Abstract:
Disclosed is a personal watercraft capable of appropriately detecting temperatures of an engine and an exhaust manifold by using one temperature sensor and in particular capable of finding that cooling water flow is stagnant in cooling systems of them based on the detection of the temperatures. The personal watercraft comprises a water-cooled multi-cylinder engine placed in an engine room of a body, an exhaust manifold for gathering an exhaust gas from the engine, the exhaust manifold being cooled by cooling water, and a temperature sensor provided so as to be located downstream of the vicinity of an end of the exhaust manifold that is located downstream in an exhaust gas flow path.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a jet-propulsion personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction.  
           [0003]    2. Description of the Related Art  
           [0004]    In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.  
           [0005]    In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.  
           [0006]    The personal watercraft has an engine room in its body. A water-cooled multi-cylinder engine is mounted in the engine room such that a crankshaft extends along the longitudinal direction of the body. The crankshaft projects rearwardly and its rear end is coupled to a pump shaft of the water jet pump, thereby allowing the water jet pump to be driven by the engine.  
           [0007]    In general, in the personal watercraft, the engine and an exhaust manifold mounted to the engine are cooled by part of the water pressurized by the water jet pump. The temperature of the exhaust manifold is affected mainly by the temperature of an exhaust gas from the engine and the smoothness of cooling water flow. The temperature of the exhaust manifold in the personal watercraft needs to be kept within a desired range according to its installation and use.  
           [0008]    How the exhaust manifold is cooled will be described below. There is provided a first cooling passage extending from the water jet pump and branching into two cooling passages. One of the branching cooling passages is connected to a second cooling passage (water jacket) of the engine and the other is connected to a third cooling passage of the exhaust manifold. The pressurized cooling water flows from the water jet pump into the first cooling passage, and further into the second cooling passage, and the third cooling passage. The cooling water flowing through the second cooling passage and the third cooling passage respectively serve to cool the engine and the exhaust manifold, which are thereby kept at proper temperatures.  
           [0009]    A temperature sensor is provided in the second cooling passage. The temperature sensor is connected to a buzzer through a signal cable. The temperature sensor is adapted to output a signal when the temperature of the cooling water flowing through the second cooling passage exceeds a predetermined value. The buzzer is actuated in accordance with the signal output from the temperature sensor. From this, a rider knows that the temperature of the engine has exceeded the predetermined value.  
           [0010]    However, the temperature of the exhaust manifold is sometimes difficult to appropriately detect because the temperature sensor is located in the second cooling passage of the engine.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention addresses the above-described condition, and an object of the present invention is to provide a personal watercraft capable of appropriately detecting temperatures of an engine and an exhaust manifold by using one temperature sensor.  
           [0012]    According to the present invention, there is provided a personal watercraft comprising: a water-cooled engine having an exhaust port; an exhaust passage connected to the exhaust port, for guiding an exhaust gas from the engine to outside of the watercraft; and a temperature sensor for detecting temperatures of the engine and the exhaust passage, wherein the temperature sensor is placed in the exhaust passage.  
           [0013]    In the personal watercraft so constituted, when the temperature of the engine increases due, for example, to stagnancy of cooling water flow in a cooling system or the like of the engine, such temperature increase affects the temperature of the exhaust gas flowing through the exhaust passage. Also, when the temperature of the exhaust passage increases due, for example, to degraded cooling, such temperature increase affects the temperature of the exhaust gas flowing through the exhaust passage. Accordingly, by detecting the temperature of the exhaust gas flowing through the exhaust passage, the temperatures of the engine and the exhaust passage can be appropriately detected.  
           [0014]    In the personal watercraft, the engine may have multiple cylinders and a plurality of exhaust ports, and the exhaust passage may include a water-cooled exhaust manifold for gathering the exhaust gas from the plurality of exhaust ports, a muffler provided downstream of the exhaust manifold in an exhaust gas flow path, and a flexible connecting passage interposed between the exhaust manifold and the muffler, for interconnecting the exhaust manifold and the muffler.  
