CA1037623A - Hydraulic elevator drive system - Google Patents

Abstract

HYDRAULIC ELEVATOR DRIVE SYSTEM
ABSTRACT OF THE DISCLOSURE
A hydraulic elevator drive system utilizes an elevator car speed signal and a commanded velocity signal to provide an electrical error signal and controls the operation of a fluid control regulating the fluid flow between a hydraulic actuator which moves the car, a hydraulic pump and a fluid reservoir. The fluid control includes a combined check and lowering valve and a by-pass valve selectively operated by a common control element including a dynamically operated control piston responding to the error signal. Another check valve couples the fluid pump to the fluid control while a pair of manually preset control valves regulate the supply of fluid to the control piston for providing pre-established acceleration limitations to the elevator car.

Description

~376~3 BACKGROUND OF THE INVENTION
This invention relates to a hydraulic elevator drive system wherein fluid control means regulates the ~luid within a hydraulic actuator operatively controlling the movement of an elevator car.
Hydraulic elevator systems have commonly employed one or more valves for controlling the supply of fluid to and from a hydraulic actuator such as a jack or the like to thereby co~trol movement of an elevator car for transporting load, such as pas-sengers, for example, between a plurality of landings within abuilding structure. Such valving structure has been selectively operated in conjunction with a hydraulic pump for selectively supplying fluid under pressure to the hydraulic iack for raising the elevator car. Likewise, valving structure has been selective~y controlLed to vent the control fluid from the hydraulic jack for permitting the car to descend.
; The use of an integrated valve structure containing a ; plurality of control valves has been found to ~e highly desirable for interconnecting a fluid pump, a fluid reservoir and the actuating jack to control both upward and downward movements of an elevator car. One desirable system is shown in the U.S.
Patent No. 3,508,468, issued on April 28, 1970 and assigned to a common assignee herewith, which employs a by-pass valve functioning with a check valve for selectively controlling the flow of fluid from a pump to an actuating jack or cylinder while a bleed valve interconnects the actuating jack or cylinder with a reservoir for controlling downward movement of the car.
Another known system employs a first valve and vaLve operator to interconnect a fluid pump with an actuating jack which functions as a combined check and lowering valve while a second -1- ~k ~ 37623 valve and associated valve operator interconnects the pump with a reservoir, such as shown in the IJ.S~ Patent No. 2,737,197, issued on March 6, 1956. The control apparatus in the 2,737,197 patent provides variable upward control by varying the opening 5 of the by-pass valve and variable downward control by varying the check and lowering valve.
Some known systems have regulated the positioning oE
a lift platform or the like by generating an electrical position responsive signal which is compared with a commanded positioned 10 signal for generating a position error control signalg such as shown in the U.S. Patent No. 3,570,2~3, issued on March 16, 1971, which controls a hydraulic pump motor operation to vary the fluid flow to the hydraulic lift actuator.
The speed of a lift or elevator has been controlled 15 by regulating the amount of fluid flow to or from a hydraulic actua~or or jack through the selective positioning of one or more valves. One known system selectively positions and regulates the movement of a deck edge elevator on the side of a ship, such as shown in the U.S. Patent No. 2,409,198, issued on October 15, 20 1946, by selectively positioning a control valve in response to a mechanical differential responsive to the speed of an operating plunger and to the speed of an electric motor.
SIJMMARY OF THE INVENTION
This invention relates to a hydraulic elevator drive 25 system wherein fluid control means regulates the fluid within a hydraulic actuator operably controlling the movement of an elevator car One aspect of the invention is directed to the generation o~ an electrical speed error signal for operatively controlling 30 the passage of fluid from the hydraulic actuator an:l controlling ~ 0376'23 the downward movement of an elevator car in a highly regulated manner. In such construction and operation, an electrical speed command signal is compared with an electrical ~elocity signal responsive to the speed of the elevator car. The employment o~
an electrical speed error signal provides a highly regulated and - desirable control which includes responding means operable to a first condition permitting fluid to be maintained by the hydraulic actuator and a second condition permitting the venting of fluid from the hydraulic actuator. The responding means desirably 10 varies the venting of fluid flow from the hydraulic actuator in response to the varying electrical speed error signal forp~GVi~
continuous and accurate speed control upon a downwardly traveling car. The responding means also functions with the electrical speed error signal and provides an accelexation limitation upon the downwardly traveling car.
The invention also includes a highly desirable con-struction for controlling the fluid flow between a fluid pump and the hydraulic actuator in response to an electrical speed error signal such as provided by the comparison of an electrical ~o speed command signal and an electrical velocity signal varying according to the speed of the car when traveling in an upward direction, Th,e electrical speed error signal operatively controls the resp~nding means and provides a first - ~' condition permitting fluid to be maintained by the hydraulic actuator and a second condition permitting fluid flow from the pump to the hydraulic actuator. The responding means alsopr~id~s ~ -means for operatively varying the fluid flow from the pump to the hydraul~c actuator in response to a varying electrical speed error signal. Such responding means also includes means func-tioning with the speed error signal and provides an accelerationlimitation upon the car.

