JP5602514B2 - NOx concentration measuring device - Google Patents

Description

  The present invention relates to a NOx concentration measuring apparatus.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, and the selective reduction catalyst A required amount of a reducing agent is added to the upstream side of the catalyst so that the reducing agent undergoes a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

  When attempting to reduce and purify NOx in exhaust gas using such a selective catalytic reduction catalyst, a NOx sensor is installed in the middle of the exhaust pipe to measure the concentration of NOx, and according to the measured value, the reducing agent concentration is reduced. Control of the amount of addition is performed (for example, refer to the following Patent Document 1).

  In general, the NOx sensor has a structure in which six layers of zirconia films are laminated. This type of zirconia film has an oxygen gas depending on the voltage applied between the electrodes formed on both sides of the zirconia film. There are oxygen pump characteristics that cause ion migration and oxygen concentration cell characteristics that an electromotive force is generated according to the difference in oxygen concentration inside and outside the zirconia membrane. By applying these characteristics, the NOx concentration in the exhaust gas I try to detect the amount.

  That is, in the NOx sensor, a first space and a second space into which exhaust gas is introduced are provided continuously in the second layer, and an air passage for referring to the oxygen concentration in the atmosphere is provided in the fourth layer. An internal heater for controlling the sensor temperature is installed between the 5th and 6th layers.

In the first space where the exhaust gas is first guided, the first zirconia film is operated as an oxygen pump by applying a voltage to remove O ₂ in the exhaust gas and reduce NO ₂ to NO. . At this time, the performance control of the oxygen pump is performed to keep the oxygen concentration in the first space constant so as not to decompose to NO.

  As a result, the exhaust gas from which all oxygen ions other than NO have been removed in the first space moves to the second space, so that NO electrolysis is performed using the third layer zirconia film as the electrolyte in the second space. At the time of decomposition, the third layer zirconia film is used as an oxygen concentration cell, and the current flowing in accordance with the oxygen concentration difference between the second space and the air passage in the atmospheric atmosphere is measured.

  Since only NO is present as the oxygen source during electrolysis in the second space, the current measured at this time is an amount corresponding to NO, so the NOx concentration in the exhaust gas is controlled based on the current value. It can be calculated by performing arithmetic processing in the apparatus.

JP 2006-57576 A

  However, if the exhaust pipe downstream of the NOx sensor is equipped with an exhaust brake that closes the exhaust flow path and increases the exhaust resistance during braking to increase the engine braking effect by compressing the piston even during the exhaust stroke. There is a problem in that the NOx sensor outputs an abnormal value when the exhaust brake is operated, and the actual situation is that the accelerator is off and almost no NOx is generated (no fuel injection). Nevertheless, there is a problem in that excessive reducing agent is added based on the abnormal value of the NOx sensor.

In other words, depending on the vehicle model and the like, there may be a case where the NOx sensor placement space can be secured only upstream of the exhaust brake due to layout restrictions in the engine room. When the amount of O _{2 in} the first space of the NOx sensor increased significantly, an erroneous measurement occurred as if O _{2 in} the first space also flowed into the second space and NOx was generated.

More specifically, since the performance control of the oxygen pump is performed so that the oxygen concentration in the first space is kept constant, the current value for this oxygen pump is increased. In the existing NOx sensor, since the pressure increase due to the exhaust brake is not assumed, the current value for the oxygen pump is short-circuited beyond the allowable value, thereby further increasing the outflow of O ₂ into the second space. As a result of short-circuiting the measured current value exceeding the allowable value, the phenomenon that the NOx sensor outputs an abnormal value has been caused.

  The present invention has been made in view of the above-described circumstances, so that even if the NOx sensor outputs an abnormal value when the exhaust brake is operated, the possibility of adversely affecting the control system based on the NOx concentration can be avoided. An object of the present invention is to provide a NOx concentration measuring apparatus.

The present invention relates to a NOx concentration measuring device including a NOx sensor provided in an exhaust pipe upstream of an exhaust brake, and a control device that calculates a NOx concentration based on an output signal of the NOx sensor.
A selective reduction catalyst is provided in the middle of the exhaust pipe through which the exhaust gas flows, and urea water addition means for injecting urea water as a reducing agent is installed in the exhaust pipe upstream of the selective reduction catalyst, the urea water The exhaust pipe is equipped with an exhaust brake upstream of the adding means.
During the operation signal of the exhaust brake is detected to constitute the control device to the output signal from the NOx sensor handled have a zero temporarily output, is added during this period of the urea water temporarily suspend so The present invention relates to a NOx concentration measuring device characterized by the above.

Thus, in this way, even if the NOx sensor outputs an abnormal value due to pressure increase while the exhaust brake is operating, the output signal is temporarily treated as zero output by the control device. In addition, the possibility of adversely affecting the control system based on the NOx concentration, such as excessive addition of urea water based on the abnormal value of the NOx sensor, is avoided, and the exhaust brake during operation, because the accelerator is in a state which is not generated substantially NOx they become braking state turned off, the output signal from the NOx sensor be treated as zero temporarily output, urea water There is no possibility of inconvenience that a large amount of NOx is discharged out of the vehicle because the control system based on the NOx concentration does not function such that the addition of NOx temporarily stops.

According to the above-described NOx concentration measuring device of the present invention, even if the NOx sensor outputs an abnormal value when the exhaust brake is operated, the control device treats the output signal from the NOx sensor as zero output temporarily. Therefore, it is possible to avoid the possibility of adversely affecting the control system based on the NOx concentration, such as excessive urea water being added based on the abnormal value of the NOx sensor. Can play.

