Flow control valve

A flow control valve used in a cooling system of a water cooling type includes a first valve body and a first valve seat for controlling a quantity of radiator flow which returns from an engine to a pump through a radiator, a second valve body and a second valve seat for controlling a quantity of bypass flow which returns from the engine to the pump without passing through the radiator, and a step motor for displacing the valve bodies integrally as a valve unit. The first valve body, the first valve seat, the second valve body, and the second valve seat are so arranged that, in a range where the radiator flow quantity becomes practically zero, the bypass flow is permitted to flow at a slightly larger quantity than the radiator flow and, in other ranges, the bypass flow quantity is equal to or lower than the radiator flow quantity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flow control valve which is provided in a cooling system for cooling an engine by circulating cooling water through the engine and which is used for controlling a flow quantity of the cooling water.

2. Description of Related Art

Cooling systems of a water cooling type conventionally used in engines have generally been arranged to control cooling water at a constant temperature of about 80° C. by means of a thermostat without reference to an operating state of the target engine. However, changing a cooling degree of an engine according to an operating state (a loaded condition, a rotational speed, etc.) of the engine was found to be effective in reducing friction of the engine, improving fuel efficiency, enhancing knocking performance, and preventing the overheating of the cooling water. Accordingly, there have been proposed several types of cooling systems using cooling water each arranged to control a cooling degree of an engine according to an operating state of the engine.

Such cooling systems of engines are disclosed in Japanese patent unexamined publications Nos. 09(1997)-195768 and 2000-18039. The cooling system disclosed in the JP unexamined publication No. 09(1997)-195768 is provided with a flow control valve including a first valve body and a first valve seat for controlling a flow quantity of the cooling water which flows out of an engine and returns to a water pump by way of a radiator (hereinafter referred to as a “radiator flow quantity”), a second valve body and a second valve seat for controlling a flow quantity of the cooling water which flows out of the engine and bypass the radiator to directly return to the water pump (hereinafter referred to as a “bypass flow quantity”), and an electromagnetic actuator which drives the first and second valve bodies integrally as a valve unit. The above electromagnetic actuator is constructed of an electromagnetic coil which attracts a shaft made of a magnetic material when electric current is applied to the coil, thereby displacing the shaft downward against the force of a spring. Upon stop of the application of electric current to the coil, on the other hand, the shaft is displaced upward by the force of the spring. In association with the shaft displacement, the first and second valve bodies are driven together as a valve unit.

Similar to the above cooling system disclosed in JP unexamined publication No. 9(1997)-195768, the cooling system disclosed in JP unexamined publication No. 2000-18039 is provided with a radiator circuit for permitting cooling water which flows out of an engine to circulate through a radiator and a bypass circuit for permitting the cooling water which flows out of the engine to bypass the radiator to flow back to the engine. In a portion at which the bypass circuit and the radiator circuit meet, there is disposed a rotary flow control valve for controlling a flow quantity (the radiator flow quantity) of the cooling water flowing in the radiator circuit and a flow quantity (the bypass flow quantity) of the cooling water flowing in the bypass circuit. This flow control valve includes a rotary valve having a cup shape rotatably provided in a housing. This flow control valve is constructed to measure the radiator flow quantity and the bypass flow quantity at an outer periphery of the rotary valve and cause the cooling water flowing in the radiator circuit and the bypass circuit to flow together to return to the engine through a pump.

And now, in the above flow control valve disclosed in JP unexamined publication No. 9(1997)-195768, at the time of driving the valve by operation of the electromagnetic actuator, this actuator is required to produce a driving torque enough to overcome the force of the spring, the force of pressure of the cooling water, and the force caused by collision of the cooling water with each valve. The first valve body is acted upon by the pressure of fluid at an inlet port of the flow control valve (namely, a radiator flow inlet pressure), while the second valve body is acted upon by the pressure of fluid at another inlet port of the flow control valve (namely, a bypass flow inlet pressure). Thus, a difference between those two pressures acts on a valve unit. If the pressure difference is large, the thrust corresponding to the difference is applied to the valve and therefore the electromagnetic actuator is requested to produce a large driving torque. In general, the diameter of a passage for the bypass flow (hereinafter referred to as a “bypass passage”) is smaller than that of a passage for the radiator flow (hereinafter referred to as a “radiator passage”). When the bypass flow quantity becomes larger than the radiator flow quantity, the pressure in the bypass passage becomes a negative pressure, resulting in a large influence on a pressure characteristic. Accordingly, bypass flow inlet pressure is largely reduced depending on a bypass flow quantity characteristic, thereby increasing the pressure difference mentioned above. As a result, the electromagnetic actuator is required to produce a large driving torque to open the flow control valve against the thrust resulting from the pressure difference. This leads to a need to upsize the actuator, which may cause problems of a deterioration in mountability of the flow control valve with respect to the engine and an increase in manufacturing cost of the flow control valve.

