This invention relates to governor assemblies of the kind for controlling the speed or acceleration of a rotating member.

More particularly, but not exclusively, the invention relates to governors for controlling the speed of a rotating shaft coupled to flight control surfaces in an aircraft.

An aircraft high lift system, such as including a flap or slat, is often displaced by mechanical actuators powered by rotation of a shaft extending along the length of the wing and driven by a motor towards the aircraft body. The shaft system may have a brake towards the wing tip. The brake is applied to stop rotation of the shaft and hence movement of the control surfaces if an anomaly is detected in the drive system, to protect against asymmetry of the control surfaces in the drive systems on the two wings. PCT/GB04/003023 describes one form of wing tip brake.

Although these arrangements can prevent excessive asymmetry, they can require very fast and expensive computing capacity if the brakes are to be applied sufficiently quickly after detection of a malfunction to prevent dangerous asymmetry. It has, therefore, been suggested that the lift system include some form of mechanical speed governor that would limit the maximum shaft speed and enable a lower speed computer to be used to control the braking. There are other applications where governors are used to control speed or acceleration.

According to one aspect of the present invention there is provided a governor assembly of the above-specified kind, characterised in that the assembly includes two radially- extending plates secured with the member to rotate with the member, an arrangement for urging the plates axially towards one another, at least one weight member disposed between the two plates and a bearing between the weight member and each plate to permit radial displacement of the weight member caused by rotation of the rotating member. The governor assembly preferably includes a brake operated by relative axial movement of the plates. Preferably the brake is arranged to reduce the speed of the rotating member when the plates are displaced axially by more than a predetermined amount. The bearing may include a radially-extending surface formation on opposed faces of the plates and the weight member and a bearing of circular section arranged to roll along the surface formations as the weight moves radially in or out. The surface formations are preferably grooves and each bearing is preferably a ball. The surface formations are preferably profiled such that outward movement of the weight member displaces the plates away from one another. The arrangement for urging the plates towards one another preferably includes two springs of different force such that rotation above a first speed enables the weight member to move radially outwardly against the action of a first spring to a first position and rotation above a second speed enables the weight member to move further outwardly to a second position. The rotating member may be an aircraft lift flap shaft. The assembly may include a sensor located adjacent the weight member to provide an output in response to radial displacement of the weight member.

According to another aspect of the present invention there is provided a shaft speed control arrangement including a first brake arranged to apply a braking force to a shaft, a ramp ball arrangement arranged to actuate the first brake, a second brake coupled with the ramp ball arrangement, a centrifugal speed governor coupled with the second brake such that the speed governor causes the second brake to apply a force to the ramp ball arrangement when shaft speed increases above a predetermined speed such that the first brake applies a force to restrain rotation of the shaft.

An aircraft wing tip brake and governor assembly according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a simplified, plan view of an aircraft flap system including a brake assembly on each wing;

Figure 2 is a sectional side elevation view through the assembly; Figure 3 is a perspective view of the assembly;

Figures 4A and 4B are sectional side elevation views of a part of the assembly showing testing at low and high speed;

Figure 5 is a perspective view of a weight in the governor;

Figure 6 is a perspective view of a stabilizing plate in the governor;

Figure 7 is a partly cut-away perspective view of the governor when stationary or at low speed;

Figure 8 is a partly cut-away perspective view of the governor at a normal speed; and

Figure 9 is a partly cut-away perspective view of the governor at an excessively high speed.

