Abstract:
A pump jet in which the axial flow of water through the device is controlled by bleeding exhaust gas into the pump jet water stream, thereby producing a thrust loss. The addition of gas into the primary pump jet water flow stream reduces the effective flow density of the exit media, thereby reducing the exit momentum (and thrust) produced by the pump jet. The thrust modulation device can be actuated using any conventional electrical or mechanical actuation subsystem via a knob or lever positioned near the throttle control.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to pump jets used with outboard motors or in inboard/outboard or stern drive units of boats and other vehicles. In particular, the invention relates to pump jets in which exhaust gas from the outboard motor is directed through the pump jet and discharged into the water stream surrounding the pump jet. 
     BACKGROUND OF THE INVENTION 
     In one type of conventional outboard motor, a propeller is driven by a powerhead to propel a boat through water. Most large outboard motors of this type inject the exhaust gas stream under water in order to reduce engine noise and increase propulsive thrust. 
     In a typical configuration shown in FIG. 1, the gas exhausted from the powerhead  10  flows downwardly through an exhaust channel  12  and exits the motor rearwardly through the propeller  14 . This type of motor is referred to as an exhaust-through-hub (ETH) motor. 
     Another type of conventional outboard motor has an axial-flow pump jet system driven by the powerhead. In a pump jet system, an impeller or rotor is mounted (e.g., spline fitted) directly on the propeller output shaft in place of the propeller. There are typically no modifications to the drive train, cooling or sealing components. A ducted housing surrounds the rotor. Such a system has the advantages of reducing hazards to swimmers in the vicinity of the motor, protecting the rotating elements from interference with and damage by foreign objects in the water, and improving the efficiency and performance of the propulsion system. Another benefit inherent with the pump jet is a directed jet of water that results in greater steering response. 
     U.S. Pat. No. 5,325,662 discloses a pump jet in which the exhaust gas discharged from the outboard motor is ducted downwardly through the central body of the motor and around a rotor shaft. An annular exhaust channel is formed in the rotor hub for receiving the exhaust gas and projecting it rearwardly of the motor. A cavity in the stator hub provides a plenum chamber for receiving the exhaust gas. Exhaust gas flows from the cavity of the stator hub to at least one hollow stator vane which serves as an exhaust pipe. In the case of multiple hollow stator vanes, the flow in the stator hub is split into multiple streams. Each stream of exhaust gas passes through a respective hollow stator vane. Discharge ports are formed in the stator housing for discharging exhaust gas into the water stream surrounding the stator housing. This arrangement will be referred to herein as an exhaust-through-vane (ETV) configuration. 
     The volumetric flow through an axial-flow pump jet device produces the propulsive thrust forces necessary to propel a boat or other watercraft. Generally, as the motor rpm approaches full throttle, the thrust forces are also reaching maximum values, provided that the boat velocity is low, as is typically encountered in work boats and pontoon boats. Often it is desirable to modulate the thrust of a pump jet while maintaining the rpm at near wide-open throttle, particularly if a quicker response is possible. In order to achieve this modulation effect at full rpm, it is necessary to control the axial flow through the pump jet device. 
     SUMMARY OF THE INVENTION 
     The present invention is a pump jet in which the axial flow of water through the device is controlled by bleeding exhaust gas into the pump jet water stream, thereby producing a thrust loss. In accordance with the preferred embodiment of the invention, an ETV-type pump jet is provided with means for bleeding exhaust gas from the plenum cavity in the stator hub directly into the exit flow stream. This addition of gas into the primary pump jet water flow stream reduces the effective flow density of the exit media, thereby reducing the exit momentum (and thrust) produced by the pump jet. The thrust modulation device can be actuated using any conventional electrical or mechanical actuation subsystem via a knob or lever positioned near the throttle control. 
