The present invention relates to a decelerator apparatus in accordance with the preamble of claim 1.

Different kinds of decelerator apparatus are in use as safety devices and brakes in the lowering of loads and people. Various decelerator apparatuses can also be used as brakes and shock absorbers. One kind of decelerator apparatus comprises traction sheave brakes based on the flow throttling of a fluid medium. In these devices the traction sheave loaded by a rope or cable is braked hydraulically or pneumatically in order to reduce the lowering speed.

One apparatus of this kind is disclosed in the US patent publication 3,907,256. The apparatus is characterized by a rotating cylinder, which is coupled to the traction sheave when the rotational speed of the sheave reaches a set upper limit. The cylinder is adapted to the frame of the apparatus and incorporates a piston, which is attached to the cylinder, thereby acting as an intermediate wall that divides the cylinder into two chambers. In addition, the apparatus has two rotational pistons and ends of the cylinder. A safety device based on this patent is further characterized by having a first closed cylinder filled with liquid and a second cylinder filled with gas. During the operation of the apparatus, the piston of the liquid cylinder forces the liquid to the other side to the piston of the gas-filled cylinder, whereby the gas is compressed and effects a braking force to the movement of the piston. In the operation of the apparatus, liquid flow occurs from side to side on both sides of the stationary center piston.

Firstly, because of the liquid flow in this apparatus through an orifice to the other side of the piston of the gas-filled cylinder, accurate control of the liquid flow is impossible, since the gas pressure is dependent on the temperature, resulting in an inaccurate control of lowering speed. Secondly, the fast movement of the pistons causes a

viscosity change in the liquid, which further results in reduced braking effect of the liquid in the orifice between the cylinders, and thereby an increased lowering speed. Moreover, the fast movement of the pistons in the liquid invokes appreciable heating, wherein an obvious risk of seizure in heavy use is imminent.

The US patent 4,173,332 discloses a safety device which differs from the above-described implementation in that the device has only a single axially reciprocating piston adapted into a cylinder to operate at a small clearance, whereby the axial movement is attained by means of interaction between a sinusoidal groove, adapted to the outside surface of the rotating piston, and pegs adapted to the fixed cylinder that protrude into the groove. The device implements the braking force by alternately sucking and compressing air at either side of the piston. Due to the compressibility of air, the braking force resulting from this arrangement becomes rather irregular, and in addition, the device has a relatively complicated valve structure required to control the air flow. Difficult control of braking power results from both the narrowness of the air ducts and the fact that part of the ducts are located inside the device, whereby a single control valve is insufficient for restricting the air flow.

Disclosed in the US patent publication 4,452,430 is a safety device in which a piston having several small-diameter flow ducts penetrating the piston is adapted into a cylinder comprised of two halves of the base. The outside surface of the piston has a zigzag groove. Between the halves of the base is adapted a traction sheave, which rotates between the halves of the base loaded by a rope. The inside surface of the sheave is provided with pegs which protrude into a groove on the outside surface of the piston. When the loaded rope rotates the sheave, the pegs moving in the groove force the piston into a lateral movement determined by the shape of the groove. The moving piston further forces the fluid contained in the cylinder to flow through the orifices provided in the piston, whereby the resistance to the fluid flow retards the

piston movement and, vie, the sheave, simultaneously also the rope movement.

Such a device results, however, in an uneven braking force. When the pegs of the sheave reach the inflection point of the groove on the piston, the lateral movement of the piston is momentarily halted until the pegs meet the opposite side of the groove and the piston is forced to move to the opposite direction. During the time the piston is halted, no fluid flow occurs in the orifices and, consequently, no braking force is generated. Due to the discontinuous nature of the braking force, vibrations arise that load the device and the rope. The vibration contributes particularly to the wear of the grooves on the piston close to the inflection points. The vibration also causes appreciable noise problems from the clapping of the pegs against the groove edges.

In addition to the drawbacks described in the foregoing, all above-described devices are hampered in that the braking effect is based on throttled flow of liquid in ducts located inside the device. Thence, the braking power cannot be regulated during the use of the device; instead, the device must be dismantled for the adjustment of braking power. Because of the lacking capability of braking power control, neither can the load be stopped amidst the braking through the use of these devices. The control method of braking power and flow disclosed in the publication is awkward and hampers the handling of the device. Tubes and valves assembled outside the device can easily be damaged when the device is used.

The aim of this invention is to achieve a durable decelerator featuring a smooth braking power.

