Underspeed control system for a hydromechanical drive system and method of operating same

An apparatus for controlling load on an engine, comprising:

• a continuously variable transmission driven by the engine;
• an engine speed sensor being adapted to sense the output speed of the engine and produce an engine speed signal indicative of the engine output speed;
• a travel speed sensor being adapted to sense the travel speed of the machine and produce a travel speed signal indicative of the machine travel speed;
• and
• an electronic controller operable to (i) compare the engine speed signal to a first underspeed value and produce an integral error signal indicative of the difference between the engine speed signal and the first underspeed value, (ii) modify the integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal, and (iii) produce a command signal based on the underspeed request signal,
• wherein the command signal is used to control the transmission ratio of the continuously variable transmission so as to control the load on the engine,
• wherein high integral gain values are used for relatively slow machine travel speeds;
• and
• low integral gain values are used for relatively high machine travel speed decreases.

An apparatus for controlling load on an engine, comprising:

• a continuously variable transmission driven by the engine, the continuously variable transmission includes a variable displacement motor;
• an engine speed sensor being adapted to sense the output speed of the engine and produce an engine speed signal indicative of the engine output speed;
• a travel speed sensor being adapted to sense the travel speed of the machine and produce a travel speed signal indicative of the machine travel speed;
• and
• an electronic controller operable to (i) compare the engine speed signal to a first underspeed value and produce an integral error signal indicative of the difference between the engine speed signal and the first underspeed value, (ii) modify the integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal, and (iii) produce a command signal based on the underspeed request signal,
• wherein the command signal is used to control the transmission ratio of the continuously variable transmission so as to control the load on the engine,
• wherein the displacement of the variable displacement motor is varied in response to receiving the command signal.

An apparatus for controlling load on an engine, comprising:

• a continuously variable transmission driven by the engine;
• an engine speed sensor being adapted to sense the output speed of the engine and produce an engine speed signal indicative of the engine output speed;
• a travel speed sensor being adapted to sense the travel speed of the machine and produce a travel speed signal indicative of the machine travel speed;
• and
• an electronic controller operable to (i) compare the engine speed signal to a first underspeed value and produce an integral error signal indicative of the difference between the engine speed signal and the first underspeed value, (ii) modify the integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal, and (iii) produce a command signal based on the underspeed request signal,
• wherein the command signal is used to control the transmission ratio of the continuously variable transmission so as to control the load on the engine,
• wherein the command signal is produced by subtracting the underspeed request signal from a desired machine speed command.

An apparatus for controlling load on an engine, comprising:

• a continuously variable transmission driven by the engine;
• an engine speed sensor being adapted to sense the output speed of the engine and produce an engine speed signal indicative of the engine output speed;
• a travel speed sensor being adapted to sense the travel speed of the machine and produce a travel speed signal indicative of the machine travel speed;
• and
• an electronic controller operable to (i) compare the engine speed signal to a first underspeed value and produce an integral error signal indicative of the difference between the engine speed signal and the first underspeed value, (ii) modify the integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal, and (iii) produce a command signal based on the underspeed request signal,
• wherein the command signal is used to control the transmission ratio of the continuously variable transmission so as to control the load on the engine,
• wherein the electronic controller is further operable to (i) compare the engine speed signal to a second underspeed value and produce an proportional error signal indicative of the difference between the engine speed signal and the second underspeed value, (ii) modify the integral error signal through a proportional plus integral feedback controller to produce an integral component of the underspeed request signal, and (iii) modify the proportional error signal through a proportional plus integral feedback controller to produce a proportional component of the underspeed request signal, and
• the second underspeed value is at an engine speed that is greater than or equal to the engine speed of the first underspeed value.

A method for controlling a load on an engine associated with a continuously variable transmission, comprising the steps of:

• sensing the engine output speed and producing an engine speed signal indicative of the engine output speed;
• sensing the travel speed of the machine and producing a travel speed signal indicative of the machine travel speed;
• activating a modified machine speed command within an electronic controller responsive to the engine speed falling below an underspeed value;
• and
• directing the modified machine speed command toward a subsequent underspeed value,
• wherein the load on the engine is decreased in response to the activation of the modified machine speed command and the transmission ratio of the continuously variable transmission is modified based on the subsequent underspeed value to obtain an engine performance condition.

