System and method for controlling wheel brakes on a trailer in a tractor-trailer

A system for controlling wheel brakes on a trailer in a tractor-trailer, comprising:

• a vehicle speed sensor configured to generate a speed signal indicative of a speed of the tractor-trailer;
• and,
• a controller configured to
• receive a command to apply a trailer wheel brake of a trailer of the tractor-trailer;
• determine, in response to the command, the speed of the tractor-trailer responsive to the speed signal;
• and
• establish a threshold speed responsive to a level of friction between the tractor-trailer and a road surface on which the tractor-trailer is travelling;
• determine, in response to the command, a value for an operating parameter of the tractor-trailer indicative of the level of friction between the tractor-trailer and the road surface on which the tractor-trailer is travelling;
• and,
• generate a control signal to control delivery of fluid pressure to the trailer wheel brake wherein the control signal is configured to cause delivery of a first fluid pressure to the trailer wheel brake when the speed meets a first predetermined condition relative to the threshold speed and the value of the operating parameter meets a second predetermined condition and the control signal is configured to cause delivery of a second fluid pressure, less than the first fluid pressure, when the speed does not meet the first predetermined condition relative to the threshold speed or the value of the operating parameter does not meet the second predetermined condition;
• wherein the controller is further configured, in establishing the threshold speed, to
• determine a torque on a wheel of the tractor-trailer,
• determine a coefficient of friction between the wheel and the road surface responsive to the torque,
• estimate a lateral force acting on the wheel responsive to a signal indicative of movement of a tractor of the tractor-trailer and not indicative of movement of the trailer,
• adjust the coefficient of friction responsive to the lateral force to obtain an adjusted coefficient of friction between the wheel and the road surface, and,
• determine the threshold speed responsive to the adjusted coefficient of friction.

An article of manufacture, comprising:

• a non-transitory computer storage medium having a computer program encoded thereon that when executed by a controller controls a trailer wheel brake on a trailer in a tractor-trailer, the computer program including code for:
• determining, in response to a command to apply a trailer wheel brake of a trailer of the tractor-trailer, a speed of the tractor-trailer responsive to a speed signal generated by a vehicle speed sensor and indicative of the speed of the tractor-trailer;
• establishing a threshold speed responsive to a level of friction between the tractor-trailer and a road surface on which the tractor-trailer is travelling;
• and,
• generating a control signal to control delivery of fluid pressure to the trailer wheel brake wherein the control signal is configured to cause delivery of a first fluid pressure to the trailer wheel brake when the speed meets a first predetermined condition relative to the threshold speed and a second fluid pressure, less than the first fluid pressure, when the speed does not meet the first predetermined condition relative to the threshold speed
• wherein the code for establishing the threshold speed includes code for:
• determining a torque on a wheel of the tractor-trailer;
• determining a coefficient of friction between the wheel and the road surface responsive to the torque;
• estimating a lateral force acting on the wheel responsive to a signal indicative of movement of a tractor of the tractor-trailer and not indicative of movement of the trailer;
• adjusting the coefficient of friction responsive to the lateral force to obtain an adjusted coefficient of friction between the wheel and the road surface;
• and,
• determining the threshold speed responsive to the adjusted coefficient of friction.

A method for controlling wheel brakes on a trailer in a tractor-trailer, comprising the steps of:

• receiving a command to apply a trailer wheel brake of a trailer of the tractor-trailer;
• determining, in response to the command, a speed of the tractor-trailer responsive to a speed signal generated by a vehicle speed sensor and indicative of the speed of the tractor-trailer
• establishing a threshold speed responsive to a level of friction between the tractor-trailer and a road surface on which the tractor-trailer is travelling;
• and,
• generating a control signal to control delivery of fluid pressure to the trailer wheel brake wherein the control signal is configured to cause delivery of a first fluid pressure to the trailer wheel brake when the speed meets a first predetermined condition relative to the threshold speed and a second fluid pressure, less than the first fluid pressure, when the speed does not meet the first predetermined condition relative to the threshold speed
• wherein the establishing step includes the substeps of
• determining a torque on a wheel of the tractor-trailer;
• determining a coefficient of friction between the wheel and the road surface responsive to the torque;
• estimating a lateral force acting on the wheel responsive to a signal indicative of movement of a tractor of the tractor-trailer and not indicative of movement of the trailer;
• adjusting the coefficient of friction responsive to the lateral force to obtain an adjusted coefficient of friction between the wheel and the road surface;
• and,
• determining the threshold speed responsive to the adjusted coefficient of friction.