Hydraulic drive system and method of operating a hydraulic drive system

A hydraulic drive system hydraulic drive system comprising components that cooperate with one another to deliver reciprocating motion and to provide piston strokes of consistent length, said system comprising:

• (a) an actuator comprising a piston disposed within a cylinder and reciprocable between two cylinder heads, whereby said piston divides said cylinder into respective first and second hydraulic fluid chambers and a piston stroke is defined by said piston traveling from a first predetermined position near one of said cylinder heads to a second predetermined position near the other one of said cylinder heads;
• (b) at least one piston rod comprising a first end connected to said piston and a second end extending through one of said two cylinder heads and out of said cylinder;
• (c) a flow switching device comprising a flow switching member that is actuatable between at least two positions by an actuator that is activatable by an electronic signal to reverse the direction of hydraulic fluid flow to or from said first and second hydraulic fluid chambers so that hydraulic fluid flows into one of said first or second hydraulic fluid chambers when hydraulic fluid is flowing out of the other one of said first or second hydraulic fluid chambers;
• (d) a hydraulic pump comprising a discharge outlet and a suction inlet;
• (e) high pressure conduits for respective fluid connections between each one of said first and second hydraulic fluid chambers and respective fluid couplings of said flow switching device, and between an inlet of said flow switching device and said discharge outlet;
• (f) low pressure conduits for connecting an outlet of said flow switching device to a hydraulic fluid reservoir and said hydraulic fluid reservoir to said suction inlet, or for connecting said outlet of said flow switching device directly to said suction inlet;
• (g) a shuttle valve and a fluid passage through said piston wherein said shuttle valve is operable to close said fluid passage when said piston is moving during one of said piston strokes, and to open said fluid passage when said piston is at the end of one of said piston strokes;
• and
• (h) a controller that is programmed to:
• determine when said piston has reached the end of each piston stroke based upon at least one of hydraulic pump speed, hydraulic fluid pressure, or elapsed time, all measured during each piston stroke;
• and
• send an electronic signal to said flow switching device to command said flow switching member to be actuated from one position to another position to reverse the hydraulic fluid flow when said controller determines that said piston has reached the end of each piston stroke,
• wherein said controller is configured to receive a signal indicative of hydraulic fluid pressure at a location at or between said hydraulic pump discharge and said hydraulic fluid chamber into which hydraulic fluid is flowing, and is programmed to determine when said piston has reached the end of a piston stroke by determining when said shuttle valve has opened and said hydraulic fluid pressure drops below a predetermined value.

A hydraulic drive system comprising components that cooperate with one another to deliver reciprocating motion and to provide piston strokes of consistent length, said system comprising:

• (a) an actuator comprising a piston disposed within a cylinder and reciprocable between two cylinder heads, whereby said piston divides said cylinder into respective first and second hydraulic fluid chambers and a piston stroke is defined by said piston traveling from a first predetermined position near one of said cylinder heads to a second predetermined position near the other one of said cylinder heads;
• (b) at least one piston rod comprising a first end connected to said piston and a second end extending through one of said two cylinder heads and out of said cylinder;
• (c) a flow switching device comprising a flow switching member that is actuatable between at least two positions by an actuator that is activatable by an electronic signal to reverse the direction of hydraulic fluid flow to or from said first and second hydraulic fluid chambers so that hydraulic fluid flows into one of said first or second hydraulic fluid chambers when hydraulic fluid is flowing out of the other one of said first or second hydraulic fluid chambers;
• (d) a hydraulic pump comprising a discharge outlet and a suction inlet;
• (e) high pressure conduits for respective fluid connections between each one of said first and second hydraulic fluid chambers and respective fluid couplings of said flow switching device, and between an inlet of said flow switching device and said discharge outlet;
• (f) low pressure conduits for connecting an outlet of said flow switching device to a hydraulic fluid reservoir and said hydraulic fluid reservoir to said suction inlet, or for connecting said outlet of said flow switching device directly to said suction inlet;
• (g) a shuttle valve and a fluid passage through said piston wherein said shuttle valve is operable to close said fluid passage when said piston is moving during one of said piston strokes, and to open said fluid passage when said piston is at the end of one of said piston strokes;
• and
• (h) a controller that is programmed to:
• determine when said piston has reached the end of each piston stroke based upon at least one of hydraulic pump speed, hydraulic fluid pressure, or elapsed time, all measured during each piston stroke;
• and
• send an electronic signal to said flow switching device to command said flow switching member to be actuated from one position to another position to reverse the hydraulic fluid flow when said controller determines that said piston has reached the end of each piston stroke,
• wherein said controller adds a predetermined delay to the timing for sending said electronic signal to said flow switching device so that said piston is stationary for at least a predetermined time between each piston stroke.

