Systems and methods for controlling working fluid in hydraulic elevators
A hydraulic elevator may comprise a bidirectional pump that controls up and down motion of an elevator car. A VVVF drive may cause the bidirectional pump to provide working fluid in a controlled manner to a hydraulic jack that supports the elevator car. A control valve may be disposed between the bidirectional pump and the hydraulic jack so that the control valve can be closed when the elevator car needs to be held in place. To avoid pressure waves that propagate when the control valve is opened with disparate pressures on the pump and jack sides of the control valve, the bidirectional pump may adjust the pressure on the pump side of the closed control valve to the pressure on the jack side of the control valve before the control valve is opened.
1. A system for controlling working fluid in a hydraulic elevator, the system comprising:
a hydraulic jack;
a control valve in fluid communication with the hydraulic jack, wherein the control valve is configurable in an open position and in a closed position;
a pump in fluid communication with the control valve, wherein the control valve is disposed between the pump and the hydraulic jack;
a motor configured to generate a force for powering the pump;
a controller, wherein when the control valve is in the closed position the controller causes the pump to at least one of adjust a first pressure on a pump side of the control valve to a second pressure on a hydraulic jack side of the control valve or maintain the first pressure at the second pressure; and
a VVVF drive configured to provide electricity from a power source to the motor, and to operate in a speed-control mode when the controller causes the pump to adjust the first pressure to be within 1.0% of the second pressure, wherein a motor speed signal from the motor is provided as feedback to the VVVF drive.
2. The system of claim 1 wherein the controller causes the pump to maintain or adjust the first pressure on the pump side of the control valve to be within 2.5% of the second pressure on the hydraulic jack side of the control valve when the control valve is in the closed position.
3. The system of claim 1 wherein the pump is a bidirectional pump.
4. The system of claim 3 wherein as the hydraulic jack moves an elevator car up and down, the control valve remains open and the bidirectional pump controls the hydraulic jack and movement of the elevator car.
5. The system of claim 1 , wherein the VVVF drive transitions from the speed-control mode to closed-loop velocity control or closed-loop flow control when the control valve moves from the closed position into the open position.
6. The system of claim 1 , wherein based on the first and second pressures, the controller provides the VVVF drive with a speed reference signal that informs the VVVF drive as to how to control a speed of the motor.
7. The system of claim 1 , further comprising:
a first pressure sensor disposed on the pump side of the control valve, wherein the first pressure sensor measures the first pressure, which is transmitted to the controller; and
a second pressure sensor disposed on the hydraulic jack side of the control valve, wherein the second pressure sensor measures the second pressure, which is transmitted to the controller.
8. The system of claim 1 wherein the controller causes the pump to adjust the first pressure within 1.0% of the second pressure less than a second prior to a time at which the control valve begins to transition from the closed position to the open position.