Abstract:
A device for preventing uncontrolled acceleration of an elevator car installed in an elevator installation. The device has a limiting cable guided over rollers in a direction of movement of the elevator car. A braking device which is joined to the elevator car is connected to the limiting cable by a release and brakes the elevator car in both a downward and upward direction when the limiting cable transmits a predetermined release force to the release. A speed limiter is connected to one of the rollers and stops the roller when the traveling speed of the elevator car exceeds a predetermined limiting speed either in a downward or upward direction. The release of the braking device is connected by a slide connection to the limiting cable for limiting the force transmitted to the release so that the limiting cable slides through on the side connection when a force is significantly larger than the release force required for releasing the braking device is transmitted from the limiting cable to the release of the braking device.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for preventing uncontrolled acceleration of an elevator car of an elevator installation both in the upward direction and in the downward direction. 
     In elevator installations an elevator car is usually connected to a counterweight by a rope over a traction sheave which transmits driving action to the car. To ensure that in the case of a functional fault such as, for example, failure of the driving device, the elevator car is not accelerated in uncontrolled manner by the difference in weight between the elevator car and the counterweight, a corresponding safety device is prescribed. Because the counterweight is usually designed so that when the elevator car is carrying half the permitted rated load there is a state of equilibrium, uncontrolled acceleration can occur in both the downward direction and in the upward direction depending on whether the elevator car is carrying more or less than half the permitted rated load. The safety device must therefore respond both when there is uncontrolled acceleration in the downward direction and in the upward direction. 
     A device for preventing uncontrolled acceleration of an elevator car in an elevator installation is known, for example, from EP 0 440 839 A1. The safety device according to that printed publication responds both in the case of an uncontrolled acceleration in downward direction and an uncontrolled acceleration in upward direction. To detect the uncontrolled acceleration of the elevator car, a governor rope is provided which is independent of the traction rope and which runs endlessly over an upper return pulley and a lower return pulley. Provided on the lower return pulley is a weight to keep the governor rope constantly taut. Located on the upper return pulley is an overspeed governor. The elevator car is connected to the governor rope via an actuating lever which serves as a tripper and which, when the elevator car is running undisturbed, is constantly transported with the latter so that the speed of rotation of the upper return pulley is proportional to the speed of the elevator car. The overspeed governor detects the speed of rotation of the upper return pulley and is so designed that, when a limit speed of rotation of the upper return pulley is exceeded, the overspeed governor blocks the latter so that the upper return pulley is brought to rest. Because the governor rope is still transported by the elevator car, the governor rope slips over a groove provided in the upper return pulley and thereby experiences a frictional resistance which causes a tripping force to be transmitted via the governor rope to the tripping mechanism of the braking device. Thereupon, the braking device responds and presses brake shoes against a guiderail of the elevator installation so that the elevator car is braked and held. Different brake shoes are provided for braking/holding the elevator car in the downward direction and the upward direction respectively. 
     As shown in detail below by means of FIGS. 10 and 11, the force which acts on the fall of the governor rope connected to the tripper depends to a substantial extent on whether the elevator car is moving in a downward or an upward direction. Stated simply, if the elevator car is moving upward, the fall of the governor rope connected to the tripper pulls on the weight of the lower return pulley directly. On the other hand, if the elevator car is moving downward, the fall of the governor rope connected to the tripper pulls on the weight of the lower return pulley via the stationary upper return pulley so that in this case the force acting on the rope fall connected to the tripper is substantially increased by friction. 
     The dimensions of the safety device, particularly of the weight connected to the lower return pulley and of the geometry of the slot provided on the upper return pulley, over which the governor rope is pulled when the upper return pulley is stationary, must therefore be based on the braking operation of the elevator car moving in the upward direction because the tripping force for this case is lower. On the other hand, this also means that the tripping force when the elevator car is moving in a downward direction becomes so large that considerable problems arise with the dimensioning of the governor rope and of the tripper of the braking device, because the governor rope and the tripper must withstand this very high tripping force in the downward direction. 
     In EP 0 440 839 A1 the suggestion is made of arranging a compensation spring in the governor rope above the tripper. However, this compensation spring increases even further the tripping force in the downward direction, which is already too high anyway, and is therefore disadvantageous. 
     SUMMARY OF THE INVENTION 
     The objective of the invention is to create a device for preventing uncontrolled acceleration of an elevator car of an elevator installation in which the tripping force transmitted to the tripper of the braking device is limited. 