In the flow control valve disclosed in JP unexamined publication No. 2000-18039, on the other hand, there is a need to measure the radiator flow quantity and the bypass flow quantity at the outer periphery of the rotary valve. Furthermore, many cooling systems currently used adopt “an internal bypass type” which is provided with a bypass circuit in the inside of an engine block to flow cooling water through the bypass circuit. Accordingly, the flow control valve disclosed in JP unexamined publication 2000-18039 could not directly be used in the internal bypass type of cooling system. To adopt the flow control valve, there is a need to change the shape of the engine or to additionally provide a bypass pipe to the outside of the engine block. Consequently, the cost of manufacturing the cooling system would be increased extremely.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and has a first object to overcome the above problems and to provide a flow control valve capable of preventing the thrust which acts on the valve due to a difference between a radiator flow pressure and a bypass flow pressure to relatively reduce the driving torque which an actuator is requested to produce, thereby achieving downsizing of an actuator.

In addition to the first object, a second object of the present invention is providing a flow control valve which can simply, inexpensively be mounted in an engine.

To achieve the purpose of the invention, there is provided a flow control valve which is used in a cooling system of a water cooling type for cooling an engine by circulating cooling water by a water pump and radiating heat of the cooling water by a radiator; the cooling system including a cooling water passage provided in the engine, a radiator flow passage for permitting the cooling water flowing out of the cooling water passage to return to the water pump through the radiator, a bypass flow passage for permitting the cooling water flowing out of the cooling water passage to directly return to the water pump without passing through the radiator, and an electronic control device for controlling the flow control valve, the radiator flow passage and the bypass flow passage being connected to the flow control valve at a position upstream from the water pump; the flow control valve including a first valve body and a first valve seat for controlling a radiator flow quantity corresponding to a flow quantity of the cooling water flowing in the radiator passage, a second valve body and a second valve seat for controlling a bypass flow quantity corresponding to a flow quantity of the cooling water flowing in the bypass passage, and an actuator for displacing the first and second valve bodies integrally as one valve; the electronic control device for controlling the actuator to displace the valve, thereby regulating the radiator flow quantity and the bypass flow quantity to control a temperature of the cooling water to a target temperature; the radiator flow quantity and the bypass flow quantity are defined in terms of ranges in relation to the displacement amount of the valve so that each structure of the first valve body and the first valve seat and each structure of the second valve body and the second valve seat are determined to have a flow quantity characteristic that the bypass flow quantity is slightly larger than the radiator flow quantity in a range where the radiator flow quantity becomes practically zero and, in other ranges, the bypass flow quantity is equal to or lower than the radiator flow quantity.

According to another aspect of the present invention, there is provided a flow control valve which is used in a cooling system of a water cooling type for cooling an engine by circulating cooling water by a water pump and radiating heat of the cooling water by a radiator; the cooling system including a cooling water passage provided in the engine, a radiator flow passage for permitting the cooling water flowing out of the cooling water passage to return to the water pump through the radiator, a bypass flow passage for permitting the cooling water flowing out of the cooling water passage to directly return to the water pump without passing through the radiator, and an electronic control device for controlling the flow control valve, the radiator flow passage and the bypass flow passage being connected to the flow control valve at a position upstream from the water pump; the flow control valve including a first valve body and a first valve seat for controlling a radiator flow quantity corresponding to a flow quantity of the cooling water flowing in the radiator passage, a second valve body and a second valve seat for controlling a bypass flow quantity corresponding to a flow quantity of the cooling water flowing in the bypass passage, and an actuator for displacing the first and second valve bodies integrally as one valve; the electronic control device for controlling the actuator to displace the valve, thereby regulating the radiator flow quantity and the bypass flow quantity to control a temperature of the cooling water to a target temperature; the radiator flow quantity and the bypass flow quantity are defined in terms of ranges in relation to the displacement amount of the valve so that each structure of the first valve body and the first valve seat and each structure of the second valve body and the second valve seat are determined to have a flow quantity characteristic that the radiator flow quantity increases with respect to an increase of displacement amount of the valve while the bypass flow quantity increases and decreases with respect to the increase of displacement amount of the valve, the bypass flow quantity is slightly larger than the radiator flow quantity in a range where the radiator flow quantity becomes practically zero and, in other ranges, the bypass flow quantity is equal to or lower than the radiator flow quantity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of a first preferred embodiment of a flow control valve embodying the present invention will now be given referring to the accompanying drawings.

