Cooling device of engine

There are provided a radiator passage, a thermostat to open and close the radiator passage according to an engine temperature, a heater passage, a flow adjusting device to adjust a flow amount of the coolant that flows in the water jacket according to the engine temperature at an engine start. The flow adjusting device is configured so as to adjust the flow amount of the coolant flowing in the water jacket to be a normal amount when the engine temperature is in an extremely-cold condition, to be zero or smaller than the normal amount when the engine is in a mild-cold condition, and to be the normal amount when the engine is in a warm condition. The heater passage is in opened sate at least when the engine is in the extremely-cold condition.

BACKGROUND OF THE INVENTION

The present invention relates to a cooling device of an engine, in which the engine is cooled with a cooling water that is circulated in a water jacket of the engine and a radiator, a heater unit for heating a vehicle cabin and the like.

A cooling system with the cooling water that is circulated between the water jacket in a cylinder block and a cylinder head and the radiator is known as an engine cooling method. In this system, the heater unit for heating the vehicle cabin with the heated cooling water is generally disposed in a cooling-water circulation passage in parallel to the radiator.

For example, Japanese Patent Laid-Open Publication No. 2004-353632 discloses the cooling device of an engine that comprises the cooling-water circulation passage in which the cooling water is circulated between the water jacket of the engine and the radiator, the heater circulation passage that has a common passage to the cooling-water circulation passage, in which the cooling water is circulated between the water jacket and the heater unit, and the thermostat provided in the cooling-water circulation passage and operative to open and close the cooling-water circulation passage led to the radiator according to the temperature of the cooling-water fed from the water jacket. In this device, the flow passage of the cooling water led to the radiator is controlled to be closed until the cooling-water temperature increases to a specified temperature, so that the cooling water can be circulated only in the heater circulation passage. Thus, the quick warming-up of the engine is attained and the emission function of the engine is improved.

Further, the above-described device has an advantage that since the cooling water is always circulated in the heater circulation passage, the heating of the vehicle cabin can be achieved properly so as to meet the passenger's heating requirement from the engine start.

Meanwhile, since the heat exchange between the air supplied to the vehicle cabin and the cooling water is conducted at the heater unit, some heat value is taken from the cooling water at the heater unit, so that there is a limit to the quick warming-up of the engine.

Herein, in the case where the engine is restarted soon after the engine stop, the cooling-temperature and the cabin temperature would not reduce to the air temperature outside the vehicle soon, so the cooling-water temperature may be increased to a specified temperature rather promptly. In this case, if the cooling water is supplied to the heater circulation passage, the heating would be conducted at the engine start, but the engine warming-up would be delayed and therefore the properly-heated air would not be supplied to the cabin promptly. In this case, some measures to heat the engine promptly should be necessary.

Herein, in the case where the air temperature outside is relatively high, such as in summer, passing the cooling water in the heater circulation passage would bring a prolonged period of the engine warming-up, thereby deteriorating the emission function of the engine.

Meanwhile, in order to give priority to the quick warming-up of the engine, for example, there could be provided a bypass passage to bypass the radiator and the heater unit or the water pump could be stopped, so that the cooling water could remain in the water jacket and the engine could be heated promptly. However, in the case where the air temperature outside is extremely low, such as in winter, it is better that the operation of the heater unit should be available from an early stage because the cabin could be heated to a certain degree with the cooling water whose temperature has not increased sufficiently yet.

Herein, in the case where the above-described bypass passage is controlled in its opening and closing with an electromagnetic valve that is activated in response to signals from sensors, this would increase costs. Meanwhile, in the case where the water pump is stopped, some control measures to drive the water pump separately from the engine operation (without a direct connection between the pump and engine) would be necessary, this would increase manufacturing costs as well.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the above-described things, and an object of the present invention is to provide a cooling device of an engine that can improve an engine's warming-up and achieve a proper emission function of the engine, meeting properly requirements of passenger's heating at the engine start. Another object of the present invention is to provide a cooling device of an engine that can perform the above-described functions at low manufacturing costs.

According to a first aspect of the present invention, there is provided a cooling device of an engine, comprising a radiator passage in which coolant is circulated by a water pump between a water jacket of the engine and a radiator, a thermostat provided in the radiator passage and operative to open the radiator passage when an engine temperature is a specified passage-opening temperature or higher, and to close the radiator passage when the engine temperature is lower than the specified passage-opening temperature, a heater passage in which the coolant is circulated between the water jacket and a heater unit for heating of a vehicle cabin, and a flow adjusting device operative to adjust a flow amount of the coolant that flows in the water jacket according to the engine temperature at an engine start, wherein the flow adjusting device is configured so as to adjust the flow amount of the coolant flowing in the water jacket to be a normal amount when the engine temperature is in an extremely-cold condition where the engine temperature is lower than an extremely-cold standard temperature that is lower than the specified passage-opening temperature, to be zero or smaller than the normal amount when the engine is in a mild-cold condition where the engine temperature is or higher than the extremely-cold standard temperature and lower than a mild-cold standard temperature that is lower than the specified passage-opening temperature, and to be the normal amount when the engine is in a warm condition where the engine temperature is or higher than the mild-cold standard temperature, and the heater passage is configured so as to be opened at least when the engine is in the extremely-cold condition.

According to the first aspect of the present invention, there is provided the flow adjusting device operative to adjust the flow amount of the coolant that flows in the water jacket according to the engine temperature at the engine start, this flow adjusting device is configured so as to adjust the flow amount of the coolant flowing in the water jacket to be the normal amount when the engine temperature is in the extremely-cold condition where the engine temperature is lower than the extremely-cold standard temperature that is lower than the specified passage-opening temperature for opening the thermostat, and the heater passage is configured so as to be opened at least when the engine is in the extremely-cold condition. Thereby, the coolant fed from the water jacket is supplied to the heater passage, so the heater unit can function from the engine start and thereby the heating of a vehicle cabin can be performed properly. Namely, when the engine is in the extremely-cold condition where the engine temperature is low, the coolant, such as a cooling water, is supplied to the heater unit, not to the radiator, so the heating is given priority to from the engine start and the passenger's heating requirement can be met properly.

Meanwhile, the flow adjusting device is configured so as to adjust the flow amount of the coolant flowing in the water jacket to be zero or smaller than the normal amount when the engine is in the mild-cold condition where the engine temperature is or higher than the extremely-cold standard temperature and lower than the mild-cold standard temperature that is lower than the specified passage-opening temperature. Thereby, the flow amount of coolant in the water jacket reduces or the coolant remains there without flowing. Accordingly, the coolant in the water jacket is increased in temperature promptly, so the quick warming-up of the engine can be attained and thus CO, HC, incomplete-combustion gas can be reduced, thereby improving the proper emission function of the engine. Also, when the engine is in the mild-cold condition, the temperature in the cabin is not so low. Accordingly, after the coolant' temperature has been increased by the quick-warming up, the sufficiently heated conditioning air can be supplied to the cabin, so the passenger's heating requirement can be met properly.