     According to the invention, it is proposed to connect the tripper of the braking device with the governor rope via a slipping connection so that the governor rope slips on the slipping connection if a force is transmitted from the governor rope to the tripper of the braking device which is substantially greater than the tripping force required to trip the braking device. By means of the proposed solution according to the invention, the maximum tripping force which is transmitted is limited, and the tripper of the braking device and the governor rope are thereby protected against overloading. In this manner, the components of the device can be so designed that on the one hand a tripping force is generated sufficient to trip the tripper of the braking device with certainty and thereby arrest an acceleration of the elevator car in the upward direction, but so that on the other hand the tripping force when arresting the elevator car in the downward direction is limited, which prevents overloading the tripper and governor rope. 
     The slipping connection can be so adjusted that the governor rope only slips on the slipping connection when the elevator car is braked in the downward direction. When the elevator car is braked in the upward direction, the governor rope then slips as hitherto over the stationary upper return pulley without activating the slipping connection according to the invention. Because a much larger force acts on the governor rope when braking the elevator car in the downward direction than when braking in the upward direction, it is sufficient for the slipping connection to slip in the downward direction. The slipping connection can be set with some margin of safety above the tripping force required to trip the braking device. 
     The slipping connection can be arranged immediately below the rope connector that connects the free ends of the governor rope to each other. 
     The slipping connection consists preferably of a base plate and a pressure plate which presses against the base plate with a specified compressive force, the governor rope being gripped between the base plate and the pressure plate. To generate the compressive force there is at least one tension screw which passes through and beyond a drilled hole of the pressure plate and can be screwed into a thread of the base plate. The depth to which the screw can be screwed into the thread, and therefore the compressive force, is limited by a tightening stop. 
     The compressive force can be generated by a compression spring compressed between the base plate and a projection of the tension screw, the compression spring consisting preferably of several cup springs arranged in a stack. The tightening stop can take the form of a sleeve surrounding the tension screw. 
     The governor rope is preferably guided in a groove in a surface of the base plate and/or the pressure plate which has a preferably triangular cross section. At the ends of the base plate and of the pressure plate the groove opens out into an area which preferably opens out both in the direction of the surface and perpendicular to the surface of the base plate and pressure plate respectively. The tripper of the braking device is fastened to either the pressure plate or the base plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention is described below by reference to the drawings. 
     The drawings show: 
     FIG. 1 is an overall view of an exemplary embodiment of the device according to the invention; 
     FIG. 2 is an exploded view of the governor rope, the rope connector, and the slipping connection; 
     FIG. 3 shows the governor rope, the rope connector, and the slipping connection in the assembled state; 
     FIG. 4 is a plan view of the slipping connection; 
     FIG. 5 is a cross section on line A—A in FIG. 4; 
     FIG. 6 is a cross section on line B—B in FIG. 4; 
     FIG. 7 is a plan view of the base plate of the slipping connection; 
     FIG. 8 is a side view of the base plate of the slipping connection; 
     FIG. 9 is a cross section on line A—A in FIG. 8; and 
     FIGS. 10 and 11 are force diagrams. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an overall view of the device according to the invention for preventing uncontrolled acceleration of an elevator car of an elevator installation. 
     Only the car frame  2  of an elevator car  1  is shown. The car frame  2  of the elevator car  1  is guided in a vertical path by an upper guide  3  and a lower guide  4  along a guiderail  5  indicated only by the broken line. The elevator car  1  is suspended on a traction rope not shown in the drawing which is reversed over a traction sheave at the upper end of the elevator hoistway and connected to a counterweight. Driving action is applied to the elevator car by the traction sheave. As a rule, the counterweight is so dimensioned that the counterweight is in equilibrium with the elevator car  1  when the elevator car  1  is loaded with approximately half its maximum rated load. Occurrence of an operational fault, especially failure of the drive device, can cause uncontrolled acceleration of the elevator car  1  due to the difference in weight between the elevator car  1  and the counterweight. If the elevator car  1  is loaded with less than half its rated load, this acceleration takes place in the upward direction. On the other hand, if the elevator car  1  is loaded with more than half its rated load, this uncontrolled acceleration takes place in the downward direction. To prevent this uncontrolled acceleration, a braking device  6  is provided which prevents uncontrolled acceleration in both the upward and the downward direction and which can be tripped by a tripper  7 . A braking device  6  of a similar type is known, for example, from DE 296 19 729 U1 and EP 0 825 145 A1, and is described in outline only below. 
