GB2119190A - Electro-hydraulic control system - Google Patents

Abstract

A control system regulating the rate of flow of hydraulic fluid includes electrical means for converting the analog signal from a hand activated controller into a binary coded decimal signal, and a variable flow valve for functionally decoding the BCD command signal into a specified rate of fluid flow using a bank of step flow cartridges each of which passes a specified flow of fluid therethrough to the fluid motor. <IMAGE>

Description

SPECIFICATION Electro-hydraulic control system Technical Field The present invention relates to a control system for hydraulically operated machines requiring relatively sensitive regulation of hydraulic oil flow to selective functions.

Background of Prior Art Many varieties of hydraulic machinery are manually operated, and levers, switches, etc.

are used by the operator to control the flow of hydraulic fluid to valves, or cylinders of fluid motors, thereby actuating the various machine functions. For example, in present aerial work platforms of the type taught generally by U.S.

Patent No. 3776367, an automatic "return to neutral" control lever is used from the work basket to control the elevation and descent of a telescopic boom by regulating the flow of hydraulic fluid to the lift cylinder.

Because such equipment is used to place workmen in elevated and often constrictive work locations, the operator must have sufficiently sensitive control over the movement of the boom and basket for safety reasons. Proportional control valves have been proposed by several manufacturers for enhancing the degree of sensitivity of control which an operator may exercise over the movement of the boom. Typically available proportional control valves are solenoid actuated and pressure based, having means for sensing and monitoring the fluid pressures on opposite sides of the fluid line, and keeping the ratio of said pressures at a preset value. Theoretically, such devices operate in response to the analog signal from the hand controller and would permit finer gradation in movement control by the operator.

Certain shortcomings in the state of the art control systems, and in particular the proportional control valve component thereof, prevent the achievement of a satisfactory solution to the industrys need for a dependable, sensitive control system. First, the cost of commercial proportional control valves is prohibitive due to their complex mechnical componentry and the high tolerances which must be maintained for proper operation. Resultingly, their acceptance has been less than unanimous by the industry.

Further, proportional control valves in present use rely upon their ability to accurately sense fluid pressures in what may be less than ideal work environments. The presence of contamination in the oil, and differences in viscosities, can operate to render the valves inaccurate if not to entirely defeat the valve.

Since the devices are on line, replacement or repair or malfunctioning valves can result in costly down time.

Finally, present machines are often designed to operate in one of several power modes under given circumstances. In the above example application, the aerial work platform may be provided with high/low engine, and high/low drive modes. Operation of the boom lift control lever must cause a different rate of elevation or descent, depending on the engine and drive mode, a requirement which further complicates the attainment of a suitable hydraulic control system.

A typical state of the art control system comprises a fluid motor, a fluid source for delivering fluid flow to the fluid motor, an electrically controlled valve system for regulating the flow of fluid between the source and the motor, and an actuator for electrically controlling operation of the valve system.

Commonly used valve systems in use comprise a solenoid actuated proportional control valve as described above which operates responsive to an analog signal.

Brief Summary of the Invention According to the invention therefore an electro-hydraulic control system as defined above is characterized in that the actuator includes a variable analog signal generator and an analog to digital converting circuit electrically inputted by the analog signal generator, and the valve system including a plurality of digitally actuated step flow valves which are electrically controlled by the analog to digital converting circuit. There may also be provided a reference voltage generating circuit having multiple discrete voltage level outputs which vary the voltage reference level of the analog signal generator, thereby varying the maximum permissible fluid flow through the valve system. The system can therefore operate in several modes, unlike presently available control systems.

The subject invention overcomes the above set forth disadvantages of state of the art electro-hydraulic control systems. First, the step flow valves in the valve system component are less expensive than proportional control valves, and are readily replaceable in the field, thereby reducing downtime. Each step valve may be individually replaced if malfunctioning, rather than the entire unit. Further, the step valves open and close in response to a digital signal, and are therefore less sensitive than analog based valves to contamination in the fluid, and fluid viscosity variation.

Among the objects of the present invention is to provide an electro-hydraulic control system which selectively regulates fluid flow between a fluid motor and a fluid pump, and which is immune to changes in fluid visocities and the present level of fluid contamination. A further objective is a serviceable control system which can be economically and easily manufactured. and which can adjust to variable operating modes.

