(1) Field of the Invention
The present invention relates to a structure of a water-cooled engine, in particular relates to a snowmobile engine cooling arrangement having cooling water passages for cooling a snowmobile engine.
(2) Description of the Prior Art
Conventionally, most small snow vehicle such as snowmobiles and the like use two-cycle engines because they are relatively simple in structure, light and compact and yet powerful. Recently, however, because of regulation of exhaust gas due to environmental issues and aiming at improvement in reduction of fuel consumption rate, there is a trend toward employing four-cycle engines.
As the engine structure for snowmobiles, water-cooled engines have been generally employed because they can stably cool the engine by cooling water, preventing the occurrence of overheating or overcooling and improving the output power and yet are effective in reducing noise.
As an example of conventional engine cooling arrangements, Japanese Patent Application Laid-Open No. 2001-12243 discloses a cooling system for a snowmobile engine. This cooling system is comprised of a cooling water jacket formed inside the engine, a heat exchanger for cooling the cooling water and a cooling water pump for transferring the cooling water so as to circulate the cooling water inside the engine, and further includes: a cooling water bypass through which the cooling water can pass, avoiding its flow into the heat exchanger; and a switching valve for permitting the cooling water to flow into the cooling water bypass, wherein the switching valve is adapted to switch the cooling water circuit in such a manner that the cooling water is allowed to pass through the heat exchanger when the cooling water is equal to or higher in temperature than a predetermined level, and the cooling water is restricted from passing through the heat exchanger and is conducted to the cooling water bypass when the temperature of the cooling water is lower than the predetermined temperature level.
Meanwhile, in contrast to two-cycle engines, which are high in power, light and compact, four-cycle engines need a camshaft and oil lubrication, inevitably tending towards large size.
In particular, when a four-cycle engine is included in a snowmobile, it is necessary to provide a contrived layout of the oil pan configuration, intake and exhaust systems and associated auxiliaries, in order to make the body and engine hood have similar size to those of a two-cycle engine.
Further, in general, when the mounted engine is of a water cooled type, a reservoir tank should be interposed within the piping of the cooling water. That is, it is necessary to take into account the installation space for this reservoir tank. Further, the reservoir tank needs to be arranged at a site where it is easy for cooling water to be re-supplied.
Since the snowmobile is used in cold areas, in order to stabilize the idling engine speed at the start of operation or in order to regulate the surging of the thermostat, it is necessary to consider the layout of the cooling water piping and the position of the thermostat.
Further, the cooling water pump for transferring cooling water is driven by a belt which is driven by the rotation of the crankshaft. This means the enlargement of the longitudinal size of the engine. Therefore it is necessary to arrange the cooling water pump at an appropriate position. Moreover, it is necessary to choose the position of the cooling water pump optimally, considering the positional relationship with an alternator, which is belt driven, so that the front-to-rear size of the engine will be minimized.
The present invention has been devised in view of the above conventional problems, it is therefore an object of the present invention to provide a cooling arrangement for a snowmobile engine, which is able to stabilize the engine idling speed at the start of operation and is improved in the work performance in supplying cooling water and realizes a space-saving engine layout.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a cooling arrangement for a snowmobile engine, includes: a cooling water jacket formed inside an engine; a heat exchanger for cooling water; a water pump for ejecting cooling water; and a thermostat for controlling supply of the cooling water ejected from the water pump into the engine, so as to cool the engine by circulating the cooling water inside the engine, and is characterized in that:
the engine is mounted with its cylinder head at top, and an exhaust manifold is disposed on the front side, with respect to the vehicle""s direction of travel, of the cylinder head while an intake manifold is disposed on the rear side, with respect to the vehicle""s direction of travel, of the cylinder head;
the water pump is disposed on the front side, with respect to the vehicle""s direction of travel, of cylinder block of the engine, under the exhaust manifold and is coupled to a crankshaft projected from one side wall, with respect to the widthwise direction of the body, of the cylinder block, so that it is driven by the rotational force which is transmitted through a drive belt from a rotational member fitted on one end of the crankshaft;
a cooling water inlet port for leading cooling water into the cooling water jacket inside the engine is provided on the front side, with respect to the vehicle""s direction of travel, of the cylinder block and under the exhaust manifold at a position close to the drive belt;
a cooling water outlet port through which cooling water is taken out from the interior of the engine is arranged on the engine""s side face at a position over and opposite to the drive belt; and
the thermostat is arranged at the cooling water outlet port, at a point downstream with respect to the flow of cooling water.
