Skid control system

Claim 2

A skid control system for skid controlling at least one skidcontrolled wheel of a multi-wheeled vehicle via fluid pressure modulation of pressure fluid applied to a brake system operatively associated with said at least one skid-controlled wheel, said skid control system comprising speed sensing means associated with said at least one skid-controlled wheel for developing a repetitive wheel speed signal whose repetition rate represents the speed of said at least one skid-controlled wheel, and skid control circuit means for developing a skid control signal for skid controlling said at least one skid-controlled wheel, said skid control circuit means comprising circuit means including reference generating means for developing from at least one selected wheel of the vehicle a repetitive reference signal, said reference generating means including modulating means for modulating the repetition rate of said reference signal in accordance with the speed of said at least one selected wheel, said modulating means comprising means for causing the repetition rate of said reference signal to represent a speed substantially corresponding to the speed of said at least one selected wheel so long as deceleration thereof does not exceed a predetermined value and for causing the repetition rate of said reference signal to change in a predetermined fashion when the deceleration of said at least one selected wheel exceeds said predetermined value, and comparator circuit means for comparing the repetition rate of said reference signal with the repetition rate of said wheel speed signal and for developing said skid control signal when the repetition rate of said wheel speed signal differs from the repetition rate of said reference signal by a predetermined amount, and modulating means operatively coupling said brake system with said circuit means and responsive to said skid control signal for modulating fluid pressure in said brake system.

Claim 3

The skid control system of claim 1 wherein said comparator circuit means comprises means for developing said skid control signal when the repetition rate of said wheel speed signal falls below the repetition rate of said reference signal.

Claim 4

The skid control system of claim 1 wherein said circuit means comprises means for causing the repetition rate of said reference signal to increase with increasing speed of said at least one selected wheel and to decrease with decreasing speed of said at least one selected wheel.

Claim 5

The skid control sytem of claim 1 wherein said circuit means comprises means for causing the repetition rate of said reference signal to represent a speed which is slightly less than the actual speed of said at least one selected wheel so long as deceleration of said at least one selected wheel does not exceed said predetermined value.

Claim 6

The skid control system of claim 1 wherein said circuit means comprises means for causing the repetition rate of said reference signal to reprEsent a speed which differs from the actual speed of said at least one selected wheel by a predetermined amount so long as deceleration of said at least one selected wheel does not exceed said predetermined value.

Claim 7

The skid control system of claim 1 wherein said circuit means comprises means for causing the repetition rate of said reference signal to be in proportion to the speed of said at least one selected wheel so long as deceleration of said at least one selected wheel does not exceed said predetermined value.

Claim 8

The skid control system of claim 1 wherein said circuit means comprises means for causing the repetition rate of said reference signal to decrease in predetermined fashion when deceleration of said at least one selected wheel exceeds said predetermined value.

Claim 9

The skid control system of claim 1 wherein said circuit means comprises means for causing the repetition rate of said reference signal to decrease at a constant rate when the deceleration of said at least one selected wheel exceeds said predetermined value.

Claim 10

The skid control system of claim 1 wherein said at least one selected wheel of the vehicle is the same as said at least one skid-controlled wheel whereby said wheel speed signal is supplied to said reference generating means, said reference generating means modulating the repetition rate of said reference signal in accordance with said wheel speed signal.

Claim 11

The skid control system of claim 1 wherein said at least one selected wheel and said at least one skid-controlled wheel are on a common axle of the vehicle.

Claim 12

The skid control system of claim 1 wherein said at least one skid-controlled wheel includes a pair of wheels and said speed sensing means includes first and second wheel speed sensors respectively operatively coupled with the respective wheels of said pair of wheels, said first and second wheel speed sensors providing first and second velocity signals respectively representing the respective velocities of the respective wheels of said pair of wheels, said speed sensing means further including sensing circuit means operatively coupled with said first and second sensors to receive said first and second velocity signals as inputs thereto and to provide said wheel speed signal as an output thereof.

Claim 13

The skid control system of claim 11 wherein said sensing circuit means includes means for causing the repetition rate of said wheel speed signal to represent exclusively the speed of one wheel of said pair of wheels.

Claim 14

The skid control system of claim 12 wherein said sensing circuit means includes means for causing the repetition rate of said wheel speed signal to represent the speed of the slower wheel of said pair of wheels.

