Disc brake for lifting machine, which combines a positive brake and a negative brake.
Patent Information
- Application Number
- ES2023707142T
- Authority / Receiving Office
- ES · ES
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-02-07
- Publication Date
- 2026-09-15
- Estimated Expiration
- 2043-02-07
Smart Images
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Abstract
Description
Disc brake for lifting machine, which combines a positive brake and a negative brake. Technical field This application relates to a disc brake particularly suitable for braking heavy loads (e.g., exceeding several tons and up to 50t), such as a brake intended to equip an elevator, a cable car or a lifting machine of the crane type, an overhead crane, etc. State of the art An elevator or lifting machine comprises, on the one hand, a high-speed line comprising a motor (generally with a variable frequency drive) and a high-speed shaft driven into rotation by the motor through a coupling system, and on the other hand, a low-speed line comprising a low-speed shaft and a drum on which the suspension cables of the load (elevator cabin or load to be lifted) are wound, the low-speed shaft being driven into rotation by the shaft of the high-speed line to which it is connected through a reducer. An elevator or lifting machine must be equipped with brakes for several functions, specifically: slowing and then stopping the elevator or lifting machine as it approaches a stopping position (service brake), locking the elevator whenever the doors open, and locking the lifting machine when it is in its stopped position, i.e., when the load is at the desired height (parking brake). Standards require that the elevator or lifting machine also be equipped with a safety brake, sometimes called an emergency brake or failsafe brake, to slow, stop, and lock the elevator or lifting machine in the event of an electrical failure or, more generally, in any type of emergency. Service brakes (high speed and low torque) are generally associated with the high-speed line, while safety brakes (low speed and high torque) are mounted on the low-speed line. A safety brake is specially configured to activate when it is no longer powered (in case of electrical failure): this is called a fault brake or negative brake. Disc brakes have been the standard for this application since the 1960s, primarily because overheating poses little to no problem. Indeed, under the effect of heat, the discs expand radially, not along their thickness, thus keeping the braking torque under control. A disc brake safety brake that generally comprises: - a disc attached to the line to be braked, on each side of which extend the two plates of a caliper capable of squeezing the disc, whose plates are equipped with friction pads, - for each plate or for one of the two plates only, a washer spring configured to impose a compressive force on said plate so as to push and hold the plates under pressure against the disc and thereby close and tighten the clamp, - a hydraulic, electromagnetic, or electromechanical actuator configured to, when under tension, compress the washer spring so as to move the plate away from the disc to open the clamp and release the rotating disc. When it comes to elevators, service and parking brakes must be rated for 10 million operations, while the safety brake must be rated for 200,000 uses. Similarly, lifting equipment manufacturers often require that the parking brakes and safety brakes they integrate into their machines be guaranteed for 4 million and 200,000 uses, respectively, although no standard currently mandates this. Some manufacturers of elevators and other lifting equipment use a single brake for both service and parking functions. Because this brake is used more frequently and / or for longer periods, its friction pads wear out faster, increasing maintenance costs. For the same reasons, the brake's lifespan decreases, requiring more frequent replacement. All of this results in periods of elevator or lifting equipment downtime that are inconvenient for users (in the case of residential elevators) or costly for the company (in the case of elevators or lifting equipment that do not meet industry standards). Other manufacturers of elevators and other lifting equipment use the safety brake as a parking brake. This necessitates oversizing the safety brake so that it is rated for 4 or 10 million uses instead of 200,000. In other words, they increase the number of washers in the safety brake to compensate for potential washer breakage that may occur over multiple uses. This results in an increased size of the brake and higher manufacturing costs. Disc brakes are also used in the automotive field. US patent 3,647,030 discloses a motor vehicle brake that combines a negative washer actuator, as described above, with a positive actuator. Therefore, US patent 3,647,030 discloses the preamble of claim 1. The positive actuator consists of a first piston mounted slidingly in a housing and a first chamber that can receive a pressurized fluid. The increase in fluid pressure in this first chamber causes the piston to move in the direction of brake compression. The return of this first piston (for brake release when the brake pedal is released) is ensured by an elastic deformation seal, housed in a groove between the outer peripheral face of the piston and the housing, as explained in US patent 3,377,076 incorporated by reference in document US 3,647,030. The negative actuator consists of a second piston and a second chamber that can receive pressurized fluid; an increase in fluid pressure in the second chamber causes the brake to open. The second piston has a collar on which a stack of spring washers rests. When a fluid pressure failure occurs in the circuit, the pressure in the second chamber drops, and the stack of spring washers can relax and push the second piston, which in turn pulls the first piston, causing the brake to close. Maintaining high pressure in the second chamber allows the brake formed by the second piston to be overridden. This type of brake has the advantage of combining, in a single device, a positive actuator that serves as a service brake and a negative actuator that serves as an emergency brake. It can be classified as a hybrid brake due to this combination. However, it presents the following drawbacks. First, the free movement (opening) of the brake in US patent 3,647,030 is limited to a few millimeters. Therefore, this brake cannot be used with large discs, making it unsuitable for lifting equipment. Indeed, lifting machines require large-diameter brake discs (sometimes several meters in diameter), unlike automobiles whose discs are typically around 250 mm in diameter. Due to their large diameter, lifting machine discs can exhibit several millimeters of deformation, which is incompatible with using a brake that has a