Cooling water circulating apparatus

The present invention provides a cooling water circulating apparatus capable of securing a required flow rate of cooling water without increasing the heads of water pumps. The apparatus includes a first water pump which has a first supply port for supplying the cooling water into the first water pump, the cooling water for flowing through the interior of an engine, and a first discharge port for discharging the supplied cooling water from the first water pump to the engine again, and which is directly connected to and rotated with a cam shaft of the engine. A control mechanism is adapted to cut off a flow of the cooling water, which is directed from a radiator to the first supply port, when the temperature of the cooling water is not higher than a predetermined level, and operatively connect the radiator and first supply port with each other when the temperature of the cooling water is higher than the predetermined level. A second water pump includes a second supply port for supplying the cooling water from the second water pump to flow through the interior of the engine, and a second discharge port for discharging the supplied cooling water from the second water pump to the supply port of the first water pump. The second water pump is not rotated when the temperature of the cooling water is not higher than a predetermined level, and is electrically rotated when the temperature of the cooling water is higher than the predetermined level.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a cooling water circulating apparatus adapted to
 send out cooling water flowing there into an engine or a radiator by a
 water pump.
 2. Description of the Related Art
 The known cooling apparatuses for internal combustion engines include an
 apparatus disclosed in Japanese Patent Laid-Open No. 88582/1997. The
 techniques included in this apparatus are to reduce the limitation placed
 on the arrangement of various auxiliary machines driven via a crankshaft,
 a belt and a chain, by driving a cooling water supply pump by a cam shaft,
 fixing the water pump to a cylinder head so as to join a discharge port of
 the water pump to an inlet port of a cooling water passage on a suction
 side of the cylinder head, thereby forming the suction side cooling water
 passage as a water passage on a discharge side of the water pump, whereby,
 even when the resistance of the suction side cooling water passage is
 large, negative pressure on a suction side of the water pump increases to
 prevent the occurrence of cavitation therein.
 However, in such a related art apparatus, the cooling water is circulated
 by a water pump alone which is driven by a cam shaft rotated with a
 rotational frequency 1/2 times as high as that of the crankshaft, so that,
 when the temperature of the cooling water increases higher than a
 predetermined level, a required flow rate of the cooling water cannot be
 secured unless the capacity of the water pump is increased. In order to
 secure a required flow rate of the cooling water, the cooling water
 discharge performance (head) of the pump has to be improved, and, in order
 to increase the pump head, the dimensions of the water pump have to be
 increased. This causes a driving force of the water pump to increase, so
 that the fuel consumption also increases.
 SUMMARY OF THE INVENTION
 Therefore, the technical problem to be solved by the present invention is
 how to provide a cooling water circulating apparatus capable of securing a
 required flow rate of cooling water without increasing the heads of water
 pumps.
 To solve the problem, a first aspect of the invention provides a cooling
 water circulating apparatus adapted to circulate cooling water through an
 engine or a radiator, including a first water pump which has a first
 supply port for supplying thereinto cooling water which is to flow through
 the interior of an engine, and a first discharge port for discharging
 therefrom the supplied cooling water to the engine again, and which is
 connected to and rotated with a cam shaft of the engine, a control
 mechanism adapted to cut off a flow of the cooling water, which is
 directed from a radiator to the first supply port, when the temperature of
 the cooling water is not higher than a predetermined level, and
 communicate the radiator and first supply port with each other when the
 temperature of the cooling water is higher than the predetermined level,
 and a second water pump which has a second supply post for supplying
 thereinto cooling water which is to flow through the interior of the
 engine, and a second discharge port for discharging therefrom the supplied
 cooling water to the supply port of the first water pump, and which is
 electrically rotated in accordance with the temperature of the cooling
 water.