The invention is based on producing the braking power by way of throttling the liquid flow occurring between two pistons operating at a slight phase shift.

More specifically, the invention is characterized by what is stated in the characterizing part of claim 1.

The invention provides outstanding benefits.

An apparatus in accordance with the invention achieves a smooth braking power and thus a smooth speed for the motion to be braked. This is particularly advantageous when loads are lowered by means of the apparatus and a rope from high locations. The braking power of the apparatus is easily controllable externally. The controllability of braking power allows a cautious and smooth lowering of the load. Because of the easy control of the braking power, the apparatus can be used as a brake in vehicles, for instance, such as those moving along different kinds of rail or cable tracks. The disclosed apparatus provides a smooth and flexible stopping of the loading force, which is not possible by means of the conventional devices described in the foregoing. The present apparatus- is capable of using different types of fluid media, whose flow is throttled for the purpose of achieving the braking power. Therefore, the apparatus is compatible with extremely harsh conditions. The durability and loadability of the apparatus is further appreciably improved by the fact that the throttling is arranged to produce a relatively low thermal density. In addition, the throttling is adapted close to the outside surface of the apparatus, whereby heat convection from the apparatus is easy.

The invention is next examined in detail with the help of the attached drawings.

Figure 1 shows a cross-section of an embodiment of the apparatus in accordance with the invention.

Figure 2 shows in a side elevation view two elements of the apparatus illustrated in Fig. 1.

Figure 3 shows in an end view one of the elements illustrated in Fig. 2.

Figure 4 shows another element illustrated in Fig. 1.

Figure 5 shows another embodiment of the element illustrated in Fig. 4.

Figure 6 shows diagrammatically the mutual position of the elements illustrated in Fig. 2. during the operation of the apparatus.

The frame of the apparatus illustrated in Fig. 1 is comprised of two frame halves l. The facingly adapted halves 1 form a space, which houses two pistons 3. The pistons 3 are rotatingly mounted to the frame halves 1 by means of a shaft 7 of polygonal cross-section, and they divide the cylindrical space formed by the frame halves into two chambers. The shaft 7 has a flow duct 10, which interconnects the chambers separated by the pistons 3. At the other end of the shaft 7, to one of the frame halves is arranged a valve 5. The valve 5 extends into the flow duct 10 of the shaft 7, and it can be used for throttling the flow in the flow duct 10.

In the center of the apparatus, between the frame halves 1 is adapted a traction sheave 4 supported by sliding bearings 8. The diameter of the inner circumference of the sheave 4 extends up to the outer circumference of the pistons 3. The inside surface of the sheave 4 has pegs 9, which protrude into grooves 16 fabricated on the pistons 3 (Fig. 2). The sheave 4 carries an attached large gearwheel 9. The lower part of the apparatus carries a small gearwheel 11 mounted on a shaft 12. Rotating the shaft 12 allows the large wheel 16 to be rotated by the means of the small gearwheel 11. The upper part of the apparatus is provided with a mounting element 13.

Figure 2 shows the pistons 3 in a side view, while Figure 3 shows them in an end view. The groove 16 with a shape of a gently undulating sine curve is fabricated on both of the pistons 3. The cross-section of the pistons 3 is circular,

and one end in each of the pistons 3 is flat. The centers of the pistons are provided with a hole 15 having a square- shaped cross-section for the shaft 7. One of the pistons 3 has a recess, while the other one of the pistons has an extension with a shape compatible with the recess. The pistons 3 are also provided with grooves for seal rings.

Illustrated in Fig. 4 is the sheave 4, whose inside surface is provided with pegs 9. The pegs 9 are placed in two parallel rows so that each of the pistons 3 meets three of the pegs 9. These sets of three pegs are spaced at 120° intervals (angle /Q ) along the inside surface circumference of the sheave 4, while the peg rows are not parallel but instead, mutually displaced by an angle of 15° (angle <-* ) viewed along the longitudinal axis of the sheave 4.

