Electric Propulsion Machine

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2024-099464 filed on Jun. 20, 2024, the entire content of which is incorporated herein by reference.

The present disclosure relates to an electric propulsion machine that propels a boat.

An electric propulsion machine is a kind of boat propulsion machine that propels a boat, and uses a motor (electric motor) as a power source that generates a propulsion force. Some electric propulsion machines include a water-cooled cooling mechanism that cools a motor. These kinds of electric propulsion machines include a pump for supplying cooling water to a water jacket provided in the motor.

JP2005-162055A describes an electric outboard motor including a pump that supplies cooling water to a water jacket of a motor. The outboard motor includes a drive shaft that transmits rotation of the motor provided in an upper portion of the outboard motor to a propeller shaft provided in a lower portion of the outboard motor, and the drive shaft extends in an upper-lower direction from a motor side to a propeller shaft side. The pump is provided on the drive shaft, and an impeller of the pump rotates integrally with the drive shaft. Further, a lower case is provided in the lower portion of the outboard motor, and a water intake port for taking water around the outboard motor into the outboard motor is provided in the lower case. The water intake port is disposed below an anti-cavitation plate of the outboard motor. On the other hand, the pump is disposed above the anti-cavitation plate. Further, a water intake passage for connecting the water intake port to a suction port of the pump and feeding water taken in from the water intake port to the pump as the cooling water is provided in the outboard motor. When the motor is driven, the drive shaft rotates, and the impeller of the pump rotates. When the impeller rotates, the cooling water taken in from the water intake port is suctioned up to the pump through the water intake passage. The cooling water suctioned up to the pump is discharged from the pump toward the water jacket of the motor.

In the boat propulsion machine having a configuration in which the water intake port is disposed below the anti-cavitation plate, the pump is disposed above the anti-cavitation plate, and the cooling water taken in from the water intake port is suctioned up by the pump, as in the electric outboard motor described in JP2005-162055A, the periphery of the impeller of the pump may not be filled with water at the start of operation of the boat propulsion machine, that is, at the start of driving of the pump. Therefore, in the pump of the boat propulsion machine, a pump that does not require priming for driving the pump, specifically, a positive displacement pump having a high suction capacity is used. In many boat propulsion machines in the related art, a rotary volume change pump having a rubber impeller is adopted as the positive displacement pump having the high suction capacity.

The rotary volume change pump has an ability to suction out the air around the impeller and the air in the water intake passage at the start of the pump drive and suction up the water taken in from the water intake port. However, since the pump has such a high suction capacity, the boat propulsion machine is large, and it is difficult to reduce the size. In the boat propulsion machine in the related art in which the rotary volume change pump is mounted on the drive shaft, it is considered that it is difficult to reduce the size of the pump, which is one of the causes of preventing the boat propulsion machine from being reduced in size.

Further, in the rotary volume change pump having the rubber impeller, when a rotation direction of the impeller changes, the impeller is likely to be damaged and therefore the durability of the pump is reduced as compared when the rotation direction of the impeller is always constant. In a case where the electric propulsion machine is configured to reverse the rotation direction of the motor when the boat is moved forward and when the boat is moved backward, the rotation direction of the drive shaft is reversed when the boat is moved forward and when the boat is moved backward, and therefore the rotation direction of the impeller is also reversed. Therefore, in the case where the rotary volume change pump having the rubber impeller is provided on the drive shaft of the electric propulsion machine having a configuration in which the rotation direction of the motor is reversed when the boat is moved forward and when the boat is moved backward, the durability of the pump becomes low.

Aspect of non-limiting embodiments of the present disclosure relates to reduce the size of an electric propulsion machine in the electric propulsion machine including a motor cooling pump, and to solve a problem that the durability of the motor cooling pump becomes low in the electric propulsion machine having a configuration in which a rotation direction of a motor is reversed.

Aspects of certain non-limiting embodiments of the present disclosure address the features discussed above and/or other features not described above. However, aspects of the non-limiting embodiments are not required to address the above features, and aspects of the non-limiting embodiments of the present disclosure may not address features described above.

