Fluid reaction surfaces (i.e. – impellers) – Having positive means for impeller adjustment – Motor bodily rotatable with impeller hub or shaft
Reexamination Certificate
1999-05-28
2001-03-06
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Having positive means for impeller adjustment
Motor bodily rotatable with impeller hub or shaft
C416S044000, C416S046000
Reexamination Certificate
active
06196801
ABSTRACT:
The invention relates to a hydraulically reversible, adjustable propeller unit for aircraft, land vehicles and watercraft, with a propeller with at least two blades, the blade angle of which is controllable by means of a control unit (controller), whereby a hydraulic connection exists between the rotating propeller and the stationary control unit for controlling the pitch of the blade, with a spring-preloaded piston which can be actuated by means of hydraulic fluid, and adjustable mechanical stop means for the start position, the brake position and/or cruise/sailing position, according to the introductory part of claim
1
.
Preferably propellers with a hydraulic system for reversing thrust (reversible propellers) are employed for reducing the landing distance of aircraft or for enhancing the maneuverability of dirigibles, amphibious aircraft or hovercrafts. Various known devices and methods are available for said purposes. Said known devices and methods offer certain advantages, for example stepless preselection of the pitch angle and of the associated engine output in the so-called beta-range (blade angle flatter than for the start position) by means of only one power control lever. However, such devices also have considerable drawbacks, for example a costly device for adjusting the pitch angle, which is set via an adjustable hydraulic valve which constantly has to be in connection with the rotating propeller. With many known power plants, such known systems can be installed only with disproportionately high expenditure. Failures on such a device represent a high safety risk both in flight and ground operations.
In connection with a known hydraulically reversible, adjustable propeller unit (DE 19600660), provision is made for a stop means for the start position. Said stop device is preloaded by means of disk springs and can be overcome by setting the pitch angle to the brake position (reverse) by means of a high-pressure hydraulic fluid, and is adjustable up to a mechanical stop device for the brake position (reverse) in order to produce a negative thrust.
Such a device makes a constant direct connection between the rotating propeller and the control unit (controller)—which is normally installed on the casing of the power plant—superfluous. In the event of any loss of pressure, the blades are automatically reset from the negative pitch angle to a positive pitch angle in order to assure normal operation.
It has been found, however, that the disk springs exhibit a tendency to corrosion in certain applications of the adjustable propeller unit, for example in watercraft, which impairs the operating mode of the adjustable propeller unit.
Therefore, the problem of the invention is to further develop a hydraulically reversible, adjustable propeller unit of the type specified above in such a way that the operating safety is increased also when such a unit is operated in wet or aggressive environments.
Said problem is solved by the invention characterized in claim
1
, i.e., in that the piston is constructed as a spring-preloaded double piston consisting of an inner piston and a ring piston arranged around the inner piston, said two pistons being lockable with each other by means of a centrifugal-force locking mechanism; that the stop motion device for the start position is designed for limiting the setting range of the locked double piston in order to prevent unintentional reversing at numbers of revolution above about 1500 rpm; and that the brake position can be reached only when the inner piston is unlocked and the propeller revolutions are below about 1500 rpm when the propeller controller is in the high-pressure range.
With the adjustable propeller unit as defined by the invention it is possible to omit the disk springs of the known adjustable propeller unit because the propeller is set to reversing thrust by means of the inner piston arranged in the double piston, said inner piston being unlocked when a number of revolutions below about 1500 rpm is reached, so that the brake position can be reached with the propeller controller in the high-pressure range.
Advantageous further developments of the invention are specified in the dependent claims.
For example, according to another advantageous development of the invention, provision is made that the control unit (controller) is designed for generating two different servo-pressures comprising a normal pressure for positive thrust for normal forward operation of about 12 to 22 bar, and a high pressure of about 32 to 48 bar for negative thrust for braking operation (reversing).
A mechanical stop means for the start position is located in the boss of the propeller. The hydraulic control unit (controller) has two excess-pressure valves, by means of which a setting pressure of about 12 to 22 bar is generated for the double piston under normal operating conditions, and a setting pressure of about 32 to 48 bar is generated for the inner piston in reversing operations in order to adjust the propeller blades in the so-called beta-range up to negative pitch angles for the braking position. The high-pressure hydraulic fluid is uncontrolled in this process in order to prevent excess revolutions per minute.
According to another advantageous development of the invention, provision is made for an electrically or mechanically controllable switching valve for reversing the control unit from normal pressure to high pressure, or from high pressure to normal pressure.
According to yet another advantageous further development of the invention, provision is made in the control unit for a safety valve which, under normal operating conditions, limits the pressure to normal pressure in order to prevent unintentional reversing of the propeller.
Finally, according to yet another advantageous further development of the invention it is possible to make provision in the control unit in the high-pressure stage for a blade pitch controller permitting stepless setting of the blade pitch in the beta range in dependence of the servo-pressure.
It is possible with such an arrangement to control the hydraulic pressure associated with the blade pitch in order to achieve in this way stepless setting of the blade pitch in the beta range corresponding with the power plant output.
REFERENCES:
patent: 3380535 (1968-04-01), Biermann
patent: 4097189 (1978-06-01), Harlamert
patent: 196 00 660 (1997-07-01), None
Collard & Roe P.C.
Look Edward K.
Mühlbauer Luftfahrttechnik GmbH
Rodriguez Hermes
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