WO1992007756A1

WO1992007756A1 - Device for damping the control stick of an aircraft

Info

Publication number: WO1992007756A1
Application number: PCT/SE1991/000679
Authority: WO
Inventors: Ragnar Haglund
Original assignee: Saab-Scania Aktiebolag
Priority date: 1990-10-30
Filing date: 1991-10-09
Publication date: 1992-05-14
Also published as: SE9003450D0

Abstract

A device for damping the control stick of an aircraft, whose movements in pitch and roll, respectively, are transferred to a rotational shaft, with a damping means for damping its rotational movement is characterized primarily by a differential gear (1) with said shaft (2) as an inwardly extending shaft and with a 1:st and a 2:nd outwardly extending shaft (7, 10), respectively, standing in mechanical rotational connection with the 1:st and 2:nd damping elements respectively of the damping means in the form of short-circuited electric motors (9, 12).

Description

T.F.VT F, FOR DAMPING THE CONTROL STICK OF AN AIRCRAFT

The present invention relates to a device for damping the con¬ trol stick of an aircraft, whose movements in pitch and roll, respectively, are transferred to a rotatable shaft, with a damping means for damping its rotational movement.

With control sticks for fast aircraft it is necessary to pro¬ vide damping means in order to prevent the aircraft operator to command too abrupt aircraft manoeuvres.

Such damping means of different constructions have been known for a long time. For. instance, U.S. 2,523,579 describes a con¬ trol system comprising a wheel, corresponding to a control stick, which via links acts upon an inwardly extending shaft to a differential gear, whose outwardly extending shafts, via links, control two control surfaces. The rotational movement of the inwardly extending shaft is damped by damping pistons with springs. In U.S. 2,695,145 a somewhat complex system is shown for transferring the movement in a control stick to two control surfaces, which comprises springs that counteract the stick movement.

Many more devices for damping the control sticks of aircraft have been proposed, some of them quite sophisticated. An es¬ sential demand, for safety reasons, is that required stick movements can be effected even if the damping means for some reason would be out of function and even lock the control stick movement. This demand is not met by the damping means of the kind shown in i.a. the above-mentioned U.S. 2,523,579.

The object of the present invention is therefore to provide a device of the kind mentioned in the introduction, which is simple in construction, and yet is reliable and, with a high degree of probability, allows a rotational movement by the rotatable shaft with damping, even if the damping means should show disturbed function. According to the invention the device of the kind mentioned in the introduction is characterized primarily by a differential gear with said shaft as an inwardly extending shaft, and a l:st and a 2:nd outwardly extending shaft, standing in mecha¬ nical rotational connection with the the l:st and 2:nd damping elements, respectively, of the damping means in the form of short-circuited electric motors . The differential gear can be designed in many ways, with conical or cylindric gear wheels.

If the l:st and 2:nd outwardly extending shafts, respectively, are provided with equally large gear wheels in mesh with the differential gear wheels, which are of the same size in all constructions, the l:st and 2:nd outwardly extending shafts, respectively, will rotate with the same rotation speed, as long as both shafts are exposed to similar moment against ro¬ tation, at a certain rotation speed on the inwardly extending shaft.

If the latter rotation speed is maintained on the inwardly ex¬ tending shaft but one outwardly extending shaft is prevented from rotating, the other outwardly extending shaft will rotate with double the rotation speed.

Should, contrarily, the list and 2:nd outwardly extending shafts, respectively, be provided with gear wheels of diffe¬ rent size in mesh with the differential gear wheels, the out¬ wardly extending shafts would rotate with different rotation speed at the same moment against rotation on both shafts . If one outwardly extending shaft in this case is prevented from rotating the other shaft will rotate faster according to the expression

0>ι = G)o(l + 2.n₁)

wherein ωo is the rotation speed or angular speed of the in¬ wardly extending shaft and ωi is the rotation speed of one outwardly extending shaft, it being understood that the rota¬ tion speed G>₂ of the other outwardly extending shaft = 0.

In a suitable embodiment of the invention a variable resis- tance, e.g. in the form of a potentiometer, is included in the short-circuiting circuits of the electric motors, so that the load on the motors, and thereby the moment they exert against a forced rotation, can be varied.

