DESCRIPTION
COOLING DEVICE FOR ENGINE
TECHNICAL FIELD
BACKGROUND ART
[0002] Generally in anieng=Ae, a large thermal load is
;applied to a piston, therefore in order to prevent abnormal
i 'combustion, such as engine knock due to high temperature of a
piston head, a cooling device, which prevents erosi,on and
abnormal combusti,on of the piston head by ejecting cooling oil
to the rear side of the piston, is used.
As depicted in FIG. 9, which is a schematic of a main
section of general piston cooling, an oil pump 5, driven by . I
. the driving force of an engine, draws up oil from an gs1 pan ,
(not'illustrated) of the engine while the engine is in ,
operation, and an oil cooler 4 cools the oil by cooling water
- .
of the engine. L
I - 9.
@ The oil cooled by the oil cooler 4 is injected from an\*
oil injection nozzle 8 to a rear face of a piston 1, whereby
the piston 1 is booled.
-9
[0003] ~a~anesPkat ent Application Laid-Open No. 2006-29127
(Patent Document 1) discloses a cooling device for a piston.
In particular Paten$"Docu 1 discloses a technology ,
P
comprising: a double structure' cleaning channel constituted by
a first oil passage (inside) and a second oil passage
(outside) formed in a piston qead unit la; a warm-up oil
supply unit which oil to one of the first oil
passage+and the when cooling the engine;
.( ' and the warm-up oil supply unit that supplies cooling oil to
the other one of the first oil passage and the second oil
passage when the piston temperature is high. i
[0004] Patent 'Document 1: Japanese Patent Application
Laid-Open No. 2006-29127 b
[0005] The oil pump 5, however, is connected to a a
'
crankshaft (not illustrated) of the engine via a gear tra-- .'
:: . , . '
henc,e the oil pump 5 operates simultaneously when th;
crankshaft of the engine rotates.
Therefore when the engine starts, the oil, pump is driven
and the oil in an oil pan'in a cooled state is injected to the
I
rear face of the piston, whereby the piston is kept cool.
I - ".
@ This means that the temperature of the piston,,head does
not rise.quickly, and that it takes time until the engine
reaches the best toperating conditions in I other words
startability is ngt-good and fuel consumption is high.
Furthermore according to Patent Document 1, the warm-up
oil supply unit that supplies a warm-up oil when cooing the I *-
/I 1 I,
ehgine and a heating up dnit for heating oil are included,
1
which increase the cost of the device, and is also not
desirable in terms of fuel consumption.
C .I. .. , , DISCLOSURE OF THE INVENTION
'i [0006] With the foregoing in view, it is an object of the
present invention to adjust the injection amount of the
i
cooling coil from the oil injection nozzle, and to adjust the
#
temperature of the cooling oil depending on whether the engine
b
is started up (engine cooled state) or whether the engine is
operating, in other words, the temperature of the piston 6
increases quickly when the engine is started up, while ov&-
-- '
cooling of the piston is prevented when output is at an
intermediate or low level, so as to improve startability of
the engine, -decrease the warm-up period, improve fuel
6
efficiency during intermediate or low output, and improve fuel
consumption efficiency.
I - r:.
O0071 To solve this problem, the present invention ,-
pr0vides.a cooling device for an engine including an oil jet
device for coolihg a piston with oil,.this cooling device
4
including: a cooling water temperature sensor that detects a
temperature of the engine; a rota'tion speed sensor that
detects rotation speed of the,engine; a load sensor that
. i #-
detects the load of the tnginei a jet nozzle that > is secured,
in a cylinder block of the engihe and injects cooling oil to
the rear face of the piston; an oil cooler disposed upstream
of the jet nozzle on a distridution path of the cooling oil;
an oil pump that is tream of the oil cooler and
' P
pumps the cooling oil to the oil cooler; a first switching
I
,*adjustment valve that is disposed between the jet nozzle and
$
' the oil cooler, and adjusts a flow dividing ratio at which the
cooling oil from the oil cooler is distributed to $he jet
nozzle side and to an oil pan side; and a control unit that,
has an oil quantity adjustment map for switching the first
switching adjustment valve based on a piston temperature
i
calculation map for calculating the temperature of the piston , t
. using the,,detection values acquired respectively by t$e
temperature sensor, the rotation speed sensor and the load ' .
sensor.
