Bi-rotational, two-stage hydraulic system

A hydraulic system including a double acting hydraulic cylinder with retract and extend chambers and first and second ports into the retract and extend chambers respectively,

• first and second reversible pumps, each of which has first and second ports which are capable of assuming pressure and suction functions depending on the direction of operation of the respective pump;
• a prime mover for operating the pumps in one direction or another;
• a reservoir for supplying fluid to the pumps and for receiving excess fluid;
• a fluid circuit for directing fluid between the reservoir, the ports of the pumps and the ports of the actuator, the first ports of both pumps fluidly connected via a first circuit portion to the first port of the hydraulic actuator, and the second ports of both pumps being fluidly connected via a second circuit portion to the second port of the hydraulic actuator;
• first valve means in the first fluid circuit portion operationally responsive to fluid pressure in the first circuit portion, for controlling flow from the first circuit portion through a first drain path to the reservoir when the fluid pressure in the first circuit portion increases above a predetermined value;
• second valve means in the second circuit portion between the second ports of the first and second pumps operationally responsive to fluid pressure in the first and second circuit portions for controlling flow between the second pump and the hydraulic actuator, with the second valve means:
• a) in an open position allowing flow between the second pump and the hydraulic actuator when i) the pressure in the first circuit portion in conjunction with the pressure in the second circuit portion at the second port of the second pump is greater than ii) the pressure in the second circuit portion at the second port of the first pump, such that flow is provided between both pumps and the hydraulic actuator;
• and
• b) in a closed position preventing flow between the second pump and the hydraulic actuator when i) the pressure in the first circuit portion in conjunction with the pressure in the second circuit portion at the second port of the second pump is less than ii) the pressure in the second circuit portion at the second port of the first pump such that flow is only provided in the second circuit portion between the first pump and the hydraulic actuator;
• third valve means operationally responsive to fluid pressure in the second circuit portion and fluidly connected to the second pump, for controlling flow through a second drain path from the second pump to the reservoir when the fluid pressure in the second circuit portion at the second port of the first pump is above a threshold value;
• and
• one-way valve means controlling flow from the reservoir to the first and second circuit portions, wherein when fluid is provided to the retract chamber and the hydraulic cylinder is in a retract movement, flow is provided i) from the extend chamber through both pumps to the retract chamber at low loads when the second valve means is in an open condition and the first valve means is in a closed condition;
• and ii) from the extend chamber only through the first pump, and from the reservoir through the third valve means and the one-way valve means to the second pump, at high loads when the second valve means is in a closed condition and the first valve means is in an open condition.

In a system for operating a hydraulic actuator in extend and retract modes, where the actuator has internal extend and retract chambers and extend and retract ports for the extend and retract chambers, respectively, the system including:

• first stage and second stage reversible pumps, each of which has first and second ports which are capable of assuming pressure and suction functions depending on the direction of operation of the respective pump;
• a prime mover for conjointly operating the pumps in one direction or another;
• a fluid circuit for directing fluid between the ports of the pumps and the ports of the actuator, the first ports of both pumps fluidly connected via a retract circuit portion to the retract port of the hydraulic actuator, and the second ports of both pumps being fluidly connected via an extend circuit portion to the extend port of the hydraulic actuator;
• first valve means in the retract circuit portion operationally responsive to fluid pressure in the retract circuit portion to compensate for different fluid capacities of the extend and retract chambers, the first valve means directing flow from the retract circuit portion through a first drain path to reservoir when actuator is in the extend mode of operation;
• second and third valve means operationally responsive to fluid pressure in the retract and extend circuit portions for i) allowing flow between both pumps and the actuator when the load on the actuator is below a second predetermined value in both the extend and retract modes of operation;
• and ii) allowing flow between the first stage pump and the actuator but isolating the actuator from the second stage pump when the load on the actuator is above the second predetermined value, in both the extend and retract modes of operation;
• and
• fourth and fifth valve means controlling flow from the reservoir to the retract and extend circuit portions respectively during extend and retract operation of the hydraulic actuator, wherein when the hydraulic actuator is in the retract operation, flow from both pumps is provided to the retract chamber during low load conditions when the second valve means is in an open condition and the first valve means is in a closed condition;
• and ii) from the extend chamber through the first pump, and from the reservoir to the second pump, at high loads when the second valve means is in a closed condition and the first valve means is in an open condition.