With reference first to. Figure 1, the aircraft has two wings 1 and 2 extending laterally from opposite sides of its body 3. Each wing supports two lift flaps 11 and 12, and 21 and 22 respectively on its trailing edge, which are extensible and deflectable to increase the lift provided by the wings such as during take-off and landing. The flaps 11 and 12 on one wing 1 are coupled to a single shaft 13 extending along the major part of the length of the wing 1 parallel to and adjacent its trailing edge. The coupling between the shaft 13 and the flaps 11 and 12 includes gearing (not shown) that steps down multiple rotations of the shaft into an angular displacement of the flaps. Similarly, the right wing 2 has a shaft 23 extending along its length coupled to the flaps 21 and 22. The shafts 13 and 23 are rotated by a common drive unit 14 mounted at the inboard end of the shafts adjacent the body 3. The drive unit 14 is controlled by a control unit 30. Mounted at the outer end of each shaft 13 and 23, towards the tip of each wing 1 and 2, is a brake and governor assembly 15, 25, which is also controlled by signals from the control unit 30. hi particular, the control unit 30 supplies signals to actuate the brakes 15 and 25 when it detects an anomaly in displacement of the flaps 11, 12, 21 and 22 or their associated mechanism inconsistent with the displacement commanded, or when there is asymmetry between operation of the flaps on the two wings. This locks the shafts 13 and 23 to prevent further displacement of the flaps 11, 12, 21 and 22. Sensors 31 located adjacent the shafts 13 and 23 or the flaps 11, 12, 21 and 22 supply signals to the control unit 30 for use in identifying an anomaly.

With reference now to Figures 2 and 3, the construction and operation of the brake assembly 25 will be described; the construction and operation of the other brake 15 is identical.

The brake assembly 25 includes an inner, axial shaft 100 of tubular form and cut with splines 101 on its inner surface at one end. These splines 101 are shaped to mate with similar splines (not shown) in a recess at the wing tip end of the shaft 23 so that the two shafts 100 and 23 rotate together. The shaft 100 is supported at its right hand end 102 by a bearing 103 mounted on an end face 104 of the outer casing 105 of the assembly. The casing 105 is generally cylindrical in shape and is formed of several parts held together by nuts and bolts. The outer casing 105 is fixed to the structure of the wing 2 so that it cannot move relative to the wing. A second bearing 106 supports the shaft 100 towards its opposite, left-hand end, adjacent the splines 101. The second bearing 106 is fixed with a left-hand end flange 107 of the casing 105.

From left to right, the casing contains a main brake unit 112, a ball ramp mechanism 120, a secondary brake unit 130, a speed governor 200 and a solenoid assembly 141.

The left-hand end of the casing 105 contains the main brake unit 112. This comprises a number of brake plate rotors 113 mounted by splines 114 on the shaft 100 so that they rotate with the shaft but can be displaced by a small distance axially along the shaft. Between each rotor plate 113 extends a respective stator plate 115, which are mounted on longitudinally-extending rods 116 fixed with the casing 105. The mounting prevents the stator plates 113 rotating but allows them to slide along the rods by a small distance. The brake plates 113 and 115 are contained at their left-hand end by a flange 117 fixed with the shaft 100 to the left of the plates. At their opposite end, the plates 113 and 115 are contacted by a second flange 118, which is slidable along the splines 114. A helical spring 119 towards the right-hand end of the brake plates 113 and 115 holds them apart, so that no braking force is applied, until an external force is applied to push them together.

The right-hand end flange 118 is engaged by the ball ramp mechanism 120. This comprises a first plate 121 in contact with the flange 118 and slidable along the splines 114. The spring 119 applies a force to the first plate 121 urging it to the right. The right-hand surface of the plate 121 has three grooves 122 of arc shape (only one of which is shown) equally spaced around the plate. Each groove 122 is symmetrical about a radial line bisecting the groove and it is deepest midway along its length, becoming shallower towards each end. The ball ramp mechanism 120 includes a second plate 123 having three grooves 124 on its left-hand surface of the same form as those on the first plate 121.The second plate 123 is formed at the left-hand end of a short tubular sleeve 125 and is supported by a bearing 126 so that it is free to rotate about the axis of the shaft 100 but cannot move axially relative to the shaft. The ball ramp mechanism 120 also includes three spherical metal bearing balls 127 between the two plates 121 and 123 and located in the grooves 122 and 124. The inclination of the two grooves 122 and 124 at their ends are such that, when the two plates 121 and 123 are rotated relative to one another, the trapped balls 127 ride up the slope of the grooves in the two plates causing the plates to separate. The left-hand plate 121 is constrained to rotate with the shaft 100 whereas the right-hand plate 123 is unconstrained and can rotate relative to the shaft but normally rotates with the left-hand plate.

