JP4867675B2 - Reducing agent supply device - Google Patents

Description

  The present invention relates to a reducing agent supply device that supplies a reducing agent to exhaust gas from an engine.

  2. Description of the Related Art Conventionally, a reducing agent supply device that supplies a reducing agent to exhaust gas in order to reduce and purify nitrogen oxide (NOx) contained in exhaust gas from an engine is known (see, for example, Patent Document 1). This reducing agent is, for example, urea water, and ammonia (NH 3) generated by decomposition of urea reacts with NO x by a catalyst to generate harmless nitrogen (N 2) and water (H 2 O). Purified. And a reducing agent is injected from the injection hole opened inside an exhaust pipe, spreads in exhaust gas, and is guide | induced to a catalyst.

By the way, since the flow rate of the exhaust gas constantly varies according to the operating state of the engine, the way in which the injected reducing agent spreads also varies with the exhaust gas flow rate. That is, when the exhaust gas flow rate is large, the injected reducing agent is swept away by the exhaust gas and cannot sufficiently spread in the radial direction. Conversely, when the exhaust gas flow velocity is small, the injected reducing agent pushes the exhaust gas and spreads rapidly in the radial direction. As a result, there is a risk that the reducing agent spray is biased in the radial direction and partially becomes high in concentration, or the amount of reducing agent attached to the pipe wall increases, which may reduce the purification efficiency of exhaust gas. is there.
JP 2006-125324 A

  The present invention has been made to solve the above-described problems, and its object is to suppress fluctuations in how the reducing agent spreads into the exhaust gas even when the exhaust gas flow rate fluctuates in the reducing agent supply device. It is to prevent a reduction in exhaust gas purification efficiency.

[Means of Claim 1]
The reducing agent supply apparatus according to claim 1 supplies the reducing agent to the exhaust gas from the engine. The reducing agent supply device is attached to a supply pump that sucks and discharges the reducing agent from a predetermined tank and an exhaust pipe through which the exhaust gas passes, and injects the reducing agent discharged from the supply pump into the exhaust pipe. An addition valve and control means for controlling the pressure of the reducing agent injected from the addition valve in accordance with a change in the flow rate of the exhaust gas are provided.
The addition valve injects the reducing agent obliquely with respect to the flow direction of the exhaust pipe.
In addition, the control means increases the pressure of the reducing agent injected from the addition valve when the exhaust gas flow rate increases, strengthens the penetration force of the reducing agent spray from the addition valve to the exhaust gas, and adds when the exhaust gas flow rate decreases. The pressure of the reducing agent injected from the valve is reduced to weaken the penetration force of the reducing agent spray from the addition valve to the exhaust gas.
Furthermore, the control means changes the valve opening degree of the addition valve in a pulse shape between an off state indicating a fully closed state and an on state indicating a state opened more than the fully closed state, thereby reducing the addition valve by the addition valve. When the pressure of the reducing agent injected from the addition valve is changed in accordance with the change in the flow rate of the exhaust gas, the ratio of the on-state time to one pulse cycle is varied. .

As a result, when the exhaust gas flow velocity is large, the reducing agent spray can be expanded in the radial direction against the exhaust gas flow by increasing the pressure of the injected reducing agent and strengthening the penetration of the reducing agent spray. it can. Conversely, when the exhaust gas flow rate is small, the rapid spread of the reducing agent spray in the radial direction can be suppressed by reducing the pressure of the injected reducing agent and weakening the penetration force of the reducing agent spray. As a result, even if the exhaust gas flow rate fluctuates, fluctuations in how the reducing agent spreads into the exhaust gas can be suppressed, and reduction in exhaust gas purification efficiency can be prevented.
Further, when the pressure of the reducing agent is changed in accordance with the change in the exhaust gas flow rate, the ratio of the on-state time to one pulse cycle is varied to inject from the addition valve in accordance with the change in the exhaust gas flow rate. Even when it is necessary to change the pressure of the reducing agent, it is possible to make the injection amount of the reducing agent substantially coincide with the target value.
For example, consider a case where the target value of the injection amount does not change before and after the fluctuation of the exhaust gas flow velocity. When the pressure of the reducing agent injected from the addition valve is increased in accordance with the fluctuation of the exhaust gas flow rate, the amount of reducing agent injected can be made substantially equal to the target value by reducing the ratio. Further, when the pressure of the reducing agent injected from the addition valve is reduced, the injection amount of the reducing agent can be substantially matched with the target value by increasing the ratio.