Further, the flow adjusting device is configured so as to adjust the flow amount of the coolant flowing in the water jacket to be the normal amount when the engine is in the warm condition where the engine temperature is or higher than the mild-cold standard temperature, i.e., when no heating is necessary.

As described above, according to the first aspect of the present invention, the temperature in the cabin is determined (assumed) based on the engine temperature and either one of requirements of the passenger's heating and the engine's quick warming-up is given priority to properly according to this temperature. Thus, both requirements can be effectively met.

Herein, although the flow adjusting device may be configured so as to detect the engine temperature directly with the temperature of the coolant flowing in the passages and the flow amount adjusting of the coolant flowing in the water jacket may be changed according to the engine condition changing from the extremely-cold condition to the mild-cold condition, it is preferable that the flow adjusting device is configured so as to detect the engine temperature based on the temperature of the coolant and to comprise a delayed-temperature changing chamber where the coolant temperature changes with a time lag relative to the temperature of the coolant outside thereof, and the extremely-cold condition of the engine is determined based on the temperature of the coolant that is in the delayed-temperature changing chamber.

Thereby, when the engine is in the extremely-cold condition at the engine start, even if the temperature of the coolant flowing in the passages increases and exceeds the extremely-cold standard temperature, the temperature of the coolant in the delayed-temperature changing chamber does not increase over the extremely-cold standard temperature soon, i.e., the coolant temperature in the delayed-temperature changing chamber changes with a specified time lag. Accordingly, when the engine condition changes from the extremely-cold condition to the mild-cold condition, the flow amount adjusting of the coolant flowing in the water jacket is also changed with the specified time lag. Or, in the case where the flow adjusting device is configured so as to detect the engine temperature directly with the temperature of the coolant flowing in the passages, and when the temperature of the coolant flowing during the above-described time lag exceeds the mild-cold standard temperature, the control of the flow adjusting device in the engine warm condition is executed, omitting the control of the flow adjusting device in the mild-cold condition.

Thus, since when the engine starts from the extremely-cold condition, the control period of the flow adjusting device in the mild-cold condition is shortened, or omitted, the period of time when the heated conditioning air is not supplied can be shortened or the supply can be maintained, thereby meeting the passenger's heating requirement sufficiently.

Although the flow adjusting device should not be limited to a particular structure, it is preferable that the flow adjusting device comprises a short-cut passage to interconnect an inlet port and an outlet port of the water pump and a valve-opening mechanism operative to open and close the short-cut passage, and the flow adjusting device is configured so as to reduce the flow amount of the coolant flowing in the water jacket by opening the short-cut passage to introduce at least part of the coolant fed from the water pump into the short-cut passage.

Thereby, the flow adjusting device can be constituted simply and at low costs by providing the short-cut passage and the valve-opening mechanism. Further, for example, even in the case where the mechanical water pump driven by the engine is used, the flow amount of the coolant flowing in the water jacket can be properly adjusted by flowing into the short-cut passage, thereby executing the proper control with the simple structure.

In this case, it is preferable that the valve-opening mechanism of the flow adjusting device comprises a valve body operative to open and close the short-cut passage, a biasing member operative to bias the valve body in its opening direction or in its closing direction, a first temperature-responsive biasing member operative to generate a biasing force according to changing of the coolant temperature so as to bias the valve body in an opposite direction to the biasing direction of the biasing member, and a second temperature-responsive biasing member operative to generate a biasing force according to changing of the coolant temperature so as to bias the valve body in the same direction as the biasing direction of the biasing member, the first and second temperature-responsive biasing member are configured such that a specified temperature thereof at which the biasing force is generated is set to either the extremely-cold standard temperature or the mild-cold standard temperature, and the valve opening mechanism is configured to so as to bias the valve body to its closed position when the engine at starting is in the extremely-clod condition, to bias the valve body to its opened position when the engine at starting is in the mild-clod condition, and to bias the valve body to its closed position when the engine at starting is in the warm condition.

Thereby, the valve-opening mechanism can be operated mechanically, thereby providing the valve-opening mechanism surely and at low costs.

Also, although the thermostat may be an electrically-operated thermostat, it is preferable that the thermostat is a mechanical thermostat that is operated mechanically.

Thereby, the cooling device according to the present invention can be constituted mechanically and at low costs.

According to a second aspect of the present invention, there is provided a cooling device of an engine, comprising a radiator passage in which coolant is circulated between a water jacket of the engine and a radiator when an engine temperature is a specified passage-opening temperature or higher, a heater passage in which the coolant is circulated between the water jacket and a heater unit for heating of a vehicle cabin, part of the heater passage overlapping with the radiator passage, a water pump operative to circulate the coolant, the water pump being disposed at an overlapping portion of the passages, a short-cut passage to interconnect an upstream passage and a downstream passage of the water pump, and a valve-opening mechanism operative to adjust a flow amount of the coolant that flows in the water jacket by opening and closing the short-cut passage, wherein the valve-opening mechanism comprises a valve body operative to open and close the short-cut passage, an elastic member operative to bias the valve body in its closing direction, a first shape-memory-alloy spring operative to bias the valve body in its opening direction by responding to a specified temperature that is a shape-restoring temperature thereof or higher, and a second shape-memory-alloy spring operative to bias the valve body in its closing direction by responding to a specified temperature that is a shape-restoring temperature thereof or higher, the shape-restoring temperature of the first shape-memory-alloy spring being set to a first switching temperature that is lower than the specified passage-opening temperature, the shape-restoring temperature of the second shape-memory-alloy spring being set to a second switching temperature that is lower than the specified passage-opening temperature and higher than the first switching temperature, and the valve opening mechanism is configured to so as to bias the valve body to its closed position when the coolant temperature is lower than the first switching temperature, to bias the valve body to its opened position when the coolant temperature is or higher than the first switching temperature and lower than the second switching temperature, and to bias the valve body to its closed position when the coolant temperature is or higher than the second switching temperature.

