Exhaust gas recirculation apparatus for engine with turbocharger

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an exhaust gas recirculation apparatus, and more particular­ly, to an exhaust gas recirculation apparatus suitable for an engine with a turbocharger.

2. Description of the Related Art

It is necessary to reduce the amount of carbon monoxide CO, hydrocarbon HC, and nitrogen oxide NOx contained in exhaust gases from vehicles such as an automobile. It is known that among these poisonous gases, nitrogen oxide NOx can be reduced by mixing inactive gases contained in exhaust gases such as HIO, N1 and COI into the combustion mixture and lowering the maximum combustion temperature by virtue of the heat capacity of the inactive gases. With this feet in mind, in order о reduce nitrogen oxide, an exhaust gas recirculation (hereinunder referred to as "EGR") apparatus which recirculates exhaust gas to an intake system is provided in various kinds of vehicles.

Of these apparatus, in an engine with a turbocharger there is an apparatus in which a bypass pipeline for connecting an exhaust line on the upstream side of an exhaust turbine and an intake line on the downstream side of a compressor is provided as a passage for circulating exhaust gas, namely an EGR passage, and midway in the EGR passage is provided a valve body for opening and closing the EGR passage in correspondence with the urging force of a diaphragm, namely an EGR valve. In this apparatus, when the engine is in a running state in which exhaust gas recirculation control is necessary, namely when the running state of the engine is in an EGR control range, a vacuum pressure from a vacuum source which sucks the diaphragm of the EGR valve is introduced to a diaphragm cham­ber, and the EGR valve is opened to open the EGR passage, whereby the exhaust gas is recirculated to the intake system. Except when the engine is in the EGR control range, the EGR valve is closed by the urging force of the diaphragm and the EGR passage is closed.

When an engine is in a high-speed and high-load state, the exhaust gas pressure increases with the increase of the load. On the other hand, in this kind of engine with a turbocharger, in order to keep boost pressure constant,

when the boost pressure is beyond a predetermined pressure, exhaust gas is re­leased to a passage detouring the turbine of the turbocharger.

As a result, even if exhaust gas pressure becomes high, the boost pressure, namely intake pressure does not exceed a predetermined value. Therefore, the difference of the pressure between the intake side of the EGR passage which connects the intake system passage with the exhaust system passage and the exhaust side thereof becomes large. Furthermore, a vacuum adjustment valve is connected to the EGR valve which is provided in the EGR passage for the purpose of controlling the amount of EGR. This vacuum adjustment valve supplies a vacuum from a vacuum source after controlling it in accordance with the electric current supplied from a controller. However, due to its inherent structure, the vacuum leaks even when the current value is zero, and this leaked vacuum is transferred to the EGR valve as a residual pressure.

Therefore, the conventional EGR apparatus has the deficiencies or problems that the pressure difference between the intake system passage side and the exhaust system passage side is large even if the EGR passage is closed by the EGR valve in the high­speed and high-load range, which is out of the EGR controlling range, and that the EGR valve is inadvertently slightly opened due to the residual pressure of the vacuum adjust­ment valve and exhaust gas flows to the intake system passage side, whereby the power of the engine is lowered or black smoke is generated.

SUMMARY OF THE INVENTORY

Accordingly it is an object of the invention to provide an EGR controlling appa­ratus for an engine with a turbocharger which can securely close the EGR valve and, hence, the EGR passage when the naming state of the engine is out of the EGR control­ling range, and can thereby prevent exhaust gas from accidentally leaking to the intake system passage side.

To achieve this aim, this invention provides an EGR controlling apparatus for an engine with a turbocharger comprising; an EGR valve which is provided in an EGR passage connecting an exhaust system passage and an intake system passage

To achieve this aim, this invention provides an EGR controlling apparatus for an engine with a turbocharger comprising: an EGR valve which is provided in an EGR passage connecting an exhaust system passage and an intake system passage of the engine for the purpose of controlling the amount of EGR; a vacuum adjustment valve for controlling the vacuum supplied from a vacuum source to the EGR valve; and a valve device for cutting off the supply of vacuum in the vacuum range which is lower than the vacuum corresponding to at least the lower limitation valve in the EGR controlling range with respect to the vacuum controlling characteristics of a vacuum adjustment valve, this valve device being provided in the passage connecting the EGR valve and the vacuum adjustment valve such as to securely close the EGR valve when the running state of the engine is out of the EGR controlling range.

The above and other objects, feature and advantages of the present invention will become clear from the following description of the preferred embodiments thereof, tak­en in conjunction with the accompanying drawings.