In accordance with the second aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that the cooling water outlet port is comprised of a thermo housing for incorporating the thermostat and a thermo cap for covering the thermostat, the thermo cap being connected to the heat exchanger by way of a cooling water passage.
In accordance with the third aspect of the present invention, the cooling arrangement for a snowmobile engine having the above second feature is characterized in that the thermo housing is formed with a first cooling water bypass passage which branches off at a point upstream, with respect to the flow of cooling water, of the thermostat and is connected by way of a throttle body to the cooling water passage at a point upstream of the water pump.
In accordance with the fourth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above second feature is characterized in that the thermo housing is formed with a second cooling water bypass passage which branches off at a point upstream of the thermostat and is connected directly to the cooling water passage at a point upstream of the water pump without passing through the throttle body.
In accordance with the fifth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above third feature is characterized in that the thermostat is used to control the outlet of cooling water after passage of the cooling water jacket inside the engine while the thermo housing side and cooling water passage side are kept so as to be in constant communication to each other through the first cooling water bypass passage and the second cooling water bypass passage.
In accordance with the sixth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above fourth feature is characterized in that the thermostat is used to control the outlet of cooling water after passage of the cooling water jacket inside the engine while the thermo housing side and cooling water passage side are kept so as to be in constant communication to each other through the first cooling water bypass passage and the second cooling water bypass passage.
In accordance with the seventh aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that, in the snowmobile, an oil filter is arranged on the front side, with respect to the vehicle""s direction of travel, of the cylinder block and an oil cooling means is interposed between the oil filter and the cylinder block.
In accordance with the eighth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that, in the snowmobile, an oil cooling means is provided on the front side, with respect to the vehicle""s direction of travel, of a crawler for causing the snowmobile to move.
In accordance with the ninth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that, in the snowmobile, a muffler is disposed in front of the engine body in the engine room and an oil cooling means is arranged in front of the muffler.
In accordance with the tenth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that the water pump is arranged between the engine and the exhaust passage provided in front of the engine.
In accordance with the eleventh aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that the water pump is arranged over an oil pan.
In accordance with the twelfth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that the water pump is arranged under the exhaust manifold.
In accordance with the thirteenth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that the engine has an alternator provided at a position opposite the water pump with the cylinder block in between, the three components being laid from the front to rear with respect to the vehicle""s direction of travel.
In accordance with the fourteenth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that a cooling water reservoir tank is arranged in the rear of the engine, at the side of the intake manifold, over an oil pan, heat exchanger and alternator.
In accordance with the fifteenth aspect of the present invention, the cooling arrangement for a snowmobile engine having the above first feature is characterized in that a cooling water reservoir tank is arranged without being projected outwards beyond a drive belt for driving an alternator and water pump, when viewed from top.
According to the present invention, the following effects can be obtained.
First, in a cooling arrangement for a snowmobile engine, the engine is mounted with its cylinder head at top, and an exhaust manifold is disposed on the front side, with respect to the vehicle""s direction of travel, of the cylinder head while an intake manifold is disposed on the rear side, with respect to the vehicle""s direction of travel, of the cylinder head. The water pump is disposed on the front side, with respect to the vehicle""s direction of travel, of the cylinder head of the engine, under the exhaust manifold and is coupled to a crankshaft projected from one side wall, with respect to the widthwise direction of the body, of the cylinder block, so that it is driven by the rotational force which is transmitted through a drive belt from a rotational member fitted on one end of the crankshaft. Further, a cooling water intake port for leading cooling water into the cooling water jacket inside the engine is provided on the front side, with respect to the vehicle""s direction of travel, of the cylinder block and under the exhaust manifold, at a position close to the drive belt while a cooling water outlet port through which cooling water is taken out from the interior of the engine is arranged on the engine""s side face opposite to the drive belt side or on the opposite side at a position above the crankshaft from which engine power is taken. This arrangement makes it possible for the cooling water to flow through the engine interior, approximately diagonally from the bottom to the top, hence the water is able to efficiently flow and be discharged without stagnation inside the cylinder head and inside the cylinder block. Accordingly, this configuration provides an engine of an improved cooling efficiency compared to the conventional configuration. Further, since supply and discharge of cooling water is achieved utilizing the dead space near the water pump and under the exhaust manifold, this arrangement realizes an engine of a highly efficient space usage.