[Means of claim 2]
According to the reducing agent supply apparatus of the second aspect, the control means varies the supply amount of the reducing agent from the supply pump to the addition valve, and changes the pressure of the reducing agent injected from the addition valve.

[Means of claim 3 ]
The reducing agent supply apparatus according to claim 3 includes engine speed detecting means for detecting the engine speed and accelerator opening degree detecting means for detecting the accelerator opening degree. The control means includes engine speed detecting means and The flow rate of the exhaust gas is estimated using the detection value obtained from the accelerator opening detection means.
Thereby, the value of the factor necessary for estimating the exhaust gas flow velocity can be acquired by using an existing sensor that functions as an engine speed detection means or an accelerator opening degree detection means. For this reason, it is not necessary to equip the reducing agent supply device with a new sensor for detecting the exhaust gas flow velocity.

The reducing agent supply device of the best mode 1 supplies a reducing agent to exhaust gas from an engine. The reducing agent supply device is attached to a supply pump that sucks and discharges the reducing agent from a predetermined tank and an exhaust pipe through which the exhaust gas passes, and injects the reducing agent discharged from the supply pump into the exhaust pipe. An addition valve and control means for controlling the pressure of the reducing agent injected from the addition valve in accordance with a change in the flow rate of the exhaust gas are provided.
The addition valve injects the reducing agent obliquely with respect to the flow direction of the exhaust pipe.
In addition, the control means increases the pressure of the reducing agent injected from the addition valve when the exhaust gas flow rate increases, strengthens the penetration force of the reducing agent spray from the addition valve to the exhaust gas, and adds when the exhaust gas flow rate decreases. The pressure of the reducing agent injected from the valve is reduced to weaken the penetration force of the reducing agent spray from the addition valve to the exhaust gas.

  The control means varies the supply amount of the reducing agent from the supply pump to the addition valve, and changes the pressure of the reducing agent injected from the addition valve. In addition, the control means changes the valve opening of the addition valve in a pulse shape between an off state indicating a fully closed state and an on state indicating a state opened more than the fully closed state, thereby reducing the addition valve by the addition valve. When the pressure of the reducing agent injected from the addition valve is changed in accordance with the change in the flow rate of the exhaust gas, the ratio of the on-state time to one pulse cycle is varied. .

The reducing agent supply device includes an engine speed detecting means for detecting the engine speed and an accelerator opening detecting means for detecting the accelerator opening, and the control means includes the engine speed detecting means and the accelerator opening. The flow rate of the exhaust gas is estimated using the detection value obtained from the detection means .

[Configuration of Example 1]
The structure of the reducing agent supply apparatus 1 of Example 1 is demonstrated using FIG.
The reducing agent supply device 1 supplies a reducing agent to exhaust gas from an engine, and is used to reduce and purify nitrogen oxides (NOx) contained in the exhaust gas. The reducing agent is, for example, urea water, and ammonia (NH 3) generated by decomposition of urea reacts with NO x by the catalyst 2 to generate harmless nitrogen (N 2) and water (H 2 O). Purified.

  The reducing agent supply apparatus 1 includes a supply pump 5 that sucks and discharges the reducing agent from a predetermined tank 4, an addition valve 7 that injects the reducing agent discharged from the supply pump 5 into the exhaust pipe 6, and a supply pump 5 and an electronic control unit (ECU) 8 for controlling the operation of the addition valve 7.

  The supply pump 5 includes, for example, a rotor on which a permanent magnet is mounted and a stator on which a coil is wound, and a brushless motor 11 that generates torque by the interaction between a magnetic field generated by the permanent magnet and a current supplied to the coil. Is an actuator. Then, the ECU 8 controls the energization of the coil, thereby changing the rotation speed and torque of the brushless motor 11 and operating the supply amount and discharge pressure of the reducing agent.

  The addition valve 7 is attached to an exhaust pipe 6 through which exhaust gas passes, and a tip portion 13 including an injection hole projects into the exhaust pipe 6. Then, the reducing agent is guided from the supply pump 5 to the addition valve 7 and directly injected into the exhaust pipe 6. The injected reducing agent is mixed with exhaust gas and then guided to the catalyst 2 to purify NOx as described above.

