DPF system for an engine generator

1. Field of the Invention

The present invention relates to an exhaust gas treatment filter for an engine generator, and in particular, to a system that removes particulate matter (PM) generated by operation of a diesel engine for a generator and accumulated in a Diesel Particulate Filter (DPF) to recover the DPF.

2. Related Art

A diesel engine generates particulate matter in addition to NOx as a result of fuel combustion in nature. To prevent the particulate matter from being emitted into the atmosphere, an increasing number of diesel engines are equipped with a DPF to collect particulate matter (PM) contained in exhaust gas. This also applies to engine-driven generators.

In an engine-driven generator equipped with a DPF, a generator G is driven by a diesel engine E, electric power is supplied to a load (not shown in the drawings) through an output terminal OUT, and exhaust gas from the diesel engine E is emitted into the atmosphere through the DPF, as shown in FIG. 5 .

However, the DPF is limited in terms of the amount of PM collected, and thus, once a certain amount of particulate matter is accumulated, the particulate matter needs to be removed by, for example, being burned by a certain method, to recover the DPF. For recovery of the DPF, the amount of the particulate matter and the temperature of the exhaust gas are measured and the engine E is controlled to burn the particulate matter.

That is, particulate matter amount measuring device PMD provided in the DPF measures the amount of the particulate matter, and temperature detecting device TD measures the exhaust gas temperature. Based on the results of measurements by the measuring device, an engine control unit ECU transmits and receives signals to and from the engine E to control the engine E. Thus, the particulate matter is burned in a timely manner to recover the DPF.

Furthermore, another method for recovering the DPF is to burn the particulate matter using an electric heater incorporated in the DPF (see Japanese Patent Laid-Open No. 2009-216075).

The recovery of the DPF as described above allows an engine generator using a diesel engine to be continuously operated. A failure to appropriately recover the DPF causes a large amount of particulate matter to be accumulated. This leads to a very disadvantageous situation that involves the shutdown of the generator and manual removal of the particulate matter in the DPF.

To recover the DPF, in other words, to burn the particulate matter, the exhaust gas needs to be hot above a certain temperature. In this case, what should be taken into account is that the installed engine generator typically has a capacity about three times as large as a rated input power for a load so as to be able to deal with, for example, starting of an electric motor when a large starting current flows rapidly.

Thus, in a steady state, the engine is operated under a light load, and the exhaust gas temperature remains low. Since the generator serves as a load on the engine, the engine is to be operated at a constant speed. Consequently, such method of increasing the speed in order to raise the exhaust gas temperature as is the case with automobiles cannot be adopted.

Therefore, the recovery of the DPF in the engine generator may involve a technique for burning the particulate matter using such a heater as illustrated in Japanese Patent Laid-Open No. 2009-216075.

However, providing a heater in order to burn the particulate matter is not always satisfactory from the viewpoint of fuel efficiency. Furthermore, a special DPF incorporating the heater is not preferable. Instead of the special DPF, a general-purpose DPF (for example, a DPF for automobiles) is desirably used, but adopting the general-purpose DPF for the engine generator is inappropriate as described above.

With the foregoing in view, it is an object of the present invention to provide a DPF system for an engine generator which prevents particulate matter from being accumulated without stopping power supply and which allows the DPF to be recovered in a fuel efficient manner.

To accomplish this object, the present invention provides:

A DPF system for an engine generator that carries out a recovery process on a filter (DPF) provided to remove particulate matter generated by combustion of fuel for an engine when an amount of the particulate matter attached to the DPF exceeds a predetermined value, the engine generator carrying out the recovery process by performing an automatic recovery operation to raise a temperature of exhaust gas from the engine to burn the particulate matter, the DPF system comprising:

a dummy load connected to the engine generator when necessary; and

control device for allowing the engine to perform an automatic recovery preparation operation in such a manner that, once the amount of the particulate matter exceeds the predetermined value, the automatic recovery operation is performed when the temperature of exhaust gas reaches an automatic recovery reference temperature, and the dummy load is connected to the generator to raise the temperature of exhaust gas when the temperature of exhaust gas does not reach the automatic recovery reference temperature.

As described above, according to the present invention, when the amount of particulate matter in the engine increases, the dummy load is connected to the generator based on the exhaust gas temperature to raise the exhaust gas temperature. Thus, the particulate matter is burned to recover the DPF. This prevents an excessive amount of particulate matter from being accumulated and furthermore allows provision of a DPF system for an engine generator which has high fuel efficiency. As a result, the engine generator can be operated without bringing about a situation in which power supply is stopped and in which the DPF is then recovered.

