Electro-hydraulic remote valve

An application of the basic system of patent application Ser. No. 149,065 for operating a remote hydraulic valve. An electro-hydraulic actuator is mechanically linked to the control member of the remote valve. An input control signal is generated by multiplying a signal from a control handle position transducer by a scale factor constant produced by a full control setting with a gain control circuit. The gain control circuit also operates to set the constant to unity in case the signal from the handle position transducer exceeds a predetermined level corresponding to a maximum control handle setting. The control handle itself has four positions: Float, Lower, Neutral and Raise. The handle is biased so that if the handle is released from any position other than Neutral, the handle will go to the Neutral position provided a detent is off. The detent is put in the "off" position by an electrical solenoid which is actuated whenever the supply pressure to the remote valve exceeds a set value. By this means the handle is released from either Raise or Lower position when conditions occur corresponding to the remote valve hitting the end of its stroke or its being overloaded.

TECHNICAL FIELD 
This invention relates to an electrical control system for operating any 
hydraulic remote valve. 
BACKGROUND OF THE INVENTION 
In our copending applications Ser. No. 149,065 filed May 12, 1980 for an 
Electro-Hydraulic Proportional Actuator and Ser. No. 166,731 filed July 7, 
1980 for an Electrically Operated Hydraulic Power Lift System, now U.S. 
Pat. No. 4,343,365, we noted that agricultural tractor controls 
traditionally have been a hydro-mechanical system wherein, for example, 
implement draft is sensed mechanically. Through appropriate mechanical 
linkage, a hydraulic valve is actuated to supply operating fluid to a 
hydraulic cylinder for raising and lowering the implement. 
The development of low-cost, reliable electronic microcomputers has 
introduced an unlimited flexibility in the design of tractor control 
systems. The primary requirement for implementing any tractor 
electro-hydraulic system is a low-cost, contaminant insensitive, 
environmentally sound interface device, preferably a hydraulic 
proportional actuator, such as is disclosed in our aforementioned 
application Ser. No. 149,065, for converting an electric signal to either 
a mechanical or hydraulic output device. 
Operation of a hydraulic proportional actuator to control, for example, a 
hydraulic remote valve, requires a compatible control system such as is 
provided by the present invention. 
SUMMARY OF THE INVENTION 
The present invention relates to an application of the basic system 
disclosed in our application Ser. No. 149,065 for operating a remote 
hydraulic valve. The hydraulic proportional actuator is mechanically 
linked to the control member of the remote valve and is electronically 
linked to a control handle. The position of the control handle is 
monitored continuously by a handle position potentiometer (transducer). An 
input control signal KVp is generated by multiplying the output signal Vp 
of the handle position transducer by a scale factor K produced by a full 
control setting with a gain control circuit. The gain control circuit also 
operates to set K to unity in the case the Vp exceeds a predetermined 
level Vp.sub.4 corresponding to a maximum control handle setting. 
The control handle itself has four positions, float, lower, neutral and 
raise. The handle is spring centered by a torsion spring arrangement so 
that if the handle is released from any position other than neutral, the 
handle will go to the neutral position provided a detent is off. The 
detent is put in the "off" position by an electrical solenoid which is 
actuated whenever the supply pressure to the remote valve exceeds a set 
value. By this means, the handle is released from either raise or lower 
position when conditions occur corresponding to the remote cylinder 
hitting the end of its stroke or its being overloaded.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, the hydraulic proportional actuator 10, as 
more fully explained in our application Ser. No. 149,065, comprises two 
three-way solenoid operated valves 11 and 12 adapted to control the flow 
of fluid from a pressure supply 13 to either side of an actuator piston 
14. The actuator piston rod 15 is mechanically coupled to a remote valve 
16 through which fluid is supplied to a hydraulic cylinder (not shown) for 
moving an implement or the like. The activation/deactivation of the 
solenoid valves is controlled by an electronic control system, the 
schematic diagram of which is shown in FIG. 1. The system shown in FIG. 1 
is adapted for a hydraulic remote valve 16 which meters flow as a function 
of the valve spool displacement. A linearly movable actuating extension of 
the valve is shown as extending from the right side of the remote valve 16 
to engage the piston rod 15 of actuator piston 14 in FIG. 1. In the 
disclosed embodiment a linear metering characteristic is assumed, but the 
control system can be adapted to a valve with any sort of metering 
characteristics that are available on the market. 
Operation of the control system is initiated by operator movement of a 
control handle 17. The control handle 17 has four detent positions, 
Neutral, Raise, Lower and Float. The position of the control handle 17 is 
monitored continuously by a handle position potentiometer (transducer) 18. 