  The addition valve 7 has a solenoid coil (not shown) that magnetically attracts a valve element (not shown) to the valve opening side when energized. Then, the ECU 8 outputs a pulsed control signal to a drive circuit (not shown) for energizing the solenoid coil, thereby changing the valve opening of the addition valve 7 in a pulsed manner, and the reduction by the addition valve 7. The injection amount of the agent is substantially matched with the target value.

  That is, as shown in FIG. 2, the ECU 8 adds the valve by changing the valve opening in a pulse shape between an off state indicating the fully closed state and an on state indicating the open state rather than the fully closed state. The amount of reducing agent injected by the valve 7 is made to substantially match the target value. Then, the ECU 8 varies the duty ratio of the control signal in accordance with the target value of the injection amount, thereby causing the addition valve 7 to inject an amount of reducing agent that is sufficient for exhaust gas purification.

  The ECU 8 is a well-known microcomputer composed of a storage device such as a CPU, ROM, and RAM, an input device, an output device, and the like that perform a control function and an arithmetic function. Various types of equipment are used according to the operating state of the engine. The actuator is commanded to control the drive of the device. That is, the ECU 8 functions as a control unit that controls the operation of the supply pump 5, the addition valve 7, and the like.

  The reducing agent supply device 1 also includes an engine speed sensor 15 as an engine speed detecting means for detecting the engine speed, and an accelerator opening sensor 16 as an accelerator opening detecting means for detecting an accelerator opening. . Then, the ECU 8 estimates the exhaust gas flow velocity using detection values obtained from the engine speed sensor 15 and the accelerator opening sensor 16.

  Then, the ECU 8 controls the pressure of the reducing agent injected from the addition valve 7 (that is, the discharge pressure of the reducing agent by the supply pump 5) according to the estimated value of the exhaust gas flow velocity. For example, as shown in FIG. 3, the ECU 8 stores the command value of the discharge pressure of the supply pump 5 with respect to the estimated value of the exhaust gas flow velocity in the form of a predetermined linear function, and the command value of the discharge pressure is increased as the estimated value increases. increase.

  That is, when the exhaust gas flow rate is high, the reducing agent spray is swept away by the exhaust gas and cannot spread sufficiently in the radial direction (see FIG. 4A), and is closer to the addition valve 7 than the central axis of the exhaust pipe 6. Unevenly formed with a high concentration. For this reason, the catalyst 2 on the opposite side of the addition valve 7 is not effectively used and ammonia discharged without being reacted increases, or the reducing agent attached to the pipe wall on the side of the addition valve 7 increases.

In addition, when the exhaust gas flow rate is small, the reducing agent spray rapidly spreads in the radial direction by pushing the exhaust gas (see FIG. 4B), and is higher than the central axis of the exhaust pipe 6 on the opposite side of the addition valve 7. Formed to a concentration. For this reason, the catalyst 2 on the side of the addition valve 7 is not effectively used, and ammonia discharged without being reacted increases, or the reducing agent attached to the tube wall on the opposite side of the addition valve 7 increases.
Therefore, the ECU 8 corrects the reducing agent spray bias by changing the discharge pressure of the supply pump 5 and operating the reducing agent spray penetration force against the reducing agent spray bias based on the fluctuation of the exhaust gas flow velocity. (See FIGS. 4C and 4D).

  Further, when the ECU 8 changes the discharge pressure of the supply pump 5 in accordance with the change in the flow rate of the exhaust gas, the ratio of the on-state time to one pulse period is varied with respect to the valve opening degree of the addition valve 7. For example, when the target value of the injection amount does not change before and after the fluctuation of the exhaust gas flow rate and the discharge pressure of the supply pump 5 is increased according to the fluctuation of the exhaust gas flow rate, the injection amount of the reducing agent is reduced by reducing the above ratio. Can be substantially matched with the target value (see FIG. 2). On the other hand, when the discharge pressure of the supply pump 5 is reduced, the injection amount of the reducing agent can be substantially matched with the target value by increasing the ratio.

