A two-speed up control system for a hydraulic elevator

Abstract: An up leveling control system for small elevators that uses an adjuster (30) having a small orifice (33) coordinating with an up speed metering edge (19) of a separate spool (17) in the form of a taper to meter the rate of flow of pilot oil from a bypass chamber (7) to control the position of a bypass valve (2) and thereby regulate the volume of oil flow proportionately to the elevator cylinder (50) and to the pump reservoir (51).

Description: The invention relates to a control system for a hydraulic elevator having two up speeds comprising a pump; a supply of oil under pressure provided by the pump; a return including a reservoir tank for such oil; an elevator cylinder for supporting an elevator; a check valve assembly connecting the pump supply with the elevator cylinder and including a check valve provided with a check valve stem, a pump pressure chamber and a check valve chamber; a bypass valve assembly connected across the pump, the supply and the return for bypassing the check valve, having a bypass chamber for receiving hydraulic fluid under pressure from the pump, and a bypass valve which is biased in an open position by a spring; a fluid restrictor for displacing the bypass valve to a closed position against the force of the spring; means including a solenoid valve for connecting the bypass chambers with the return; an up leveling speed regulator assembly for controlling the up leveling speed of the elevator including an up speed adjuster with an orifice that coordinates with a metering edge in the form of a taper on a separate up speed spool to proportionately regulate the volume of oil flow to the elevator cylinder and the reservoir tank,; a bypass pressure chamber in the up leveling speed regulator assembly immediately adjacent to the pump pressure chamber in the check valve assembly, and a bore in the valve body through which bore the check valve stem extends for engaging and moving the up speed spool. Such a system is described in US-A-4 637 495 or DE 36 17 666 A1 which are completely included as reference. With this system and other methods for the up leveling of a hydraulic elevator the slower speed or up leveling speed of the elevator is achieved by bypassing a part of the oil flow from the pump directly back to the reservoir of the power unit, allowing the remaining flow from the pump to be directed to the elevator cylinder, thereby producing the required up leveling speed. With this control system, the up leveling speed regulator assembly is located in a chamber adjacent to the check valve assembly including a pump pressure chamber. This requires that seals be employed to prevent pressure of the pump pressure chamber escaping to the bypass pressure chamber of the up leveling speed regulator assembly. Otherwise, the elevator would sink downwards. In the case of residential elevators and other small elevators requiring extremely low rates of oil flow, existing up leveling valve designs as set forth above suffer from excess friction due to seals or the integration of other elements which cause a sensitive up leveling system to deviate from the constant speed desired. It is the object of the invention to provide a simple, low-priced, reliable, adjustable two-speed up control system of the generic kind that is stable in up leveling operation at very low rates of oil flow, such as two liters per hour or 1/2 g/s, allowing wide variations in operating pressures and oil tmeperature, even if unclean oil is used. This object is achieved with the control system for a hydraulic elevator having two up speeds according to the generic kind in that the check valve stem is a close fit in the bore of the valve body such that a controlled leakage of oil from the pump pressure chamber to the bypass pressure chamber joins pilot oil from the bypass valve chamber to effect a correction in the position of the metering edge to offset viscosity changes in the oil as its temperature varies to present a slowing down in the up leveling speed of the elevator as the oil temperature increases and in that a pilot line check valve is provided in a passage connecting the bypass pressure chamber and the bypass chamber for preventing that the leakage of oil through the bore in the valve body effects the up acceleration of the elevator at the start of up travel. Preferably the diameter of orifice is approximately 0.5 mm, and the angle of tape of the metering edge is approximately 2°. Advantageously, an up speed spool passage for pilot oil flow passes through the up speed spool to provide access of flow from the bypass chamber to the orifice of the up speed adjuster. It is preferred that the fluid restricter is protected by a filter built into the bypass valve in a position whereby the turbulence of oil being discharged through a channel in the proximity of the filter causes any contamination which may have settled against the filter to be washed away to non-sensitive parts of the system. With the control system according to the invention the small oil leakage between the check valve stem and the bore of the valve body which increases in volume as sea oil becomes warmer and thinner, adds to the flow of pilot oil already passing between the metering edge and the orifice of the up speed ajuster and has the effect of causing the metering edge to open up the orifice a slight amount by causing the bypass valve to close slightly, in turn