similar degree of free movement (it is important that the brake pads do not rub against the disc when the brake is in the open position; furthermore, in the closed position, the braking force applied by the pads to the disc must be controllable and not dependent on the disc's angular position). Furthermore, considering the brake design described in US patent 3,647,030, in the event of a failure of its positive actuator, such as a brake fluid leak, it is necessary to release the brake and completely disassemble it for repair. For a motor vehicle brake, this is not a problem in itself. However, for a lifting machine brake, whose weight and size are disproportionate to those of motor vehicle brakes, the ability to intervene on-site and repair the brake without having to disassemble it would be advantageous. Patent FR2092932 discloses a hybrid motor vehicle brake that presents similar drawbacks to those described in US patent 3,647,030, particularly in terms of free movement, and is therefore unsuitable for lifting machines. The same applies to document DE3509042, which discloses another hybrid brake. Presentation of the invention Throughout this continuation, the expression "lifting machine" also encompasses both industrial lifting machines such as cranes, lifting bridges, etc., and elevators, for industrial or domestic use. The invention aims to overcome at least one of the aforementioned drawbacks by proposing a suitable brake for lifting machines, which can be used simultaneously as a parking brake and an emergency brake, or even as a service brake if lifting standards evolve in this direction, without sacrificing safety, the brake's compactness, or its simplicity of design, and without increasing its manufacturing and maintenance costs. The invention has the special aim of proposing a hybrid brake that has a large free movement so that it can be used with large diameter discs, for example, discs from one to several meters in diameter. Another objective of the invention, in a preferred version, is to easily and cost-effectively transform an existing safety brake into a hybrid brake. Another objective of the invention, in a preferred version, is to provide a hybrid brake for a lifting machine that is easier to maintain. To achieve the aforementioned objectives, the invention proposes a hybrid brake for a lifting machine, intended to cooperate with a disc of the lifting machine that extends in a plane orthogonal to an axial direction, the hybrid brake comprising: - two plates that extend parallel to the disc on each side of the latter, the two plates forming a caliper that can be operated between an open brake position in which the plates are at a distance from the disc and a closed brake position in which the plates squeeze the disc, - a rigid body comprising a tubular upper portion, called the upper stirrup half, located on one side of the disc, one of the plates, called the upper plate, being supported by a shoe mounted to slide in the axial direction in a central recess passing through the upper stirrup half, - a stack of spring washers arranged in the central recess of the upper stirrup half around a central axis parallel to the axial direction, the stack of spring washers being compressible beyond a level, called the emergency braking compression, at which the stack exerts a force on the shoe corresponding to a desired emergency clamping force on the disc, - a negative actuator, comprising a negative piston driven by a first power source, the negative piston having a face on which a lower end of the stack of spring washers rests,the negative piston being mounted in sliding position in the axial direction in the central recess of the upper half-stirrup between a high open brake position in which the negative piston compresses the stack of spring washers beyond the emergency brake compression, and a low closed brake position in which the brake is closed and in which the negative piston maintains the stack of spring washers at the emergency brake compression on one side and is in direct or indirect support on the shoe on the other side, the negative piston being in its high open brake position when the first power source is activated and in its low closed brake position when said first power source is inactive (either because there is an electrical fault or because the first source is not activated or is intentionally deactivated), - a positive actuator comprising a positive piston moved by a second energy source, the positive piston being mounted in sliding position in the axial direction between a high open brake position (in which the brake is open) and a low closed brake position (in which the brake is closed and more or less tightened), the positive piston being placed in its high open brake position when the second energy source is inactive and being able to be placed in its low closed brake position when the second energy source is activated. The hybrid brake according to the invention is characterized in that it comprises a positive piston return spring, configured to raise the positive piston to its open brake high position. In case of emergency, the negative actuator is deactivated and the brake closes with a desired emergency tightening force, which is fixed by the structure of the spring washer stack. The positive actuator can be used as a parking brake, and even as a service brake subject to changes in regulations, and as such, it must be sized to be rated for approximately one million cycles of use (preferably rated for several million, for example, at least 10 million cycles of use). The positive actuator can also be used for short-term static load holding (short-term parking brake when the installation is energized, with the negative actuator always on standby to ensure load safety). Given its design, the negative brake is automatically engaged in the event of an electrical failure (secondary power source unavailable and negative actuator inactive). The negative brake can also be actively used for any dynamic emergency braking (in case of any failure) and for long-term static load holding (long-term parking brake, for example, when the installation is taken out of service). Therefore, the spring washer stack, which constitutes the negative brake's energy reserve for emergency braking, must be sized to be rated for 200,000 cycles. Since the negative brake is not used as a service brake, the spring washer stack does not need to be sized for several million cycles, thus limiting its size and cost. Thanks to the return spring, the positive piston can be displaced over a much larger stroke than the positive piston of US patent 3,647,030, for example. In other words, the brake can have a much larger opening, making it compatible with a large-diameter disc on a lifting machine. In a preferred version: - the negative piston comprises a cylindrical upper cavity that receives a