FIG. 1is a side view of the flow control valve in the first embodiment. FIG.2is a plane view of the valve in FIG.1.FIG. 3is a longitudinal sectional view of the valve taken along a line A—A in FIG.2.FIG. 4is a cross sectional view of the valve taken along a line B—B in FIG.3.FIG. 5is a cross sectional view of the valve taken along a line C—C in FIG.3. Arrows inFIG. 5indicate the flow of water.

The flow control valve1, which is integrated in a cooling system of a water-cooled engine used for automobiles, is used to control a flow quantity of cooling water.FIG. 6is a schematic structural view of the cooling system. InFIG. 6, an engine2is internally provided with a cooling water passage3including a water jacket and others. An outlet port of the flow control valve1is connected to a water pump (W/P)5through a pump passage4. The water pump5is connected to an inlet of the cooling water passage3. An outlet of this passage3is connected to a radiator passage6and a bypass passage7. The radiator passage6is connected to the flow control valve1via a radiator8. The bypass passage7is directly connected to the valve1, not via the radiator8.

In an open state of the flow control valve1, when the water pump5is actuated in conjunction with operation of the engine2, the pump5discharges cooling water into the cooling water passage3of the engine2. The cooling water circulates through the engine2and then flows out from the outlet of the passage3. A part of the cooling water flowing out of the passage3flows into the valve1through the radiator passage6and the radiator8, while a part of the cooling water flowing out of the passage3flows into the valve1through the bypass passage7. The valve1controls a radiator flow quantity of the cooling water flowing from the radiator passage6into the valve1and a bypass flow quantity of the cooling water flowing from the bypass passage7into the valve1. The cooling water of a controlled flow quantity is then delivered to the water pump5through the pump passage4and discharged again into the cooling water passage3. This circulation of the cooling water cools the engine2at suitable temperatures.

By the above control of the radiator flow quantity by the flow control valve1, the temperature of the cooling water flowing through the passage3of the engine2is controlled. Specifically, when the radiator flow quantity is controlled by the flow control valve1to increase, the ratio of the cooling water having radiated heat through the radiator8in the cooling water flowing through the passage3increases. Accordingly, the temperature of the cooling water which cools the engine2becomes relatively lower. When the radiator flow quantity is controlled by the flow control valve1to decrease, on the other hand, the ratio of the cooling water having radiated heat through the radiator8in the cooling water flowing through the passage3decreases. Due to this, the temperature of the cooling water contributing to cooling of the engine2becomes relatively higher.

The flow control valve1is connected to an electronic control unit (ECU)11for controlling the engine2as shown in FIG.6. The ECU11controls the valve1to adjust the degree of cooling the engine2in response to an operating state of the engine2. For execution of control to open/close the valve1, the ECU11receives signals representing parameters such as an engine rotational speed, an intake air pressure, an engine outlet water temperature, and a radiator outlet water temperature, from various sensors. The engine outlet water temperature of the above parameters is the temperature of cooling water detected by a first water temperature sensor12disposed close to the outlet of the cooling water passage3. The radiator outlet water temperature is the temperature of cooling water detected by a second water temperature sensor13disposed close to the outlet of the radiator8. The ECU11controls the opening and closing (an opening degree) of the valve1in response to the operating state of the engine2based on the signals representing the various parameters.

As shown inFIG. 1, the flow control valve1is mounted in a thermostat housing21formed in a block2aof the engine2(hereinafter simply referred to as an “engine block”). The housing21is communicated with the pump passage4and the bypass passage7respectively. The pump passage4is communicated with the water pump5. The housing21is generally used to hold a well known thermostat. In the present embodiment, however, the housing21is used to mount therein the flow control valve1.

More specifically, the engine block2aof the engine2includes the housing21for mounting the thermostat, the pump passage4for permitting cooling water to flow into the water pump5from the housing21, and the bypass passage7for permitting cooling water that returns to the water pump5without passing through the radiator8to flow into the housing21. This housing21is utilized to mount therein the flow control valve1.

