JP4483393B2 - 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.

  In addition, although 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, there is a problem of a structure in which a valve must be provided to perform the zero point calibration.

  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 gas purification apparatus having zero point calibration means for calibrating the zero point of the differential pressure sensor when the engine is stopped, the zero point calibration means detects the value detected by the differential pressure sensor immediately after the engine is stopped. On the basis of this, zero point calibration is performed after a predetermined delay time is set longer when the differential pressure is larger than when the differential pressure is small .

  According to the present invention, when the differential pressure upstream and downstream of the filter becomes zero, the zero point calibration of the differential pressure sensor can be performed accurately.

  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, a required time (timer value) tx until the differential pressure ΔP upstream and downstream of the filter 1 becomes zero is set based on the output value Px of the differential pressure sensor 3 when the engine is stopped.

  Even when the engine is stopped, the differential pressure ΔP between the upstream and downstream of the filter 1 does not immediately become zero, but decreases according to the degree of clogging of the filter 1 due to the amount of particulates collected, and approaches zero. Decrease is slow and goes to zero after the required time.

  FIG. 3 shows a decrease state of the differential pressure ΔP upstream and downstream of the filter 1 after the engine is stopped. When the collected amount of particulates in the filter 1 is small (the output value Px of the differential pressure sensor 3 when the engine is stopped is small), the differential pressure ΔP upstream and downstream of the filter 1 becomes zero in a short time, When the collected amount of particulates of the filter 1 is large (the output value Px of the differential pressure sensor 3 when the engine is stopped is large), the differential pressure ΔP upstream and downstream of the filter 1 becomes zero in a long time.

That is, based on the output value Px of the differential pressure sensor 3 when the engine is stopped, the required time tx (t ₀ , t ₁ ,...) Until the differential pressure ΔP upstream and downstream of the filter 1 becomes zero is mapped. By determining the data or the like, the time required tx until the differential pressure ΔP upstream and downstream of the filter 1 becomes zero can be grasped according to the output value Px of the differential pressure sensor 3 when the engine is stopped.

  In step S6, the time t after the engine is stopped is measured by a timer, and when the set required time tx has elapsed, the process proceeds to step S7.

  In step S7, zero point calibration of the differential pressure sensor 3 is performed. When the output value Pout of the differential pressure sensor 3 is not zero, the output value Pout is calibrated to the zero point.

  With such a configuration, the zero point calibration of the differential pressure sensor 3 can be performed with high accuracy after the engine is stopped.

  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, based on the output value Px of the differential pressure sensor 3 when the engine is stopped, the required time tx until the differential pressure ΔP upstream and downstream of the filter 1 becomes zero is set, and the required time tx has elapsed. Since the zero point calibration of the differential pressure sensor 3 is performed, the zero point calibration can be performed with high accuracy.

  The time until the differential pressure ΔP upstream and downstream of the filter 1 becomes zero after the engine stops depends on the amount of particulates collected, but is obtained based on the output value Px of the differential pressure sensor 3 when the engine stops. be able to. Therefore, when the differential pressure ΔP upstream and downstream of the filter 1 becomes zero, the zero point calibration of the differential pressure sensor 3 can be performed quickly and accurately.

  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 (3)

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 sets a predetermined delay time that is set longer when the differential pressure is larger than when the differential pressure is small based on the detection value of the differential pressure sensor immediately after the engine is stopped. An exhaust emission control device that performs zero point calibration after a lapse of time. The exhaust emission control device according to claim 1, wherein the zero point calibration means performs zero point calibration when the engine temperature exceeds a predetermined temperature . The exhaust purification apparatus according to claim 1 or 2, wherein the zero point calibration means performs zero point calibration when the outside air temperature is below a predetermined temperature .

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