The responding means also functions with the speed error signal in a highly desirable manner to provide a third condition for venting fluid from the hydraulic actuator and moving the car in a downward directionO
The fluid control means regulating the -Eluid within the hydraulic actuator provides a highly novel first and second valve means which are select;vely operable by a control member having a first position operativeLy maintaining fluid within the hydraulic actuator and a second position operatively venting fluid from the hydraulic actuator by the simultaneous opening of the first and second valve means.
In a highly desirable construction, a fluid pressure control chamber provides a first control force upon the control member which, in turn, also experiences a second control force.
The fluid pressure within the pressure chamber is selectively controlled for positioning the control member between the -first and second positions and the selective opening of the first and second valve means. The pressure controlling means utilizes selectively operable vent means for regulating fluid pressure within the pressure chamber. In a highly desirable operation, the venting of fluid from the pressure chamber is selectively varied in response to an error signal derived in response to a movement command signal and a car operational responsive signal, In a preferred form of the invention, a pair of pressure chambers are utilized to provide the first and second control forces to selectively position the control member. The employment of a pair of pressure control chambers provides a highly desirable uniform control for effecting both upward and downward movement and for maintaining the car in a stopped position. With such construction, the control member can also assume a third position permitting fluid flow from the pump to the hydraulic actuator.
The pressure controlling means provides vent means which vents fluid from the first pressure chamber for establishing the second position for downward elevator travel and also vents fluid from the second pressure chamber for establishing the third position for upward car movement, The variable venting of the pair of pressure chambers thus operatively controls the movement of the control member in response to the error signal derived from a movemen~ command signal and an operational responsive signal for establishing a highly desirable closed loop control in'iboth the up and down directions of travel. The pair of pressure chambers may 3 lso be selectively vented with car travel in a first direction to provide accurate speed control as dictated by the command signal, A highly desirable acceleration limitation control operates in conjunction with the pressura chamber and the operation of the control member. Such acceleration limitation control includes means which selectively varies the rate of fluid flow to the pressure chamber thereby lim;ting the rate of response of the control member and the movement of the elevator car. In a pre-ferred construction, independently adjustable first and second valves interconnect a fluid source to.the pressure control chambers ; for independently establishing first and second preselected acceleration li~itations for the up and down directions, respectively.
The utilization of first and second valve means selectively operable by a control member provides a highly desirable up and down control because the control member can assume a first position to operatively maintain fluid within the hydraulic actuator, a second position for operatively venting fluid from the hydraulic actuator by the simultaneous opening of the first and second valve ~ 0376Z3means, and a third position permitting fluid flow from a pump to the hydraulic actuator. The first position provided by the control member can operatively function with the actuation of the pump so that pumped fluid supplied to the fluid control means is operatively vented therefrom and the elevator car is maintained in a stationary condition. Such sequence of operation avoids the transient conditions otherwise frequently experienced upon initiation of pump actuation thereby providing greater riding com-Eort to passengers.
In a preferred embodiment of the invention, the fluid control means includes a control structure providing a chamber having a first port operatively connected to the hydraulic actuator, a second port operatively connected to the pump, and a third port operatively connected to vent fluid such as to a storage tank, for example. A first normally closed valve is positioned within the second port and operates in response to the operation of the fluid pump to permit fluid entry into the chamber. A second valve is positioned with the first port which is normally biased to a closed condition and is selectively oper-ated in response to an increase of pressure within the chamber to permit fluid flow to the hydraulic actuator. A third valve is positioned within the third port and is selectively operable between open and closed positions for regulating the venting of fluid from the chamber.
A valve operator selectively operates the second and third valves between open and closed positions and includes a piston connected through a valve stem to the third valve. First and second piston chamber portions are spaced on opposite sides of the piston and are supplied fluid under pressure such as through a conduit connected to the output of the first port. The - , . . .

