Dual mode hybrid hydrostatic driveline

A method of operating a hybrid driveline for a vehicle in a hydrostatic drive mode and a direct drive mode, the method comprising the steps of:

• providing a power source;
• providing a first hydrostatic unit drivingly engaged with the power source;
• providing a second hydrostatic unit selectively drivingly engaged with a vehicle output, the second hydrostatic unit in fluid communication with the first hydrostatic unit;
• providing a first fluid conduit fluidly connecting a first fluid port of the first hydrostatic unit to a first fluid port of the second hydrostatic unit;
• providing a second fluid conduit fluidly connecting a second fluid port of the first hydrostatic unit to a second fluid port of the second hydrostatic unit;
• providing an accumulator assembly in fluid communication with the first hydrostatic unit and the second hydrostatic unit, wherein the accumulator assembly comprises a low pressure accumulator, a high pressure accumulator, and at least one control valve, wherein the at least one control valve has at least a first position and a second position, the at least one control valve in the first position facilitating fluid communication between the high pressure accumulator and the first fluid conduit and between the low pressure accumulator and the second fluid conduit, and the at least one control valve in the second position facilitating fluid communication between the high pressure accumulator and the second fluid conduit and between the low pressure accumulator and the first fluid conduit;
• providing a clutching device selectively drivingly engaged with the vehicle output and one of the first hydrostatic unit and the second hydrostatic unit;
• providing a first fluid conduit fluidly connecting a first fluid port of the first hydrostatic unit to a first fluid port of the second hydrostatic unit;
• providing a second fluid conduit fluidly connecting a second fluid port of the first hydrostatic unit to a second fluid port of the second hydrostatic unit;
• providing a low range gear;
• providing a high range gear;
• drivingly engaging the second hydrostatic unit with the vehicle output through the low range gear using the clutching device and transferring power from the power source to the vehicle output via the first hydrostatic unit, the fluid conduits, the second hydrostatic unit and the clutching device to place the hybrid driveline in the hydrostatic drive mode;
• and
• drivingly engaging the power source with the vehicle output through the high range gear using the clutching device to place the hybrid driveline in the direct drive mode.