These, and other objectives, which will be appraant to one skilled in the art, are achieved by a preferred embodiment which is described in detail below, and which is illustrated by the accompanying drawings.

Brief Description of the Drawings An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which; Figure 1A is a logic schematic of the analog to digital conversion circuits of the subject variable flow control system.

Figure 1B is a logic schematic of the circuitry providing the command signal output for the subject control system. Fig. 1 B and 1A are continuously adjoined along line C-C.

Figure 2 ia a logic schematic of the switching circuits of the present invention which set the analog range of the control mechanisms according to the appropriate operation mode.

Figure 3 is a block level schematic of the variable flow control valve system as set forth by the present invention.

Description of the Preferred Embodiment Referring to Fig. 1A, a pair of parallel analog voltage to digital conversion circuits 2, 4 are provided of preferred type LM3914, providing multiple parallel outputs 1-15 indicated generally at numberal 6. Components 2,4 receive via terminal 5 an analog voltage input signal, and activate digitally an output corresponding to the magnitude of the input voltage. For example, if the range of analog inputs is between 0 and 8 volts, components 2, 4 can be calibrated to deliver a digital output for every .5 volts if input. Thus line 1 2 would go high upon an input of 6 volts at terminal 5; line 9 upon input of 4.5 volts; line 4 upon input of 2 volts; etc.Lines 1 - 1 6 of components 2, 4 are coupled to positive voltage source 8 through 10K ohm resistors 10, while excess lines 17-20 of units 4 are coupled to source 8 through 100K ohm resistors 12.

Referring to Fig. 1 B, which represents the logic diagram continuation of Fig. 1A, four 8 input NAND gates of preferred type MM 74030 are shown schematically as converting the decimal output from lines 1-1 6 of A/D converters 2, 4 into a binary coded decimal format. The outputs of NAND gates 14, 16, 18, 20 are coupled through 5.1K ohm resistors 30 to a two stage amplification network consisting of transistors 22, 24 of type GES6O1O, D45H2, biased by voltage sources 26, 34 respectively. Resistive values selected are a 100K ohm resistor 28, and a 120 ohm resistor 32, coupled to ground by a 1 5K ohm resistor 36 and IN914 diode 38.

The command signal outputs 40, 42, 44, 46 represent the four binary digits of the 8421 BCD Code, and serve to control operation of the variable control valve in a manner explained fully below.

Referring to Fig. 2, a voltage switching network is shown for varying the analog range of the controller of the subject machine funtion according to the appropriately indicated operating mode. For example, an aerial work platform has an articulating boom which is raised by a lift cylinder. The machine may function in a high/low engine mode in which the pump directs more or less fluid to the lift cylinder, depending upon the angular position of the boom. When the boom angle exceeds horizontal, less fluid is supplied to the cylinder, which decreases the speed of elevation for safety reasons.

Similarly, in machines which are capable of ground movement while the boom is raised or lowered, it is desirable to switch from high drive to low drive when the angular position of the boom exceeds the horizontal for the same reasons of safety.

Pursuant to the present invention, a hand controller (not shown) is used to control the boom lift cylinder, which controller being of the type comprising a return to neutral lever which swings through a finite arcuate path, stroking a potentiometer therealong.

Electrically, the analog voltage signal produced by the potentiometer is of a magnitude determined by the arcuate location of the control lever or joystick. The range of the analog voltage signals produced by the potentiometer may be changed by operation of the switching network of Fig. 2 in accordance with the appropriate engine/drive mode variables. The high drive signal is inputted to terminal 48, and the high engine signal to 50. The switching logic comprises four two input AND gates 54, 56, 58, 60. AND gate 60 feeds into a transistive network while gates 54, 56, 58 feed into a voltage switching circuit 61 of type LF13202. The AND gates 54, 56, 58, 60 are inputted through signal terminals 48, 50 and inverters 52 of type MM 74C04 are provided where indicated to logically invert the received signals.

The output from AND gates 54, 56, 58, 60 switch high and select the voltage output range via amplifier switch/lines 63-62; 64-62; 65-62; and 66 which output a voltage level to the hand controller at terminal 74, and receive an 8.2 volt input from the hand controller at terminal 75. The output from AND gate 60 is logically inverted by inverter 67 of type MM 74C04 and fed into a switching network comprising 1 2 volt source 68, 24K ohm resistor 69, 10K ohm resistor 70, diode 71 of type IN914, and switching transistor 72 of type GES2907.

