JP5195277B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to a selective reduction type NOx purification catalyst provided on an exhaust passage of an engine, an addition valve for adding a liquid reducing agent in an exhaust passage upstream of the NOx purification catalyst, and the reducing agent. The present invention relates to an engine exhaust gas purification apparatus that includes an electric pump that supplies a reducing agent from a storage tank to be stored to the addition valve through a predetermined supply pipe, and a control unit that controls the operation of the addition valve and the electric pump.

  Conventionally, for example, as shown in Patent Document 1 below, a selective reduction type NOx purification catalyst (SCR catalyst) provided on an exhaust passage of an engine, a urea water tank for storing urea water as a liquid reducing agent, An electric pump (urea water pump) for pumping urea water in the tank; and a urea water addition valve provided in an exhaust passage upstream of the NOx purification catalyst, from the electric pump through a urea water supply pipe There is known an exhaust gas purification apparatus in which a specific exhaust gas purification reaction is promoted by the NOx purification catalyst by adding and supplying pressurized urea water into the exhaust passage by the urea water addition valve.

In particular, in the technique of Patent Document 1, when the engine stops, the electric pump is reversely driven to suck back the urea water remaining in the urea water supply pipe and collect it in the urea water tank. I am doing so. By doing in this way, after an engine stop, the advantage that damage to the said urea water supply pipe | tube etc. resulting from the urea water remaining in a urea water supply pipe | tube or a urea water addition valve freezing is acquired.
JP 2008-101564 A

  By the way, in the exhaust emission control device disclosed in Patent Document 1, when the engine is stopped and the urea water is sucked back and then restarted, urea water is supplied from the addition valve to the NOx purification catalyst. As a preparation for adding the urea water, it is necessary to fill the urea water supply pipe and the urea water addition valve in advance with the urea water by driving the electric pump to rotate forward and pumping the urea water from the urea water tank. However, since the addition of the urea water is performed after the exhaust temperature has increased to some extent, if the drive start timing of the electric pump is too early with respect to this addition start timing, the electric pump is driven wastefully for a long time. As a result, there is a problem that energy efficiency is deteriorated.

  The present invention has been made in view of the above circumstances, and wasteful power consumption is achieved by appropriately controlling the driving of an electric pump that supplies a reducing agent added to a selective reduction type NOx purification catalyst. It aims at suppressing energy consumption and improving energy efficiency more.

In order to solve the above problems, the present invention provides a selective reduction type NOx purification catalyst provided on the exhaust passage of an engine, and a liquid reducing agent in the exhaust passage upstream of the NOx purification catalyst. An addition valve for addition; an electric pump for supplying the reducing agent to the addition valve through a predetermined supply pipe from a storage tank for storing the reducing agent; and a control means for controlling the operation of the addition valve and the electric pump. An exhaust emission control device for an engine, comprising: parameter value detection means for detecting a parameter value related to the temperature of the NOx purification catalyst, wherein the addition valve is a valve of the NOx purification catalyst obtained from a detection value of the parameter value detection means. temperature is controlled such that addition of the reducing agent at a predetermined temperature or higher, said control means on when the temperature of the NOx purification catalyst is lower than the predetermined temperature Determine the rate of temperature rise of the NOx purification catalyst, is characterized in delaying the drive start timing of the electric pump as compared to when large when the temperature increase rate is small (claim 1).

  According to the present invention, since the drive start timing of the electric pump that supplies the reducing agent to the addition valve is determined based on the temperature of the NOx purification catalyst, the drive of the electric pump is performed after the catalyst temperature increases to some extent after the engine is started. By starting, it is possible to prevent the electric pump from being wasted when the catalyst temperature is low and it is not necessary to add a reducing agent, effectively reducing the power consumption of the electric pump and further improving energy efficiency. There is an advantage that can be made.

More specifically, in the present invention, when the rate of temperature increase of the NOx purification catalyst is small, the drive start timing of the electric pump is delayed compared to when it is large. Therefore, it is linked with the timing when the temperature of the NOx purification catalyst reaches a predetermined temperature. Thus, the drive start timing of the electric pump is determined . Thereby, the pressure of the reducing agent can be increased to a predetermined pressure at an appropriate timing according to the time when the catalyst temperature reaches the predetermined temperature, and the reducing agent from the addition valve is effectively reduced while reducing the power consumption of the electric pump. There is an advantage that the addition of can be started at an appropriate time.