*
[0008] Because of this configuration, the giston
temperature can be calculated and deterioration of
I - 2 ,
&artability and fuel consumption rate of the engine, due to
over-cooling of the piston, can be prevented.
t
[0009] In the present invention, it is preferable that the
1 -
control unit adjusts a second switching adjustment valve
disposed between the oil cooler and the oil pump on the
distribution path of the ,Sooli g oil based on an oil
11 4 \ I
tBmperature adjustment m8p whi~h determines a flow divFding
Y
ratio at which the cooling oil from the oil pump is
distributed to the oil cooler side and to a bypass circuit
side which is connected between the oil coolet and the first
b' 1 p r \:
switching adjustment valve, widreby the temperature of the
- ...
.cooling oil, after passing through the bypass circuit, is
[OOlO] Because of this configuration, the quanti;ty of the
cooling oil that ,flows through the oil cooler can be adjusted,
1
whereby fine control of the oil temperature becomes possible, ,
an excessive increase in oil temperature can be controlled,
and deterioration of oil can be prevented. 4
' 1
Furthermore a bypass circuit is included, therefare over-,
cooling of the piston due to excessive cooling of the cooling '
oil can be prevented.
[OOll] In the present invention, it is preferable that when
the engine is started or when the load is intermediate or low,
the value calculated using the piston temperature calculation
bp is compared with a value detected by a cylinder "
temperature sensor for detecting a cylinder temperature of the
engine and/or a value detected by a c linder Yl inder head temperature
sensor for detecting a temperature of the cylinder head, and
when the difference therebetween is a threshold or more,
priority is given to the value(s) detected by the cylinder
I #.
temperature sensor and/of the 4 ylinder head sensor.
P I
I
[0012] Because of this configuration, the temperature of
the cylinder and/or the cylinder head when the engine is
running can be monit0red.i.n real-time, therefore fine cooling
M' I $
I\b
control can be performed. duri$& transient operation, and
_ C , ., .' .
.efficient operation becomes possible.
I
*J
Furthermore over-cooling of the piston in the initial
phase of starting the engine can be prevented, andithe fuel
consumption rate,in the initial phase can be improved.
I
b [0013] When the engine is started (engine cooled state),
cooling of the piston is stopped by diverting the oil from the'
4
oil pump before reaching the oil injection nozzle, so- as to *;
I
increase the temperature of the piston quickly, wher&$
staktability of the engine is improved, the fuel consumption' ' ,
rate is improved due to a decrease in the warm-up period, and
cost can be reduced. L
BRIEF DESCRIPTION OF THE DRAWINGS
6
I - ?'.
40141 F I G . 1 is a schematic block diagram of an engine
cooling device according to Embodiment 1 of the present
invention; 1, .
3
F I G . 2 is a biigram depicting a flow to control a
switching valve according to Embodiment 1 of the present
invention; . , *- i
F I G . 3A shows a configura6':on of an oil quantity
adjustment map of the present invention, and F I G . 3B shows
flow rate ratios in the map; j
v!: I '1 F I G . 4,is a schematk.~b ld,$k diagram of an engine cooling
% 2 device .ac'cording to Embodiment 2 of the present invention;
I
*j F I G . 5 is a diagram depicting a flow to control a
switching valve according to Embodiment 2 of the present
5 invention;
I
F I G . 6A shows a configuration of an oil quantity b
adjustment map of the present invention, and F I G . 6B shows
flow rate ratios in the map; a
F I G . "7 is a schematic block diagram of an engine5 dooling
device according to Embodiment 3 of the present invention;
F I G . 8 'is a diagram depicting a flow to control a
b
switching valve according to Embodiment 3 of the present
invention; and
F I G . 9 is a diagram depicting a prior art.
BEST MODE FOR CARRYING OUT THE INVENTION
1 i
[0015] The present invention will now be described using
\ -
the embodiments with reference to the drawings.
Dimensions, materials, shapes, relative positions or the
8 *. I ljke of the composing el$ments described in the embodiments -
I
are not intended to limit the s'kope of the invention to these
embodiments, but are merely examples for explanatory purposes.
FIG.. 1 shows a piston 1 which vertically slides in a
'cylinder 2 formed in an engine main unit. j
A cylinder head 3 is installed in an upper part of the
piston 1 so as to close the cylinder 2. In the cylinder head
#
3, a fuel injection nozzle 31 that injects fuel into a I
combustion chamber 34, an inlet valve 32 that introduces air
into the cylinder, and an exhaust valve 33 that exhausts
combustion gas are installed.