Claim 15

The skid control system of claim 13 wherein said system includes means for causing a signal representative of the speed of the faster wheel of said pair of wheels to be supplied to said reference generating means, said reference generating means modulating the repetition rate of said reference signal in accordance with the speed of said faster wheel.

Claim 16

A digital skid control system for skid controlling at least one skid-controlled wheel of a multi-wheeled vehicle via fluid pressure modulation of pressure fluid applied to a brake system operatively associated with said at least one skid-controlled wheel, said digital skid control system comprising speed sensing means associated with said at least one skid-controlled wheel for developing a digital wheel speed signal whose frequency represents the speed of said at least one skid-controlled wheel, and skid control circuit means for developing a skid control signal for skid controlling said at least one skid-controlled wheel, said skid control circuit means comprising circuit means including reference generating means for developing from at least one selected wheel of the vehicle a digital reference signal, said reference generating means including modulating means for modulating the frequency of said reference signal in accorDance with the speed of said at least one selected wheel such that so long as deceleration of said at least one selected wheel does not exceed a predetermined value, the frequency of said digital reference signal represents a speed substantially corresponding to the speed of said at least one selected wheel, but when the deceleration of said at least one selected wheel exceeds said predetermined value, the frequency of said digital reference signal changes in a predetermined fashion and comparator circuit means for comparing the frequency of said digital reference signal with the frequency of said digital wheel speed signal and for developing said skid control signal when the frequency of said digital wheel speed signal differs from the frequency of said digital reference signal by a predetermined amount, and modulating means operatively coupling said brake system with said skid control circuit means and responsive to said skid control signal for modulating the fluid pressure in said brake system.

Claim 17

A digital skid control system for skid controlling at least one skid-controlled wheel of a multi-wheeled vehicle via fluid pressure modulation of pressure fluid applied to a brake system operatively associated with said at least one skid-controlled wheel, said digital skid control system comprising speed sensing means associated with said at least one skid-controlled wheel for developing a digital wheel speed signal whose frequency represents the speed of said at least one skid-controlled wheel, and skid control circuit means for developing a skid control signal for skid controlling said at least one skid-controlled wheel, said skid control circuit means comprising circuit means including reference generating means for developing from at least one selected wheel of the vehicle a digital reference signal, said reference generating means including modulating means for modulating the frequency of said reference signal in accorDance with the speed of said at least one selected wheel such that so long as deceleration of said at least one selected wheel does not exceed a predetermined value, the frequency of said digital reference signal represents a speed substantially corresponding to the speed of said at least one selected wheel, but when the deceleration of said at least one selected wheel exceeds said predetermined value, the frequency of said digital reference signal changes in a predetermined fashion and comparator circuit means for comparing the frequency of said digital reference signal with the frequency of said digital wheel speed signal and for developing said skid control signal when the frequency of said digital wheel speed signal differs from the frequency of said digital reference signal by a predetermined amount, and modulating means operatively coupling said brake system with said skid control circuit means and responsive to said skid control signal for modulating the fluid pressure in said brake system.

Claim 18

The digital skid control system of claim 15 wherein said comparator circuit means comprises means for developing said skid control signal when the frequency of said digital wheel speed signal falls below the frequency of said digital reference signal.

Claim 19

The digital skid control system of claim 15 wherein said circuit means comprises means for causing the frequency of said digital reference signal to increase with increasing speed of said at least one selected wheel and to decrease with decreasing speed of said at least one selected wheel.

Claim 20

The digital skid control system of claim 15 wherein said circuit means comprises means for causing the frequency of said digital reference signal to represent a speed which is slightly less than the actual speed of said at least one selected wheel so long as deceleration of said at least one selected wheel does not exceed said predetermined value.

Claim 21

The digital skid control system of claim 15 wherein said circuit means comprises means for causing the frequency of said digital reference signal to represent a speed which differs from the actual speed of said at least one selected wheel by a predetermined amount so long as deceleration of said at least one selected wheel does not exceed said predetermined value.

Claim 22

The digital skid control system of claim 15 wherein said circuit means comprises means for causing the frequency of said digital reference signal to be in proportion to the speed of said at least one selected wheel so long as deceleration of said at least one selected wheel does not exceed said predetermined value.

Claim 23

The digital skid control system of claim 15 wherein said circuit means comprises means for causing the frequency of said digital reference signal to decrease in predetermined fashion when deceleration of said at least one selected wheel exceeds said predetermined value.

