Patent Publication Number: US-2015059327-A1

Title: Dual channel pulsed variable pressure hydraulic test apparatus

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/812,798, filed Apr. 17, 2013, which is herein incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to hydraulic apparatus, and more particularly, to apparatus for pulsed pressure testing of hydraulic apparatus sealing components. 
     BACKGROUND OF THE INVENTION 
     Hydraulic systems are widely used in many industries. Examples include motor vehicle engines, braking systems, aeronautical control systems, industrial pumping systems, presses, rolling mills, earth-moving equipment, floor conveyors, agricultural machines, truck loading cranes, injection molding machines, marine hydraulics, and many others. 
     So as to ensure reliability and longevity even under challenging conditions, it is often necessary to submit hydraulic designs to rigorous and prolonged pressure testing, so as to ensure that there is no excessive material fatigue or seal wear even after long term, demanding use. For certain applications, the pressure testing requires repeated application and release of a specified hydraulic pressure to the part under test (“PUT”). This “pulsed pressure” testing is typically carried out for a specified number of pressure cycles. 
       FIG. 1  illustrates a typical test apparatus that is used for pulsed pressure hydraulic testing. A rotary pump  100  pressurizes hydraulic fluid, and a manually controlled regulator  102  controls the pressure at the output of the pump  100  by allowing some of the hydraulic fluid to flow into a reservoir  104 . The regulator  102  is manually adjusted until the pressure at the output of the pump  100  is set to a desired pressure P as measured by a pressure measuring device  106 , such as a pressure gage. 
     The output of the pump  100  is also connected through a solenoid control valve  108  to the PUT  110 . The solenoid valve  108  is opened and closed by a control signal  112 , which is typically supplied as a train of “square” voltage pulses  112  that cause the system to repetitively apply the hydraulic pressure P to the PUT, and then to release the pressure again. Typically, a counter (not shown) counts the voltage pulses  112 , and stops the test after a specified number of repetitions N has been applied. If the PUT does not include a mechanism that returns it to its starting configuration after each pressure pulse is applied, then a return spring  114  or other such mechanism is provided. 
     As testing requirements have become more demanding and sophisticated, for example requiring 360,000 pressure pulse cycles or more, the maximum rate at which hydraulic testing apparatus can apply pressure pulses has often proven to be too slow, due to pressure delays in the hydraulic lines and limitations in the operating speed of the solenoid valve. In particular, it is not uncommon for the solenoid valve to require 60 ms or more to switch on and off. As a result, weeks or even months may be required to apply a specified number of pressure pulses to the PUT. 
     In addition, systems such as the apparatus illustrated in  FIG. 1  are limited to a single applied pressure, and are unable to apply hydraulic fluid to the PUT at more than one pressure during a test. 
     What is needed, therefore, is a hydraulic testing apparatus that is faster and more flexible than current designs. 
     SUMMARY OF THE INVENTION 
     The present invention is an enhanced pressure testing apparatus that is faster and more flexible than current designs. Pressure delays in the hydraulic lines are minimized by using hydraulic lines that are significantly larger in diameter than previous designs. For example, lines that are 1¼ inches in diameter are used in some embodiments for applications where ¼ inch diameter lines have typically been used in the past. A fluid accumulator is used to avoid pump output capacity delays by storing a volume of hydraulic fluid that is pre-pressurized while the control valve is closed, and then supplements the pump output when the control valve is open. Delays that might otherwise arise due to the enlarged volume of the hydraulic lines are thereby avoided. 
     Rather than providing only a single pressure delivery channel, the present invention includes two pressure delivery channels, each of which includes its own pump, regulator, accumulator, and control valve. As a result, a PUT that requires a separately applied pneumatic pressure to return it to its initial configuration can be easily accommodated. And in some embodiments, if it is desirable to apply pressure to a single input of the PUT at two different pressure values, for example alternately, the outputs of the two delivery channels can be combined at the input of the PUT. 
     Embodiments of the present invention use servo valves, which typically switch much faster than solenoid valves (for example 10 ms switching time for a servo valve compared to 60 ms for a solenoid valve). In some of these embodiments, output signals of pressure transducers provided at the outputs of the servo valves are used by feedback comparators in a “proportional integral and derivative” (“PID”) loop to obtain a desired pressure output from each servo valve. In various embodiments, by controlling and shaping the servo valve control voltages, a wide range of different pressure outputs, and even pressure output profiles, can be provided on either or both pressure channels. 