A method for controlling a load on an engine associated with a continuously variable transmission, comprising the steps of:

• sensing the engine output speed and producing an engine speed signal indicative of the engine output speed;
• sensing the travel speed of the machine and producing a travel speed signal indicative of the machine travel speed;
• comparing the engine speed signal to a first underspeed value and producing an integral error signal indicative of the difference between the engine speed signal and the first underspeed value;
• determining an integral gain value based on the machine travel speed signal;
• modifying the integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal;
• generating a command signal based on the underspeed request signal;
• controlling the transmission ratio of the continuously variable transmission with the command signal so as to regulate the load on the engine;
• and
• activating the proportional term of the proportional plus integral feedback controller in response to the engine speed falling below a second underspeed value,
• wherein the second underspeed value is at a higher engine speed than the first underspeed value.

An apparatus for controlling load on an engine, comprising:

• a continuously variable transmission driven by the engine;
• an engine speed sensor being adapted to sense the output speed of the engine and produce an engine speed signal indicative of the engine output speed;
• a travel speed sensor being adapted to sense the travel speed of the machine and produce a travel speed signal indicative of the machine travel speed;
• and
• an electronic controller operative to (i) activate a modified machine speed command responsive to the engine speed falling below an underspeed value, (ii) direct the modified machine speed command toward a subsequent underspeed value, and (iii) manipulate the modified machine speed command based on predetermined gain data and the gain data being based on machine travel speed,
• wherein the load on the engine is decreased in response to activation of the modified machine speed command and a transmission ratio of the continuously variable transmission is modified based on the subsequent underspeed value to obtain an engine performance condition.

An apparatus for controlling load on an engine, comprising:

• a continuously variable transmission driven by the engine;
• an engine speed sensor being adapted to sense the output speed of the engine and produce an engine speed signal indicative of the engine output speed;
• a travel speed sensor being adapted to sense the travel speed of the machine and produce a travel speed signal indicative of the machine travel speed;
• and
• an electronic controller operable to (i) compare the engine speed signal to a first underspeed value and produce an integral error signal indicative of the difference between the engine speed signal and the first underspeed value, (ii) supply an integral gain value based on the machine travel speed and the integral error signal, (iii) modify integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal, and (iv) produce a command signal based on the underspeed request signal,
• wherein the command signal is used to control the transmission ratio of the continuously variable transmission so as to control the load on the engine,
• wherein high integral gain values are used for relatively high positive integral errors;
• low integral gain values are used for low negative integral errors;
• and intermediate integral gain values are used for high negative integral errors.

A method for controlling a load on an engine associated with a continuously variable transmission, comprising the steps of:

• sensing the output speed of the and producing an engine speed signal indicative of the engine output speed;
• sensing the travel speed of the machine and producing a travel speed signal indicative of the machine travel speed;
• activating a modified machine speed command responsive to the engine speed falling below an underspeed value;
• directing the modified machine speed command toward a subsequent underspeed value;
• and
• manipulating the modified machine speed command based on predetermined gain data and the gain data being based on machine travel speed,
• wherein the load on the engine is decreased in response to activation of the modified machine speed command and a transmission ratio of the continuously variable transmission is modified based on the subsequent underspeed value to obtain an engine performance condition.

A method for controlling a load on an engine associated with a continuously variable transmission, comprising the steps of:

• sensing the output speed of the and producing an engine speed signal indicative of the engine output speed;
• sensing the travel speed of the machine and producing a travel speed signal indicative of the machine travel speed;
• comparing the engine speed signal to a first underspeed value and producing an integral error signal indicative of the difference between the engine speed signal and the first underspeed value;
• determining an integral gain value based on the machine travel speed and the integral error signal;
• modifying the integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal;
• generating a command signal based on the underspeed request signal;
• controlling the transmission ratio of the continuously variable transmission with the command signal so as to regulate the load on the engine;
• and
• activating a proportional term of the proportional plus integral feedback controller in response to the engine speed falling below a second underspeed value and activating the integral term of the proportional plus integral feedback controller in response to the engine speed falling below the first underspeed value,
• wherein the second underspeed value is at a higher engine speed than the first underspeed value.

A method for controlling a load on an engine associated with a continuously variable transmission, comprising the steps of:

• sensing the output speed of the and producing an engine speed signal indicative of the engine output speed;
• sensing the travel speed of the machine and producing a travel speed signal indicative of the machine travel speed;
• comparing the engine speed signal to a first underspeed value and producing an integral error signal indicative of the difference between the engine speed signal and the first underspeed value;
• determining an integral gain value based on the machine travel speed and the integral error signal;
• modifying the integral error signal through a proportional plus integral feedback controller to produce an underspeed request signal;
• generating a command signal based on the underspeed request signal;
• controlling the transmission ratio of the continuously variable transmission with the command signal so as to regulate the load on the engine;
• activating the proportional plus integral feedback controller in response to the engine speed falling below the second underspeed value;
• and
• de-activating the underspeed control in response to a modified machine speed command reaching the desired speed command.