     The invention also encompasses a method for operating an ETV pump jet comprising the steps of: activating a motor of an ETV pump jet to cause a rotor to impel a stream of water through the volume between a stator hub and a stator housing, and to cause exhaust gas to pass through a cavity in the stator hub and a hollow stator vane; and bleeding exhaust gas from said cavity inside the stator hub into said water stream. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a prior art ETH motor with a propeller. 
     FIG. 2 is a partial sectional view of an ETV pump jet having exhaust streams discharged through at least two stator vanes. 
     FIG. 3 is a side elevational view showing the manner of attachment of the pump jet of FIG. 2 to an outboard motor. 
     FIG. 4 is a partial sectional view of an ETV pump jet of the type shown in FIG. 2 having an axial flow control device for bleeding exhaust gas into the exit flow water stream. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the invention is an outboard motor having a pump jet  16  of the ETV type shown in FIG.  2 . The pump jet includes a rotor comprising a plurality of blades  18  extending radially outward from an outer rotor hub  20 . The outer rotor hub  20  is securely mounted on an inner rotor hub  22 . The rotor and inner rotor hub are assembled prior to installation. During pump jet installation, this one-piece rotor assembly is inserted onto one end of a propeller shaft  24  and secured to the shaft by a nut  26 . The other end of the propeller shaft is rotatably mounted in a bearing (not shown) which is housed in propeller shaft bearing housing  25 . Inner rotor hub  22  is connected to outer rotor hub  20  by means of radial struts, which are not visible in the partially sectional view of FIG.  2 . 
     In conventional fashion, the powerhead  10  drives the propeller shaft  24  to rotate via a drive shaft and gears, neither of which are shown in FIG.  2 . The drive shaft extends inside the lower housing unit  28 , while the gears are arranged inside the gear case  30 . Rotation of the propeller shaft in turn causes the rotor assembly to rotate. During rotation in forward gear, the angled blades  18  of the rotor impel water axially rearward to produce a forward thrust. In reverse gear, a reverse thrust is produced. 
     The rotor assembly is surrounded by a non-rotating rotor housing  32 . The rotor housing  32  is part of a one-piece rotor housing assembly, which also comprises a plurality of inlet vanes  34  and an inlet vane hub  36 . Each inlet vane  34  is joined at one end to the inlet vane hub  36  and at the other end to the rotor housing  32 . The inlet vanes direct water flow into the blades  18  of the rotor. The inlet vanes also block debris, sea creatures or human limbs from contacting the rotating blades of the rotor. 
     During pump jet installation, the rotor housing assembly is installed prior to installation of the rotor assembly. The inlet vane hub  36  is inserted into the downstream end of the gear case  30 . Referring to FIG. 3, the rotor housing assembly is joined to an anti-cavitation plate  38  by means of an upper bracket  40  and is joined to skeg  42  by means of a clamp  44 . Screw  45  squeezes the clamp  44  onto the skeg  42 . Screws  46  secure the clamp  44  to the rotor housing  32 . Screws  48  and bolts  50  attach the upper bracket  40  to the anti-cavitation plate  38 . 
     Referring again to FIG. 2, the rotor housing  32 , which has an inlet  33  for the intake of water, forms the upstream portion of the shroud which fully encloses the pump jet. The rearward portion of the shroud comprises a stator housing  52  which has an outlet  53  for the water propelled rearward by the rotor blades  18 . The stator housing  52  has an upstream edge which form fits with the downstream edge of the rotor housing  32 . Installation of a pump jet involves three steps: (1) attach the rotor housing to the anti-cavitation plate and skeg; (2) install the rotor on the propellor shaft; and (3) attach the stator housing to the rotor housing by means of screws (not shown in FIG.  2 ). The stator housing  52  has a generally conical portion which decreases in internal diameter in the downstream direction. The minimum internal diameter of stator housing  52  is preferably located at the outlet  53 . 