According to the second aspect of the present invention, there are provided the short-cut passage to interconnect the upstream passage and the downstream passage of the water pump, and the valve-opening mechanism operative to adjust the flow amount of the coolant that flows in the water jacket by opening and closing the short-cut passage, and this valve-opening mechanism is configured so as to open and close the valve body according to the coolant temperature by using characteristics of the first and second shape-memory-alloy springs having different shape-restoring temperatures. Thereby, the degree of the passenger's heating requirement can be determined easily by the mechanical structure with the coolant temperature at the engine start by associating the first and second switching temperature with a relevant temperature in the vehicle cabin, and either one of requirements of the passenger's heating and the engine's quick warming-up is given priority to properly according to this degree of the passenger's heating requirement with a proper third-stage switching of the coolant passages for the other requirement. Thus, both requirements can be effectively met at low costs.

Namely, when the coolant temperature is lower than the first switching temperature, the first and second shape-memory-alloy springs do not reach their shape-restoring temperatures, so their valve bodies are biased to its closed position by the biasing force of the elastic member. Also, since the coolant temperature does not reach the specified passage-opening temperature, the radiator passage is closed. Thereby, the coolant is circulated between the water jacket and the heater unit in this condition. Herein, by setting the coolant temperature that is considered to correspond to the low temperature in the cabin to the first switching temperature, the coolant is supplied to the heater unit, not to the radiator, so the heating is given priority to from the engine start and the passenger's heating requirement can be met properly.

Meanwhile, when the coolant temperature at the engine start is higher than the first switching temperature and lower than the second switching temperature, the first shape-memory-alloy spring reaches its shape-restoring temperature and generates the biasing force. Thereby, the valve body is biased to the closed position. In this situation, since the coolant can be heated promptly, the valve body is changed to the opened position and thus the flow amount of the coolant flowing in the water jacket is stopped or reduced less than the above-described normal flow amount. Thus, the coolant temperature in the water jacket is increased promptly, so the quick warming-up of the engine can be attained and thus CO, HC, incomplete-combustion gas can be reduced, thereby improving the proper emission function of the engine. Also, since the temperature in the cabin is not so low at this moment, after the coolant' temperature has been increased by the quick-warming up, the sufficiently heated conditioning air is supplied to the cabin, so the passenger's heating requirement can be met properly.

Also, when the coolant temperature at the engine start is or higher than the second switching temperature, both the first and second shape-memory-alloy springs reach their shape-restoring temperatures and generate the biasing forces. Thereby, the valve bodies are biased to the closed position. In this situation, since the heating is not necessary, the flow amount of the coolant flowing in the water jacket is adjusted to the normal flow amount by closing the short-cut passage, thereby maintaining the normal operation state.

Further, since the valve body is controlled by a simple mechanical structure, the cost increase for modification can be suppressed properly.

Herein, although the first shape-memory-alloy spring may be disposed at a location where it can respond quickly to changing of the coolant temperature in the passages, it is preferable that the valve body comprises a delayed-temperature changing chamber where the coolant temperature changes with a time lag relative to the temperature of the coolant outside thereof and the first shape-memory-alloy spring is disposed in the delayed-temperature changing chamber.

Thereby, when the engine is started in the state where the coolant temperature is lower than the first switching temperature, even if the temperature of the coolant flowing in the passages increases and exceeds the first switching temperature, the temperature of the coolant in the delayed-temperature changing chamber does not increase over the first switching temperature soon, i.e., the coolant temperature in the delayed-temperature changing chamber changes with a specified time lag. Accordingly, when the engine temperature increases to the first switching temperature after the engine start, the flow amount adjusting of the coolant flowing in the water jacket is also changed with the specified time lag. Or, when the temperature of the coolant flowing during the above-described time lag exceeds the second switching temperature, the total biasing force of the elastic member and the second shape-memory-alloy spring is greater than that of the first shape-memory-alloy spring and the control that the coolant temperature is increased to the second switching temperature and higher is executed, omitting the control of the valve body being changed to the opened position. Namely, the closed position of the valve body is maintained.

Thus, since when the engine starts from the coolant temperature lower than the first switching temperature, for example, from the extremely-cold condition, the period of the valve body being opened is shortened, or omitted, the period of time when the heated conditioning air is not supplied can be shortened or the supply can be maintained, thereby meeting the passenger's heating requirement sufficiently.

Herein, although the heater passage may be kept in the opened position all the time, it is preferable that the opening valve mechanism is disposed in a housing that is located near the water pump, there is provided a heater-inlet port to introduce the coolant fed from the heater unit into the housing, and the valve body is disposed in the housing in such a manner that the heater-inlet port is closed by the valve body in its opened position, while the heater-inlet port is opened by the valve body in its closed position.

Thereby, the open/close control of the heater-inlet port can be attained by using the valve body for the short-cut passage, so the period of engine warming-up can be further shortened by closing the heater-inlet port during the period of changing from the first switching temperature to the second switching temperature and remaining the coolant in the water jacket.

Herein, although the specific structure of the water pump should not be limited to a particular one and the above-described housing for accommodating the valve-opening mechanism may be provided separately, it is preferable that the water pump is a centrifugal water pump that is provided upstream the water jacket and downstream of the housing, an inside of the housing is connected to an upstream-end portion of the water jacket via the short-cut passage, and there are provided in the hosing a radiator-inlet port to introduce the coolant fed from the radiator into the housing and a thermostat operative to open and close the radiator passage according to the temperature of the coolant.

Thereby, the water pump can be made at low manufacturing costs by using a widely-used pump of the centrifugal water pump, and the housing for accommodating the valve-opening mechanism can be formed by utilizing the existing thermostat housing. Thus, the cooling device according to the present invention can be provided without big design modifications from devices that have been used widely. Namely, the proper cooling device can be manufactured at low costs. Also, in the case where the centrifugal water pump that is driven by the engine is used, the flow amount of the coolant in the water jacket can be reduced or remained with a simple structure of the open/close control of the short-cut passage, and the passage switching can be surely conducted at low costs.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described referring to the accompanying drawings.FIG. 1is a schematic perspective view of a cooling device of an engine according to the present invention, andFIG. 2is an explanatory diagram showing schematically this cooling device.

An engine1is disposed laterally in an engine room behind a engine hood at the front of a vehicle in such a manner that its crank shat extends in a vehicle width direction. The engine1is a 4-cylinder inline engine having four cylinders disposed in line, and a cross-flow type of engine, in which intake ports11opening at respective combustion chambers of cylinders10A–10D are disposed at one side of the cylinders and exhaust ports12opening at respective combustion chambers of the cylinders10A–10D are disposed at the other side of the cylinders. Thereby, as shown inFIG. 2, the intake ports11are located at the front side of the engine1, while the exhaust ports12are located at the rear side of the engine1.

The engine1is a type of engine in which the combustion heat generated at the cylinders10A–10D is cooled with coolant, such as cooling water, that performs the heat exchange with air outside. Thus, the engine1has a cooling device comprising a radiator5and so forth.

