Control system and method for automatic selection of a low range gear ratio for a vehicle drivetrain

A method for automatically controlling a drivetrain coupled to at least one drive wheel of a vehicle, the drivetrain including a first assembly including a low range drive ratio and a high range drive ratio, and a second assembly including a reverse drive ratio and a plurality of forward drive ratios, the method comprising:

• providing an electronic control unit configured to receive information from at least one sensor located on the vehicle and to provide an output signal based on the information;
• providing an actuator mechanism configured to cause the first assembly to operate at a selected one of the low range drive ratio and the high range drive ratio;
• automatically causing the actuator mechanism to select one of the low range drive ratio and the high range drive ratio independently of a selection of one of the reverse drive ratio and the plurality of forward drive ratios and based on the output signal from the electronic control unit;
• driving the at least one drive wheel at the selected one of the low range drive ratio and the high range drive ratio and simultaneously with one of the reverse drive ratio and a ratio of the plurality of forward drive ratios;
• and
• determining a plurality of vehicle operation parameters using the electronic control unit;
• wherein:
• automatically causing the actuator mechanism to select one of the low range drive ratio and the high range drive ratio based on the plurality of vehicle parameters and through the use of the electronic control unit;
• determining includes:
• collecting data indicating at least one of vehicle speed, accelerator pedal position, and vehicle acceleration;
• comparing the data with a corresponding one of maximum speed, minimum position, and maximum acceleration;
• collecting switch data indicating a position of a manual shift control switch;
• comparing the switch data with a switch value;
• collecting actuator data indicating a position of the actuator mechanism;
• and
• comparing the actuator data to a high range position when the switch data equals the switch value;
• and
• automatically causing the actuator mechanism to select includes causing the actuator to select the low range drive ratio when the actuator data is unequal the high range position.

A system for automatically controlling a two-speed gear reduction assembly in series with a multi-ratio transmission assembly of a vehicle, the two-speed gear reduction assembly including a low range drive ratio and a high range drive ratio, and the multi-ratio transmission assembly including a reverse drive ratio and a plurality of forward drive ratios, the system comprising:

• an actuator selectively movable between a low range position where the actuator couples the low range drive ratio in series with one of the reverse drive ratio and the plurality of forward drive ratios and a high range position where the actuator couples the high range drive ratio in series with the selected one of the reverse drive ratio and the plurality of forward drive ratios;
• a vehicle speed sensor;
• a vehicle acceleration sensor;
• and
• a controller in electrical communication with each of the actuator, the vehicle speed sensor and the vehicle acceleration sensor and configured to
• automatically select one of the low range drive ratio and the high range drive ratio regardless of a manipulation of one of the reverse drive ratio and the plurality of forward drive ratios and based on electrical signals received from the vehicle speed sensor and the vehicle acceleration sensor, and
• automatically signal the actuator to move to a respective one of the low range position and the high range position when one of the low range drive ratio and the high range drive ratio is automatically selected.

A method for automatically controlling a drivetrain assembly driving at least one wheel of a vehicle, the drivetrain including a two-speed gear reduction assembly in series with a multi-ratio transmission assembly, the two-speed drive assembly including a low range drive ratio and a high range drive ratio, and the multi-ratio transmission assembly including a reverse drive ratio and a plurality of forward drive ratios, the method comprising:

• providing a switch that can be manually shifted from an automatic position to a manual position;
• determining a position of the switch;
• causing the drivetrain to operate in the low range drive ratio when the position of the switch equals the manual position;
• comparing a vehicle speed with a maximum vehicle speed when the position of the switch is equal to the automatic position;
• comparing an accelerator pedal position to a minimum position when the vehicle speed is less than the maximum speed;
• comparing a vehicle acceleration to a maximum acceleration when the accelerator pedal position is greater than the minimum position;
• causing the drivetrain to operate in the low range drive ratio when the vehicle acceleration is less than the maximum acceleration;
• causing the drivetrain to operate in the high range drive ratio when the position of the switch is equal to the automatic position and when one of the vehicle speed is at least equal to the maximum speed, the accelerator pedal position is at most equal to the minimum position, and the vehicle acceleration is at least equal to the maximum acceleration;
• and
• driving the at least one wheel at the selected one of the low range drive ratio and the high range drive ratio and with one of the reverse drive ratio and the plurality of forward drive ratios.

A drivetrain for a vehicle comprising:

• a multi-ratio transmission assembly including a reverse drive ratio and a plurality of forward drive ratios;
• a two-speed drive assembly including,
• a low range drive ratio engageable in series with one of the reverse drive ratio and the plurality of forward drive ratios, and
• a high range drive ratio engageable in series with one of the reverse drive ratio and the plurality of forward drive ratios;
• an actuator selectively movable between a low range position where the actuator couples the low range drive ratio in series with a selected one of the reverse drive ratio and the plurality of forward drive ratios and a high range position where the actuator couples the high range drive ratio in series with the selected one of the reverse drive ratio and the plurality of forward drive ratios;
• a vehicle speed sensor;
• a vehicle acceleration sensor;
• a controller in electrical communication with each of the actuator, the vehicle speed sensor and the vehicle acceleration sensor, and configured to
• automatically select one of the low range drive ratio and the high range drive ratio regardless of a manipulation of one of the reverse drive ratio and the plurality of forward drive ratios and based on electrical signals received from the vehicle speed sensor and the vehicle acceleration sensor, and
• automatically signal the actuator to move to a respective one of the low range position and the high range position when one of the low range drive ratio and the high range drive ratio is automatically selected;
• and
• at least one drive wheel driven by each of one of the reverse drive ratio and the plurality of forward drive ratios and the selected one of the low range drive ratio and the high range drive ratio.