Technical Field
[0001] This invention concerns hydraulic valve control systems and is particularly, though
not exclusively, useful in hydraulic elevators.
Background Art
[0002] In an attempt to control a hydraulic elevator with precision approximating the more
sophisticated and usually more expensive traction elevators, feedback control is used.
But, even using feedback control, comparable performance has been difficult to achieve,
and the main problem is the dynamic characteristics of the fluid. Its viscosity shifts
with the ambient temperature and also from the heating that occurs as the elevator
car is raised and lowered. These variables produce some measure of unpredictability
in the motion of the elevator car. The different levels of feedback that have been
utilized are typically expensive and require excess pump capacity, which increases
the cost and lowers system efficiency.
[0003] A technique illustrating feedback is shown in U.S. Patent 4,205,592, where the flow
through the valve and to an object, such as a hydraulic elevator, is passed through
a flow meter that includes a potentiometer. As the flow increases, the output voltage
associated with the motion of the potentiometer wiper changes, manifesting the magnitude
of the flow. U.S. Patent 4,381,699 shows a similar type of valve control.
[0004] U.S. Patent 4,418,794 is illustrative of the type of valve that may be used in systems
that do not sense the fluid flow but, using a larger feedback loop, perhaps sense
the position of the elevator car and control the operation of the valve.
Disclosure of Invention
[0005] Although the invention described herein was made in connection with hydraulic valve
controls in elevators and is described, for convenience, in that context, the invention
may be useful in other systems having similar control requirements.
[0006] According to the present invention, a linear flow control valve is operated by a
stepper motor to control flow between the pump and the hydraulic cylinder when the
object, e.g., elevator car, is raised and the return flow from the cylinder to the
tank when the car is lowered. The time- related motion of this valve mirrors the flow
to the car, thus also the car's velocity profile. The operation of the valve begins
by placing it in a position at which the fluid from the pump is completely bypassed
from the car. The valve is then progressively closed, decreasing that bypass flow.
When the pressure applied to the elevator car exceeds the pressure required to sustain
the car, motion of the valve is programmed to the desired elevator velocity profile.
[0007] According to the invention, the pressure differential that arises when the output
pump pressure just exceeds the pressure required to hold the car in place is sensed
from the motion of a check valve across which the pump pressure and car pressure are
oppositely applied. Movement of the check valve to an open position at which the car
will just about start to move is detected by an electrical switch that produces an
electrical control signal that is applied to the main valve control. That control
signal acts as the starting point for main valve programmed positioning that determines
the velocity profile of the elevator car when the car is moved up.
[0008] According to the invention, the connection between the motor and the valve is through
a resilient coupling, such as a spring. This connection allows the valve to be moved
to bypass fluid flow from the pump back to the tank when the valve is in a position
in which all the pump output is directed by the valve to the actuator. A pressure
release valve is operated when the pump pressure exceeds a certain level, and that
operation applies fluid under pressure to the valve, which, in response, moves against
the resilient coupling to connect the pump output to the tank. This valve operation
relieves the pump pressure.
[0009] There are many features to the present invention. Most significant, it provides very
precise performance because the fluid and load characteristics may control the operation
of the valve. Yet, it is simple and reliable because feedback is used selectively
to adjust for those characteristics. For the most part, the valve flow is controlled
without feedback.
Brief Description of the Drawing
[0010] The drawing is a schematic view showing by way of example only a hydraulic elevator
control system embodying the present invention.
[0011] Fig. 1 shows a hydraulic.elevator control system for moving an elevator car 10 between
a plurality of floors or landings. The floors or landings are not shown. The car is
attached to a car piston (plunger) 11 that extends from a cylinder 12, and fluid is
pumped into or discharged from the cylinder to raise and lower the car respectively,
that flow being controlled and regulated in a manner that will be described in detail.