lower part of the stack of spring washers, the negative piston further comprising a lower end configured to rest directly or indirectly on the shoe when the negative piston is in the lowered position, so that the pressure exerted by the stack of spring washers at the bottom of the piston cavity is transmitted to the shoe (when the negative piston is in the lowered position), - the positive piston comprises a shaft extending along the central axis through the stack of spring washers, the shaft having a lower end configured to engage with the shoe and an upper end which protrudes out of the upper half-stirrup independently of the position of the positive piston. Therefore, the configuration is, in a way, "inverted" with respect to that proposed by US patent 3,647,030 (where the central shaft corresponds to the negative piston and not the positive piston). This configuration offers two main advantages. First, such a brake can be derived from an existing safety brake, which includes only a negative actuator consisting of a negative piston that rests directly or indirectly on a brake shoe, and a stack of spring washers that rests on one face of the negative piston. A positive actuator can easily be formed from a shaft-shaped piston (having a lower end capable of engaging the brake shoe) and a cap positioned above the half-stirrup. A central hole is provided in the bottom of the negative piston, if required, and the shaft can be easily inserted into the central hole of the spring washers and the negative piston. The cap is also arranged to receive the means for actuating the shaft (positive piston) about the central axis. Secondly, this brake is advantageous because its positive actuator, which, as the service brake, is the most frequently used actuator and therefore the most susceptible to failure, is directly accessible from an upper outer face of the half-swing, without requiring the removal of another important part of the brake, such as the negative actuator, and without disconnecting the hybrid brake. Maintenance and any necessary repairs of the positive actuator are easy. They can be carried out in situ, without disconnecting the brake, which is particularly useful when the brake is large and / or heavy. Furthermore, the power source and the means of activating the positive piston can be located on top of or above the half-swing (for example, in a cover that extends over the half-swing), making them easily accessible as well.Maintenance and repair operations are made easier, and maintenance costs are reduced. According to a possible feature of the invention, the first power source (negative actuator power source) is hydraulic. The negative piston has an external shoulder facing the disc, which defines a chamber called the negative hydraulic chamber within the central recess of the stirrup. Filling this negative hydraulic chamber with fluid from the first power source exerts pressure on the shoulder in the opposite direction to the disc, causing the negative piston to move in the opposite direction. In this variant, the first energy source can be electromagnetic or electromechanical. According to a possible feature of the invention, the second energy source (positive actuator energy source) is hydraulic, electromechanical, or electromagnetic. Conventionally, each plate is equipped with one or more friction pads. According to a possible feature of the invention, the brake comprises a wear recovery device between the stack of spring washers and the brake shoe to compensate for wear of the friction pads. Advantageously, according to the invention, this wear recovery device comprises: - a thread called the recovery thread, arranged on the positive actuator shaft between the lower end of the spring washer stack and the lower end of the shaft, - the housings called recovery housings, arranged around the recovery thread, each recovery housing having a threaded face complementary to the recovery thread, - for each recovery housing, a recess disposed in the negative piston and in which said housing is housed, the recess having an axial dimension greater than an axial size of the recovery housing increased by at least one recovery thread pitch so that the recovery housing can be axially displaced in this recess over an axial distance of at least one thread pitch, the recess also having radially sufficient depth so that the housing can be radially displaced over a radial distance corresponding at least to the depth of the recovery thread pitch so that the threading of the housing can be disengaged from the recovery thread,- an elastic ring surrounding the housings, exerting a centripetal radial pressure that tends to keep the retrieval housings pressed against the retrieval thread. For example, the elastic ring rests on a peripheral outer face of the housings opposite its threaded face. According to a possible feature of the invention, the recovery housings are a total of three, distributed evenly around the recovery thread, i.e., arranged on the radii that form between them the angles of 120°. According to one possible feature, the wear recovery device further comprises an actuator configured to drive the positive piston in rotation and the steering means of said actuator. Therefore, wear recovery can be performed not only automatically through step skipping as explained later in the detailed description with reference to the attached figures, but also in a directed manner by rotation of the positive piston (and therefore of the recovery thread) by means of the dedicated actuator mentioned above. The hybrid brake according to the invention can be a sliding brake or a symmetrical brake. If the hybrid brake according to the invention is a sliding brake: - In addition to the upper half-stirrup, the rigid body of the brake comprises a lower part, called the counter-stirrup, located on the other side of the disc; the other plate, called the lower plate, is located on this counter-stirrup and is fixed in relation to the latter. - the brake is devoid of an actuator for braking on the counter-stirrup side; therefore, it preferably comprises only the negative actuator and the positive actuator defined above, which are arranged in the upper half-stirrup, - the brake comprises a column on which the rigid body (half stirrup + counter-stirrup) is mounted in sliding along the axial direction. If the hybrid brake according to the invention is a symmetrical brake: - In addition to the upper half-stirrup, the rigid brake body comprises a lower half-stirrup, located on the other side of the disc. - Like the upper plate, the lower plate is supported by a lower shoe mounted in a sliding position along the axial direction in a central recess of the lower half-stirrup. The brake comprises a second positive actuator and a second negative actuator located on the lower half of the caliper and configured to move the lower