Claim 24

The digital skid control system of claim 15 wherein said circuit means comprises means for causing the frequency of said digital reference signal to decrease at a constant rate when the deceleration of said at least one selected wheel exceeds said predetermined value.

Claim 25

The digital skid control system of claim 15 wherein said means for developing said digital reference signal from said at least one selected wheel comprises a rate limited phase locked loop circuit for developing said digital reference signal.

Claim 26

The digital skid control system of claim 23 wherein said rate limited phase locked loop circuit comprises means for developing an output signal whose frequency is a multiple of the frequency of said digital reference signal and wherein said skid control circuit means includes means for frequency dividing the frequency of said output signal to generate said digital reference signal.

Claim 27

The digital skid control system of claim 15 wherein said skid control circuit means comprises analogue circuit means for developing a vehicle velocity analogue signal whose magnitude represents a speeD substantially corresponding to the speed of said at least one selected wheel so long as deceleration of said at least one selected wheel does not exceed said predetermined value, but when the deceleration of said at least one selected wheel exceeds said predetermined value, the magnitude of said vehicle velocity analogue signal changes in a predetermined fashion and digital circuit means operatively coupled with said analogue circuit means and responsive to said vehicle velocity analogue signal for causing the frequency of said digital reference signal to vary in accordance with the magnitude of said vehicle velocity analogue signal.

Claim 28

The digital skid control system of claim 25 wherein said digital circuit means includes a voltage controlled oscillator responsive to the magnitude of said vehicle velocity analogue signal.

Claim 29

The digital skid control system of claim 26 including means for setting an operating characteristics of said voltage controlled oscillator such that the frequency thereof includes a slip factor representing a predetermined amount by which the frequency of the digital reference signal differs from a frequency corresponding to the actual speed of said selected wheel.

Claim 30

The digital skid control system of claim 15 wherein said at least one selected wheel of the vehicle is the same as said at least one skid-controlled wheel whereby said digital wheel speed signal is supplied to said reference generating means, said reference generating means modulating the frequency of said reference signal in accordance with said digital wheel speed signal.

Claim 31

The digital skid control system of claim 15 wherein said at least one selected wheel and said at least one skid-controlled wheel are on a common axle of the vehicle.

Claim 32

The digital skid control system of claim 15 wherein said at least one skid-controlled wheel includes a pair of wheels and said speed sensing means includes first and second wheel speed sensors respectively operatively coupled with the respective wheels of said pair of wheels, said first and second wheel speed sensors providing first and second velocity signals respectively representing the respective velocities of the respective wheels of said pair of wheels, said speed sensing means further including sensing circuit means operatively coupled with said first and second sensors to receive said first and second velocity signals as inputs thereto and to provide said digital wheel speed signal as an output thereof.

Claim 33

The digital skid control system of claim 30 wherein said sensing circuit means includes means for causing the frequency of said digital wheel speed signal to represent exclusively the speed of one wheel of said pair of wheels.

Claim 34

The digital skid control system of claim 31 wherein said sensing circuit means includes means for causing the frequency of said digital wheel speed signal to represent the speed of the slower wheel of said pair of wheels.

Claim 35

The digital skid control system of claim 32 wherein said system includes means for causing a signal representative of the speed of the faster wheel of said pair of wheels to be supplied to said reference generating means, said reference generating means modulating the repetition rate of said reference signal in accordance with the speed of said faster wheel.

Claim 36

A skid control system for skid controlling at least one skid-controlled wheel of a multi-wheeled vehicle via fluid pressure modulation of pressure fluid applied to a brake system operatively associated with said at least one skid-controlled wheel, said skid control system comprising wheel speed sensing means associated with said at least one skid-controlled wheel for developing a repetitive wheel speed signal whose repetition rate represents the speed of said at least one skid-controlled wheel, and skid control means for skid controlling said at least one skid-controlled wheel comprising skid control circuit means, means operatively coupling said skid control circuit means with said wheeL speed sensing means so that said wheel speed signal is supplied to said skid control circuit means, said skid control circuit means comprising reference generating means for developing from at least one selected wheel of the vehicle a repetitive reference speed signal, said reference generating means including modulating means for modulating the repetition rate of said reference speed signal such that the repetition rate of said reference speed signal represents a speed substantially corresponding to the speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition and for modulating the repetition rate of said reference speed signal such that the repetition rate of said reference speed signal changes in a predetermined fashion representing desired vehicle deceleration when said at least one selected wheel is in an incipient skid condition, said skid control circuit means further including comparator circuit means for comparing the repetition rate of said reference speed signal with the repetition rate of said wheel speed signal and for developing a skid control signal when the repetition rate of said wheel speed signal differs from the repetition rate of said reference speed signal by a predetermined amount and modulator means operatively coupling said brake system with said skid control circuit means and responsive to said skid control signal for modulating the fluid pressure in said brake system.