Namely, the cooling device of the engine1comprises an engine body2with a water jacket20, the radiator5disposed in front of the engine body2, a heater unit6disposed behind the engine body2, inlet pipes13,14to supply the cooling water from the water jacket20to the radiator5and the heater unit6, outlet pipes15,16to return the coolant from the radiator5and the heater unit6to the water jacket20, a bypass pipe17to bypass these radiator5and heater unit6, a pressure adjusting pipe18having a pressure relief valve23to adjust pressure in the inlet pipes13,14and the bypass pipe17(seeFIG. 2), a thermostat7that is disposed in a thermostat housing71connected respectively to lower ends of the above-described pipes15,16,17and18and that open and close passages of the cooling water flowing in, and a water pump8that is disposed between the thermostat7and the water jacket20and circulates the cooling water.

In the present embodiment, as shown inFIG. 2, in the bypass passage17are provided an oil cooler50(heat exchanger) to cool engine oil with heat exchange and a ATF warmer52(heat exchanger) to warm oil for an automatic transmission51disposed beside the engine1.

Thus, the cooling device has a cooling-water circulation passage comprising a radiator passage operative to circulate the cooling water between the water jacket20and the radiator5, a heater passage operative to circulate the cooling water between the water jacket20and the heater unit6, a bypass passage (sub circulation passage) operative to connect a cooling-water inlet port (a front opening of a cooling-water inlet port231, which will be described below) to a cooling-water outlet port205of the water jacket20including the bypass pipe17, and a pressure-adjusting bypass passage operative to adjust the cooling-water pressure in the upstream passages that bypass the radiator5, heater unit6, oil cooler50and ATF warmer52. Herein, part of these passages (the heater passage and the bypass passage in the present embodiment) may be overlapped with each other.

Specifically, the engine1comprises, as shown inFIG. 1, the engine body2having the cylinders, an oil pan3provided at the bottom of the engine body2, and a cylinder head cover4provided at the top of the engine body2. The engine body2, which is made by casting from cast iron or aluminum alloy, comprises a cylinder block21forming a cylinder body and a cylinder head22disposed on the cylinder block21via gasket (not shown) to form the top of cylinders. In the cylinder block21and the cylinder head22are provided a block-side water jacket20aand a head-side water jacket20b, which form the cooling-water circulation passage formed in the engine body2. Namely, these water jackets20a,20bare space formed around the cylinders10A–10D at the cylinder block21and the cylinder head22to constitute the passage of cooling water (cooling passage). Many kinds of circulation ways of the cooling water flowing in the water jackets20a,20bare known. In the present embodiment, however, a U-turn type is adopted to the block-side water jacket20a, in which the cooling water is circulated around the cylinders10A–10D in one-way direction. Meanwhile, an axis-flow type is adopted to the head-side water jacket20b, in which the cooling water flows along the cylinder' line at both sides from the front to the rear of the engine.

The block-side water jacket20ais, as shown inFIG. 2, disposed along the periphery of the cylinder block21, surrounding the cylinders10A–10D. One end of that is connected to the cooling-water inlet port231and the other end of that is connected to the water jacket20bof the cylinder head22.

The head-side water jacket20bextends from one end to the other end of the cylinder head between a bottom deck (not illustrated) and a middle deck (not illustrated) as shown inFIG. 2. One end of that is connected to the head-side water jacket20bvia first through forth connecting passages201–204, which will be descried below. The other end of that is connected to a water outlet member24via the cooling-water outlet port205. The passages201–204open at the one end portion of the head-side water jacket20ball together, which can provide the cooling water flowing along the cylinder line. The head-side water jacket20bis also connected to the block-side water jacket20avia an air-release passage (not illustrated) with a cross section that is smaller than that of the passages201–204.

The block-side water jacket20awill be described more in detail. This water jacket20aincludes a first cooling passage232athat extends rearward from the cooling-water inlet port231on one longitudinal-side (right side in the figure) of the cylinder block21, a second cooling passage232bthat is connected to the first cooling passage232aand extends along the cylinder line on the exhaust side of the cylinder block21to the other longitudinal-side (left side in the figure) of the cylinder block21, a third cooling passage232cthat is connected to the second cooling passage232band extends forward on the other longitudinal-side (left side in the figure) of the cylinder block21, and a forth cooling passage232dthat is connected to the third cooling passage232cand extends along the cylinder line on the intake side of the cylinder block21to the one longitudinal-side (right side in the figure) of the cylinder block21. The cooling water flows in order of the first through forth cooling passages232a–232d.

The first and second connecting passages201,202connecting to the head-side water jacket20bopen to the first cooling passage232aof the block-side water jacket20a. The third and forth connecting passages203,204connecting to the head-side water jacket20bopen to an upstream-end portion of the second cooling passage232band a downstream-end portion of the forth cooling passage232d.

In the present embodiment the first through forth connecting passages201–204are configured so as to have different area of their passage-cross sections to each other in such a manner that the flow amount of cooling-water flow from the block-side water jacket20ato the head-side water jacket20bthrough the first through forth passages201–204becomes larger in the order of the second, first, forth and third connecting passages202,201,204and203.

Meanwhile, the cooling-water inlet port231extends substantially in the same direction as the extending direction of the first cooling passage232a, which can reduce a resistance of the flow to the first cooling passage232a. At a peripheral portion of the cylinder block21between the base end portion of the first cooling passage232aand the front end portion of the forth cooling passage232dis provided a short-cut passage232ethat connects to the first cooling passage232aat its one end. A partition wall233separates the short-cut passage232efrom the forth cooling passage232d, so no cooling water flows directly between them.

The short-cut passage232e, as shown inFIG. 3, comprises a jacket portion2321that extends along the periphery of the cylinder10A located at one end of the cylinder block21from the first cooling passage232ato the forth cooling passage232dand a short-cut port2322that extends from the front end portion of the jacket portion2321substantially in parallel to the cooling-water inlet port231in the thermostat housing71, which will be described below. A heater inlet port7a, which will be described below, opens to the short-cut port2322at its one end as shown with a two-dotted broken line inFIG. 3, and there is provided a valve body91of a valve-opening mechanism9.

