JPH0430357Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for protecting an oxygen sensor used for air-fuel ratio control in a turbocharged internal combustion engine from the heat of exhaust gas.

[Conventional technology]

In order to purify the exhaust gas of internal combustion engines,
It is well known to use a three-way catalyst that can purify all three components, CO, HO, and NOx. In order to make the three-way catalyst work effectively, it is necessary to control the air-fuel ratio of the combustion air-fuel mixture to the stoichiometric air-fuel ratio. For this reason, an oxygen sensor that detects the oxygen concentration in the exhaust gas is installed in the exhaust pipe, and the air-fuel ratio is feedback-controlled based on the signal from the oxygen sensor.

Today's oxygen sensors, for example, are made of a bottomed cylindrical zirconia element coated with platinum on both the inside and outside surfaces. It generates voltage.

[The problem that the idea attempts to solve]

Since this type of oxygen sensor is installed protruding inside the exhaust pipe, it is directly exposed to the high-temperature exhaust gas flow, and its performance may deteriorate due to heat. Therefore, in the conventional technology, a recess (a large part in external shape) is provided in the exhaust manifold or exhaust pipe, an oxygen sensor is attached to this recess, and a bimetal is provided to suppress the flow of exhaust gas into the recess. An oxygen sensor that protects the oxygen sensor from the heat of the exhaust gas flow has been proposed (Utility Model Publication No. 52-138106).
Publication No.). This protection device can effectively protect the oxygen sensor from heat in a normal engine.

However, in a turbocharged engine, although high output is obtained during supercharging, the exhaust gas temperature becomes very high, so it is particularly desirable to protect the oxygen sensor from heat. However, in a turbocharged engine, the structure of the exhaust pipe is restricted due to the installation of the turbocharger, making it difficult to apply the above proposal.

An object of the present invention is to provide a heat protection device for a turbocharged engine that can effectively protect an oxygen sensor from the heat of the exhaust gas flow without significantly changing the external configuration of the exhaust pipe.

[Means to solve the problem]

The present invention solves this problem by providing a turbocharger, a turbine housing housing an exhaust turbine as part of the turbocharger, and a gas inlet provided in the turbine housing for the exhaust turbine to be used for combustion in an engine. an exhaust pipe connected to the chamber; an exhaust bypass passage branching from the exhaust pipe on an upstream side of the gas inlet so as to bypass the exhaust turbine;
a control valve that is provided at a branch point in the exhaust pipe and opens an inlet of the bypass passage when boost pressure increases, and at the same time narrows the flow path of the exhaust pipe to limit the exhaust flow rate to the exhaust turbine; provided at a position within the exhaust pipe that is covered by the control valve when the control valve opens the inlet of the bypass passage and narrows the flow path of the exhaust pipe to limit the exhaust flow rate to the exhaust turbine; An internal combustion engine with a turbocharger, characterized in that the control valve is configured to protect the oxygen sensor from the heat of the high-temperature exhaust gas flow when the supercharging pressure increases when the exhaust gas temperature increases. Provides a heat protection device for oxygen sensors.

[Effect]

When the exhaust gas temperature increases and the boost pressure increases,
The control valve opens the bypass passage and diverts a portion of the exhaust gas from the exhaust pipe toward the bypass passage, but at the same time the control valve opens the bypass passage and narrows the flow path of the exhaust pipe, the exhaust flow rate to the exhaust turbine decreases. This limits the increase in supercharging pressure and protects the engine and turbocharger itself. The present invention utilizes a control valve that operates to narrow the flow path of the exhaust pipe when the supercharging pressure rises and the exhaust gas temperature rises to reduce the flow rate in the part of the exhaust pipe covered by the control valve. Since the oxygen sensor is provided, the flow of high temperature exhaust gas is diverted by the control valve and does not directly impinge on the oxygen sensor, thereby preventing deterioration of the oxygen sensor due to overheating.

〔Example〕

Next, embodiments of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the turbocharger 10 includes a center housing 12, a compressor housing 14, and a turbine housing 16. An impeller 18 is housed in the compressor housing 14, and an exhaust turbine 20 is housed in the turbine housing 16, and these are fixed to an integral shaft that is pivotally supported by the center housing 12. An intake pipe 24 equipped with a throttle valve 22 is connected to the inlet of the compressor housing 14, and an intake pipe 30 communicating with the engine combustion chamber 28 via an intake valve 26 is connected to the discharge side of the compressor housing 14. It's connected. The gas inlet of the turbine housing 16 is connected to the combustion chamber 2 by an exhaust pipe 32.
It is connected to 8. Therefore, the exhaust turbine 20 is rotated by the high-temperature, high-pressure exhaust gas generated by combustion in the combustion chamber 28, which rotationally drives the impeller 18 of the compressor to compress intake air and supercharge the engine combustion chamber.

The exhaust pipe 32 on the upstream side of the gas inlet provided in the turbine housing 16 is provided with a bypass 34 that branches off from the exhaust pipe 32 and bypasses the exhaust turbine 20, and a bypass 34 is provided at the branch point to open and close the inlet of the bypass 34. A control valve 36 (hereinafter referred to as a wastegate valve) is pivotally supported by a valve shaft 38 and is opened and closed by an actuator 40 in accordance with boost pressure. This waste gate valve 36 not only opens and closes the inlet of the bypass 34, but also narrows the flow area of the exhaust pipe 32 that supplies exhaust gas to the exhaust turbine 20 at the same time when the inlet of the bypass 34 is opened. .
The output rod 42 of the actuator 40 is connected to the valve stem 38 by a link bar 44, and the working chamber 48 defined by the diaphragm 46 is communicated with the intake pipe 30 by a conduit 50. Note that the diaphragm 46 is biased by a spring 52 in a direction to close the wastegate valve 36.

