Internal-combustion engines – Charge forming device – Supercharger
Utility Patent
1999-07-07
2001-01-02
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Supercharger
C251S129110, C318S696000
Utility Patent
active
06167873
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for controlling an EGR (Exhaust Gas Recirculation) valve of a diesel engine and a method for controlling an EGR valve of a diesel engine, more particularly, to such an apparatus and such a method that are intended to prevent a so-called “step out” from occurring in a step motor type EGR valve.
Conventionally, to an EGR passage for recirculating a part of the exhaust gas in the exhaust passage of a diesel engine into the inlet passage thereof, there is one which is provided with an EGR valve that is driven to be opened and closed by the drive force from a step motor according to the operational conditions of the diesel engine.
Also, Japanese Patent Application Laid-Open No. H8-51795 discloses a construction that stops the drive of the step motor when there is the likelihood that a so-called “step out” will occur in this step motor.
SUMMARY OF THE INVENTION
According to the studies made by the present inventor, especially when it is constructed in such a manner that such an EGR valve is disposed on a side of exhaust passage as viewed from a valve seat thereof, it sometimes happens that when the drive force applied from the step motor to a valve body of the EGR valve decreases in correspondence with a decrease in the drive current to the step motor, or particularly a coil current thereof, the valve body becomes unable to resist the exhaust gas pressure applied to this valve body in the valve closing direction. And in such a case, there is a case where the step out occurs in the step motor. Once the step out occurs in the step motor, it becomes difficult to control the valve body as preset. For example, it is considered that the degree of opening of the EGR valve becomes smaller than a preset one, the EGR valve becomes fully closed before it should be brought to such a fully closed state, etc.
Accordingly, a new configuration of the EGR valve is required in which the step out is prevented in the step motor.
However, for example, in a case that a configuration where devices, circuits or the like for detecting the coil current supplied to the step motor is provided and thereby the drive of the step motor is stopped when the coil current decrease is detected, it becomes necessary as a matter of course to provide a detector for detecting the coil current, with the result that the configuration becomes complicated and the cost also increases.
Also, in the case of a configuration where the coil current is detected in this way, it is surely convenient that such the configuration is of a type wherein when the valve of the coil current is smaller than a predetermined value, the drive of the EGR valve is equally stopped to thereby fully close this EGR valve. However, since the EGR flow is forcedly stopped equally, the discharged amount of NOx in the exhaust gas increases. This phenomenon is still more prominent when the exhaust pressure is at a high level.
In addition, as a configuration for preventing the step out in the step motor, there is considered a configuration that makes the valve diameter of the EGR valve small and thereby decreasing the pressure-receiving area thereof for receiving the pressure of the exhaust gas, a configuration that uses a step motor whose drive force is large in magnitude, or the like. However, the former configuration cannot sufficiently answer the request of effectively purifying the exhaust gas by the EGR flow. The latter construction inconveniently leads to the increase in the occupation area due to the increase in size of the step motor and to the increase in cost. Therefore, any of these configurations can not become a decisive one.
The present invention has been made as a result of the above-described studies made by the present inventor and has an object to provide an apparatus for controlling the EGR valve of a diesel engine and a method for the same, which basically eliminate the necessity of installing additional detectors, namely, only uses conventionally existing detectors, and which effectively abate the forced stop of the EGR flow and can prevent the step out in the step motor type EGR valve.
To attain the above object, an apparatus for controlling an EGR valve of a diesel engine, according to the present invention, has an object to be controlled, that is, an EGR valve provided in an EGR passage for recirculating a part of the exhaust gas in an exhaust passage of the diesel engine to return its flow to an inlet passage thereof. The EGR valve includes a valve body, a valve seat, and a step motor that fully closes the EGR passage by moving the valve body so as to abut to the valve seat and that opens the EGR passage by moving the valve body away from the valve seat, and the valve body is located on a side of the exhaust passage as viewed from the valve seat. Here, the apparatus for controlling an EGR valve of a diesel engine according to the present invention comprises a battery voltage determining section determining whether the voltage of a battery connected to the step motor is not higher in level than a predetermined voltage, a water temperature determining section determining whether the temperature of a cooling water of the diesel engine is not lower than a predetermined temperature, an exhaust gas pressure determining section determining whether the exhaust gas pressure of the diesel engine is at a level corresponding to a predetermined pressure or at a level corresponding to a pressure higher than the predetermined pressure, and a forcedly fully closing section that forcedly fully closes the EGR valve when it is determined in the battery voltage determining section that the voltage of the battery is not higher than the predetermined voltage, and/or it is determined in the water temperature determining section that the temperature of the cooling water of the diesel engine is not lower than the predetermined temperature, and it is determined in the exhaust gas pressure determining section that the exhaust gas pressure of the diesel engine is at the level corresponding to a predetermined pressure or at the level corresponding to a pressure higher than the predetermined pressure.
In other words, the apparatus for controlling an EGR valve of a diesel engine according to the present invention comprises battery voltage determining means determining whether the voltage of a battery connected to the step motor is relatively low, water temperature determining means determining whether the temperature of a cooling water of the diesel engine is relatively high, exhaust gas pressure determining means determining whether the exhaust gas pressure of the diesel engine is at a relatively high level, and forcedly fully closing means that forcedly fully closes the EGR valve when it is determined in the battery voltage determining means that the voltage of the battery is relatively low, and/or it is determined in the water temperature determining means that the temperature of the cooling water of the diesel engine is relatively high, and it is determined in the exhaust gas pressure determining means that the exhaust gas pressure of the diesel engine is at the relatively high level.
In the meanwhile, a method for controlling an EGR valve of a diesel engine according to the present invention has the same EGR valve as an object to be controlled, and comprises the steps of determining whether the voltage of the battery connected to the step motor is relatively low, determining whether the temperature of a cooling water of the diesel engine is relatively high, determining whether the exhaust gas pressure of the diesel engine is at the relatively high level, and forcedly fully closing the EGR valve when it is determined that the voltage of the battery is relatively low, and/or it is determined that the temperature of the cooling water of the diesel engine is relatively high, and it is determined that the exhaust gas pressure of the diesel engine is at the relatively high level.
REFERENCES:
patent: 4674464 (1987-06-01), Akagi
patent: 5579743 (1996-12-01), Kadowaki
patent: 5769390 (1998-06-0
Castro Arnold
Foley & Lardner
Nissan Motor Co,. Ltd.
Yuen Henry C.
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