     The tripper  7  consists of a lever  9  articulated on a suspension  8  and of a rod  10  connected to the lever  9  which engages in a cam plate  12  supported in a bearing  11 . When the lever  9  in FIG. 1 tilts upward, the rod  10  is pushed upward and turns the cam  12  so that a first brake element  13  is pressed into contact with the guiderail  5  (shown only as a broken line) so that the guiderail  5  is gripped between a brake shoe  14  and the first brake element  13 . The gripping force is provided by two cup spring assemblies  15  and  16  acting on the brake shoe  14 . Deceleration of the elevator car  1  then takes place by removal of metal from the guiderail  5  (shown only as a broken line). The braking process described above relates to braking the elevator car  1  in the case of uncontrolled acceleration in the downward direction. 
     To decelerate or arrest the elevator car  1  in the case of uncontrolled accelerating movement in the upward direction, the lever  9  in FIG. 1 is tilted downward and the rod  10  pushed downward. As a result, a second brake element  17  is brought into engagement with the guiderail  5  so that the guiderail  5  is gripped between the brake shoe  14  and the second brake element  17 . 
     Tripping of the tripper  7  of the braking device  6  takes place via a governor rope  18 , with which the elevator car  1  is connected by the tripper  7  of the braking device  6 . In the exemplary embodiment, the governor rope  18  takes the form of an endless rope running over an upper return pulley  19  and a lower return pulley  20 . By means of a weight  21  acting on the lower return pulley  20  via a rod  22  which is articulated in a bearing  23 , the governor rope  18  is held taut between the upper return pulley  19  and the lower return pulley  20 . The free ends  24  and  25  of the governor rope  18  are joined to each other by a rope connector  26 . 
     On the upper return pulley  19  there is an overspeed governor  27  which, on exceeding a specified speed of rotation, brings the upper return pulley  19  to rest, i.e. blocks it. Overspeed governors  27  of this type are known, constructed in various ways. 
     During normal operation of the elevator installation, the governor rope  18  is transported congruently with the elevator car  1 , and the upper return pulley  19  is in its unblocked state. Because the speed of the governor rope  18  is the same as the speed of the elevator car  1 , the rotational speed of the upper return pulley  19  is proportional to the speed of the elevator car  1 . If the rotational speed of the upper return pulley  19  exceeds a specified limit value, the overspeed governor  27  blocks the upper return pulley  19  so that the governor rope  18  is in slipping contact with the stationary upper return pulley  19 . As a result, a force component is exerted on the governor rope  18  which the latter transmits to the tripper  7  of the braking device  6 , which in turn causes the braking device  6  to be tripped. 
     Problematical with such a device for preventing uncontrolled acceleration of the elevator car  1  is that when the elevator car  1  moves in the downward direction, a much greater braking force acts on the governor rope  18  than when the elevator car  1  moves in the upward direction. This situation is explained in greater detail below by reference to FIGS. 10 and 11. 
     FIG. 10 illustrates the situation regarding forces on the governor rope  18 , on the upper return pulley  19 , and on the lower return pulley  20  when braking the elevator car  1  in the downward direction. After the upper return pulley  19  has been brought to rest, the left-hand fall  18   a  of the governor rope  18  in FIGS. 1 and 10 is at first transported downward. On both the left-hand fall  18   a  of the governor rope  18  and on the right-hand fall  18   b  of the governor rope  18  a force G/2 equivalent to half of the weight  21  acts via the corresponding lever on the rod  22 . Acting against this force in both the left-hand fall  18   a  and in the right-hand fall  18   b  of the governor rope  18  is a vectorially opposite counterforce G/2. Also acting on both the left-hand fall  18   a  and on the right-hand fall  18   b  of the governor rope  18  is a force G S  attributable to the weight of the respective fall of the rope. In this case, the governor rope is pulled to the left over the upper return pulley  19 . The right-hand force on the stationary upper return pulley  19  is given by the resultant force S 1 , which is made up of the rope-weight force G S  and the force G/2. Acting on the left-hand fall  18   a  of the governor rope is a correspondingly greater force S 2 , which is correspondingly increased by the friction on the groove of the upper return pulley  19 . To trip the braking device  6 , a tripping force can be used consisting of a force F 1  acting vectorially downward which results from the difference between the force S 2  acting in the opposite direction, the rope weight force G S  plus the force G/2. 
     FIG. 11 illustrates the situation when braking the elevator car  1  in downward direction. In this case the governor rope  18  is pulled to the right over the stationary upper return pulley  19 . The right-hand force S 1  on the upper return pulley  19  is accordingly greater than the left-hand force S 2 . The result is therefore a vectorially upward directed force F 2 on the left-hand fall  18   a  of the governor rope  18 , which can be used as tripping force for the braking device  6 . 
     The weight force G acting on the lower return pulley  20 , and the geometry of the groove of the upper return pulley  19  which determines the relationship between the forces S 1  and S 2 , must be so dimensioned that when the elevator car  1  is braked in the upward direction, the available tripping force F 2  is still sufficient to trip the braking device  6  with certainty. Inevitably, when the elevator car  1  is braked in the downward direction, the resulting tripping force F 1  is much greater, as FIG. 10 shows. 
     The same result is obtained if the tripping force F for braking the elevator car either downward or upward is determined by calculation. For the case of braking the elevator car  1  downward, the following equations apply: 
     