The secondary brake unit 130 is located to the right of the ball ramp mechanism 120. This is similar to the main brake unit 112 but is smaller and only capable of applying a much smaller braking force. The secondary brake unit 130 includes several brake rotor plates 131 mounted on longitudinally-extending splines 132 around the external surface of the sleeve 125 so that the plates rotate with the sleeve and can be moved a small distance along the length of the sleeve. The stator brake plates 133 are mounted on the rods 116 fixed with the casing 105 so that they cannot rotate but can be displaced a small distance axially. The right- hand end of the stack of brake plates 131 and 133 is engaged by the left-hand end of a short sleeve 134. The right-hand end of the sleeve 134 is a sliding fit within the left-hand end of a pusher tube 135 and is engaged by an internal ledge 136 around a pusher tube towards its left-hand end. The right-hand end of the pusher tube 135 embraces the left-hand end of a slidable iron core piece 140 of a solenoid armature assembly 141.

The solenoid assembly 141 also includes a fixed iron core piece 142 and a dual coil 143, which is also fixed in position relative to the casing 105. The two core pieces 140 and 142 are separated from one another by an air gap 144. The slidable core piece 140 is urged to the left by a disc spring pack 145, which bears on a flange 146 at the right-hand end of a tubular rod 147, which is slidable relative to the fixed core piece 142 but which is screwed at its left-hand end into the movable core piece 140. The force applied by the spring pack 145, therefore, tends to push the core piece 140, the pusher tube 135 and the sleeve 134 to the left, which tends to apply a braking force between the two sets of brake plates 131 and 133 in the secondary brake unit 130. The core pieces 140 and 141 interact electromagnetically with the dual coil 143 so that the combination of the armature and coils provides actuation means in the form of an electrical solenoid. The coils 143 and armature pieces 140 and 141 are arranged so that when power is applied to the coils it causes an axial force on the armature acting against that of the spring pack 145, that is, tending to move the armature to the right, to close the gap 144. It can be seen, therefore, that when power is applied to the coil 143 the secondary brake 130 is off and, when no power is applied, the secondary brake is on.

In normal operation of the aircraft, the control unit 30 applies power to the coils 143 in each brake assembly 15 and 25 so that the secondary brake 130 is held off. This allows the two plates 121 and 123 to rotate together and assume a configuration with minimum separation between them. This in turn ensures that no force is applied against the action of the spring 119 in the main brake unit 112, so that plates 113 and 115 of this brake unit are free to rotate relative to one another and no braking force is applied to the shaft 100. The shafts 13 and 23 are, therefore, free to rotate to displace the flaps 11, 12, 21 and 22 as commanded. When an anomaly is detected, such as asymmetry between the displacement of the flaps or shafts in opposite wings, the control unit 30 immediately terminates supply of power to each brake assembly 15 and 25. The spring pack 145 is now free to displace the core piece 140 to the left, which applies a force pushing the stator and rotor brake plates 133 and 131 together in the secondary brake 130. This increases friction between the plates 133 and 131 and applies abraking force between the casing 105 and the sleeve 125. The sleeve 125 and the plate 123, therefore, stop rotating. The other plate 121 of the ball mechanism 120 continues to rotate through a small angle causing the balls 127 to ride up the incline of the grooves 122 and 124 and force the two plates apart. Since the right-hand plate 123 is fixed axiaily, all the displacement is produced in the left-hand plate 121. Movement of this plate 121 is transferred to the flange 118 and hence to the brake plates 113 and 115 of the main brake unit 112. The expansion and force applied by the ball ramp mechanism 120 is sufficient fully to apply the main brake 112 and prevent rotation of the shaft 100. This in turn brakes rotation of the shafts 13 and 23 so that the flaps 11, 12, 21 and 22 are locked in position. The flaps 11, 12, 21 and 22 remain locked as long as the brake assemblies 15 and 25 are on. When the flaps 11, 12, 21 and 22 need to be released, the control unit 30 supplies power to each brake assembly 15 and 25 to energize the coils 143 and pull the core piece 140 against the action of the spring 145 to release the secondary brake unit 130. The right-hand plate 123 of the ball ramp 120 can now rotate to allow the balls 127 to ride down the ramp of the grooves 122 and 124, aided by the spring 119, and thereby allow the left-hand plate 121 to move towards the other plate and release the braking force applied by the main brake unit 112 so that the shaft 100 can rotate freely.