The motion of the car is detected by a pickup 13. Associated with a stationary position
tape 14, the pickup provides a signal (POSITION) on line 15, that is supplied to a
pump and valve control (PVC) 17. The POSITION signal manifests the car position and
velocity. The position of the car thus sensed is used for controlling the flow of
fluid to and from the cylinder, controlling the position of the car piston or plunger
11. The PVC 17 controls a hydraulic valve system that includes a pump 21 and a fluid
reservoir (tank) 5. The pump supplies fluid to a hydraulic control valve assembly
A through a check valve 6 (to prevent back flow), and this assembly is controlled,
along with the pump, by the PVC 17. The pump is turned on or off (activated/deactivated)
by a pump on/off signal on a line 22, and the fluid from the pump is applied under
pressure through the check valve 6 to a first port 25.
[0012] The port 25 leads to a "key-shaped" valve window 26 that is part of a linear valve
27, one that moves back and forth linearly between two positions Pl, P2. The position
of the valve 27 is controlled by a stepper motor 28 which receives a signal (SPEED)
on the line 20 from the PVC 17. That signal comprises successive pulses, and the frequency
of those pulses determines the motor's 28 speed; hence also the longitudinal (see
arrow Al) rate of positioning of the valve 27. Each pulse in the SPEED signal represents
an incremental distance along the length of motion of the valve 27 between points
Pl and P2. The position (location) of the valve is represented by the accumulated
count between those positions. The valve window 26 comprises a large window 26a and
an adjacent narrower window 26b, giving it a "key-shaped" appearance. At one point,
P2, the large window 26a is adjacent the first inlet port 25, and the narrower adjacent
portion 26b is located next to a second port 31. At this point, the valve 27 is "open".
That second port 31 leads to a line 32 that goes to the tank 5. At position Pl, the
small window 26b is mostly adjacent to the port 25, and the path to the port 31 is
blocked by the solid part of the valve. At that position, the valve 27 is "closed".
In the open position, at P2, fluid flows from the pump through the line 24; this is
"flow-up" (FU), flow to raise the car. The fluid then passes into the large window
26a and, from there, through the small window 26b back to the line 32, then to the
tank. The FU flow is thus bypassed when the pump is started. But, as the valve 27
closes (moves to position Pl), the pressure of the FU fluid flow begins to build in
an internal port 35, while the bypass flow on line 32 decreases as the path through
window 26b to port 31 decreases. As the valve 27 moves to position Pl (nonbypass position),
there is some overlap of the two windows 26a, 26b and the main inlet port 25, meaning
that the path through the large window 26a decreases, while the path through the smaller
window 26b increases. But, the area of the smaller window 26b is more dependent than
with the case of the larger window on the longitudinal position of the valve 27. As
a result of this, the change in flow is controlled by the smaller valve window area
to outlet port 31, which reduces as the main valve begins to move towards the closed
position at Pl, at which all the FU flow passes from the port 25 to the inlet 35;
there being no path between the port 25 and the outlet port 31.
[0013] The fluid pressure PS1 in the internal port 35 is applied to a main check valve (MCV)
40. This valve has a small stem 41 that rests in a guide 41a. The MCV may freely move
up and down in response to the pressure differentials between the port 35 and the
port 43, where the pressures are PS1 and PS2, respectively. When the pump is turned
on and the main valve 27 closes, moves towards position P1, the MCV 40 is pushed upward
when PS1 exceeds PS2, allowing the FU flow to pass through the MCV into the line 42
that extends to the cylinder 12. This happens as the bypass flow decreases. The resultant
fluid flow displaces the car piston 11 upward, moving the car in the same direction.
[0014] When the car 10 is at rest, pressure in the line 42 and the pressure in the chamber
43 are the same, pressure PS2. With the pump 21 off, this pressure pushes the MCV
40 down, and the down flow (FD) in the line 42 is then blocked, holding the car 10
in position. No flow through the line 42 and back to the tank 5 is possible under
this condition. To allow this flow to occur, the MCV 40 must be lifted, and this is
effected by the operation of a main check valve actuator 50.