The handle is spring centered by a torsion spring (not shown) so that if 
the handle is released from any position other than Neutral, the handle 
will go to the Neutral position provided a detent (not shown) is off. The 
detent can be put in the off condition by means of an electrical force 
solenoid 19. This solenoid is actuated whenever the supply pressure to the 
remote valve exceeds a set value in an electrical pressure switch 21. The 
legend in the box 21 indicating the pressure switch indicates, for 
example, that the pump (supply source) switch would be "on" at 2500 psi 
(175.75 kgm/cm.sup.2). The purpose of providing the pressure switch 
operated detent mechanism is to provide for the automatic release of the 
handle from either Raise or Lower positions so that the handle (and the 
remote valve) can return to the Neutral position when the system pressure 
exceeds the switch pre-set value. This condition is normally experienced 
whenever the cylinder (or motor) being operated by the remote valve hits 
the end of its stroke or is overloaded. A flow control knob 22 is provided 
at the control console of the tractor to set the maximum flow from the 
remote valve when the handle is in either Raise or Lower detent positions. 
The translation of the position of the control handle 17 into a position of 
the remote valve spool occurs as follows. The output Vp of the control 
handle position transducer 18 is first fed into a gain control device 23 
that attenuates the signal in proportion to the flow control 22 setting at 
the control console. When the control handle 17 is moved to the Float 
position, the flow control setting is overridden and the signal goes 
through with a unity gain. The desired position of the remote valve 16, 
KVp, is compared with the actual position of the valve, Vv, as determined 
by a valve spool transducer 24. The difference KVp-Vv is the output 
Ve.sub.2 of the summing device 25. The error signal Ve.sub.2 is used to 
drive the electro-hydraulic proportional actuator 10. As previously 
described, the actuator piston 14 is attached to the spool (not visible) 
of the remote valve 16. 
In the Neutral condition, when the control handle is within the Neutral 
zone, as defined by the magnitude of (Vp-Vp.sub.2) being within V.sub.3, 
both solenoid valves are turned off. The actuator piston is free to float 
in this condition and the position of the remote valve is determined by 
centering springs on the remote valve spool. In the Float position of the 
valve spool, the two output ports of the remote valve are connected 
together and to the sump. 
If Ve.sub.2 is greater than V.sub.3, the actual position of the remote 
valve lags the desired position and solenoid valve 11 is turned on and 
solenoid valve 12 is turned off. This makes the actuator piston 14 move to 
the right, as viewed in FIG. 2, as a speed determined by the actuator flow 
control valve 26. If Ve.sub.2 is less than -V.sub.3, solenoid valve 12 is 
turned on and solenoid valve 11 is turned off. This makes the actuator 
piston 14 move to the left. When the difference between the desired 
position and actual position of the valve is within a prescribed tolerance 
band, both the solenoid valves 11 and 12 are turned on. This effectively 
holds the actuator at that position because of the two check valves 27 in 
the pressure inlet lines to the valves. 
The clock 28 is used to set a maximum rate at which the solenoids 11 and 12 
are turned on and off. During the sampling time intervale, when the clock 
output is "high", the sample and hold device allows Ve.sub.2 to go through 
the logic module 29 which makes the decisions on turning the two solenoids 
11 and 12 on or off. If, during the the clock period, the desired position 
is reached, as evidenced by either the two solenoids 11 and 12 being both 
on or both off, the sample and hold circuit 31 freezes the value of 
Ve.sub.2 at that instant so that no further decisions are made by the 
logic module 29 until the next sampling time interval. This effectively 
ensures that the solenoids can be turned on and off only once during a 
clock period. This provides for an acceptable cycle life for the solenoid 
valves. The clock frequency is a function of the fastest input signal 
frequency to be followed. If the input handle 17 where to be moved with a 
speed equivalent to a 5 Hz signal, the desirable clock frequency would be 
about 20 Hz. It is possible for the control system to automatically vary 
the clock frequency as a function of input requirements so that at slower 
speeds, a slower frequency can be used, which further extends the life of 
the solenoid valves. 
The advantages of the electro-hydraulic remote valve are: 
It permits the use of simple on/off, three-way solenoid valves which are 
inexpensive and relatively insensitive to contamination. 
It may be used on current mechanical/hydraulic remote valves where space is 
available to mount the proportional electro-hydraulic actuator. 
In tractors with enclosed cabs, the electro-hydraulic remote valve system 
will help reduce noise levels due to the use of noise-tight electrical 
connectors; it will also save time during assembly and disassembly of cabs 
from tractors. 
The remote valves can be located at great distances from the operator since 
no linkages or hoses are involved between the control station and the 
valve (either few wires or two wires and an optical cable or one conductor 
cable carrying multiplexed signals). 
The life of the solenoid valves is extended by limiting the maximum 
sampling frequency in the control system. The valves are turned off at the 
Neutral position. 
It is to be understood that this invention is not limited to the exact 
construction illustrated and described above, but that various changes and 
modifications may be made without departing from the spirit and scope of 
the invention as defined in the appended claims.