JP4483394B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to an exhaust emission control device that processes exhaust particulates of, for example, a diesel engine.

  In the case where a filter (DPF) is disposed in the exhaust system in order to process exhaust particulates (carbon particles, etc.) discharged from a diesel engine, the filter is removed when the particulate collection amount in the filter reaches a predetermined amount. The filter is regenerated by burning the collected particulates by heating with a heating device, raising the exhaust gas temperature by changing the fuel injection timing, or performing so-called post-injection.

  In this case, a differential pressure sensor that detects the differential pressure between the upstream pressure and the downstream pressure of the filter is provided to determine whether the particulate collection amount has reached a predetermined amount, that is, whether the filter is to be regenerated. However, if there is a detection error in the differential pressure sensor, it is difficult to accurately grasp the regeneration timing of the filter.

Therefore, one that performs zero point calibration of the differential pressure sensor during engine idle operation (for example, Patent Document 1), one that performs zero point calibration of the differential pressure sensor immediately before or after the engine key switch is turned on (for example, Patent Document 1) 2).
JP2002-206419 JP2003-314248

  However, as in Patent Document 1, when the engine is operating, the differential pressure is unstable depending on the exhaust pulsation and the degree of clogging of the filter, and it is difficult to calibrate the zero point with high accuracy.

  Further, in Patent Document 2, the zero point calibration is performed immediately before the engine key switch is turned on or immediately after the engine key switch is turned on. Depending on the atmospheric temperature of the differential pressure sensor at the time of zero point calibration or the temperature of the differential pressure sensor itself, Since the output value varies, it is difficult to calibrate the zero point accurately.

  It is an object of the present invention to accurately perform zero point calibration of a differential pressure sensor when the engine is stopped.

The present invention includes a filter that is disposed in an exhaust passage of an engine and collects particulates in exhaust, a differential pressure sensor that detects a differential pressure between an exhaust pressure on the upstream side of the filter and an exhaust pressure on the downstream side of the filter, in the exhaust purification apparatus provided with a zero-point calibration means for performing a zero-point calibration of the differential pressure sensor in the engine stop state, the zero point calibration means, the engine temperature exceeds a predetermined temperature, the outside air temperature is Ru near the predetermined temperature or less If so, perform zero point calibration.

  According to the present invention, the zero point calibration can be performed at a temperature as close as possible to the condition for determining the regeneration timing of the filter by monitoring the output of the differential pressure sensor, and the zero point calibration of the differential pressure sensor can be accurately performed. Can be done.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In FIG. 1, 20 is a diesel engine, 21 is an intake passage, and 22 is an exhaust passage. The exhaust passage 22 is provided with a filter 1 that collects particulates in the exhaust.

  When the collected amount of the particulates of the filter 1 reaches a predetermined value, the controller 30 is provided to perform the regeneration process of the filter 1. The controller 30 includes a microprocessor, a memory, an input / output interface, and the like.

  In order to detect a pressure difference between the upstream and downstream of the filter 1, a differential pressure sensor 3 is provided in a differential pressure detection passage that bypasses the filter 1. Further, an engine rotation speed sensor 6 and an engine load sensor 7 are provided for detecting the engine exhaust flow rate, and a water temperature sensor 10 is provided for detecting the engine temperature (cooling water temperature). Moreover, although not shown in figure, the outside temperature sensor etc. which detect outside temperature are provided.

  The outputs of these sensors are sent to the controller 30, and the controller 30 determines the particulate collection amount of the filter 1 based on them, and performs the regeneration processing of the filter 1 at a predetermined timing.

  The differential pressure between the upstream and downstream of the filter 1 increases as the particulate collection amount increases, but fluctuates according to the exhaust flow rate at that time, and the exhaust flow rate increases at the same collection amount. The differential pressure increases. That is, when the differential pressure detected by the differential pressure sensor 3 reaches a predetermined pressure set based on the exhaust gas flow rate, it is determined that the filter 1 is to be regenerated and the filter 1 is regenerated. In this regeneration process, the injection timing of the fuel injected from the fuel injection device (for example, common rail type injection device) 2 of the diesel engine 20 is delayed from the injection timing during normal operation, or is injected once more after normal injection ( This is done by raising the exhaust gas temperature by injecting it (post-injection), etc., and incinerating it.

  On the other hand, since an error occurs in detection of the differential pressure sensor 3 due to a change with time or the like, the controller 30 performs zero point calibration of the differential pressure sensor 3.

  The processing content of the zero point calibration of the differential pressure sensor 3 will be described based on the flowchart of FIG.

  In step S1, it is checked whether the engine key switch is turned off.

  In step S2, when the engine key switch is turned off, it is checked whether the engine is stopped (engine rotation is almost 0). If the engine is stopped, the process proceeds to step S3.

  In step S3, it is determined whether or not the engine coolant temperature Tw is equal to or higher than the reference temperature a.

  The reference temperature a is, for example, an engine coolant temperature that is equivalent to a temperature condition at 60 ° C. when the regeneration timing of the filter 1 is determined by monitoring the output of the differential pressure sensor 3 during engine operation.