       
           S   2   =G   S   +{fraction (G/2)}+F   1   (1) 
       
     
     
       
           S   2   =S   1   +·e   f (μ)·α  (2) 
       
     
     
       
           S   1   =G   S   +{fraction (G/2)}   (3) 
       
     
     For the case of braking the elevator car  1  in the upward direction, the following equations apply: 
     
       
         S 2   =G   S   +{fraction (G/2)}−F   2   (4) 
       
     
     
       
           S   1   =S   2   ·e   f (μ)·α  (5) 
       
     
     
       
           S   1   =G   S   +G   S   +{fraction (G/2)}   (6) 
       
     
     In this system of equations the symbols have the following meanings: 
     S 1  tension on the right of the upper return pulley  19   
     S 2  tension on the left of the return pulley  19   
     G S  half the weight of the governor rope  18   
     G tension acting on the lower return pulley  20  caused by the weight  21   
     F ½  force acting on the tripper  7   
     α angle of wrap on the upper return pulley  19  (α=180°) 
     f(μ) coefficient of friction depending on the shape of the groove of the upper return pulley  19   
     Taking the above equations (4), (5), and (6), and assuming a normal geometry for the groove on the upper return pulley  19 , to calculate first the weight force G of the weight  21  acting on the lower return pulley  20  to obtain a specified tripping force in the upward direction F 2 , and if the required weight force G determined in this manner is inserted in the equations (1), (2), and (3), the effective tripping force acting downward F 1  is obtained, which depends on the effective tripping force acting upward F 2 . For example, if certain tripping of the braking device  6  requires a tripping force of 400N, and if the weight  21  is so dimensioned that these 400N are attained in the upward direction, a force of approximately 1550N is obtained for the tripping force in the downward direction F 1 , in other words a force almost four times as large as the upwardly acting tripping force F 2 . This means that both the governor rope  18  and the tripper  7 , as well as the associated braking device  6  must be able to withstand this very high tripping force in the downward direction, which requires special design measures and thereby increases the manufacturing costs for the braking device  6  and the tripper  7 . Furthermore, a standardized braking device  6  with associated tripper  7  which has official type approval for braking the elevator car in the downward direction, cannot necessarily be used in the upward direction because of the excessive tripping force. 
     To solve this problem, the present invention proposes to limit the force transmitted to the tripper  7  by connecting the tripper  7  of the braking device  6  to the governor rope  18  by means of a slipping connection  30 . The governor rope  18  slips on the slipping connection  30  if a force is transmitted from the governor rope  18  onto the tripper  7  which is significantly greater than the tripping force needed to trip the braking device  6 . If the tripping force required is, for example, 400N, the slipping connection  30  can be set so that the latter slips at, for example, 800N. This represents an adequate safety margin relative to the required tripping force of 400N and limits the tripping force of 1550N in the downward direction, which would otherwise occur, to the stated 800N. 
     An exemplary design embodiment of this slipping connection  30  is illustrated in FIGS. 2 to  9 . FIG. 2 shows the individual parts and their positions for assembly, while FIG. 3 shows the fully assembled slipping connection  30 , which is preferably mounted below the rope connector  26  on the governor rope  18 . Mounting in a position directly under the rope connector  26  has the advantage that when the slipping connection  30  slips on the governor rope  18  there is an unlimited length available for slipping downward. 
     In the illustrated exemplary embodiment, the slipping connection  30  comprises a base plate  31 , two tension screws  33 , two compression springs  34 , two tightening stops  35  in the form of sleeves, and assembly screws  36 . Between the tension screws  33  and the compression springs  34  first washers  37  are laid, while between the installation screws  36  and the lever  9  of the tripper  7  second washers  38  are laid. On the base plate  31  there is a groove  40  to guide the governor rope  18 . It is self-evident that as an alternative, the groove  40  can also be formed on the pressure plate  32 , or on both the pressure plate  32  and the base plate  31 . 
     The exemplary embodiment of the slipping connection  30  illustrated in FIGS. 2 and 3 is described in detail below by reference to FIGS. 4 and 6. FIG. 4 shows a plan view of the slipping connection  30 , FIG. 5 a section along the line A—A in FIG. 4, and FIG. 6 a section along the line B—B in FIG.  4 . Elements which have already been described are given the same reference numbers to facilitate identification. 