~376~Z3 valve stem of the valve operator includes a control chamber having a first control port communicating with the first chamber portion and a second control port communicating with the second chamber portion while a third control port communicates with the vent 5 provided by the third port. A control element is movably disposed within the control chamber and includes a control channel having a first end operatively communicating with the vent at the third port and a second end selectively communicating with the first and second control ports.
In operation, the control element assumes a first position to close the first and second control ports for maintaining the valve stem at a first position which operatively opens the thi~d valve and permits the second valve to close and hold the car at a stationary condition. The valve element is selectively moved to a second position and closes the first control port and communicates the second control port with the second end of the control channel for opexatively moving the valve stem to a second position to close the third valve so that the operation of the pump will open the first and second valves to move the car in an upward direction. The control element is selectively moved to a third position and closes the second control port and communicates the third control port with the second end of the control channel for operatively moving the valve stem to a third position to open the second and third valves to move the car in a downward direction.
The control element is desirably positioned by a motor operated cam to provide a variable control which is capable of continually varying the movement of the valve operator. Such variable control is provided by the electrically controlled positioning of the cam output in response to an electrical speed error signal responsive to a speed command signal and a sensed car speed signal for providing continuous and desirable speed control of the hydraulic system.
The invention thus provides a highly desirable electrical and hydraulic control to selectively move an elevator car with riding comfort to passengers and efficient service by the desirable regulation of speed control and the limitations upon acceleration~
Such objectives are readily accomplished through the provision of a highly responsive fluid valving structure which may be readily constructed for compact installation.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings furnished herewith illustrate the best mode presently contemplated by the inventor and clearly discloses the above advantages and features as well as others which will be readily understood from the detailed description thereof.
In the drawings:
Fig. 1 is a diagrammatic view of a hydraulic elevator system illustrating an electrical control in block diagrammatic form operating a hydraulic control for controlling the movement of an elevator car; and Fig. 2 is a front sectionalized view of a portion of the hydraulic control of Fig. 1.
DESCRIPTION OF THE PREFERRED I~LUSTRATED EMBODIMENT
Fig. 1 illustrates a hydraulic elevator drive system 1 wherein an elevator car 2 is movably mounted to a plurality of guide rails 3 for transporting a load between a plurality of landings in a building structure (not shown). The car 2 is pro-vided with one or more access openings in which selectivel~ operable doors are mounted for permitting load transfer at a selected landing which is well known and understood in the art and further detailed description thereof is deemed unnecessary to a full and clear understanding of the invention.