[Effect of Example 1]
According to the reducing agent supply apparatus 1 of the first embodiment, the addition valve 7 is attached to the exhaust pipe 6 and directly injects the reducing agent discharged from the supply pump 5 into the exhaust pipe 6. Accordingly, the discharge pressure of the supply pump 5 is controlled.
As a result, when the exhaust gas flow velocity is large, the reducing agent spray can be expanded in the radial direction against the exhaust gas flow by increasing the pressure of the injected reducing agent and strengthening the penetration of the reducing agent spray. it can. Conversely, when the exhaust gas flow rate is small, the rapid spread of the reducing agent spray in the radial direction can be suppressed by reducing the pressure of the injected reducing agent and weakening the penetration force of the reducing agent spray. As a result, even if the exhaust gas flow rate fluctuates, fluctuations in how the reducing agent spreads into the exhaust gas can be suppressed, and reduction in exhaust gas purification efficiency can be prevented.

Further, the ECU 8 changes the valve opening of the addition valve 7 in a pulse shape between the off state and the on state, thereby causing the injection amount of the reducing agent by the addition valve 7 to substantially coincide with the target value, and the flow rate of the exhaust gas. When the discharge pressure of the supply pump 5 is changed in accordance with the change in the ratio, the ratio of the on-state time to one pulse period is varied.
Thereby, even when the exhaust gas flow rate fluctuates and the pressure of the reducing agent injected from the addition valve 7 needs to be changed, the amount of reducing agent injected can be made to substantially match the target value.

  The ECU 8 of the first embodiment varies the duty ratio of the long-cycle pulse control signal and operates the time during which the valve opening is on to adjust the injection amount of the reducing agent to substantially match the target value. This method is adopted, but the duty ratio of the control signal of the short cycle pulse is varied, and the amount of reducing agent injection is targeted by substantially matching the valve opening to a predetermined value between the on state and the off state. You may employ | adopt the area metering system made to substantially correspond to a value.

Further, the ECU 8 estimates the exhaust gas flow velocity using the detection values obtained from the engine speed sensor 15 and the accelerator opening sensor 16.
Thereby, the value of the factor required for estimating the exhaust gas flow velocity using the existing sensor can be acquired. For this reason, it is not necessary to equip the reducing agent supply apparatus 1 with a new sensor for detecting the exhaust gas flow velocity .

[Reference Example 1]
As shown in FIG. 5, the reducing agent supply apparatus 1 of Reference Example 1 includes a compressor 18 as a pneumatic feeding means that pressurizes and discharges air, and the addition valve 7 has a flow path for air discharged from the compressor 18. It opens and closes with respect to 19 and operates supply of the reducing agent discharged from the supply pump 5 to the flow path 19. Further, the reducing agent supply apparatus 1 includes a nozzle 20 at the tip of the flow path 19. The nozzle 20 opens in the direction of the flow of exhaust gas at the center inside the exhaust pipe 6 and injects the reducing agent mixed with the air supplied from the addition valve 7 and discharged from the compressor 18 into the exhaust pipe 6.

  The ECU 8 controls the pressure of the reducing agent supplied from the addition valve 7 to the flow path 19 and the pressure of air discharged from the compressor 18 according to the exhaust gas flow rate. That is, the ECU 8 controls the discharge pressure of the supply pump 5 and the discharge pressure of the compressor 18 according to the estimated value of the exhaust gas flow velocity. That is, as in FIG. 3, the ECU 8 stores the command values of the discharge pressure of the supply pump 5 and the compressor 18 with respect to the estimated value of the exhaust gas flow velocity in the form of a predetermined linear function, respectively, and the supply pump increases as the estimated value increases. 5 and the discharge pressure command value of the compressor 18 are increased.

  As a result, the penetration of the reducing agent spray on the exhaust gas can be strengthened or weakened. Decline can be prevented.

  That is, when the exhaust gas flow rate is large, the reducing agent spray is swept away by the exhaust gas and cannot spread sufficiently in the radial direction (see FIG. 6A), and is concentrated near the central axis of the exhaust pipe 6 to a high concentration. It is formed. For this reason, the catalyst 2 on the outer peripheral side closer to the tube wall is not effectively used, and ammonia discharged without being reacted increases.

Further, when the exhaust gas flow rate is small, the reducing agent spray spreads radially in the direction of pushing the exhaust gas (see FIG. 6B). For this reason, the reducing agent which does not reach the catalyst 2 and adheres to the pipe wall increases.
Therefore, the ECU 8 operates the penetrating force of the reducing agent spray by changing the discharge pressure of the supply pump 5 and the discharge pressure of the compressor 18 against the bias of the reducing agent spray based on the fluctuation of the exhaust gas flow velocity, thereby reducing the reducing agent spray. (See FIGS. 6C and 6D).