As shown inFIGS. 1 and 2, the flow control valve1is constructed of three sections including a first body22, a second body23serving as a joint body of the present invention, and a step motor24serving as an actuator of the present invention. The second body23is designed to have the outer diameter relatively smaller than the inner diameter of the housing21and the height equal to the depth of the housing21. This dimensional design permits the second body23to be received and mounted in the housing21. In this mounted state, the first and second bodies22and23are both secured to the engine block2awith screws25. A seal ring26is provided between the first body22and the engine block2a. The step motor24is secured to the first body22with screws27. The first body22is provided with a joint pipe28which is connected to the radiator passage6. Between the step motor24and the first body22, there is sandwiched a shim29for adjustment of valve opening steps. A wiring connector30is provided in the step motor24.

As described above, the flow control valve1controls the radiator flow quantity of the cooling water which flows out of the cooling water passage3of the engine2and returns to the water pump5through the radiator passage6and the radiator8and simultaneously controls the bypass flow quantity of the cooling water which flows out of the passage3and returns to the water pump5without passing through the radiator8. The valve1is provided, as shown inFIG. 3, with a first valve body31and a first valve seat35for controlling the radiator flow quantity and a second valve body32and a second valve seat36for controlling the bypass flow quantity. These first and second valve bodies31and32are configured so as to be driven and displaced integrally as one valve unit20by the step motor24.

As shown inFIG. 3, the second body23having a cylindrical shape is formed with a bypass port33in the lower portion. This bypass port33is communicated with the bypass passage7. The body23is also formed with a pump port34in the upper portion. In the body23, the first valve seat35to be used for the first valve body31and the second valve seat36to be used for the second valve body32are disposed on the upper and lower sides of the pump port34. The bypass port33can be communicated with the pump port34through a valve opening36aof the second valve seat36. A seal ring37for sealing a gap between the bypass passage7and the thermostat housing21is disposed in the lower portion of the body23. The first body22is divided into an upper and lower chambers39and40by a partition wall38. A valve shaft42is provided penetrating the partition wall38. The lower chamber40is communicated with a radiator port41in the joint pipe28. This radiator port41can be communicated with the pump port34through a valve opening35aof the first valve seat35.

As shown inFIG. 3, a back spring46is disposed between the second valve body32and a boss43. This back spring46presses the second valve body32as well as the first valve body31by a predetermined urging force to urge the first valve body31in an opening direction. In the present embodiment, the output power (thrust) of the step motor24is minimized, so that the urging force of the back spring46can be determined at a minimum.

An O-ring47is disposed between the first and second bodies22and23for sealing a gap therebetween. A seal member48is provided in the first body22to seal a gap between the partition wall38and the valve shaft42. Thus, this seal member48serves to prevent the cooling water flowing in the lower chamber40of the first body22from entering the upper chamber39communicated with the step motor24.

In the cooling system including the flow control valve1in the present embodiment, as shown inFIG. 3, the bypass passage7and the bypass port33each have the inner diameter smaller than each inner diameter of the radiator passage6and the radiator port41as in the case of generally used valves. Accordingly, when the bypass flow quantity is larger than the radiator flow quantity, a pressure drop in the bypass passage7at the bypass port33becomes larger than that in the radiator passage6at the radiator port41. As a result, a difference is generated between pressures which are exerted on the first and second valve bodies31and32respectively, thus producing a force acting on the valve bodies31and32in a closing direction. This results in a large influence on the pressure characteristic. More specifically, the influence of the pressure of the cooling water acting on the valve20of the flow control valve1becomes more significant when the bypass flow quantity is changed as compared with the case where the radiator flow quantity is changed. In the present embodiment, the inner diameter D1of the bypass port33is determined to be larger than the outer diameter D2of the boss43.

Next, detailed explanations are made on each structure of the first valve body31and the first valve seat35and each structure of the second valve body32and the second valve seat36.FIGS. 7to9show enlarged views of the first and second valve bodies31and32and others to explain motions thereof.

As shown inFIGS. 3 and 7to9, the first and second valve bodies31and32are fixed one above the other on the single valve shaft42, thus constituting the valve unit20. The valve shaft42is held in the partition wall38and the boss43of the second body23through bearings44and45so that the shaft42is movable in a thrust direction (in a vertical direction in FIG.3).

