Internal-combustion engines – Cooling – Automatic coolant flow control
Reexamination Certificate
1999-06-03
2001-07-24
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Cooling
Automatic coolant flow control
C123S041150, C440S08800J
Reexamination Certificate
active
06263839
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an engine overheat detection system and more particularly to an improved engine overheat detection system that is most suitable to a marine engine.
2. Description of Related Art
Watercraft powered by inboard or outboard motors typically include an electrical system. The motor includes a water propulsion device which is powered by an internal combustion engine. As is well known, an ignition system is utilized to fire one or more ignition elements corresponding to each combustion chamber of the engine, igniting the air and fuel mixture in each combustion chamber of the engine.
These engines commonly include a liquid cooling system. Liquid coolant in the form of water in which the watercraft is operating is supplied to various cooling passages or jackets associated with the engine. In some instances, the cooling system is arranged such that the coolant drains from the coolant jackets when the engine is stopped.
In order to prevent engine overheating, an overheat detection system may be associated with the engine. The detection system includes a sensor for sensing the temperature of the engine. The output of the sensor may be used by an engine control unit to shut off the engine by disabling the ignition system.
This system has the drawback that at certain times a condition of engine overheat may be indicated when in fact the engine is not in an overheat condition. This drawback is likely to happen particularly in connection with an engine that operates on a four stroke principle. Because such a four stroke engine has an oil pan therein for lubrication and lubricant contained in this oil pan tends to accumulate much heat during the engine operation.
Referring to
FIG. 1
, when the engine is operating normally and coolant is in the water jacket(s), the temperature inside the water jacket Tw remains lower than a predetermined high temperature or threshold temperature Tlim (85° C. in FIG.
1
). When the engine is shut off, however, the coolant drains from the jacket. In addition, the temperature To of the lubricant contained in the oil pan is still high for some time after the engine is stopped. Because the lubricant temperature To is around 130° C. when the engine is running and the temperature To is hard to fall down. Since no coolant remains in the water jacket and the lubricant temperature To is high, the temperature in the jacket rises immediately after the engine has been stopped. The temperature may rise to a point well above the predetermined high temperature Tlim. Then, with the lubricant temperature To falling down, the temperature inside the water jacket Tw falls back below the temperature Tlim.
If the engine is subsequently restarted before the temperature in the jacket Tw falls back below the temperature Tlim, the overheat detection system will indicate that the engine is overheated. This is due primarily because coolant is not yet being supplied to the cooling jacket(s).
In order to prevent the wrong determination of overheat from being occurring when the engine is restarted immediately after being stopped, one idea may be proposed wherein no overheat detection is made during a predetermined time after the engine is started.
FIG. 2
shows a flowchart of an overheat detection routine in accordance with this idea as an example.
Immediately after the engine is started, the program goes to a step S
1
and checks if an overheat sensor (thermal switch) is on or off. If it is on, i.e., the temperature inside the water jacket Tw is higher than the predetermined high temperature Tlim, the program goes to a step S
2
to determine if the engine has been just started or not. This state is represented by that the engine speed is less than 2000 rpm. If this is negative, the program goes to a step S
3
and prevents an overheat signal from being output for 20 seconds. Then, the program goes to a step S
4
to check again with the overheat sensor if it is still on. If it is positive, the program permits to output an overheat signal in a step S
6
. Meanwhile, if the engine speed is equal to or greater than 2000 rpm in the step S
2
, the program goes to a step S
5
and prevents the overheat signal from being output for 90 seconds. Thus, the wrong determination of overheat is prevented. The method and system for this overheat detection will be described more in detail later.
However, another problem arises if the prevention time (indicated as Ts in
FIG. 1
) is relatively long. That is, in the event an actual overheat happens, no overheat signal is provided during the prevention time and the engine must operates under this overheat condition for a while.
It is, therefore, a principal object to provide an improved engine overheat detection system which overcomes the above-stated problems.
SUMMARY OF THE INVENTION
This invention is adapted to be embodied in an internal combustion engine. The engine has a cooling system provided that includes at least one coolant jacket into which coolant is supplied for cooling at least a portion of the engine, the coolant jacket has an inlet portion through which the coolant is induced and an outlet portion from which the coolant is discharged during the engine is running. The cooling system is arranged to drain the coolant from the coolant jacket when the engine is not running,
In accordance with one aspect of this invention, an overheat detection system comprises a sensor for sensing a temperature associated with the coolant jacket to output a temperature signal. The sensor is positioned at an aft part of the coolant jacket including the outlet portion. Means is provided for determining an overheat of the engine based upon the temperature signal from the sensor when a sensed temperature exceeds a predetermined temperature to output an overheat signal.
In accordance with another aspect of this invention, the overheat detection system comprises at least two sensors for sensing temperatures associated with the coolant jacket to output temperature signals. One of the sensors is positioned at a fore part of the coolant jacket including the inlet portion. Another one of the sensors is positioned downstream of the one sensor. Means is provided for determining an overheat of the engine based upon the temperature signals from the sensors when at least one of sensed temperatures exceeds a predetermined temperature.
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Hoshiba Akihiko
Nakamura Kazuhiro
Suganuma Yasuo
Harris Katrina B.
Knobbe Martens Olson & Bear LLP
Sanshin Kogyo Kabushiki Kaisha
Wolfe Willis R.
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