As a preferred mode of the present invention, the control means includes a timing at which the temperature of the NOx purification catalyst rises to the predetermined temperature, and the pressure of the reducing agent in the supply pipe reaches a predetermined pressure, so that the reducing agent from the addition valve The drive start timing of the electric pump is determined so that the timing when the addition becomes possible coincides ( claim 2 ).

  According to this configuration, it is possible to reduce the power consumption more effectively by eliminating the period in which the electric pump is driven wastefully, and since the addition of the reducing agent can be started at the same time as the catalyst temperature reaches the predetermined temperature, energy efficiency There is an advantage that improvement in NOx purification performance can be achieved at a high level.

As a more preferred form, the control means predicts a time until the temperature of the NOx purification catalyst reaches the predetermined temperature based on the temperature increase rate, and after the estimated time and the electric pump is driven. the pressure of the reducing agent in the supply pipe is based on the time required to reach the predetermined pressure, determining the drive start timing of the electric pump (claim 3).

  According to this configuration, there is an advantage that the power consumption can be more effectively reduced by driving the electric pump at an appropriate timing based on the prediction using the temperature increase rate of the NOx purification catalyst.

As a preferred mode of the present invention, after the engine is stopped, the control means operates a switching valve provided in the supply pipe, so that the reducing agent remaining in the supply pipe is sucked by the electric pump with the storage tank. The flow of the reducing agent is switched so as to return to the inside ( claim 4 ).

  According to this configuration, there is an advantage that it is possible to effectively prevent breakage of the supply pipe due to freezing of the reducing agent remaining in the supply pipe after the engine is started.

  As described above, according to the present invention, by appropriately controlling the driving of the electric pump that supplies the reducing agent added to the selective reduction type NOx purification catalyst, wasteful power consumption can be suppressed and energy efficiency can be reduced. It can be improved further.

  FIG. 1 is a schematic view showing an exhaust emission control device for an engine according to an embodiment of the present invention. The exhaust gas purification apparatus shown in this figure purifies exhaust gas discharged from an engine other than the figure such as a diesel engine, for example, and, as its basic component, the exhaust passage 1 through which the exhaust gas flows is provided. A NOx purification catalyst 3 provided in the middle part and an addition valve 5 for adding urea water as a reducing agent into the pipe 1a upstream of the NOx purification catalyst 3 in the exhaust passage 1 are provided. . That is, the exhaust gas purification apparatus shown in FIG. 1 adds (injects) urea water into the exhaust passage 1 from the addition valve 5 in accordance with the operating state, and performs a reduction reaction at the downstream side NOx purification catalyst 3. It is provided as a purifying device for a so-called urea SCR (Selective Catalytic Reduction) system that can purify NOx in exhaust gas with a high purification rate by promoting it by the action of the urea water.

  Specifically, when urea water is added to the exhaust gas from the addition valve 5, hydrolysis is performed by the heat of the exhaust gas to generate ammonia. Then, the produced ammonia is adsorbed to the downstream side NOx purification catalyst 3, and the denitration reaction occurs between the adsorbed ammonia and NOx in the exhaust gas, so that the reduction of NOx is promoted. It has become.

  The addition valve 5 has substantially the same structure as an existing fuel injection valve (injector), and is constituted by, for example, an electromagnetic open / close needle valve. Then, when the addition valve 5 is opened or closed based on a control signal from the ECU 21 described later, urea water is injected into the exhaust passage 1 through the nozzle at the tip thereof, or the injection is stopped. It is like that.

  Next, a urea water supply system that supplies urea water to the addition valve 5 will be described. That is, urea water is sequentially supplied from the storage tank 9 to the addition valve 5 through the supply pipe 13, and urea water stored in the storage tank 9 is provided in the middle of the supply pipe 13. An electric pump 7 is disposed for pumping up and pumping the fuel to the addition valve 5. The electric pump 7 is composed of, for example, a three-phase AC motor, and its driving is controlled according to a control signal from the ECU 21 described later.