~3q6~3 The car 2 is mounted upon a hydraulic actuator or iack 4 including a plunger 5 mounted for vertical reciprocating movement within a cylinder 6. A conduit 7 bi-directionallY conducts a hydraulic actuating fluid between the cylinder 6 and a port 8 5 provided by a fluid control 9, A reservoir or storage tank 10 contains hydraulic actuating fluid 11 consisting of oil or any other appropriate hydraulic fluid. While reservoir 10 is shown holding the hydraulic fluid 11 under atmospheric condi~ions, it is understood that fluid 11 could be stored in a closed contaîner 10 and maintained under pre-established conditions concerning pressure and temperature for appropriate operation. A hydraulic pump 12 may be of a constant displacement type and is connected to the hydraulic fluid 11 within reservoir 10 through a conduit 13. Pump 12 is also connected through a conduit 14 for supplying hydraulic fluid to a port 15 within the fluid control 9. A port 16, also within the fluid control 9, is connected to the reservoir 10 through a conduit 17.
A supervisory contxol 18 is connected through an electrical lead 19 to selectively operate pump 12 to supply hydraulic ~luid to the port 15. The supervisory control 18 also selectively provides an electrical speed command signal which is supplied to a comparitor circuit 20 through an electrical lead 21. The com-manded or desired speed signal at lead 21 is summated and/ox compared within comparitor 20 with an electrical speed signal supplied from a tachometer 22 associated with the elevator car 2 through a lead 23, The tachometer 22 is selected from any one of well known commercial analog or digital velocity sensing apparatus which is capable of supplying a velocity dependent signal to the comparitor 20. The comparitor 20, in turn, functions to provide a speed error signal to a control and regulating circuit 24 through 371~Z3 an electrical lead 25, The control and regulating circuit 24, in turn, operates in response to the speed error signal and supplies a motor operating control signal throu~h a lead 26 to control the operation of an electrical motor 27. An output shaft 28 of 5 motor ~7 is connected to an eccentric cam 29 having an outer con-trol surface 30 which slidably engages a movable control element 31 provided by the fluid control 9. The motive unit 27 is shown operating as a stepper motor while the control and regulating circuit 24 responds to the speed error signal and supplies controlled stepper pulses of a pre-selected polarity. A logic element 24a may constitute a forward logic circuit and a reverse logic circuit which selectively respond to the error signal at lead 25 to supply forward and reverse direction control pulses to the motor 27. The cam element 29 thus selectively rotates in either a Eorward or reverse direction by prescribed-amounts as dictated by the speed error signal appearing on the lead 25.
The fluid control 9 is more fully shown in Fig. 2 and includes a valve body 32 which is illustrated as a unitary structure but which may optionally be constructed of separate parts which are fixedly interconnected to form the body structure 32.
The structure 32 includes an upper cavity or chamber 33 which freely communicates with port 8 and an intermediate cavity or chamber 34 which communicates with the upper chamber 33 through a valve seat 35. A poppet type check valve 36 is mounted for vertical movement within the upper chamber 33 and includes a valve head 37 formed to selectively seal with valve seat 35 and includes a valve stem 38 which is slidably disposed within an annular opening 39 provided by a protruding annular guide flange 40 pro-truding from the upper portion of the chamber 33. A biasing spring 41 surrounds the annular guide protrusion 40 and interconnects ~ )376~3 the wall of chamber 33 with the valve head 37 for biasing the che~ valve 36 toward a normally closed condition to seal the valve head 37 with seat 35.
: The intermediate chamber 34 also communicates with the 5 port 15 through a poppet type check valve 42 which operates to ' selectively seal a valve seat 43 located within the port lS. The -check valve 42 includes a valve head 44 and an annular valve stem 45 which is movably mounted within an annular opening 46 provided by a guide projection 47 protruding from the wall of port 15. A
lO biasing spring 48 is connected to an annular stop 49 connected to~an outer end of the valve stem 45 and is further connected to ~: the guide projection 47. The spring 48 operates to bias the valve head 44 to a normally closed condition to seal with the valve seat 43 for closing the port 15.
15A lower chamber 50 is interconnected with the intermediate chamber 34 through a valve seat 51. The lower chamber 50 also communicates with the port 16. A vertically movable valve head 52 operates to selectively seal with the valve seat 51 to provide a by-pass valve 53. The valve head 52 is fixedly connected to a valve stem 54 and to an outer stem projection 55 and is selectively operated by a valve operator 56. A piston 57 of the valve operator 56 is fixedly connected to the valve stem 54 and is positioned within a piston chamber 58. The piston 57 is annularly formed tb movably engage the annular side walls 59 while an O~ring seal 60 prevents fluid leakage between an upper chamber portion 61 and a lower chamber portion 62.
Hydraulic fluid within the upper chamber 33 is supplied through a channel 63 formed within the wall of the body structure 32 to the upper chamber portion 61 through an inlet passageway 64 and also to the lower chamber portion 62 through an inlet ~ L0376~3 passageway 65. Fluid flow through the passageways 6~1 and 65 is varied and controlled by the selective adjustment of a pair of needle valves 66 and 67, respectively. In operation, the accu-mulated pressure within the upper chamber 61 operates upon an 5 upper surface 68 of the piston 57 wh;le the fluid pressure within the lower chamber 62 operates upon a lower surface 69.
A portion 70 of the valve stem 54 contains an annular control chamber 71 which is connected to communicate with the lower chamber 50 through a T-shaped cont,rol port 72 and further 10 communicates with the upper chamber portion 61 through a control port 73 and with the lower chamber portion 62 through a control port 74.