An oil injection unit 8 is secured in the engine main
I .
unit (not illustrated) facing the rear face of the piston 1 in
the lower part of the piston 1.
5 denotes an oil pump which is connected to a crankshaft
(not illustrated) of the engine via a gear train, and is
I - 9.
dtiven simultaneously with the start of the engine., to draw'-up
cooling oil from an oil pan 10 of the engine.
1,
An oil cooler 4 is normally installed on the side of the
8 -
engine main unit, and cools the cooling oil using the cooling
water of the engine. . ,
6 denotes a first adjustment valve, which
"p
controls a quantity of the cooiing oil, which is supplied from
the oil cooler 4, to be distributed to an oil injection nozzle
8 side and to the oil pan 10 siide, under control of a control
unit 30.
~ h &co ntrol unit 30 controls the first switching
I
-(adjustment valve 6 based on the respective detected values
1
I acquired by a load sensor 37 (engine torque), a rotation speed
i
sensor 36 and a cooling water temperature sensor 35.
#
t
[0017] 11 denotes a distribution path, which draws up the
b
cooling oil from the oil pan 10 using the oil pump 5 via a
,
first oil feed tube 111 when the engine is started. The 1
'
cooling oil drawn up by the oil pump 5 is fed into the 01- - ''4 .I I *-
cooler 4 via a second oil feed tube 112, and is cooled by the
' .
cooling water of the engine.
- -
The flow of the cooled cooling oil is divided by a first
switching adjustment valve' 6, which is disposed in an
intermediate portion of a third oil feed tube 113 based on an
oil quantity adjustment map 41 (provided in the control unit
I - 9.
@), for determining a flow quantity ratio at which the ,.
cooling oil is distributed to the oil injection nozzle 8 side
and to the oil pan 10 side, depending on the operating state
3
of the engine. 'l -
One of the divided flows of the cooling oil is
distributed to the oil in, j.ec tiy n nozzle 8 side, and is
I
i 4 ihjected into the rear slde ofzthe piston 1, and cools'the
1
#
piston 1.
The other side of the diqided flows is returned to the
oil pan 10 via a fourth lp-: 11 feed tube 114.
< 2 {;ti,
. .
[0018] ' < .' The first switching adjustment valve 6 adjusts the
I
*(oil quantity according to the valve control flow of the first
switching adjustment valve 6 shown in FIG. 2.
The operating state of the engine is calculated using a
#
piston temperature calculation map 20 based on the detected'
values acquired by the cooling water temperature sensor 35,
the rotation speed sensor 36 and the load sensor 37. The
4
piston temperature calculation map 20 has a characteristib- .' 3 4
,' , <
curv,e of the piston temperature generated by determi;ing the '
' .
temperature of the piston 1 based on experiment values, and
plotting the temperature values on the abscissa as the
L
rotation speed (rpm) and qn the ordinate as the torque (T).
The load sensor 37 measures the fuel injection quantity,
or an amount by which the accelerator pedal is depressed.
- 5.
Based on the temperature calculated using the piston
temperature calculation map 20, the flow rate ratio of the
first switching adjustment valve 6 isidetermined using the oil
quantity adjustme~t- map -41.
As FIG. 3A shows, the oi; quantity adjustment map 41 is
divided into squared areaq whi h are plotted on the abscissa
'1 1 1 a9 the engine rotation speed (ypm) and on the ordinate-as the
4
piston temperature (temperature calculated using the piston
temperature calculation map 20,).
In each area, the o8 ;e: ning/!d egree of the first switching
adjustment valve (flow rate ratio) is classified into levels:
'AO, Al, A2, A3 and A4.
' j
[0020] If the piston temperature is low and it is
immediately after the engine started, for example, A0 is
8
selected.
b
Then as FIG. 3B shows, the control unit 30 adjusts the
valve position of the first switching adjustment valve 6 by 4
C 1
setting the flow rate on the oil injection nozzle 8 side z*O-
-- '
(zero), so that the flow rate on the oil pan 10 side becomes 4
' ,
(entire quantity).
- .
As the engine warms up and the temperature of piston 1
and the engine rotation speed increases, an area to be
selected sequentially changes as area A1 and area A2, and the
flow rate on the oil injection nozzle 8 side and the flow rate
I - e.