  The storage tank 9 is composed of a sealed container in which a predetermined concentration of urea water is accommodated, and urea water can be replenished as needed from a liquid supply cap (not shown) provided at the predetermined portion. Yes. In addition, as a measure for preventing the urea water in the storage tank 9 from freezing when it is cold, the storage tank 9 is provided with a heater, a heat insulating material, or the like as necessary.

  A filter 11 for filtering urea water is provided in the storage tank 9 so as to be immersed in the urea water. One end of the supply pipe 13 is connected to the filter 11. . On the other hand, the other end of the supply pipe 13 is connected to the addition valve 5, and urea water filtered by the filter 11 is added through the supply pipe 13 in response to the driving of the electric pump 7. 5 is supplied.

  A pressure control valve 17 for adjusting the pressure of urea water inside the supply pipe 13 and a switching valve 19 for switching the flow of urea water in the supply pipe 13 are disposed in the middle of the supply pipe 13, respectively. ing.

  The pressure control valve 17 returns the excess urea water to the storage tank 9 and maintains the pressure in the supply pipe 13 at a predetermined pressure. That is, a return pipe 15 extending from the storage tank 9 is connected to the pressure control valve 17, and the pressure control valve 17 is opened when the pressure of the urea water in the supply pipe 13 exceeds a predetermined pressure. Then, the excess urea water is returned from the return pipe 15 to the storage tank 9 and, when the pressure in the supply pipe 13 falls below a predetermined pressure, the pressure control valve 17 is closed and the return pipe 15 is closed. By stopping the flow from the storage tank 9 to the storage tank 9, the pressure of the urea water in the supply pipe 13 is maintained at a predetermined pressure.

  The switching valve 19 is an electromagnetic open / close direction control valve that operates in response to a control signal from the ECU 21 to be described later, and includes first to fourth pipes 13a to 13d that constitute the supply pipe 13 (details will be described later). ) Are connected, the urea water flows from the storage tank 9 toward the addition valve 5 by changing the communication state of the four ports, and conversely, from the addition valve 5 to the storage tank 9. The flow direction can be switched between the state in which the urea water flows toward (see FIG. 4).

  The supply pipe 13 is disposed between a first pipe 13a disposed between the filter 11 and the switching valve 19, and between the switching valve 19 and the pressure control valve 17, and the electric pump 7 is disposed in the middle. A second pipe 13b provided, a third pipe 13c disposed between the pressure control valve 17 and the switching valve 19, and a fourth pipe 13d disposed between the switching valve 19 and the addition valve 5. And have.

  When the switching valve 19 is in the state shown in FIG. 1, the first pipe 13a and the second pipe 13b are communicated, and the third pipe 13c and the fourth pipe 13d are communicated. As indicated by the arrow 1, urea water pumped from the storage tank 9 by the suction force of the electric pump 7 flows in the order of the first pipe 13 a, the second pipe 13 b, the third pipe 13 c, and the fourth pipe 13 d. Then, it is supplied to the addition valve 5. On the other hand, when the switching valve 19 operates from this state and is displaced to the state shown in FIG. 4, the first pipe 13a and the third pipe 13c are communicated with each other, and the second pipe 13b and the fourth pipe 13d are connected. As shown in FIG. 4, the suction force of the electric pump 7 acts in the opposite direction, and the urea water remaining in the pipes 13 a to 13 d is returned to the storage tank 9. It is like that.

  Next, the control system of the exhaust emission control device of this embodiment will be described. Operations of the respective parts such as the addition valve 5, the electric pump 7, and the switching valve 19 are comprehensively controlled by an ECU 21 as a control means. The ECU 21 includes a conventionally known CPU, various memories, and the like, and is electrically connected to the addition valve 5, the electric pump 7, and the switching valve 19.