According to an aspect of the present disclosure, there is provided an electric propulsion machine for propelling a boat, the electric propulsion machine including:

An electric propulsion machine according to an embodiment of the present disclosure is an electric propulsion machine for propelling a boat and includes: a motor provided in an upper portion of the electric propulsion machine; a propeller shaft provided in a lower portion of the electric propulsion machine; a propeller provided in the propeller shaft; a drive shaft extending in an upper-lower direction and configured to transmit rotation of the motor to the propeller shaft; and a first non-positive displacement pump provided in the propeller shaft and configured to supply cooling water cooling the motor to the motor.

In the electric propulsion machine of the present embodiment, the pump is provided in the propeller shaft. In a state in which the electric propulsion machine is attached to the boat, the propeller shaft is located below a water surface, and the pump provided on the propeller shaft is also located below the water surface. Accordingly, it is possible to easily ensure priming of the pump, that is, it is possible to easily obtain a state in which the periphery of the impeller is filled with water at the start of driving of the pump. Therefore, it is possible to use a non-positive displacement pump that requires priming. The non-positive displacement pump is easily reduced in size as compared with a rotary volume change pump having a rubber impeller. Therefore, according to the electric propulsion machine of the present embodiment, it is possible to reduce the size of the electric propulsion machine by using the non-positive displacement pump.

In the electric propulsion machine of the present embodiment, the rotation of the motor is transmitted to the propeller shaft via the drive shaft. When the rotation direction of the motor is reversed, the rotation direction of the propeller shaft is reversed. The pump is provided on the propeller shaft and rotates integrally with the propeller shaft. When the rotation direction of the motor is reversed, the rotation direction of the impeller of the pump is also reversed. In a case where the pump is used in the manner that the rotation direction of the impeller is reversed, when the durability of the rotary volume change pump having the rubber impeller is compared to the durability of the non-positive displacement pump, the durability of the non-positive displacement pump is significantly higher. Therefore, according to the electric propulsion machine of the present embodiment using the non-positive displacement pump, it is possible to solve the above problem that the durability of the motor cooling pump decreases in the electric propulsion machine having a configuration in which the rotation direction of the motor is reversed.

Two embodiments of the electric propulsion machine of the present disclosure will be described with reference to. In the description, when describing directions of the upper (Ud), the lower (Dd), the front (Fd), and the rear (Bd), please follow arrows drawn at the lower right of each figure.

illustrates an outboard motorthat is a first embodiment of the electric propulsion machine of the present disclosure.illustrates a cross section of a lower portion of the outboard motorwhich is divided into two parts that are left and right parts along a plane passing through a center in the left-right direction of the outboard motor. FIG.is an enlarged view of a portion where the water pumpis provided in the lower portion of the outboard motorin.

The outboard motoris a device configured to propel a boat and is attached to the boat. As illustrated in, the outboard motorincludes a motorthat is a power source configured to generate a propulsion force of a boat, a motor control deviceconfigured to control driving of the motor, a propellerconfigured to generate a propulsion force of the boat from the rotation of the motor, a propeller shaftto which the propelleris fixed, a drive shaftconfigured to transmit the rotation of the motorto the propeller shaft, and a gear mechanismconfigured to transmit the rotation of the motorto the propeller shafttogether with the drive shaft.

The motorand the motor control deviceare provided in an upper portion of the outboard motorand located above the water surface in a state in which the outboard motoris attached to the boat. The outboard motoralso includes an upper case. The motorand the motor control deviceare accommodated in the upper case.

The propeller, the propeller shaft, and the gear mechanismare provided in the lower portion of the outboard motor, and are located below the water surface in the state in which the outboard motoris attached to the boat. The propeller shaftextends in a front-rear direction. The propelleris fixed to a rear end portion of the propeller shaft. The outboard motoralso includes a lower case. A front portion of the propeller shaftand the gear mechanismare accommodated in the lower case. An anti-cavitation plateis provided in the lower case.

The drive shaftextends in an upper-lower direction from the motortoward the propeller shaft. An upper portion of the drive shaftis located inside the upper case. An upper end portion of the drive shaftis connected to an output shaft of the motor. A lower portion of the drive shaftis located in the lower case. A lower end portion of the drive shaftis connected to the propeller shaftvia the gear mechanism. Specifically, the gear mechanismincludes a drive gearand a driven gear. The drive gearis fixed to the lower end portion of the drive shaft. The driven gearis fixed to the front portion of the propeller shaft. The drive gearand the driven gearare bevel gears and mesh with each other.