The control element 31 includes an annular control stem 75 which is slidably movable within the controL chamber 71 15 and carries an 0-ring seal 76 for preventing,fluid leakage between the control chamber 71 and the exterior of the fluid control 9.
The stem 75 of the control element 31 contains a control channe'L
77 having an outer end 78 communicating with the control chamber 71 and a T-shaped outer end 79 communicating with an annular 20 recess 80 formed between the control stem 75 and the wall of the control chamber 71. An outer flange 81 is connected to the stem 75 and mounts a biasin~ spring 82,which, in turn, is connected to a lower surface 83 of the body structure 32, The outer flange 81 also provides a cam following surface 84 which engages the cam 25 surface 30 of cam 29 as illustrated in Fig. 1.
The shown position of the elements in Fig. 2 illustrates a condition where elevator car 2 is stationary such as at a landing for permitting passenger transfer. The hydraulic fluid within the cylinder 6 which supports the car 2 communicates with 30 the upper chamber 33 through the port 8 and conduit 7 and functions with the biasing spring 41 to close the poppet valve 36 with valve head 37 engaging valve seat 35. The closure of check va Lve 36 ~ 0376;~3 maintains the hydraulic fluid within cylinder 6 and holds car 2 at a stationary postion.
The registration of demand for service for the elevator is~sensed by the supervisory control 18 to control the movement of 5 car 2. As an example! the registration of a hall call or of a car call by a passenger entering into the car 2 and requiring upward movement initiates a door closure and further supplies a pump start-up signal to lead 19 by closing a switch 85. ~ydraulic fluid -from reservoir 10 is thereafter supplied by pump 12 to the port 15 through conduits 13 and 14. The increase of pressure occurring at port 15 because of the pump operation opens the poppet valve 42 permitting hydraulic fluid to flow into the intermediate chamber 34. The valve 53, however, is maintained at an opened position as shown so that fluid is vented through the chamber 50 and port 16 to be returned to the reservoir 10.
Upward movement is established by supervisory control 18 when a speed command signal is supplied at lead 21 having a first polarity and a pre-determined magnitude for commanding a pre-deter-mined velocity ~or the elevator car 2. Because car 2 is initially stationary, a zero magnitude velocity signal exists on lead.23 so that the error signal on lead 25 is dominated by the command signal on lead 21. Such a substantial error signal operates the stepper motor to rotate the cam surface 30 in a counter-clockwise . direction to allow the control element 31 to vertically descend by the operation of the biasing spring 82. On the other hand, the command signal on lead 21 can be varied by predetermined increments or in response to a continuous electrical signal pattern thereby gradually operating the stepper motor 27 b~ the continuously varying error signal.
The descent of stem 75 of the control element 31 permits the annular opening 80 to communicate with the control port 74 and vent the fluid within the lower chamber portion 62 to the lower ~0;~7623 chamber 50 through the control port 74, annular chamber 80, control channel 77, control chamber 71 and the control port 72, The descending control stem 75 also maintains the control port 73 closed. As a result, the descent of control element 31 effectively decreases the pressure or force exerted against the piston side 69 so that piston 57 becomes unbalanced and is forced to move down-wardly carrying the valve stem 54 and the by-pass ~alve head 52 with it. The amount of downward movement of control element 31 establishes the rate of fluid venting from chamber portion 62 by 10 varying the size of the communicating opening between control port 74 and annular chamber 80.
The downward movement of the control element-31 thus regulate and controlg the downward movement o~ piston 57 which effectively operates as a force multiplier to vary the closure of the by-pass valve 53. Because of the substantial error signal and the operation of the p,ump 12, the by-pass valve is initially substantially closed so that fluid entering through poppet valve 42 increases the pressure within intermediate chamber 34 and opens poppet valve 36 so that hydraulic fluid is supplied to the hydraulic actuator 4 to move the car 2 in an upward direction. The maximum velocity attainable by car 2 when traveling in an upward direction is established by the selective positioning of the by-pass valve 53, the pumping capabilities of pump 12, and the physical limitations of the system.
The fluid control 9 provides a highly desirable feature when the system is conditioned to initiate operation in an upward direction by permitting fluid flow from the pump 12 to the reservoir 10 for a short period of time before the by-pass ~alve 53 starts to close. Such a sequence allows the fluid pump 12 to ; 30 operate to capacity before being required to direct fluid to the ~0376Z3 hydraulic actuator 4 which reduces the transient conditions which may otherwise be subjected upon the pump 12.
As car 2 travels upwardly at an increasing speed, a speed signal is supplied from tachometer 22 to the comparitor 20 5 and reduces the error signal at lead 25. As the error varies, the cam surface 30 is selectively rotated in a clockwise direction to gradually raise the control element 31.
The corresponding upward movement of contro:L stem 75 gradually decreases the opening between control port 74 and annular.
10 chamber 80 so that the pressure within chamber portion 62 gradualLy increases while control port 73 remains closed. The increase of pressure within chamber portion 62 thus operatively moves piston S7 upwardly in a gradual manner to gradually open the by-pass valve 53.