     In some embodiments, the hydraulic pump is a variable-vane pump, which allows the system to adapt to a wider range of pressure requirements and PUT volumes. 
     Certain embodiments further include selectable high and low pressure ranges on one or both of the pressure channels. In some of these embodiments, the hydraulic output of the pump is split into two parallel channels, passed through parallel regulators, accumulators, and control valves, and then recombined. 
     The present invention is a system for applying hydraulic pressure pulses to a part under test (“PUT”). The system includes: 
     a first pressure channel including:
         a first pump configured to pressurize hydraulic fluid in the first pressure channel;   a first fluid accumulator in fluid communication with an output of the first pump;   a first regulator configured to establish a first fluid pressure in the first fluid accumulator; and   a first control valve having a first pressure channel output in fluid communication with the PUT, the first pressure channel output being switchable by the first control valve between fluid communication with the first accumulator and fluid communication with a hydraulic fluid reservoir, the first control valve being actuated by a first electrical control signal received from a system controller; and
 
a second pressure channel including:
   a second pump configured to pressurize hydraulic fluid in the second pressure channel;   a second fluid accumulator in fluid communication with an output of the second pump;   a second regulator configured to establish a second fluid pressure in the second fluid accumulator; and   a second control valve having a second pressure channel output in fluid communication with the PUT, the second pressure channel output being switchable by the second control valve between fluid communication with the second accumulator and fluid communication with the hydraulic fluid reservoir, the second control valve being actuated by a second electrical control signal received from the system controller.       

     Embodiments further include a first pressure transducer configured to measure a pressure of the first pressure channel output and a second pressure transducer configured to measure a pressure of the second pressure channel output. 
     In some embodiments at least one of the control valves is a servo valve. In some of these embodiments the output of the servo valve provides a variable pressure channel output according to a varying amplitude of the corresponding electrical control signal. In other of these embodiments the variable pressure channel output is linearly proportional to the varying amplitude of the corresponding electrical control signal. 
     In various embodiments the first pressure channel output and the second pressure channel output can be combined and applied jointly to the PUT, thereby allowing the system controller to apply pressure from either pressure channel to the PUT in any desired sequence. 
     In certain embodiments, the output of the first pump is in simultaneous fluid communication with a high pressure branch and a low pressure branch, each of the high and low pressure branches including a pressure regulator, a fluid accumulator, and a control valve, outputs of the high and low pressure branches being in combined fluid communication with the first control valve, so that a fluid pressure delivered to the first control valve is selectable between a pressure set by the high pressure branch regulator and a pressure set by the low pressure branch regulator. And in some of these embodiments the first control valve is a servo valve that provides a variable pressure output according to a variable electrical control signal, selection of the high or low pressure channel thereby selecting between a high pressure range and a low pressure range over which the first control valve is able to vary the first pressure channel output. 
     And in various embodiments at least one of the first and second pumps is a variable vane pump. 
     The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a prior art configuration of a hydraulic testing apparatus; 
         FIG. 2  is a block diagram illustrating an embodiment of the present invention; 
         FIG. 3  is a block diagram that illustrates combining of both pressure channel outputs into a single PUT input in an embodiment of the present invention; 
         FIG. 4A  is a graphical illustration of a basic pressure pulsing cycle; 
         FIG. 4B  is a graphical illustration of a pressure pulsing cycle that includes pressure profiles in an embodiment of the present invention; and 
         FIG. 5  is a block diagram that illustrates an embodiment of the present invention that provides selectable high and low pressure ranges on both pressure channels. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is an enhanced pressure testing apparatus that is faster and more flexible than current designs. Pressure delays in the hydraulic lines are minimized by using hydraulic lines that are larger in diameter than previous designs. For example, lines that are 1¼ inches in diameter are used in some embodiments for applications where ¼ inch diameter lines have typically been used in the past. 
     With reference to  FIG. 2 , rather than providing only a single pressure delivery channel, the present invention includes two pressure delivery channels, each of which includes its own pump, which can be a rotary pump  100  as shown in  FIG. 1 , or a variable-vane pump  208  as shown in  FIG. 2 . Each pressure delivery channels further includes a regulator  102  and control valve, which in some embodiments is a solenoid valve  108  and in other embodiments is a servo valve  202 . As a result, a PUT  206  that requires separately applied pneumatic pressure to return to its initial configuration can be easily accommodated. 