  Further, the ECU 21 includes a temperature sensor 23 (corresponding to a parameter value detecting means according to the present invention) provided at the end of the upstream pipe 1a that is directly upstream of the NOx purification catalyst 3 in the exhaust passage 1. A NOx sensor 25 provided on the upstream side of the temperature sensor 23 and a hydraulic pressure sensor 27 provided in the middle part of the supply pipe 13 (the fourth pipe 13d in the illustrated example) are electrically connected. The exhaust gas temperature immediately upstream of the NOx purification catalyst 3 detected by the temperature sensor 23 (that is, the same as the temperature of the NOx purification catalyst 3), the NOx concentration in the exhaust gas detected by the NOx sensor 25, and The pressure of the urea water in the supply pipe 13 detected by the hydraulic pressure sensor 27 is input to the ECU 21 as an electrical signal. In the following, the temperature of the NOx purification catalyst 3 detected by the temperature sensor 23 is Ts, the NOx concentration detected by the NOx sensor is Dn, and the urea water in the supply pipe 13 detected by the hydraulic pressure sensor 27. Is expressed as Pr.

  By the ECU 21 configured as described above, the exhaust purification device of the present embodiment is controlled as follows, for example.

  First, the control operation after the engine is started will be briefly described. When the engine is started, the electric pump 7 is maintained in a stopped state for a while thereafter. That is, in the initial stage after engine startup, the temperature of the exhaust gas is low and there is no environment in which ammonia is sufficiently generated by hydrolysis of urea water, so urea water is added from the addition valve 5 into the exhaust passage 1. Can not do it. For this reason, it is not necessary to drive the electric pump 7 immediately after starting the engine, and the electric pump 7 is maintained in a stopped state for a while.

  The timing for starting driving the electric pump 7 is determined based on the temperature Ts of the NOx purification catalyst 3 detected by the temperature sensor 23. Specifically, based on the rate of change of the catalyst temperature Ts, the timing at which the catalyst temperature Ts rises to a temperature at which urea water is sufficiently hydrolyzed (that is, a temperature at which ammonia is generated at a sufficient rate). It is expected that the electric pump 7 starts to be driven at a somewhat earlier timing. In the following, a temperature at which the urea water is sufficiently hydrolyzed as described above is referred to as a predetermined temperature Tsq (see FIG. 3 (e)).

  As described above, the electric pump 7 is driven before the catalyst temperature Ts reaches the predetermined temperature Tsq. After the electric pump 7 is driven, the supply pipe 13 is sufficiently filled with urea water, and the addition valve This is because a certain amount of time is required until the urea water from 5 can be added. That is, in this embodiment, as will be described later, when the engine is stopped, urea water is sucked out from the supply pipe 13 and returned to the storage tank 9 (that is, the supply pipe 13 is emptied), so that the engine is started again. Then, when the electric pump 7 is driven, the supply pipe 13 is sufficiently filled with urea water from that time, and the pressure Pr rises to the relief pressure of the pressure control valve 17. A certain amount of time is required until the urea water can be added. Therefore, the electric pump 7 is driven early in anticipation of such time. Hereinafter, the pressure at which the urea water is sufficiently filled in the supply pipe 13 as described above and the urea water can be added (same as the relief pressure of the pressure control valve 17) is referred to as a predetermined pressure Prq (FIG. 3 (d)).

  When the drive of the electric pump 7 is started as described above and the supply pipe 13 is sufficiently filled with urea water, the urea water is then added from the addition valve 5 into the exhaust passage 1 as necessary. The The amount of urea water added at this time is set based on the temperature Ts of the NOx purification catalyst 3 detected by the temperature sensor 23, the NOx concentration Dn in the exhaust gas detected by the NOx sensor 25, and the like.

  Next, the control operation after the engine is stopped will be described. When the engine is stopped, the switching valve 19 is actuated to be displaced to the state shown in FIG. 4 and the electric pump 7 is kept driven for a while, so that the flow direction of the urea water is reversed, and the supply pipe The urea water remaining in 13 is returned to the storage tank 9 by the suction force of the electric pump 7. This is a measure for preventing damage to the supply pipe 13 due to freezing of the urea water remaining in the supply pipe 13. In other words, if the urea water remains in the supply pipe 13 when the temperature falls below the freezing point (about −11 ° C.) of the urea water at the time of cold, the urea water is frozen and the supply pipe 13 and the addition valve are thus frozen. 5 may be damaged, but if the urea water in the supply pipe 13 is recovered in the storage tank 9 after the engine is stopped as described above, the above situation can be avoided and the supply pipe 13 or addition can be avoided. It is possible to effectively prevent the valve 5 from being damaged.