In certain applications it is suitable that the mentioned motors show a linear relationship between the rotational speed and the moment against forced rotation.

In one embodiment of the invention, which in certain cases may be suitable, the device comprises a unit, arranged to sense the potential drop over the respective resistance and at dif¬ ferences emit a signal to an indication means . Said unit can also suitably be arranged so that on sensing the potential drop over the resistance at a predetermined value of the quo- tient between the respective potential drop and/or a certain relatively low threshold value for the potential drop on either resistance it connects one additional resistance in series with the other resistance, the additional resistance preferably being as great as the other resistance.

The invention will now be described more in detail with refe¬ rence to the accompanying figures, of which:

figure 1 shows a block diagram of a device according to the invention, whereas

figure 2 shows schematically a longitudinal section through a differential gear, included in a device according to the in¬ vention;

figure 3 shows a block diagram of a part of an alternative de¬ vice according to the invention. In figure 1, 1 designates a differential gear with an inwardly extending shaft 2, which stands in rotational connection with a control stick, in the figure schematically represented by a block 3 and a two-way arrow 4, which shows the possible move¬ ment patterns of the control stick. The control stick is acted upon by a spring means 5, which works to return the control stick to a neutral position. The position of the control stick is registered by a position indicator 6, which in a way not shown stands in connection with those means which are desira¬ ble to act upon with the rotational movement of the control stick. It can be e.g. the pitch or roll movements of an air¬ craft. The differential gear is provided with a l:st outwardly extending shaft 7_, which via a l:st gear 8 stands in mechanic- al rotational connection with a l:st electric motor 9. The differential gear 1 is also provided with a 2:nd outwardly ex¬ tending shaft 10, which via a 2:nd gear 11 stands in mechan¬ ical rotational connection with a 2:nd electric motor 12. Each of the electric motors 9, 12 is short-circuited through short- circuiting circuits 13, 14 in which variable resistances 15, 16 are included. In one embodiment the motors can also be short-circuited in series.

The electric motors can be of different construction, but it is suitable to use motors provided with permanent magnetic rotor and windings in the stator, so that slip-rings or the like are avoided. For said application, i.e. in connection with the control stick of an aircraft, it is advantageous if said motors show a linear relationship between the rotational speed on the shaft of the motors and the appearing moment against the forced rotation.

In figure 2 a differential gear 1 is shown in more detail. The inwardly extending shaft 2 is rigidly connected with a diffe- rential case 17, in which the outwardly extending shafts 7 and 10 are mounted concentrically, provided with the conical gear wheels 18 and 19 having both the same number of teeths. Perpendicular to the inwardly and outwardly extending shafts, two conical differential gear wheels 20 and 21 are mounted, each in mesh with the afore-mentioned gear wheels 18 and 19. With this construction the inwardly and outwardly extending shafts will thus rotate with the same rotation speed, as long as both outwardly extending shafts are acted upon by- equally large moments, acting against the rotation. If, contrarily, one shaft is prevented entirely from rotating, e.g. due to faulty function in the motor with which it stands in rotatio- nal connection, the other shaft will rotate with double the rotation speed compared with the inwardly extending shaft.

The device functions according to the following. It is under¬ stood, that the motors exert a moment against forced rotation, which rises linearly with the rotation speed.

In the neutral position the device functions normally, and a rotational movement effected via the inwardly extending shaft 1 from the control stick 3, which gives the shaft 1 a rota- tional speed = COo, results in the rotational speeds

0>_l = ©₂ = CD_. °^{n tne} outwardly extending shafts 7 and 10. Cor¬ responding to the resistances that have been set with the potentiometers 15 and 16 and the above-mentioned linear rela¬ tionship between rotation speed and moment, the two motors will each exert a moment Ti acting against the rotational movement of the control stick, transferred via the gears 8 and 11, and the differential gear 1 to the control stick 3, i.e. the sum 2Tι (+ a certain friction) .