causing more oil to flow through the check valve to the elvator cylinder, and thus maintain the required leveling speed. Since the amount of this leakage increases significantly with the increase in oil temperature, an automatic compensation of flow through the check valve takes place as the metering edge along the check valve moves to allow the increased pilot oil flow to pass through the orifice. Because the up acceleration of the elevator should depend only upon the rate of pilot oil flowing through the fluid restrictor, alone, the small pilot line check valve is positioned in the passage between the bypass pressure chamber and the bypass chamber to prevent the oil intentionally being leaked through the bore of the valve body flowing through a passage into the bypass chamber where it would otherwise cause the bypass valve to close at a faster rate, particularly at higher oil temperatures. Further the oil leaking through between the check valve stem and the bore in the valve body is used to reduce friction in the up leveling speed regulator assembly. An embodiment of the invention is described by means of a drawing, showing schematically the up control section of a hydraulic elevator valve. As shown in the drawing an elevator 52 is moved by means of a piston in a cylinder 50 which is supplied with hydraulic oil through a line 49 which opens into a valve body 1, into which three main assembly elements, a bypass valve assembly 56, a check valve assembly 57 and an up leveling speed regulator assembly 58 are positioned and to which elements a pump 60 is associated. When the pump 60 is not running, a bypass valve 2 with flow metering slots 3 is kept in its open position by a spring 8 which holds the bypass valve 2 against a bypass adjuster 9. A check valve 10 is held in its closed position by a spring 15 and also by the oil pressure in a chamber 40 connected with the cylinder pressure through a cylinder connecting line 49. The pump 60 driven by an electric motor 61 provides the main oil flow into a channel 27. Depending on the switched position of a solenoid 44 effecting the position by the bypass valve 2, the oil volume will flow from the channel 27, through the slots 3 in the bypass valve 2 and through a channel 29 back (not shown) to a tank 51. In this case, the elevator 52 will move at slow speed. Alternatively, with solenoid 44 in its closed position causing the bypass valve 2 to close, oil will flow from the channel 27 through a channel 28, through the check valve 10, through the chamber 40, into the cylinder connecting line 49, and to the cylinder 50 which raises the elevator 52 at full speed. When the pump 60 is running, a fluid restrictor or bypass valve orifice 4 protected by a filter 26 in the bypass valve 2 allows oil to flow into a bypass chamber 7 where it builds up pressure to force the bypass valve 2 closed against the spring 8. Flow from the pump 60 is then forced to pass through the channel 28, to the check valve 10 which opens, through the line 49 and into the cylinder 50. The filter 26 because of its proximity to the main turbulent oil flow from the pump 60, is self-cleaning, which is of significant importance for reliable and service-free operation of the system. The degree of taper of a spool 14 of the check valve 10 determines how far the check valve 10 must open to allow a specific volume of oil to flow to the cylinder 50 when the pump 60 is running. The length of opening movement of the check valve 10 is a measure which indicates the rate of flow of oil and therefore the speed of the elevator 52. The check valve 10 has a check valve stem 11 which is a close fit in a bore 12 of the valve body 1 and serves the purposes of moving an up speed spool 17 against a positioning spring 36 and also of metering a controlled leakage of oil from a pump pressure chamber 13 into a bypass pressure chamber 38 of the up speed spool 17, the purpose of which shall be explained later. The up speed spool 17, essentially a close fit in an up speed adjuster 30, meters the flow of oil in the pilot pressure system between the bypass chamber 7 and the tank 51. The up speed spool 17 consists of a taper 21, a metering edge 19, flow passages 23 and 24, and a spring centering stem 25. A suitable angle of taper of the metering edge 19 is approximately 2°. The positioning spring 36 forces the up speed spool 17 against the check valve stem 11 so that the up speed spool 17 and the check valve stem 11 move as one unit whenever oil flows through the check valve 10. The advantage of the up speed spool 17 and the check valve stem 11 being separate is that close tolerance fits of the diameters are possible without the danger of the parts binding or being subject to unrequired friction during their axial movement. The up speed adjuster 30 can be screw-adjusted along its axis by means of a socket 32 and a thread 31, in either direction to increase or decrease the up leveling speed of the elevator 52. This is achieved in that an orifice 33 in the up speed adjuster 30, in relation to the position of the metering edge 19 of the up speed spool 17, controls the flow of pilot oil out of the bypass chamber 7 which in turn controls the position of the bypass valve 2 and thereby the volume of oil being directed back to the tank 51 through the metering slots 3. The remaining volume of oil from the pump 61 flows to the cylinder 50. The solenoid valve 44, in opening the passage for pilot oil from the bypass