     The stator housing  52  is part of a one-piece stator housing assembly, which also comprises a plurality of stator vanes  54  and a stator hub  56 . Each stator vane  54  is joined at one end to the stator hub  56  and at the other end to the stator housing  52 . The stator vanes convert rotational energy imparted to the water flow by the rotor blades into axial flow energy at the outlet of the stator housing  52 . One or more of the stator vanes  54  is hollow. Similarly, an internal cavity in the stator hub  56  forms a plenum cavity  58 , which is in flow communication with each hollow stator vane. Nut  26  extends into plenum cavity  58  in stator hub  56 . 
     The exhaust gas from the powerhead  10  flows downwardly through an exhaust channel  60 . The lower end of the exhaust channel  60  is in flow communication with a hub exhaust channel  62  which channels the exhaust stream rearward through the hub. The hub exhaust channel  62  is an annular space, which is bounded internally by the propeller shaft bearing housing  25  and the inner rotor hub  22 , and externally by the wall of the gear case  30 , the inlet vane hub  36  and the outer rotor hub  20 . The exhaust stream flows from the hub exhaust channel  62  to the plenum cavity  58  in stator hub  56 , and then into the hollow stator vanes  54  which communicate with the plenum cavity. Preferably at least a portion of the stator hub  56  is conical in shape. The exhaust stream in each hollow stator vane flows the length of the stator vane and discharges from a respective exhaust port  64  into the water stream surrounding the stator housing  52 . 
     In accordance with the preferred embodiment of he invention shown in FIG. 4, exhaust gas is bled into the exit flow water stream from the plenum cavity. The terminal section of the stator hub is replaced by a flow control valve  66  which can be operated by the boat operator. In the preferred embodiment, the flow control valve  66  is slidable between open and closed positions, and comprises a conical valve head  68 , a valve stem  70 , a valve piston  72 , a cylinder  74  and a compression spring  86 . One end of the valve stem  70  is coupled to the valve piston  72 . The valve head  68  is mounted on the other end of the valve stem  70 . The valve piston  72  is axially slidable inside the cylinder  74 . One end of the cylinder  74  acts as a bearing for the sliding valve stem  70 . The cylinder  74  is supported in a position coaxial with the pump jet centerline by a plurality (e.g., three) of radial struts  76 . 
     In accordance with the preferred embodiment, the flow control valve  66  is actuated by a valve actuator assembly  78  comprising a displaceable actuator rod  80  having an actuator  82  mounted on its distal end. Although not shown in FIG. 4, the actuator rod  80  is preferably supported by a pair of bearings which allow the rod to displace along its longitudinal axis in response to manipulation of the proximal end of the rod by the boat operator. Preferably, the proximal end of the actuator rod has a knob, lever or handle (not shown) mounted thereon which is readily accessible to the boat operator. Although FIG. 4 depicts the actuator rod  80  as passing through one of the hollow stator vanes  52 , a person skilled in the art will appreciate that the disclosed design could be modified to allow the rod  80  to pass through a separate opening in the stator housing, instead of through a hollow stator vane, that separate opening also acting as a bearing for the sliding actuator rod. 
     In accordance with the preferred embodiment, the actuator assembly is displaceable between upper and lower positions, the upper actuator position corresponding to the valve closed position and the lower actuator position corresponding to the valve open position. The upper position of the actuator is shown by dashed lines  82 ′, the closed position of the valve head is shown by dashed lines  68 ′ and the valve piston position corresponding to the valve head closed position is shown by dashed line  72 ′ in FIG. 4; the lower position of the actuator  82 , the open position of the valve head  68 ′ and the position of the valve piston  72  corresponding to the valve head open position are shown by solid lines in FIG.  4 . 