  When the engine coolant temperature Tw is lower than the reference temperature a, the zero point calibration is not performed and the process is terminated.

  When the engine coolant temperature Tw is equal to or higher than the reference temperature a, the process proceeds to step S4.

  In step S4, it is checked whether or not the outside air temperature Ta is equal to or lower than a predetermined temperature b (for example, 30 ° C.).

  When the outside air temperature Ta is higher than the predetermined temperature b, the zero point calibration is not performed and the process ends.

  When the outside air temperature Ta is not more than the predetermined temperature b, the process proceeds to step S5.

  In step S5, an elapsed time t after engine stop is measured by a timer.

  Even if the engine is stopped, the differential pressure ΔP between the upstream and downstream of the filter 1 does not immediately become zero, decreases according to the degree of clogging of the filter 1 due to the amount of particulates collected, and approaches zero. The decrease becomes slower, and it takes time to reach zero.

  FIG. 3 shows a decrease state of the differential pressure ΔP between the upstream and downstream of the filter 1 with respect to the elapsed time t after the engine is stopped when the particulate collection amount of the filter 1 is the maximum amount (the amount when regeneration is performed). Show. The differential pressure ΔP upstream and downstream of the filter 1 becomes zero when the required time c elapses after the engine is stopped. The required time c is set to the time when the amount of particulates collected by the filter 1 is the maximum amount. However, the clogging degree changes depending on the capacity of the filter 1 and the temperature of the filter 1, and the required time c changes. Therefore, it is set according to the capacity of the filter 1 and the temperature of the filter 1 (which may be the engine coolant temperature Tw) (for example, 1 second to several tens of seconds).

  When the elapsed time t after the engine stops reaches the required time c, the zero point calibration of the differential pressure sensor 3 is performed in step S6.

  That is, if the output value Pout of the differential pressure sensor 3 is not zero, the output value Pout is calibrated to the zero point.

  Thus, when the engine coolant temperature Tw is equal to or higher than the reference temperature a, the outside air temperature Ta is equal to or lower than the predetermined temperature b, and the required time c has elapsed after the engine is stopped, the zero pressure calibration of the differential pressure sensor 3 is performed. As a result, zero-point calibration can be performed with high accuracy.

  Zero-point calibration when the engine coolant temperature Tw is equal to or higher than a reference temperature a (for example, 60 ° C.), that is, the temperature is as close as possible to the condition for determining the regeneration timing of the filter 1 by monitoring the output of the differential pressure sensor 3 Therefore, zero point calibration can be performed properly.

  Further, since the zero point calibration is performed when the outside air temperature Ta is equal to or lower than a predetermined temperature b (for example, 30 ° C.), the zero point calibration of the differential pressure sensor 3 can be appropriately performed.

  When the temperature of the differential pressure sensor 3 and the ambient temperature are extremely high or extremely low, the differential pressure sensor 3 has large detection variations and errors as shown in FIG. As described above, the zero point calibration is performed when the temperature of the filter 1 is as close as possible to the condition for determining the regeneration time of the filter 1 by monitoring the output of the differential pressure sensor 3 and the outside air temperature Ta is a predetermined temperature b (for example, 30 ° C.) or less. Therefore, the zero point calibration of the differential pressure sensor 3 can be accurately performed in an appropriate temperature range.

  Then, after the engine is stopped, the zero point calibration of the differential pressure sensor 3 is performed when a required time c has elapsed in which the differential pressure ΔP upstream and downstream of the filter 1 is reliably zero with respect to the degree of clogging of the filter 1. Therefore, zero point calibration can be performed with high accuracy.

  Therefore, since the regeneration time of the filter 1 can be optimally determined by the accurate zero point calibration of the differential pressure sensor 3, it is not necessary to regenerate the filter 1 early. It is possible to suppress the deterioration of the fuel consumption of the fuel injection.

  The present invention can be applied to an exhaust emission control device for vehicles and engines other than vehicles.

It is a schematic block diagram of embodiment of this invention. It is a flowchart of a zero point calibration. It is a figure which shows the decreasing characteristic of the differential pressure | voltage upstream and downstream of a filter. It is a figure which shows the variation of the detection with respect to the temperature of a differential pressure sensor, and the characteristic of an error.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filter 2 Fuel-injection apparatus 3 Differential pressure sensor 6 Engine rotational speed sensor 7 Engine load sensor 10 Water temperature sensor 20 Engine 21 Intake passage 22 Exhaust passage 30 Controller

Claims (2)

A filter that is disposed in the exhaust passage of the engine and collects particulates in the exhaust; a differential pressure sensor that detects a differential pressure between the exhaust pressure upstream of the filter and the exhaust pressure downstream of the filter; and In an exhaust purification device comprising a zero point calibration means for performing zero point calibration of a differential pressure sensor,
The zero point calibration means, the engine temperature exceeds a predetermined temperature, the exhaust gas purifying apparatus outside air temperature is equal to or performing a zero-point calibration when Ru near the predetermined temperature or less. The exhaust emission control device according to claim 1, wherein the zero point calibration means performs zero point calibration after a predetermined time has elapsed since the engine stopped.

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