and the fuel injection timing at which the exhaust gas becomes the cleanest according to the rate deterioration.

  The injection timing determination unit includes an injection timing map when the standard fuel injection timing is referred to by an engine parameter when the purification rate is good, and a purification rate deterioration when the fuel injection timing at which the exhaust gas is most purified is referred to by an engine parameter. An injection timing map, an interpolation coefficient map in which an interpolation coefficient is set in advance for each purification rate deterioration, a standard fuel injection timing read with reference to the injection timing map when the purification rate is good, and the injection timing when the purification rate deteriorates The fuel injection timing at which the exhaust gas read out with reference to the map is the cleanest is interpolated with the interpolation coefficient read out by referring to the interpolation coefficient map by the amount of deterioration of the purification rate, and the fuel injection timing as a determination result is calculated. An interpolation calculation unit to be obtained may be provided.

  The present invention exhibits the following excellent effects.

  (1) The fuel efficiency can be improved while preventing the purification performance from deteriorating.

It is a block block diagram of the fuel-injection control apparatus of the engine with a selective reduction catalyst apparatus which shows one Embodiment of this invention. It is a block diagram of the exhaust system of the vehicle carrying the fuel-injection control apparatus of FIG. It is a graph which shows the NOx density | concentration of the upstream of the SCR apparatus in this invention, and downstream. It is a graph which shows the NOx density | concentration of the upstream and downstream of the conventional SCR apparatus.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIGS. 1 and 2, a fuel injection control device (hereinafter referred to as a fuel injection control device) 1 for an engine with a selective catalytic reduction device according to the present invention is an SCR device installed in an exhaust pipe 3 of an engine 2. 4, an upstream NOx sensor 5 that detects the NOx concentration upstream of the SCR device 4, a downstream NOx sensor 6 that detects the NOx concentration downstream of the SCR device 4, and an upstream NOx sensor 5. Based on the NOx concentration and the NOx concentration detected by the downstream NOx sensor 6, the purification rate calculation unit 7 that calculates the purification rate E in the SCR device 4, and the fuel injection of the engine 2 when the purification rate E in the SCR device 4 is good The timing is controlled to the standard fuel injection timing, and when the purification rate E in the SCR device 4 deteriorates, the fuel injection timing of the engine 2 is cleaner than the standard fuel injection timing. Is obtained by a fuel injection timing control section 8 for controlling the fuel injection timing becomes.

  The fuel injection timing control unit 8 calculates a purification rate deterioration component calculation unit 9 that calculates a difference between the purification rate E calculated by the purification rate calculation unit 7 with respect to a theoretical purification rate in the SCR device 4 set in advance as a purification rate deterioration component Δ. And an injection timing determination unit 10 that determines the fuel injection timing τ between the standard fuel injection timing and the fuel injection timing at which the exhaust gas is most clean in accordance with the purification rate deterioration Δ.

  The injection timing determining unit 10 includes a purification rate good injection timing map 11 in which the standard fuel injection timing is referred to by an engine parameter, and a purification rate deterioration in which the fuel injection timing at which the exhaust gas is most clean is referred to by an engine parameter. Standard fuel injection timing and purification rate read with reference to the injection timing map 12, the interpolation coefficient map 13 in which the interpolation coefficient K is set in advance for each purification rate deterioration Δ, and the purification rate favorable injection timing map 11 The fuel injection timing at which the exhaust gas read with reference to the deterioration injection timing map 12 is the cleanest is interpolated by the interpolation coefficient K read with reference to the interpolation coefficient map 13 by the purification rate deterioration Δ, and determined. And an interpolation calculation unit 14 for obtaining the resulting fuel injection timing τ.