           [0015]    The aforementioned effects can be obtained in the personal watercraft comprising the multi-cylinder engine, the exhaust manifold, the muffler, and the flexible connecting passage interconnecting the exhaust manifold and the muffler.  
           [0016]    In the personal watercraft, the flexible connecting passage may be made of rubber.  
           [0017]    The aforementioned effects can be obtained by using the rubber flexible connecting passage connecting the exhaust manifold and the muffler.  
           [0018]    In the personal watercraft, the muffler may be a water-cooled muffler.  
           [0019]    The aforementioned effects can be obtained by using the water-cooled muffler as one type of muffler.  
           [0020]    In the personal watercraft, the temperature sensor may be placed in the vicinity of a portion where the flexible connecting passage is connected to the muffler.  
           [0021]    The temperatures of the engine and the exhaust manifold can be appropriately detected by using the temperature sensor placed in the vicinity of the portion where the flexible connecting passage is connected to the muffler.  
           [0022]    In the personal watercraft, the temperature sensor may be placed in the vicinity of a portion where the exhaust manifold is connected to the flexible connecting passage.  
           [0023]    The temperatures of the engine and the exhaust manifold can be appropriately detected by using the temperature sensor placed in the vicinity of the portion where the exhaust manifold is connected to the flexible connecting passage.  
           [0024]    In the personal watercraft, the exhaust passage may further include an expansion chamber interposed between the exhaust manifold and the flexible connecting passage, for interconnecting the exhaust manifold and the flexible connecting passage.  
           [0025]    The temperatures of the engine and the exhaust manifold can be appropriately detected in the same manner as described above in the personal watercraft comprising the expansion chamber interconnecting the exhaust manifold and the flexible connecting passage, in addition to the multi-cylinder engine, the exhaust manifold, the muffler, and the flexible connecting passage interconnecting the exhaust manifold and the muffler.  
           [0026]    In the personal watercraft, the temperature sensor may be placed in the vicinity of a portion where the expansion chamber is connected to the flexible connecting passage.  
           [0027]    The temperatures of the engine and the exhaust manifold can be appropriately detected by using the temperature sensor placed in the vicinity of the portion where the expansion chamber is connected to the flexible connecting passage.  
           [0028]    In the personal watercraft, the temperature sensor may be placed in the vicinity of a portion where the exhaust manifold is connected to the expansion chamber.  
           [0029]    The temperatures of the engine and the exhaust manifold can be appropriately detected by using the temperature sensor placed in the vicinity of the portion where the exhaust manifold is connected to the expansion chamber.  
           [0030]    In the personal watercraft, the temperature sensor may be partially exposed outside of the exhaust passage.  
           [0031]    In the personal watercraft so constituted, the temperature sensor can be easily attached/detached and easily wired because part of the temperature sensor is exposed outside of the exhaust passage. Therefore, inspection and replacement of the temperature sensor can be easily carried out.  
           [0032]    The personal watercraft may further comprise a water-supply mechanism for supplying water to the exhaust gas in the exhaust passage, and the water-supply mechanism may be adapted to supply water at a portion of the exhaust passage which is located upstream of where the temperature sensor is placed, in the exhaust gas flow path.  
           [0033]    In the personal watercraft so constituted, the temperature sensor detects the temperature of the exhaust gas, which is reduced because of the supplied water. In this case, the temperature sensor adapted to detect temperatures within a range including a relatively lower upper limit can be used. Also, by narrowing the detection temperature range, higher accuracy temperature sensor can be used.  
           [0034]    The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    [0035]FIG. 1 is a plan view showing a personal watercraft according to an embodiment of the present invention;  
         [0036]    [0036]FIG. 2 is a side view of the personal watercraft of FIG. 1;  
         [0037]    [0037]FIG. 3 is a partially cutaway plan view of the jet-propulsion personal watercraft according to the embodiment of the present invention, showing a simplified constitution of a cooling passage provided between an engine and an exhaust manifold, and a water jet pump;  
         [0038]    [0038]FIG. 4 is a view taken in the direction of arrows IV-IV of FIG. 3, in which an outer wall of the exhaust manifold is partially cutaway; and  
         [0039]    [0039]FIG. 5 is a cross-sectional view taken in the direction of arrows V-V of a portion where an expansion chamber is connected to a water muffler in FIG. 3 and showing placement of a temperature sensor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]    Hereinafter, a jet-propulsion watercraft according to embodiments of the present invention will be described with reference to drawings in terms of a personal watercraft.  