chamber 7 to the tank 51 via the up speed control, initiates the elevator speed change from fast speed into leveling speed. A throttle 47 controls the rate of pilot oil flow exhausting to the tank 51 and thereby the rate of change of speed of the elevator 52 from fast to leveling speed; in other words the declaration of the elevator. As the pump 60 is started and the solenoid 44 is energized so that the solenoid 44 takes up closed position 45, oil initially flows from the pump 61, through the slots 3 of the bypass valve 2, and back to the tank 51. At this instant, there is no flow to the cylinder 50 of the elevator 52. The back pressure, caused by the restricting effect of slots 3 of the bypass valve 2, whose slot size is adjustable through the adjuster 9, increases, causing oil to flow through the orifice 4. This causes a build up of pressure in the bypass chamber 7, causing the bypass valve 2 to close smoothly. Since the flow from the pump 61 no longer can pass freely through the bypass valve 2 back to the tank 51, the pressure in the chamber 13 of the check valve 10 builds up until it overcomes the force of the spring 15 together with the oil pressure on the check valve 10 in the chamber 40, causing the check valve 10 to open and oil flow to pass through the check valve 10 to the cylinder 50, resulting in the elevator 52 accelerating upwards into full speed as the bypass valve 2 fully closes. With the check valve 10 in its fully open or back position together with attached check valve stem 11, the up speed spool 17 under pressure from the positioning spring 36 is in its forward position pressing against the check valve stem 11. In this forward position the metering edge 19 exposes the orifice 33 of the up speed adjuster 30. With the operation of a slowdown switch (not shown) in the elevator shaft, an electrical command for the elevator 52 to change from full speed into leveling speed is transmitted to the solenoid valve 44 which is de-energized, allowing the solenoid valve 44 to move into its open position 46. An outlet for pilot oil flow from the bypass chamber 7, through a pilot line check valve 48, through passages 23 and 24 of the up speed spool 11, through the orifice 33, the passage 43, the solenoid passage 46, and the throttle 47 to the tank 51, is thus provided. This causes oil pressure in the bypass chamber 7 to fall and the bypass valve 2 to open under the pressure exerted by the spring 8 and oil pressure under a bypass valve seat 5. As the bypass opens, part of the oil previously flowing to the cylinder 50 now passes through the bypass valve 2 to the tank 51. With less oil flowing through the check valve 10, the check valve 10 starts to close. The check valve stem 11 pushes the up speed spool 17 back against its positioning spring 36 until the metering edge 19 begins to cover the orifice 33. This partial blockage at the orifice 33 reduces the flow of pilot oil passing from the bypass chamber 7 to the tank 51, to the point where the oil flowing out of the bypass chamber 7 through orifice 33 is equal to the oil flowing into the bypass chamber 7 through the orifice 4 in the body of the bypass valve 2. A state of hydraulic balance then occurs with the metering edge 19, whose position is directly related to the flow of oil through check valve 10, controlling the flow of pilot oil through the orifice 33, which controls the position of the bypass valve 2, which controls the flow through the check valve 10. A stable closed circuit control system is the result. By turning up speed adjuster 30 by means of a key in the socket 32, and through the screw thread 31, the position of the orifice 33 can be axially changed so that a different up speed can be set. Because thinner oil due to higher oil temperatures can pass through a smaller opening than thicker oil, the hydraulic balance described above in the case of hot oil takes place with the check valve 10 slightly more closed than with colder oil; that is to say, with less oil flow passing through the check valve 10 to cylinder 50 and therefore with a slower up leveling speed. In order to compensate for this undesirable slowing down effect at higher oil temperatures, a small flow of pilot oil is allowed to leak between the stem 11 and the bore 12 of the valve body 1. This small leakage which increases in volume as the oil becomes warmer and thinner adds to the flow of pilot oil already passing between the metering edge 19 and the orifice 33, and has the effect of causing the metering edge 19 to open up the orifice 33 a slight amount by causing the bypass valve 2 to close slightly, in turn causing more oil to flow through the check valve 10 to the cylinder 50, and thus maintain the required leveling speed. Since the amount of this leakage increases significantly with the increase in oil temperature, an automatic compensation of flow through the check valve 10 takes place as the metering edge 19 along with check valve 10 moves to allow the increased pilot oil flow to pass through the orifice 33. Because the up acceleration of the elevator 52 should depend only upon the rate of pilot oil flowing through orifice 4, alone, it is necessary to position the small pilot line check valve 48 in the passage 42 to prevent the oil intentionally being leaked through bore 12 to flow through a passage 42 into the bypass chamber 7 where it would otherwise cause the bypass valve 2 to close at a faster rate, particularly at higher oil temperatures.