Since the cooling water outlet port is formed with a thermo housing incorporating a thermostat and a thermo cap covering the thermostat while the thermo cap is connected to the heat exchanger by way of a cooling water passage, e.g., a cooling water hose so as to control the cooling water at the cooling water outlet, by making a so-called outlet control, it is possible to perform correct cooling water control at a stable cooling water temperature.
Since the thermo housing is formed with a first cooling water bypass passage which branches off at a point upstream, with respect to the flow of cooling water, of the thermostat and is connected by way of a throttle body to the cooling water passage at a point upstream of the water pump, it is possible to prevent icing and make stable intake control by maintaining the cooling water supplied to the throttle valve at an approximately fixed temperature.
Since the thermo housing is formed with a second cooling water bypass passage which branches off at a point upstream, with respect to the flow of cooling water, of the thermostat and is connected directly to the cooling water passage at a point upstream, with respect to the flow of cooling water, of the water pump without passing through the throttle body, the cooling water warmed by the engine is supplied to the engine. This makes it possible to regulate the temperature of the cooling water at an approximately constant level under the thermostat control of supply of the cooling water cooled through the heat exchanger, hence realizing a good operational condition of the engine.
Since control of cooling water by the thermostat is performed by regulating the outlet of cooling water after passage of the cooling water jacket inside the engine, it is possible to make reliable cooling water control based on the cooling water of a stabilized water temperature. Further, since the thermo housing side and cooling water passage side are kept so as to be in constant communication to each other through the first cooling water bypass passage and the second cooling water bypass passage, this makes it possible to regulate the temperature of the cooling water in the engine at an approximately constant level. As a result, the thermostat for opening and closing the main cooling water passage in response to the cooling water temperature quickly reacts to the cooling water temperature that varies dependent on the operational state of the engine, to thereby prevent the occurrence of engine seizure and other troubles.
Since, in the snowmobile, an oil filter is arranged on the front side, with respect to the vehicle""s direction of travel, of the cylinder block and an oil cooling means, e.g., an oil cooler, is interposed between the oil filter and the cylinder block, it is possible to efficiently cool not only the engine but also the engine oil, thus achieving a beneficial operational condition of the engine.
Since, in the snowmobile, an oil cooling means is provided on the front side, with respect to the vehicle""s direction of travel, of a crawler for causing the snowmobile to move, it is possible to perform improved cooling by cooling oil with the scattered snow. Further, since two divided heat exchanging means or heat exchangers are provided, where one is used as usual for cooling water and the other for cooling oil, it is possible to realize different cooling functions with a simple structure.
Since a muffler is disposed in front of the engine body in the engine room in the snowmobile and an oil cooling means is arranged in front of the muffler, this arrangement allows the oil cooling means to receive the flow of air, during travel, ahead of the muffler and exhaust pipe which are higher in temperature than the oil cooler. Thus, it is possible to cool the oil at an improved efficiency.
Since the water pump is arranged between the engine and the exhaust passage provided in front of the engine, it is possible to realize a space-saving engine layout utilizing the dead space under the exhaust passage.
Since the water pump is arranged over an oil pan, it is possible to prevent the engine height from increasing.
Since the water pump is arranged under the exhaust manifold, it is possible to realize a space-saving engine layout utilizing the dead space under the exhaust manifold.
Since the engine has an alternator provided at a position opposite the water pump with the cylinder block in between, the three components being laid from the front to rear with respect to the vehicle""s direction of travel, it is possible to realize a space-saving and well-balanced drive belt layout.
Since a cooling water reservoir tank is arranged in the rear of the engine, at the side of the intake manifold, over an oil pan, heat exchanger and alternator, this arrangement of the reservoir tank at the top of the engine room makes it easy for cooling water to be re-supplied and other maintenance.
Since a cooling water reservoir tank is arranged without being projected outwards beyond a drive belt for driving an alternator and water pump, when viewed from top, this arrangement realizes a compact engine configuration.