JP3600522B2 - Reducing agent supply device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reducing agent supply device for an internal combustion engine, and more particularly to a reducing agent supply device for supplying a reducing agent to a NOx catalyst that purifies nitrogen oxides (NOx) discharged from the internal combustion engine.
[0002]
[Prior art]
As a reducing agent supply device that is provided in an exhaust system of an internal combustion engine and supplies a reducing agent to a NOx catalyst that purifies nitrogen oxides (hereinafter, simply referred to as NOx) discharged from the internal combustion engine, for example, Japanese Unexamined Patent Application Publication No. The reducing agent supply device disclosed in Japanese Patent No. 272331 can be exemplified.
[0003]
In the reducing agent supply device disclosed in Japanese Patent Application Laid-Open No. Hei 5-272331, urea CO (NH) capable of reducing NOx at a high purification rate even at low temperatures₂  )₂Is used as a reducing agent, and the urea is supplied to a NOx catalyst to promote purification of NOx contained in exhaust gas.
[0004]
More specifically, after receiving a reducing agent supply command from an electronic control unit for engine control (hereinafter simply referred to as an ECU), the solid urea stored in the storage tank is heated and gasified in a furnace tube. The gasified urea is supplied upstream of the NOx catalyst in the engine exhaust passage to promote NOx purification.
[0005]
By the way, the solid reducing agent has a smaller volume than the gaseous reducing agent and the liquid reducing agent and is excellent in mountability on a vehicle, but cannot be supplied to the NOx catalyst because the particles are large as they are. Therefore, it is necessary to heat and gasify the solid reducing agent in the furnace tube as in the above-described reducing agent supply device, so that the NOx catalyst can be supplied to the NOx catalyst (transformation).
[0006]
[Problems to be solved by the invention]
However, in the conventional reducing agent supply device, the reducing agent is gasified and supplied to the NOx catalyst after receiving the reducing agent supply instruction from the ECU. There was also.
[0007]
In particular, the reducing agent containing solid urea as a main component not only takes a long time to gasify, but also is released to the atmosphere without reacting with NOx and emits an offensive odor when supplied to the NOx catalyst at an appropriate timing. There is a fear. Therefore, the development of a reducing agent supply device that can immediately respond to a reducing agent supply instruction is urgently required.
[0008]
If the required supply amount of the reducing agent exceeds the amount of the reducing gas (reducing agent) generated in the furnace cylinder, the supply of the reducing gas cannot catch up, and an appropriate amount of the reducing agent is supplied to the NOx catalyst. Could not supply. Therefore, the purification rate of NOx in the NOx catalyst is greatly reduced, which may lead to a reduction in exhaust emission.
[0009]
Further, in the conventional reducing agent supply device, since the reducing gas generated in the furnace tube is directly supplied to the exhaust passage, the supply pressure of the reducing agent is not stable, and an appropriate amount of the reducing agent corresponding to the required supply amount is used. Could not be supplied to the NOx catalyst.
[0010]
Therefore, an object of the present invention is to provide a reducing agent supply device for an internal combustion engine that can supply a predetermined amount of reducing agent immediately without delay in response to a reducing agent supply command.
[0011]
[Means for Solving the Problems]
In order to solve the above technical problems, the present invention employs the following solutions. That is,
A reducing agent supply device for supplying a reducing agent to a NOx catalyst provided in an exhaust system of an internal combustion engine for purifying nitrogen oxides discharged from the internal combustion engine,
Main reducing agent storage means for storing a solid reducing agent,
The solid reducing agent stored in the main reducing agent storage means isBy gasification, the reducing agentFluidizing means for fluidizing a reducing agent,
Secondary reducing agent storage means for temporarily storing the reducing agent fluidized by the reducing agent fluidizing means,
Reducing agent supply amount calculating means for calculating a supply amount of the reducing agent to be supplied to the NOx catalyst based on an operation state of the engine body;
The reducing agent stored in the sub-reducing agent storage means is used as the reducing agent supply amount calculating means.StepReducing agent adding means for adding upstream of the NOx catalyst in the exhaust system of the internal combustion engine based on the supply amount calculated by
WithAnd
The sub-reducing agent storage unit includes a remaining amount calculating unit that calculates a remaining amount of the reducing agent stored in the sub-reducing agent storage unit, and a sub-reducing agent storage chamber that temporarily stores the fluidized reducing agent. Pressure detecting means for detecting the pressure in the secondary reducing agent storage chamber,
The reducing agent fluidizing unit fluidizes the solid reducing agent stored in the main reducing agent storage unit in response to the remaining amount calculated by the remaining amount calculating unit being less than a predetermined value. Replenish the auxiliary reducing agent storage means,
The remaining amount calculating unit determines that the remaining amount of the reducing agent is large when the pressure detected by the pressure detecting unit is high, and determines the remaining amount of the reducing agent when the pressure detected by the pressure detecting unit is low. Judge it is lessIt is characterized by the following.
