JP3560658B2 - Engine air-fuel ratio detector - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an air-fuel ratio detection device for an engine that detects an air-fuel ratio of combustion gas taken directly from a cylinder.
[0002]
[Prior art]
Conventionally, in a four-cycle engine, combustion control has been performed in which the air-fuel ratio of exhaust gas flowing through an exhaust passage is detected and the fuel supply amount is feedback-controlled so that the air-fuel ratio becomes a stoichiometric air-fuel ratio. However, for example, in a two-stroke engine used in an outboard motor, the exhaust gas flowing in the exhaust passage includes not only combustion gas but also blow-by gas of fresh air, so that the air-fuel ratio of the exhaust gas flowing in the exhaust passage is determined. Even if it is detected, the above-described feedback control cannot be performed with high accuracy.
[0003]
Therefore, conventionally, in a two-cycle engine, the combustion gas is directly taken out of the cylinder without passing through the exhaust passage, and the air-fuel ratio of the combustion gas containing almost no blow-by gas of the fresh air is detected. Feedback control may be performed.
[0004]
[Problems to be solved by the invention]
However, in the case of the method of directly extracting the combustion gas from the cylinder, in order to avoid mixing of fresh air, the combustion gas before the expansion is sufficiently performed at the beginning of the expansion stroke, that is, the high-temperature combustion gas is extracted. Therefore, the temperature of the combustion gas introduced into the air-fuel ratio detection sensor is approximately 800 ° C. in the low-speed rotation region of the engine, and is 1000 ° C. or more in the medium-high rotation speed region.
[0005]
Here, the heat-resistant temperature of the air-fuel ratio detection sensor is about 800 to 900 ° C., and particularly in an operation state exceeding a medium speed rotation range, a combustion gas having a temperature higher than the heat-resistant temperature may flow into the air-fuel ratio detection sensor. Therefore, the durability of the air-fuel ratio detection sensor is reduced, and a problem that accurate air-fuel ratio cannot be detected and combustion control of the engine cannot be performed accurately occurs.
[0006]
The present invention has been made in view of the above-mentioned conventional problems, and an air-fuel ratio detection device for an engine capable of accurately detecting an air-fuel ratio even at a middle speed range or higher of an engine and ensuring durability of an air-fuel ratio detection sensor. It is intended to provide.
[0007]
[Means for Solving the Problems]
The invention according to claim 1 is an air-fuel ratio detection device for an engine, wherein the air-fuel ratio detection device detects an air-fuel ratio of combustion gas taken out through a gas sampling passage communicating with a combustion chamber of the cylinder. A sensor cooling jacket is provided around the sensor cooling jacket, and the sensor cooling jacket and the portion of the engine cooling water passage upstream of the thermostat valve are connected to each other through a water supply passage, and the sensor cooling jacket is connected to the thermostat valve of the engine cooling water passage. It is characterized in that it is connected to the downstream part by a drain passage .
[0009]
[Action]
According to the engine air-fuel ratio detection device of the first aspect of the present invention, the sensor cooling jacket is provided around the air-fuel ratio detection sensor, and the sensor cooling jacket is connected to the engine cooling water passage. The cooling water can be used for cooling, the durability of the air-fuel ratio detection sensor can be ensured, the air-fuel ratio can be accurately detected, and the combustion control of the engine can be performed accurately.
[0010]
Also, since the water supply passage to the sensor cooling jacket is connected upstream of the thermostat valve of the engine cooling water passage, and the drain passage is connected downstream of the thermostat valve of the cooling water passage, during warm-up operation of the engine, Even when the thermostat valve is closed, the cooling water can be reliably guided to the sensor cooling jacket.
[0011]
By the way, high temperature combustion gas flows into the air-fuel ratio detection sensor immediately after the start of the engine, but there is almost no flow of cooling water in the engine cooling water passage because the thermostat valve is closed before the warm-up operation is completed. . Therefore, cooling water cannot be circulated in spite of high-temperature gas flowing into the sensor cooling jacket depending on the water supply passage and drain passage of the sensor cooling jacket.