The braking force that stops rotation of the shaft 100 is applied solely by the main braking unit 112 and the casing 105. The axial load generated by the ball ramp mechanism 120 is contained within the braking unit 112 and the shaft 100 and does not influence the braking unit 130. This ensures that there is no risk of self-generated forces jamming the ball ramp mechanism 120. This arrangement enables the brake assembly to be released electrically, remotely without the need for manual unlocking.

Within the casing 105, between the solenoid 140 and the secondary brake 130 is located the speed governor assembly 200, which cooperates with the secondary brake to limit the maximum rotational speed of the shaft 100. The construction and operation of the governor 200 is also shown in Figures 4 to 9. The governor 200 has two radially-extending, circular plates 201 and 202 mounted on the shaft 100 at axially spaced locations. The plates 201 and 202 are mounted on splines 203 on the shaft so that they rotate with the shaft but can slide along it by small distances, as limited by stops 204 and 205 fixed with the shaft. The two facing surfaces 206 and 207 of the plates 201 and 202 each have three short ramp grooves 208 extending radially outwardly and equally spaced around the plates. The grooves 208 are located towards the outer edge of the plates and open at the outer edge. The grooves 208 have a circular profile and are inclined slightly, becoming shallower towards the edge. Each groove 208 locates a spherical steel ball 209 having a diameter approximately twice the depth of the groove so that it projects from the groove. The governor 200 also includes three steel weights 210, most clearly shown in Figure 5, located between the two plates 201 and 202 and aligned with respective ones of the grooves 208. The weights 210 each have a raceway or ramp groove 211 and 212 extending radially on opposite faces and aligned with respective ramp grooves 208 on the plates 201 and 202. The grooves 211 and 212 have a similar section to the grooves 208 and extend radially from an inner edge to a location close to the outer edge. The grooves 211 and 212 are both inclined along their length but in the opposite sense from the grooves 208, so that the grooves are deeper towards the outer edge. The grooves 211 and 212 each seat a respective one of the six steel balls 209, so that each weight is engaged by two balls. Each weight 210 also has a channel 213 extending radially along opposite edges. The position of the weights 210 is maintained by a steel stabilizing plate 214, most clearly seen in Figure 6, which has a Maltese cross shape with three radial slots 215. The weights 210 locate in the slots 215 with the edges of the slots extending along the channels 213 in the plates. The plate 214 stabilizes the weights 210 to prevent them tipping.

The left-hand plate 201 is urged towards the right-hand plate 212, which is, in turn, urged against the stop 205 by the combined effect of two sets 216 and 217 of six helical springs each. The springs 216 of the right-hand set are supported on a disc assembly 220 mounted radially on the shaft 100 to the left of the plate 201, with the springs extending longitudinally parallel to the axis. The disc assembly 220 is slidable axially relative to the shaft 100 and is constrained to rotate with the plate 201 by means of a pin 221. Axial movement of the disc assembly 220 is limited by engagement with the stop 204. On its forward face, the assembly 220 has a low wall 222 of circular shape and with a flat top 223 providing a contact surface closely spaced from the left-hand surface of the left-hand plate 201 by an annular gap 224. The left-hand surface of the disc assembly 220 supports a needle roller bearing 225, which engages the right-hand face of a thrust plate 226 secured with the sleeve 134 when the disc assembly is displaced to the left. The second set of springs 217 is sandwiched between the left-hand surface of the disc assembly 220 and a locating plate 227 rotated with the shaft 100. The second set of springs 217 again extends parallel to the axis and applies an additional force urging the disc assembly 220 to the right.