[0012]
According to the present invention employing such a means, the reducing agent having fluidity so that it can be added by the reducing agent fluidizing means is prepared and stored in advance in the sub-reducing agent storage means. The reducing agent can be supplied immediately in response to the supply command. Further, since the reducing gas is always stored in the auxiliary reducing agent storage tank 40, a stable supply of the reducing agent can be performed even when a large amount of the reducing agent is required. The fluidization of the reducing agent is an action for facilitating diffusion of the added reducing agent when the reducing agent is added by the reducing agent adding unit. That is, in the present invention, fluidization generally refers to actions such as gasification, liquefaction, gelation, and powderization as fluidization.
[0013]
The reducing agent fluidizing means gasifies the solid reducing agent to give the reducing agent fluidity.You.That is, the solid reducing agent is gasified to improve the diffusion of the added reducing agent when added by the reducing agent adding means.
[0014]
Further, the sub-reducing agent storing means includes a remaining amount calculating means for calculating a remaining amount of the reducing agent stored in the sub-reducing agent storing means, and the reducing agent fluidizing means is provided by the remaining amount calculating means. When the calculated remaining amount becomes less than the predetermined value, the solid reducing agent stored in the main reducing agent storage unit is fluidized and supplied to the auxiliary reducing agent storage unit.You.
[0015]
That is, in this means, when the remaining amount of the reducing agent stored in the sub-reducing agent storage unit becomes small, the solid reducing agent is newly fluidized and supplied to the sub-reducing agent storage unit. Therefore, the reducing agent can always be secured in the auxiliary reducing agent storage unit without unnecessarily fluidizing the solid reducing agent. The volume of the solid reducing agent generally increases with gasification and liquefaction. Therefore, if the solid reducing agent is fluidized unnecessarily, it is necessary to increase the capacity of the reducing agent storage means in the device, which leads to an increase in the size of the device. Therefore, by fluidizing only the required amount as described above, the size of the apparatus can be minimized. Here, the predetermined value is a numerical value excluding zero, and is a value that can be arbitrarily set based on an empirical rule or the like.
[0016]
Further, the sub-reducing agent storage means includes a sub-reducing agent storage chamber for temporarily storing the fluidized reducing agent, and pressure detection means for detecting a pressure in the sub-reducing agent storage chamber, The calculating means determines that the remaining amount of the reducing agent is large when the pressure detected by the pressure detecting means is high, and determines that the remaining amount of the reducing agent is small when the pressure detected by the pressure detecting means is low. YouYou.That is, the remaining amount of the reducing agent stored in the sub-reducing agent storage chamber is determined based on the pressure change in the sub-reducing agent storage chamber.
[0017]
Further, the reducing agent adding means,A reducing agent addition valve that is provided in the exhaust system upstream of the NOx catalyst and that adds the reducing agent stored in the sub-reducing agent storage chamber to the upstream of the NOx catalyst when the valve is opened; and a pressure detected by the pressure detection means. And an addition valve control means for controlling a valve opening time of the reducing agent addition valve.
[0018]
That is, in this means, the supply pressure of the reducing agent acting on the reducing agent addition valve is grasped by detecting the pressure in the auxiliary reducing agent storage chamber by the pressure detecting means. Then, the supply amount of the reducing agent supplied from the reducing agent addition valve to the NOx catalyst is controlled so as to always reach the target value. Therefore, even if the pressure in the secondary reducing agent storage chamber fluctuates, the reducing agent that matches the required supply amount can be supplied to the NOx catalyst.
[0019]
Note that the addition valve control means reduces the valve opening time of the reducing agent addition valve when the pressure in the auxiliary reducing agent storage chamber is high, and reduces the addition of the reducing agent when the pressure in the auxiliary reducing agent storage is low. The valve opening time of the valve may be lengthened.
[0020]
That is, when the pressure in the sub-reducing agent storage chamber is high, the supply amount of the reducing agent per unit time is increased, so that the valve opening time is shortened. The supply time of the reducing agent supplied from the reducing agent addition valve is maintained at a target value by lengthening the valve opening time because the supply amount of the reducing agent in (1) decreases.