  The purification rate calculation unit 7 subtracts the NOx concentration detected by the downstream NOx sensor 6 from the NOx concentration detected by the upstream NOx sensor 5 and divides by the NOx concentration detected by the upstream NOx sensor 5, for example. The purification rate E is obtained. In this case, when the NOx purification performance in the SCR device 4 is good, the purification rate E is closest to 1, which is said to be good. When the NOx purification performance in the SCR device 4 is poor, the purification rate E approaches 0, which is said to be that the purification rate has deteriorated.

  The purification rate calculation unit 7 and the fuel injection timing control unit 8 are provided as software in a program digital circuit called an ECM (Engine Control Module) or ECU (Engine Control Unit).

  The purification rate deterioration calculation unit 9 subtracts the purification rate E calculated by the purification rate calculation unit 7 from a preset theoretical purification rate to obtain a purification rate deterioration Δ. If the purification rate is good, the purification rate deterioration Δ is the smallest, and if the purification rate is deteriorated, the purification rate deterioration Δ increases. The theoretical purification rate is set in the theoretical purification rate map 15 and is referred to by an engine parameter or a parameter used for SCR control.

  The injection timing determination unit 10 basically refers to the injection timing map with engine parameters such as the accelerator opening and the engine speed, as in the prior art. In the present invention, the injection timing determination unit 10 An intermediate value is obtained by interpolating both fuel injection timings with reference to both the purification rate deterioration injection timing maps 12. More specifically, the interpolation calculation unit 14 reads the interpolation coefficient K with reference to the interpolation coefficient map 13 by the purification rate deterioration Δ, and performs interpolation calculation using the interpolation coefficient K. The interpolation coefficient K takes such a value that a result close to the fuel injection timing read from the injection timing map 11 when the purification rate is good is small when the purification rate deterioration Δ is small. It is a coefficient that takes a value that gives a result close to the fuel injection timing read from the rate deterioration time injection timing map 12. As the specific value of the interpolation coefficient K and the interpolation calculation formula, it is preferable to adopt an optimum one by experiment.

  As shown in FIG. 2, a DPF (Diesel Particulate Filter) 16 is installed in the exhaust pipe 3 of the engine 2, a urea water injection device 17 is installed downstream of the DPF 16, and an SCR is installed downstream of the urea water injection device 17. A device 4 is installed. The engine 2 is, for example, the engine 2 provided with a pressure accumulation type injection device. The urea water injection device 17 is controlled by an SCR control device (not shown) and injects urea water into the exhaust pipe 3. The SCR device 4 includes a selective reduction catalyst 18 that neutralizes ammonia generated from urea water and NOx in the exhaust gas. The upstream NOx sensor 5 is provided at the inlet of the SCR device 4, and the downstream NOx sensor 6 is provided at the outlet of the SCR device 4. Since the upstream NOx sensor 5 and the downstream NOx sensor 6 are made of known NOx sensors, description thereof is omitted.

  Next, the operation of the fuel injection control device 1 will be described.

  The injection timing determination unit 10 determines the midpoint between the fuel injection timing obtained from the injection timing map 11 when the purification rate is good and the fuel injection timing obtained from the injection timing map 12 when the purification rate is deteriorated at the start of the fuel injection timing control. The fuel injection timing is determined unconditionally (default). Engine control is performed at this fuel injection timing, while the SCR control device starts SCR control.

  The NOx concentrations output from the upstream NOx sensor 5 and the downstream NOx sensor 6 are always read into the purification rate calculation unit 7 (for example, at a sampling interval shorter than one combustion cycle). Is calculated. In the purification rate deterioration calculation unit 9, the difference between the purification rate E calculated by the purification rate calculation unit 7 with respect to the theoretical purification rate in the SCR device 4 set in advance is calculated as the purification rate deterioration Δ. If the NOx purification rate in the SCR device 4 is good, the purification rate deterioration Δ is the smallest value. If the purification rate has deteriorated, the purification rate deterioration Δ increases in accordance with the degree of deterioration.

