Control system for variable speed drive

Claim 2

A control circuit for effecting control of a fluid pressure operated, variable speed drive, comprising; a source of fluid under pressure; an on-off fluid control valve connected to apply fluid pressure from said source to said drive for effecting control thereof and operable upon a predetermined input; means responsive to the output of said drive for generating a signal, means generating a signal representing a desired output; a control circuit having its input connected to respond to the difference between said signals and its output connected to operate said fluid control valve; an oscillator having a period of oscillation less than the natural response time of said drive but which is greater than the maximum response time of said valve and a frequency independent of the output speed of the variable speed drive; and means connecting the output of said oscillator in superposition on the output of said control circuit to effect operation of said valve in accordance with said oscillator rate for time periods corresponding to that portion of the oscillator wave form which exceeds said valve predetermined input.

Claim 3

The control circuit of claim 1 further comprising means for varying the frequency of said oscillator.

Claim 4

The control circuit of claim 1 further comprising means for varying the wave form of said oscillator output.

Claim 5

The circuit of claim 1 further including an accumulator positioned between said on-off valve and said drive and wherein this period of said oscillator is less than the response time of the fluid system which includes said drive and said accumulator.

Claim 6

The control circuit of claIm 1 in which said variable speed drive is of the oil shear type having a series of interfitting stator and rotor plates operated by an oil film through the speed control is effected by varying the coupling therebetween.

Claim 7

The control system for the control of the output speed of a slip type oil shear variable speed drive in which said output speed is controlled by varying the coupling between a series of interfitting plates with a fluid operated piston unit controlled from a source of fluid pressure, comprising an electrically operated on-off valve operable upon a predetermined minimum input signal and connected to such source and adapted to apply such source to said fluid piston for increasing said output speed by connecting said fluid pressure source to said piston and for decreasing said output speed by disconnecting said fluid pressure source from said piston, means for generating a signal representing said output speed, reference means forming a signal of a desired output speed, means comparing said reference and output speed signals including a DC amplifier, the output of said amplifier being connected to control said valve, an oscillator, the output frequency of which is independent of the output speed of the variable speed drive, forming a signal of alternating predetermined wave form connected to superimpose said wave form on the DC output of said amplifier and having a frequency which substantially exceeds the response rate of said drive but which is less than the maximum response rate of said valve, the amplitude of said alternating wave form being such that said valve is controlled primarily by said wave form to provide a control for said drive when said difference signal is less than said valve minimum input signal.

Claim 8

The control system for the control of the output speed of a slip type oil shear variable speed drive in which said output speed is controlled by varying the coupling between a series of interfitting plates with a fluid operated piston unit controlled from a source of fluid pressure, comprising an electrically operated on-off valve operable upon a predetermined minimum input signal and connected to such source and adapted to apply such source to said fluid piston for increasing said output speed by connecting said fluid pressure source to said piston and for decreasing said output speed by disconnecting said fluid pressure source from said piston, means for generating a signal representing said output speed, reference means forming a signal of a desired output speed, means comparing said reference and output speed signals including a DC amplifier, the output of said amplifier being connected to control said valve, an oscillator, the output frequency of which is independent of the output speed of the variable speed drive, forming a signal of alternating predetermined wave form connected to superimpose said wave form on the DC output of said amplifier and having a frequency which substantially exceeds the response rate of said drive but which is less than the maximum response rate of said valve, the amplitude of said alternating wave form being such that said valve is controlled primarily by said wave form to provide a control for said drive when said difference signal is less than said valve minimum input signal.

Claim 9

The control system of claim 6 in which the response rate of said variable speed drive is nonlinear with respect to said difference signal and where the wave form of said oscillator is nonlinear in amplitude to compensate in part for the nonlinearity of said drive response.