Planetary gear transmission systems or components – With transmission cooling or heating means
Reexamination Certificate
2002-01-03
2004-05-25
Lorence, Richard M. (Department: 3681)
Planetary gear transmission systems or components
With transmission cooling or heating means
C165S916000, C137S599140, C074S60600R
Reexamination Certificate
active
06740000
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a transmission fluid cooling system for an automotive vehicle, and specifically to a transmission-fluid cooling system equipped with both a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other and capable of cooling working fluid circulating through a transmission oil pump, a hydraulic control circuit, and a lubrication circuit in the transmission.
BACKGROUND ART
As shown in
FIG. 4
, a transmission fluid cooling system
30
often uses both a water-cooled oil cooler
31
and an air-cooled oil cooler
32
fluidly connected in series to each other, for enhanced cooling performance. Water-cooled oil cooler
31
serves to remove heat from working fluid by the forced circulation of engine coolant. Air-cooled oil cooler
32
serves to cool the working fluid by close contact with a large volume of outside air. Oil coolers
31
and
32
are fluidly connected to a control valve
35
and a lubrication circuit
36
in an automatic transmission
33
via a hydraulic line
37
. Control valve
35
is incorporated in a control valve body
34
included in a hydraulic control circuit laid out in an automatic transmission
33
. An oil pump
38
is provided to pressurize and send working fluid through its outlet port into the hydraulic line. The working fluid discharged from oil pump
38
circulates through control valve
35
, water-cooled oil cooler
31
, air-cooled oil cooler
32
, and lubrication circuit
36
, in that order (see FIG.
4
). The working-fluid pressure produced by oil pump
38
is called “line pressure”. In other words, the line pressure is created on the working fluid in a connection line
39
between the inlet port of control valve
35
and the outlet port of oil pump
38
. A hydraulic pressure substantially proportional to and less than the line pressure is created on the working fluid in a hydraulic line
40
leading from the outlet port of control valve
35
to water-cooled oil cooler
31
. Transmission fluid cooling system
30
also includes a bypass valve
41
and a relief valve
42
. Bypass valve
41
is constructed as an oil-temperature sensing element equipped bypass valve. The oil-temperature sensing element incorporated in bypass valve
41
is able to sense working-fluid temperature. When a temperature value of the working-fluid temperature detected by the oil-temperature sensing element of bypass valve
41
is low, bypass valve
41
fully opens to permit the working fluid to circulate via the bypass valve through the oil passages in automatic transmission
33
, bypassing both the water-cooled oil cooler
31
and air-cooled oil cooler
32
. This enhances the engine warm-up performance and prevents overcooling of the working fluid. Pressure relief valve
42
is provided to prevent an excessive rise in the line pressure. When the line pressure exceeds a set pressure level of relief valve
42
, the relief valve fully opens to permit the working fluid to circulate via water-cooled oil cooler
31
and relief valve
42
through the oil passages in automatic transmission
33
, bypassing only the air-cooled oil cooler
32
.
Referring now to
FIG. 5
, there is shown a diagram of opening and closing characteristics of bypass valve
41
and relief valve
42
for line pressure and working-fluid temperature. As can be seen from the characteristic diagram of
FIG. 5
, in the transmission fluid cooling system
30
of
FIG. 4
, there are four control mode areas A, B, C, and D. In the first control mode area A that the engine is cold and thus the working-fluid temperature is very low, bypass valve
41
opens in response to the temperature sensed by the oil-temperature sensing element built in bypass valve
41
, and therefore the working fluid is permitted to flow via bypass valve
41
through the oil passages in automatic transmission
33
, bypassing two oil coolers
31
and
32
. In the area B that the working-fluid temperature rises to a certain extent while the line pressure does not yet reach a predetermined pressure level, bypass valve
41
is repeatedly opened and closed depending upon a temperature rise/fall of working-fluid temperature. In the area C that the working-fluid temperature rises to a certain extent while the line pressure exceeds the predetermined pressure level, relief valve
42
opens due to the line pressure above the predetermined pressure level. Thus, in the area C, the working fluid is permitted to flow via water-cooled oil cooler
31
and relief valve
42
through the oil passages in automatic transmission
33
, bypassing only the air-cooled oil cooler
32
. In the area D that the working-fluid temperature exceeds a preset temperature value, for example when the engine has been warmed up and approaches operating temperature, bypass valve
41
and relief valve
42
are both closed to permit working-fluid flow flowing through both the water-cooled oil cooler
31
and air-cooled oil cooler
32
so as to increase the cooling action. One such transmission-fluid cooling system has been disclosed in Japanese Patent Provisional Publication No. 2000-46156.
SUMMARY OF THE INVENTION
In the transmission fluid cooling system
30
as shown in
FIGS. 4 and 5
, there are some drawbacks. First, in the low working-fluid temperature area A of
FIG. 5
, bypass valve
41
fully opens regardless of the magnitude of line pressure. In this case, there is no flow through water-cooled oil cooler
31
, in other words, the working fluid cannot be rapidly warmed by way of engine-coolant circulation. A viscosity of working fluid supplied to moving transmission parts (for example clutch plates, transmission input shaft, planetary-gear system, and various bushings and bearings) for lubrication tends to be high. This increases fuel consumption.
Second, in the medium working-fluid temperature, low line-pressure area B of
FIG. 5
, assuming that the working-fluid temperature is above the preset temperature value but not sufficiently high, bypass valve
41
closes to permit working-fluid flow through both the water-cooled oil cooler
31
and air-cooled oil cooler
32
. In this case, owing to a comparatively high viscous resistance (in particular, a higher viscous resistance of working fluid flowing through air-cooled oil cooler
32
) and low line pressure, and thereby prevents adequate working-fluid supply into the oil passages. This results in re-cooling of the working fluid.
Third, in the transmission fluid cooling system
30
as shown in
FIGS. 4 and 5
, bypass valve
41
is located outside of the control valve
35
of control valve body
34
. Thus, a bypass oil passage tends to be lengthened and complicated. In such a case, apart of the oil passages is exposed to the outside air. If the outside air temperature is low, there is an increased tendency for the fluid-flow resistance of working fluid flowing through the oil passages to increase. Due to the increased fluid-flow resistance, it is impossible to attain adequate working-fluid supply needed for good lubrication.
Accordingly, it is an object of the invention to provide a cooling system for working fluid used in an automatic transmission of an automotive vehicle, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a cooling system for working fluid used in an automatic transmission of an automotive vehicle equipped with a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other, which ensures optimal switching between operative and inoperative modes of each of the water-cooled oil cooler and air-cooled oil cooler depending upon the magnitude of line pressure as well as working-fluid temperature, when the working-fluid temperature is low.
It is a further object of the invention to provide a cooling system for working fluid used in an automatic transmission of an automotive vehicle equipped with a water-cooled oil cooler and an air-cooled oil cooler connected in series to each other, which permits an operative mode of the water-cooled oil cooler and an inoperative mode of the air-coo
Foley & Lardner LLP
Jatco LTD
Le David D.
Lorence Richard M.
LandOfFree
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