It is the schematic which shows an example of the form which implements this invention. It is a flowchart regarding the process of NOx sensor output in the control apparatus of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 and 2 show an example of an embodiment of the present invention. In the example shown here, an exhaust pipe 4 through which exhaust gas 3 discharged from a diesel engine 1 through an exhaust manifold 2 flows is shown. In the middle of this, a selective reduction catalyst 5 having the property of selectively reacting NOx with ammonia even in the presence of oxygen is provided.

A urea water addition injector 7 (urea water addition means) for injecting urea water 6 as a reducing agent is installed in the exhaust pipe 4 upstream of the selective reduction catalyst 5 and the selective reduction catalyst. Immediately after 5, an NH ₃ slip catalyst 8 that oxidizes excess ammonia as a countermeasure against leaked ammonia is provided.

  Further, an existing NOx sensor 9 as already described in detail as the prior art is installed in the most upstream part of the exhaust pipe 4, and the exhaust passage is closed at the downstream side of the NOx sensor 9 during braking. An exhaust brake 10 is provided that increases the exhaust resistance to increase the effect of the engine brake by compressing the piston even in the exhaust stroke.

  The output signal 9a of the NOx sensor 9 is input to a control device 11 that also serves as an engine control computer (ECU: Electronic Control Unit). The concentration of NOx is calculated by calculation processing based on the output signal 9a, and the addition amount of the urea water 6 is determined based on the NOx concentration calculated here and is output to the injector 7 as a control signal 7a. It has become.

  Here, in determining the amount of urea water 6 to be added, it is necessary to calculate the NOx generation amount based on the calculated NOx concentration, so the flow rate of the exhaust gas 3 must be grasped. Also serves as an engine control computer and already has information on the rotational speed and load of the diesel engine 1 based on the detection signals 12a and 13a from the rotation sensor 12 and the accelerator sensor 13, so that exhaust gas can be exhausted using them. 3 is used to control the amount of urea water 6 added.

  Further, the control device 11 is in the middle of traveling based on the detection signals 12a and 13a from the rotation sensor 12 and the accelerator sensor 13 under the condition that the ON signal 14a from the exhaust brake switch 14 in the driver's seat (not shown) is input. When the accelerator-off is detected, an operation signal 10a of the exhaust brake 10 is output to the magnetic valve 15 of the air drive system of the exhaust brake 10 to operate the exhaust brake 10.

  While the operation signal 10a of the exhaust brake 10 is detected in the control device 11, the output signal 9a from the NOx sensor 9 is temporarily treated as zero output. The addition of water 6 is temporarily interrupted.

  That is, as shown in the flowchart in FIG. 2, when the output signal 9a from the NOx sensor 9 is recognized by the control device 11 in step S1, it is determined whether or not the exhaust brake 10 is in operation in the next step S2. (Confirmation of the presence or absence of the operation signal 10a toward the magnetic valve 15) If the exhaust brake 10 is in operation, the process proceeds to "YES" and the output signal 9a from the NOx sensor 9 is temporarily zero in step S3. If the exhaust brake 10 is not in operation, the process proceeds to “NO” and the output signal 9a from the NOx sensor 9 is adopted as it is in step S4 and used for controlling the amount of urea water 6 added. It has become.

  In FIG. 1, reference numeral 16 denotes an oxidation catalyst that enhances the function of oxidizing unburned fuel in the exhaust gas 3, and 17 denotes a particulate filter that collects particulates in the exhaust gas 3. After the main injection on the engine 1 side, post injection is performed at a non-ignition timing later than the compression top dead center, and unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 3 by this post injection. The oxidation reaction is performed by the oxidation catalyst 16, and the particulate filter 17 can be forcibly regenerated by the reaction heat.

  Thus, in this way, even if the NOx sensor 9 outputs an abnormal value due to a pressure increase while the exhaust brake 10 is operating, the output signal 9a is temporarily output by the control device 11 to zero. Therefore, the possibility that excessive urea water 6 is added based on the abnormal value of the NOx sensor 9 (adverse effect on the control system based on the NOx concentration) is avoided in advance. In addition, when the exhaust brake 10 is operated, since the brake is in a state where the accelerator is off and NOx is not substantially generated, the output signal 9a from the NOx sensor 9 is temporarily zero. Even if it is handled as an output, there is no possibility of inconvenience that a large amount of NOx is discharged outside the vehicle due to the temporary interruption of the addition of the urea water 6.

  Therefore, according to the above embodiment, even when the NOx sensor 9 outputs an abnormal value when the exhaust brake 10 is operated, the control device 11 temporarily treats the output signal 9a from the NOx sensor 9 as zero output. Therefore, excessive urea water 6 is added based on the abnormal value of the NOx sensor 9 in spite of the fact that the accelerator is off and the NOx is hardly generated. It is possible to avoid the fear that the control system is adversely affected (adverse effects on the control system based on the NOx concentration).

It should be noted that the NOx concentration measuring device of the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the scope of the present invention.

4 Exhaust pipe 9 NOx sensor 9a Output signal 10 Exhaust brake 10a Actuation signal 11 Controller

Claims (1)

In a NOx concentration measuring device comprising: a NOx sensor provided in an exhaust pipe upstream from an exhaust brake; and a control device that calculates a NOx concentration based on an output signal of the NOx sensor;
A selective reduction catalyst is provided in the middle of the exhaust pipe through which the exhaust gas flows, and urea water addition means for injecting urea water as a reducing agent is installed in the exhaust pipe upstream of the selective reduction catalyst, the urea water The exhaust pipe is equipped with an exhaust brake upstream of the adding means.
During the operation signal of the exhaust brake is detected to constitute the control device to the output signal from the NOx sensor handled have a zero temporarily output, is added during this period of the urea water temporarily suspend so A NOx concentration measuring device characterized by that.

Images