[0021]
The NOx catalyst is preferably a selective reduction type NOx catalyst that decomposes or reduces nitrogen oxides in the presence of a reducing agent. The solid reducing agent is preferably a reducing agent that generates a reducing gas based on ammonia when gasified by the reducing agent fluidizing means.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a reducing agent supply device according to the present invention will be described with reference to the drawings. The embodiments described below are embodiments in which the reducing agent supply device of the present invention is applied to a vehicle diesel engine.
[0023]
<Overview of internal combustion engine>
Before describing the reducing agent supply device of the present invention, a diesel engine equipped with the reducing agent supply device will be described with reference to FIG.
[0024]
A diesel engine 1 (hereinafter, simply referred to as an engine) includes a combustion chamber 2 including a piston 3, a cylinder 4, a cylinder head 5, and the like, and a fuel injection valve 6 that supplies engine fuel to the combustion chamber 2. Have. Further, an intake pipe 8 having an air flow meter 7 for measuring an air intake amount is connected to the combustion chamber 2. In the combustion chamber 2, air introduced through the intake pipe 8 and a fuel injection valve 6 are provided. And the engine fuel supplied by the engine is mixed to perform engine combustion by self-ignition.
[0025]
On the other hand, exhaust gas generated due to engine combustion in the combustion chamber 2 passes through an exhaust pipe 10 which is connected to the combustion chamber 2 and includes a selective reduction type NOx catalyst 9 and a muffler (not shown) in the middle of the path. Exhausted to the atmosphere. In the following description, the selective reduction type NOx catalyst may be simply referred to as a NOx catalyst.
[0026]
The selective reduction type NOx catalyst 9 provided in the exhaust pipe 10 is a catalyst mainly for effectively purifying nitrogen oxides (hereinafter simply referred to as NOx) in exhaust gas, and reduces or reduces NOx in the presence of a reducing agent. It is a catalyst that decomposes and purifies.
[0027]
Examples of the selective reduction type NOx catalyst 9 include a catalyst in which a transition metal such as Cu is supported on zeolite by ion exchange, a catalyst in which a noble metal is supported on zeolite or alumina, and a catalyst in which vanadium is supported on titanium. , Etc. can be exemplified.
[0028]
A NOx sensor 11, an incoming gas pressure sensor 12, an exhaust gas temperature sensor 13 and the like are provided on the exhaust pipe 10 on the upstream side of the NOx catalyst 9, and a reducing agent sensor 14 is provided on the downstream side of the NOx catalyst 9. ing. The NOx sensor 11 is a sensor that measures the NOx concentration in the exhaust gas. The incoming gas pressure sensor 12 is a sensor that measures a pipe pressure (exhaust pressure) in the exhaust pipe 10. Further, the exhaust gas temperature sensor 13 is a sensor that measures the temperature of the exhaust gas flowing into the NOx catalyst 9. The reducing agent sensor 14 is a sensor that measures the concentration of the reducing agent in the exhaust gas. The various sensors are connected to input ports of an engine control electronic control unit 15 described later.
[0029]
The engine 1 is controlled by an engine control electronic control unit 15 (hereinafter simply referred to as ECU 15) in accordance with the operating state. The ECU 15 includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, an output port, an A / D converter, etc., which are interconnected by a bidirectional bus. For example, based on output signals from various sensors input to the input port and referring to various control maps developed on the ROM, for example, fuel injection control in the fuel injection valve 5 is performed. In the present invention, the control of the reducing agent supply device 16 is also performed at the same time.
[0030]
In the present invention, in order that the NOx catalyst 9 purifies NOx in the exhaust gas discharged with the engine combustion of the engine 1, ammonia gas (NH 3) as a reducing agent is supplied to the NOx catalyst 9. ) Is provided.
Hereinafter, the reducing agent addition device 16 which is the gist of the present invention will be described in detail with reference to FIG.
[0031]
<Structure of reducing agent supply device>
First, the structure of the reducing agent supply device 16 will be described.
The reducing agent supply device 16 heats a main reducing agent storage tank 20 (main reducing agent storing means) for storing a solid reducing agent therein and a solid reducing agent stored in the main reducing agent storage tank 20. A reducing gas generating unit 30 (reducing agent fluidizing means) for generating a reducing gas, and a sub-reducing agent storage tank 40 (sub-reducing agent storing means) for temporarily storing the reducing gas generated by the reducing gas generating unit 30; And a reducing agent addition valve 50 (reducing agent adding means) for adding the reducing gas stored in the auxiliary reducing agent storage tank 40 to the NOx catalyst 9 according to a reducing agent supply command from the ECU 15.