(Li the oil pan 10 side are adjusted according to the operation
state of'the engine (determined based on the detected value
acquired by each !sensor) . i
In the case bf-a high-load operation state where the
position temperature is high and the engine rotation speed is
high, A4 is selected, and the valve position of . 1- 1 the first
I 14
saitching adjustment val$e 6 is adjusted by setting the flow '
i
#
rate on the oil injection nozzle 8 side to 4 (entire quantity),
so that the flow rate on the oil pan 10 side becomes 0 (zero).
I
[0021] According to odiment, the operation state of
the engine is on detected values acquired
'from the cooling water temperature sensor 35, the rotation
*j
speed sensor 36 and the load sensor 37, and the piston
temperature is calculated using the piston tem~erat~ure
calculation map 20. Based on these calculation results, the
I
injection quantity of the cooling oil to the piston 1 is
L
finely controlled, whereby deterioration of startability of ,
the engine and the fuel consumption rate of the engine, due to
'
over-cooling of the piston 1, can be minimized.
_< ,
[0022] (Embodiment 2 )
An engine cooling device according to Embodiment 2 will
L
be described with reference to the schematic dlock diagram
shown in FIG.- 4.
- ?- .
@ A composing element the same as in Ernbodiment:l is , .
denoted with a same reference symbol, for which description is
omitted. $, i
'\ -
LO0231 In a distribution path 12, the cooling oil is drawn
up from the oil pan 10 by the,,oil pump 5 via the first oil
feed tube 111. A sec0nd,,~.wit&4iand~j ustment valve 7 is
f l \ '1 ihserted into the interm&diate,portion of the second oil feed
tube 112 connecting an oil pump 5 and the oil cooler 4.
The third oil feed tube 1\13, which has the first
switching adjustment valp 6 sh the intermediation portion, is
F
i " 4
disposed at the downstream side of the distribution path 12 of . L
'the oil cooler 4.
*j
The oil injection nozzle 8 is disposed further at the
i
downstream side.
1
The first switching adjustment valve 6 is controlled
b
(divides flow) based on an oil quantity adjustment map 41,
which is disposed in the control unit 40, and determines a E
3
ratio of quantity of oil distributed to the oil injectionkc -
,' , , -- ,
nozzle 8 side and to the oil pan 10 side.
One of the controlled (divided) flows of the cooling oil
- -
is distributed to the oil injection nozzle 8 side, is injected
into the rear side of the piston 1, and cools the piston 1.
-
I The other side of the divided flows is returned to the-
I
I oil pan 10 via the fourth oil feed tube 114.
I
I t
I [0024] A second switching adjustmeht valve 7 is connected
to a bypass circuyt-9, of which one end is connected between
the first switching adjustment valve 6 of the third oil feed
tube 113 and the oil cool, e+- r 4, and the other end is connected
\ I 4
tb the second switching Adjustment valve 7.
The second switching adjustment valve 7 is disposed for
dividing the flow of the cool3,ng oil into the oil cooler 4
side and the bypass circFt 9 )Bide, so as to adjust the
P 91
temperature when the cooling oil cooled by the oil cooler 4
.il and the cooling oil, which passed through the bypass circuit 9,
are mixed again in the third oil feed tube 113.
The second switching adjustment valve 7 is conitrolled
using the oil teGperature adjustment map 51 disposed in the,
control unit 40, generated from the result of calculating the '
operation state of the engine using the piston temperature
4
calculation map 20 based on the detected values acquired by <
the cooling water temperature sensor 35, the rotation:speed ,
sensor 36 and the load sensor 37. ' ,
The oil quantity adjustment by the second switching
I
adjustment valve 7 is performed according to a valve control
flow by the second switching adjustment valve 7 shown in FIG.
*1 - *. The operation state of the engine is calculated using the
piston temperature calculation map 20 based on the detected
values acquired By the cooling water femperature sensor 35,
the rotation speed sensor 36 and the load sensor 37.
[0025] Based on the temperature calculated using the piston
temperature calculation mqp 20 the flow rate ratio of the
4
\ second switching adjustment 7 is determined using the
t
oil temperature adjustment map 51.
As FIG. 6A shows, the oil\ temperature adjustment map 51
I is divided into squared &teas ldhich are plotted on the
1 !
abscissa as the engine rotation speed (rpm), and on the
'ordinate as the piston temperature (temperature calculated &i
using the piston temperature calculation map 20).
i
In each area, the opening degree of the second switching
adjustment valve (flow dividing ratio) is classified into I
levels: BO, B1, B2, B3 and B4.
b
[0026] If the piston temperature is low and it is 1
!
immediately after the engine started, for example, BO is 4-- -
,I
_. ,
selected.