A hydraulic drive system comprising components that cooperate with one another to deliver reciprocating motion and to provide piston strokes of consistent length in each actuation stroke, said system comprising:

• (a) an actuator comprising a piston disposed within a cylinder and reciprocable between two cylinder heads in each actuation stroke, whereby said piston divides said cylinder into respective first and second hydraulic fluid chambers and a piston stroke is defined by said piston traveling from a first predetermined position near one of said cylinder heads to a second predetermined position near the other one of said cylinder heads;
• (b) at least one piston rod comprising a first end connected to said piston and a second end extending through one of said two cylinder heads and out of said cylinder;
• (c) a flow switching device comprising a flow switching member that is actuatable between at least two positions to reverse the direction of hydraulic fluid flow to or from said first and second hydraulic fluid chambers so that hydraulic fluid flows into one of said first or second hydraulic fluid chambers when hydraulic fluid is flowing out of the other one of said first or second hydraulic fluid chambers;
• (d) a hydraulic pump comprising a discharge outlet and a suction inlet;
• (e) high pressure conduits for respective fluid connections between each one of said first and second hydraulic fluid chambers and respective fluid couplings of said flow switching device, and between an inlet of said flow switching device and said discharge outlet;
• (f) low pressure conduits for connecting an outlet of said flow switching device to a hydraulic fluid reservoir and said hydraulic fluid reservoir to said suction inlet, or for connecting said outlet of said flow switching device directly to said suction inlet;
• and
• (g) a shuttle valve and a fluid passage through said piston wherein said shuttle valve is operable to close said fluid passage when said piston is moving during one of said piston strokes and to open said fluid passage when said piston is at the end of one of said piston strokes, and wherein said shuttle valve comprises a valve member shaped with two sealing surfaces associated with opposite ends of said valve member, which is movable between two closed positions where said sealing surfaces can cooperate with respective valve seats to seal said fluid passage, said valve member being in an open position when said valve member is disposed between said two closed positions with both of said sealing surfaces spaced apart from said respective valve seats;
• wherein said fluid passage and said shuttle valve are sized such that when said shuttle valve is in said open position, movement of said piston is halted.

A method of operating a hydraulic drive system, said method comprising:

• reciprocating a hydraulic piston within a cylinder to provide piston strokes of consistent length in each actuation stroke by reversing the direction of hydraulic fluid flow to said cylinder to alternate between:
• delivering hydraulic fluid from a reservoir to a first hydraulic fluid chamber associated with one side of said hydraulic piston while draining hydraulic fluid to said reservoir from a second hydraulic fluid chamber associated with an opposite side of said hydraulic piston, and
• delivering hydraulic fluid from said reservoir to said second hydraulic fluid chamber while draining hydraulic fluid to said reservoir from said first hydraulic fluid chamber;
• mechanically actuating a shuttle valve when said hydraulic piston is a predetermined distance from a cylinder head to fluidly connect the first hydraulic fluid chamber to said second hydraulic fluid chamber while one of said first or second hydraulic fluid chambers is fluidly connected to said reservoir, thereby halting movement of said hydraulic piston and defining an end position for a piston stroke;
• determining when said hydraulic piston reaches said end position based upon measurements taken during said piston stroke of at least one of hydraulic pump speed, hydraulic fluid pressure, or elapsed time;
• and
• when it has been determined that said hydraulic piston has reached said end position, sending an electronic signal to actuate a flow switching device to reverse the hydraulic fluid flow direction, whereupon said shuttle valve closes and said hydraulic piston commences a new piston stroke, moving in a direction opposite to movement of said piston during said piston stroke just ended.