Claim 37

A skid control system for skid controlling at least one skid-controlled wheel of a multi-wheeled vehicle via fluid pressure modulation of pressure fluid applied to a brake system operatively associated with said at least one skid-controlled wheel, said skid control system comprising wheel speed sensing means associated with said at least one skid-controlled wheel for developing a repetitive wheel speed signal whose repetition rate represents the speed of said at least one skid-controlled wheel, and skid control means for skid controlling said at least one skid-controlled wheel comprising skid control circuit means, means operatively coupling said skid control circuit means with said wheeL speed sensing means so that said wheel speed signal is supplied to said skid control circuit means, said skid control circuit means comprising reference generating means for developing from at least one selected wheel of the vehicle a repetitive reference speed signal, said reference generating means including modulating means for modulating the repetition rate of said reference speed signal such that the repetition rate of said reference speed signal represents a speed substantially corresponding to the speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition and for modulating the repetition rate of said reference speed signal such that the repetition rate of said reference speed signal changes in a predetermined fashion representing desired vehicle deceleration when said at least one selected wheel is in an incipient skid condition, said skid control circuit means further including comparator circuit means for comparing the repetition rate of said reference speed signal with the repetition rate of said wheel speed signal and for developing a skid control signal when the repetition rate of said wheel speed signal differs from the repetition rate of said reference speed signal by a predetermined amount and modulator means operatively coupling said brake system with said skid control circuit means and responsive to said skid control signal for modulating the fluid pressure in said brake system.

Claim 38

The skid control system of claim 34 wherein said reference generating means comprises means for causing the repetition rate of said reference speed signal to represent a speed which is equivalent to the actual speed of said at least one selected wheel modified by a predetermined quantity so long as said at least one selected wheel is not in an incipient skid condition.

Claim 39

The skid control system of claim 34 wherein said reference generating means comprises means for causing the repetition rate of said reference speed signal to represent a speed which differs from the actual speed of said at least one selected wheel by a preselected amount so long as said at least one selected wheel is not in an incipient skid condition.

Claim 40

The skid control system of claim 34 wherein said reference generating means comprises means for causing the repetition rate of said reference speed signal to represent a speed which differs from the actual speed of said at least one selected wheel by a preselected amount so long as said at least one selected wheel is not in an incipient skid condition.

Claim 41

The skid control system of claim 34 wherein said reference generating means comprises means for causing the repetition rate of said reference speed signal to represent a speed which is slightly less than the actual speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 42

The skid control system of claim 34 wherein said reference generating means comprises means for causing the repetition rate of said reference speed signal to represent a speed in proportion to the actual speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 43

The skid control system of claim 39 wherein said reference generating means comprises means for causing the repetition rate of said reference speed signal to increase with increasing speed of said at least one selected wheel and to decrease with decreasing speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 44

The skid control system of claim 40 wherein said skid control circuit means comprises means for causing the repetition rate of said reference speed signal to decrease in predetermined fashion when said at least one selected wheel is in an incipient skid condition.

Claim 45

The skid control system of claim 40 wherein said skid control circuit means comprises means for causing the Repetition rate of said reference speed signal to decrease at a constant rate when said at least one selected wheel is in an incipient skid condition.

Claim 46

The skid condition system of claim 42 wherein said comparator circuit means comprises means for developing said skid control signal when the repetition rate of said wheel speed signal falls below the repetition rate of said reference speed signal.

Claim 47

The skid control system of claim 34 wherein said means for developing the repetitive reference speed signal comprises means for causing the repetition rate of said reference speed signal to increase with increasing vehicle speed and to decrease with decreasing vehicle speed.

Claim 48

The skid control system of claim 44 wherein said skid control circuit means comprises means for causing the repetition rate of said reference speed signal to decrease in predetermined fashion when said at least one selected wheel is in an incipient skid condition.

Claim 49

The skid control system of claim 45 wherein said skid control circuit means comprises means for causing the repetition rate of said reference speed signal to decrease at a constant rate when said at least one selected wheel is in an incipient skid condition.