In a system for operating a hydraulic actuator in extend and retract modes of operation, where the actuator has first and second ports into retract and extend chambers, respectively, the system including:

• first and second reversible pumps, each of which has first and second ports which are capable of assuming pressure and suction functions depending on the direction of operation of the respective pump;
• a prime mover for operating the pumps in one direction or another;
• a reservoir for supplying fluid to the pumps and for receiving excess fluid;
• a fluid circuit for directing fluid between the reservoir, the ports of the pumps and the ports of the actuator, the first ports of both pumps fluidly connected via a first circuit portion to the first port of the hydraulic actuator, and the second ports of both pumps being fluidly connected via a second circuit portion to the second port of the hydraulic actuator;
• a relief valve in the first fluid circuit portion operationally responsive to fluid pressure in the first circuit portion, the relief valve allowing flow from the first circuit portion through a first drain path to the reservoir when the fluid pressure in the first circuit portion increases above a predetermined value during the retract mode of operation;
• a non-return check valve in the second circuit portion between the second ports of the first and second pumps operationally responsive to fluid pressure in the first and second circuit portions for controlling flow between the second pump and the hydraulic actuator, with the non-return check valve:
• (a) in an open position allowing flow between the second pump and the hydraulic actuator when i) the pressure in the first circuit portion in conjunction with the pressure in the second circuit portion at the second port of the second pump is greater than ii) the pressure in the second circuit portion at the second port of the first pump, such that flow is provided between both pumps and the hydraulic actuator;
• and
• (b) in a closed position preventing flow between the second pump and the hydraulic actuator when i) the pressure in the first circuit portion in conjunction with the pressure in the second circuit portion at the second port of the second pump is less than ii) the pressure in the second circuit portion at the second port of the first pump, such that flow is provided only in the second circuit portion between the first pump and the hydraulic actuator;
• an unloader valve operationally responsive to fluid pressure in the second circuit portion and fluidly connected to the second pump, the unloader valve allowing flow between the reservoir and second pump when the fluid pressure in the second circuit portion at the second port of the first pump is above a threshold value, the flow being i) from the second pump to the reservoir when the hydraulic actuator is in the extend mode of operation, and ii) from the reservoir to the second pump when the hydraulic cylinder is in the retract mode of operation;
• and
• a first supply path from the reservoir to the first port of the second pump, and a second supply path from the reservoir to the second port of the second pump, a first one-way check valve in the first supply path and a second one-way check valve in the second supply path, the check valves respectively controlling fluid from the reservoir to the first and second ports of the second pump during operation of the hydraulic actuator, wherein flow is provided from the reservoir, through the second check valve to the second port of the second pump, and from the second pump through the first port of the second pump and to the first circuit portion,
• wherein flow is provided during the retract mode of operation i) from the extend chamber through both pumps to the retract chamber when the relief valve is in a closed condition and the non-return check valve is open;
• and ii) from the extend chamber through only the first pump to the retract chamber, and from the reservoir through the second pump, when the relief valve is in an open condition and the non-return check valve is closed.

In a system for operating a hydraulic actuator in extend and retract modes of operation, where the actuator has first and second ports into retract and extend chambers, respectively, with the retract chamber having a smaller volume than the extend chamber, the system including:

• first and second reversible pumps, each of which has first and second ports which are capable of assuming pressure and suction functions depending on the direction of operation of the respective pump;
• a prime mover for operating the pumps in one direction or another;
• a reservoir for supplying fluid to the pumps and for receiving excess fluid;
• a fluid circuit for directing fluid between the reservoir, the ports of the pumps and the ports of the actuator, the first ports of both pumps fluidly connected via a first circuit portion to the first port of the hydraulic actuator, and the second ports of both pumps being fluidly connected via a second circuit portion to the second port of the hydraulic actuator;
• a relief valve in the first fluid circuit portion operationally responsive to fluid pressure in the first circuit portion, the relief valve allowing flow from the first circuit portion through a first drain path to the reservoir when the actuator is in the retract mode of operation and preventing flow through the first drain path when the actuator is in the extend mode of operation;
• a non-return check valve in the second circuit portion between the second ports of the first and second pumps operationally responsive to fluid pressure in the first and second circuit portions for controlling flow between the second pump and the hydraulic actuator, the non-return check valve moving from an open position during low pressure loads on the actuator, to a closed position at high pressure loads on the actuator and isolating the second pump from the extend chamber of the actuator;
• and
• an unloader valve operationally responsive to fluid pressure in the second circuit portion and fluidly connected to the second pump, the unloader valve allowing flow between the reservoir and the second pump during high pressure loads, and preventing flow between the reservoir and the second pump during low pressure loads,
• a first supply path from the reservoir to the first port of the second pump, and a second supply path from the reservoir to the second port of the second pump, a first one-way check valve in the first supply path arid a second one-way check valve in the second supply path, the check valves allowing flow from the reservoir to the first and second circuit portions during operation of the hydraulic actuator, wherein flow is provided during the retract mode of operation i) from the extend chamber through both pumps to the retract chamber at low loads when the relief valve is closed and the non-return cheek valve is open;
• and ii) from the extend chamber through only the first pump to the retract chamber, and from the reservoir through the second pump, at high loads when the relief valve is open and the non-return check valve is closed.