The re~ulated opening of the by-pass valve 53 varies the pressure of the ~luid within chamber 34~and regulates the opening of poppet valve 36 and the fluid flow therethrough. As the car speed reaches the desired speed of the command signal, a zero or null error signal will appear at lead 25 which effectively positions the cam surface 30 to correspondingly position the control element 31 substantially as shown in Fig. 2 whereby both control ports 73 and 74 are closed by the control stem 75. In such a condition, the by-pass valve 53 is held in a partially opened position to regulate the pressure within the intermediate chamber 34 to maintain the check valve 36 at a proper open position to maintain the commanded velocity for the car 2 as dictated by the command signal at lead 21.
Should the car speed when traveling in an upward direction exceed the commanded speed, the output of comparitor 20 provides an error signal which rotates the cam surface 30 in a counter-clockwise direction to correspondingly raise the control element 31. The control stem 75 correspondingly rises to communicate the control port 73 with the annular chamber 80 to vent fluid from the chamber portion 61 to the lower chamber 50 through the 5 control channel 77. The resulting decreased pressure within chamber portion 61 causes piston 57 to rise thereby increasing the opening within the by-pass valve 53 to corxespondingly decrease the pressure within intermediate chamber 34. Thus greater quantities of fluid are by-passed by the valve 53 to decrease the 10 upward speed imparted to car 20 It is therefore evident that the closed loop control p~ovided by the drive system 1 continually monitors the operation o~ the elevator car 2 to maintain an exacting control which is self-regulating in accordance with the commanded velocity provided by the supervisory control 18.
When it is desired to stop the car 2, the velocity command signal at lead 21 is decreased to a zero magnitude thus dictating zero velocity so that the speed error signal at lead 25 is dominated by the speed signal at lead 23. Such a large error signal rotates the cam surface 30 in the appropriate direction to open the by-pass valve 53 while the switch 85 opens to de-activate the pump motor 12. The poppet valve 42 thus closes with pump 12 de-activated to seal the port 15 while the opened by-pass valve 53 creates a substantial pressure drop within intermediate chamber 34 so that the check valve 36 rapidly closes and main-tains car 2 in a stationary position. The stopping of car 2 thus results in a zero speed signal at lead 23 so that the error signal at 25 decreases to zero at which point the cam surface 30 positions the control element 31 substantially as shown in Fig. 2.
When service demand required that the elevator car 2 travel in a downward direction, the supervisory control maintains ~ L~376~3 switch 85 open and thus likewise maintains pump 12 de-activated so that poppet valve 42 remainslclosed to seal port 15. Downward movement is initiated by a velocity command signal being supplied to the comparitor 20 through lead 21, which, when compared with a zero speed signal on lead 23, provides a substantial error signal on lead 25 to rotate the cam surface 30 in a clockwise direction to correspondingly raise the control element 31.
Because of the developed error signal, the rotation of cam surface 30 raises control element 31 and communicates the control 10 port 73 with the annular chamber 80. Fluid is thus vented from the chamber portion 61 to the lower chamber 50 through the control channel 77, the control chamber 71 and the control port 72. The pressure within chamber portion 61 rapidly decreases to corres-pondingly permit rapid upward movement of piston 57. The valve stem 54 and the upper stem portion 55 correspondingly rapidly raise so that the upper stem portion 55 engages the valve head 37 and physically opens the poppet valve 36 to a substantially open position. The upward movement of the valve stem 54 also opens the by-pass valve 53 so that fluid drains from the hydraulic actuator 4 to the reservoir 10 through the conduit 7, port 8, upper chamber 33, intermediate chamber 34, lower chamber 50, port 16 and conduit 17.
As the downward traveling car increases in speed, the speed signal on lead 23 increases to correspondingly decrease the error signal at 25 which gradually rotates the cam surface 30 in a counter-clockwise direction. Such decreasing error signal thus gradually lowers the control element 31 and the venting of fluid through the control port 73 is gradually decreased to correspond-ingly increase the pressure within control chamber 61. Thus, as the vehicle speed increases in a downward direction, the control `` 1037623 piston 57 gradually descends to gradually close the poppet valve 36 and decrease the fluid flow from the hydraulic actuator 4.
When the downward speed reaches the commanded speed on lead 21, the errox signal.at 25 goes to zero and the poppet valve 36 is held at a desired open position for maintaining the desired velocity for car 2, The downward travellng velocity of .
the system is self-regulating and variances in speed are reflected in the error signal which appropriately positions the cam surface 30 and hence the control element 31 to appropriately control the opening of the poppet valve 36.
When it is desired to stop a downwardly traveling car, the commanded velocity signal on lead 21 is decreased to zero so that the vehicle velocity signal on lead 23 dominates the error signal to rotate the cam surface 30 in a counter-cloclcwise direc-tion. The resulting downward movement of the control element 31decreases the pressure within chamber portion 62 and requires the piston 57 to travel downwardly to a position permitting the poppet valve 36 to close and hold the car stationary.
The response of the system can be readily adjusted by varying the needle valves 66 and 67 and regulating the rate at which pressure changes are permitted to occur within the chamber portions 61 and 62. The manual pre-selected setting of needle valve 66 establishes a predetermined maximum acceleration limitation for downward movement by limiting the rate of pressure change within chamber portion 61. Such pressure rate limitation cor-respondingly limits the rate of opening movement of the poppet valve 36. The manual pre-selected setting of the needle valve 67 likewise establishes a predetermined maximum acceleration limita-tion for upward movement by limiting the rate of pressure change within the chamber portion 62 and thus the rate of closing move-ment of the by-pass valve 53.