  Next, more specific contents of the control operation performed by the ECU 21 after engine startup will be described using the flowchart of FIG. 2 and the time chart of FIG. As a premise of starting this control operation, the engine is stopped before time t0 in FIG. 3, and at time t0 when the engine is started, the addition valve 5 is closed (OFF) and the electric pump 7 is stopped ( OFF), the pressure Pr in the supply pipe 13 is lower than the predetermined pressure Prq, and the catalyst temperature Ts is lower than the predetermined temperature Tsq.

  When the engine is started and the flowchart of FIG. 2 is started, the ECU 21 first performs control to input “0” indicating that the electric pump is stopped to the pump driving flag F indicating the driving state of the electric pump 7. Execute (Step S1).

  Next, the ECU 21 acquires the temperature Ts of the NOx purification catalyst 3 detected by the temperature sensor 23 (step S2), and executes control for determining whether or not the catalyst temperature Ts is equal to or higher than a predetermined threshold value α. (Step S3). The threshold value α is set to a temperature lower than a predetermined temperature Tsq as shown in FIG.

  When it is determined YES in step S3 and it is confirmed that the catalyst temperature Ts ≧ the threshold α, the ECU 21 starts from the time t1 when the catalyst temperature Ts reaches the threshold α, as shown in FIG. Control for calculating the change rate ΔTs of the catalyst temperature Ts until the time point t2 when the predetermined time has elapsed is executed (step S4). For example, the change rate ΔTs is obtained by subtracting the catalyst temperature Ts (= threshold value α) at the time point t1 from the catalyst temperature Ts at the time point t2, and the obtained temperature difference is the time difference (t2−t1) between the two time points. It can be calculated by dividing by.

  Next, the ECU 21 increases the catalyst temperature Ts up to the predetermined temperature Tsq (that is, the temperature at which urea water is sufficiently hydrolyzed to generate ammonia) based on the catalyst temperature change rate ΔTs calculated in step S4. Control for predicting the time tt1 (see FIG. 3 (e)) required for this is executed (step S5). That is, after obtaining the temperature difference between the catalyst temperature Ts at the present time (time point t2) and the predetermined temperature Tsq, the time required for the catalyst temperature Ts to rise by this temperature difference is determined as the catalyst temperature. The required time tt1 is predicted by calculating based on the change rate ΔTs. At this time, the larger the temperature change rate ΔTs, the faster the predetermined temperature Tsq is reached. Therefore, the required time tt1 is predicted to be shorter as the temperature change rate ΔTs is larger.

  When the prediction of the required time tt1 is completed in this way, the ECU 21 determines that the urea water pressure Pr in the supply pipe 13 is the predetermined pressure Prq (that is, the relief of the pressure control valve 17) when the electric pump 7 is driven. The time tt2 (see FIG. 3D) required to rise to (pressure) is acquired (step S6), and control for starting the counting of the built-in timer is executed (step S7). The required time tt2 for the urea water pressure Pr to reach the predetermined pressure Prq is obtained in advance by, for example, experiments and stored in the storage unit of the ECU 21.

  Next, the ECU 21 determines whether or not the count value C of the timer is equal to a time difference (tt1−tt2) between the required time tt1 predicted in step S5 and the required time tt2 acquired in step S6. Control to determine is executed (step S8). And when it determines with YES here, ie, when it is confirmed that time has passed since the time difference (tt1-tt2) from the time t2 when the timer starts counting, at the time t3, The drive of the electric pump 7 is started. Specifically, the count value C of the timer is reset (step S9), and “1” indicating that the pump is being driven is input to the pump drive flag F (step S10). A predetermined control signal is output to the pump 7 to start driving the electric pump 7 (step S11).