The operation of the switching network of Fig. 2 will be appreciated from the following.

The voltage range of the hand controller is determined by the engine and drive mode variables of the machine. When the position of the boom indicates that low engine and low drive are appropriate (for example, boom elevation above horizontal), output from AND gate 58 goes high and switches line 64 to output terminal 74. The 8.2 volt input from terminal 74 is applied through the 6.2K ohm series resistance of line 64, and the voltage level is supplied to the hand controller from 74. Thus, as the hand controller swings through its arcuate path, an analog voltage signal is incrementally produced. This analog signal is applied to input 1 of Fig. 1A and a BCD coded command signal is generated as described previously.Similarly, if high engine and drive are indicated as appropriate by the boom attitude, output from AND gate 60 goes high, is inverted by 67, and transistor 72 switches the 1 2 volt source voltage source 68 to the hand controller via output terminal 74.

Resultingly, the same arcuate sweep of the hand controller will incrementally generate an analog voltage up to 1 2 volts which will be converted into BCD formate by the circuit of Fig. 1A and 1 B as previously explained.

Referring to Fig. 3, P stands for the hydraulic fluid pressure to the variable flow valve 76 entering at input port 78. A regulated port 80 is provided to direct oil from valve 76 to a directional control valve, which in the case of the example presented thus far, would direct oil to the boom lift cylinder. A By-pass port 82 diverts excess oil that is not needed, as determined by the command signal to the valve, back to tank, As shown, four step flow cartridge valves 84, 86, 88, 90 of a type commercially available are arranged in parallel and are configured to electrically open by solenoid actuation upon address by the digital command signal. When no command signal is being sent to the valve from the hand controller, none of the four cartridge valves are open.

The sizing of the step flow cartridge valves 84, 86, 88, 90 is selected as 1, 2, 4, 8 gallons per minute corresponding to the BCD format. The flow which enters port 78, is sensed by a pressure flow compensator 92 which comprises an integral component of the valve. The function of compensator 92 is to sense the pressure at the regulated port 80 and the pressure of the oil flow which is building up from port 78. The compensator 92 then opens to bypass the oil through port 82 to tank so that the pump is not deadheaded against the closed cartridge valves 84, 86, 88, 90. Valve 94 is a relief that senses maximum system pressure and causes all pump flow to exit through port 82.

An example of the operation of the subject system will be appreciated from the following with reference to the drawings. Referring to Fig. 2, assuming that the position of the boom of an aerial work platform of the like, indicates via a sensor and logic elements that low engine, low drive is the appropriate mode of machine operation. The terminal input to 48, 50 is therefore low, causing AND gate 58 to switch high. The 8.2 volts at 75 is switched through the 6.2K to the hand controller (not shown) via terminal 74.

A hand controller or lever, which controls the elevation of the boom, operates in an arcuate path to stroke a potentiomer. The analog output signal from the potentiometer therefore ranges in magnitude from 0 to the maximum volts at 74, as the control lever swings through its travel. Assume that the position of the control lever sends an analog signal of 7 volts to the Analog to Digital circuit of Fig. 1A at 5. The line 14 of LM3914 circuit 4 goes high and is converted to BCD format 0111 by the NAND gates and driver circuits of Fig. 1 B.The BCD command signal 0111 is then applied via output terminals 40, 42, 44, 46 to the variable flow valve 76 of Fig. 3 Referring to Fig. 3, assuming that when no command signal is being sent the four cartridge valves 84, 86, 88, 90 are closed, and a fixed displacement pump delivers fluid to port 78 at a rate of 1 5 gallons per minute.

The four cartridge valves 84, 86, 88, 90 respectively are sized to allow a flow of 1, 2, 4, 8 8 gallons per minute therethrough, upon command, corresponding to the BCD format.

As the operator moves the hand controller, a BCD coded command signal 1000 is generated which instructs valve 84 to open, while valves 86, 88, and 90 remain closed. Resultingly, 1 gallon of fluid per minute is directed from regulated port 80 to the controlled line, while 14 gallons per minute is dumped through By-pass port to tank by operation of the pressure flow compensator 92. As the operator moves the control lever to the second step gradient, the generated command signal closes off valve 84 and opens valve 86 to pass two gallons per minute. In the example presented above, the 0111 command signal will open valves 86, 88, 90 and fourteen gallons per minute will pass to regulated port 80, with 1 gallon per minute returning to tank.