FIG. 1 is a block diagram showing a configuration of a DPF system for an engine generator according to the present invention;

FIG. 2 is a diagram illustrating a configuration of a DPF installed in the engine generator;

FIG. 3 is a flowchart showing a basic control operation for recovery of the DPF in the engine generator comprising FIGS. 3A and B;

FIG. 4 is a flowchart showing a DPF recovery control operation according to an embodiment of the present invention comprising FIGS. 4A and B; and

FIG. 5 is a block diagram showing a configuration of a DPF system in a conventional engine generator.

Embodiments of the present invention will be described with reference to the accompanying drawings as follows.

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention. As shown in FIG. 1 , a generator G includes a dummy load L and a contactor MC both provided on an output side of the generator G; the contactor MC applies the dummy load L on the generator G and removes the dummy load L. The contactor MC is turned on and off to connect the dummy load L such as a resistor to the generator G when necessary. The generator G is then operated to increase power output from the engine E.

Based on results of measurements by particulate matter amount measuring device PMD and temperature measuring device TD, the contactor MC is controlled by an engine controlling additional unit G-ECU connected to an engine control unit ECU via a CAN (Controller Area Network). That is, the engine controlling additional unit G-ECU turns the contactor MC on and off in accordance with engine control performed by the engine control unit ECU to controllably apply the dummy load L on the generator G and cuts off the dummy load L.

That is, when necessary, the dummy load L is connected to the generator G to increase the power output from the engine E to raise the temperature of exhaust gas. Thus, particulate matter in a DPF is burned and removed to recover the DPF.

In this case, the engine control unit ECU is, for example, a control apparatus attached to an automobile diesel engine E. The engine controlling additional unit G-ECU is a control apparatus added in order to control the contactor MC so as to apply the dummy load L to the engine E and to cut off the dummy load in accordance with operation of the engine E.

FIG. 2 illustrates the structure of the DPF. The DPF in a broad sense consists of an oxidation catalyst DOC and a DPF main body that is the DPF in a narrow sense. The DOC and the DPF main body integrally operate to treat exhaust gas IN to generate exhaust gas OUT. Then, the particulate matter amount measuring device PMD detects the amount of particulate matter based on, for example, a difference in pressure between an input and an output of the DPF.

FIG. 3 is a flowchart showing a basic operation of DPF recovery control in the engine generator shown in FIG. 5 , that is, the operation corresponding to a prerequisite for the present invention. With reference to FIG. 3 , description will be provided which relates to a normal operation and a DPF recovery operation of an engine generator equipped with a DPF system.

Normal Operation and DPF Recovery Operation of the Engine Generator Equipped with the DPF System

First, an operator performs manual operations of starting the engine E (S 1 ), setting the engine E to rotate at a rated speed (S 2 ), and applying a load on the generator G (S 3 ). Thereby, the engine generator performs a normal operation (S 4 ).

As the engine E is operated, particulate matter is generated in exhaust gas and gradually accumulated in the DPF (S 5 ). At this time, when the exhaust gas temperature in the engine E is equal to or higher than a DPF recoverable temperature at which the DPF can be recovered, in other words, the temperature at which the particulate matter is burned (S 6 ), the particulate matter in the DPF is spontaneously burned (S 7 ). In other words, the DPF is spontaneously recovered while the engine E continues the normal operation.

On the other hand, when the exhaust gas temperature is lower than the DPF recoverable temperature, the process proceeds to step S 8 to determine whether or not the PM amount is equal to or more than an automatic recovery reference amount. When the PM amount is less than the automatic recovery reference amount, the process returns to step S 4 where the engine E continues the normal operation.

When it is determined in step S 8 that the accumulated PM amount is equal to or more than the reference amount, that is, the PM amount indicates that the DPF is to be recovered, the process proceeds to step S 9 to start automatic recovery if the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature (S 10 ).

In this case, the automatic recovery reference temperature refers to a temperature equal to a recoverable temperature minus a temperature to which the exhaust gas temperature can be raised by controlling the engine to the extent that the generator can be used in a manner equivalent to the manner during the normal operation.

In the automatic recovery operation, the engine E is controlled by the engine control unit ECU to the extent that the generator G can be used in a manner similar to the manner during the normal operation, based on the amount of particulate matter (PM amount) measured by the particulate matter amount measuring device PMD provided in the engine E and on the exhaust gas temperature measured by the temperature measuring device TD also provided in the engine E.

Then, the process proceeds to step S 11 where the engine E is controlled to burn the particulate matter in the DPF (automatic recovery). The engine control includes post injection (fuel injection during piston exhaust) intake restriction and the like. During the automatic recovery, the engine E is controlled to the extent that the generator can be used in a manner equivalent to the manner during the normal operation.