Claim 50

The skid control system of claim 46 wherein said comparator circuit means comprises means for developing said skid control signal when the repetition rate of said wheel speed signal falls below the repetition rate of said reference speed signal.

Claim 51

The skid control system of claim 34 wherein said reference generating means includes phase locked loop circuit means operatively coupled with said at least one selected wheel.

Claim 52

The skid control system of claim 48 wherein said phase locked loop circuit means includes means for limiting the rate of change of the repetition rate of said reference speed signal to thereby cause the repetition rate of said reference speed signal to change in said predetermined fashion when said at least one selected wheel is in an incipient skid condition.

Claim 53

The skid control system of claim 49 wherein said phase locked loop circuit means includes means for causing the rate of decrease in the repetition rate of said reference speed signal to be rate limited thereby causing the repetition rate of said reference speed signal to change in said predetermined fashion.

Claim 54

The skid control system of claim 49 wherein said skid control circuit means comprises means for modifying the repetition rate of the output signal of said phase locked loop circuit means by a predetermined quantity to thereby generate said reference speed signal.

Claim 55

The skid control system of claim 51 wherein said means for modifying the repetition rate of the output signal of said phase locked loop circuit means by a predetermined quantity comprises means for subtracting a predetermined repetition rate from the repetition rate of the output signal of said phase locked loop circuit means.

Claim 56

The skid control system of claim 34 wherein said means for developing said reference speed signal includes counting circuit means operatively coupled with said at least one selected wheel such that the count in said counting circuit means corresponds to the speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition and means operatively coupled with said counting circuit means for causing the repetition rate of said reference speed signal to vary in accordance with the count in said counting circuit means.

Claim 57

The skid control system of claim 34 wherein said skid control circuit means comprises analogue circuit means operatively coupled with said at least one selected wheel for developing an analogue reference speed signal whose magnitude represents a speed substantially corresponding to the speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition and means operatively coupled with said analogue circuit means for causing tHe repetition rate of said reference speed signal to vary in accordance with the magnitude of the analogue reference speed signal.

Claim 58

The skid control system of claim 54 wherein said means operatively coupled with said analogue circuit means comprises a voltage controlled oscillator.

Claim 59

A digital skid control system for skid controlling at least one skid-controlled wheel of a multi-wheeled vehicle via fluid pressure modulation of pressure fluid applied to a brake system operatively associated with said at least one skid-controlled wheel, said skid control system comprising wheel speed sensing means associated with said at least one skid-controlled wheel for developing a digital wheel speed signal whose frequency represents the speed of said at least one skid-controlled wheel and skid control means for skid controlling said at least one skid-controlled wheel comprising skid control circuit means, means operatively coupling said skid control circuit means with said wheel speed sensing means so that said wheel speed signal is supplied to said skid control circuit means, said skid control circuit means comprising reference generating means for developing from at least one selected wheel of the vehicle a digital reference speed signal, said reference generating means including modulating means for modulating the frequency of said reference speed signal such that the frequency of said reference speed signal represents a speed substantially corresponding to the speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition and for modulating the frequency of said reference speed signal such that the frequency of said reference speed signal changes in a predetermined fashion representing desired vehicle deceleration when said at least one selected wheel is in an incipient skid condition, said skid control circuit means further including comparator circuit means for comparing the frequency of said digital reference speed signal with the frequency of said digital wheel speed signal and for developing a skid control signal when the frequency of said digital wheel speed signal differs from the frequency of said digital reference speed signal by a predetermined amount and modulator means operatively coupled said brake system with said skid control circuit means and responsive to said skid control signal for modulating the fluid pressure in said brake system.

Claim 60

A digital skid control system for skid controlling at least one skid-controlled wheel of a multi-wheeled vehicle via fluid pressure modulation of pressure fluid applied to a brake system operatively associated with said at least one skid-controlled wheel, said skid control system comprising wheel speed sensing means associated with said at least one skid-controlled wheel for developing a digital wheel speed signal whose frequency represents the speed of said at least one skid-controlled wheel and skid control means for skid controlling said at least one skid-controlled wheel comprising skid control circuit means, means operatively coupling said skid control circuit means with said wheel speed sensing means so that said wheel speed signal is supplied to said skid control circuit means, said skid control circuit means comprising reference generating means for developing from at least one selected wheel of the vehicle a digital reference speed signal, said reference generating means including modulating means for modulating the frequency of said reference speed signal such that the frequency of said reference speed signal represents a speed substantially corresponding to the speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition and for modulating the frequency of said reference speed signal such that the frequency of said reference speed signal changes in a predetermined fashion representing desired vehicle deceleration when said at least one selected wheel is in an incipient skid condition, said skid control circuit means further including comparator circuit means for comparing the frequency of said digital reference speed signal with the frequency of said digital wheel speed signal and for developing a skid control signal when the frequency of said digital wheel speed signal differs from the frequency of said digital reference speed signal by a predetermined amount and modulator means operatively coupled said brake system with said skid control circuit means and responsive to said skid control signal for modulating the fluid pressure in said brake system.