brake shoe. The second negative and positive actuators may be identical, respectively, to the negative and positive actuators of the upper half of the caliper, but arranged symmetrically (with respect to the braking plane represented by the disc) on the lower half of the caliper. In summary, the brake assembly may be symmetrical with respect to the disc. The invention extends to a braking system comprising a hybrid brake as defined above and a microprocessor controller(s) to which the positive and negative actuators of said hybrid brake are connected, the controller being configured to use the positive actuator for all dynamic service braking and all static maintenance when the lifting machine is in service, under power and in the absence of faults (short-term static maintenance), and to use the negative actuator for all emergency dynamic braking and all static maintenance (long-term) when the lifting machine is taken out of service (i.e., no longer under power), the negative actuator also being, by design, automatically activated without action of the controller for all emergency dynamic braking in the event of an electrical fault. The invention extends to a lifting machine characterized in that it is equipped with a hybrid brake as defined above. In the preceding sentence, the expression "a hybrid brake" should not be understood to mean "one and only" hybrid brake, but rather "at least one" hybrid brake, i.e., one or more hybrid brakes. Brief description of the drawings The invention, according to an exemplary embodiment, will be better understood and its advantages will become clearer upon reading the following detailed description, given by way of indication and in no way limiting, with reference to the accompanying drawings in which: [Fig. 1] Figure 1 is a cross-section through an axial plane of an embodiment of a hybrid brake according to the invention; [Fig.2] Figure 2 is a symbolic representation of the hybrid brake of Figure 1; [Fig.3] Figure 3 is a symbolic representation of a wear recovery device that can equip a hybrid brake according to the invention, showing the brake in the case of new friction pads and with the positive piston in the high open brake position, the negative piston being in the high position; [Fig.4] Figure 4 is a symbolic representation of the wear recovery device of Fig. 3 in the case of new friction pads and with the positive piston in the low position of the closed brake, the negative piston being in the high position; [Fig.5] Figure 5 is a symbolic representation of the wear recovery device of Fig. 3 to 5 in the case of worn friction pads, simulating the closing of the positive brake, i.e., the descent of the positive piston in the direction of the disc from its high position, with the negative piston unused and therefore fixed in the high position; [Fig.6] Figure 6 is a symbolic representation of the wear recovery device of Fig. 5 (with worn friction pads), which simulates the opening of the positive brake, i.e., the lifting of the positive piston in the opposite direction to the disc, after braking consecutive to the situation of Fig. 5, with the negative piston always fixed in the upper position. Detailed description The identical elements represented in the figures mentioned above are identified through identical numerical references. Throughout this description, the brake is defined and described in the position shown in the accompanying figures. The terms "up," "down," "superior," "inferior," "above," "below," "rises," "descends," etc., refer to this position and are unrelated to the direction of gravity, as the brake can function in any position. Therefore, for example, when the brake is described in a position where its actuators are located above the disc, the expression "the piston descends" is used more generally to mean that the piston moves in the direction of the disc (which does not necessarily mean it follows the direction of gravity), while the expression "the piston rises" means that the piston moves away from the disc. Figure 1 represents a hybrid brake 100 according to the invention, viewed in section along an axial plane (plane containing the central axis of the brake body). More precisely, the axial plane in question is a plane of symmetry of the brake. The hybrid brake 100 is associated with a disc 1 of a lifting machine (not shown), the disc being integral with a rotating line of said lifting machine. The hybrid brake 100 comprises an upper plate 2 equipped with friction pads 7 (also called wear linings) and a lower plate 3, similarly equipped with friction pads 7. The plates and the disc are parallel to each other and orthogonal to a central axis X100 of the brake, reference X1 also designating the axis of rotation of the disc 1, which is parallel to the central axis X100. The terms "axial direction" refer to the direction of the central axis X100 of the brake. The hybrid brake 100 further comprises a rigid body consisting of an upper half-stirrup 4, hereinafter referred to simply as the "half-stirrup," and a counter-stirrup 5. The half-stirrup 4 is tubular: it comprises a central cavity 40 running axially through it. This central cavity 40 is not necessarily cylindrical; it may comprise a series of sections of varying diameters forming several internal shoulders. Furthermore, for reasons of economy, these different sections preferably have a circular cross-section to allow for sealing and guidance using conventional gaskets. However, other cross-sections (polygonal, for example, especially square) are possible, provided that the appropriate gaskets are used. Plate 2 is supported by a sliding shoe 6 inside the central recess 40 of the half-stirrup (plate 2 could, in the variant, correspond to the lower face of said shoe 6), while plate 3 is supported by the counter-stirrup 5 (it is, for example, fixed to the upper face of the latter). The hybrid brake 100 also comprises a stack of spring washers 10. The spring washers are selected for their dimensional characteristics / materials / properties (especially inflexibility), just as the linings are selected for their coefficient of friction, especially depending on the maximum load that the brake is intended to handle.Therefore, the stacking of spring washers is dimensioned so as to generate a clamping force, called the emergency clamping force, which induces (through the pads and, therefore, according to the coefficient of friction of the latter) a braking force which must correspond to the braking force necessary to instantly stop the maximum load. The hybrid brake 100 further comprises both a negative actuator 8 and a positive actuator 9, which together with the stacking of spring washers 10 form a negative brake (or fault brake) and a positive brake, respectively. The illustrated hybrid brake 100 is a sliding brake: the two actuators are located on the same side of the disc 