[0012]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 are views for explaining the air-fuel ratio detection system for an engine according to an embodiment of the invention of claim 1, FIG. 1 is a left side view of the present embodiment engine, FIG. 2 of the engine emissions FIG. 3 is a cross-sectional side view of a main part of the engine.
[0013]
In the drawing, reference numeral 1 denotes a three-cylinder two-stroke engine having a vertically mounted crankshaft for an outboard motor, which includes a cylinder head 3 on the left mating surface of the cylinder block 2 and a crankcase 4 on the right mating surface. In this structure, an intake system 5 is connected to the crankcase 4, and a piston 7a arranged in a cylinder bore 2a of the cylinder block 2 is connected to a crankshaft 7c by a connecting rod 7b.
[0014]
The cylinder head 3 includes a head body 3a having a recessed combustion chamber 8 and a head cover 3b mounted on the head body 3a and forming a cooling jacket 9 with the head body 3a. An ignition plug 6 is screwed into the chamber 8.
[0015]
The cooling jacket 9 is defined by an inner jacket 9a surrounding the combustion chamber 8 and an outer jacket 9b by a gasket 10 disposed between the mating surfaces of the head body 3a and the head cover 3b. A liner jacket formed so as to surround the cylinder bore 2a on the cylinder block 2 side communicates with the inner jacket 9a through a communication hole 9c. Reference numeral 9d denotes a throttle for allowing the cooling water to flow evenly throughout the liner jacket.
[0016]
A thermostat valve 11 is provided at the upper end of the head cover 3b. The thermostat valve 11 moves the valve body 11a forward and backward by expansion and contraction of the wax 11b. The communication hole 9e between the inner jacket 9a and the outer jacket 9b is cooled by the valve body 11a so that the cooling water is below a predetermined temperature. Is closed, and is opened when the temperature exceeds a predetermined temperature.
[0017]
An air-fuel ratio detecting device 12 for directly collecting the combustion gas generated in the combustion chamber 8 and detecting the air-fuel ratio is attached to a portion of the head cover 3b adjacent to the upper cylinder ignition plug 6. Detection device 12 includes a sensor case 13 which is bolted to the head cover 3b, and the O ₂ sensor 14 which is screwed into the sensor casing 13.
[0018]
The sensor case 13 has a rectangular tubular shape, the detection portion 14a of the O ₂ sensor 14 in the interior of the gas sampling chamber 13a is protruded. Further, the combustion chamber 8 communicates with the gas sampling chamber 13 a through a gas sampling passage 15. The gas sampling passage 15 is formed so as to penetrate through the wall surfaces of the head main body 3a and the head cover 3b.
[0019]
A sensor cooling jacket 13b is formed in the sensor case 13 so as to surround the gas sampling chamber 13a. The lower portion of the sensor cooling jacket 13b communicates with an inner jacket 9a located upstream of the thermostat valve 11 by a water supply passage 16a formed through the head cover 3b and the gasket 10. The upper part of the cooling jacket 13b communicates with an outer jacket 9b located downstream of the thermostat valve 11 by a drain passage 16b formed in the head cover 3b.
[0020]
Next, the operation and effect of this embodiment will be described.
When starting the present embodiment the engine 1, a portion of the combustion gas generated in the combustion chamber 8 is introduced through the gas sampling passage 15 into the gas collection chamber 13a, the air-fuel ratio of the combustion gas by the O ₂ sensor 14 The detected value is output to an ECU (not shown) via the signal cable 14b. In this case, since the combustion gas in which the fresh air in the combustion chamber 8 is hardly mixed is supplied to the gas sampling chamber 13a, an accurate air-fuel ratio can be detected.
[0021]
During the warm-up operation of the engine 1, the flow of the cooling water does not occur between the inner jacket 9a and the outer jacket 9b because the thermostat valve 11 closes the communication passage 9e. On the other hand, the sensor cooling jacket 13b communicates with the upstream side (high pressure side) of the thermostat valve 11 through a water supply passage 16a, and communicates with the downstream side (low pressure side) of the thermostat valve 11 through a drain passage 16b. Therefore, even during the period in which the thermostat valve 11 is closed, a part of the cooling water flows from the inner jacket 9a (high pressure side) through the sensor cooling jacket 13b to the outer jacket 9b (low pressure side). (See dashed arrow a in FIG. 3).