         [0041]    Referring now to FIGS. 1, 2, A denotes a body. The body A comprises a hull H and a deck D covering the hull H from above. A line at which the hull H and the deck D are connected over the entire perimeter thereof is called a gunnel line G. In this embodiment, the gunnel line G is located above a waterline L of the personal watercraft.  
         [0042]    As shown in FIG. 1, an opening  16 , which has a substantially rectangular shape as seen from above, is formed at a relatively rear section of the deck D, such that it extends in the longitudinal direction of the body A, and a riding seat S is provided above the opening  16  such that it covers the opening  16  as shown in FIGS. 1, 2.  
         [0043]    An engine E is provided in a chamber  20  surrounded by the hull H and the deck D below the seat S. The engine E is a two-cycle engine of a fuel injection type and has multiple cylinders (e.g., three cylinders). As shown in FIG. 2, a crankshaft  26  of the engine E is mounted along the longitudinal direction of the body A. An output end of the crankshaft  26  is rotatably coupled integrally with a pump shaft  21 S of a water jet pump P through a propeller shaft  27 . An impeller  21  is attached on the pump shaft  21 S of the water jet pump P. The impeller  21  is covered with a pump casing  21 C on the outer periphery thereof.  
         [0044]    A water intake  17  is provided on the bottom of the watercraft. The water is sucked from the water intake  17  and fed to the water jet pump P through a water intake passage. The water jet pump P pressurizes and accelerates the water by rotation of the impeller  21 . The pressurized and accelerated water is discharged through a pump nozzle  21 R having a cross-sectional area of flow gradually reduced rearward, and from an outlet port  21 K provided on the rear end of the pump nozzle  21 R, thereby obtaining a propulsion force.  
         [0045]    In FIG. 2, reference numeral  21 V denotes fairing vanes for fairing water flow behind the impeller  21 . As shown in FIGS. 1, 2, reference numeral  24  denotes a bar-type steering handle. The handle  24  operates in association with a steering nozzle  18  swingable around a swing shaft (not shown) to the right or to the left behind the pump nozzle  21 R. When the rider rotates the handle  24  clockwise or counterclockwise, the steering nozzle  18  behind the pump nozzle  21 R is swung toward the opposite direction so that the watercraft can be correspondingly turned to any desired direction while the water jet pump P is generating the propulsion force. Also, as shown in FIG. 1, the handle  24  is provided with a throttle lever Lt in the vicinity of a right grip, for controlling an engine speed of the engine E.  
         [0046]    As shown in FIG. 2, a bowl-shaped reverse deflector  19  is provided above the rear side of the steering nozzle  18  such that it can swing downward around a horizontally mounted swinging shaft  19   a . The deflector  19  is swung downward to a lower position behind the steering nozzle  18  to deflect the ejected water from the steering nozzle  18  forward and, as the resulting reaction, the personal watercraft moves rearward.  
         [0047]    In FIGS. 1, 2, reference numeral  22  denotes a rear deck. The rear deck  22  is provided with an openable rear hatch cover  29 . A rear compartment (not shown) with a small capacity is provided under the rear hatch cover  29 . In FIGS. 1, 2, reference numeral  23  denotes a front hatch cover. A front compartment (not shown) is provided under the front hatch cover  23  for storing equipments and the like.  
