Hydraulic drive system with precharge logic

A hydraulic drive system for use with a motor vehicle, comprising:

• a high pressure storage device;
• a low pressure storage device;
• a pump-motor operating at a range of pump-motor speeds for converting between hydraulic energy and mechanical energy, said pump-motor disposed between said high pressure storage device and said low pressure storage device, said pump-motor entering a precharge mode to precharge said high pressure storage device when a pressure associated with said high pressure storage device is below a minimum threshold and an external command is received requesting an increased level of energy to move the motor vehicle in the form of a acceleration that would typically result in discharging of pressure from said high pressure storage device;
• said pump-motor including a swash plate that is adjustable from a neutral orientation to a first angular orientation for converting hydraulic energy to mechanical energy and to a second angular orientation for converting mechanical energy to hydraulic energy, said swash-plate moved to said second angular orientation;
• a switch, said switch having a first state indicating that said pressure within said high pressure storage device is below said minimum threshold, wherein said switch prohibits flow of hydraulic fluid from said high pressure storage device toward said low pressure storage device when in said first state, but permitting the flow of hydraulic fluid from said low pressure storage derive into said high pressure storage device during said precharge mode, said switch changing to a second state when said pressure associated with said high pressure storage device exceeds said minimum threshold, thereby permitting the flow of hydraulic fluid from said high pressure storage device;
• a selectively rotating shaft associated with the mechanical energy;
• a clutch for selectively transferring the mechanical energy between said rotating shaft and said pump-motor;
• and
• wherein a clutch engagement transfers mechanical energy to hydraulic energy by way of said pump-motor during said precharge mode.

A method associated with a hydraulic drive system of a motor vehicle and having a high pressure storage device and a low pressure storage device, a pump-motor for converting between hydraulic energy and mechanical energy, the pump-motor disposed between the high pressure storage device and the low pressure storage device, and comprising the steps of:

• determining that a measured pressure associated with said high pressure storage device is below a minimum threshold;
• a switch maintaining a first state such that hydraulic fluid entering said high pressure storage device will not be released;
• moving said pump-motor into a precharge mode;
• receiving an external command that would typically result in discharging of pressure from said high pressure storage device;
• said pump-motor converting mechanical energy to hydraulic energy subsequent to receipt of said command and increasing said measured pressure;
• and
• ceasing said converting step when said measured pressure is at least equal to said minimum threshold.