Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2000-05-26
2003-10-07
Kwon, John (Department: 3754)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S689000, C403S335000, C285S405000
Reexamination Certificate
active
06629521
ABSTRACT:
PRIORITY INFORMATION
This application is based on and claims priority to Japanese Patent Application No. 11-147271, filed May 26, 1999, the entire contents of which is hereby expressly incorporated reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an engine sensor and a feedback-control system for an engine. More specifically, the present invention relates to an improved engine sensor assembly used for a feedback-control system of an outboard motor engine.
2. Description of Related Art
In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high or higher power output. In pursuit of better fuel economy and emission control, various types of control systems have been developed in conjunction with internal combustion engines. One of the more effective types of controls is so-called “feedback” control. With this type of control, a basic air/fuel ratio is set for the engine. Adjustments are then made from the basic setting based upon the output of a sensor that senses the air/fuel ratio in the combustion chamber in order to bring the air/fuel ratio into the desired range.
Normally, the type of sensor employed for such feedback-control is an oxygen (O
2
) sensor which outputs an electrical signal. Generally, when the output signal voltage is high, little oxygen is present in the exhaust, indicating that a combusted air/fuel charge was rich in fuel. On the other hand, when the output signal voltage is low, substantial amounts of oxygen are present in the exhaust, thus indicating that a combusted charge was rich in air.
A conventional oxygen sensor is normally associated with a wave forming circuit which manipulates the output of the sensor to indicate an “On” signal when the voltage of the output signal exceeds a reference voltage (i.e., a signal which results when the supplied charge is rich in fuel). On the other hand, the circuit manipulates the signal to indicate that the sensor is “off” when the voltage of the output signal does not exceed the reference voltage (i.e., a signal which results from a supplied charge is rich in air).
The control operates on a feedback-control principle, continuously making corrections to accommodate deviations from the desired air/fuel ratio. Adjustments are made in stepped intervals until the sensor output goes to the opposite sense from its previous signal. For example, if the mixture is too rich in fuel (i.e., the sensor signal is “on”), then lean adjustments are made until the mixture strength is sensed to be lean (i.e., the sensor signal turns “off”). Adjustments are then made back into the rich direction in order to approximately maintain the desired ratio.
Most commonly, the oxygen sensor is the type which utilizes inner and outer platinum or platinum coated electrodes. However, the platinum acts as a catalyst, which catalyzes exhaust. For example, oxygen remaining in the exhaust may be catalyzed with carbon monoxide at the platinum electrode interface, creating carbon dioxide. When the effects of the platinum in improving exhaust gas emissions may be advantageous, the oxygen content of the gas being sensed can be affected to a degree which causes the sensor to provide inaccurate data, causing the control to adjust the air/fuel ratio erroneously.
For example, while the actual oxygen content of the exhaust system may correspond to an air rich air/fuel charge such that the actual signal from the sensor should indicate that the sensor is “off” the above-described effect may cause the sensor to indicate little oxygen is present (i.e., as if a rich fuel charge has been supplied) by an “on” signal. In that instance, the feedback-control is arranged to adjust the air/fuel ratio in the fuel rich direction in response to the “on” signal even though the mixture is already fuel rich.
A known mounting arrangement for an oxygen sensor is illustrated in FIG.
1
. As shown in
FIG. 1
, an oxygen sensor assembly
10
includes an oxygen sensor
12
, an oxygen sensor housing
14
, and a sleeve
16
.
The housing assembly
14
includes a sensor chamber
18
defined in a housing body
20
. A sensor element
22
of the oxygen sensor
12
is disposed within the sensor chamber
20
. The sensor chamber
18
tapers radially inwardly towards a lower end thereof and communicates with a gas guide
24
via a communication passage
26
. The housing body
20
is connected to an engine block
28
and communicates with a cylinder bore
30
defined in the cylinder block
28
via a throughole
32
which extends between the cylinder bore
30
and an outer surface of the engine body
28
.
The sleeve
16
is disposed within the throughole
32
. Additionally, the sleeve
16
includes an inner flange
34
disposed on an inner end of the sleeve, i.e., proximate to the cylinder bore
30
and an outer flange
36
disposed at a distal end of the sleeve
16
, i.e., distal from the cylinder bore
30
.
As shown in
FIG. 1
, the inner and outer flanges
34
,
36
are relatively thick. Additionally, the inner flange
36
contacts both the engine body
28
and the housing body
20
. Between the flanges
34
,
36
, and annular air gap
38
is formed between an outer surface of the sleeve
16
and an inner surface of the throughole
32
.
SUMMARY OF THE INVENTION
One aspect of the present invention includes the realization that known engine sensing assemblies, such as oxygen sensor assemblies, have proven to be inadequate. In particular, it has been found that known combustion condition sensors do not satisfactorily maintain the temperature of combustion products for sensing purposes. For example, it has been found that sleeves, such as the sleeve
16
illustrated in
FIG. 1
, allow an excess amount of heat, under some operating conditions, to escape from the combustion gases flowing through the throughole
32
, thus lowering the temperature of the gases sufficiently to prevent the reliable operation of the oxygen sensor. It has been found that the escaping heat is transferred into the housing body
20
of the sensor assembly
14
via one of the sleeve flanges.
As shown in
FIG. 1
, the inner flange
36
has a substantial thickness and contacts both the inner surface of the throughole
32
formed in the engine body
28
and the inner surface of the guide passage
24
formed in the housing body
20
. Thus, heat from the. combustion gases flowing through the sleeve
16
can be transferred into the housing body.
20
via the inner flange
36
, thus cooling the sleeve
16
. Additionally, heat can also be transferred between the engine body
28
and the housing body
20
, because the flange
36
contacts both the engine body
28
and the housing body
20
. It has been found that by constructing the sleeve
16
so as to have only two thick flanges
34
,
36
at its proximate and distal ends, such that the outer flange
36
contacts both the throughole
32
formed in the engine body
28
and the guide passage
24
formed in the housing body
20
, the sleeve
16
is excessively cooled, thereby allowing deposits to enter the guide passage
24
and damage the sensor element
22
. Thus, it is desireable to provide a sleeve that better maintains the temperature of combustion gases flowing therethrough.
Heat stored in the sleeve
16
is also useful for burning deposits that may enter the sleeve
16
, thus preventing such deposits from adhering to the sensor element
22
of the oxygen sensor
12
. It has been found that by constructing the sleeve
16
so as to have only two thick flanges
34
,
36
at its proximate and distal ends, such that the outer flange
36
overlaps both the throughole
32
formed in the engine body
28
and the guide passage
24
formed in the housing body
20
, the sleeve
16
is excessively cooled, thereby allowing deposits to enter the guide passage
24
and damage the sensor element
22
.
As noted above, direct injected engines are becoming more popular. In a direct injected engine, lubricant is delivered directly to the crankc
Knobbe Martens Olson & Bear LLP
Kwon John
Yamaha Marine Kabushiki Kaisha
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