[0032]
The main reducing agent storage tank 20 has a tank main body 21 that contains therein solid ammonium carbamate as a reducing agent, and a heat insulating member 22 provided so as to surround the tank main body 21, which will be described later. It is provided detachably with respect to the reducing gas generator 30.
[0033]
Note that ammonium carbamate is a kind of reducing agent based on ammonia, and has a property of being solid at room temperature and gasifying at around 40 degrees Celsius. Also, since it has a much stronger reducing action than the conventionally used reducing agents such as hydrocarbon (HC) and carbon monoxide (CO), NOx can be purified with a high purification efficiency even at a relatively low temperature. It has such advantages.
[0034]
The reason why the main reducing agent storage tank 20 is detachably provided to the reducing gas generator 30 is that when the ammonium carbamate stored inside is exhausted, a new main reducing agent storing new ammonium carbamate is used. This is because the agent storage tank 20 and the empty main reducing agent storage tank after use can be easily replaced. That is, the main reducing agent storage tank 20 is of a cartridge type.
[0035]
The reducing gas generation unit 30 is connected to the main reducing agent storage tank 20 and is provided to surround the heating chamber 31 with a heating chamber 31 for promoting gasification of the reducing agent stored in the main reducing agent storage tank 20. And an outer wall 32. A space 33 is formed between the heating chamber 31 and the outer wall 32 and communicates with a water jacket (not shown) that serves as a circulation path for the engine cooling water, and the engine cooling water warmed by engine combustion is provided in this space. The inside of the heating chamber 31 is heated by flowing into the inside of the heating chamber 31.
[0036]
Further, between the water jacket and the reducing gas generator 30 (space 33), an engine cooling water control valve 34 for regulating the flow of the engine cooling water into the reducing gas generator 30 is provided (see FIG. 1). ). The opening and closing operation of the engine cooling water control valve 34 is controlled by the ECU 15 so that the flow rate of the engine cooling water flowing into the heating chamber 31 is controlled so that the room temperature in the heating chamber 31 can be arbitrarily adjusted. ing.
[0037]
Then, when the engine cooling water control valve 34 is opened to guide the engine cooling water warmed by the engine combustion to the reducing gas generation unit 30 (space 33), the room temperature in the heating chamber 31 increases. Ammonium carbamate in the main reducing agent storage tank 20 communicating with the heating chamber 31 is gasified. In the following description, the gasified ammonium carbamate may be simply referred to as a reducing gas.
[0038]
The auxiliary reducing agent storage tank 40 detects a tank body 41 for storing gaseous ammonium carbamate as a reducing agent, a heat insulating member 42 provided to surround the tank body 41, and a pressure in the tank body 41. A pressure sensor 43 (pressure detecting means) is provided, and the tank body 41 and the above-described reducing gas generator 30 are connected to each other via a connection pipe 60. Therefore, the ammonium carbamate gasified in the reducing gas generator 30 flows into the secondary reducing agent storage tank 40 via the connecting pipe 60 and is temporarily stored in the secondary reducing agent storage tank 40.
[0039]
The reducing agent addition valve 50 is provided in the exhaust pipe 10 on the upstream side of the NOx catalyst 9, and upon receiving a reducing agent supply command from the ECU 15, converts the reducing gas stored in the sub-reducing agent storage tank 40 into the upstream of the NOx catalyst 9. To the side exhaust pipe 10.
[0040]
The reducing agent addition valve 50 includes a nozzle part 53 including a valve body 51 and a guide 52 supporting the valve body 51, a solenoid 54 for opening and closing the valve body 51 provided in the nozzle part 53, An introduction passage 55 connected to the connecting pipe 60 for guiding the reducing gas stored in the sub-reducing agent storage tank 40 to the nozzle portion 53; The gas flows down the passage 55 and is guided to the nozzle 53. The reducing gas is added to the exhaust pipe 10 at an appropriate amount and at an appropriate timing by controlling the opening and closing of the valve element 51 by the solenoid 54.
[0041]
The duty ratio of the solenoid 54 that opens and closes the valve element 51 is controlled by the ECU 15, and the valve element 51 is opened when a valve opening voltage is applied to add the reducing gas in the auxiliary reducing agent storage tank 40 to the exhaust pipe 10. Like that. The internal pressure of the sub-reducing agent storage tank 40 is always maintained higher than the exhaust pressure in the exhaust pipe 10, and when the reducing gas is added, the pressure difference is used to add the reducing gas. I'm trying to get. The pressure adjustment of the auxiliary reducing agent storage tank 40 will be described in detail in the following description of the reducing agent supply control.
[0042]
<Control of reducing agent supply device>
Hereinafter, the reducing agent supply control according to the above-described reducing agent supply device will be described.