  When the electric pump 7 is driven as described above, at the time t3, as shown in FIG. 3B, the addition valve 5 is temporarily opened (ON) and collected in the supply pipe 13. The air that has been discharged is vented. When the air is exhausted, the addition valve 5 is closed again (OFF). Thereafter, at the time t4 when the pressure Pr of the urea water in the supply pipe 13 reaches the predetermined pressure Prq, for example, as indicated by a broken line in the figure. As described above, by performing control to repeatedly turn on and off the addition valve 5 at a predetermined duty ratio, a necessary amount of urea water is added into the exhaust passage 1.

  As described above, the drive start timing of the electric pump 7 is such that the pressure Pr in the supply pipe 13 is higher than the time when the catalyst temperature Ts is predicted to reach the predetermined temperature Tsq (the time when the required time tt1 has elapsed from the time t2). The time t3 is set earlier by the time tt2 required to reach the predetermined pressure Prq. Accordingly, when the required time tt2 elapses from the time point t3, the timing when the pressure Pr reaches the predetermined pressure Prq and the urea water starts to be added from the addition valve 5 is the timing when the catalyst temperature Ts reaches the predetermined temperature Tsq. (Both at time t4). Then, the urea water added into the exhaust passage 1 from the addition valve 5 at such timing is sufficiently hydrolyzed by the temperature of the exhaust gas that has risen above the predetermined temperature Tsq, and the resulting ammonia is converted into the above-described ammonia. By promoting the reduction reaction in the NOx purification catalyst 3, NOx in the exhaust gas is purified with a higher purification rate.

  Returning to the flowchart of FIG. 2 again, the control operation when NO is determined in step S3 will be described. If NO is determined in step S3, that is, if it is confirmed that the catalyst temperature Ts detected by the temperature sensor 23 is smaller than the threshold value α, the EUC 21 determines whether the pump drive flag F = 1. That is, it is determined whether or not the electric pump 7 has already been driven (step S12). If YES is determined here, the process proceeds to step S11 and the driving of the electric pump 7 is continuously maintained. That is, after the electric pump 7 is once driven, the catalyst temperature Ts may temporarily decrease for some reason and fall below the threshold value α. In such a case, the driving of the electric pump 7 should be stopped one by one. The drive is maintained.

  On the other hand, when it is determined NO in step S12 and it is confirmed that the pump drive flag F = 0, that is, when it is confirmed that the electric pump 7 has not been driven yet after the engine is started. Maintains the electric pump 7 in a stopped state (step S13) and returns.

  As described above, the exhaust purification system of this embodiment includes the selective reduction type NOx purification catalyst 3 provided on the exhaust passage 1 of the engine, and the exhaust passage 1 (upstream) upstream of the NOx purification catalyst 3. An addition valve 5 for adding urea water as a reducing agent in the side pipe 1a), an electric pump 7 for supplying urea water to the addition valve 5 through a supply pipe 13 from a storage tank 9 for storing the urea water, An ECU 21 as control means for controlling the operation of the addition valve 5 and the electric pump 7 and a temperature sensor 23 for detecting the temperature Ts of the NOx purification catalyst 3 are provided. When the electric pump 7 is driven after the engine is started, the timing at which the temperature Ts of the NOx purification catalyst 3 rises to a predetermined temperature Tsq at which the urea water is sufficiently hydrolyzed, and the supply pipe 13 The drive start timing of the electric pump 7 is determined so that the pressure Pr of the urea water reaches the predetermined pressure Prq and the timing at which the urea water from the addition valve 5 can be added coincides. Yes. According to such a configuration, there is an advantage that energy efficiency can be further improved by suppressing useless power consumption of the electric pump 7.

  That is, in the above embodiment, the timing at which the temperature Ts of the NOx purification catalyst 3 reaches the predetermined temperature Tsq (time point t4 in FIG. 3) is determined based on the detection value of the temperature sensor 23, and at the same timing, the supply pipe Since the drive start timing of the electric pump 7 is determined so that the pressure Pr of the urea water in 13 reaches the predetermined pressure Prq, the catalyst temperature Ts is low and it is not necessary to add urea water There is no wasteful pressurization of urea water by the electric pump 7, and there is an advantage that the electric power consumed by the electric pump 7 can be effectively reduced and the energy efficiency can be further improved.