This valve-opening mechanism9is disposed downstream of the short-cut passage232eand in the thermostat housing71, and it is configured so as to open and close mechanically according to the temperature of the cooling water flowing in the housing71. When the short-cut passage232eis opened, most of the cooling water flowing in from the cooling-water inlet port231is introduced into the short-cut passage232ewith its reduced pressure due to the suction force of the water pump8, and then flows down into the thermostat housing71upstream the water pump8via the short-cut passage232e. Accordingly, during opening of the short-cut passage232e, most of the cooling water fed from the water pump8circulates in the short-cut passage232e, so that the flow amount of the cooling water flowing in the blocks-side and head-side water jacket20a,20breduces to almost zero. Namely, these short-cut passage232eand valve-opening mechanism9correspond to an example of a flow adjusting device operative to adjust the flow amount of the cooling water flowing in the water jacket20.

The valve-opening mechanism9closes the short-cut passage232ewhen the engine is in the extremely-cold condition, i.e., when the cooling-water temperature in a delayed-temperature changing chamber91f, which will be described below, is lower than a radiator-passage opening temperature (76–82 degrees centigrade in the present embodiment) and lower than a specified extremely-cold standard temperature (approximately 20 degrees centigrade in the present embodiment). Meanwhile, when the engine is in the mild-cold condition, i.e., when the cooling-water temperature in the thermostat housing71is lower than a specified mild-cold standard temperature (approximately 70 degrees centigrade in the present embodiment) that is lower than the radiator-passage opening temperature and exceeds the above-described extremely-cold standard temperature, the valve-opening mechanism9opens the short-cut passage232e. And when the engine is in the warm condition, i.e., when the cooling-water temperature exceeds the mild-cold standard temperature, the valve-opening mechanism9closes the short-cut passage232e.

Specifically, the valve-opening mechanism9, as shown inFIG. 3, comprises the valve body91to open and close the short-cut passage232e, a biasing member92to bias the valve body91in its opening direction with its biasing force, a first temperature-responsive biasing member93to generate a specified biasing force when the cooling-water temperature exceeds the above-described extremely-cold standard temperature so as to bias the valve body91in its opening direction with this generated biasing force and the biasing force of the above-described biasing member92, and a second temperature-responsive biasing member94to generate a specified biasing force when the cooling-water temperature exceeds the above-described mild-cold standard temperature so as to bias the valve body91in its closing direction with this generated biasing force and the biasing forces of the above-described biasing members92,93.

As shown inFIG. 3, the valve body91is formed according to the shape of cross section of the short-cut port2322of the short-cut passage232e. A valve main body91aprovided at a tip of the valve body91is located at the short-cut port2322to close the passage232e, while it is located at the water jacket portion2321to open the passage232e. The valve main body91ais supported at a valve rod91bthat is formed integrally therewith. The valve rod91bhas a cylindrical housing portion91cwith a bottom at its one end that is located on an opposite side to the valve main body91a.

The housing portion91chas an stepwise-enlarged peripheral wall and a flange91dat its opening edge91d, and accommodates the first temperature-responsive biasing member91dtherein at its narrow portion. The narrow portion of the housing portion91cis inserted into the short-cut port2322of the short-cut passage232e, and the heater inlet port7aopening at the short-cut port2322is opened or closed by the periphery of this narrow portion of the valve body91moving in the present embodiment. Namely, when the valve body91is in the closed position, as shown inFIG. 3, the heater inlet port7ais not closed by the narrow portion of the housing portion91c. And when the valve body91is in the opened position, as shown inFIG. 4, the heater inlet port7ais closed by the narrow portion of the housing portion91c. Herein, the short-cut port2322, the thermostat housing71and the valve body91are configured such that the cooling water flowing in from the heater inlet port7ais introduced to the water pump8via the thermostat housing71, which is not illustrated.

A flow-suppressing lid91eto suppress the cooling water flowing into a accommodation space of the first temperature-responsive biasing member93is inserted into a wide portion of the hosing portion91c. The flow-suppressing lid91eis formed separately from the housing portion91c, and attached at a specified portion of the thermostat housing71. This attachment portion is configured such that the flow-suppressing lid91econtacts a transitional portion where the diameter of the housing portion91cchanges when the valve body91is in the closed position.

And the flow-suppressing lid91eis formed such that its outer periphery contacts and slides on an inner surface of the wide portion of the housing portion91c. Accordingly, although it may not be easy for the cooling water to flow into the accommodation space of the housing portion91cthat is closed by the flow-suppressing lid91efrom a passage outside the housing portion91c, the cooling water can flow through a small gap between the outer periphery of the flow-suppressing lid91eand the inner surface of the housing portion91c. As a result, the temperature of the cooling water located inside the hosing portion91cchanges with a time lag relative to the temperature of the cooling water located outside the housing portion91c, so that the accommodation space in the housing portion91cfunctions as the delayed-temperature changing chamber91f.

In the delayed-temperature changing chamber91fis provided the above-described first temperature-responsive biasing member93. The first temperature-responsive biasing member93is a compression coil spring made of a shape-memory alloy (e.g., Ni—Ti alloy, Cu—Zu—Al alloy), which extends with a shape restoring and thereby bias the valve main body91ain the opening direction.

The first temperature-responsive biasing member93, which has the one-way shape-memory function that memorizes its shape to keep when the temperature increases, changes the valve main body91abetween its opened position and its closed position by a bias method with the bias member92as a bias spring. Herein, the bias method is a method in which the shape-memory alloy with the one-way shape-memory function is burdened by a specified outer force (e.g., the biasing force by a bias spring) so as to provide the both-way shape-memory function, so that the member can change in shape not only when the temperature increase but when the temperature decreases.

The shape-restoring temperature of this first temperature-responsive biasing member93, i.e., the temperature to restore its original shape with the shape-memory effect, is set to the extremely-cold standard temperature (approximately 20 degrees centigrade in the present embodiment). Thus, when the cooling-water temperature in the delayed-temperature changing chamber91fincreases to the extremely-cold standard temperature or higher, the first temperature-responsive biasing member93generates the biasing force to bias the valve main body91ain the opening direction. This biasing force of the first temperature-responsive biasing member93is set to be greater than a biasing force generated by the biasing member92. Accordingly, the first temperature-responsive biasing member93can change the valve body91from its closed position inFIG. 3to its opened position inFIG. 4against the biasing force of the basing member92that biases the valve body91in its closing direction, which will be described below in detail.

The biasing member92is a compression coil spring that is made of steel iron or the like, and it functions as a bias spring to the first and second temperature-responsive biasing members93,94. The biasing member92is disposed outside the valve body91(specifically, the wide portion of the housing portion91c), whose one end contacts the flange91dof the housing portion91cand whose the other end contacts a bottom face71aof the thermostat housing71, thereby biasing the valve body91to its closed position.