The process continues the automatic recovery until the PM amount decreases to an automatic recovery end reference amount, while checking whether or not the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature (S 11 →S 12 →S 13 →S 11 → . . . ). When, by the automatic recovery, the PM amount decreases below the automatic recovery end reference amount, the automatic recovery ends and the engine E returns to the normal operation (S 15 →S 4 ).

On the other hand, during an automatic recovery operation, the load may decrease to lower the exhaust gas temperature below the automatic recovery reference temperature. At this time, in other words, when the exhaust gas temperature falls below the automatic recovery reference temperature though the PM amount has not decreased to the automatic recovery end reference (S 13 ), the process suspends the automatic recovery (S 14 ) and proceeds to step S 16 to determine whether or not the PM amount is equal to or more than the reference amount at which manual recovery is to be carried out.

When the PM amount is less than the reference amount at which the manual recovery is to be carried out, the process returns to step S 4 where the engine E is operated in a normal manner. However, when the PM amount is equal to or more than the manual recovery reference, the process proceeds to step S 17 to issue a manual recovery request. When the manual recovery request is issued, the process proceeds to step S 18 where the operator performs determination and needed manual operations.

The manual recovery is the last DPF recovery that can be carried out by the engine control, and the manual recovery reference for the PM amount is close to a limit amount at which the DPF can be safely recovered. For the manual recovery, the power output, the rotation speed, and the like need to be adjusted and controlled up to a larger region exceeding the range of the engine control for the automatic control.

This may preclude the generator from performing a normal operation, and thus, power supply needs to be stopped. However, sudden power outage is risky, and the operator's determination and manual operations are involved in the process in order to stop power supply with the usage of the load, the progress of the operation, and the like taken into account. The recovery in this stage is referred to as the “manual recovery”, but the recovery operation itself is automatically performed by the engine control apparatus ECU.

First, in step S 18 , the operator determines whether or not to accept the manual recovery request. If the operator accepts the manual recovery request, the process is manually continued to step S 19 where the load on the generator G is cut off, with the engine E kept in an idling state. Then, the operator depresses a manual recovery button (switch) (S 20 ).

Thus, a manual recovery operation is started (S 21 ), and the engine E is controlled to burn the particulate matter (S 22 ). The control is performed until the PM amount decreases down to the manual recovery end reference amount (S 23 ). The control ends when the PM amount reaches the manual recovery end reference amount (S 24 ). The process then returns to step S 2 .

On the other hand, when the operator determines not to accept the manual recovery request or overlooks the manual recovery request, the process proceeds to step S 25 where the engine control unit ECU determines whether or not the PM amount is equal to or more than an emergency stop reference amount. Then, when the PM amount is less than the emergency stop reference amount, the process proceeds to step S 4 where the engine E is operated in a normal manner. When the PM amount has reached the emergency stop reference amount, the engine E is brought to an emergency stop (S 26 ) because the particulate matter may be subjected to abnormal combustion to cause an accident.

Automatic Recovery Operation by the DPF System According to the Present Invention

FIG. 4 is a flowchart illustrating a recovery operation of the system according to the present invention which operation is to be inserted between steps S 8 and S 17 in FIG. 3 instead of steps S 9 to S 16 with such expressions as found in activity diagrams.

The flowchart illustrates the contents of an operation by steps S 101 to S 124 , and the description below follows this order of steps.

First, in step S 8 in the flowchart in FIG. 3 , the process proceeds to step S 101 when the PM amount is equal to or more than the automatic recovery reference amount. Step S 101 determines whether or not the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature. When the exhaust gas temperature is equal to or higher than the reference temperature, the process proceeds to step S 108 to start an automatic recovery operation. When the exhaust gas temperature is lower than the reference temperature, the process proceeds to step S 102 where the dummy load L is applied on the generator.

When the dummy load L is applied on the generator, the control unit ECU for the engine E controls the engine E to increase the amount of fuel injection to maintain a constant-speed operation. As a result, the exhaust gas temperature rises, but due to a time delay in the rise of the gas temperature, the result of the operation of the control apparatus appears with the time delay. Therefore, step S 103 deals with the time delay using a timer (retention time 1).

That is, when the retention time 1 elapses, determination is made as to whether or not the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature (S 107 ). When it is determined that the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature, the process proceeds to step S 108 to start the automatic recovery operation in step S 109 and the subsequent steps.

On the other hand, when the exhaust gas temperature is lower than the automatic recovery reference temperature, the process proceeds to step S 124 where the dummy load L is cut off, and in step S 16 , determination is made as to whether or not the PM amount is equal to or higher than the manual recovery reference amount. When the PM amount is less than the manual recovery reference amount, the process returns to step S 4 where the engine E is operated in a normal manner. When the PM amount is equal to or more than the manual recovery reference amount, the process proceeds to step S 17 to issue a manual recovery request.