The operation of the above described apparatus is as follows. The rope to be braked is set to pass over the sheave 4, and the apparatus is firmly mounted by its mounting element 13. The desired braking power is adjusted by a valve 5. In case no desired value for the braking power is known in beforehand, the valve 5 can be shut, whereby the- sheave 4 is locked stationary. Then, a desired braking power can be adjusted by slowly adjusting the valve 5 after the attachment of the load. The loaded rope starts thereby rotating the sheave 4. During the rotation of the sheave, the pegs 9 move along the grooves 16 of the pistons 3. The pegs 9 push the pistons 3 laterally at the sides of the grooves 16 forcing the pistons to move. Because the pistons 3 are mounted movable on the square-section shaft 7, they are incapable of rotating with the sheave 4 and the pegs 9. The lateral movement of the pistons 3 reduces the volume of the chamber located in the direction of their movement and forces the fluid contained in the chamber to flow via flow ducts 2 and 10 through the shaft 7 into the chamber located in the opposite end of the cylinder. Because the cross-section of the flow duct 10 is throttled by means of the valve 5, the valve 5 effects a flow resistance which resists the flow of the fluid from one side of the pistons 3 to the other. By

virtue of the restricted movement of the pistons 5, they can effect a braking action to the movement of the sheave 4 and the rope via the grooves 16 and the pegs 9.

The movement of the pistons 3 in the direction of the shaft is illustrated in the graph shown in Fig. 6. The vertical axis of the graph represents the distance of the piston 3 from its center position, while the rotation angle of the sheave 4 is assigned to the horizontal axis of the graph. The horizontal axis in the center of the graph is the zero position axis, which represents the center position of the movement of the piston 3. Plotted curves 24 and 23 describe the deviation of each piston 3 from their center positions, respectively. The outer horizontal axes represent the end positions of the movements of the pistons 3.

The movements of the pistons 3 are as follows. The proximal piston in the direction of the movement is started from its extreme position in respect to the direction of the movement (curve 24). Since the grooves 16 on the pistons 3 are coincident and there is a 15° phase shift between the pistons, the distal piston cannot start from its extreme position (curve 25). The pistons move 3 at identical speeds dictated by the pitch of the grooves 16. The distal piston is first to reach its extreme position in the direction of the movement. Then, there is a small dead zone in its movement, during which the direction of its motion is reversed. Simultaneously, the proximal piston continues its movement pumping fluid via the valve 5 and the flow ducts 2 and 10. When the proximal piston reaches its extreme position, its movement also experiences a similar dead zone as that of the distal piston. In this position the piston is stationary and therefore incapable of pumping the liquid, whereby no braking force is generated. At the reach of the dead zone by the proximal piston, the distal piston has already managed to pass its corresponding dead zone and is in motion in the opposite direction. At the same the piston pumps fluid to the opposite direction via the flow ducts 2 and 10, thus effecting a counteracting force. The proximal piston moved

first now follows the piston started second in the manner described above, and the reversal of motion occurs in a corresponding fashion at the other extreme point of the movement. By virtue of such a phased motion of the pistons 3, the braking power is retained at a constant level also during the reversal of motion, allowing the apparatus to achieve an extremely smooth motion of the load to be decelerated.

In addition to the preferred embodiment described above, a decelerator in accordance with the invention can be implemented in several alternative ways according to the desired application. Another preferred embodiment for heavy loads is shown in Fig. 5. Illustrated in the figure is a piston 3 enclosed by a sheave 4. In this embodiment, each of the pegs 9 is replaced by two pegs 9 attached to a fixture element 17. The fixture element 17 is adapted to the sheave 4 so that the element is slightly rotatable laterally. Then, the pegs 9 and the fixture element 17 align themselves parallel with the groove 16 on the piston 3 during the rotation of the sheave 4 and both pegs 9 contact the edge of the groove 16 simultaneously. The ends of the pegs 9 are provided with rotating bushings 18, which reduce the friction between the edge of the groove 16 and the peg, thereby contributing to reduced wear. An advantage of this embodiment is that the contact pressure between the groove 16 and the pegs is lower, which gives the apparatus an appreciably improved load-bearing capability. The contact pressure can alternatively be reduced by making the pistons 3 longer and providing each piston 3 with two or more grooves 16, and the sheave 4, correspondingly, with several rows of pegs.

Replacing the sheave 4, the apparatus can be provided with any other load-bearing element such as a mounting flange or v-belt pulley. The apparatus can then be used as the braking element in several different kinds of machines and equipment. In the illustrated embodiment, the needle control valve 5 can be replaced by any other suitable valve, even allowing the use of a remote-controlled valve when necessary. The shaft 12 can be complemented with a crank thus making it possible to

use the apparatus for lifting loads, for instance. Instead of the crank, the shaft can be connected to an electric motor or any other rotating power source suitable for the application.

The pumped fluid medium can be a desired kind of liquid. A preferred medium is hydraulic brake fluid rated for low and high temperatures. Alternatively, the medium can be different kind of oil, or even water or air.