Figure 7 shows the weights 210 at their rest or very low speed position, at an inward position. The weights 210 remain in the inner position with the balls 209 at the deepest part of the grooves 208 and 211 and with the minimum spacing between the two plates 201 and 202 until the centrifugal force developed by the rotating weights overcomes the preload force applied to the plates by the springs 216. The springs 216 are chosen to allow the weights 210 to move outwardly to a normal position, as shown in Figure 8, when the shaft 100 is operating at normal operating speeds. This radial movement of the weights 210 is translated into an axial movement of the plate 201 just sufficient to close the gap 224. The weights 210 remain at this radius during normal operation. If the shaft 100 should rotate at excessive speeds, typically about twice normal operating speed, the weights 210 will be flung out further to a position of maximum radius, as shown in Figure 9, thereby displacing the left- hand plate 201 further to the left. This causes the sleeve 134 also to be pushed to the left and thereby causes the secondary brake 130 to be applied to limit rotation of the ball ramp thrust plate 123. This causes the other thrust plate 121 to move to the left and apply a braking force to the shaft 100 to react the accelerating torque on the system. The spring rate of the two springs 216 and 217 and the ramp angle of the grooves 208 is selected to ensure that the weights 210 move positively when the trigger speed is reached.

Because the solenoid 140 acts on the secondary brake 130 via the pusher tube 135 and the sleeve 134, and because the sleeve can move to the left relative to the pusher tube, the governor 200 can act independently on the secondary brake when the solenoid is energized without having to counteract the force of the solenoid spring pack 145. When the solenoid 140 is de-energized, the brake 112 is applied so the governor 200 has no effect.

The balls used in the governor provide a very low friction and thereby ensure reliable operation over prolonged periods. The casing is preferably oil-filled so as to prevent contamination and corrosion. The shape of the governor weights is such as to present a relatively small cross sectional area when rotating within the oil. The arrangement of the grooves and balls also means that the force applied by the oil is directed into the side of the grooves perpendicular to the direction of movement of the balls. As the coefficient of friction between a ball and a raceway is small, the influence of the oil on the governing weights is negligible. Instead of having ball bearings, the governor could have some other form of rolling bearing, such as roller bearings.

The governor described is specifically arranged to cause the weights to move at normal operating speeds to a first position and then to move further out at excessive speeds. It would be possible instead for the governor to be arranged such that the weights remain at a rest position until the excessive speed is reached. The problem with such an arrangement is that the governor weights would probably never move because the excessive speed situation is a very rare event in aircraft flight surface control applications. It can be undesirable for a mechanical device of this kind to remain stationary for many years because of the risk that the prolonged inactivity might cause stiction and prevent displacement of the weights when this is needed. Also, there is a difficulty in testing operation of the governor. The arrangement described above, by contrast, does enable the governor to be tested, at least to detect whether the weights have moved to their intermediate, normal speed position. This is achieved in the manner illustrated in Figures 4 A and 4B.

With the aircraft on the ground, a blanking nut 300 is removed from a test port 301 in the casing 105 situated radially outwardly of the governor 200. A proximity sensor 302 is then screwed into the test port 301. The sensor 302 may be of various different kinds, such as optical, magnetic, capacitive, acoustic, microwave or the like. The tip 303 of the sensor 302 is arranged to extend close to the edge of the weights 210 when they are displaced outwardly, as shown in Figure 4B but to be displaced from the weights when the weights are at a rest position, as shown in Figure 4A. When testing operation of the governor 200, the shaft 100 is initially at rest and is then rotated up to its normal operating speed while the output of the proximity sensor 302 is monitored. If the weights 210 are moving correctly this should cause a change in the output of the sensor 302 and a further change back to its original state when the shaft 100 is subsequently slowed down to rest. It will be appreciated that the proximity sensor could be located at different positions relative to the governor weights, such as at one side. The governor could have a proximity sensor built in so that correct operation of the governor can be confirmed during flight.

The invention is not confined to governors for aircraft flight surface controls but could be used in other applications. It may not be essential in some applications for the governor to operate via a brake to slow down the rotating member since the outward movement of the weights themselves might be sufficient to achieve the desired degree of slowing.