Digital proportional spool position control of compensated valves

Claim 2

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal the number of said pulses being independent of the time taken in generation of said manual control signal, and intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal.

Claim 3

A valve assembly as set forth in claim 1 wherein said linear step output means includes a stepper motor means interconnected to a rotary to linear motion translating means.

Claim 4

A valve assembly as set forth in claim 1 wherein said linear step output means includes fluid power force amplifying means.

Claim 5

A valve assembly as set forth in claim 3 wherein said fluid power force amplifying means includes linear step distance amplifying means.

Claim 6

A valve assembly as set forth in claim 4 wherein said linear step distance amplifying means includes servo beam means.

Claim 7

A valve assembly as set forth in claim 1 wherein limiting force transmitting lost motion means is interposed between said linear step output means and said valve means.

Claim 8

A valve assembly as set forth in claim 1 wherein manual control means is interconnected to said valve means.

Claim 9

A valve assembly as set forth in claim 1 wherein said intermittent pulse type control signal transmitting means has electrical pulse transmitting means.

Claim 10

A valve assembly as set forth in claim 1 wherein said intermittent pulse type control signal transmitting means includes first transducer means operable to convert an electrical signal into a light signal, transmitting means operable to transmit said light signal, a second transducer means operable to convert a light signal into an electrical signal.

Claim 11

A valve assembly as set forth in claim 1 wherein said intermittent pulse type control signal transmitting means includes first transducer means operable to convert an electrical signal into a ratio wave signal and second transducer means operable to convert said ratio wave signal into an electrical signal.

Claim 12

A valve assembly as set forth in claim 1 wherein a switching logic means is interposed between said intermittent pulse type control signal generating means and said linear step output means.

Claim 13

A valve assembly as set forth in claim 1 wherein said linear step output means includes adjusting means operable to synchronize said linear step output means with a pulse type signal generated by said intermittent pulse type control signal generating means.

Claim 14

A valve assembly as set forth in claim 1 wherein a closed loop digital synchronizing means is interposed between said control signal generating means and said linear step output means.

Claim 15

A valve assembly as set forth in claim 13 wherein said closed loop digital synchronizing means has fiber optics signal transmitting means.

Claim 16

A valve assembly as set forth in claim 13 wherein said closed loop digital synchronizing means has radio wave signal transmitting means.

Claim 17

A valve assembly as set forth in claim 1 wherein said manual input control means has manual synchronizing means operable to synchronize the position of said manual input control means with the output of said linear step output means.

Claim 18

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal.

Claim 19

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal.

Claim 20

A valve assembly as set forth in claim 17 wherein said linear step output means includes a stepper motor means interconnected to a rotary to linear motion translating means.

Claim 21

A valve assembly as set forth in claim 17 wherein limiting force translating lost motion means is interposed between said force amplifying means and said valve means.

Claim 22

A valve assembly as set forth in claim 17 wherein manual control means is interconnected to said valve means.

Claim 23

A valve assembly as set forth in claim 17 wherein a switching logic means is interposed between said intermittent pulse type control signal generating means and said linear step output means.

Claim 24

A valve assembly as set forth in claim 17 wherein said pressure fluid operated force amplifying means includes positioning means of said valve means and pilot valve means operable to control the position of said positioning means.

Claim 25

A valve assembly as set forth in claim 22 wherein a servo link means is interposed between said pilot valve means and said linear step output means.

Claim 26

A valve assembly as set forth in claim 17 wherein said intermittent pulse type control signal generating means includes electrical pulse generating means.

Claim 27

A valve assembly as set forth in claim 17 wherein said intermittent pulse type control signal generating means includes light pulse generating means.

Claim 28

A valve assembly as set forth in claim 17 wherein said intermittent pulse type control signal generating means includes radio wave pulse generating means.

Claim 29

A valve assembly as set forth in claim 17 wherein said intermittent pulse type control signal transmitting means has electrical pulse transmitting means.

Claim 30

A valve assembly as set forth in claim 17 wherein said intermittent pulse type control signal transmitting means includes first transducer means operable to convert an electrical signal into a light signal, transmitting means operable to transmit said light signal, and second transducer means operable to convert a light signal into an electrical signal.