1, both acting on the upper plate 2, and the brake is without an actuator on the other side of the disc. The upper plate 2 can move closer to or further from the disc under the effect of the actuators, while the lower plate 3 remains stationary. Therefore, for the two plates to exert a combined pinching force on the disc, the rigid brake body must be able to move axially. To this end, the brake comprises a column 12 on which the rigid brake body (half-stirrup 4 + counter-stirrup 5) is mounted to slide axially by means of a pin 120, which, in this example, extends the counter-stirrup 5, thus forming a sliding joint between the pin 120 and the column 12. The column 12 is fixed to a platform 15.The brake 100 also includes a screw 121 which allows the rigid body to be locked onto the column 12 if necessary, especially during maintenance operations. In this variant, the hybrid brake could be a symmetrical brake. It would then comprise four actuators, that is, one positive and one negative actuator on each side of the disc. The sliding brake is preferred because it has lower manufacturing and maintenance costs, as well as greater reliability (fewer actuators, therefore less risk of failure or breakage). The negative actuator 8 comprises a negative piston 80 slidably mounted in the central recess 40 of the half stirrup. The illustrated example uses a hydraulic negative actuator 8. Therefore, a chamber 81 (referred to as the negative chamber) is provided, which is bounded by the inner face of the recess 40 and the outer face of the negative piston. More precisely, the negative chamber 81 is bounded by an outer shoulder 84 of the downward-facing piston (i.e., in the direction of disc 1) and an inner shoulder 401 of the upward-facing half-stirrup (i.e., in the opposite direction to disc 1). This negative chamber 81 is connected to a pressurized fluid supply device (not shown), which constitutes the hydraulic power source (referred to as the first power source) for the operation of the negative actuator 8. In this variant, the negative actuator could be electromechanical or electromagnetic, and the person skilled in the art could, without demonstrating inventive activity, adapt the shape of the stirrup half and integrate into it, for example, the electromagnets necessary for the displacement of the negative piston to its high position when the electromagnets are under voltage for the realization of an electromagnetic negative brake. The negative piston 80 has an upper cavity 82 in which a lower part of the spring washer stack 10 is housed. Therefore, the lower end of the stack 10 rests on a bottom 83 of the upper cavity 82. The upper end of the spring washer stack 10 also comes to rest against a fixed element of the rigid brake body, in this case the underside of a cap 11 fixed to the top of the half-stirrup 4. The presence of the cover facilitates maintenance by allowing access to the interior of the stirrup half and, in particular, to the spring washer stack 10. For example, if a broken spring washer needs to be replaced, simply unscrew the screws that pass through the lower flange of the cover 11 and secure it to the stirrup half 4, and then remove the cover to access the spring washer stack 10 housed in the upper cavity 82 of the negative piston. This cover also allows easy access to the positive piston 90, which is described in detail later. The central hole 40 of the half stirrup extends axially through a central hole 110 that passes through the cover 11 in the axial direction. With the stack of spring washers 10 locked between the lower face of the cover 11 (which is fixed) and the bottom 83 of the upper cavity of the negative piston 80, the compressive force of the stack of spring washers 10 tends to displace the negative piston 80 downwards, in the direction of the shoe 6. When the chamber 81 of the negative actuator is empty or when a low or zero pressure is imposed on the fluid contained in said chamber, the negative piston 80 descends under the effect of the thrust of the stack of spring washers 10; the lower end 85 of the negative piston 80 comes to rest, directly or indirectly, on a stop or ball joint 97 supported by the lower end of the positive piston 90; The stop or ball joint 97 engages with the shoe 6 and the negative piston pushes the shoe 6 in the direction of the disc 1 as the stack of spring washers 10 relaxes. When the friction pads 7 of plate 2 make contact with disc 1, the rigid brake body slides upwards along column 12 while the negative piston 80 continues to descend relative to the half-stirrup, until the negative piston 80 is in a closed, low brake position. In this position, the friction pads of both plates are in contact with the disc and together exert a clamping force on it. The clamping force, called the emergency clamping force, then imposed on the disc depends on the residual compression of the stack of spring washers 10 in this low position of the negative piston. This residual compression can be adjusted during brake design by varying the number, stiffness, material, and / or dimensions of the washers used. This allows for obtaining a desired emergency clamping force. When the negative piston 80 is in the high position as illustrated in Fig. 1, i.e., when the chamber 81 is filled with a fluid pressure greater than or equal to a certain threshold value, the stack of spring washers 10 is compressed beyond the emergency braking compression (which corresponds to the low position of piston 80). In the event of an electrical failure or if the fluid supply to chamber 81 is intentionally stopped—that is, if the (first) power source of actuator 8 is inactive (or deactivated)—the pressure in chamber 81 drops sharply and the chamber empties; the negative piston 80 drops to the lowered position and the brake closes in a fraction of a second. Therefore, actuator 8 is, in effect, a negative actuator. The positive actuator 9, for its part, comprises a positive piston 90 slidably mounted in the central recesses 40 and 110 of the half stirrup and the cover. In the illustrated example, the positive actuator 9 is also hydraulic. It therefore comprises a chamber 91 (referred to as the positive chamber) provided above an upward-facing face of the positive piston 90 (opposite the direction of the disc), which chamber is supplied with fluid through a supply conduit 92. This fluid constitutes a second source of energy, which enables the operation of the positive actuator 9. The positive piston 90 comprises, from top to bottom, a first section 901 of smaller diameter and then a second section 902 of larger diameter, so that an upward-facing external shoulder 903 (i.e., in the opposite direction to disc 1) is formed between the first and second piston sections. The positive chamber 91 of the positive actuator is bounded by the outer face of the positive piston 90 and by the inner face of