Abstract:
An elevator system that includes a cab unit is connected by a hoisting system to a counterweight unit so that both units move at the same speed over vertical rails. A single governor rope is trained in an endless loop between an upper drive sheave and a lower tensioning sheave so that a pair of vertically disposed parallel runs of rope pass between the units. A bidirectional governor brake is arranged to retard the ropes speed when an over speed condition is encountered. Safeties associated with both units are connected to the opposite runs of the governor rope and are tripped when the governor rope is braked.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to elevator safety systems, and in particular to a governor for sensing an over speed condition in an elevator system. 
     BACKGROUND OF THE INVENTION 
     A typical traction elevator system used in buildings includes a cab that is supported upon a hoist rope. The hoist rope, in turn, is passed over a motor driven drive sheave and the other end of the rope is connected to a counterweight. As the drive sheave is turned, the cab unit and the counterweight unit move vertically along guide rails in opposite directions. The counterweight generally has a weight equal to that of the cab unit plus some additional weight which is a percentage of the cab&#39;s rated load capacity. 
     Safety systems are installed to prevent potentially dangerous over speeding of the cab. To this end, safety units, generally referred to as “safeties”, are provided to bring the cab to a controlled halt any time an over speed condition is detected. Safeties generally employ clamps, wedges, rollers or combinations thereof that apply a holding force against the guide rails of the cab unit and/or the counterweight unit to bring the cab to a rapid, safe halt. 
     In most cases, a governor is used to sense the occurrence of an over speed condition and take some type of responsive action to activate the safeties on both the cab unit and the counterweight unit. As shown in FIG. 1, the governor unit  10  that is in wide use today, includes a pair of governor ropes  11 ,  13 , one of which is connected to the elevator cab  12  and the other of which is attached to the counterweight unit  14 . Each governor rope passes over an upper sheave  15 ,  16  and a lower sheave  17 , 18  to create a pair of endless loops. Weights  19  and  10  are suspended from the lower sheaves which serve to tension the associated governor rope and maintain the opposed runs of each governor rope in parallel alignment. The governor ropes are connected in a well known manner with safeties  22  associated with each of the units. A governor brake  24  is associated with each governor unit which is adapted to engage the governor rope when the speed of the rope exceeds a given velocity. An over speed condition may be detected by flyweights or electrical sensors which activate the governor brake slowing the governor rope down. This, in turn, trips the unit safeties bringing the elevator to a halt. 
     This type of prior art governor works extremely well in practice, as evidenced by the safety record of traction elevators. However, as should be evident from the disclosure above, the system requires a separate governor rope for both the cab unit and the counterweight unit. This, in turn, is space consuming, increases installation and maintenance time, and increases the overall cost of the system. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to improve traction elevator systems. 
     It is a further object of the present invention to improve governors employed in elevator systems. 
     A still further object of the present invention is to reduce the number of component needed in as elevator governor. 
     Another object of the present invention is to provide an elevator governor that requires only a single governor rope for sensing an over speed condition and activating the safeties on both the cab unit and counter weight unit of the system. 
     Yet another object of the present invention is to reduce the amount of space an elevator governor requires within a hoist way. 
     These and other objects of the invention are attained in an elevator system having a cab unit that is movably suspended between a first pair of guide rails that is connected by a hoist rope to a counter weight unit that is movably suspended between a second pair of guide rails. Safeties are mounted upon both units which are adapted to brake against the guide rails when an over speed condition is detected. A single governor rope is trained in an endless loop over an upper sheave and a lower tensioning sheave so that two parallel vertically disposed runs of rope pass between the two units. The rope is attached to one of the units so that it travels of the same speed as the units. A bidirectional governor brake is operatively associated with the upper sheave of the governor rope for applying a braking force to the rope in the event an over speed condition is encountered. Safety actuators in the form of lever arms are connected to the governor rope which are arranged to trip the safeties when the governor rope is braked to bring the elevator cab to a rapid and safe halt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a further understanding of these and objects of the invention, reference will be made to the following detailed description of the invention which is to be read in connection with the accompanying drawing, wherein: 
     FIG. 1 is a schematic representation of a typical elevator system found in the prior art employing two separate governor units; 
     FIG. 2 is a schematic drawing showing an elevator system embodying the teachings of the present invention; 
     FIG. 3 is a partial view of a link used to attach the governor rope of the present invention to the safeties of the counter weight unit; 
     FIG. 4 is a schematic drawing of an elevator system containing a second embodiment of the present invention; 
     FIG. 5 is an enlarged front elevation of a governor sheave that is capable of braking the governor rope when the rope speed in either direction exceeds a given velocity; and 
     FIG. 6 is a further enlarged partial side view with portions broken away showing the bidirectional sheave illustrated in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 2 and 3, there is illustrated an elevator system, generally referenced  30 , that embodies the teachings of the present invention. The system includes a cab unit  32  that is suspended within the hoist way between a pair of spaced apart vertically disposed guide rails  33  and  34 . A counterweight unit  35  is similarly mounted between a second pair of guide rails  37  and  38 . One end of a hoist rope  40  is attached to the cab  41  and is passed over a drive sheave  42  and an idler pulley  43  with the other end of the rope being connected to the weights  45  of the counterweight unit. The drive sheave is connected to an electrical motor (not shown) which is capable of lifting the cab at relatively high speeds. 