When the temperature of the engine coolant reaches about 40 degrees Celsius with the start of operation of the engine 1 (start of engine combustion), the ECU 15 performs gasification of the reducing agent stored in the main reducing agent storage tank 20 in order to gasify the reducing agent. First, the engine cooling water control valve 34 is opened to introduce the engine cooling water into the reducing gas generator 30.
[0043]
When the space temperature in the heating chamber 31 reaches about 40 degrees Celsius due to the engine cooling water, part of the ammonium carbamate in the main reducing agent storage tank 20 communicating with the reducing gas generator 30 is gasified, and the connection path After 60, the secondary reducing agent storage tank 40 is filled.
[0044]
At this time, the ECU 15 knows the amount of the reducing gas filled in the sub-reducing agent storage tank 40 based on the output value of the pressure sensor 43, and detects the sub-reducing agent storage tank 40 detected by the pressure sensor 43. When the internal pressure reaches a predetermined value, it is considered that the charging amount of the reducing gas has reached the specified amount, and the engine cooling water control valve 34 is closed to temporarily suspend the gasification of ammonium carbamate. ing.
[0045]
Here, the predetermined value is a value obtained by various preliminary experiments, for example, a maximum allowable pressure of the auxiliary reducing agent storage tank 40, an average exhaust pressure in the exhaust pipe 10, a consumption amount of the reducing gas per unit time, and the like. Is a value arbitrarily set in consideration of
[0046]
In the ECU 15, when the pressure of the sub-reducing agent storage tank 40 detected by the pressure sensor 43 does not increase even after the lapse of a predetermined time, the ammonium carbamate stored in the main reducing agent storage tank 20 does not increase. Is exhausted, a warning lamp 19 is lit on an indicator panel 18 provided in the vehicle to notify the driver of the fact.
[0047]
In addition, the ECU 15 controls the target supply amount of the reducing agent based on the engine load, the engine speed, the NOx concentration, the catalyst temperature, the charging pressure of the reducing gas, and the like in order to control the supply of the reducing agent to promote the purification of NOx. Is controlled, and the solenoid 54 in the reducing agent addition valve 50 is controlled so that a reducing agent corresponding to the calculated target supply amount is added to the NOx catalyst 9 at an appropriate timing.
[0048]
The control of the reducing agent addition valve 50 will be described in detail. The output signal from the air flow meter 7 and the output signal from the NOx sensor 11 are input to the ECU 15 through the input port and the A / D converter as described above. I have. The ECU 15 calculates the amount of NOx discharged per unit time from the air intake amount detected by the air flow meter 7 and the NOx concentration detected by the NOx sensor 11, and calculates the calculated amount. A target supply amount of the reducing agent corresponding to the NOx emission amount is set (reducing agent supply amount calculating means).
[0049]
Further, an output signal from the pressure sensor 43 provided in the sub-reducing agent storage tank 40 and an output signal from the incoming gas pressure sensor 12 provided in the exhaust pipe 10 are input to the ECU 15. The pressure sensor 43 outputs an output voltage proportional to the internal pressure of the auxiliary reducing agent storage tank 40, and the incoming gas pressure sensor 12 outputs an output voltage proportional to the exhaust pressure in the exhaust pipe 10. Then, the ECU 15 obtains a pressure difference between the pressure of the auxiliary reducing agent storage tank 40 and the pressure in the exhaust pipe 10 (discharge pressure) based on the output values from the pressure sensors 43 and 12. The supply pressure of the reducing gas to the exhaust pipe 10 is calculated.
[0050]
Also, the ECU 15 calculates the duty ratio of the valve element 51 of the reducing agent addition valve 50 in consideration of the calculated supply pressure of the reducing gas so that the supply amount of the reducing gas per unit time becomes the target supply amount. Then, duty ratio control of the reducing agent addition valve 50 is performed based on the calculated duty ratio (addition valve control means). Here, the duty ratio means the number of times the valve body 51 is opened and closed per unit time. Therefore, in the duty ratio control, as the number of times of opening and closing of the valve element 51 per unit time increases, more reducing gas is supplied to the exhaust pipe 10.
[0051]
That is, when the supply pressure of the reducing gas is high, the duty ratio is set small because the supply amount of the reducing gas per unit time is inevitably increased. Conversely, when the supply pressure of the reducing gas is low, the reduction per unit time is performed. The duty ratio is set large because the supply amount of gas decreases.