the recess 110 of the cover 11 above this outer shoulder 903. In other words, the positive chamber is formed inside the cover 11, outside the middle stirrup 4. It can be seen that the positive actuator assembly 9 (piston 90, chamber 91, chamber fluid feed conduit and valve 92, return spring 98) is accessible simply by opening the cover 11. This facilitates maintenance operations (e.g., checking and repairing any leaks) of the positive actuator, which is the most frequently used component and therefore the most susceptible to wear. Similarly, the stack of spring washers 10 (the washers themselves being breakable parts) is accessible once the cover 11 and piston 90 have been removed.Therefore, the main faults of the hybrid brake can be resolved on site, without needing to release the brake. The outer diameter of the second section 902 of the positive piston is substantially equivalent (with a close clearance, reduced to a minimum) to the inner diameter of a corresponding section of the central recess 110 of the cover, to allow the piston 90 to slide along the central axis X100 while preventing fluid leakage from the chamber 91 between the outer face of the piston and the inner face of the recess 110 of the cover. A seal may be provided to limit such leakage, as well as a groove 94 and a channel 95 for recovering any leakage downstream (i.e., below) the seal. The positive piston 90 then comprises a third section forming a shaft 904 which passes through the stack of spring washers 10 (the shaft 904 passes through the center hole of each of the spring washers); the shaft 904 also passes through the lower end 85 of the negative piston 80. As mentioned above, the lower end of the shaft 904 of the positive piston is provided with a stop (fig. 1) or a ball joint (fig. 2), referenced 97 in both cases, which fits into a corresponding niche 60 of the shoe 6 when the positive piston 90 moves downwards in the direction of the disc 1. It is noted that the lower end 96 of the piston may be without the ball joint or stop and configured to fit directly into the shoe 6. A bellows 99, fixed on one side to the outer face of the lower portion 85 of the negative piston and on the other side to the lower end 96 of the positive piston (for example, to the stop or ball joint 97), is advantageously provided to prevent the entry of dust and coating particles that could disrupt the wear recovery system. The hybrid brake 100 is also associated with a controller (not shown) which allows control of the positive 9 and negative 8 actuators, acting on the power supply of these actuators. When dynamic service braking or static parking braking is required, the controller commands the injection of pressurized fluid into the positive chamber 91 (activation of the second power source) of the positive actuator 9. This causes the positive piston 90 to move downwards until the stop or ball joint 97 at the lower end of the shaft 904 engages with the shoe 6 and then pushes the shoe towards the disc 1. When the friction pads 7 of plate 2 make contact with the disc 1, the rigid brake body slides a block upwards along the column 12 while the positive piston 90 continues to descend relative to the half-stirrup, until the friction pads of both plates are in contact with the disc and together exert a clamping force on the disc. The clamping force then imposed on the disc 1 is a function of the fluid pressure in the positive chamber 91.Therefore, the positive brake can be controlled so that it exerts a variable control squeezing force. During this time, the negative brake 8 is kept open as illustrated in Figure 1, i.e., a fluid pressure at least equal to a predetermined threshold pressure (capable of compensating for the emergency braking compression of stack 10) is maintained in the negative chamber 81 in order for the negative piston 80 to remain in the high position as illustrated in Figure 1. According to the invention, the brake 100 comprises a return spring 98 configured to raise the positive piston 90 to its open brake high position. In the illustrated example, the return spring 98 is housed around the shaft 904 inside the spring washer stack 10. The return spring 98 is supported on one side by the bottom 83 of the upper cavity of the negative piston and on the other side by an external shoulder 905 of the positive piston, which shoulder is located at the junction between sections 902 and 904 of the piston (hence, the shoulder 905 is downward-facing). The return of the positive piston 90 through this spring 98 allows for significant free movement of the positive piston, which makes the hybrid brake according to the invention suitable for lifting machines equipped with a large diameter disc. The illustrated hybrid brake 100 further comprises a wear recovery device 13 arranged between the stack of spring washers 10 and the shoe 6, which will now be described with reference to Fig. 3 to 6, in which one half of the positive and negative brake actuators is symbolically represented, the other half being obtained by symmetry with respect to the X100 axis. The wear recovery device 13 comprises: - a thread 131, called the recovery thread, arranged on a lower portion of the 904 shaft of the positive piston, - a plurality of housings 130, for example, three housings 130 arranged 120° apart around the thread 131, - an elastic ring 133 surrounding the housings and exerting on them the centripetal radial forces which keep the housings in contact with the retrieval thread 131; each housing 130 has an inner face 132 (face facing the X100 axis) which is threaded with a screw pitch complementary to the screw pitch of the retrieval thread 131, so that the threaded inner face 132 of the housings fits into the retrieval thread 131, under the pressure of the elastic ring 133. - for each housing 130, a housing 134 receiving said housing (the housing being suitable for said housing or common to several housings), said housing 134 being disposed in the negative piston 80 and open towards the central axis X100, the housing having an axial dimension greater than that of the housing so that the housing can be axially displaced in the housing over a stroke at least equal to the pitch of the thread 131, the housing also having a radial depth sufficient to allow the housing to be radially displaced over a stroke that allows the thread 132 to come out of the thread 131.It is noted that the recovery device 13 may comprise a plurality of separate housings 134, in particular one housing per housing 130, or a single circular housing which goes around the shaft 904 (i.e., a circular groove arranged on the inner face of the negative piston 80) and which houses all the housings 130, or even a plurality of housings each accommodating several housings. In figures 3 and 4, the brake has wear-free friction pads 7. In figure 3, the negative piston 80 is in the high open