Now, if for example, one motor 9 or its gear 8 is subjected to faulty function, so that the shaft 7 is prevented from rota¬ ting, the shaft 7 will rotate with the rotational speed 2c_o if the rotational speed of the inwardly extending shaft is un¬ changed. This means that the motor 9 will rotate with double the speed compared with the neutral position, and thereby ex¬ ert a moment of 2Tι_ which means that the inwardly extending shaft 2 is damped with double the moment, i.e. Tι_f at unchanged rotational speed = 0_o. Since it is highly unlikely that any one of the outwardly extending shafts 7, 10 of the differential gear, without increasing biting, instantaneously becomes unrotatable, the disadvantage with the double damping moment on the inwardly extending shaft 2 that is acted upon by the control stick is of no importance in practice. The desired advantage is attained, that the control stick can be operated despite disturbances in the damping means.

There is, however, a possibility to remove the disadvantage with double damping moment. In figure 3 it is schematically shown how a unit 22 for monitoring and resistance compensation can be connected to the short-circuiting circuits 13, 14 partly to monitor and indicate if the damping means functions normally or if there is a disturbance in the form of biting, and partly to compensate the electric resistance so that damp¬ ing effected by a motor becomes the same as with two functio¬ ning motors. Over the resistance 15 two cables 23, 24 are con¬ nected and over the resistance 16 correspondingly connected cables 25, 26. The cables 23-26 leads to the unit 22, which is arranged, in a way not shown, to sense the potential drop over the respective resistances 15, 16 and compare them. When there is a difference a warning signal is emitted to an indication means 27. In the short-circuiting circuit 13 a breaker 28 has been included, which has two positions, a first one where the short-circuiting circuit 13 remains unbroken and a second one, where the resistance 15 is connected in series with one addi¬ tional variable resistance 29, the resistances 15 and 29 mainly being intended to be set on principally the same electric resistance. The unit 22 controls the breaker 28 via a switching means 30, not shown in detail. The short-circuiting circuit 14 has similarly been completed by a breaker 31 and a variable resistance 23, which is controlled correspondingly by the unit 22 via a switching means 33.

The unit 22 is now so arranged, that when the detection of the potential drop over the resistances 15 and 16 partly shows different values for the two resistances and partly shows a certain predetermined quotient value or alternatively a cer¬ tain low threshold value for one resistance, i.e. the resis¬ tance 15, the switching means 32 in this case resets the breaker 31, so that the resistance 33 is connected in series with the resistance 16. In this way the doubled rotation speed of the motor 12 is compensated by a doubled load resistance, which approximately gives an unchanged damping moment on the inwardly extending shaft 2 of the differential gear. The same is true in the case when the measuring of the potential drop over the resistances 15 and 16 shows that disturbance has occurred in the damping function of the motor 12.

If the highly unlikely situation should occur, that there would be no damping at all for any one of the outwardly exten¬ ding shafts 7, 10 there would naturally be no damping of the rotational movement of the inwardly extending shaft 2, which would be a certain disadvantage, however, the occurrence of which must be considered highly unlikely.

According to needs a suitable damping moment can be set with the aid of the potentiometers 15, 16.

Claims

1. A device for damping the control stick of an aircraft, whose movements in pitch and roll, respectively, are transferred to a rotatable shaft, with a damping means for damping its rotational movement, characterized by a differential gear (1) with said shaft (2) as an inwardly extending shaft and with a l.st and a 2:nd outwardly ex¬ tending shaft (7, 10), respectively, standing in mechan- ical rotational connection with the l:st and 2:nd damping elements, respectively, in the form of short-circuited electric motors (9, 12) .

2. A device according to claim 1, characterized in that each of the electric motors (9, 12) is connected over a variable resistance (15, 16) .

3. A device according to claim 1 or claim 2, character¬ ized in that said motors (9, 12) show a linear relation- ship with the rotational speed and moment against forced rotation.

.

4. A device according to claim 1 or claim 3, character¬ ized by a unit (22), arranged to sense the potential drop over the respective resistances (15, 16) and at a difference emit a signal to an indication means (27) .

5. A device according to any one of claims 2 to 4, cha¬ racterized by a unit (22), arranged to sense the po- tential drop over the respective resistances (15, 16) and at a predetermined value of the quotient between the re¬ spective potential drop and/or a certain relatively low threshold value for the potential drop over either resis¬ tance (15, 16) to connect an additional resistance (32, 29) in series with the other resistance (16, 15), the ad¬ ditional resistance being preferably as great as the other resistance (16, 15) .