Claim 61

The digital skid control system of claim 56 wherein said reference generating means comprises means for causing the frequency of said digital reference speed signal to represent a speed which is equivalent to the actual speed of said at least one selected wheel modified by a predetermined quantity so long as said at least one selected wheel is not in an incipient skid condition.

Claim 62

The digital skid control system of claim 56 wherein said reference generating means comprises means for causing the frequency of said digital reference speed signal to represent a speed which is a selected fraction of the actual speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 63

The digital skid control system of claim 56 wherein said reference generating means comprises means for causing the frequency of said digital reference speed signal to represent a speed which differs from the actual speed of said at least one selected wheel by a preselected amount so long as said at least one selected wheel is not in an incipient skid condition.

Claim 64

The digital skid control system of claim 56 wherein said reference generating means comprises means for causing the frequency of said digital reference speed signal to represent a speed which is less than the actual speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 65

The digital skid control system of claim 56 wherein said reference generating means comprises means fOr causing the frequency of said digital reference speed signal to be proportional to the actual speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 66

The digital skid control system of claim 61 wherein said reference generating means comprises means for causing the frequency of said digital reference speed signal to increase with increasing speed of said at least one selected wheel and to decrease with decreasing speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 67

The digital skid control system of claim 62 wherein said skid control circuit means comprises means for causing the frequency of said digital reference speed signal to decrease in predetermined fashion when said at least one selected wheel is in an incipient skid condition.

Claim 68

The digital skid control system of claim 62 wherein said skid control circuit means comprises means for causing the frequency of said digital reference speed signal to decrease at a constant rate when said at least one selected wheel is in an incipient skid condition.

Claim 69

The digital skid control system of claim 64 wherein said comparator circuit means comprises means for developing said skid control signal when the frequency of said digital wheel speed signal falls below the frequency of said digital reference speed signal.

Claim 70

The digital skid control system of claim 56 wherein said reference generating means comprises means for causing the frequency of said digital reference speed signal to increase with increasing speed of said at least one selected wheel and to decrease with decreasing speed of said at least one selected wheel so long as said at least one selected wheel is not in an incipient skid condition.

Claim 71

The digital skid control system of claim 66 wherein said skid control circuit means comprises means for causing the frequency of said digital reference speed signal to decrease in predetermined fashion when said at least one selected wheel is in an incipient skid condition.

Claim 72

The digital skid control system of claim 67 wherein said skid control circuit means comprises means for causing the frequency of said digital reference speed signal to decrease at a constant rate when said at least one selected wheel is in an incipient skid condition.

Claim 73

The digital skid control system of claim 56 wherein said reference generating means includes phase locked loop circuit means operatively coupled with said at least one selected wheel.

Claim 74

The digital skid control system of claim 69 wherein said phase locked loop circuit means includes means for limiting the rate of change of the frequency of said digital reference speed signal to thereby cause the frequency of said digital reference speed signal to change in said predetermined fashion when said at least one selected wheel is in an incipient skid condition.

Claim 75

The digital skid control system of claim 70 wherein said phase locked loop circuit means includes means for causing the rate of decrease in the frequency of said digital reference speed signal to be rate limited thereby causing the frequency of said digital reference speed signal to change in said predetermined fashion.

Claim 76

The digital skid control system of claim 70 wherein said skid control circuit means comprises means for frequency modifying the output signal of said phase locked loop circuit means by a predetermined quantity to thereby generate said digital reference speed signal.

Claim 77

The digital skid control system of claim 72 wherein said means for frequency modifying the frequency of the output signal of said phase locked loop circuit means by a predetermined quantity comprises means for subtracting a predetermined frequency from the frequency of the output signal of said phase locked loop circuit means.