[0052]
An output signal from the exhaust temperature sensor 13 is input to the ECU 15. The exhaust temperature sensor 13 outputs an output voltage proportional to the temperature of the exhaust gas, and is used for grasping the catalyst temperature of the NOx catalyst 9. In response to the fact that the catalyst temperature detected by the exhaust gas temperature sensor 13 has reached the activation temperature at which NOx can be purified, the ECU 15 controls the duty of the reducing agent addition valve 50 to match the calculated target supply amount. And the reducing gas is added to the NOx catalyst 9.
[0053]
Further, an output signal from the reducing agent sensor 14 is input to the ECU 15. When a large amount of the reducing agent is unintentionally supplied due to a failure of the reducing agent supply device 16 or the like, the ECU 15 senses the reducing agent with the reducing agent sensor 14 and immediately stops the supply of the reducing agent. Is performed.
[0054]
On the other hand, the reducing gas stored in the sub-reducing agent storage tank 40 is consumed by the addition from the reducing agent addition valve 50, and the remaining amount thereof decreases with time. Therefore, the ECU 15 always grasps the remaining amount of the reducing gas in the sub-reducing agent storage tank 40 so as not to run out of the reducing gas stored in the sub-reducing agent storage tank 40, and when the remaining amount decreases, Reducing gas replenishment control for replenishing the auxiliary reducing agent storage tank 40 with reducing gas is performed.
[0055]
In order to grasp the remaining amount of the reducing gas by the ECU 15, the remaining amount is grasped by using the output signal of the pressure sensor 43 described above. That is, when the reducing gas in the auxiliary reducing agent storage tank 40 is consumed, the internal pressure of the auxiliary reducing agent storage tank 40 also decreases. Therefore, by monitoring the output value of the pressure sensor 43, the remaining amount in the auxiliary reducing agent storage tank 40 can be grasped (remaining amount detecting means).
[0056]
The ECU 15 opens the engine cooling water control valve 34 in response to the fact that the pressure in the auxiliary reducing agent storage tank 40 (the filling pressure of the reducing gas) detected by the pressure sensor 43 has become less than a predetermined value. The valve is heated to heat the heating chamber 31, and the ammonium carbamate stored in the main reducing agent storage tank 20 is newly gasified. As a result, the newly gasified ammonium carbamate flows into the sub-reducing agent storage tank 40 and replenishes the sub-reducing agent storage tank 40 with the reducing gas.
[0057]
Here, the predetermined value is a value that can be arbitrarily set, but is preferably a value that is sufficiently large with respect to the exhaust pressure. That is, by increasing the filling pressure of the reducing gas, the diffusion of the reducing gas into the exhaust pipe 10 is improved, and the supply amount per unit time with respect to the change in the exhaust pressure is also stabilized.
[0058]
When the internal pressure of the sub-reducing agent storage tank 40 becomes equal to or higher than a predetermined value, the engine cooling water control valve 34 is closed as described above to stop the gasification of ammonium carbamate.
[0059]
As described above, in the reducing agent supply device 16 of the present invention, the solid reducing agent is gasified and stored and prepared in the auxiliary reducing agent storage tank 40 in advance so that addition from the reducing agent addition valve 50 can be performed. It is possible to immediately respond to a reducing agent addition command from the ECU 15.
[0060]
The above description is merely one embodiment of the present invention, and details can be arbitrarily changed. For example, when the ECU 15 calculates the NOx emission amount, the ECU 15 may prepare a NOx emission amount map and use the map to calculate the NOx emission amount.
[0061]
The NOx emission map maps the relationship between these parameters and the NOx emission per unit time obtained by various preliminary experiments, using the engine load and the engine speed as parameters. Therefore, when the output signal of the accelerator opening sensor (not shown) and the output signal of the crank angle sensor are input to the ECU 15 and compared with the NOx emission map, the NOx emission per unit time can be calculated.
[0062]
The accelerator opening sensor outputs an output voltage proportional to the accelerator opening to the ECU 15, and the output voltage is used for calculating the engine load. On the other hand, the crank angle sensor outputs an output pulse to the ECU 15 every time a crankshaft (not shown) of the engine 1 rotates by a predetermined angle, and the output pulse is used for calculating the engine speed.
[0063]
In the above-described example, the supply pressure of the reducing agent acting on the reducing agent addition valve 50 is obtained from the output value of the incoming gas pressure sensor 12 and the output value of the pressure sensor 43. Can be estimated from an exhaust pressure map created using the engine load and the engine speed as parameters. Therefore, the supply pressure of the reducing agent may be calculated based on the output value of the pressure sensor 43 and the exhaust pressure calculated on the exhaust pressure map.