Claim 31

A valve assembly as set forth in claim 28 wherein said first transduer means is interconnected to said intermittent pulse type control signal generating means.

Claim 32

A valve assembly as set forth in claim 28 wherein said second transducer means is functionally interconnected to said linear step output means.

Claim 33

A valve assembly as set forth in claim 28 wherein said transmitting means includes fiber optic light transmitting means.

Claim 34

A valve assembly as set forth in claim 17 wherein said intermittent pulse type control signal transmitting means includes first transducer means operable to convert an electrical signal into a radio wave signal and second transducer means operable to convert said radio wave signal into an electrical signal.

Claim 35

A valve assembly as set forth in claim 32 wherein said first transducer means is interconnected to said intermittent pulse type control signal generating means.

Claim 36

A valve assembly as set forth in claim 32 wherein said second transducer means is functionally interconnected to said linear step output means.

Claim 37

A valve assembly as set forth in claim 34 wherein a switching logic means is interposed between said second transducer means and said linear step output means.

Claim 38

A valve assembly as set forth in claim 17 wherein said manual input control means includes manual lever means functionally interconnected to said intermittent pulse type control signal generating means and to reverse rotation signal generating means.

Claim 39

A valve assembly as set forth in claim 36 wherein first manually operated switching means is interconnected to said intermittent pulse type control signal generating means.

Claim 40

A valve assembly as set forth in claim 36 wherein a second reverse switching means is interposed between said manual lever means and said reverse rotation signal generating means.

Claim 41

A valve assembly as set forth in claim 36 wherein switching logic means is interposed between said linear step output means and said reverse rotation signal generating means.

Claim 42

A valve assembly as set forth in claim 17, wherein said manual input control means has synchronizing means operable to synchronize said manual input control means with said linear step output means.

Claim 43

A valve assembly as set forth in claim 17, wherein said manual input control means includes reverse signal generating means.

Claim 44

A valve assembly as set forth in claim 17, wherein said manual input control means includes manual lever means operable to generate a number of pulses proportional to a manual input signal when displaced in forward and reverse directions and also operable to engage a reverse signal generating means when displaced in said reverse direction.

Claim 45

A valve assembly as set forth in claim 17, wherein said manual input control means includes manual lever means and activating means of said intermittent pulse type control signal generating means.

Claim 46

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an opposing load, second fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in an intermittent pulse type control signal said linear step output means having control means responsive to said intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said control means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 47

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an opposing load, second fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in an intermittent pulse type control signal said linear step output means having control means responsive to said intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said control means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 48

A valve assembly as set forth in claim 44 wherein said linear step output means includes a stepper motor means interconnected to a rotary to linear motion translating means.

Claim 49

A valve assembly as set forth in claim 44 wherein said linear step ouput means includes fluid power force amplifying means.

Claim 50

A valve assembly as set forth in claim 44 wherein limiting force transmitting lost motion means is interposed between said linear step output means and said valve means.

Claim 51

A valve assembly as set forth in claim 44 wherein manual control means is interconnected to said valve means.

Claim 52

A valve assembly as set forth in claim 44 wherein switching logic means is interposed between said intermittent pulse type control signal generating means and said linear step output means.

Claim 53

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an opposing load, second fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an aiding load, pressure fluid operated force amplifying means operably connected to said valve means, and linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 54

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an opposing load, second fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an aiding load, pressure fluid operated force amplifying means operably connected to said valve means, and linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 55

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means, second fluid throttling means positioned adjacent to said valve means, pilot valve means operable through said first fluid throttling means to control pressure differential across said valve means during control of an opposing load and also operable through said second fluid throttling means to control pressure differential across said valve means during control of an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in intermittent pulse type control signal said linear step output means having control means responsive to said intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said control means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 56

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means, second fluid throttling means positioned adjacent to said valve means, pilot valve means operable through said first fluid throttling means to control pressure differential across said valve means during control of an opposing load and also operable through said second fluid throttling means to control pressure differential across said valve means during control of an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in intermittent pulse type control signal said linear step output means having control means responsive to said intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said control means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 57