[0022]
On the other hand, when the thermostat valve 11 opens the communication hole 9e due to the completion of the warm-up operation, the cooling water flows from the inner jacket 9a into the outer jacket 9b through the communication hole 9e as shown by an arrow b in FIG. Also in this case, there is no change in the relationship between the high pressure and the low pressure, so that a part of the cooling water flows in the sensor cooling jacket 13b as in the warm-up operation.
[0023]
As described above, in the present embodiment, since the sensor cooling jacket 13b is provided so as to surround the detection unit 14a of the O ₂ sensor 14, even if high-temperature combustion gas is introduced into the gas sampling chamber 13a, the detection unit 14a is abnormal. can be avoided to be a high temperature, it is possible to avoid a reduction in durability of the O ₂ sensor 14, which is accurately detectable fuel ratio.
[0024]
In forming the water supply passage and the drainage passage to the sensor cooling jacket 13b, the water supply passage 16a is connected to the upstream side of the thermostat valve 11 and the drainage passage 16b is connected to the downstream side, so that the thermostat valve 11 is closed. Even during the warm-up operation, the cooling water can be supplied to the sensor cooling jacket 13b. In this respect, the durability of the sensor can be improved and the air-fuel ratio detection accuracy can be improved.
[0025]
Since the sensor case 13 is attached to the head cover 3b, the structure of the communication passage connecting the sensor cooling jacket 13b to the upstream side and the downstream side of the thermostat valve 11 is simple. Since the inner jacket 9a located on the upstream side of the thermostat valve 11 and the outer jacket 9b located on the downstream side are arranged adjacent to each other, the sensor case 13 is arranged between the ignition plugs 6 and 6 of the adjacent cylinders. The structure of the water supply passage 16a and the drainage passage 16b for communicating the sensor case 13 with the upstream and downstream sides is extremely simple.
[0026]
【The invention's effect】
As described above, according to the air-fuel ratio detection device for an engine according to the first aspect of the present invention, the sensor cooling jacket is provided around the air-fuel ratio detection sensor, and the sensor cooling jacket is connected to the engine cooling water passage. In addition, the sensor can be cooled with engine cooling water, the durability of the air-fuel ratio detection sensor can be ensured, and the air-fuel ratio can be accurately detected, and the combustion control can be accurately performed.
[0027]
Further , since the water supply passage to the sensor cooling jacket is connected to the upstream of the thermostat valve of the engine cooling water passage, and the drain passage is connected to the downstream of the thermostat valve of the cooling water passage, during warm-up operation of the engine, Even when the thermostat valve is closed, the cooling water can be reliably guided to the sensor cooling jacket, and there is an effect that the durability of the sensor and the air-fuel ratio detection accuracy can be further improved.
[Brief description of the drawings]
FIG. 1 is a left side view of an engine to which an air-fuel ratio detection device according to one embodiment of the present invention is applied.
FIG. 2 is a rear view of the engine of the embodiment.
FIG. 3 is an enlarged sectional view of a main part showing the apparatus of the embodiment.
[Explanation of symbols]
1 Engine 8 Combustion chamber 9a Inner jacket (upstream side)
9b Outer jacket (downstream part)
Reference Signs List 11 thermostat valve 12 air-fuel ratio detecting device 13b sensor cooling jacket 14 O ₂ sensor (air-fuel ratio detecting sensor)
16a Water supply passage 16b Drainage passage

Claims (1)

The air-fuel ratio detecting device of an engine as an air-fuel ratio of the combustion gas is taken out through the gas sampling passage communicating with the combustion chamber of the cylinder is detected by the air-fuel ratio sensor, the sensor cooling jacket provided around the air-fuel ratio detection sensor A water supply passage connecting the sensor cooling jacket to a portion of the engine cooling water passage upstream of the thermostat valve, and a drain passage connecting the sensor cooling jacket and the engine cooling water passage downstream of the thermostat valve. An air-fuel ratio detection device for an engine, wherein the air-fuel ratio detection device is connected in communication .

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