Method For Controlling Two Variable Displacement Hydrostatic Units In An Infinitely Variable Hydro-Mechanical Transmission

A method for engaging a synchronizer of a hydro-mechanical transmission at startup, the hydro-mechanical transmission having a hydrostatic transmission including:

• a first hydrostatic element (CU);
• a second hydrostatic element (RU) in fluid communication with the first hydrostatic element (CU);
• a mechanical transmission having a planetary gear system including a first torque-coupling device (C1), a second torque-coupling device (C2), a third torque-coupling device (C3) and a fourth torque-coupling device (C4);
• a first element (S1) coupled to an input shaft and driven thereby;
• a second element (R2) in driving engagement with the second hydrostatic element (20);
• a third element (28) selectively coupled to the first hydrostatic element (18) by the third torque-coupling device (C3);
• a fourth element (S2) selectively coupled to the first hydrostatic element (18) by the fourth torque-coupling device (C4), the fourth element drivingly coupled to the second element (R2);
• a fifth element (S3) coupled to an output, the fifth element (S3) being selectively coupled to the third element (28) by the first torque-coupling devices (C1), and selectively coupled to the fourth element (S2) by the second torque-coupling devices (C2), and a sixth element (R3) selectively coupled to ground by a reverse brake (48) the method comprising the steps of:
• a.) engaging one or more of the torque-coupling devices (C3 and/or 48) to stop the third element (28) thereby forcing the first torque-coupling device (C1) speed to zero and causing a second element (R2) speed (and therefore RU speed) to increase;
• b.) when the second element (R2) speed is fast enough, triggering a second hydrostatic unit (RU) closed-loop control with a target of zero degrees (CU speed of zero);
• c.) when the first hydrostatic element (CU) speed and first torque-coupling device (C1) speed are near zero engaging the first torque-coupling device (C1);
• d.) disengaging the one or more torque-coupling devices (C3 and/or 48) and stopping the closed-loop control;
• e.) ramping the second hydrostatic unit (RU) down until the first hydrostatic element (CU) speed is below a negative threshold;
• f.) ramping the second hydrostatic unit (RU) up until the first hydrostatic element (CU) reaches a sufficient positive speed;
• and,
• g.) ramping the second hydrostatic unit (RU) back to zero so gear can be engaged.