[0064]
In the above-described example, the duty ratio control in the reducing agent addition valve 50 is performed in consideration of the output value of the incoming gas pressure sensor 12 and the output value of the pressure sensor 43. If the storage pressure of the reducing gas is sufficiently increased with respect to the pressure in the exhaust pipe 10, the fluctuation of the supply amount of the reducing agent per unit time due to the influence of the exhaust pressure can be relatively reduced. That is, if the storage pressure of the reducing gas in the sub-reducing agent storage tank 40 is set to a sufficiently large value, the duty ratio control of the reducing agent addition valve 50 may be performed by considering only the pressure in the sub-reducing agent storage tank 40. Good.
[0065]
In the above-described example, the gasified reducing agent is stored in the form of the sub-reducing agent storage tank 40 as it is. However, the generated reducing agent is compressed and cooled to reduce the volume to reduce the volume of the reducing agent. It may be stored in the storage tank 40. That is, by compressing the reducing gas and storing it in the auxiliary reducing agent storage tank 40, the size of the apparatus can be further reduced. For example, in this case, a method of mechanically reducing the volume of the auxiliary reducing agent storage tank 40 to compress the reducing gas, and providing a cooling fin or the like around the reducing agent storage tank 40 to cool the reducing gas is used. Can be illustrated.
[0066]
Alternatively, the reducing gas may be stored in the auxiliary reducing agent storage tank 40 in a state where the ammonia storing alloy is stored in the auxiliary reducing agent storage tank 40 and the reducing gas is stored in the ammonia storing alloy. Since the ammonia storage alloy stores the reducing gas in combination with the reducing gas, the reducing gas can be stored in the auxiliary reducing agent storage tank 40 at a higher density.
[0067]
In the above-described example, the solid reducing agent is gasified and stored in the sub-reducing agent storage tank 40. The reducing agent may be stored in the auxiliary reducing agent storage tank 40 in a liquefied state. That is, the form of the reducing agent stored in the sub-reducing agent storage tank 40 may be any form that can be added immediately by the reducing agent addition valve 50.
[0068]
Further, in the above example, ammonium carbamate was applied as a solid reducing agent, but of course, urea CO (NH₂  )₂Other substances may be employed as the reducing agent. When a reducing agent that gasifies at a relatively high temperature such as urea is employed, the reducing gas generating unit 30 may be configured with an electric heater or the like to gasify the reducing agent. Further, heating may be performed using heat of the engine lubricating oil.
[0069]
Next, the operation and effect of the engine employing the reducing agent supply device having such a configuration will be described.
As described above, the ECU 15 controls the duty ratio of the reducing agent addition valve 50 according to the NOx emission amount, and adds the reducing agent corresponding to the target supply amount to the NOx catalyst 9 at an appropriate timing. At this time, in the reducing agent supply device 16 of the present invention, solid ammonium carbamate is heated and gasified in the reducing gas generating section 30 and stored and prepared in advance in the sub-reducing agent storage tank 40. Can immediately respond to the addition order. Further, since the reducing gas is always stored in the auxiliary reducing agent storage tank 40, even when a large amount of reducing agent is required, a stable supply of the reducing agent can be performed.
[0070]
Further, the duty ratio control in the reducing agent addition valve 50 is controlled in consideration of the supply pressure of the reducing agent. Moreover, since the gasified reducing agent is added after being temporarily stored in the auxiliary reducing agent storage tank 40, the supply pressure of the reducing gas to the reducing agent addition valve 50 is always stable. Therefore, the ECU 15 can easily control the duty ratio in the reducing agent addition valve 50, and can surely supply the NOx catalyst 9 with the reducing agent corresponding to the target supply amount.
[0071]
Further, the remaining amount of the reducing gas is grasped by the ECU 15 using the pressure change in the auxiliary reducing agent storage tank 40. Therefore, the ECU 15 can control the gasification of the solid reducing agent based on the remaining amount of the reducing gas, and does not unnecessarily gasify the reducing agent. Therefore, a stable supply of the reducing agent can be achieved without securing a large volume in the reducing agent supply device 16.
[0072]
As described above, in the engine employing the reducing agent supply device 16 of the present invention, the reducing agent is supplied at an appropriate amount and at an appropriate timing. it can. Further, since a stable addition of the reducing agent can be performed without securing a large volume in the reducing agent supply device 16, the device main body can be manufactured in a small size, and the mountability to a vehicle can be greatly improved.
[0073]
In the engine 1 described above, a selective reduction type NOx catalyst is applied as a catalyst for purifying NOx. However, the reducing agent supply device 16 of the present invention is, of course, also useful for a storage reduction type NOx catalyst. The storage-reduction type NOx catalyst is a catalyst that stores NOx in an oxygen-excess atmosphere and releases the stored NOx when the oxygen concentration decreases to purify the NOx.