A method of operating a hydraulic drive system, said method comprising:

• reciprocating a hydraulic piston within a cylinder by reversing the direction of hydraulic fluid flow to said cylinder to alternate between:
• delivering hydraulic fluid from a reservoir to a first hydraulic fluid chamber associated with one side of said hydraulic piston while draining hydraulic fluid to said reservoir from a second hydraulic fluid chamber associated with an opposite side of said hydraulic piston, and
• delivering hydraulic fluid from said reservoir to said second hydraulic fluid chamber while draining hydraulic fluid to said reservoir from said first hydraulic fluid chamber;
• mechanically actuating a shuttle valve when said hydraulic piston is a predetermined distance from a cylinder head to fluidly connect the first hydraulic fluid chamber to said second hydraulic fluid chamber while one of said first or second hydraulic fluid chambers is fluidly connected to said reservoir, thereby halting movement of said hydraulic piston and defining an end position for a piston stroke;
• determining when said hydraulic piston reaches said end position based upon measurements taken during said piston stroke of at least one of hydraulic pump speed, hydraulic fluid pressure, or elapsed time;
• and
• when it has been determined that said hydraulic piston has reached said end position, sending an electronic signal to actuate a flow switching device to reverse the hydraulic fluid flow direction, whereupon said shuttle valve closes and said hydraulic piston commences a new piston stroke, moving in a direction opposite to movement of said piston during said piston stroke just ended,
• wherein said step of determining when said hydraulic piston reaches said end position comprises monitoring hydraulic fluid pressure at a location where the measured pressure correlates to pressure within the one of said first and second hydraulic fluid chambers that is being filled with hydraulic fluid, and determining that said piston is at the end of each piston stroke when the measured pressure drops below a predetermined threshold value.

A method of operating a hydraulic drive system, said method comprising:

• reciprocating a hydraulic piston within a cylinder by reversing the direction of hydraulic fluid flow to said cylinder to alternate between:
• delivering hydraulic fluid from a reservoir to a first hydraulic fluid chamber associated with one side of said hydraulic piston while draining hydraulic fluid to said reservoir from a second hydraulic fluid chamber associated with an opposite side of said hydraulic piston, and
• delivering hydraulic fluid from said reservoir to said second hydraulic fluid chamber while draining hydraulic fluid to said reservoir from said first hydraulic fluid chamber;
• mechanically actuating a shuttle valve when said hydraulic piston is a predetermined distance from a cylinder head to fluidly connect the first hydraulic fluid chamber to said second hydraulic fluid chamber while one of said first or second hydraulic fluid chambers is fluidly connected to said reservoir, thereby halting movement of said hydraulic piston and defining an end position for a piston stroke;
• determining when said hydraulic piston reaches said end position based upon measurements taken during said piston stroke of at least one of hydraulic pump speed, hydraulic fluid pressure, or elapsed time;
• and
• when it has been determined that said hydraulic piston has reached said end position, sending an electronic signal to actuate a flow switching device to reverse the hydraulic fluid flow direction, whereupon said shuttle valve closes and said hydraulic piston commences a new piston stroke, moving in a direction opposite to movement of said piston during said piston stroke just ended;
• and
• incorporating a safety factor in the determination of when said hydraulic piston position reaches said end position so that there is a delay between the time when it is determined that said piston has reached the end of said piston stroke and the time when said electronic signal is sent to said flow switching device.