The motor control deviceincludes, for example, an inverter configured to generate a drive current driving the motor, a host control unit configured to control the inverter in accordance with an operation input from the outside of the outboard motor, and the like. When driving the motor, the motor control deviceselects the rotation direction of the motorin response to the operation input from the outside of the outboard motor. Specifically, the motor control deviceis configured to rotate the motorin one direction in a case where the boat is moved forward, and is configured to rotate the motorin the other direction in a case where the boat is moved backward. In a case where the motorrotates in one direction under the control of the motor control device, the rotation of the motoris transmitted from the output shaft to the drive shaft, and the drive shaftrotates. Further, the rotation of the drive shaftis transmitted to the propeller shaftvia the gear mechanism, causing the propeller shaftand the propellerto rotate forward. The forward rotation of the propellergenerates the propulsion force for moving the boat forward. In a case where the motorrotates in the other direction under the control of the motor control device, the rotation is transmitted to the propeller shaftvia the drive shaftand the gear mechanism, and the propeller shaftand the propellerrotate reversely. The reverse rotation of the propellergenerates a propulsion force for moving the boat backward.

Further, the outboard motoris provided with a clamp bracketthat attaches the outboard motorto a transom of the boat, and a swivel bracketthat connects the outboard motorto the boat such that a horizontal direction of the propellerwith respect to the boat can be changed.

Further, the outboard motorincludes a water-cooling cooling mechanismconfigured to cool the motor. The cooling mechanismincludes a water intake portconfigured to take in water around the outboard motorinto the outboard motoras cooling water, a water pumpconfigured to supply the cooling water taken in from the water intake portto the motor, and a water jacketconfigured to cool the motorby making the cooling water flow to, for example, an outer peripheral portion of the motor.

The water pumpis a non-positive displacement pump, for example, a centrifugal pump. The water pumpis provided at a front end side of the propeller shaft. Specifically, as illustrated in, the water pumpincludes a pump shaftand an impeller. The pump shaftextends in the front-rear direction. A rear end portion of the pump shaftis connected to a front end portion of the propeller shaft. The impelleris fixed to a front end portion of the pump shaft. The pump shaftand the impellerrotate integrally with the propeller shaft. A support memberthat supports the front end portion of the propeller shaftand the pump shaftis provided in a front portion of a lower portion in the lower case. The front end portion of the propeller shaftand the pump shaftare rotatably supported by the support membervia bearings. A pump chamberis formed in the front portion of the lower portion of the lower casein front of the support member. The impelleris disposed in the pump chamber. Further, a suction portis formed in a front portion of the pump chamber. A discharge portis formed in an upper portion of the pump chamber.

The water intake portis provided in the front portion of the lower portion in the lower case. The water intake portis disposed in front of the propeller shaft. The water intake portis disposed in front of the water pump. Specifically, the water intake portis disposed immediately in front of the pump chamberand the impeller. The suction portand the impellerface the water intake port. A strainer for preventing dust or the like in water from entering the inside of the outboard motoris provided in the water intake port. A water intake passageis provided between the water intake portand the suction port. The water intake passageextends in the front-rear direction. The water intake passageis extremely short, and the water intake portand the suction portare extremely close to each other.

As illustrated in, the water jacketis provided in the motor. The water jacketis implemented by, for example, a cooling water passage formed to cover the entire outer peripheral portion of the motor. A transfer passageconfigured to transfer the cooling water from the water pumpto the water jacketis provided between the discharge portof the pump chamberand the water jacket. The transfer passageis provided in front of the drive shaftin the outboard motor. A lower portion of the transfer passageis disposed in the lower caseas illustrated in. A lower end portion of the transfer passageis connected to the discharge portof the pump chamberas illustrated in. Further, an upper portion of the transfer passageis disposed in the upper caseas illustrated in. An upper end portion of the transfer passageis connected to a cooling water inletof the water jacket. A drain passageconfigured to discharge the cooling water after flowing through the water jacketto the outside of the outboard motoris connected to a cooling water outletof the water jacket.