[0015] This actuator includes a rod 50a, which contacts the stem 41 when pushed upward;
a first member 50b which is pushed upward against the rod; a second member 50c which
when pushed upward moves the first member. The rod 50a is thrust upward, pushing the
MCV 40 upward, when fluid, at pressure PS2, is applied to the inlet line 52, and that
happens only when a LOWER signal is applied to the line 53 that goes to a solenoid
control release valve 55. The fluid pressure in the line 52 is then applied to the
bottom of the members (pistons) 50b, 50c. The combined surface area of those members
is greater than the upper surface area 62 of the valve 40. The second member moves
until it strikes the wall 50d of the chamber 50e. The first member also moves with
the second member because of the flange 50f. This small motion (as far as the wall
50d) "cracks" open the MCV 40, equalizing the pressures PS1 and PS2. Then the first
member continues to move upward, until it too strikes the wall, fully opening the
MCV 40. This allows return flow (FD) from the chamber 35 that passes through the windows
26a, 26b, and line 32. The FD flow through line 25 is blocked by the check valve 6.
The position of the valve 27 determines the rate of the FD flow, thus the speed profile
of the car as it descends. The valve is moved from the closed P1 position by the SPEED
signal towards the open position P2. The duration and frequency of the SPEED signal
sets the down velocity profile.
[0016] There is switch 70 that is adjacent the MCV 40, and the upward motion of the MCV
40 causes the switch to operate. That operation provides a signal (CV) on the line
71 going to the PVC 17. The CV signal shows that the valve has moved in the up direction
for elevator travel. It represents that the pressure in the chamber 35 has slightly
exceeded the pressure in the chamber 43. Using this signal, the PVC may control the
further motion of the valve spool by controlling the pulse rate and duration comprising
the SPEED signal, which is applied to the line 29. The CV signal occurs just when
the pressure of PS1 35 exceeds the pressure PS2, and that occurs just before there
is actual flow. Generation of the CV signal consequently provides a definitive manifestation
of "anticipated" flow.
[0017] The stepper motor controlled valve 27 also provides a pressure release function for
the port 35. The stepper motor 28 has an output link 28a, and a collar or ring 28b
is attached to that link. The link and collar fit in a hollow portion of the valve
27 but separated from the flow area (windows 26a, 26b) by the valve wall 27a, which
is opposite another wall 27b. (The valve 27 is shaped like a hollow cylinder; fluid
flows through its interior). A spring 28c fits between the wall 27b and the collar
28b. As the stepper motor operates, the link moves up or down, in steps corresponding
to the steps in the SPEED signal. As a result of this, the change in flow is controlled
by the smaller valve window area to outlet port 31, which reduces as the main valve
begins to move towards the closed position at P1, at which all the FU flow passes
from the port 25 to the inlet 35; there being no path between the port 25 and the
outlet port 31. This link motion is transmitted to the wall 27a through the spring
to the valve 27, which moves in synchronism with the link. If the pressure in the
pump output line 21a is sufficient to open the pressure release valve (PRV), the pressure
is applied to the top of the valve 27b and the entire valve 27 is forced down, allowing
the flow from the pump to pass through the line 32, to the tank 5, to relieve the
"overpressure" condition.
[0018] For manually lowering the car, a manually operated valve 80 is operated to allow
the fluid to flow from the chamber 43 directly back to the tank 5.
[0019] The preferred embodiment of the invention has been described, and one of ordinary
skill in the art to which the invention relates may make modifications and variations
to that embodiment, in whole or part, without departing from the true scope of the
invention.
1. A hydraulic valve (A) comprising:
a main inlet (25) adapted for connection to a pump (21);
a main outlet (43) adapted for connection to an actuator comprising a piston (11)
and a cylinder (12);
a secondary outlet (31) adapted for connection to a fluid tank (5);
a flow control valve (27) for controlling fluid flow from the main inlet to the main
outlet;
the hydraulic valve (A) being characterized by :
the flow control valve being continuously movable between two positions to control
progressively, from a minimum to a maximum equalling the pump output, the flow between
the main inlet and the main outlet or discharge from the main outlet to the tank,
at one position the main inlet and secondary outlet being connected, at the other
position the main inlet and the main outlet being connected and the main inlet and
secondary outlet being disconnected;
a motor (28) for moving the valve linearly in discrete steps;
a resilient member (28c) interconnecting the motor and the valve;
the motor applying force through the resilient member to move the valve to said one
position and to hold the valve in any position against the pressure on the valve by
the fluid in the main outlet from the main outlet; and
a pressure operated valve (PRV) connected to the pump output and the flow control
valve (27);
the flow control valve beinq movable against the force of the resilient menber towards
said one position in response to fluid applied thereto by the pressure operated valve
when the pump output pressure exceeds a certain level.