brake position as illustrated in figure 1 (the negative chamber 81 contains a pressurized fluid that exerts a force on the piston 80 greater than the compressive force of emergency braking). The positive piston 90 is also in the high open brake position (the positive chamber 91 is empty and the shoulder 903 (see figure 1) of the piston 90 is in contact with or near the cap 11). In this position, each housing 130 rests against the upper face 135 (or upper stop) of its housing 134. When the positive actuator 9 is actuated, for example, for a service operation, the positive piston 90 is pushed down by the pressurized fluid injected into the positive chamber 91, and the positive piston 90 moves from its high position (Fig. 3) to its low closed brake position, illustrated in Fig. 4. During this time the negative piston 80 remains fixed in its high open brake position. When the positive piston 90 is in the closed brake low position, the friction pads 7 are in contact with the disc 1. During the descent of the piston and, therefore, of the thread 131, the housings follow it until they come into contact with the lower face (or bottom stop) 136 of the housing. The thread may descend slightly further than the housings (this is the case in Fig. 4), with the latter bearing radially, however, without reaching the point where the thread 132 of the housings disengages from the thread 131. Figure 5 illustrates the positive piston 90 in the downward phase, but in the case where the friction pads 7 are worn. In this case, when the positive piston 90 reaches the height shown in Figure 4 (which corresponds to the lowered position of the closed brake when the pads are new), the (worn) pads 7 are still at a distance from the disc 1 because they have a reduced thickness due to wear, and the piston can continue descending, pushed by the pressurized fluid in the positive chamber 91. The housings 130 can no longer descend, held by the lower face 136 (or lower stop) of the housing. They are then forced to move radially, pushed by the thread 131, until their threads 132 disengage from the thread 131. It is noted that the threads of the retrieval thread 131 and the threading 132 of the retrieval housings advantageously have a triangular cross-section with an upper face orthogonal to the central axis X100 and an inclined lower face. Therefore, when the positive piston 90 descends, the retrieval thread exerts a force on the retrieval housings 130 comprising both an axial component, which drives the housings downwards, and a radial component, which tends to displace the housings radially outwards when they have come to rest against the lower face 136 of the housing. Conversely, when the positive piston 90 rises, the retrieval thread 131 exerts a purely axial force on each housing 130, which ensures that the threading 132 of the housings remains engaged with the retrieval thread 131 of the shaft, even when the housings come to rest against the upper face 135 of the housing. Having reached the position shown in Fig. 5, piston 90 continues to descend, and the housings advance one thread pitch 131, or possibly several pitches, to the position illustrated in Fig. 6. When the positive braking power source is then deactivated or reduced, piston 90 rises until the housings come to rest against the upper face (or top stop) 135 of the housing, thus stopping piston 90 in a new open brake high position (Fig. 6). This new open brake high position is offset by one or more thread pitches 131 relative to the previous high position, the offset corresponding to the thickness lost due to wear of the friction pads 7. Therefore, with the same stroke, actuating the positive piston 90 always allows the brake to close, regardless of whether the pads are worn or not. The return mechanism also applies to the negative brake, since when the positive brake is not used and the negative piston 80 is in the open brake position (see Fig. 3 and Fig. 5), the housings are always in contact with the upper face 135 of the negative piston housing. However, in the example described, the negative piston 80 acts on (i.e., comes into contact with) the brake shoe 6 by means of the return mechanism 13, more precisely by means of the housings 130, the return thread 131, and the lower end 96 of the shaft 904. Therefore, when the negative piston 80 is in the open brake position, the lower end of the negative piston is already in indirect contact with the brake shoe via the housings 130 and the shaft 904 of the positive piston. Consequently, when the emergency brake is activated, the negative piston 80 immediately pushes the brake shoe 6 towards the disc.The relative position of the housings 130 and the thread 131, taking into account the thickness of the friction pads 7 and their possible wear, guarantees the closing of the brake (with a predetermined emergency braking torque) with the same stroke of the negative piston 80, whether the pads are worn or not. The presence of a positive brake in the hybrid brake does not interfere with the emergency braking function. The negative piston 80 can be actuated (lowered) independently of the position of the positive piston 90. If the positive piston 90 is in the open brake position, as described above, the negative piston 80 actuates the housings 130 and shoe 6 from the beginning of its stroke. If the positive brake is in use and the positive piston 90 is, for example, in the closed brake position, the negative piston 80 will only press the housings 130 and shoe 6 at the end of its stroke, to ensure that the torque applied to the disc is at least equal to the emergency braking torque.If the positive brake is in use and the positive piston 90 is in an intermediate position (in the downward or upward phase), the negative piston 80 will take over at an intermediate point in its own stroke when the upper face 135 of the housings 134 comes into contact with the housings 130. It should be noted that, even when in the upward phase, the positive piston 90 does not oppose the downward movement of the emergency negative piston, since the upward movement of the positive piston is effected with negative energy (the chamber 91 is emptied) and the return spring 98, which pushes the positive piston upward, rests on the negative piston 80 (therefore, the spring 98 exerts a downward force on the negative piston 80, which compensates for the upward force exerted on the negative piston 80 by the positive piston 90 through the housings of the recovery device). Finally, the hybrid brake 100 also preferably includes a recentering device 14 which allows the brake body to be recentered with respect to the disc in order to ensure symmetrical opening with respect to the disc throughout the wear range of the friction pads 7 (the pads on plate 2 may be more or less worn than those on plate 3). In this case, this device will not be described in detail.