 According to the first aspect of the invention, when the temperature of the
 cooling water is not higher than a predetermined level, the first water
 pump is rotated with the cam shaft of the engine, receives the supply of
 cooling water from the first supply port and discharges the same toward
 the first discharge port. The discharged cooling water cools the engine on
 the inner side thereof. When the temperature of the cooling water becomes
 higher than a predetermined level, the radiator and first supply port are
 communicated with each other by the control mechanism, and the cooling
 water discharged from the first water pump is supplied to the engine and
 radiator. Since the cam shaft is rotated with a rotational frequency 1/2
 times as high as that of the crankshaft, it is considered that, when the
 cooling water is discharged to the engine and radiator, a discharge rate
 of the first water pump decreases in some cases. According to the
 invention, the second water pump is rotated electrically in accordance
 with the temperature of the cooling water. Therefore, when the driving of
 the first water pump alone causes a discharge rate of the cabling water to
 decrease, the second water pump is rotated to enable the shortage of the
 discharge rate to be filled up. Owing to this operation, a suitable
 quantity of cooling water can always be circulated. Since the second water
 pump is electrically operated, the rotational frequency thereof can be
 controlled, and the flow rate of the cooling water can also be arbitrarily
 regulated.
 A case where the second water pump is set so that it is not rotated when
 the temperature of the cooling water is not higher than a predetermined
 level, and rotated electrically when the temperature of the cooling water
 is higher than a predetermined level as described in the statement of a
 second aspect of the invention will be discussed. When the temperature of
 the cooling water becomes higher than a predetermined level, the second
 water pump is driven, and the control mechanism communicates the radiator
 and first supply port with each other. Consequently, the cooling water is
 supplied from the second supply port, and discharged from the second
 discharge port.
 Since the cooling water is thus circulated at a required flow rate through
 both the engine and radiator by rotating the electrically driven second
 water pump, it becomes possible to secure a required flow rate of the
 cooling water without increasing the dimensions of the first water pump
 even when the first water pump is driven with the cam shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 A mode of embodiment of the present invention will now be described with
 reference to the drawings. FIGS. 1 to 4 are drawings showing the cooling
 water circulating apparatus of a mode of embodiment of the present
 invention, wherein FIG. 1 is a system diagram of a cooling water
 circulating apparatus 1, FIG. 2 a sectional view of a first water pump,
 FIG. 3 is a sectional view of a second water pump, and FIG. 4 is a
 characteristic diagram of the second water pump.
 The cooling water circulating apparatus 1 is an apparatus for circulating
 cooling water through an engine 2 and a radiator 3, and provided with a
 first water pump 4 which has a first supply port 5 for supplying cooling
 water flowing through the engine 2, and a first discharge port 6 for
 discharging the supplied cooling water to the engine 2 again, and which is
 connected to and rotated with a cam shaft 2A (two-dot chain lines in FIG.
 2) of the engine 2, a thermostat 7 as a control mechanism adapted to cut
 off a flow of the cooling water which is supplied from the radiator 3 to
 the first supply port 5 when the temperature of the cooling water is not
 higher than a predetermined level, and communicate the radiator 3 and
 first supply port 5 when the temperature of the cooling water is higher
 than a predetermined level, and a second water pump 8 which has a second
 supply port 9 for supplying the cooling water flowing through the interior
 of the engine 2, and a second discharge port 10 for discharging the
 supplied cooling water toward the first supply port 5 of the first water
 pump 4, and which is not rotated when the temperature of the cooling water
 is not higher than a predetermined level, and rotated electrically when
 the temperature of the cooling water is higher than a predetermined level,
 the cooling water being circulated through the interior of the radiator 3
 in accordance with the temperature of the cooling water.
 The construction of each constituent part will be described in detail. As
 shown in FIG. 2, the firewater pump 4 is formed of a driving shaft 11
 rotated with the cam shaft 2A, a rotor 12 mounted on a free end portion of
 the driving shaft 11, first supply port 5 for supplying the cooling water
 therefrom, and the first discharge port 6 for discharging the supplied
 cooling water to the engine 2, and this water pump 4 is rotated with the
 same rotational frequency as the cam shaft 2A, i.e., with a rotational
 frequency 1/2 of that of the crankshaft.