The description of the operation returns to step S 103 . When the load increases rapidly during the set duration for the timer in step 103 (S 104 a ), the process immediately proceeds to step S 105 where the dummy load L is cut off. The process then returns to step S 101 . In this case, the dummy load L is cut off in response to the rapid increase in load in order to provide all of the power supply capability of the engine generator to the load on the assumption that the rapid increase in load is due to, for example, starting of the electric motor. This also applies to a period of an automatic recovery operation described below.

Furthermore, when the load becomes equal to or more than the reference value during the set duration for the timer (S 104 b ), the process proceeds to step S 106 where the dummy load L is cut off using another timer (retention time 2) (S 105 ). The process then returns to step S 101 . Furthermore, when the load becomes less than the reference value during the set duration for another timer, the process returns to step S 103 with the dummy load L remaining applied on the generator.

Dummy Load Control During an Automatic Recovery Operation According to the Present Invention

When an automatic recovery operation is started in step S 108 as described above, the engine E is controlled to burn the particulate matter (automatic recovery) in step S 109 . The process then proceeds to step S 110 .

Step S 110 determines whether or not the dummy load L is currently applied on the generator. If the dummy load is currently applied on the generator, when the load increases rapidly (S 111 ) or is equal to or more than the reference value (S 113 ), the dummy load L is cut off in step S 112 .

Furthermore, when, in step S 113 , the load is less than the reference value, the process proceeds to step S 114 to determine whether or not the PM amount has reached the automatic recovery end reference amount. When the PM amount has reached the automatic recovery end reference amount, the automatic recovery ends (S 118 ). On the other hand, when the PM amount is less than the automatic recovery end reference amount, the process proceeds to step S 121 . Step 121 determines whether or not the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature. When the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature, the process returns to step S 109 to continue the automatic recovery operation.

If, in step S 110 , the dummy load L has not been applied on the generator, when the load increases rapidly (S 115 ) or is equal to or more than the reference value (S 116 ), the process proceeds to S 114 . Furthermore, when the load is less than the reference value, the dummy load L is applied on the generator (S 117 ) and proceeds to step S 114 to determine whether or not the PM amount meets the automatic recovery end reference.

When, in step S 114 , the PM amount has reached the automatic recovery end reference amount, the process proceeds to step S 118 to end the automatic recovery and then proceeds to step S 119 to check whether or not the dummy load L has been applied on the generator. When the dummy load L has been applied on the generator, the process proceeds to step S 120 to cut off the dummy load L. When the dummy load L has not been applied on the generator, the process returns to step S 4 where the engine generator is operated in a normal manner.

On the other hand, when step S 114 determines that the PM amount does not meet the automatic recovery end reference, step S 121 determines whether or not the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature. When the exhaust gas temperature is lower than the automatic recovery reference temperature, the process temporarily suspends the automatic recovery (S 122 ) and proceeds to step S 123 to determine whether or not the dummy load L has been applied on the generator. When the dummy load L has not been applied on the generator, the dummy load L is applied on the generator (S 102 ). When the dummy load has been applied on the generator, (determining the automatic recovery to be no longer effective) the dummy load L is cut off (S 124 ) and proceeds to S 17 to issue a manual recovery request.

When, in step S 121 , the exhaust gas temperature is equal to or higher than the automatic recovery reference temperature, the process proceeds to step S 109 to continue the automatic recovery. This is followed by the operation in step S 110 and the subsequent steps.

Now, a technical prerequisite for the present invention is that a state is basically avoided in which, even though the dummy load L is applied on the generator (S 102 ) to increase the load on the engine E, the exhaust gas temperature fails to rise and is lower than the automatic recovery reference. Such a state could only occur when there should have been a very abnormal situation such as an extreme decrease in outside temperature to an unexpected value or a failure in mechanical element.

Embodiment 1 above is described on the premise that the output power voltage from the generator is fixed. However, given that many generators on the markets are switchable between a three-phase 400 V class and a three-phase 200 V class, the dummy load L is desirably made switchable in response to switching of the voltage.

To achieve this, for example, a voltage detecting relay may be provided in an input section of the dummy load L so as to allow automatic switching of the dummy load L according to the voltage of the generator. In the dummy load L, resistors may be connected to be switchable between a series connection and a parallel connection or between a star connection and a delta connection. When the output power voltage from the generator is high, the connection may be switched to the series connection or the star connection. When the output power voltage from the generator is low, the connection may be switched to the parallel connection or the delta connection.

E Engine

G Generator

DPF Diesel particulate filter

DOC Oxidation catalyst

TD Temperature measuring device

PMD Particulate matter amount measuring device

ECU Engine control unit

G-ECU Engine controlling additional unit

MC Contactor

L Dummy load