The second temperature-responsive biasing member94is disposed outside the basing member92. The second temperature-responsive biasing member94is a compression coil spring made of a shape-memory alloy (e.g., Ni—Ti alloy, Cu—Zu—Al alloy), which extends with a shape restoring and thereby bias the valve main body91ain the closing direction. One end of the second temperature-responsive biasing member94contacts the flange91dof the housing portion91cand the other end of that contacts the bottom face71aof the thermostat housing71, thereby biasing the valve body91to its closed position with its shape restoring.

The second temperature-responsive biasing member94, which has the one-way shape-memory function that memorizes its shape to keep when the temperature increases, changes the valve main body91abetween its opened position and its closed position by the bias method with the bias member92and the first temperature-responsive biasing member93as the bias springs. The shape-restoring temperature of this second temperature-responsive biasing member94is set to the mild-cold standard temperature (approximately 70 degrees centigrade in the present embodiment) that is higher than the shape-restoring temperature of the first temperature-responsive biasing member93. Thus, when the temperature of the cooling water that is located outside the housing portion91cand flows inside the thermostat housing71increases to the mild-cold standard temperature or higher, the second temperature-responsive biasing member94generates the biasing force against the opening-direction biasing forces of the biasing member92and the first temperature-responsive biasing member93to bias the valve main body91ato its closed position. Namely, the biasing force of the second temperature-responsive biasing member94is set to be greater than the total biasing forces that are generated by the biasing member92and the first temperature-responsive biasing member93. Accordingly, the second temperature-responsive biasing member94can change the valve body91from its opened position inFIG. 4to its closed position inFIG. 3against the biasing forces of the basing member92and the first temperature-responsive biasing member93.

Meanwhile, returning toFIGS. 1 and 2, there is provided the water pump8upstream the block-side water jacket20a. Specifically, the water pump8is attached to one end portion at the front and upper portion of the cylinder block21(at the right upper portion of the front face in the figure). The water pump8, the centrifugal water pump, is coupled to a crank pulley55that is provided at a lower end portion of a side face of the cylinder block21via a V belt (not illustrated). An impeller82disposed in a water pump housing81(seeFIG. 3) is driven by rotation of the crank pulley55. Thus, a rotational speed of the water pump8is set by an engine rotational speed. Accordingly, the flow amount of the cooling water that is fed into the block-side and head-side water jackets20a,20bby the water pump8in the normal condition, where the short-cut passage232eis closed, is according to the engine rotational speed.

Upstream the water pump8is provided the thermostat7to maintain the cooling-water temperature at the proper temperature by opening and closing the radiator passage according to the cooling-water temperature. The thermostat7is disposed in the thermostat housing71attached to the front face of the cylinder block21near the water pump8.

The thermostat7, not illustrated, adjusts the cooling-water temperature within the proper range during the engine operation by opening and closing the radiator passage according to the cooling-water temperature. In the present embodiment, the thermostat7is a wax type of thermostat, in which a needle of the thermostat is pushed out by a wax that is melt and expanded by an increased wax's temperature and this pushing-out force functions to open a valve body that is biased in the closing direction. Herein, the thermostat7is configured such that its valve-body opening temperature (the passage-opening temperature) is set to approximately 76–82 degrees centigrade in the present embodiment. Namely, this thermostat7is operated mechanically, not electrically.

The thermostat housing71comprises, as shown inFIGS. 3 and 4, a block-side case72that is formed integrally with the cylinder block21and has a front-opening shape, and a lid-shaped case73that is provided to close this opening of the case72. The valve opening mechanism9is disposed in the block-side case72, and the thermostat7is disposed in the lid-shaped case73. The block-side case72is connected to the block-side water jacket20avia the short-cut passage232eat its bottom face71a, and connected to the water pump housing81at its peripheral side face.

The thermostat housing7has, as shown inFIGS. 1 and 2, the heater inlet port7aformed at its top face, and a pressure-adjusting inlet port7band a radiator outlet port7cthat are formed at its front face. A common pipe19formed by the heater outlet pipe16and the bypass pipe17downstream is connected to the heater inlet port7a. The pressure-adjusting inlet port7bis connected to the pressure-adjusting pipe18, while the radiator inlet port7cis connected to the radiator outlet pipe15to return the cooling water that is heat-exchanged at the radiator5to the engine body2.

The water outlet member24is provided at an upper portion on the side face of the engine body2, which is opposite to the side where the water pump8is attached. One end of the water outlet member24is connected to the head-side water jacket20band the other end is divided into three ports of the radiator outlet port, heater outlet port and pressure-adjusting outlet port. To these ports are respectively connected the radiator inlet pipe13and the heater inlet pipe14, which supply the cooling water heated at the engine body2, and the bypass pipe17and the pressure-adjusting pipe18.

Herein, the pressure relief valve23that is provided in the pressure-adjusting pipe18is a direct-operation type of pressure reducing valve, whose detailed description is omitted here, but it should not be limited to this type, but any other types can be adopted.

Next, the function of the cooling device of the engine1described above will be described.FIG. 5is an explanatory diagram showing a time change of the cooling-water coolant temperature and the like, in which (a) shows the time change of the cooling-water coolant temperature according to the engine start and (b)–(d) show the time changes of the open/close state of respective passages according to the engine state.

In the device of the present embodiment, the engine temperature (cooling-water temperature) at the engine start is detected based on the shape-memory function of the first and second temperature-responsive biasing members93,94, and the circulation passage of the cooling water is switched according to this engine temperature.

First, the situation where the engine1is started from a point S1ofFIG. 5(a), i.e., from the engine's extremely-cold condition, will be described. When the engine1is in the extremely-cold condition, the cooling-water temperature is still lower than the shape-restoring temperature of the first and second temperature-responsive biasing members93,94. Accordingly, since only the biasing member92generates its biasing force, the short-cut passage232eis kept closed with the valve body91of the valve opening mechanism9in this stage. And since the heater inlet port7ais not closed by the housing portion91cof the valve body91but still opened, the heater passage and the bypass passage are kept opened. Also, since the cooling-water temperature does not reach the passage-opening temperature yet, the radiator passage is kept closed by the thermostat7.

The crank pulley55rotates with the engine1starting, thereby the water pump8operates. All cooling water fed from the water pump8is introduced into the first cooling passage232aof the water jacket20. Then, part of the cooling water flows in the head-side water jacket20bvia the first through third connecting passages201–203, and the rest of that flows through the block-side water jacket20aand cools the cylinder block21from the exhaust side, and then flows in the head-side water jacket20bvia the forth connecting passage204. In the head-side water jacket20b, the cooling water from the second and third connecting passages202,203flows down in the cylinder-line direction on the exhaust-side of the cylinder head22, while the cooling water from the first and forth connecting passages201,204flows down in the cylinder-line direction on the intake-side of the cylinder block21. The cooling water flowing down in the head-side water jacket20bgather and gets out of the outlet port205into the water outlet member24.