Claims: A control system for a hydraulic elevator having two up speeds comprising a pump (60), a supply of oil under pressure provided by the pump (60), a return including a reservoir tank (51) for such oil, an elevator cylinder (50) for supporting an elevator (52), a check valve assembly (57) connecting the pump supply with the elevator cylinder (50) and including a check valve (10) provided with a check valve stem (11), a pump pressure chamber (13) and a check valve chamber (40), a bypass valve assembly (56) connected across the pump (60), the supply and the return for bypassing the check valve (10), having a bypass chamber (7) for receiving hydraulic fluid under pressure from the pump (60), and a bypass valve (2) which is biased in an open position by a spring (8), a fluid restrictor (4) for displacing the bypass valve (2) to a closed position against the force of the spring (8), means including a solenoid valve (44) for connecting the bypass chamber (7) with the return, an up leveling speed regulator assembly (58) for controlling the up leveling speed of the elevator (52) including an up speed adjuster (30) with an orifice (33) that coordinates with a metering edge (19) in the form of a taper (21) on a separate up speed spool (17) to proportionately regulate the volume of oil flow to the elevator cylinder (50) and the reservoir tank (51), a bypass pressure chamber (38) in the up leveling speed regulator assembly (58) immediately adjacent to the pump pressure chamber (13) in the check valve assembly (57), and a bore (12) in the valve body (1) through which bore (12) the check valve stem (11) extends for engaging and moving the up speed spool (17), characterized in that the check valve stem (11) is a close fit in the bore (12) of the valve body such that a controlled leakage of oil from the pump pressure chamber (13) to the bypass pressure chamber (38) joins pilot oil from the bypass valve chamber (7) to effect a correction in the position of the metering edge (19) to offset viscosity changes in the oil as its temperature varies to present a slowing down in the up leveling speed of the elevator (52) as the oil temperature increases and in that a pilot line check valve (48) is provided in a passage (42) connecting the bypass pressure chamber (38) and the bypass chamber (7) for preventing that the leakage of oil through the bore (12) in the valve body (1) effects the up acceleration of the elevator (52) at the start of up travel. A control system acccording to claim 1, characterized in that the diameter of the orifice (33) of the up speed adjuster (30) is approximately 0.5 mm and that the angle of taper of the metering edge (19) is approximately 2°. A control system according to claim 1 or 2, characterized in that an up speed spool passage (23, 24) for pilot oil flow passes through the up speed spool (17) to provide access of flow from the bypass chamber (7) to the orifice (33) of the up speed adjuster (30). A control system according to one of the claims 1 to 3, characterized in that the fluid restrictor (4) is protected by a filter (26) built into the bypass valve (2) in a position whereby the turbulence of oil being discharged through a channel (27) in the proximity of the filter (26) causes any contamination which may have settled against the filter (26) to be washed away to non-sensitive parts of the system.

Inventors: BLAIN ROY W, BLAIN, ROY W.
Applicants: BLAIN ROY W, BLAIN, ROY W.
Application year: 1992
Main classification: B66B1
IPC codes: B66B1