     As will be explained in greater detail below, each unit is equipped with a pair of safeties  50  and  51  which are adapted to engage the associated rails when the governor  50  sent over speed condition. As is well known in the art, the safeties are designed to bring the cab to a rapid, safe stop. 
     Unlike the more conventional governor systems, the present governor employs a single drop  51 . The governor rope is trained over an upper governor sheave  52  and a lower ion sheave  53  to establish two vertically disposed parallel runs  55 ,  56  of rope that pass between the cab unit and the counterweight unit. A weight  58  may be hung from the tension sheave to keep the runs in parallel alignment or alternatively the tension sheave may be held in a desired position by means of a suitable mounting bracket. 
     A bidirectional upper governor sheave employing a brake of the type described in U.S. Pat. No. 5,617,933 to Ericson is employed in the practice of the present invention. However, it should be clear to one skilled in the art that any suitable bi-directional brake can be employed in the practice of the present invention. The disclosure in the Ericson patent is incorporated herein by reference. The upper sheave  52  is rotatably supported in frame  55  having a pair of spaced apart vertically disposed side wall  56  and  57  that are integral with the base  58 . The base is secured to the floor  59  of the machine room by any suitable means. A U-shaped bracket  61  is rotatably mounted inside the frame in as inverted position. The bracket includes a pair of opposed arms  63  and  64  that are conjoined by a cross member  65 . The axis of rotation  67  of the bracket is vertically aligned with the axis of rotation  68  of the sheave and is raised above the axis of rotation of the sheave within the frame. 
     A friction brake assembly  70  is secured in the midsection of the cross member over the sheave groove  71 . The brake assembly is equipped with a friction brake pad  73  that is arranged to move into friction contact with governor rope when the bracket is rotated out of its vertical home position in either a clockwise or counter clockwise direction. The frame is held in the vertical home position by an urged pair of detent pins  74 . Each pin has a conical shaped head  75  at its distal end that is wedged into a complimentary axially aligned groove formed in the bracket by a biasing spring  76 . 
     Flyweights  78  are rotatably mounted on one side wall  79  of the sheave  52 . When the sheave reaches a given angular velocity indicative of an over speed condition, the flyweights extend outwardly beyond the rim of the sheave and contact a arm  80  attached to the frame with sufficient force to move the detent pin back against the spring and thus release the bracket. As best illustrated in FIG. 6, the bracket car swing in either direction depending on the direction of rotation of the sheave whereupon the brake moves into friction drawing contact with the governor rope to slow down the movement of the governor. Accordingly, the sheave, through the flyweights has the ability to sense an over speed condition in either direction and, in response thereto, brake the governor regardless of the direction of rotation of the sheave. 
     Referring once again to FIG. 2 the safeties  50  and  51  associated with the cab  41  are attached to one run  56  of the governor rope by means of an operating lever arm  85  that is associated with a trip linkage (not shown) of well known design. When the governor rope is slowed down a speed difference is produced between the cab and the governor rope. This in turn, causes the lever arm to be displaced thereby activating the safeties on the cab. The lever arm  87  associated with the safeties on the counterweight unit is similarly displaced at this time to activate the safeties associated with counterweight unit bringing the cab to a rapid and safe halt. 
     As illustrated in FIG. 3 a link  88  is tied into run  55  of the governor rope and is arrange to engage the lever arm  87  associated with the counterweight unit. The link contains an elongated slotted hole  89  that is coaxially aligned with the governor rope. The distal end of lever arm  87  is bent to form a 90° angle with the body of the arm and the distal end of the arm is passed through the slotted hole in the link. This, in turn, establishes a predetermined amount of lost motion between the rope and the lever arm. This lost motion accommodates for any elongation in the rope that might otherwise adversely effect the operation of the governor. The link further serves to keep tension on the generator rope under all conditions. 
     A further embodiment of the present invention is presented in FIG. 4 wherein like reference numerals are used to identify like components previously shown in FIG.  2 . Here again the cab unit  32  and the counterweight unit  35 , as movably suspended in a hoist way between guide rails. The two units are connected by means of a hoist rope  40  which is trained over drive sheave  42  and idler pulley  43  so that the two units move in opposite directions at the same speed. The safeties  50  and  51  of each unit are connected to the governor rope  51  by lever arms  85  and  87  which are adapted to trip the safeties in the event an overspeed condition is detected. 
     Here again the upper governor sheave  52  is equipped with a bi-direction brake for slowing down the speed of the governor rope in case of as over speed in either direction. 
     In this embodiment of the invention, an idler pulley  90  is mounted is the machine room adjacent to upper governor sheave  52 . A similar lower idler pulley  91  is mounted adjacent the lower sheave  53  in vertical alignment with the upper idler pulley so that the two opposed runs of the governor rope are mounted in parallel alignment. As can be seen, through use of this idler pulley arrangement, the horizontal distance (d) between the governor rope runs can be adjusted to accommodate for changes in the spacing between the two units. In this way, the present single rope governor can be easily and inexpensively adapted to accommodate any number of existing and new elevator systems. 
     While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.