         [0048]    Subsequently, a constitution of the main components of the present invention in the personal watercraft so constituted will be described. FIG. 3 is a partially cutaway plan view of the jet-propulsion personal watercraft, showing a simplified constitution of a cooling passage provided between the engine E and an exhaust manifold M, and the water jet pump P. FIG. 4 is a view taken in the direction of arrows IV-IV of FIG. 3, in which an outer wall of the exhaust manifold M is partially cutaway. FIG. 5 is a cross-sectional view taken in the direction of arrows V-V of a portion where an expansion chamber  4  is connected to a water muffler  6  in FIG. 3 and showing placement of a temperature sensor  8 .  
         [0049]    As shown in FIGS. 3, 4, the watercraft comprises the exhaust manifold M connected to a plurality of exhaust ports (not shown) provided in the engine E. An end of the exhaust manifold M, which is located downstream in an exhaust gas flow path (hereinafter also referred to as a downstream end of the exhaust manifold M), is connected to the expansion chamber  4  through an exhaust pipe  2 . The expansion chamber  4  is, in this embodiment, connected to the water-cooled water muffler  6  through a flexible connecting passage  7  made of rubber.  
         [0050]    In the watercraft, as shown in FIG. 3, a cooling passage  1  extends from the water jet pump P to the engine E and the exhaust manifold M. More specifically, the casing  21 C on the rear side of the impeller  21  is provided with a small-diameter to which a starting end  1 A of the cooling passage  1  is connected. A terminating end  1 B of the cooling passage  1  is connected to another opening (not shown) as a cooling water inlet of the engine E and the exhaust manifold M, which is located in the vicinity of the portion where the exhaust manifold M is connected to the engine E. Part of the water pressurized by the water jet pump P flows into the cooling passage  1  as cooling water. The cooling water flowing through the cooling passage  1  is branched in the vicinity of the portion where the exhaust manifold M is connected to the engine E. The branched cooling water flows into respective cooling passages of the engine E and the exhaust manifold M.  
         [0051]    The cooling water flowing through the cooling passage inside of the engine E cools the engine E and then flows from an upper end portion of a cylinder head Ch into and exhaust pipe  2  through a hose  10 . Meanwhile, the cooling water flowing through the cooling passage inside of the exhaust manifold M cools the exhaust manifold M and then flows into the exhaust pipe  2 . As a result, the cooling water which has cooled the engine E and the cooling water which has cooled the exhaust manifold M are gathered into the exhaust pipe  2 .  
         [0052]    The exhaust pipe  2  has a double-pipe structure. An exhaust gas flows through inside of an inner pipe of the exhaust pipe  2  and the cooling water flows through a space between the inner pipe and an outer pipe. Part of the cooling water gathered into the exhaust pipe  2  is discharged outside the watercraft through a discharge passage  3  extending from the exhaust pipe  2  to outside of the watercraft.  
         [0053]    The remaining cooling water, which has passed through the exhaust pipe  2 , without being discharged outside through the discharge passage  3 , flows through inside of the expansion chamber  4 . The expansion chamber  4  has a double-pipe structure similar to the exhaust pipe  2 . The exhaust gas flows through inside of an inner pipe  4   a  (see FIG. 5) of the expansion chamber  4  and the cooling water flows through a space between the inner pipe  4   a  and an outer pipe  4   b  (see FIG. 5). In the expansion chamber  4 , the inner pipe  4   a  is provided with a waterdrop hole (water-supply mechanism)  5  (see FIG. 5) in the vicinity of an exhaust port located downstream in the exhaust gas flow path. Part of the cooling water drops to the exhaust gas in the expansion chamber  4  through the waterdrop hole  5 . Most of the remaining cooling water is discharged outside the watercraft through a discharge passage  9  extended from a lower portion of the expansion chamber  4  to outside of the watercraft.  
         [0054]    The water-supply mechanism for supplying water to the exhaust gas is not intended to be limited to the waterdrop hole  5 . As an alternative, a spray nozzle may be attached to the inner pipe  4   a  of the expansion chamber  4  so that water from a passage independent of the passage through which the cooling water flows is led to the spray nozzle so as to be supplied to the exhaust gas.  
