Abstract: An apparatus for generating a reference signal in a brake control system stores a reference signal representative of a reference braking condition and compares this reference signal with a conditioned wheel signal. Depending on the outcome of the comparison, the reference signal is either updated to correspond to a reduced reference braking condition or ramped to correspond to an increased braking condition. The reference signal is not simultaneously ramped and updated, and is, therefore, precisely controlled. In a first embodiment, the amount by which the reference signal is ramped is a function of the past history of the reference signal: each time the reference signal is ramped the ramp rate is increased and each time the reference signal is updated the ramp rate is decreased.

Abstract: An improved modulator for an anti-skid brake control system generates a modulated brake control signal as a time integral function of the difference between an input signal indicative of a braking condition and a variable threshold signal. The preferred embodiment includes a computer which stores a number of threshold signals. An appropriate one of these threshold signals is selected depending on the magnitude of the velocity of the braked wheel. Furthermore, the modulator adjusts the value of the modulated brake control signal in response to skids more severe than a preset level in a manner that varies in response to the frequency of such more severe skids.

Abstract: An initialization apparatus for an antiskid brake control system including a modulator which generates a brake control signal as a time integral function of an error signal operates to initialize the modulator to a preselected value of the brake control signal when excessive braking action is sensed after a period of antiskid inactivity. The initialization apparatus also operates to initialize a reference signal in the direction of more aggressive braking and to bias the reference signal and a wheel signal toward more aggressive braking for a selected time period following initialization of the modulator.

Abstract: An antiskid braking system includes an improved apparatus for generating a lead signal to provide lead compensation. According to one feature of this apparatus, the gain of the apparatus is made to vary as a function of a signal, such as the brake control signal generated by the antiskid system, which is indicative of the coefficient of braking under severe braking conditions. Another feature of the invention is that the apparatus operates to reduce the magnitude of the lead signal when it exceeds a limit value, preferably by clamping the lead signal to a maximum magnitude.

Abstract: An antiskid braking system includes an improved apparatus for generating a lead signal to provide lead compensation. According to one feature of this apparatus the gain is a function of the algebraic sign of the input signal to the apparatus. Preferably, higher gains are used when the input signal corresponds to wheel deceleration than when it corresponds to acceleration. Another feature of the invention is that the apparatus operates to reduce the magnitude of the lead signal when it exceeds a limit value, preferably by clamping the lead signal to a maximum magnitude. A third feature is that first and second order lead signals are utilized in such a way as to preclude adverse cancellation between the two.

Abstract: A spin-up detection apparatus for a brake control system operates to monitor a wheel speed signal indicative of the rotational velocity of a wheel until the wheel speed signal exceeds an absolute velocity threshold. Once this threshold is exceeded, the apparatus then monitors the rate of change of the wheel speed signal. When this rate of change falls below a predetermined level, a control signal is generated to indicate that wheel spin-up is substantially complete.

Abstract: An apparatus for precisely measuring the period of a wheel signal generated by a transducer in a brake control system includes a clock for generating a periodic clock signal, a first counter for maintaining a count of clock signal cycles, a second counter for maintaining a count of wheel signal cycles, a gate for selectively enabling and disabling the first and second counters at substantially the same phase angle of the wheel signal, and a computer programmed to read the first and second counters, to control the gate to enable the first and second counters for a period of time, and then to read the first and second counters again to arrive at measure of the elapsed time and the number of wheel signal cycles occurring during the measurement period.

Abstract: An antiskid braking system includes an improved apparatus for generating a lead signal to provide lead compensation. According to one feature of this apparatus the gain is a function of the algebraic sign of the input signal to the apparatus. Preferably, higher gains are used when the input signal corresponds to wheel deceleration than when it corresponds to acceleration. Another feature of the invention is that the apparatus operates to reduce the magnitude of the lead signal when it exceeds a limit value, preferably by clamping the lead signal to a maximum magnitude.

Abstract: An improved modulator for an anti-skid brake control system generates a modulated brake control signal as a time integral function of the difference between an input signal indicative of a braking condition and a variable threshold signal. The preferred embodiment includes a computer which stores a number of threshold signals. An appropriate one of these threshold signals is selected depending on the magnitude of the velocity of the braked wheel.

Abstract: An initialization apparatus for an antiskid brake control system including a modulator which generates a brake control signal as a time integral function of an error signal operates to initialize the modulator to a preselected value of the brake control signal when excessive braking action is sensed after a period of antiskid inactivity. The initialization apparatus also operates to initialize a reference signal in the direction of more aggressive braking and to bias the reference signal toward more aggressive braking for a selected time period following initialization of the modulator.

Abstract: An antiskid brake control system responsive to a periodically posted wheel signal operates to generate and store a modulator control signal and a transient control signal. The control system then waits until a new value of the wheel signal is posted, and then promptly generates a lead signal as a function of the new value. This lead signal is then promptly combined with the stored modulator and transient control signals to produce a composite brake control signal. In this way the time delay between the posting of a new value of the wheel signal and the generation of a new lead signal and composite signal is minimized.

Abstract: An apparatus for generating a reference signal in a brake control system stores a reference signal representative of a reference braking condition and compares this reference signal with a conditioned wheel signal. Depending on the outcome of the comparison, the reference signal is either updated to correspond to a reduced reference braking condition or ramped to correspond to an increased braking condition. The reference signal is not simultaneously ramped and updated, and is, therefore, precisely controlled. The amount by which the reference signal is ramped is a function of the past history of the reference signal: each time the reference signal is ramped the ramp rate is increased and each time the reference signal is updated the ramp rate is decreased.

Abstract: A memory control device for a multiple wheel brake control system includes a control bit under computer control. This control bit is coupled to one of a plurality of address terminals of a memory device such that the one address terminal can be controlled by the computer, independent of normal addressing. In this way the computer can configure the memory device to access either of two distinct blocks of memory.

Abstract: An apparatus for precisely measuring the period of a wheel signal generated by a transducer in a brake control system includes a clock for generating a periodic clock signal, a first counter for maintaining a count of clock signal cycles, a second counter for maintaining a count of wheel signal cycles, a gate for selectively enabling and disabling the first and second counters at substantially the same phase angle of the wheel signal, and a computer programmed to read the first and second counters, to control the gate to enable the first and second counters for a period of time, and then to read the first and second counters again to arrive at measure of the elapsed time and the number of wheel signal cycles occurring during the measurement period.

Abstract: A wheel speed sensing system for a brake control system is characterized in that the periodic signal generated by a wheel speed transducer is used to trigger a series of digital signals having a frequency proportional to that of the periodic transducer signal. Clock signals are counted between a selected pair of digital signals to provide a digital measure of the time interval separating the digital signals and hence the period of the periodic signal. In a preferred embodiment the number of intervening digital signals separating the selected pair of digital signals is automatically chosen to maintain the time resolution of the measurement above a preselected value.

Abstract: An encoder is disclosed for providing an accurate digital representation of the altitude of an aircraft vehicle by comparing an output signal from a pressure transducer which is a function of the barometric pressure at the altitude of the vehicle with an internally generated waveform which represents a curve of altitude vs. barometric pressure on its X--Y axis. The waveform is generated by a closed loop having an integrator circuit for providing the waveform, a comparator, a filter, a voltage controlled oscillator, and a counter, which all maintain the amplitude of the waveform within precise limits. The output signal from the transducer and the wave form from the closed loop are compared by a second comparator to provide a signal which transfers temporary information in the counter to a storage device which provides a coded digital output of the altitude of the vehicle.