  The interpolation calculation unit 14 reads the interpolation coefficient K with reference to the interpolation coefficient map 13 by the purification rate deterioration Δ. At the same time, the interpolation calculation unit 14 reads the fuel injection timing by referring to the injection timing map 11 when the purification rate is good and the injection timing map 12 when the purification rate is deteriorated, respectively, with engine parameters such as the accelerator opening and the engine speed. The standard fuel injection timing is read from the injection timing map 11 when the purification rate is good. What is read from the injection timing map 12 when the purification rate deteriorates is the fuel injection timing at which the exhaust gas becomes the cleanest. Next, the interpolation calculation unit 14 interpolates the two fuel injection timings with the interpolation coefficient K to obtain the fuel injection timing τ that is the determination result.

  Thus, when the purification rate is relatively good, the fuel injection timing τ is close to the standard fuel injection timing, and when the purification rate deteriorates, the fuel injection timing τ approaches the fuel injection timing at which the exhaust gas is most clean. To go. The fuel injection timing τ may be determined, for example, every one combustion cycle.

  Note that the fuel injection timing based on the injection timing map 11 when the purification rate is good and the fuel injection timing based on the injection timing map 12 when the purification rate is deteriorated with the same engine parameters are different for each engine model as in the conventional injection timing map. An experiment for measuring the NOx concentration while changing it may be performed, and an optimum value obtained from the experiment result may be set.

  Since such fuel injection timing control is performed, when the NOx purification rate in the SCR device 4 is good, the engine performs fuel injection at the standard fuel injection timing, and as the NOx purification rate in the SCR device 4 deteriorates. The engine changes to fuel injection at the fuel injection timing when the exhaust becomes clean. Therefore, finally, NOx discharged to the atmosphere is reduced.

  Here, the same conditions as in FIG. 4, that is, other engine parameters except the fuel injection timing were the same, and changes in the NOx concentration upstream and downstream of the SCR device 4 in the present invention were observed.

  As shown in FIG. 3, if the purification performance of the SCR device 4 is good at the peak where the NOx concentration (line 31) upstream of the SCR device 4 is increasing, the NOx concentration (downstream of the SCR device 4 ( Line 32) does not increase. When the purification performance of the SCR device 4 deteriorates, the increase in the NOx concentration downstream (line 33) is suppressed at the peak of the increase in NOx concentration upstream as compared with the conventional case (FIG. 4).

  From this experimental result, when the purification rate in the SCR device 4 is deteriorated, the fuel injection timing of the engine 2 is controlled to the fuel injection timing at which the exhaust gas becomes cleaner compared to the standard fuel injection timing, thereby being discharged into the atmosphere. NOx was demonstrated to be reduced.

  In the present embodiment, the engine 2 is provided with a pressure accumulating injection device. However, even in the case where the engine 2 is provided with a distribution-type injection device, the engine 2 is electronically controlled by changing the injection timing by electronically controlling a timer that gives an advance angle to the pump. The invention can be applied.

  As described above, according to the present invention, when the purification rate in the SCR device 4 is good, the fuel injection timing of the engine 2 is controlled to the standard fuel injection timing, and when the purification rate in the SCR device 4 deteriorates, Since the fuel injection timing is controlled to the fuel injection timing at which the exhaust gas is cleaner than the standard fuel injection timing, the final purification performance is not only when the purification rate in the SCR device 4 is good but also when it deteriorates. Deterioration can be prevented. Therefore, even in the configuration in which the indicator lamp is turned on when the purification performance is deteriorated, it is possible to avoid lighting.

  The standard fuel injection timing used in the present invention is an engine condition with better fuel consumption than the fuel injection timing when the exhaust gas is cleaner than that. Therefore, according to the present invention, when the purification rate in the SCR device 4 is good or the deterioration is not so serious, fuel injection is performed at the standard fuel injection timing or a fuel injection timing close thereto. Fuel consumption can be improved.