Claim 78

In a skid control system for skid controlling at least one wheel of a multi-wheeled vehicle via fluid pressure moduLation of pressure fluid applied to a brake system operatively associated with said at least one wheel, skid control circuit means for developing a skid control signal for skid controlling said at least one wheel, said skid control circuit means including electronic circuit means for generating a repetitive reference signal, said electronic circuit means including modulating means for causing the repetition rate of said reference signal to represent a speed substantially corresponding to the speed of at least one selected wheel of the vehicle so long as the deceleration of said at least one selected wheel does not exceed a predetermined value, and for causing the repetition rate of said reference signal to change in a predetermined fashion representing desired vehicle deceleration when the deceleration of said at least one selected wheel exceeds said predetermined value.

Claim 79

In a skid control system for skid controlling at least one wheel of a multi-wheeled vehicle via fluid pressure moduLation of pressure fluid applied to a brake system operatively associated with said at least one wheel, skid control circuit means for developing a skid control signal for skid controlling said at least one wheel, said skid control circuit means including electronic circuit means for generating a repetitive reference signal, said electronic circuit means including modulating means for causing the repetition rate of said reference signal to represent a speed substantially corresponding to the speed of at least one selected wheel of the vehicle so long as the deceleration of said at least one selected wheel does not exceed a predetermined value, and for causing the repetition rate of said reference signal to change in a predetermined fashion representing desired vehicle deceleration when the deceleration of said at least one selected wheel exceeds said predetermined value.

Claim 80

The skid control circuit means of claim 74 wherein said circuit means includes means for causing the repetition rate of said reference signal to increase when the speed of said at least one selected wheel increases and to decrease when the speed of said at least one selected wheel decreases so long as the deceleration of said at least one selected wheel does not exceed said predetermined value.

Claim 81

The skid control circuit means of claim 75 wherein said circuit means includes means for causing the rate of decrease of the repetition rate of said reference signal to be limited to a predetermined rate when the deceleration of said at least one selected wheel exceeds said predetermined value.

Claim 82

The skid control circuit means of claim 74 wherein said circuit means includes means for generating said reference signal in digital form.

Claim 83

The skid control circuit means of claim 74 further including speed sensing means operatively associated with said at least one selected wheel for supplying to said electronic circuit means a periodic speed signal whose frequency represents the speed of said at least one selected wheel.

Claim 84

A wheel control system for controlling the speed of a wheel of a multi-wheeled vehicle comprising speed sensing means associated with said wheel for developing a repetitive wheel speed signal whose repetition rate represents the speed of said wheel and wheel control circuit means for developing a wheel control signal for controlling the speed of said wheel, said wheel control circuit means comprising circuit means including reference generating means for developing from another wheel of the vehicle a repetitive reference signal said reference generating means including modulating means for causing the repetition rate of said reference signal to represent a speed substantially corresponding to the speed of said last-mentioned wheel so long as deceleration thereof does not exceed a predetermined value and for causing, when the deceleration of said last-mentioned wheel exceeds said predetermined value, the frequency of said reference signal to change in a predetermined fashion and comparator circuit means for comparing the repetition rate of said reference signal with the repetition rate of said wheel speed signal and for developing said wheel control signal when the repetition rate of said wheel speed signal differs from the repetition rate of said reference signal by a predetermined amount, and modulating means operatively coupling said first wheel with said circuit means and responsive to said wheel control signal for modulating the speed of said first wheel.

Claim 85

A wheel control system for controlling the speed of a wheel of a multi-wheeled vehicle comprising speed sensing means associated with said wheel for developing a repetitive wheel speed signal whose repetition rate represents the speed of said wheel and wheel control circuit means for developing a wheel control signal for controlling the speed of said wheel, said wheel control circuit means comprising circuit means including reference generating means for developing from another wheel of the vehicle a repetitive reference signal said reference generating means including modulating means for causing the repetition rate of said reference signal to represent a speed substantially corresponding to the speed of said last-mentioned wheel so long as deceleration thereof does not exceed a predetermined value and for causing, when the deceleration of said last-mentioned wheel exceeds said predetermined value, the frequency of said reference signal to change in a predetermined fashion and comparator circuit means for comparing the repetition rate of said reference signal with the repetition rate of said wheel speed signal and for developing said wheel control signal when the repetition rate of said wheel speed signal differs from the repetition rate of said reference signal by a predetermined amount, and modulating means operatively coupling said first wheel with said circuit means and responsive to said wheel control signal for modulating the speed of said first wheel.