2. A valve (A) according to claim 1, characterized by:
the flow control valve (27) comprising a hollow cylinder with windows (26a, 26b) through
which fluid enters and leaves the interior of the cylinder, said resilient member
being disposed between the motor and one end of the cylinder, and the other, opposite
end of the cylinder being located in a chamber connected to the pressure operated
valve.
3. A hydraulic valve (A) comprising:
a main inlet (25) adapted for connection to a pump (21);
a main outlet (43) adapted for connection to an actuator comprising a piston (11)
and a cylinder (12);
a secondary outlet (31) adapted for connection to a fluid tank;
a flow control valve (27) for controlling fluid flow from the main inlet (25) to the
main outlet (43);
the hydraulic valve (P.) being characterized by:
a check valve (MCV) with its inlet (35) connected to the flow control valve (27) and
its outlet connected to the main outlet (43), the check valve being operable to open
and connect its inlet and outlet when the pressure in the inlet exceeds the pressure
in the outlet and also being mechanically operable to open;
a switch (70) that is actuated by the check valve when it opens and closes; and
the flow control valve being continuously movable between two positions to control,
from a minimum flow to a maximum flow equalling the pump output, the flow between
the main inlet and the main outlet through the check valve and to control the discharge
flow from the main outlet to the tank.
4. A valve according to claim 3, further characterized by:
a hydraulic actuator (50) that moves to open the check valve;
a solenoid valve (55) operable for connecting the actuator with the main outlet.
5. A valve according to claim 4, characterized in that the actuator comprises:
a first pressure responsive member (50c) and a second pressure responsive member (50b)
that can move simultaneously for a first distance to slightly open the valve, the
second member (50b) being additionally movable beyond that first distance to open
the valve further, the combined surface area of the two members being greater than
the area of the check valve, so that the force of the two members exceeds the opposing
force of the valve caused by the main outlet (43) pressure.
6. A valve according to claim 3, 4 or 5 further characterized by:
a stepper motor (28); and
the flow control valve (27) being a linear motion valve, and the stepper motor being
connected to the valve for moving it linearly in finite steps in response to a stepper
signal, the stepper signal comprising variable frequency pulses.
7. A valve according to any of claims 3 to 6, further characterized by:
the flow control valve (27) being a hollow cylinder that contains a first pair of
diametrically-opposed windows (26a) and adjacent thereto a second pair of diametrically-opposed
windows (26b) for controlling the flow from the main inlet;
the flow through area of the first pair of windows from the main inlet increasing
more for each unit of movement by the flow control valve than the flow through area
from the main inlet through the second pair of windows.
8. A hydraulic control system comprising:
a hydraulic actuator (11,12);
a pump (21) ;
a tank (5),and a valve (A) for controlling flow between the tank and the actuator
with the pump, comprising:
a main inlet (25) adapted for connection to a pump (21);
a main outlet (43) adapted for connection to the actuator)
a secondary outlet (31) adapted for connection to the tank.
a flow control valve (27) for controlling fluid flow from the main inlet (25) to the
main outlet (43);
characterized by the valve (A) comprising:
a check valve (MCV) with its inlet (35) connected to the flow control valve (27) and
its outlet connected to the main outlet (43), the check valve being operable to open
and connect its inlet and outlet when the pressure in the inlet exceeds the pressure
in the outlet and also being mechanically operable to open;
a switch (70) that is actuated by the check valve when it opens and closes;
the flow control valve being continuously movable between two positions to control,
from a minimum flow to a maximum flow equalling the pump output, the flow between
the main inlet and the main outlet through the check valve and to control the discharge
flow from the main outlet to the tank, and by:
a motor (28) to move the flow control valve; and
means (17) for controlling the operation of the motor in response to an electrical
signal produced by operation of said switch.