The first valve body31having a cylindrical shape is mounted on the valve shaft42. The first valve body31is constituted of a flange-shaped measuring part31aformed in the upper portion and a cylindrical maximum flow quantity limiting part31bformed under the measuring part31a. The measuring part31ais conformable to (can be engaged in) the valve opening35aof the first valve seat35. To be specific, the measuring part31aincludes a cylindrical part31cand a large-diameter part31dhaving the outer diameter larger than that of the cylindrical part31c. The valve opening35aof the first valve seat35includes a circumferential part35bwhose surface conforms to the outer surface of the cylindrical part31cand a tapered part35cwhose surface conforms to the outer surface of the large-diameter part31d. It is to be noted that the circumferential part35bserves as a first sealing part and the tapered part35cserves as a second sealing part. When the first valve body31is moved up and down integrally with the valve shaft42, a valve opening degree for the radiator flow (hereinafter referred to as a “radiator-side opening degree”) defined by a clearance between the first valve body31and the first valve seat35is changed.FIGS. 3 and 9show the valve20in a full open state for the radiator-side opening degree. As the first valve body31is moved downward from this full open state shown inFIGS. 3 and 9to a full closed state, the radiator-side opening degree is reduced.

The second valve body32placed under the first valve body31has a cylindrical shape of the outer diameter substantially equal to that of the measuring part31aof the first valve body31. This valve body32is constructed of an upper measuring part32aand a lower measuring part32bpositioned one above the other, a maximum flow quantity limiting part32cformed between the upper and lower measuring parts32aand32b, and a tapered part32dserving as a flow quantity changing part positioned between the upper measuring part32aand the maximum flow quantity limiting part32c. Those upper and lower measuring parts32aand32bcan be individually engaged in a valve opening36aof the second valve seat36. This valve opening36aincludes a circumferential part36bwhose surface conforms to each outer surface of the upper and lower measuring parts32aand32band a tapered part36cformed under the circumferential part36b. When the second valve body32is moved as a unit with the first valve body31and the valve shaft42, a valve opening degree for the bypass flow (hereinafter referred to as a “bypass-side opening degree”) which is defined by a clearance between each of the upper and lower measuring parts32aand32bof the second valve body32and the second valve seat36is changed.FIGS. 3 and 9show the valve20in a state where the lower measuring part32bis engaged in the circumferential part36b, thereby closing the second valve seat36. As the second valve body32is moved downward from this state, the lower measuring part32bis gradually moved away from the circumferential part36b, the maximum flow quantity limiting part32ccomes through the circumferential part36b, and then the upper measuring part32agradually comes close to the circumferential part36b. Thus, the bypass-side opening degree is increased from a full closed state to a full open state and then decreased to return to the full closed state again.

The structure of the step motor24is explained below. As shown inFIG. 3, the step motor24is provided with two stators51aand51band a rotor52disposed inside of those stators51aand51b. Each of the stators51aand51bincludes a core53having triangular teeth arranged alternately extending from above and below and a bobbin54disposed in the core53, and a coil55. The coils55of the stators51aand51bare wound onto the corresponding bobbins54in opposite winding directions to each other. Accordingly, when the application of electric current to either one of the two coils55is switched to the other one, the direction of a magnetic pole exciting the core53can be changed. The two stators51aand51bare fixedly placed one above the other with their cores53positioned in disagreement with each other.

In the present embodiment, the rotor52is a magnet whose outer periphery is previously magnetized in the north pole and the south pole alternately. As shown inFIG. 3, a center shaft56is centrally disposed in the rotor52so that the shaft56is rotatable together with the rotor52. A guide57is attached to the lower part of the center shaft56formed with a male screw56aon the outer periphery. The guide57is formed with a female screw57awhich engages with the male screw56aof the center shaft56. With this structure, the rotation of the rotor52is converted into the movement of the guide57in the thrust direction through the center shaft56. The guide57is connected to the valve shaft42through a joint58. Between the guide57and the joint58, a relief spring59is disposed.

The following explanation is made on the flow quantity characteristic of the flow control valve1, which results from the structures of the first valve body31and the first valve seat35and those of the second valve body32and the second valve seat36.

FIGS. 10A and 10Bare graphs showing the flow quantity characteristic and the pressure characteristic of the flow control valve1. InFIG. 10B, the lateral axis indicates the number of motor steps of the step motor24and the vertical axis indicates a flow quantity of the cooling water (including the radiator flow quantity and the bypass flow quantity). InFIG. 10A, the lateral axis indicates the number of motor steps of the step motor24and the vertical axis indicates the pressure of the radiator flow (hereinafter referred to as “radiator flow pressure”) exerting on the radiator port41and the pressure of the bypass flow (hereinafter referred to as “bypass flow pressure”) exerting on the bypass port33. In this case, the number of motor steps in the lateral axis corresponds to the opening degree of the valve20(valve opening degree). The number of motor steps of “0” corresponds to a “full closed state” of the valve20and the number of motor steps of “about 230” corresponds to a “full open state” of the valve20. That is, in the present embodiment, the radiator flow quantity and the bypass flow quantity are expressed in ranges in relation to the valve opening degree representing a displaced amount of the valve20.