From the foregoing, it will be appreciated that the valve system 76 operates to decode the digitally formatted BCD command signal into gallons per minute hydraulic units. Four cartridges are selected to correspond with the BCD code, however, more values could be used within the contemplation of the present invention in order to give a greater number of gradations and therefore more control, up to the limit of the BCD code and the pumping system. The cartridge valves may be sized differently than set forth above for specific applications. It should be noted that the cartridge valves are digitally activated, and obviate the need for expensive analog controlled valves which are relatively complex mechanically and sensitive to environmental factors which degrade their performance. Also, the subject invention readily facilitates the convenient replacement of defective or malfunctioning cartridge valves if needed, which enhances the systems flexibility and reduces downtime.

While the above sets forth the preferred embodiment, other embodiments which are not set forth but which utilizes the teachings hereof, are intended to be within the scope and spirit of the present invention.

Claims (16)

1. A variable flow hydraulic system for regulating the rate of flow of hydraulic fluid, comprising: actuator means for generating an analog signal having a value variable within a specified range; analog to digital conversion means for generating a binary coded decimal command signal corresponding to said analog signal value; variable flow control valve means for decoding said binary coded decimal command signal into a unique rate of fluid flow, and directing said rate of fluid flow to hydraulically actuated means.

2. A system as set forth in claim 1, wherein said control valve means having input port means for receiving hydraulic fluid; output port means through which said rate of fluid flow is directed; and a plurality of parallel step flow valve means interposed between said input and output means, each said step flow valve means responding to said command signal and permitting a respective rate of fluid flow therethrough.

3. A system as set forth in claim 1, said variable flow control valve means further comprising by-pass port means, and means for diverting the flow portion not passing through said step flow valve means through said bypass port means.

4. A system as set forth in claim 1, wherein said step flow valve means being normally closed in the absence of said command signal.

5. A system as set forth in claim 1, further comprising circuit means for selectively varying said specified value range of said analog signal.

6. A system as set forth in claim 5, wherein said circuit means comprising: terminal means for delivering a maximum voltage level to said actuator means; a reference voltage source; parallel voltage dividing network switching means for coupling said reference voltage to said terminal means whereby said maximum voltage level at said terminal means is one of several selectably discrete values; logic circuit means for selecting said network means in response to the status of variable inputs.

7. A system as set forth in claim 6, wherein said reference voltage source is a 1 2 volt system battery.

8. A system as set forth in claim 7, wherein said logic circuit means comprising NAND gates receiving said variable inputs and logically selecting said appropriate network switching means.

9. A system as set forth in claim 1, wherein said actuator means comprising a potentiometer.

10. A system as set forth in claim 1, wherein said analog to digital conversion means comprising: circuit means receiving said analog signal and digitally actuating an output line corresponding to the magnitude of said signal; logic gate means having terminal outputs representing said binary code, said logic gate means being coupled to said output lines of said circuit means and generating a binary coded decimal word at said terminal outputs in response to said activated circuit means output.

11. A variable flow hydraulic system for regulating the rate of flow of hydraulic fluid, comprising: switching network means for delivering an output voltage level; actuator means for generating an analog signal having a value up to said switching network output voltage level; analog to digital conversion means for generating a binary coded decimal command signal corresponding to said analog signal value; variable flow control valve means for decoding said binary coded decimal command signal into a unique rate of fluid flow, and directing said rate of fluid flow to hydraulically actuated means.

12. A system as set forth in claim 11, wherein said control valve means having input port means for receiving hydraulic fluid; output port means through which said rate of fluid flow is directed; and a plurality of parallel step flow valve means interposed between said input and output means, each said step flow valve means responding to said command signal and permitting a respective rate of fluid flow therethrough.

1 3. A system as set forth in claim 11, said variable flow control valve means further comprising by-pass port means, and means for diverting the flow portion not passing through said step flow valve means through said by-pass port means.

14. A system as set forth in claim 11, wherein said step flow valve means being normally closed in the absence of said command signal.

15. A system as set forth in claim 11, wherein said switching network means delivering one of several possible output voltage levels in response to the status of at least one input variable

16. A system as set forth in claim 15, wherein said switching network means deriving said output voltage level from a reference voltage source.