The cooling water is divided in the water outlet member24and introduced into the heater inlet pipe14and the bypass pipe17, which are opened in the engine's extremely-cold condition. Thus, when the engine is in the extremely-cold condition, the cooling water flows in the heater passage and the bypass passage with its normal flow amount, which is according to the engine speed. Accordingly, although the cooling-water temperature has not increased sufficiently yet, the cooling water is supplied to the heater unit6and thereby the heating of the vehicle cabin can be attained effectively. Namely, since the air temperature of the cabin is rather low in the engine's extremely-cold condition, the cooling-water introduced into the heater unit may conduct the heat exchange effectively with the air in the cabin. Thus, the passenger's heating requirement can be met to some extent, compared with a case where the heater unit6does not operate until the cooling-water temperature has increased to sufficiently high temperature.

As the engine rotational speed increases quickly, the amount of water fed by the water pump8also increases, so that the internal pressure of the bypass pipe17upstream the ATF warmer52and the heater inlet pipe14increase. Generally, there is a concern that the increase of the internal pressure of the pipes17,14might cause a pipe's falling-off. According to the device of the present embodiment, however, the internal pressure of the pressure-adjusting pipe18also increases and thereby the pressure relief valve23is opened, so that the pipes14,17can be prevented from falling off properly.

The cooling water from the heater unit6, oil cooler50and ATF warmer52is introduced into the thermostat housing71via the heater inlet port7a. Then, it is again fed to the water pump8via the thermostat housing71.

As the cooling water circulates in the heater passage and the bypass passage, the temperature of the cooling water increases efficiently and exceeds the extremely-cold standard temperature Tb. At this point when the temperature of the cooling water flowing in the thermostat housing71exceeds the extremely-cold standard temperature Tb, the first temperature-responsive basing member93dose not generate the biasing force yet. Because the first temperature-responsive basing member93is located in the delayed-temperature changing chamber91fand the temperature of the cooling water in the chamber has the time lag in changing (increasing), so the generation of the biasing force has the time lag accordingly. Herein, in the present embodiment this time lag is set to be longer than a period of time it takes that the cooling-water temperature in the passages in the normal condition of the engine1changes from the extremely-cold standard temperature Tb to the mild-cold standard temperature Ts. Thus, the bias force is not generated yet by the first temperature-responsive basing member93in the mild condition of the engine1, so the valve opening mechanism9still closes the short-cut passage232e.

Then, when the temperature of the cooling water flowing in the thermostat housing71exceeds the mild-cold standard temperature Tb, the second temperature-responsive basing member94generates its biasing force. The second temperature-responsive basing member94biases the valve body91of the valve opening mechanism9in the closing direction, so the valve body91is kept to close the short-cut passage232e. Herein, since the biasing force of the first temperature-responsive basing member93is smaller than the total biasing forces of the biasing member92and the second temperature-responsive basing member94, the valve body91is kept to close the short-cut passage232eeven if the temperature of the cooling water flowing in the delayed-temperature changing chamber91fexceeds the extremely-cold standard temperature Tb and the first temperature-responsive basing member93generates the biasing force.

Subsequently, when the cooling-water temperature further increases and exceeds the passage-opening temperature To, the thermostat7opens the radiator passage and the cooling water is cooled efficiently by the radiator5. As a consequence, as the cooling-water temperature decreases below the passage-opening temperature To, the thermostat7closes and the cooling-temperature starts increasing again. This operation repeats and thereby the cooling-water temperature is controlled within the proper range.

As described above, when the engine1is in the extremely-cold condition at the engine start, as shown inFIG. 5(a) the normal amount of cooling water flows in the water jacket20with the closed short-cut passage232e. And the heater passage is in the opened state and ready to operate the heater unit6just after the engine start, so the relatively warm air can be supplied to the cabin with the very cold temperature. Thus, the heating can be met to the passenger's requirement from the engine start. Also, the cooling water flows in the heater passage and the bypass passage, not in the radiator5, in the extremely-cold engine condition of the present device, so relatively quick engine warming-up can be attained.

Next, the case where the engine1is started from the mild-cold condition of the engine, i.e., from a S2point inFIG. 5(a) will be described. In this condition, although it does not reach the shape-restoring temperature of the second temperature-responsive basing member94, the cooling-water temperature has reached that of the first temperature-responsive basing member93. Namely, the engine1in the mild-cold condition at its start means that it has not taken so long after the engine has stopped and therefore the temperature of the cooling water in the delayed-temperature changing chamber91fis at least higher than extremely-cold standard temperature Tb. Accordingly, not only the biasing member92but the first temperature-responsive biasing member93generate the biasing forces. Thus, the valve body91of the valve opening mechanism9opens and the short-cut232eis in the opened state because the first temperature-responsive biasing member93biases the valve body91in the opening direction with the biasing force that is larger than that of the biasing member92. Herein, the heater inlet port7ais closed by the housing portion91cof the valve body91, and the heater passage and the bypass passage are closed. Meanwhile, since the cooling-water temperature does not reach the passage-opening temperature, the thermostat7closes the radiator passage.

When the crank pulley55rotates with the engine1starting, the water pump8operates, and all cooling water fed from the water pump8is introduced into the first cooling passage232aof the water jacket20. Herein, since the short-cut passage232eis opened, the internal pressure of the short-cut passage232eis reduced by the water pump8nearby. Also the respective passages of the heater, bypass and radiator passages are closed. Accordingly, all amount of the cooling water is introduced into the thermostat housing71via the short-cut passage232e, and then suck into the water pump8again. Namely, the cooling water is circulated in the short-cut passage232eand thus the cooling water remains in the water jacket20. Thereby, the cooling water in the water jacket20is heated promptly, so the quick warming-up of the engine can be attained and thus CO, HC, incomplete-combustion gas can be reduced, thereby improving the proper emission function of the engine.

When the cooling water circulates in the short-cut passage and its temperature increases the mild-cold standard temperature Ts, the second temperature-responsive biasing member94generates the biasing force. Since the total biasing forces of the second temperature-responsive biasing member94and the biasing member92is grater than the biasing force of the first temperature-responsive biasing member93, the valve body91changes from its opened position to its closed position, so the short-cut passage232eis closed. Thereby, the heater inlet port7ais opened by the valve body91and the heater passage and the bypass passage are opened.

In this state, the heater unit6can be operated, and to the heater unit6is supplied the cooling water with the temperature higher than the mild-cold standard temperature Ts. Thus, the cooling water with a relatively high and stable temperature can be supplied to the cabin, so the passenger's heating requirement can be met properly.