The radiator flow quantity shows a tendency to increase as shown inFIG. 10Bas the displacement amount of the valve20(namely, the valve opening degree) increases. This characteristic is determined by the radiator-side opening degree from the full closed state of the first valve body31shown inFIG. 7to the full open state shown inFIG. 9via the half-open state shown in FIG.8.

The bypass flow quantity shows an increase and a decrease as shown inFIG. 10Bas the displacement amount of the valve20(namely, the valve opening degree) increases. This characteristic is determined by the bypass-side opening degree from the full closed state of the second valve body32shown inFIG. 7to the full closed state shown inFIG. 9via the half-open state shown in FIG.8.

The above flow quantity characteristic is determined so that the bypass flow quantity becomes slightly larger than the radiator flow quantity in the range where the radiator flow quantity is approximately zero (corresponding to the “warm-up range” in FIG.10B), while the bypass flow quantity is equal to or smaller than the radiator flow quantity. Particularly, inFIG. 10B, the flow quantity characteristic in the “low flow quantity range” where the number of motor steps becomes “30 to 80” is determined such that the bypass flow quantity is smaller than the radiator flow quantity, and the radiator flow quantity almost linearly increases rapidly while the bypass flow quantity substantially remains unchanged.

The above flow characteristic in the “warm-up range” corresponds to the characteristic determined by the first valve body31that is moved from the full closed state shown inFIG. 7into a slightly open state. More specifically, this flow characteristic is obtained while the cylindrical part31cof the first valve body31is in contact with the circumferential part35bof the first valve seat35. In this range, the radiator flow quantity is maintained at zero while the cylindrical part31cis moved in contact with the circumferential part35b. During this period of time, on the other hand, the upper measuring part32aof the second valve body32is in contact with the circumferential part36bof the second valve seat36. In this contact state, a fine clearance previously provided between the upper measuring part32aand the circumferential part36bsteadily provides the bypass flow of a corresponding small quantity. Accordingly, the bypass flow is permitted to flow at a quantity slightly larger than the radiator flow by the small bypass flow quantity allowed through the fine clearance.

The flow characteristic of the radiator flow quantity in the “low flow quantity range” is obtained during a period from the time when the cylindrical part31cof the first valve body31begins to be separated from the circumferential part35bof the first valve seat35until the time when the cylindrical part31creaches a half-open state shown inFIG. 8, passing through the tapered part35cof the first valve seat35. In this range, as the cylindrical part31ccomes through and off the tapered part35c, the radiator flow quantity substantially linearly increases. In almost all this range, the upper measuring part32aof the second valve body32is in the vicinity of the circumferential part36bof the second valve seat36, so that the fine clearance between the upper measuring part32aand the circumferential part36bis maintained. Accordingly, the bypass flow quantity does not essentially increase.

InFIG. 10B, in the larger range than the “low flow quantity range”, up to the full open state, the radiator flow quantity increases in a quadratic curve as the valve opening degree increases to reach the “maximum flow quantity range”. This flow characteristic of the radiator flow is obtained when the measuring part31aof the first valve body31changes from the half-open state shown inFIG. 8to the full open state shown inFIG. 9while the measuring part31acomes off the first valve seat35and the second valve body32comes close to the first valve seat35. The bypass flow quantity, on the other hand, slowly increases and slowly decreases while the valve opening degree increases. This bypass flow characteristic is obtained when the second valve body32changes from the state shown inFIG. 8to the state shown inFIG. 9while the upper measuring part32acomes off the second valve seat36, whereas the lower measuring part32bcomes close to the second valve body32. It is to be noted that the bypass flow does not become zero even when the second valve body32is brought into the state shown in FIG.9. This is because a slight clearance is provided between the lower measuring part32bof the second valve body32and the circumferential part36bof the second valve seat36, thereby producing the bypass flow of a quantity corresponding to the clearance.

According to the flow control valve1described above in the present embodiment, which is used in the engine cooling system shown inFIG. 6, the ECU11determines a valve opening degree according to an operating state of the engine2to control the step motor24of the flow control valve1. Thus, the flow characteristic can be obtained in correspondence with the determined valve opening degree.