3L~37~Z3 While the pump 12 is described as a constant displacemen~
type, a variable displacement type pump could also be employed with the invention to provide an added control feature if desired.
While the supervisory control 18 is only partially illustrated for brevity and could constitute a manual control, it should be understood that a completely automated supervisory control may be desirable which senses car and hall calls to auto-matically provide a plurality of control signals for operating the system including the provision of the pump start signal on lead 19 and the commanded velocity signal on lead 21. It is further noted that the commanded velocity signal on lead 21 could be a constant magnitude signal or a velocity pattern signal which continuously varies. Such a continuously varying speed command signal could also provide pre-selected or predetermined velocity, acceleration and rate of change of acceleration limitations for generating a highly desirabLe error signal. While the control " and regulating circuit 24 is shown in block form as a pulse source coupled through a logic circuit to selectively supply forward and reverse pulses to the stepper motor 27, it is understood that other circuit arrangements could also be provided for responding to the error signal and operating the control element 31.
The invention thus provides a highly desirable hydraulic ! elevator drive system which is accurately controlled to provide riding comfort and efficient elevator service.
This is a division o~ Canadian Application Serial No. 246,556 ~iled February 25, 1976.

Claims (9)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:
I claim:

1. A hydraulic elevator drive system wherein a fluid pump is operatively connected through fluid control means to a hydraulic actuator operatively controlling the movement of an elevator car, wherein said fluid control means comprises means providing an electrical speed command signal, means sensing the speed of said car and providing an electrical velocity signal, means responding to said command and velocity signals and providing an electrical error signal, and means responding to said electrical error signal and controlling the passage of fluid to said hydraulic actuator.

2. The elevator drive system of claim 1, wherein said error responding means provides a first condition permitting fluid to be retained by said hydraulic actuator and a second condition permitting fluid flow from said pump to said hydraulic actuator in response to said error signal.

3. The elevator drive system of claim 2, wherein said error responding means. provides a third condition permitting the venting of fluid from said hydraulic actuator.

4. The elevator drive system of claim 1, wherein said error responding means includes means operatively varying the fluid flow from said pump to said hydraulic actuator in response to said electrical error signal.

5. The elevator drive system of claim 1, wherein said responding means includes means operatively providing an acceleration limitation upon said car.

6. A hydraulic elevator drive system wherein fluid control means regulates the fluid within a hydraulic actuator operatively controlling the movement of an elevator car, wherein said fluid control means comprises means providing an electrical speed command signal, means sensing the speed of said car and providing an electrical velocity signal, means responding to said command and velocity signals and providing an electrical error signal, and means responding to said electrical error signal and controlling the passage of fluid from said hydraulic actuator.

7. The elevator drive system of claim 6, wherein said error responding means provides a first condition permitting fluid to be retained by said hydraulic actuator and a second condition permitting the venting of fluid from said hydraulic actuator.

8. The elevator drive system of claim 6 , wherein said error responding means includes means operatively varying the venting of fluid flow from said hydraulic actuator in response to said error signal.

9. The elevator drive system of claim 6, wherein said error responding means includes means operatively providing an acceleration limitation upon said car.