[Modification]
The ECU 8 according to the first embodiment and the reference example 1 estimates the exhaust gas flow velocity using the detection values obtained from the engine speed sensor 15 and the accelerator opening sensor 16, but a dedicated sensor for detecting the exhaust gas flow velocity is provided in the exhaust pipe 6. It may be equipped and the exhaust gas flow velocity may be detected directly.

Moreover, although ECU8 of the reference example 1 varied both the discharge pressure of the supply pump 5 and the discharge pressure of the compressor 18 according to the exhaust gas flow velocity, either one of the discharge pressure of the supply pump 5 or the discharge pressure of the compressor 18 is changed. Even if it is made variable, the penetration force of the reducing agent spray can be manipulated.

It is a block diagram of a reducing agent supply apparatus (Example 1). It is a time chart which shows transition of the valve opening degree of an addition valve (Example 1). (Example 1) which is a control map which shows the correlation with the estimated value of exhaust gas flow velocity, and the command value of the discharge pressure of a supply pump. (A) is explanatory drawing which shows the reducing agent spray before the correction | amendment with large exhaust gas flow velocity and correction, (b) is explanatory drawing which shows the reducing agent spray before small exhaust gas flow velocity and correction, (c) is exhaust gas flow velocity. It is explanatory drawing which shows the reducing agent spray after large and correction, (d) is explanatory drawing which shows the reducing agent spray after small exhaust gas flow velocity and correction (Example 1). It is a block diagram of a reducing agent supply apparatus ( reference example 1 ). (A) is explanatory drawing which shows the reducing agent spray before the correction | amendment with large exhaust gas flow velocity and correction, (b) is explanatory drawing which shows the reducing agent spray before small exhaust gas flow velocity and correction, (c) is exhaust gas flow velocity. It is explanatory drawing which shows the reducing agent spray which is large and corrected, (d) is explanatory drawing which shows the reducing agent spray after correction | amendment with small exhaust gas flow velocity ( reference example 1 ).

DESCRIPTION OF SYMBOLS 1 Reducing agent supply apparatus 4 Tank 5 Supply pump 6 Exhaust pipe 7 Addition valve 8 ECU (control means)
15 Engine speed sensor (Engine speed detector)
16 Accelerator opening sensor (Accelerator opening detecting means)
18 compressors
1 9 passage
20 nozzles

Claims (3)

In the reducing agent supply device that supplies the reducing agent to the exhaust gas from the engine,
A supply pump for sucking and discharging the reducing agent from a predetermined tank;
An addition valve that is attached to an exhaust pipe through which exhaust gas passes and injects a reducing agent discharged from the supply pump into the exhaust pipe;
Control means for controlling to change the pressure of the reducing agent injected from the addition valve according to the change in the flow rate of the exhaust gas,
The addition valve injects the reducing agent obliquely with respect to the flow direction of the exhaust pipe,
The control means includes
When the flow rate of the exhaust gas increases, the pressure of the reducing agent injected from the addition valve is increased to increase the penetration force of the reducing agent spray from the addition valve to the exhaust gas,
When the flow rate of the exhaust gas is reduced, the pressure of the reducing agent injected from the addition valve is reduced to weaken the penetration force of the reducing agent spray from the addition valve to the exhaust gas,
Further, the control means includes
By changing the valve opening degree of the addition valve in a pulse shape between an off state indicating a fully closed state and an on state indicating a state opened more than the fully closed state, an injection amount of the reducing agent by the addition valve Approximately match the target value,
A reducing agent supply apparatus , wherein when the pressure of the reducing agent injected from the addition valve is changed in accordance with a change in the flow rate of exhaust gas, the ratio of the on-state time to one pulse period is varied . The reducing agent supply apparatus according to claim 1,
The control means changes the pressure of the reducing agent injected from the addition valve by changing the amount of the reducing agent supplied from the supply pump to the addition valve. In the reducing agent supply apparatus according to claim 1 or 2,
An engine speed detecting means for detecting the engine speed and an accelerator opening detecting means for detecting the accelerator opening;
The control means estimates a flow rate of exhaust gas using detection values obtained from the engine speed detection means and the accelerator opening detection means .

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