To start the engine2from a cold state, for instance, the ECU11controls the step motor24at a required number of motor steps to selectively use the “warm-up range” of the above mentioned flow characteristic. In this case, the radiator flow quantity becomes practically zero, so that the cooling water flowing through the cooling water passage3in the engine2does not pass through the radiator8, not radiating heat, and the bypass flow of a very small quantity is provided. That is, the bypass flow quantity is slightly larger than the radiator flow quantity in the “warm-up range” where the radiator flow quantity is practically zero. The cooling water flowing out of the engine2is therefore permitted to return to the water pump5by the very small quantity of the bypass flow and circulate through the engine2again even where no circulation including heat radiation by the radiator8is caused. Accordingly, the cooling water of the very small quantity is permitted to flow through the passage3and the first water temperature sensor12detects the engine outlet water temperature reflecting the current temperature of the engine2.

Supposing that the bypass flow quantity is set at zero, the cooling water is not permitted to flow through the cooling water passage3. As a result, the first water temperature sensor12could not detect an appropriate engine outlet water temperature reflecting the current temperature of the engine2, but would detect a temperature of the cooling water staying in the vicinity of the outlet of the passage3, which is an inappropriate temperature for the engine outlet water temperature. In the present embodiment, the above disadvantages can be avoided and the engine2can be efficiently warmed up as needed in the cold state. Thus, the temperature of the engine2can be properly reflected in the control of the flow control valve1.

Furthermore, the ECU11controls the step motor24at a required number of motor steps to selectively use a range between the “warm-up range” and the “maximum flow quantity range” in the flow characteristic shown inFIG. 10B, thereby controlling the cooling degree of the engine2. In this case, the cooling water flowing through the passage3is permitted to flow in both the radiator passage6and the bypass passage7. The first water temperature sensor12thus detects an appropriate temperature of the cooling water at the engine outlet, reflecting the temperature of the engine2. The second water temperature sensor13, on the other hand, detects an appropriate temperature of the cooling water at the radiator outlet, reflecting the radiating state of the radiator8. To ensure the radiator flow quantity required for cooling the engine2, furthermore, the flow control valve1can be appropriately controlled based on the engine outlet water temperature and the radiator outlet water temperature both detected in the above manner. In the range between the “warm-up range” and the “maximum flow quantity range”, the radiator flow quantity changes in an almost secondary curve with respect to the number of motor steps (i.e., the valve opening degree). Thus, the ECU11can smoothly perform feedback control of the cooling water temperature to a target temperature.

During a high-load operation of the engine2, the ECU11controls the step motor24of the valve1at a required number of motor steps in order to selectively use the “maximum flow quantity range” in the flow quantity characteristic shown in FIG.10B. In this case, the radiator flow quantity becomes maximum, the circulation quantity of the cooling water circulating through the cooling water passage3and then passing through the radiator8becomes maximum, and thus the heat-radiating efficiency of the cooling water in the radiator8becomes maximum. Accordingly, the temperature rise of the cooling water can be suppressed to a minimum so that the engine2is cooled maximally.

In the flow control valve1in the present embodiment, meanwhile, the bypass flow quantity has a relatively larger influence on the pressure characteristic as compared with the radiator flow quantity. As shown inFIG. 10B, in the ranges other than the “warm-up range” where the radiator flow quantity becomes practically zero, the bypass flow quantity having the large influence on the pressure characteristic of the cooling water is equal to or smaller than the radiator flow quantity. Thus, a difference in pressure between the pressure of the radiator flow acting on the first valve body31(hereinafter referred to as “radiator flow pressure”) and the pressure of the bypass flow acting on the second valve body32(hereinafter referred to as “bypass flow pressure”) is reduced at every valve opening degrees as shown in FIG.10A. The thrust produced by the pressure of the cooling water acting on the valve unit20is correspondingly reduced. This also reduces the thrust produced by the pressure of the cooling water which acts on the step motor24from the valve20through the joint58and the guide57, so that the driving torque to be requested to the step motor24can be decreased by just that much. As a result, the step motor24can be downsized according to a reduction in driving torque (power), thereby achieving downsizing of the flow control valve1. Accordingly, the mountability of the flow control valve1to the engine2can be enhanced.