  Moreover, since the addition of the urea water from the addition valve 5 can be started simultaneously with the catalyst temperature Ts reaching the predetermined temperature Tsq at which the urea water is sufficiently hydrolyzed, the drive control of the electric pump 7 as described above is performed. While reducing the power consumption, the addition of urea water is started at an appropriate timing to effectively promote the reduction reaction in the NOx purification catalyst 3, thereby improving the energy efficiency and the NOx purification performance. There is an advantage that both dimensions can be achieved.

  In particular, in the above embodiment, it is calculated when the temperature Ts of the NOx purification catalyst 3 is lower than the predetermined temperature Tsq (a predetermined period after the catalyst temperature Ts exceeds the threshold value α in the examples of FIGS. 2 and 3). Based on the temperature increase rate ΔTs of the NOx purification catalyst 3, the time tt1 until the catalyst temperature Ts reaches the predetermined temperature Tsq is predicted, and the predicted time tt1 and the electric pump 7 are driven to Since the drive start timing of the electric pump 7 is determined based on the required time tt2 until the pressure Pr of the urea water in the supply pipe 13 reaches the predetermined pressure Prq, the temperature rise of the NOx purification catalyst 3 is increased. By driving the electric pump 7 at an appropriate timing based on prediction using the rate ΔTs, there is an advantage that the power consumption can be more effectively reduced. .

  That is, in the above embodiment, the required time tt2 required to drive the electric pump 7 and raise the pressure Pr of the urea water to the predetermined pressure Prq from the predicted time tt1 until the catalyst temperature Ts reaches the predetermined temperature Tsq. The subtracted time is counted by a timer, and the electric pump 7 is driven when the count is completed (time t3 in FIG. 3). Therefore, the timing at which the urea water pressure Pr rises to the predetermined pressure Prq is set to the catalyst temperature. The time when Ts reaches the predetermined temperature Tsq (time t4 in the figure) can be accurately matched, and the period during which the electric pump 7 is wasted is brought closer to zero and the power consumption can be reduced more effectively. Can be planned.

  In the above embodiment, the electric pump is arranged so that the timing at which the temperature Ts of the NOx purification catalyst 3 reaches the predetermined temperature Tsq coincides with the timing at which the pressure Pr of the urea water in the supply pipe 13 reaches the predetermined pressure Prq. However, it is not always necessary to accurately match the arrival timing to the predetermined temperature Tsq and the arrival timing to the predetermined pressure Prq, and slightly differs from the arrival timing to the predetermined temperature Tsq. The electric pump 7 may be driven so that the pressure Pr in the supply pipe 13 reaches a predetermined pressure Prq at a predetermined timing. In any case, the temperature increase rate ΔTs of the NOx purification catalyst 3 is obtained, and when the increase rate ΔTs is small, the drive start timing of the electric pump 7 is delayed compared to when the increase rate ΔTs is large. If the drive start timing of the electric pump 7 is determined in conjunction with the arrival timing, the urea water pressure Pr is set to the predetermined pressure Prq at an appropriate timing according to the time when the catalyst temperature Ts reaches the predetermined temperature Tsq. There is an advantage that the addition of urea water from the addition valve 5 can be started at an appropriate time while effectively reducing the power consumption of the electric pump 7.

  Further, as another aspect, it is confirmed that the temperature Ts of the NOx purification catalyst 3 has reached the predetermined temperature Tsq based on the detection value of the temperature sensor 23, and the electric pump 7 is started to be driven after that time. After waiting for the pressure in the pipe 13 to reach the predetermined pressure Prq, the addition of urea water from the addition valve 5 may be started. Of course, if this is done, the addition of urea water from the addition valve 5 can only be started after a predetermined time lag (required time tt2 in FIG. 3) has elapsed after the catalyst temperature Ts reaches the predetermined temperature Tsq. It is somewhat disadvantageous in terms of purification performance. However, as shown in FIG. 3, the required time tt2 from when the electric pump 7 is driven until the pressure Pr in the supply pipe 13 reaches the predetermined pressure Prq is the temperature of the NOx purification catalyst 3 after the engine is started. Since Ts is considerably shorter than the time required to reach the predetermined temperature Tsq, even if there is a time lag as described above, it is considered that the effect on the NOx purification performance due to this is small.

