Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2001-07-06
2003-07-08
Chin, Gary (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C123S041120, C123S041440
Reexamination Certificate
active
06591174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cooling system for a vehicle, in particular to a cooling system controller for a vehicle which is capable of improving cooling efficiency of a radiator by maintaining a coolant temperature as high as possible, and minimizing the required power of a cooling fan by maintaining the cooling fan speed as low as possible.
2. Description of the Prior Art
A cooling system for a vehicle is for cooling the heat generated by components such as an engine and a transmission, and maintaining the optimum temperature of the components. The temperature of combustion gas inside of the cylinder of the engine of a vehicle rises above 2,000° C. when the vehicle operates, and the temperature of a cylinder, a cylinder head and a piston valve also rises according to it. Unless this heat is removed, it may cause problems such as a mechanical trouble and a life span lowering problem due to degradation of the strength of structural parts, a power decrease due to deterioration of combustion, and an abnormal abrasion problem or a seizing problem of moving parts due to oil film damage or oil degeneration on mechanical friction portions caused by the high temperature. Accordingly, a cooling system for cooling the components is required. Meanwhile, if the coolant temperature becomes too low due to overcooling, the exhaust gas state becomes worse and the efficiency of the engine is lowered, and accordingly the cooling system is required to have a function for maintaining the temperature of the heat-generating device appropriately so as not to be too high or low.
There are two cooling methods for keeping the temperature of the heat-generating device appropriately. One is an air i.e., gas cooling method which cools the heat-generating device by using the ambient air as the heat transfer medium, and the other is a liquid cooling method which cools the heat-generating device by circulating a liquid coolant and then exhausting heat from the liquid coolant to the ambient. The latter shows better cooling efficiency than the former, and accordingly the liquid cooling method is used in general.
In the cooling system for an engine adapting the liquid cooling method, in order to cool the heat-generating device, a low temperature water-based coolant is flowed through a water jacket installed around or in an outer part of the heat-generating device such as the engine in order to cool the heat-generating device to the appropriate temperature, and while cooling the heat-generating device, the low temperature coolant becomes heated to a high temperature by heat exchange from the heat-generating device, and the high temperature coolant is flowed to a radiator and become low temperature coolant by transferring its heat to the ambient air at the radiator, and the low temperature coolant is flowed again into the water jacket of the heat-generating device by a pump in order to cool the heat-generating device, and the above-described process is performed continuously. Herein, a cooling fan is installed on one side of the radiator in order to force the cooling air for cooling the liquid coolant flow through the radiator, and the heat exchange between the cooling air and the liquid coolant is performed by the radiator.
As depicted in
FIG. 1
, the required power HP needed for driving the rotating operation of the cooling fan and the cooling air flow rate Q provided to the radiator by the rotating operation of the cooling fan have a nonlinear relation to the cooling fan speed n. In particular, the required power is considered to be proportional to the cube of the cooling fan speed. Accordingly, when the cooling fan speed is lowered, the required power decreases greatly. Meanwhile, the heat transfer efficiency or cooling efficiency heightens in proportion to the higher temperature of the coolant at the inlet of the radiator flowed from the heat-generating device, because the heat transfer from the radiator to the cooling air can be quickly performed when the temperature difference between the hot coolant and the cooling air is large, and accordingly, the higher the coolant temperature rises, the smaller the cooling air flow rate required to perform the cooling sufficiently, and the cooling fan speed can be lowered accordingly. As described above, maintaining the temperature of the coolant at a high state enables the decreasing of the cooling fan speed and the required power for the cooling the fan.
As depicted in
FIG. 1
, by raising the coolant temperature at the radiator, the cooling fan speed can be lowered from n
1
to n
2
and the cooling air flow rate is decreased from Q
1
to Q
2
. Although the cooling effect is the same, the required cooling power for driving the cooling fan can be different in accordance with a control method of the cooling fan.
There are two control methods for controlling the cooling fan. One method is an ON/OFF control method as the simplest method which controls the cooling fan to be either ON/OFF, and the other method is to adjust the average speed of the cooling fan about time to be n
1
by controlling the ON/OFF state of the cooling fan repeatedly. The average speed increases in proportion to the time duration of the ON state of the cooling fan, and the required power increases in proportion to average speed. It can be defined by Equation 1.
HPd2
=
(
n
2
n
1
)
HPd1
[
Equation
1
]
As defined in Equation 1, the required power decreases in proportion to the variation of flow rate of the cooling air. However, the required power is in direct 1:1 proportion to the fan speed. Accordingly, the advantage of the higher coolant temperature is not so great because the decrease in the required power from HPd
1
to HPd
2
is small.
The other method is a stepless speed control method which is capable of reducing the required power more in comparison with the ON/OFF control method with the equal flow rate of the cooling air, and accordingly it is a more efficient method than the ON/OFF control method. Applying the example described above, the cooling fan speed can be lowered from n
1
to n
2
when the flow rate of the cooling air is decreased from Q
1
to Q
2
. The required power decreases from HPc
1
to HPc
2
due to the increase in the coolant temperature, namely, the change of the required power is in proportion to the cube of the cooling fan speed. It can be defined as in the following Equation 2.
HPc2
=
(
n
2
n
1
)
3
HPc1
[
Equation
2
]
In this case, the required power for the cooling fan is very sensitive to the variation in the coolant temperature and decreases on a large scale with a small change in the flow rate of the cooling air. Therefore, it is clear that the stepless speed control method is more efficient, and the coolant temperature in the radiator should be kept as high as possible in order to obtain the highest efficiency from the cooling system.
In the conventional cooling control methods, the coolant temperature is maintained lower than the optimum coolant temperature in order to prevent overheating, and the cooling fan speed is controlled by various methods in accordance with the coolant temperature. As depicted in
FIG.2
, a multilevel speed control method has been dominant among the conventional methods. In this method, the cooling fan speed is determined in accordance with the coolant temperature by referring to a look-up table in a digital control unit, or is controlled by a thermostatic switch in a sequence control unit. The control of the cooling fan speed is divided into about four steps. As depicted in
FIG.2
, the coolant temperature is usually controlled in a much lower range than the optimum temperature because of the large variation between steps. This type of control method is described in U.S. Pat. Nos. 4,955,431, 5,018,484, 5,133,302, and Korean Patent 0185443 and Korean Laid-Open Patent Publication No. 1998-053909.
Meanwhile, in the conventional stepless variable speed control method, the cooling fan speed is controlled in pro
Chung Soon Bae
Kim Tae Jin
Kim Yong Won
Oh Chul Sung
Seol In Whan
Agency for Defense Development
Chin Gary
Scully Scott Murphy & Presser
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