Motor vehicles – Surface effect vehicles – Having propulsion or control means
Reexamination Certificate
2001-04-25
2003-07-15
Hurley, Kevin (Department: 3611)
Motor vehicles
Surface effect vehicles
Having propulsion or control means
C180S118000
Reexamination Certificate
active
06591928
ABSTRACT:
The invention relates to a hovercraft with at least one lift fan for producing an air cushion and at least one thrust unit, which acts on the top surface of the craft, where the thrust unit serves to propel the craft and/or control its direction, and both the lift fan and the thrust unit have at least one airscrew that is driven by means of a motor and generates an air current.
All known hovercraft designs are very heavy. Moreover, the weight is distributed unevenly over the craft as a result of its design or operation. In this type of craft, however, uniform weight distribution is of particular importance, as a poorly balanced hovercraft can easily transition from an ideal hovering state to unsteady behaviour. Uneven weight distribution must then be corrected by a complex and heavy ballast system.
In known hovercraft of the type described, particularly relatively small ones, the thrust unit is often mounted in rigid fashion in the stern region of the deck and the weight concentrated there.
The rigid thrust unit of this design is equipped with one or more rudders for steering, with which the generated air current must be deflected, this entailing high frictional losses. Another design involves several rigid thrust units, which control the direction of travel by individually controlling the airscrew rotational speed of each individual thrust unit. In both hovercraft designs, the motor is close to the rigidly mounted thrust unit(s) and thus concentrates even more weight in the stern region of the hovercraft. In order to achieve the required uniform weight distribution in this case, a ballast system, such as a tank for holding ballast water, must be provided in the bow region. This further increases the weight, gives the hovercraft very high inertia and reduces the useable space.
In order to manoeuvre, a torque must be induced in the known hovercraft with a rigid thrust unit. This torque steers the craft in the desired direction. In this respect, the manoeuvrability is similar to that of a ship. Due to the high inertia of the hovercraft and the low resistance of the air to the motion of the craft, however, turning can only be stopped by applying a torque in the opposite direction. The high inertia of the craft again has a disadvantageous effect in this context.
The above designs also have disadvantages in terms of fluid dynamics, particularly during forward travel, as the motor provided in the vicinity of the thrust unit hinders the flow of air on the intake side of the airscrew in this case. In addition, a mechanical driveline that links the drive motor to the air screw must be provided. It consists, for example, of shafts, joints, gears, clutches, etc. that also add to the weight of the craft and thus increase its inertia.
Among larger hovercraft, such as large hovercraft ferries, there is a known design with thrust units that are designed to pivot about a vertical axis. In this case, the air current can be turned in the desired direction in order to steer. The pivoting thrust units are referred to below as “pivoting units”. They have drive shafts arranged parallel to, or even along, the vertical pivoting axis of the pivoting unit. The drive shaft is driven by a separate motor via an angular gearbox or the like and, in turn, drives the airscrew via another angular gearbox. The motors and additional angular gearboxes increase and concentrate the weight in the area of the pivoting unit.
In order to reduce the weight, the drive energy of a single motor could be fed to several pivoting units. However, this would entail the disadvantage that the drivelines would greatly restrict the useable space.
Depending on how many pivoting units are provided and where, an additional ballast system must also be provided in this design in order to achieve uniform weight distribution throughout the craft.
In relatively small hovercraft, the use of heavy pivoting units with separate motors is dispensed with due to the great weight and the problems with weight distribution.
In order to decelerate the known hovercraft, it is necessary to reverse the direction of the air current. For example, this can be achieved in the known fashion by reversing the sense of rotation of the airscrew, this having the disadvantage that the airscrew must be first brought to a standstill and then accelerated in the opposite rotational direction. Another solution provides for the adjustment of the airscrew blades, where the air current is reversed while the airscrew continues to rotate in the same direction. This, however, requires a mechanically complex adjusting mechanism to adjust the airscrew blades.
The object of the invention is to design a hovercraft that can be operated with a little expenditure of energy and has good manoeuvrability, good space utilisation and a high payload relative to its weight.
According to the invention, the object is solved in that the motor takes the form of an electric motor located directly on the airscrew, and in that at least one central energy generator, which supplies the electric motor with drive energy via an energy line, is provided in order to generate the electrical drive energy required by said electric motor.
This measure creates a hovercraft, the useable space of which is not restricted by a driveline and which therefore has particularly good space utilisation. The energy line is provided in the form of an electrical line, which feeds the drive energy to the electric motor. It is considerably lighter than a mechanical driveline and is laid such that it does not restrict the useable space of the hovercraft.
As a result of technical advancements in the field of electrical machines and controllers, electric motors and generators are available that have a very high power density relative to their weight. Only this new drive technology makes it possible to provide an electric motor directly on the airscrew. With this design, the thrust unit is particularly light and requires only little installation space.
As a result of this new method, thrust units can be mounted at various locations on the hovercraft, such as on the roof of the hovercraft, which is favourable in terms of fluid dynamics. The previous design problems, namely uniform weight distribution throughout the craft, can now easily be solved. Steering by means of a rudder, and the associated efficiency loss in propulsion, can be dispensed with. The ballast system is only required to compensate for unevenly distributed cargo and can be of a much smaller and lighter design. The central energy generator can be positioned at a favourable location. For example, it is possible to compensate for a slight imbalance in a hovercraft provided with two, light stern pivoting units by placing the energy generator in a suitable position to act as counter-ballast. The hovercraft thus has less inertia and is easy to manoeuvre. In addition, the payload and useable space of the craft are increased.
With the proposed invention, the propulsion power can be controlled very easily by regulating the rotational speed of the airscrew. As the airscrew is driven by an electric motor, there is no need for complex and very heavy gears to change the rotational speed, which can be controlled in infinitely variable fashion and very precisely. In addition, the airscrew need not be designed with adjustable airscrew blades to regulate the propulsion power.
Decelerating the hovercraft by reversing the direction of the air flow is also possible with the known methods when using electric motors to drive the airscrew, namely by reversing the sense of rotation of the airscrew or adjusting the airscrew blades while the sense of rotation of the airscrew remains the same. With the new hovercraft, however, deceleration can also be simply performed by rotating the pivoting unit through 180° and the complex methods described above can be dispensed with. No mechanical driveline has to be pivoted at the same time and pivoting can thus be achieved with very little design effort.
In order to prevent the thrust of the pivoting unit from turning the hovercraft during pivoti
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