Then as FIG. 6B shows, the control unit 40 adjusts the
- .
valve position of the second switching adjustment value 7 by
setting the flow rate of the oil cooler side to 0 (zero), so
that the flow rate on the bypass circuit 9 side becomes 4
(entire quantity).
- c:. bb As the engine warms up and the temperature of .the piston
1 rises and the engine rotation speed increases, an area to be
selected sequentially changes as area.Bl.and area B2, and the
-3
flow rate on the .pi1 cooler 4 side and the flow rate on the
bypass circuit 9 side are adjusted according to the operation
state of the engine (determined based on the detected value
a~quired by each sensor); 4
P I
i
f
In the case of high-load operation state where the piston
temperature is high and the engine rotation speed is high, B4
is selected, and the valve position of the second switching Y I
adjustment valve 7 is adjuste$!\by setting the flow rate on the
.oil cooler 4 side to 4 (entire quantity), so that the flow
I . i
.. rate on the bypass circuit 9 side becomes 0 (zero).
The control of the first switching adjustment;valve 6,is
the same as Embodiment 1, so description thereof is omitted.
I
[0027] According to this embodiment, with the bypass b
circuit 9 of the oil cooler 4 being installed, the operation '
C
state of the engine is calculated based on the detected values* t
acquired from the cooling water temperature sensor 35,'the
rotation speed sensor 36 and the load sensor 37, and the
piston temperature is calculated using the piston temperature
calculation map 20. Based on the calculated temperature of
the piston 1, the quantity of oil distributed to the oil
cooler 4 and the quantity of oil distributed to the bypass
circuit 9 is controlled, whereby the temperature of the
-
Jooling oil is finely controlled, accuracy of controlling the
temperature of the piston 1 is improved, and deterioration of
the fuel consumpr'ion rate can be prevpnted.
.) -
[0028] (Embodiment 3 )
An engine cooling'device'according to Embodiment 3 will
be described with refereiidk to; schematic block diagram
> 1\ ,
shown in FIG. 8.
L
A composing element the same as in Embodiment 1 or
Embodiment 2 is denoted with a same reference-symbol, for
YC; which description is omikfed.
11
11
; [0029] In the distribution path 12, the cooling oil is
i 'drawn up from the oil pan 10 by the oil pump 5 via the first
oil feed tube 111. The second switching adjustment valve 7 is
&
inserted into the second oil feed tube connecting the oil pump
#
5 and the oil cooler 4.
The third oil feed tube 113, which has the first
switching adjustment valve 6 in the intermediate portion, is . ,
disposed ip the downstream side of the distribution p-ath 12 of
the.oil cooler 4, and the oil injection nozzle 8 is disposed? .
further at the downstream side.
- -
4
The second switching adjustment valve 7 i"s connected to
the bypass circuit 9, of which one end is connected between
the first switching adjustment valve 6 of the third oil feed
- ..
&be 113 and the oil cooler 4, and the other end is connected
to the second switching adjustment valve 7.
A control unit 50 has the oil qdintity adjustment map 41
for controlling the-first switching adjustment valve 6, and
the oil temperature adjustment for controlling the
second switching adj ustmeqt valve 7.
/'I
\ 4 'p I
In order to recognize the'operation state of the engine,
detected values acquired by the cooling water temperature
sensor 35, the rotation speedjsensor 36, the load sensor 47
and a cylinder temperatu"e sen$or 38 (and/or a cylinder head
lc 2 1; fl,
tempera,.t,ures ensor 39) are infit to the control unit 50. -. . ,
*[i0 030] Control of this embodiment will now be described
according to the valve control flow of the first switching
adjustment valve 6 and the second switching adjustGent valke 7
#
in FIG. 8:
To recognize the operation state of the engine, .the
temperature of the piston 1 is calculated using the piston
0 , I
temperature calculation map 20 based on the detected val~-- .
, '
acqu,ired by the cooling water temperature sensor 35, the
rotation speed sensor 36 and the load sensor 47.
the other hand, the cylinder temperatyre sensor
installed in the cylinder'2, and the cylinder head temperature
sensor 39 is installed in the cylinder head (not illustrated),
I - 9,
30 as to directly detect the temperature using these sensor3
respectively.