[0074]
In the above-described embodiment, a diesel engine has been described as an example. However, the reducing agent supply device 16 of the present invention is extremely useful not only in a diesel engine but also in a lean burn gasoline engine capable of lean burn. .
[0075]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a reducing agent supply device for an internal combustion engine that can immediately supply a predetermined amount of reducing agent without delay in response to a reducing agent supply command.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a diesel engine employing a reducing agent supply device according to the present embodiment.
FIG. 2 is a schematic configuration diagram of a reducing agent supply device according to the present embodiment.
[Explanation of symbols]
1 Diesel engine (engine)
2 Combustion chamber
3 piston
4 cylinder
5 Cylinder head
6 Fuel injection valve
7 Air flow meter
8 Intake pipe
9. Selective reduction type NOx catalyst (NOx catalyst)
10 Exhaust pipe
11 NOx sensor
12 gas pressure sensor
13 Exhaust gas temperature sensor
14 Reducing agent sensor
15 Electronic control unit (ECU) for engine control
16 Reducing agent supply device
18 Indicator panel
19 Warning lamp
20 Main reducing agent storage tank
21 Tank body
22 Thermal insulation material
30 Reducing gas generator
31 heating room
32 Outer wall
33 Space
34 Engine cooling water control valve
40 Sub-reducing agent storage tank
41 Tank body
42 Insulation member
43 Pressure sensor
50 Reducing agent addition valve
51 valve body
52 Guide
53 Nozzle
54 solenoid
55 Introductory passage
60 Connecting pipe

Claims (5)

A reducing agent supply device for supplying a reducing agent to a NOx catalyst provided in an exhaust system of an internal combustion engine for purifying nitrogen oxides discharged from the internal combustion engine,
Main reducing agent storage means for storing a solid reducing agent,
Reducing agent fluidizing means for fluidizing the reducing agent by gasifying a solid reducing agent stored in the main reducing agent storage means,
Auxiliary reducing agent storage means for temporarily storing the reducing agent fluidized by the reducing agent fluidizing means,
Reducing agent supply amount calculating means for calculating a supply amount of the reducing agent to be supplied to the NOx catalyst based on an operation state of the engine body;
The reducing agent is stored in the auxiliary reducing agent storage unit, and a reducing agent addition means for adding the NOx catalyst upstream in the exhaust system of the internal combustion engine based on the supply amount calculated by the reducing agent supply amount calculating hand stage,
Have a,
The sub-reducing agent storage unit includes a remaining amount calculating unit that calculates a remaining amount of the reducing agent stored in the sub-reducing agent storage unit, and a sub-reducing agent storage chamber that temporarily stores the fluidized reducing agent. Pressure detecting means for detecting the pressure in the secondary reducing agent storage chamber,
The reducing agent fluidizing unit fluidizes the solid reducing agent stored in the main reducing agent storage unit in response to the remaining amount calculated by the remaining amount calculating unit being less than a predetermined value. Replenish the auxiliary reducing agent storage means,
The remaining amount calculating unit determines that the remaining amount of the reducing agent is large when the pressure detected by the pressure detecting unit is high, and determines the remaining amount of the reducing agent when the pressure detected by the pressure detecting unit is low. A reducing agent supply device for an internal combustion engine, which determines that the amount is small .   The reducing agent adding means includes the NO. x The reducing agent provided in the exhaust system upstream of the catalyst and stored in the sub-reducing agent storage chamber when the valve is opened is the NO. x A reductant addition valve added upstream of a catalyst, and addition valve control means for controlling a valve opening time of the reductant addition valve based on a pressure detected by the pressure detection means, wherein: 2. The reducing agent supply device for an internal combustion engine according to 1.   The addition valve control means, when the pressure in the secondary reducing agent storage chamber is high, shortens the opening time of the reducing agent addition valve, and when the pressure in the secondary reducing agent storage is low, The reducing agent supply device for an internal combustion engine according to claim 2, wherein the valve opening time is lengthened.   NO x The catalyst is a selective reduction type NO that decomposes or reduces nitrogen oxides in the presence of a reducing agent. x 4. The reducing agent supply device for an internal combustion engine according to claim 1, wherein the device is a catalyst.   The reducing agent for an internal combustion engine according to any one of claims 1 to 4, wherein the solid reducing agent generates a reducing gas based on ammonia when gasified by the reducing agent fluidizing means. Feeding device.

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