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means, second fluid throttling means positioned adjacent to said valve means, pilot valve means operable through said first fluid throttling means to control pressure differential across said valve means during control of an opposing load and also operable through said second fluid throttling means to control pressure differential across said valve means during control of an aiding load, pressure fluid operated force amplifying means operably connected to said valve means, and linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce an intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 58

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means, second fluid throttling means positioned adjacent to said valve means, pilot valve means operable through said first fluid throttling means to control pressure differential across said valve means during control of an opposing load and also operable through said second fluid throttling means to control pressure differential across said valve means during control of an aiding load, pressure fluid operated force amplifying means operably connected to said valve means, and linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce an intermittent pulse type control signal the number of said pulses being independent of the time taken in generation of said intermittent pulse type control signal, and pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for varying fluid flow to and from said fluid motor proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 59

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load, linear step output means operable to actuate said valve means in discrete linear steps equal in number to a number of pulses in an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal, intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, and limiting force transmitting lost motion means interposed between said linear step output means and said valve means.

Claim 60

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load, linear step output means operable to actuate said valve means in discrete linear steps equal in number to a number of pulses in an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal, intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, and limiting force transmitting lost motion means interposed between said linear step output means and said valve means.

Claim 61

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal the number of said pulses being independent of the time taken in generation of said manual control signal, intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means, and synchronizing means in said manual input control means operable to synchronize said manual input control means with said linear step output means.

Claim 62

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal the number of said pulses being independent of the time taken in generation of said manual control signal, intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means, and synchronizing means in said manual input control means operable to synchronize said manual input control means with said linear step output means.

Claim 63

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal, intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, and synchronizing means in said manual input control means operable to synchronize said manual input control means with said linear step output means.

Claim 64

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal, intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, and synchronizing means in said manual input control means operable to synchronize said manual input control means with said linear step output means.

Claim 65

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal, intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, and limiting force translating lost motion means interposed between said force amplifying means and said valve means.

Claim 66

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal, intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, and limiting force translating lost motion means interposed between said force amplifying means and said valve means.

Claim 67

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal, intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, positioning means of said valve means and pilot valve means operable to control the position of said positioning means, and servo link means interposed between said pilot valve means and said linear step output means.

Claim 68

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or an aiding load pressure, fluid operated force amplifying means operably connected to said valve means, linear step output means operable through said force amplifying means to actuate said valve means in discrete linear steps in response to an intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal, intermittent pulse type signal transmitting means interconnecting said intermittent pulse type control signal generating means and said linear step output means for actuating said valve means through a distance proportional to the magnitude of said manual input signal, positioning means of said valve means and pilot valve means operable to control the position of said positioning means, and servo link means interposed between said pilot valve means and said linear step output means.

Claim 69

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an opposing load, second fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in an intermittent pulse type control signal said linear step output means having control means responsive to said intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal and intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said control means, and limited force transmitting lost motion means interposed between said linear step output means and said valve means whereby fluid flow to and from said fluid motor can be varied proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.

Claim 70

A valve assembly having valve means operable to control by throttling fluid flow to and from a fluid motor subjected to an opposing or aiding load, first fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an opposing load, second fluid throttling means positioned adjacent to said valve means having means operable to control pressure differential across said valve means during control of an aiding load, linear step output means operable to actuate said valve means in discrete steps equal in number to a number of pulses in an intermittent pulse type control signal said linear step output means having control means responsive to said intermittent pulse type control signal, intermittent pulse type control signal generating means having manual input control means operable to generate a number of pulses proportional to a manual input signal to produce intermittent pulse type control signal and intermittent pulse type control signal transmitting means interconnecting said intermittent pulse type control signal generating means and said control means, and limited force transmitting lost motion means interposed between said linear step output means and said valve means whereby fluid flow to and from said fluid motor can be varied proportionally to the magnitude of said manual input signal irrespective of the magnitude of said aiding or said opposing load.