As described above, when the engine1is in the mild-cold condition at the engine start, as shown inFIG. 5(c) the cooling water remains in the water jacket20with the opened short-cut passage232eand the heater passage is closed. Thus, the cooling water is heated promptly, so the quick warming-up of the engine can be attained and the proper emission function of the engine can be provided. Then, after the engine1has changed to the warm condition, the short-cut passage is closed and thereby the normal flow amount of the cooling water flows in the water jacket20with the closed shot-cut passage. And the heater passage is opened and thereby the heater unit6is ready to operate. Thus, the cooling water with the relatively high and stable temperature can be supplied to the cabin, so the passenger's heating requirement can be met properly.

Next, the case where the engine1is started from the warm condition of the engine, i.e., from a S3point inFIG. 5(a) will be described. In this condition, the cooling-water temperature has reached the shape-restoring temperature of the first and second temperature-responsive basing members93,94. Namely, the valve body91is in its closed position and closes the short-cut232ebecause the biasing forces of the biasing member92and the second temperature-responsive biasing member94is larger than that of the first temperature-responsive biasing member93. Herein, the heater inlet port7ais opened by the housing portion91cof the valve body91, and the heater passage and the bypass passage are opened. Meanwhile, since the cooling-water temperature does not reach the passage-opening temperature, the thermostat7is still kept closing the radiator passage.

In this sate, the engine1has been warmed up sufficiently. Also, the cooling water has the relatively high temperature and so the air supplied to the cabin has a relatively high temperature. Accordingly, the normal engine operation can be maintained and the passenger's heating requirement can be met.

Then, the cooling-water temperature increases further and reach the passing-opening temperature To, and the thermostat7changed to its opened position. Thus, the cooling water flows in the radiator passage and the cooling water is cooled by the radiator5efficiently. As a consequence, when the cooling-water temperature becomes below the passing-opening temperature To, the thermostat7is closed and the cooling-water temperature increases again. With this operation repeated, the cooling-water temperature is controlled to be within the proper temperature range.

As described above, when the engine1is in the mild-cold condition at the engine start, as shown inFIG. 5(d), the normal amount of cooling water, which is according to the engine rotational speed, flows in the water jacket20with the closed short-cut passage. This cooling water then flows down the heater passage and the bypass passage, so that the normal engine operation state of the engine1is maintained.

As described above, according to the cooling device of the engine1of the present embodiment, the temperature of the engine1is determined mechanically, not eclectically, and either one of requirements of the passenger's heating and the engine's quick warming-up is given priority to according to the temperature in the vehicle cabin based on this engine temperature, so that the both requirements can be met effectively.

Further, the cooling-water temperature can be determined by utilizing the biasing forces of the first and second temperature-responsive biasing members93,94with different shape-restoring temperatures, and the amount of the cooling water in the water jacket20can be adjusted surely and at low costs with the mechanical structure. Also, by using the thermostat with the mechanical structure, the flow adjustment can be attained further surely and lower costs.

The present invention should not limited to the above-described embodiment, and any other modifications can be adopted within a scope of the present invention.

The following are some examples of such modifications.

(1) Although in the above-described embodiment the cooling water flows in the cylinder block21on the exhaust side first and then on the intake side, the structure of the block-side water jacket20aof the cylinder block21should not to be limited to a particular one.

For example, as shown inFIGS. 6 and 7, the cooling water may be configured so as to flow in the cylinder block21on the intake side first and then on the exhaust side. In this modification the cylinder block structure differs from the above-described embodiment. A different point will be described.

A cylinder block121of this modification adopts the U-turn type likewise, but a water jacket120asurrounds the cylinders10A–10D and has no the partition wall233of the above-described embodiment.

Specifically, the block-side water jacket120a, as shown inFIG. 6, includes a intake-side cooling passage332athat extends, along the cylinder line, from a cooling-water inlet port331to the other longitudinal-side (left side in the figure) of the cylinder block121on the front side of the cylinder block121, i.e., on the intake side of the cylinder block121, a turn cooling passage332bthat is connected to the intake-side cooling-water passage332aand extends rearward on the other longitudinal-side (left side in the figure) of the cylinder block121, an exhaust-side cooling passage332cthat is connected to the turn cooling passage232band extends along the cylinder line on the rear side, i.e., on the intake side of the cylinder block121, to the one longitudinal-side (right side in the figure) of the cylinder block121, and a connecting cooling passage332dthat is connected to the exhaust-side cooling-water passage332cand extends forward on the one longitudinal-side (right side in the figure) of the cylinder block121. The cooling water flows in order of the first through forth cooling passages332a–332d. A short-cut passage332eopens at a base end portion of the intake-side cooling passage332alike the above-described embodiment, which constitutes the short-cut passage.

Herein, the cooling-water inlet port331is configured as shown inFIG. 7such that its downstream end is inclined toward the inside of the cylinder block121, so the cooling water can be easily introduced into the intake-side cooling passage332a.

Accordingly, with either one of requirements of the passenger's heating and the engine's quick warming-up being given priority to properly, the both requirements can be effectively met. Also, since the block-side water jacket120asurrounds the cylinders10A–10D, part of the cooling water can be circulated in the block-side water jacket120ain the engine mild-cold condition, the quick warming-up of engine can be attained efficiently with the proper heat exchanging.

(2) Although the cooling water remains in the water jacket20in the engine mild-cold condition in the above-described embodiment, part of the cooling water may be circulated, for example, in the bypass passage. In this case the same effect as the above-described embodiment can be obtained.

(3) Although in the above-described embodiment the biasing member92biases the valve body91in its closing direction, the first temperature-responsive biasing member93biases the valve body91in its opening direction and the second temperature-responsive biasing member94biases the valve body91in its closing direction, the same operation of the valve body91can be provided by properly setting the shape-restoring temperature and the biasing forces other than these.

(4) The oil cooler50and others, which are adopted at the bypass pipe17in the above-described embodiment, may be omitted. In this case, the cooling water is circulated in the water jacket20without substantial heat exchanging at the bypass pipe17, so the cooling-water temperature can be increased efficiently.

(5) In the above-described embodiment when the engine is started from the extremely-cold condition, the valve body91remains in its closed position even if the cooling-water temperature exceeds the extremely-cold standard temperature Tb and thus the opening control of the valve body91in the warm condition is conducted. However, the time lag of the delayed-temperature changing chamber91fmay be shorter, for example, by narrowing the volume of this chamber91for forming a through hole to connect the outside at this chamber91f, so the valve body91may be changed to its opened position when the cooling-water temperature has increased and is in the engine mild-cold condition.