Claims
1. Hybrid brake for a lifting machine, intended to cooperate with a disc of the lifting machine extending in a plane orthogonal to an axial direction, the hybrid brake comprising: - two plates (2, 3) extending parallel to the disc on each side thereof, the two plates forming a caliper that can be operated between an open brake position in which the plates are at a distance from the disc and a closed brake position in which the plates clamp the disc, - a rigid body (4, 5) comprising a tubular upper part (4), called the upper half-stirrup, located on one side of the disc, one of the plates (2), called the upper plate, being supported by a shoe (6) mounted to slide in the axial direction in a central through-hole (40) of the upper half-stirrup,- a stack of spring washers (10) arranged in the central recess (40) of the upper half-stirrup around a central axis (X100) parallel to the axial direction, the stack of spring washers (10) being configured to be compressible beyond a level, called the emergency braking compression, at which the stack exerts a force on the shoe (6) corresponding to a desired emergency clamping force on the disc, - a negative actuator (8), comprising a negative piston (80) driven by a first power source, the negative piston having a face (83) on which a lower end of the stack of spring washers (10) rests,the negative piston (80) being mounted in sliding position in the axial direction in the central recess (40) of the upper half-stirrup between a high open brake position in which the negative piston (80) compresses the stack of spring washers (10) beyond the emergency brake compression, and a low closed brake position in which the brake is closed and in which the negative piston (80) maintains the stack of spring washers (10) in the emergency brake compression on one side and is in direct or indirect support on the shoe (6) on the other side, the negative piston being in its high open brake position when the first power source is activated and in its low closed brake position when said first power source is inactive, - a positive actuator (9) comprising a positive piston (90) driven by a second power source,the positive piston being mounted in sliding position in the axial direction between a high open brake position in which the brake is open, and a low closed brake position in which the brake is closed, the positive piston being in its high open brake position when the second energy source is inactive and being able to be in its low closed brake position when the second energy source is active, the hybrid brake being characterized in that it comprises a return spring (98) of the positive piston, configured to raise the positive piston (90) to its high open brake position.
2. Hybrid brake according to claim 1, characterized in that: - the negative piston (80) comprises a cylindrical upper cavity (82) that receives a lower portion of the stack of spring washers (10),further comprising the negative piston a lower end (85) configured to rest directly or indirectly on the brake shoe (6) when the negative piston is in the closed, low brake position; the positive piston (90) comprises a shaft (904) extending along the central axis (X100) through the stack of spring washers (10), said shaft having a lower end configured to engage with the brake shoe (6) and an upper end which protrudes from the upper bracket half (4) independently of the position of the positive piston.
3. Hybrid brake according to any one of claims 1 or 2, characterized in that the first power source is hydraulic, the negative piston (80) having an external shoulder (84) which is oriented towards the disc (1) and which delimits, in the central recess (40) of the bracket half, a hydraulic chamber (81) called the negative chamber.
4. Hybrid brake according to any one of claims 1 or 2,characterized in that the first energy source is electromagnetic or electromechanical.
5. Hybrid brake according to any one of claims 1 to 4, characterized in that the second energy source is hydraulic or electromechanical or electromagnetic.
6. Hybrid brake according to any one of claims 1 to 5, characterized in that each plate (2, 3) is equipped with one or more friction pads (7) and in that the brake comprises a wear recovery device (13) between the stack of spring washers (10) and the shoe (6) to compensate for wear of the friction pads.
7. Hybrid brake according to claim 6 and according to claim 2, characterized in that the wear recovery device (13) comprises: - a thread (131), called the recovery thread, disposed on the shaft (904) of the positive actuator between the lower end of the stack of spring washers (10) and the lower end (96) of the shaft, - the housings (130),called recovery housings, arranged around the recovery thread (131), each recovery housing (130) having a threaded face (132) complementary to the recovery thread (131), - for each recovery housing (130), a recess (134) arranged in the negative piston (80) and in which said housing is accommodated, the recess (134) having an axial dimension greater than an axial size of the recovery housing increased by at least one recovery thread pitch so that the recovery housing (130) can be axially displaced in that recess over an axial distance of at least one thread pitch, the recess also having radially sufficient depth so that the housing can be radially displaced over a radial distance corresponding to at least one depth of the recovery thread pitch,- an elastic ring (133) surrounding the housings, exerting a centripetal radial pressure on them that tends to keep the recovery housings (130) pressed against the recovery thread (131).
8. Hybrid brake according to claim 7, characterized in that the wear recovery device further comprises an actuator configured to drive the positive piston (90) in rotation and piloting means for said actuator.
9. Hybrid brake according to any one of claims 1 to 8, characterized in that: - in addition to the upper stirrup half (4), the rigid brake body comprises a lower part (5), called the counter-stirrup, located on the other side of the disc (1), the other plate (3), called the lower plate, being located on this counter-stirrup (5) and being fixed with respect to the latter,- the brake is devoid of the actuator for braking on the counter-stirrup side (5); - the brake comprises a column (12) on which the rigid body (4, 5) is mounted and slides in the axial direction.
10. Braking system for a lifting machine, comprising a hybrid brake according to any one of claims 1 to 9 and a microprocessor controller(s) to which the positive actuator (9) and the negative actuator (8) of said hybrid brake are connected, the controller being configured to use the positive actuator for any dynamic service braking and for any static maintenance when the lifting machine is in service, under load and in the absence of a fault,and to use the negative actuator for any emergency dynamic braking in case of failure and for any static maintenance when the lifting machine is out of service.
11. Lifting machine characterized in that it is equipped with a hybrid brake according to any one of claims 1 to 9.