 As shown in FIG. 3, the second water pump 8 is a DC brushless motor
 provided with a metal rotor 15 for sucking and discharging the cooling
 water, a rotary shaft 17 which has the rotor 15 mounted fixedly on a free
 end portion thereof, and is which is rotated with the rotor 15, a housing
 18 fixed to the engine 2, bearings 19, 20 supporting the rotary shaft 17
 on the housing 18 so that the rotary shaft 17 can be rotated relatively to
 the housing 18, a magnet 16 formed on an outer circumferential surface of
 the rotary shaft 17, cores 21 arranged on an inner circumference of the
 housing 18, and a plurality of coils 22 wound around each core 21 and
 forming a magnetic circuit with the magnet 16. The second water pump 8 is
 formed so that, when an electric current flows in the coils 22, the rotary
 shaft 17 is rotated with the magnet 16 when the rotor 15 also rotated,
 whereby the cooling water flowing from the second supply port 9 is
 discharged from the second discharge port 10. The rotational frequency of
 the rotor 15 can be varied arbitrarily within the volume of the pump in
 accordance with the level of the electric current flowing in the coils 22.
 In this mode of embodiment, a CPU (not shown) rotates the second water
 pump 8 by controlling the electric current, which flows in the coils 22,
 in accordance with the temperature of the cooling water.
 The construction of the second water pump 8 will further be described with
 reference to FIG. 4. As shown in FIG. 4, the second discharge port 10 is
 formed so as to deviate from the center of rotation of the rotor 15, and
 blades 15a of the rotor 15 so as to extend radially with respect to the
 mentioned center of rotation. The direction of rotation of the rotary
 shaft 17 is switched by changing the direction of the electric current I
 flowing in the coils 22.
 In the cooling water circulating apparatus 1 in this mode of embodiment, a
 hot water type heater 23 is provided between the engine 2 and second
 supply port 9, and the warmed cooling water is subjected to heat exchange
 in the heater 23, a blower (not shown) being operated to warm the interior
 of a vehicle. Since the second water pump 8 is electrically driven, the
 rotational frequency can be controlled with a high accuracy, and a flow
 rate of the cooling water sent to the heater 23 is secured, so that the
 performance of the heater is improved.
 The thermostat 7 is a wax type thermostat adapted to switch the circulation
 and cut off of the cooling water, which is sent from the radiator 3 to the
 first water pump 4, from one to the other by utilizing the expansion and
 contraction, which occur in accordance with the temperature of thermowax.
 The operation of the cooling water circulating apparatus 1 will be
 described. When the engine 2 is started and causes the driving shaft 11
 and the rotor 12 of the first water pump 4 to be rotated in accordance
 with the rotation of the cam shaft 2A, the cooling water is supplied from
 the first supply port 5 owing to pumping actions of the first water pump
 4, and the supplied cooling water is discharged toward the first discharge
 port 6.
 When the temperature of the cooling water during a cooling operation is
 lower than a predetermined level, the cooling water is not circulated in
 the radiator 3 so as to rapidly warm the engine 2. In this case, the
 thermostat 7 is closed to cut off the flow of cooling water from the
 radiator 3 to the first supply port 5. The second water pump 8 is not
 rotated. During this time, the cooling water is discharged from the first
 discharge port 6 of the first water pump 4 into the interior of the engine
 2, and flows in the interior of the engine 2 and then into the supply port
 9 of the second water pump 8 via the heater 23. Since the second water
 pump 8 is not rotated, the cooling water flows from the second supply port
 9 into the second discharge port 10, and then into the first supply port 5
 of the first water pump 4, and the cooling water is thereafter discharged
 from the first discharge port 6 owing to the pumping actions. The cooling
 water discharged from the first discharge port 6 flows into the interior
 of the engine 2, and then returns to the first supply port 5 via the
 thermostat 7, the resultant cooling water being then circulated in the
 interior of the engine 2 again. This operation is repeated until the
 temperature of the cooling water reaches a predetermined level.