     In the closed position, an annular contact face of the valve head  68  abuts an annular valve seat  84 , the opposing surfaces forming a seal preventing the escape of exhaust gas from the plenum cavity  58  into the exit flow water stream. In the closed position shown by dashed lines  68 ′ in FIG. 4, the valve head is held against the valve seat  84  by the action of the compression spring  86 . In the closed position, the boat can be operated at full throttle without thrust modulation. When the valve head is displaced rearward, the annular contact face of the valve head  68  moves away from the annular valve seat  84 , forming a gap  88  through which exhaust gas from the plenum cavity  58  flows into the exit flow water stream. In the open position, the thrust can be modulated by controlling the width of the gap  88 , i.e., the greater the gap width, then the greater the thrust loss will be. 
     In the preferred embodiment depicted in FIG. 4, the flow control valve is actuated by displacing the actuator assembly downward from the upper position (dashed lines) to the lower position (solid lines). During this downward displacement, the actuator  82  pushes the valve piston  72  rearward (rightward in FIG.  4 ), causing the valve head  68  to move away from the valve seat  84 . 
     In accordance with one preferred embodiment of the invention, the actuator  82  has a planar camming surface  90  which is disposed to bear against a rounded protruding end of the valve piston  72 . The camming surface is inclined at an acute angle (e.g., 45°) relative to the pump jet centerline. When the planar camming surface  90  is in contact with the rounded end of the valve piston  72 , the width of gap  88  will increase linearly as a function of the downward displacement of actuator. However, a person skilled in the art will readily appreciate that the camming surface need not be planar and may instead be a concave curved surface. 
     In order to restore full thrust, the boat operator causes the actuator  82  to displace from the lower position (solid lines) to the upper position (dashed lines) shown in FIG.  4 . As the point of contact between the actuator  82  and the valve piston  72  changes during upward displacement of the actuator, the compression spring  86  urges the piston forward (leftward in FIG.  4 ), causing the valve head  68  to return to the closed position. 
     In accordance with the preferred embodiment shown in FIG. 4, the conical outer surface of the valve head  68  functions as part of the stator hub when the flow control valve is closed. In accordance with an alternative embodiment, a valve assembly is arranged inside a stator hub having one or more exhaust gas outlets. In the rearmost valve head position, the valve head closes the exhaust gas outlets. In response to manipulation of an actuator by the boat operator, the valve head moves forward to uncover the exhaust gas outlets, allowing the exhaust gas in the plenum cavity to escape into the exit flow water stream. For example, in order to accomplish forward displacement of the valve head, the valve piston is provided with an extension having a transverse arm which is contacted by an actuator. In this case, the camming surface of the actuator is arranged to cam the arm forward (instead of rearward as in the embodiment shown in FIG. 4) when the actuator is displaced downwardly, thereby causing the flow control valve to open. 
     The invention has application in both outboard drive units and inboard/outboard or stern drive units for watercraft and other vehicles. A propulsor of a stern drive unit is typically mounted to the stern or transom of a boat hull via a transom mount assembly or bracket. The shaft on which the pump jet rotor is mounted is driven to rotate by an engine mounted inside the boat via conventional gear assemblies mounted outside the boat. 
     While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In particular, a person skilled in the art will have little difficulty designing functionally equivalent devices for actuating the flow control valve. For example, it will be obvious to a skilled artisan that the change in position of the valve piston could be actuated hydraulically or pneumatically, e.g., by closing the open end of the cylinder  74  and then supplying liquid or gas to a chamber defined by the newly closed end of the cylinder and the forward end of the valve piston. The boat operator may then actuate opening of the flow control valve by activating a pump which supplies liquid or gas to the aforementioned chamber in the cylinder. In accordance with a further alternative, valve opening could be actuated electrically, e.g., by coupling the valve piston to a solenoid, the state of the solenoid being controlled by the boat operator. Also, numerous alternative devices could be readily designed for opening the flow control valve mechanically. For example, a rack and pinion arrangement could be employed to convert rotation (instead of downward displacement) of an actuator shaft into rearward (or forward) displacement of the valve piston. In addition, many modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 
     As used in the claims, the term “marine engine” includes both inboard and outboard motors.