  According to the present invention, the deterioration of the purification rate is not represented by the magnitude of the purification rate E calculated from the NOx concentration difference, but is represented by the purification rate deterioration Δ that is the difference of the calculated purification rate E with respect to the theoretical purification rate. Since it did in this way, the deterioration of the performance of the SCR apparatus 4 can be evaluated appropriately. That is, according to the logic that evaluates that the performance of the SCR device 4 has deteriorated when the purification rate E is low, the purification rate E is originally low (that is, the theoretical purification rate is low) depending on various conditions such as the exhaust gas temperature. However, if this is evaluated by the purification rate deterioration Δ, the case where the purification rate E deviates from the theoretical purification rate is regarded as the deterioration of the performance of the SCR device 4. Can be evaluated.

  According to the present invention, the injection timing map 11 at the time of good purification rate in which the standard fuel injection timing is referred to by the engine parameter and the injection timing map at the time of deterioration of the purification rate in which the fuel injection timing at which the exhaust gas is most clean is referred to by the engine parameter. Since the two fuel injection timing maps 11 and 12 are used to calculate the fuel injection timing τ by performing the two fuel injection timing interpolation operations read out from these maps, all the two fuel injection timing maps 11 and 12 are used. The fuel injection timing τ can be determined corresponding to the purification rate deterioration Δ.

DESCRIPTION OF SYMBOLS 1 Fuel injection control apparatus 2 Engine 3 Exhaust pipe 4 SCR apparatus 5 Upstream side NOx sensor 6 Downstream side NOx sensor 7 Purification rate calculation part 8 Fuel injection timing control part 9 Purification rate deterioration part calculation part 10 Injection timing determination part 11 Good purification rate Injection timing map 12 Purification rate deterioration injection timing map 13 Interpolation coefficient map 14 Interpolation calculation unit 15 Theoretical purification rate map

Claims (3)

An SCR (Selective Reduction Catalyst) device installed in the exhaust pipe of the engine;
An upstream NOx sensor for detecting the NOx concentration upstream of the SCR device;
A downstream NOx sensor for detecting the NOx concentration downstream of the SCR device;
A purification rate calculation unit for calculating a purification rate in the SCR device based on the NOx concentration detected by the upstream NOx sensor and the NOx concentration detected by the downstream NOx sensor;
When the purification rate in the SCR device is good, the fuel injection timing of the engine is controlled to a standard fuel injection timing, and when the purification rate in the SCR device is deteriorated, the fuel injection timing of the engine is set to the standard fuel injection timing. A fuel injection control device for an engine with a selective reduction catalyst device, comprising: a fuel injection timing control unit that controls the fuel injection timing so that the exhaust gas becomes cleaner than that. The fuel injection timing control unit
A purification rate deterioration calculation unit that calculates a difference between the purification rates calculated by the purification rate calculation unit with respect to a theoretical purification rate in the SCR device set in advance as a purification rate deterioration;
The fuel injection timing determination unit according to claim 1, further comprising: an injection timing determination unit that determines a fuel injection timing between the standard fuel injection timing and a fuel injection timing at which exhaust gas is most clean in accordance with the deterioration of the purification rate. A fuel injection control device for an engine with a selective reduction catalyst device. The injection timing determination unit
An injection timing map when the purification rate is good in which the standard fuel injection timing is referred to by an engine parameter;
A fuel injection timing map at which the exhaust gas becomes the cleanest, and a purification rate deterioration injection timing map in which engine parameters are referred to,
An interpolation coefficient map in which an interpolation coefficient is set for each purification rate deterioration, and
A standard fuel injection timing read with reference to the injection timing map when the purification rate is good and a fuel injection timing when the exhaust gas read with reference to the injection timing map when the purification rate deterioration is the cleanest are the interpolation coefficient map. The engine with a selective catalytic reduction catalyst device according to claim 2, further comprising: an interpolation calculation unit that performs an interpolation calculation using an interpolation coefficient that is read with reference to the deterioration rate of the purification rate and obtains a fuel injection timing that is a determination result. Fuel injection control device.

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