Patent GB-1369596-A (GB)
Title: Solenoid device
IPC: H01F7/13
Filed: 1970-10-07
Abstract: 1369596 Brake valves, valves NATIONAL RESEARCH DEVELOPMENT CORP 5 Oct 1971 [7 Oct 1970] 47598/70 Headings F2V and F2F [Also in Division H1] A solenoid 6 (Fig. 1) has an axially sliding core 7 with a push-rod 8 sliding within sleeve 10 threaded into housing 1 and cap 12 to carry a metal indenter 14 with coned face engaging a resilient rubber block 15 as the core moves on energization; the block developing a non- linearly variable force with a deflection opposed to the non-linearly variable force developed during the travel of the core, so that the latter assumes a variable position in working range dependent on coil current. This is supplied as rectangular pulses of constant amplitude and mark/space modulation from a shaping circuit 33 controlled by, e.g. a brake pedal 34. The remote end of the core is connected over pushrod 16 to a a valve spool 17 moving within a slidable sleeve 18 of housing 1, travel being limited by the abutment of indenter 13 on sleeve 9 and adjusting screw 19. A diaphragm 28 carried by the sleeve 18 defines chambers to which atmosphere is admitted over 20, 21. As shown the force patterns of core 7 and block 15 are balanced and core and sleeve 7, 9 are in abutment separated by nonmagnetic spacer 31. Port 5 connected to the active side of a brake servo (not shown) is disconnected from port 20 but connected to the vacuum port 4 of the servo so that brakes are not applied, due to the vacuum on both sides of the diaphragm. Deflection of core 7 to the left causes edge 24 of the valve spool 17 to cover port 23 of the outer sleeve 18 to disconnect spaces 2, 3. Further such movement admits air from port 20 to space 3 over 25, 26, 77; destroying pressure equality and applying the brakes. Diaphragm 28 is deflected to the left, and sleeve 18 deflects spring 29 and closes port 27 to disconnect ports 20 and 5; the system then assuming a stable state of brake application dependent on the deflection of core 7, and linearly related to the mark/space ratio of the coil energization. On interruption of the latter the core and spool valve deflect to the right, and spring 29 restores the sleeve 18, so that brakes are released; the restoration being assisted by gravity if the device is mounted vertically. A spiral variable rate spring may replace block 15. Alternatively (Figs. 2, 3, not shown) the solenoid has three coils in series to reduce capacitance, with two indenter members on a centre pivoted bridge carried on the end of the core, which bear on a annular resilient forcetransducer of linear characteristics, the signal from which representing the force thereon and being fed as input to the mark/space shaping circuit together with a control signal; the shaping circuit being programmed to convert the linear transducer signal to a nonlinear signal of flow corresponding to that of the core deflection. The solenoid is then energized by the error between this signal and the control signal. Non- linear resilient blocks may replace the transducer, as before, and the device of Fig. 1 may be combined with a positional feedback system to compensate hysteresis error. The required characteristics of the nonlinear block are described (Fig. 4, not shown).