When the wastegate valve 36 opens the inlet of the bypass 34 in a state where the boost pressure exceeds a predetermined value, the valve plate of the wastegate valve 36 is connected to the exhaust pipe 3.
The exhaust pipe 32 protrudes into the inside of the exhaust pipe 32 and narrows the flow path area, but at that time it becomes a shadow of the waste gate valve 36.
An oxygen sensor 54 is attached to a portion of the. This oxygen sensor 54 is a known one, and its input signal is input to an air-fuel ratio control circuit (not shown). It is preferable to provide a partition wall 56 in the longitudinal direction in the exhaust pipe 32 facing the oxygen sensor 54 to form an exhaust gas passage 58 for oxygen concentration detection.

Next, the effect will be explained.

During low-speed, low-load operation of the engine, the opening degree of the throttle valve 22 is small and the exhaust gas flow rate is small, so the discharge pressure of the compressor is low and the boost pressure is small. Therefore, the diaphragm 46 of the actuator 40 is moved to the left in FIG. 1 by the action of the spring 52, and the wastegate valve 36 is closed as shown in FIG. Therefore, under this operating condition, the exhaust gas flow flows through the oxygen concentration detection exhaust gas passage 58 and directly reaches the oxygen sensor 54.
The oxygen concentration in the exhaust gas can be detected.

During high-speed, high-load operation, the opening degree of the throttle valve 22 is large and the flow rate of exhaust gas passing through the exhaust turbine 20 increases, so the impeller 18 of the compressor is rotated at high speed and the supercharging pressure in the intake pipe 30 increases. do. This pressure is transmitted through conduit 50 to the working chamber 48 of actuator 40, causing diaphragm 46 to move to the right against the action of spring 52, as shown in FIG. Open the valve counterclockwise. As a result, a portion of the exhaust gas bypasses the exhaust turbine 20 and flows through the bypass 34 to the turbocharger 10.
At the same time, the exhaust gas passage 58 for oxygen concentration detection is substantially blocked by the waste gate valve 36. Therefore, in this state, a large amount of exhaust gas flow does not directly impinge on the oxygen sensor 54, so the oxygen sensor 54 is isolated from the heat of the exhaust gas flow.

[Effect of idea]

In this invention, when the control valve (wastegate valve) opens the entrance of the bypass passage when the boost pressure increases, and at the same time narrows the flow path of the exhaust pipe to limit the exhaust flow rate to the exhaust turbine, the control valve By installing the oxygen sensor in a part of the exhaust pipe that is covered, the oxygen sensor is protected from direct collision with high-temperature exhaust gas, so when boost pressure increases, high-temperature exhaust gas does not collide with the oxygen sensor. While avoiding collision with the oxygen sensor, it is possible to install the oxygen sensor in the upstream exhaust pipe through which the highest temperature exhaust gas flows as much as possible to prevent unstable operation due to cooling of the oxygen sensor. This invention has the remarkable effect of being able to solve the problems of the prior art very easily without being subject to the above limitations.

In this way, by taking measures against the rise in supercharging pressure when the exhaust gas temperature rises and by ensuring that the oxygen sensor is fully protected against heat, it is possible to install the oxygen sensor in the exhaust pipe upstream of the exhaust turbine. This makes it possible to enhance the functionality of the oxygen sensor in engine operating conditions with low boost pressure and low exhaust gas temperature, enabling highly accurate air-fuel ratio feedback control in all engine operating ranges. . Moreover,
It is possible to prevent deterioration of the oxygen sensor and maintain high performance over a long period of time.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view of a turbocharged engine equipped with the oxygen sensor/thermal structure of the present invention, showing the waste gate valve in the closed state, and Fig. 2 is a partial view of Fig. 1, showing the waste gate valve in the closed state. The gate valve is shown open. 10...Turbo charger, 20...Exhaust turbine, 32...Exhaust pipe, 34...Bypass, 36
...Wastegate valve, 54...Oxygen sensor.

Claims (1)

[Scope of utility model registration request] a turbocharger; a turbine housing housing an exhaust turbine as part of the turbocharger; an exhaust pipe connecting a gas inlet in the turbine housing for the exhaust turbine to a combustion chamber of the engine; an exhaust bypass passage branching from the exhaust pipe upstream of the gas inlet so as to bypass the gas inlet, and an exhaust bypass passage provided at a branch point in the exhaust pipe opening the entrance of the bypass passage when boost pressure increases. At the same time, a control valve narrows the flow path of the exhaust pipe to limit the exhaust flow rate to the exhaust turbine, and when boost pressure increases, the control valve opens the inlet of the bypass passage and narrows the flow path of the exhaust pipe. The oxygen sensor is provided at a position within the exhaust pipe that is covered by the control valve when the exhaust gas flow rate to the exhaust turbine is narrowed and the exhaust gas flow rate to the exhaust turbine is restricted, and when the supercharging pressure increases when the exhaust gas temperature increases, the control valve A heat protection device for an oxygen sensor of an internal combustion engine with a turbocharger, characterized in that the oxygen sensor is configured to protect the oxygen sensor from the heat of a high-temperature exhaust gas flow.