In the outboard motor, the pump chamberis disposed right behind the water intake port, and the position of the pump chamberand the position of the water intake portare the same in the upper-lower direction. Therefore, in a case where the outboard motoris attached to the boat and the water intake portcompletely sinks in water, water around the outboard motornaturally flows into the pump chamberfrom the water intake port. As a result, the pump chamberis filled with water, and the periphery of the impelleris filled with water. In this way, in the outboard motor, the water intake portis completely submerged in water, so that the priming of the water pumpis ensured.

Thereafter, when the motoris driven and the propeller shaftrotates, the impellerof the water pumprotates together with the propeller shaft. Water that has flowed from the water intake portinto the pump chamberas the cooling water is fed to the water jacketvia the transfer passageby the rotation of the impeller. The cooling water fed to the water jacketflows through the inside of the water jacket. Accordingly, the motoris cooled. The cooling water after flowing through the inside of the water jacketis discharged to the outside of the outboard motorfrom a discharge port provided in, for example, a boss portion of the propellervia the drain passage.

Further, since a rotation direction of the impellerof the water pumpis determined by a rotation direction of the propeller shaft, the rotation direction of the impelleris opposite when the propeller shaftrotates forward and when the propeller shaftrotates reversely. However, the water pumpprovided in the outboard motorexhibits a suction capacity and a discharge capacity regardless of the rotation direction of the impeller.

Further, since the water intake portis disposed immediately in front of the suction portof the pump chamber, when the boat moves forward, water around the outboard motorflows vigorously into the pump chamberthrough the water intake port. The water pressure at this time assists in the direction of promoting the rotation of the impeller, and as a result, the smoothness of the flow of the cooling water from the water intake portto the water jacketis improved.

As described above, in the outboard motorof the first embodiment of the present disclosure, the water pumpis provided on the propeller shaft. Since the water pumpis provided on the propeller shaft, the water pumpis located below the anti-cavitation plate, and when the outboard motoris attached to the boat, the entire water pumpis located below the water surface. As a result, it is easy to ensure priming of the water pump. Therefore, in the outboard motor, the non-positive displacement pump that requires priming can be adopted as the water pump. The non-positive displacement pump is easily reduced in size as compared with the rotary volume change pump having the rubber impeller used in many boat propulsion machines in the related art. According to the outboard motorof the present embodiment, it is possible to reduce the size of the outboard motor by using the non-positive displacement pump. Further, among the non-positive displacement pumps, the centrifugal pump has a simple structure and therefore has a small size and is lightweight. By using the centrifugal pump as the water pump, it is possible to promote size reduction and weight reduction of the outboard motor.

Further, in the outboard motorof the present embodiment, the rotation direction of the impelleris reversed in response to the switching of the rotation direction of the propeller. Generally, in the case where the pump is used in the manner that the rotation direction of the impeller is reversed, when the durability of the rotary volume change pump having the rubber impeller is compared to the durability of the non-positive displacement pump, the durability of the non-positive displacement pump is significantly higher. Therefore, according to the outboard motorof the present embodiment using the non-positive displacement pump as the water pump, it is possible to solve the above problem that the durability of the motor cooling pump decreases in the electric propulsion machine having a configuration in which the rotation direction of the motor is reversed.