  In the above embodiment, the temperature sensor 23 is provided at the end of the upstream pipe 1a corresponding to the upstream portion of the NOx purification catalyst 3 in the exhaust passage 1, and the temperature Ts of the NOx purification catalyst 3 is directly measured by the temperature sensor 23. For example, the temperature Ts of the NOx purification catalyst 3 is obtained by detecting the temperature of the exhaust gas flowing upstream from the NOx purification catalyst 3 by a predetermined distance and multiplying the detected temperature by a predetermined correction coefficient. You may do it. Further, the temperature Ts of the NOx purification catalyst 3 may be estimated based on the operating state of the engine determined from the engine load and the rotational speed, the duration in the operating state, and the like. In any case, in order to examine the temperature Ts of the NOx purification catalyst 3, it is only necessary to detect some parameter value related to the temperature Ts, and there is no particular limitation as to what state quantity is specifically detected.

  In the above embodiment, urea water is used as the reducing agent for promoting the reduction reaction in the NOx purification catalyst 3, but the present invention is not limited to this as long as the same effect can be obtained. For example, the NOx purification catalyst 3 Depending on the type, ammonia water or alcohols may be used as the reducing agent.

1 is a schematic view showing an exhaust emission control device for an engine according to an embodiment of the present invention. It is a flowchart for demonstrating control operation | movement of the said exhaust gas purification apparatus. It is a time chart for demonstrating control operation | movement of the said exhaust gas purification apparatus. FIG. 2 is a view corresponding to FIG. 1 for explaining a situation when urea water is collected after the engine is stopped.

DESCRIPTION OF SYMBOLS 1 Exhaust passage 3 NOx purification catalyst 5 Addition valve 7 Electric pump 9 Storage tank 13 Supply pipe 19 Switching valve 21 ECU (control means)
23 Temperature sensor (parameter value detection means)
Ts (NOx purification catalyst) temperature ΔTs Temperature increase rate Tsq Predetermined temperature Pr (Reducing agent) pressure Prq Predetermined pressure tt1 Estimated time (until the predetermined temperature is reached) tt2 Required time (until the predetermined pressure is reached)

Claims (4)

A selective reduction type NOx purification catalyst provided on the exhaust passage of the engine, an addition valve for adding a liquid reducing agent into the exhaust passage upstream of the NOx purification catalyst, and a storage tank for storing the reducing agent An engine exhaust purification device comprising: an electric pump for supplying a reducing agent to the addition valve through a predetermined supply pipe; and a control means for controlling the operation of the addition valve and the electric pump,
Parameter value detecting means for detecting a parameter value related to the temperature of the NOx purification catalyst,
The addition valve is controlled to add the reducing agent when the temperature of the NOx purification catalyst determined from the detection value of the parameter value detection means is equal to or higher than a predetermined temperature,
The control means obtains the temperature increase rate of the NOx purification catalyst when the temperature of the NOx purification catalyst is lower than the predetermined temperature, and when the temperature increase rate is small, the drive start timing of the electric pump compared to when it is large. Engine exhaust purification device characterized by delaying the engine. The exhaust emission control device for an engine according to claim 1 ,
The control means includes a timing at which the temperature of the NOx purification catalyst rises to the predetermined temperature, and a timing at which the pressure of the reducing agent in the supply pipe reaches a predetermined pressure so that the reducing agent can be added from the addition valve. The engine exhaust gas purification apparatus determines the drive start timing of the electric pump so as to match. The exhaust emission control device for an engine according to claim 2 ,
The control means predicts the time until the temperature of the NOx purification catalyst reaches the predetermined temperature based on the rate of temperature increase, and the predicted time and the reduction in the supply pipe after the electric pump is driven. The engine exhaust gas purification apparatus, wherein the drive start timing of the electric pump is determined based on a time required for the pressure of the agent to reach the predetermined pressure. The engine exhaust gas purification apparatus according to any one of claims 1 to 3 ,
The control means operates the switching valve provided in the supply pipe after the engine is stopped so that the reducing agent remaining in the supply pipe is returned to the storage tank by the suction force of the electric pump. An exhaust emission control device for an engine, wherein the flow of the agent is switched.

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