 When the temperature of the cooling water in the engine 2 in this condition
 becomes not lower than a predetermined level, it is necessary to regulate
 this temperature so as to maintain the temperature of the water in the
 engine 2 at a predetermined level. In this case, the thermostat 7 is
 opened, and the radiator 3 and first supply port 5 communicate with each
 other, so that the cooling water cooled in the radiator 3 is supplied to
 the first water pump 4 with the cooling water circulated through the
 engine 2. The cooling water flowing through the interior of the engine 2
 and warmed is sent to the heater 23, and then passes through the second
 supply port 9 of the second water pump 8, the resultant cooling water
 being discharged from the second discharge port 10 thereof. The cooling
 water is then supplied to the first supply port 5 of the first water pump
 4, and to the interior of the engine 2 again. Therefore, the cooling water
 cooled by the radiator 3 and heater 23 is supplied to the engine 2, and
 the temperature of the water in the engine 2 is thereby maintained at a
 suitable level. Since the second water pump 8 is driven when the
 temperature of the cooling water attains a level not lower than a
 predetermined level, the pump head of the cooling water circulating
 apparatus 1 as a whole becomes equal to the sum of the pump head of the
 first water pump 4 and that of the second water pump 8, and a flow rate of
 the cooling water to the engine 2 and radiator 3 is secured.
 According to this mode of embodiment, using the electrically driven second
 water pump 8 makes it possible to secure a flow rate of the cooling water
 circulated through the radiator 3 and engine 2, without increasing the
 head of the first water pump 4 rotated with the camshaft 2A. This enables
 the fuel consumption to be improved.
 Moreover, in this mode of embodiment, the second discharge port 10 of the
 second water pump 8 is formed so as to deviate from the center of rotation
 of the rotor 15, and the blades 15a of the rotor 15 so as to extend
 radially with respect to the same center of rotation. Accordingly, it
 becomes possible to control the flow of the cooling water by rotating the
 rotor 15 both forward and backward. Owing to this construction, the
 cooling water flows, from the second water pump 8 to the first water pump
 4 without passing through the thermostat 7 when the cooling water flowing
 out from the engine 2 is sent to the first water pump 4. Therefore, the
 thermostat 7 can be formed so that the cooling water flowing out from the
 engine 2 is not supplied thereto. This enables one of the valves of the
 thermostat 7 to be omitted, and the resistance of the cooling water
 exerted on the thermostat 7 to be lowered, whereby the durability of the
 thermostat 7 is improved.
 According to the first aspect of the invention, when the cooling water is
 circulated through both the engine and radiator, the electrically driven
 second water pump is rotated, whereby the circulation of the cooling water
 is carried out at a required flow rate. Therefore, when the driving of the
 first water pump alone causes a discharge rate of the cooling water to
 become short, the second water pump is rotated to enable the shortage of
 the discharge rate to be filled up. Owing to this operation, a suitable
 quantity of cooling water can always be circulated. Since the second water
 pump is electrically driven, the rotational frequency can be controlled,
 and the flow rate of the cooling water can also be arbitrarily regulated.
 According to the second invention, the cooling water is circulated at a
 required flow rate through both the engine and radiator by rotating the
 electrically driven second water pump. Therefore, it becomes possible to
 secure a required flow rate of the cooling water without increasing the
 dimensions of the first water pump even when the first water pump is
 driven with the cam shaft, this invention thus proving to be preferable.
 A mode of embodiment of the present invention has been described above. The
 cooling water circulating apparatus according to the invention is not
 intended to be limited to the above-described mode of embodiment. Any mode
 of embodiment is within the scope of the present invention as long as it
 is in agreement with the gist of the invention as described in the claims
 appended hereto.