Further, in the outboard motorof the present embodiment, the water pumpis provided in the front end side of the propeller shaft. By providing the water pumpat the front end side of the propeller shaft, the lower caseof the outboard motorof the present embodiment can be prevented from becoming larger than a lower case of an outboard motor using an engine (internal combustion engine) while the water pumpis provided on the propeller shaft. That is, most of the outboard motors using the engine as the power source that generates the propulsion force of the boat include a shift device that switches the rotation direction of the propeller (see, for example, JP2012-144186A). Since it is difficult for the engine to reverse the rotation direction of a crankshaft, most of the outboard motors using the engine include a shift device, and the rotation direction of the propeller is switched by the shift device. Specifically, in the outboard motor using the engine as the power source, the gear mechanism is provided between the lower end portion of the drive shaft extending downward from the engine and the front portion of the propeller shaft. The gear mechanism includes the drive gear fixed to the lower end portion of the drive shaft, a forward gear that meshes with the drive gear and rotates in the forward direction by the rotation of the drive shaft, a reverse gear that meshes with the drive gear and rotates in the reverse direction by the rotation of the drive shaft, and a dog clutch that switches between connecting the forward gear to the propeller shaft to rotate the propeller shaft forward and connecting the reverse gear to the propeller shaft to rotate the propeller shaft reversely. The shift device controls the dog clutch according to an operation input for switching the rotation direction of the propeller and switches the rotation directions of the propeller shaft and the propeller. Generally, in the outboard motor using the engine, a portion to which an operation for switching the rotation direction of the propeller is input is the front portion of the upper portion of the outboard motor, and on the other hand, the dog clutch to be controlled by the shift device is disposed in the lower portion of the outboard motor. Therefore, the shift device includes a shift rod for transmitting the operation input for switching the rotation direction of the propeller to the dog clutch, and the shift rod extends in the upper-lower direction at a portion in front of the drive shaft in the outboard motor. Further, the shift device includes a shift slider that connects a lower end portion of the shift rod to the dog clutch, and the shift slider is provided at the front end side of the propeller shaft. In the outboard motorof the present embodiment, the power source that generates the propulsion force of the boat is the motor, and the rotation direction of the propelleris switched by switching the rotation direction of the motorby the control of the motor control device. Therefore, the shift device is unnecessary in the outboard motorof the present embodiment, and the shift device is not provided in the outboard motorof the present embodiment. Therefore, the shift slider is not provided at the front end side of the propeller shaft. According to the outboard motorof the present embodiment, since the water pumpis disposed at the front end side of the propeller shaft, a place where the shift slider of the shift device is disposed in the outboard motor using the engine can be used as the disposition place of the water pump. Further, by using a small non-positive displacement pump as the water pump, the water pumpcan be disposed at the place without enlarging a space of the place where the shift slider of the shift device is provided in the outboard motor using the engine. Therefore, according to the outboard motorof the present embodiment, the lower casecan be prevented from becoming larger than the lower case of the outboard motor using the engine while the water pumpis provided on the propeller shaft.

Further, the outboard motorof the present embodiment includes the transfer passagethat transfers the cooling water from the water pumpto the water jacketof the motor, and the transfer passageis provided in front of the drive shaftinside the outboard motor. According to the outboard motorof the present embodiment, since the transfer passageis disposed in front of the drive shaftin the outboard motor, a place where the shift rod of the shift device is disposed in the outboard motor using the engine can be used as the disposition place of the transfer passage. Therefore, it is possible to prevent the lower caseof the outboard motorof the present embodiment from becoming larger than the lower case of the outboard motor using the engine.

In the outboard motorof the present embodiment, the water intake portis provided in front of the propeller shaft, and the water pumpfaces the water intake port. The suction portof the pump chamberin which the impellerof the water pumpis disposed is disposed right behind the water intake port. According to this configuration, it is possible to make a distance between the water intake portand the water pumpextremely short, and it is possible to easily take in water around the outboard motorinto the outboard motorfrom the water pumpvia the water intake port. Further, even if the suction capacity of the water pumpis low, the water around the outboard motorcan be sufficiently taken into the outboard motorvia the water intake port. Since the water intake portand the pump chamberare extremely close to each other, water around the outboard motorflows extremely smoothly into the pump chamberwhile the water pumpis stopped. As a result, water can be quickly filled in the pump chamber, and the priming of the water pumpcan be quickly and reliably ensured. Further, since the water intake portand the water pumpare extremely close to each other and the water intake portis disposed in front of the water pump, when the boat moves forward, the water around the outboard motorcan flow vigorously from the water intake porttoward the water pump, and the pressure of the water can be used to promote the rotation of the impeller, thereby improving the smoothness of the flow of the cooling water from the water intake portto the water jacket.

Further, in the outboard motorof the present embodiment, the rear end portion of the pump shaftof the water pumpis connected to the front end portion of the propeller shaft. According to this configuration, the rotation of the propeller shaftcan be transmitted to the impellerof the water pumpprovided at the front end side of the propeller shaftby a simple structure.

illustrates a cross section of a lower portion of an outboard motorthat is a second embodiment of the electric propulsion machine of the present disclosure. In the outboard motorof the second embodiment illustrated in, the same components as those of the outboard motorof the above first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified. The outboard motorof the second embodiment is characterized in that another water pumpthat transfers cooling water discharged from the water pumpto the water jacketof the motoris provided between the water pumpand the motor. In the following description of the second embodiment, the water pumpdisposed right behind the water intake portis referred to as a “first water pump”, and the water pumpdisposed between the first water pumpand the motoris referred to as a “second water pump”.