According to the flow characteristic of the flow control valve1in the present embodiment, as shown inFIG. 10B, the radiator flow quantity is increased toward the maximum flow quantity in proportion to an increase in the displacement amount (the valve opening degree) of the valve20. The bypass flow quantity is increased once and then decreased as the displacement amount of the valve20(the valve opening degree) is increased. Consequently, in the “maximum flow quantity range” where the radiator flow quantity becomes maximum, the bypass flow quantity is decreased. By this decreased bypass flow quantity, the cooling water which circulates as a radiator flow is increased. During the high-load operation of the engine2which needs to be cooled maximally, the cooling water of the maximum flow quantity can be radiated in the radiator8to be cooled, thereby enhancing the cooling effect of the engine2.

In the present embodiment, the engine block2aconstructing the engine2includes the housing21, the pump passage4, and the bypass passage7. This configured engine block2ais one of engines of an “internal bypass type” which causes cooling water to flow through the internally provided bypass passage7. This type has currently been adopted in many engines.

As described above, according to the flow control valve1in the first embodiment, as shown inFIGS. 1 and 3to5, the housing21previously provided in the engine block2aof the current “internal bypass type” can be utilized for holding the second body23to mount the flow control valve1in the engine block2a. In this mounted state, the bypass port33of the second body23is communicated with the bypass passage7of the engine block2a. Thus, the bypass flow quantity passing through the flow control valve1can be provided. The pump port34of the second body23is communicated with the pump passage4of the engine block2a. Accordingly, the radiator flow quantity and the bypass flow quantity controlled by the flow control valve1are returned to the water pump5through the pump passage4. In this way, the housing21of the engine block2acan be used for mounting the flow control valve1, which can avoid the need to change the shape of the engine block2aand additionally provide external bypass pipe and others to the engine block2afor the purpose of mounting the flow control valve1. Consequently, the flow control valve1can be mounted in the engine2simply and inexpensively, and therefore, the cost of manufacturing the cooling system can be prevented from extremely rising.

Next, a second embodiment of a flow control valve embodying the present invention will be described with reference to the accompanying drawings. It is to be noted that like elements corresponding to those in the first embodiment are indicated by like numerals, and their explanations are omitted. This second embodiment is explained with a focus on different structures from those in the first embodiment.

FIG. 11is a longitudinal sectional view of a flow control valve61in the present embodiment.FIG. 11is based on FIG.3. This flow control valve61includes a first valve body71and a first valve seat72which differ from those of the flow control valve1in the first embodiment.

The first valve body71has a substantially short cylindrical shape including a flange-shaped measuring part71aformed in the upper portion. The first valve body71does not include the maximum flow quantity limiting part31bprovided in the first valve body31in the first embodiment. In the present embodiment, the valve shaft42directly underneath the first valve body71has the same function as the maximum flow quantity limiting part31b. The measuring part71aof the first valve body71can be engaged in a valve opening72aof the first valve seat72. To be specific, the measuring part71aincludes a cylindrical part71band a large-diameter part71chaving the outer diameter than that of the cylindrical part71b. The valve opening72aof the first valve body72includes a circumferential part72bwhose surface conforms to the outer surface of the cylindrical part71bof the first valve body71and a sealing part72cwhose surface conforms to the outer surface of the large-diameter part71c. The sealing part72cis provided by baking rubber on a substrate forming the first valve seat72. When the first valve body71is moved up and down integrally with the valve shaft42, the radiator-side opening degree defined by a clearance between the valve body71and the valve seat72is changed.FIG. 11shows the valve20in a full open state for the radiator-side opening degree. In a full closed state for the radiator-side opening degree, the cylindrical part71bof the first valve body71is engaged in the circumferential part72bof the first valve seat72and the large-diameter part71cof the first valve body71is brought into close contact with the sealing part72cof the first valve seat72.

According to the flow control valve61in the second embodiment, the same effects as those by the flow control valve1in the first embodiment can be obtained. In addition, the maximum flow quantity of the radiator flow can be more increased as compared with in the first embodiment by the quantity resulting from that the first valve body71includes no maximum flow quantity limiting part. Furthermore, the first valve body71is provided with the large-diameter part71cand the first valve seat72is provided with the sealing part72cwhich can come into close contact with the large-diameter part71c, so that the sealing ability against the cooling water can be enhanced when the radiator-side opening degree is brought into the full closed state.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

In the above embodiments, the flow quantity characteristics of the flow control valves1and61are each determined so that the radiator flow quantity increases as the displacement amount of the valve20increases, and the bypass flow quantity increases and decreases as the displacement amount of the valve20increases. The increase and decrease relation between the radiator flow quantity and the bypass flow quantity is not limited to the above mentioned and may be changed as appropriate.

Although the step motor24is used as an actuator in the above embodiments, different types of actuators such as a DC motor and a linear solenoid may be used.