         [0055]    A temperature sensor  8  is provided downstream of the vicinity of the downstream end of the manifold M. More specifically, in this embodiment, the temperature sensor  8  is attached at a position of the expansion chamber  4  provided downstream of the exhaust manifold M so as to be located downstream of the waterdrop hole  5  (see FIGS. 4, 5).  
         [0056]    The temperature sensor  8  is attached to an upper surface of the expansion chamber  4 . Through experiments carried out by inventors of the present invention, it has been found that the temperature can be detected with higher accuracy when the temperature sensor  8  is attached to the upper surface of the expansion chamber  4  rather than when attached to another portion. In addition, part of the temperature sensor  8  is exposed in an outer wall face of the expansion chamber  4 . This facilitates operator&#39;s works such as attaching, wiring, maintenance, replacement, or the like, of the temperature sensor  8 .  
         [0057]    As shown in FIG. 5, the temperature sensor  8  is connected to a buzzer Ba through an electric wire  13 . The buzzer Ba is actuated, for example, when the temperature detected by the temperature sensor  8  exceeds a threshold, and sounds alarm.  
         [0058]    Thus, by placing the temperature sensor  8  at the position of an exhaust passage  30  as shown in FIGS. 4, 5, the temperature increase in the engine E and the temperature increase in the exhaust manifold M can be detected by using one temperature sensor  8 .  
         [0059]    When the cooling water does not flow smoothly in the cooling passage of the engine E or the cooling passage of the exhaust manifold M, the temperature of the exhaust gas flowing from the exhaust manifold M toward downstream in the exhaust gas flow path thereby increases. Therefore, by using one temperature sensor  8  provided downstream of the vicinity of the downstream end of the exhaust manifold M, it is possible to know the temperatures of both of the engine E and the exhaust manifold M. This makes it possible to know whether or not the flow of the cooling water is stagnant in these cooling passages.  
         [0060]    The position at which the temperature sensor  8  is attached is not intended to be limited to the above. The temperature sensor may be placed in the vicinity of the downstream end of the exhaust manifold M (e.g., temperature sensor  8   a  indicated by a dot-dash line in FIG. 4), or may be placed in the exhaust pipe  2  (e.g., temperature sensor  8   b  indicated by a dot-dash line in FIG. 4). Alternatively, the temperature sensor may be placed in the flexible connecting passage  7  (temperature sensor  8   c  indicated by a dot-dash line in FIG. 4). Further, the temperature sensor may be placed at a portion where the flexible connecting passage  7  is connected to the water muffler  6  (temperature sensor  8   d  indicated by a dot-dash line in FIG. 4).  
         [0061]    In any case, the temperature sensor may be placed at any position of the exhaust passage  30  comprised of the exhaust manifold M, the exhaust pipe  2 , the expansion chamber  4 , the flexible connecting passage  7 , the muffler  6 , and the like, which are arranged downstream in the exhaust gas flow path in this order from the exhaust ports of the engine E. It should be appreciated that, as shown in FIG. 5, the temperature sensor  8  is placed downstream of the waterdrop hole  5  in the exhaust gas flow path, because the temperature sensor adapted to detect temperatures within a range including a relatively low upper limit can be advantageously used. This is because the temperature of the exhaust gas decreases by the water supplied through the waterdrop hole  5 .  
         [0062]    In a four-cycle engine for the watercraft, the expansion chamber  4  can be dispensed with. This follows that the exhaust passage  30  is comprised of the exhaust manifold M, the exhaust pipe  2 , the flexible connecting passage  7 , the water muffler  7 , and the like. Also, in that case, the temperature sensor may be placed at any position of the above-identified components of the exhaust passage  30 .  
         [0063]    A watercraft using a dry muffler in place of the wet muffler mentioned above can achieve the same effects as described above.  
         [0064]    [0064]FIGS. 5, 11 denote an inspection port of the waterdrop hole  5 . In FIG. 3, T donates a fuel tank, Bt denotes a battery,  12  denotes a bilge intake port, and  14  denotes an exhaust end pipe for guiding the exhaust gas from the water muffler  6  to outside of the watercraft.  
         [0065]    As this embodiment may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.