     In addition, each pressure channel includes a fluid accumulator  200  in which a volume of hydraulic fluid is pre-pressurized while the control valve  202  is closed, and then supplements the pump output when the control valve  202  is open, so that the larger volume of the hydraulic lines does not cause pressure delivery delays due to limited pump output capacity. 
     Embodiments of the present invention use servo valves  202 , which typically switch much faster than solenoid valves (for example 10 ms switching time for a servo valve  108  compared to 60 ms for a solenoid valve  202 ). In some of these embodiments, pressure transducers  204  are provided at the outputs of the servo valves  202 , and the outputs of the pressure transducers  204  are used by feedback comparators (not shown) in a “proportional integral and derivative” (“PID”) loop to obtain a desired pressure output from each servo valve  202 . In various embodiments, by controlling and shaping the valve control voltages, a wide range of different pressure outputs, and even pressure output profiles, can be provided on either or both pressure channels. 
     In some embodiments, the hydraulic pump  208  is a variable-vane pump  208 , which allows the system to adapt to a wider range of pressure requirements and PUT volumes as compared to a rotary pump  100 . 
     With reference to  FIG. 3 , in some embodiments where the PUT  110  does not require separately applied pneumatic pressure to return to its initial configuration, if it is desirable to apply pressure to the single input of the PUT  110  at two different pressure values, for example alternately, the outputs of the two delivery channels can be combined at the input of the PUT  110 . In the embodiment of  FIG. 3 , the servo valves  300  are able to switch their outputs between the input pressure channel  302 ,  304 , the fluid reservoir  104 , and a blocked input. Accordingly, as is illustrated in the figure, when one of the pressure channel outputs  302  is applying hydraulic pressure to the PUT  110 , the output of the other pressure channel  304  can be blocked so that it will not interfere. The valves  300  can then be switched so that the pressure is drained into the reservoir  104 , after which the first pressure channel output  302  can be blocked while the second pressure channel output  304  applies hydraulic pressure to the PUT  110 . 
     With reference to  FIG. 4A , in some embodiments the present invention can produce a series of pressure pulses that rise rapidly to a pre-set pressure P, and then fall again after a pulse duration Tp. The pulses are repeated with a cycle time Tc until a total desired number N of pulses has been applied. 
     With reference to  FIG. 4B , in other embodiments the control valves  202  are servo valves  202  having output pressures that are proportional to the amplitude of the control voltage. In some of these embodiments, pressure pulses having shaped profiles can be applied to the PUT  206  by applying control voltages with corresponding shape profiles to the servo valves  202 . In the embodiment of  FIG. 4B , the pressure is ramped at a controlled rate to a first pressure Pl, where it is held for a set amount of time, after which it is ramped up to a second pressure P 2 , followed by a third pressure P 3 , before being released at a controlled rate. In similar embodiments, pressure profiles of almost any arbitrary shape can be applied. 
     With reference to  FIG. 5 , certain embodiments further include selectable high and low pressure ranges on one or both of the pressure channels. In the embodiment of  FIG. 5 , the output of a variable vane hydraulic pump  208  in each pressure channel is split into two parallel branches, passed through parallel regulators  500 , accumulators  200 , and control valves  502 , and then recombined. Each of the parallel branch regulators  500  is set to a desired pressure, which determines the range over which the primary control valve  202  in that channel can vary the output pressure. The dedicated fluid accumulator in each branch is pre-pressurized to the set pressure for its parallel branch while the other branch is in use, and then drives the fluid output of its branch when needed. In similar embodiments, a single accumulator provided at the output of the pump is pre-pressurized to the pressure of the pump output when neither pressure branch is in use, and then drives the pressure output when one of the pressure branches is in use. 
     In embodiments, the control voltages are supplied to the control valves  202  by programmable logic controllers (“PLC&#39;s”), and in some embodiments operator control is available through a graphical user interface such as LabView. In various embodiments, the system displays the pressures measured by the pressure transducers  106 ,  204  as well as the number of completed cycles N, and in some embodiments these parameters are periodically recorded and logged for later review. In similar embodiments, the current and/or logged values of these parameters can be monitored remotely using any internet-capable device. 
     The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.