In, the second water pumpis a non-positive displacement pump, and is, for example, a mixed flow pump. The second water pumpis disposed at a rear stage of the first water pumpin the flow direction of the cooling water, and is disposed between the first water pumpand the water jacketof the motor. Specifically, the second water pumpis disposed at a boundary portion between the upper caseand the lower case. The impellerof the second water pumpis fixed to the drive shaft. Further, at the boundary between the upper caseand the lower case, a pump chamberaccommodating the impellerof the second water pumpis provided on an outer periphery of the drive shaft. Further, a suction portis provided in a lower portion of the pump chamber. A discharge portis provided in an upper portion of the pump chamber.

Further, the outboard motorof the above first embodiment is provided with the transfer passagetransferring the cooling water from the water pumpto the water jacketof the motor. However, in the outboard motorof the second embodiment, the transfer passage is divided into a lower transfer passageconnecting the first water pumpto the second water pump, and an upper transfer passageconnecting the second water pumpto the water jacketof the motor. An introduction passageis provided between an upper end portion of the lower transfer passageand the suction portof the pump chamberto guide the cooling water flowing through the lower transfer passageto the suction port.

When the motoris driven, the drive shaftand the propeller shaftrotate respectively. The impellerof the second water pumprotates together with the drive shaft, and the impellerof the first water pumprotates together with the propeller shaft. As the impellerof the first water pumpand the impellerof the second water pumprotate, the water taken in from the water intake portflows as the cooling water sequentially through the pump chamber, the lower transfer passage, the introduction passage, the pump chamber, and the upper transfer passage, and is supplied to the water jacket. The cooling water supplied to the water jacketflows in the water jacket. Accordingly, the motoris cooled. The cooling water after flowing through the inside of the water jacketis discharged to the outside of the outboard motorfrom a discharge port provided in, for example, a boss portion of the propellervia the drain passage.

The outboard motorof the second embodiment of the present disclosure having the configuration has operational effects similar to those of the outboard motorof the first embodiment of the present disclosure. That is, the second water pumpis a non-positive displacement pump, and the non-positive displacement pump is easily reduced in size as compared with a rotary volume change pump having a rubber impeller. Therefore, according to the outboard motorof the second embodiment, even though the first water pumpand the second water pumpare provided, the outboard motorcan be reduced in size as compared with an outboard motor in the related art. Further, by making each of the first water pumpand the second water pumpas the non-positive displacement pump, it is possible to solve the above problem that the durability of the motor cooling pump decreases in the electric propulsion machine having the configuration in which the rotation direction of the motoris reversed.

Further, since the outboard motorof the second embodiment includes the second water pump, even when the discharge capacity of the first water pumpis low, the cooling water can be smoothly fed to the water jacketof the motorin cooperation with the first water pumpand the second water pump. Therefore, a small-sized pump having a low discharge capacity can be used as the first water pump, and the outboard motorcan be reduced in size. Further, since the first water pumpand the second water pumpare in cooperation with each other, the second water pumpcan be reduced in size, which also makes it possible to reduce the size of the outboard motor.

Although the centrifugal pump is used as the water pumpin the above first embodiment and the mixed flow pump is used as the water pumpin the above second embodiment, the present disclosure is not limited thereto. Other types or models of non-positive displacement pumps may also be used as the water pumpor the water pump.

Further, in the above first embodiment, the case where the cooling water is supplied to the water jacketof the motorfrom the water pumpto cool the motorhas been described as an example. For example, a water jacket may be provided for an inverter of the motor control device, and cooling water may be supplied from the water pumpto the water jacketof the motorand the water jacket of the inverter to cool the motorand the inverter, respectively. This configuration may be applied to the above second embodiment.

Further, as described above, the outboard motor has been given as an example in each of the first and second embodiments of the present disclosure, but the present disclosure is not limited thereto. For example, the present disclosure can be applied to other types of electric propulsion machines such as a stern drive.

The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.