Tire air pressure drop detecting system

A system for use with an automotive vehicle supported on front and rear pairs of road wheels to detect a drop in a tire air pressure for each of the road wheels, comprising:

• sensor means for detecting angular speeds of rotation of the respective road wheels;
• means for calculating a first ratio of the detected angular speeds of rotation of the front-left and -right road wheels;
• means for calculating a second ratio of the detected angular speeds of rotation of the rear-left and -right road wheels;
• means for producing a command signal when an operation point represented by a coordinate pair of the first and second ratios is in a predetermined range, the predetermined range having a first and second range, the first range expanding .+-.d with respect to a first locus of change of the second ratio obtained with changes in the first ratio when the vehicle is operating in a steady straight line driving condition, where d is a small width, the second range expanding .+-.d with respect to a second locus of change of the first ratio obtained with changes in the second ratio when the vehicle is operating in the steady straight line driving condition;
• and
• means responsive to the command signal for specifying the road wheel having a dropped tire air pressure based on the detected angular road wheel speeds.

An automotive vehicle, comprising:

• a front-left road wheel with a tire;
• a front-right road wheel with a tire;
• a rear-left road wheel with a tire;
• a rear-right road wheel with a tire;
• a plurality of road wheel speed sensors for detecting angular speeds of rotation of said front-left, front-right, rear-left and rear-right wheels;
• and
• a control unit specifying one of said road wheels which is experiencing a drop in tire air pressure,
• where
• said control unit calculates a first wheel speed ratio (P.sub.F) between said detected angular speed of rotation of said front-left road wheel (V.sub.WFL) and said detected angular speed of rotation of said front-right road wheel (V.sub.WFR) and a second wheel speed ratio (P.sub.R) between said detected angular speed of rotation of said rear-left road wheel (V.sub.WRL) and said detected angular speed of rotation of said rear-right road wheel (V.sub.WRR);
• said control unit determines whether or not, in a Cartesian coordinate system having said first wheel speed ratio on a horizontal axis thereof and said second wheel speed ratio on a vertical axis thereof, and operation point expressed in said Cartesian coordinate system by said calculated first and second wheel speed ratios falls in one of a first range and a second range in said Cartesian coordinate system, said first range being in the form of a predetermined window about a first line (L1) intersecting a predetermined reference operation point (C), said first line reflecting a first predetermined amount of change of said second wheel speed ratio in a first direction, parallel to said vertical axis, away from said predetermined reference operation point for a unit amount of change of said first wheel speed ratio in a second direction, parallel to said horizontal axis, away from said reference operation point,
• said first direction being oriented leftwards viewing in said second direction,
• said second range being in the form of a predetermined window about a second line (L2) intersecting said reference operation point (C),
• said second line reflecting a second predetermined amount of change of said first wheel speed ratio in a third direction, parallel to said horizontal axis, away from said reference operation point for a unit amount of change of said second wheel speed ratio in a fourth direction, parallel to said vertical axis, away from said reference operation point,
• said third direction being oriented rightwards viewing in said fourth direction;
• said control unit initiates execution of processing of said detected angular speeds of rotation of said front-left, front-right, rear-left and rear-right wheels to determine which one of said road wheels is experiencing a drop in tire air pressure when said control unit has determined that said operation point expressed in said Cartesian coordinate system by said calculated first and second wheel speed ratios falls in one of said first and second ranges in said Cartesian coordinate system, but otherwise terminates execution of processing of said detected angular speeds of rotation of said front-left, front-right, rear-left and rear-right wheels.

An automotive vehicle, comprising:

• a front-left road wheel with a tire;
• a front-right road wheel with a tire;
• a rear-left road wheel with a tire;
• a rear-right raod wheel with a tire;
• a plurality of road wheel speed sensors for detecting angular speeds of rotation of said front-left, front-right, rear-left and rear-right wheels;
• and
• a control unit specifying one of said road wheels which is experiencing a drop in tire air pressure,
• wherein
• said control unit determines whether or not the automotive vehicle drives in a predetermined state;
• said control unit calculates a first wheel speed ratio (P.sub.F) between said detected angular speed of rotation of said front-left road wheel (V.sub.WFL) and said detected angular speed of rotation of said front-right road wheel (V.sub.WFR) and a second wheel speed ratio (P.sub.R) between said detected angular speed of rotation of said rear-left road wheel (V.sub.WRL) and said detected angular speed of rotation of said rear-right road wheel (V.sub.WRR) when said control unit has determined that the automotive vehicle drives in said predetermined state;
• said control unit determines whether or not, in a Cartesian coordinate system having said first wheel speed ratio on a horizontal axis thereof and said second wheel speed ratio on a vertical axis thereof, and operation point expressed in said Cartesian coordinate system by said calculated first and second wheel speed ratios falls in one of a first range and asecond range in said Cartesian coordinate system, said first range being in the form of a predetermined window about a first line (L1) intersecting a predetermined reference operation point (C) which is expressed in said Cartesian coordinate system by said first and second wheel speed ratios when the automotive vehicle drives in a predetermined steady straight line with said tires of said road wheels normally infleated, said first line reflecting a first predetermined amount of change of said second wheel speed ratio in a first direction, parallel to said vertical axis, away from said predetermined reference operation point for a unit amount of change of said first wheel speed ratio in a second direction, parallel to said horizontal axis, away from said reference operation point,
• said first direction being oriented leftwards viewing in said second direction,
• said second range being in the form of a predetermined window about a second line (L2) intersecting said reference operation point (C),
• said second line reflecting a second predetermined amount of change of said first wheel speed ratio in a third direction, parallel to said horizontal axis, away from said reference operation point for a unit amount of change of said second wheel speed ratio in a fourth direction, parallel to said vertical axis, away from said reference operation point,
• said third direction being oriented rightwards viewing in said fourth direction;
• said control unit initiates execution of processing of said detected angular speeds of rotation of said front-left, front-right, rear-left, and rear-right wheels to determine which one of said road wheels is experiencing a drop in tire air pressure when said control unit has determined that said operation point expressed in said Cartesian coordinate system by said calculated first and second wheel speed ratios falls in one of said first and second ranges in said Cartesian coordinate system, but otherwise terminates execution of processing of said detected angular speeds of rotation of said front-left, front-right, rear-left and rear-right wheels.

A method of determining which one of tires of road wheels of an automotive vehicle is experiencing a drop in tire air pressure, the method comprising the steps of:

• detecting an angular speed of rotation of a front-left road wheel;
• detecting an angular speed of rotation of a front-right road wheel;
• detecting an angular speed of rotation of a rear-left road wheel;
• detecting an angular speed of rotation of a rear-right road wheel;
• calculating a first-wheel speed ratio (P.sub.F) between said detected angular speed of rotation of said front-left road wheel (V.sub.WFL) and said detected angular speed of rotation of said front-right road wheel (V.sub.WFR) and a second wheel speed ratio (P.sub.R) between said detected angular speed of rotation of said rear-left road wheel (V.sub.WRL) and said detected angular speed of rotation of said rear-right road wheel (V.sub.WRR);
• determining whether or not, in a Cartesian coordinate system having said first wheel speed ratio on a horizontal axis thereof and said second wheel speed ratio on a vertical axis thereof, an operation point expressed in said Cartesian coordinate system by said calculated first and second wheel speed ratios falls in one of a first range and a second range in said Cartesian coordinate system, said first range being in the form of a predetermined window about a first line (L1) intersecting a predetermined reference operation point (C) which is expressed in said Cartesian coordinate system by said first and second wheel speed ratios when the automotive vehicle drives in a predetermined steady straight line with said tires of said road wheels normally inflated, said first line reflecting a first predetermined amount of change of said second wheel speed ratio in a first direction, parallel to said vertical axis, away from said predetermined reference operation point for a unit amount of change of said first wheel speed ratio in a second direction, parallel to said horizontal axis, away from said reference operation point,
• said first direction being oriented leftwards viewing in said second direction,
• said second range being in the form of a predetermined window about a second (L2) intersecting said reference operation point (C),
• said second line reflecting a second predetermined amount of change of said first wheel speed ratio in a third direction, parallel to said horizontal axis, away from said reference operation point for a unit amount of change of said second wheel speed ratio in a fourth direction, parallel to said vertical axis, away from said reference operation point,
• said third direction being oriented rightwards viewing in said fourth direction;
• initiating execution of processing of said detected angular speeds of rotation of said front-left, front-right, rear-left and rear-right wheels to determine which one of said road wheels is experiencing a drop in tire air pressure when it is determined that said operation point expressed in said Cartesian coordinate system by said calculated first and second wheel speed ratios falls in one of said first and second ranges in said Cartesian coordinate system;
• and
• terminating execution of processing of said detected angular speeds of rotation of said front-left, front-right, rear-left and rear-right wheels when it is determined that said operation point expressed in said Cartesian coordinate system by said calculated first and second wheel speed ratios fails to fall in one of said first and second ranges in said Cartesian coordinate system.