$ <
It is assumed that the detected balue by the cylinder
'\ -
temperature sensor 38 and the detected value by the cylinder
head temperature sensor 39 are compared, and the higher
temperature in the is the detected value K.
"p
If the difference between'phe detected value K and the
piston temperature calculation value calculated using the
piston temperature calculation\ map 20 is a threshold value or
more, the priority is giFen tdlt the detected value K, and the
' 3 " 4
detected yalue K is regarded as' the temperature of the piston
'I, and becomes a control element in the oil quantity
' j
adjustment map 41 and the oil temperature adjustment map 51.
i
If the difference is the threshold or more, the piston
?
temperature calculation value is used.
b
The method for'controlling the oil quantity adju-stment
map 41 and the oil temperature adjustment map 51 is the same . P
as Embodiment 2, therefore description is omitted. -,. ' '- - 'i
-'In this embodiment, the detected value by the cylinder ,
temperature sensor 38 and the detected value by the cylinder
head temperature sensor 39 are compared, and p;riority is given
to the higher value, but only one of the detected value by the
cylinder temperature sensor 38 and the detected value by the
cylinder head temperature sensor 39 may be used.
In this case, cost can be reduced.
[0031] There may be a situation where the temperature
t ,
calculated using the piston temperatuke calculation map. 20 and
\ -
the actual temperature may differ, depending on the
environment for the engine (e-g. cold climate, high altitude).
However, according to thi? emb diment, the cylinder
I 1
temperature sensor 38 anh the ~ylinder head temperature sensdr
* i
39 directly measure the respective temperature, therefore, in
use of the measured values as control elements of the oil
I
quantity adjustment map 41 and^ the oil tempergture adjustment 8;' 1.i
map 51, it is possible to':monr,or in real-time the temperature
' - "d
.of the cylinder 2 and the temperature of the cylinder head,
'$when the engine is operating. Therefore fine cooling control
is possible during transient operation.
h
INDUSTRIAL APPLICABILITY b
[0032] The present invention can be suitably applied to an E ,
engine cooling device for which improvement of startabili@y-of 3 ,I _. .
the engine and fuel consumption is performed by preventing
over-cooling of the piston when the engine, having the piston
cooling device, is started.

WE CLAIMS
1. A cooling device for an engine including an oil jet
device for cooling a piston with oil,^the cooling device
comprising:
a cooling water temperature sensor that detects a
temperature of the engin,e; A
> I • ' \ - •
a rotation speed sensor thkt detects rotation speed of
the engine;
a load sensor that detects load of the engine;
a .jet: nozzle that is secured in a cylinder block of the
^engine and injects cooling oil onto the rear face of the
piston;
an oil cooler disposed upstream of the jet nozzle on a
distribution path of the cooling oil; '
an oil pump that is located upstream of the oil cooler
and pumps the cooling oil to the oil cooler; %
a fir,.st switching adjustment valve that is disponed ?
between the jet nozzle and the oil cooler, and adjusts a flow
dividing ratio at which the cooling oil from the oil cooler is
distributed to the jet nozzle side and to an oil pan side; and
a control unit that has an oil quantity adjustment map
for switching the first switching adjustment valve based on a
21
"(tiston temperature calculation map for calculating .the
temperature of the piston using the detection values acquired
respectively by the temperature sensor, the rotation speed
sensor and the lo^d-sensor.
2. The cooling device for anjengine according to Claim 1, wherein
the control unit adjusts a second switching adjustment
valve disposed between the oil cooler and the,oil pump on the
•J,' 'I
distribution path of the'lcoolinig oil based on an oil
temperature adjustment map which determines a flow dividing
>/ratio at which the cooling oil from the oil pump is
distributed to the oil cooler side and to a bypass circuit
side which is connected between the oil cooler and the first
switching adjustment valve, whereby the temperature of the ,.
cooling oil, after passing through the bypass circuit, is *•
adjusted. '
3. The cooling device for an engine according to Claim 1, wherein, when the engine is started or when the load is intermediate -or low, the value calculated using the piston temperature calculation map is compared with a value detected
22 Wy a cylinder temperature sensor for detecting a cylinder temperature of the engine and/or a value detected by a cylinder head temperature sensor for detecting a temperature
of the cylinder Head, and when a the difference therebetween is a threshold or more, priority is given to the value (s) detected by the cylinder temperature sensor and/or the cylinder; head sensor.