     As can be seen from FIG. 5, the governor rope  18  is gripped between the base plate  31  and the pressure plate  32 . A threaded shaft  50  of each tension screw  33  is screwed into a thread  51  of the base plate  31 . By tightening the tension screws  33 , an associated compression spring  34 , which in the exemplary embodiment illustrated consists of several cup springs  53  arranged in a stack, is gripped between a screw head  52  of the associated tension screw  33 , or more precisely the washer  37 , and the pressure plate  32 . The compressive force exerted by the compression spring  34  depends on the pretension, and therefore on the depth to which the threaded shaft  50  is screwed into the baseplate  31 . The depth to which the tension screw  33  is screwed into the base plate  31  is limited by the tightening stop  35 . In the illustrated exemplary embodiment, each tightening stop  35  takes the form of a sleeve which surrounds the threaded shaft  50  of the respective tension screw  33 . Provided in the pressure plate  32  for each tension screw  33  and each tightening stop  35  is a drilled hole  54  through which both the threaded shaft  50  of the tension screw  33  and the sleeve-shape tightening stop  35  pass and project. The sleeve-shaped tightening stop  35  is gripped between the screw head  52 , or more precisely between the washer  37 , and the surface  55  of the base plate  31 . 
     In the illustrated exemplary embodiment, two tension screws  33  are provided. It is self-evident that within the scope of the invention only one single tension screw  33 , or three or more tension screws  33 , can be used. 
     As can be seen from FIG. 6, in the exemplary embodiment the pressure plate  32  has threaded holes  56  into which the assembly screws  36  can be screwed, so that the lever  9  of the tripper  7  is connected to the pressure plate  32 . As an alternative, it is self-evidently also possible to connect the lever  9  of the tripper  7  to the base plate  31 . 
     Due to the pretension of the compression springs  37  being defined, the force with which the governor rope  18  is gripped between the tension plate  32  and the base plate  31  is defined. By correspondingly dimensioning the length of the sleeve-shaped tightening stop  35 , the pretension of the compression springs  37  can be exactly and reproducibly determined. This permits an exact and reproducible determination of that force between the governor rope  18  and the tripper  7  at whose being exceeded the governor rope  18  slips on the slipping connection  30 . 
     The geometry of the groove  40  formed in the base plate  31  is described in greater detail below by reference to FIGS. 7,  8 , and  9 . FIG. 7 shows a plan view of the base plate  31 , FIG. 8 shows a side view of the base plate  31  illustrated in FIG. 7, and FIG. 9 shows a section along the line A—A in FIG.  8 . Elements which have already been described are given the same reference numbers to facilitate identification. 
     Visible in FIG. 7 is the groove  40  which runs longitudinally in the surface  55  of the base plate  31 , and which widens at each end  60  and  61  of the base plate  31  into an opening area  62  and  63  which will be described in more detail. Visible in FIG. 8, which shows a side view of the base plate  31  looking onto one of the two ends  60 , is the preferred triangular cross section of the groove  40 . Also visible is that in the opening area  62 , the groove  40  opens both in the direction of the surface  55  and also perpendicular to the surface  55  of the base plate  31 . 
     Visible in FIG. 9 is the section along the line A—A in FIG. 8 in which the preferred opening angle of 15° can be seen. The angle formed by the two flanks of the triangular groove  40  is preferably approximately 90°. 
     By means of the opening areas  62  and  63 , an abrupt kinking of the governor rope  18  is avoided, should the longitudinal axis  64  of the groove  40  not run exactly parallel to the direction of tension of the governor rope  18 . 
     As already mentioned, it is self-evident that the groove  40  can also be alternatively or additionally provided on the pressure plate  32 . 
     Within the scope of the invention it is also conceivable that not only the upper return pulley  19  or the lower return pulley  20  is brought to rest by the response of the overspeed governor  27 , but the governor rope  18  itself. For this purpose, the pulleys  19  and  20  can take the form of, for example, synchronized tangential pulleys instead of return pulleys. By means of the flexible slipping connection  30 , created according to the invention between the tripper  7  and the governor rope  18  instead of the rigid connection used hitherto, the slipping connection  30  which is connected via the tripper  7  and the braking device  6  to the elevator car  1  can slip both in the upward and in the downward direction after the tripping force required to trip the braking device  6  is exceeded. This increases the flexibility of the construction of the safety device. 
     Thus, while there have been shown and described and pointed out fundamental novel features of the present invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the present invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale but that they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.