HYDRAULIC SYSTEM WITH ENERGY REGENERATION

Abstract

A hydraulic system includes a tank for hydraulic fluid, a supply line connected to the tank and a plurality of hydraulic functions connected to the supply line. Each hydraulic function includes an actuator that is connectable to a load and that has a first side and a second side. Each function includes a first control valve connected to the first side and a second control valve connected to the second side. Each function also has an independent tank line, and the first and second control valves are connected to both the supply line and the independent tank line. A third control valve is connected between the independent tank line and the tank, and a check valve is connected between the supply line and the independent tank line.

Description

TECHNICAL FIELD

The present invention relates to hydraulic system, and more particularly to a hydraulic system used to raise and lower a load.

BACKGROUND OF THE INVENTION

Hydraulic systems are commonly used in heavy machinery, such as earth-moving machines or agricultural equipment. Generally, hydraulic systems use valves to control circulation of pressurized fluid through a network of lines. Selective operation of the valves controls the fluid pressure in hydraulic actuators, such as cylinders, to carry out various functions on one or more loads.

Currently-known hydraulic systems often waste energy when lowering a load. For example, when gravity lowers a load during a first operation, the fluid expelled from a non-operating portion of an actuator (e.g., a cylinder) may be drained directly to a tank. To provide pressurized fluid for another operation (e.g., operating an arm at the end of the load, raising the load at a later time, etc.), a pump must consume additional energy because when the fluid is expelled, the potential energy in the drained fluid from the first operation is lost to heat and therefore is not available for use by any other operation. Thus, the second operation must draw energy from the engine to increase the fluid pressure to an operational level.

Some hydraulic systems capture energy by routing expelled fluid to another portion of the actuator or even to different actuator. The captured energy can reduce the amount of additional energy needed to pressurize the fluid for another operation and may also reduce the cycle time of the hydraulic system. Re-routing fluid to use the potential or stored energy in the fluid is often referred to as “regeneration.”

Some regeneration systems can only recycle fluid from one cylinder chamber to another or store fluid under pressure in an accumulator. This limits the applications in which energy regeneration can be used. Other systems allow regeneration among multiple functions, but regeneration in one function may negatively affect another function because the tank lines for different functions are interconnected. For example, raising the tank line pressure in one function raises the tank line pressure in the entire system, thereby reducing the ability to overcome external forces acting on the cylinder. If the other functions attempt to move their respective loads in the opposite direction of this external force, the system efficiency decreases because the supply pressure must overcome both forces (e.g., gravitational forces) on the load and the raised tank pressure to move the load in the desired manner.

There is a desire for a multi-function hydraulic system that isolates the functions from each other yet still allows cross-function regeneration when desired.

SUMMARY

A hydraulic system according to one aspect includes a tank for hydraulic fluid, a supply line connected to the tank, and a plurality of hydraulic functions connected to the supply line. Each hydraulic function includes an actuator that is connectable to a load. The actuator itself has a first side and a second side. Each function includes a first control valve connected to the first side and a second control valve connected to the second side. Each function also has an independent tank line, and the first and second control valves are connected to both the supply line and the independent tank line. A third control valve is connected between the independent tank line and the tank, and a check valve is connected between the supply line and the independent tank line.

A hydraulic system according to another aspect includes a tank for hydraulic fluid, a controller, a supply line connected to the tank, a pump connected between the tank and the supply line, a plurality of loads, and a plurality of hydraulic functions, where each hydraulic function is connected to one of the loads and the supply line. Each hydraulic function includes a cylinder and a piston disposed within the cylinder. The piston is connected to the load and divides the piston into a rod side and a head side. Each hydraulic function also includes a first operated control valve connected to the rod side and responsive to a first signal from the controller and a second control valve connected to the head side and responsive to a second signal from the controller. Each function also includes an independent tank line, and the first and second control valves are connected to the supply line and the independent tank line. A third control valve is connected between the independent tank line and the tank, and a pressure-operated check valve is connected between the supply line and the independent tank line. Each function also includes three pressure sensors to monitor pressure at the rod side of the cylinder, at the head side of the cylinder, and in the independent tank line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a hydraulic circuit according to one embodiment of the invention;

FIG. 2 is a schematic of a hydraulic circuit according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic of a hydraulic system 10 according to one embodiment of the invention. For illustrative purposes only, the system 10 shown in FIG. 1 has three separate functions 12, 14, 16. However, it should be understood that the system 10 can contain any number of functions without departing from the scope of the invention.

The functions 12, 14, 16 are linked together by a shared supply line 18 that supplies hydraulic fluid from a tank 20 to the functions 12, 14, 16 via a pump 22. A supply line sensor 24 may be included to monitor fluid pressure in the supply line 18.

Each function 12, 14, 16 has a corresponding actuator, such as a cylinder 26, 28, containing a piston 32, 34, 36 that drives a load 38, 40, 42. Note that other hydraulic actuators may be used in the system 10. Each function 12, 14, 16 may carry out a different operation corresponding to the particular load 38, 40, 42. For example, on an excavator, load 38 may be a bucket, load 40 may be a boom, and load 42 may be an arm. Other loads, load combinations, and/or operations may also be used in the system 10. Each function 12, 14, 16 also has an associated independent tank line 43, 44, 45 that acts as a separate, parallel link between each function 12, 14, 16 and the tank 20. Thus, each function 12, 14, 16 shares a connection to the tank 20 via the supply line 18 and also has its own, independent connection to the tank 20 via its corresponding independent tank line 43, 44, 45.

For simplicity, the details of the functions 12, 14, 16 will now be described with respect to function 12 only because the other functions 14, 16 have the same internal circuit structure. The piston 32 divides the cylinder 26 into a rod side 26a and a head side 26b. Each side 26a, 26b is a fluid chamber, and the fluid pressure in each side 26a, 26b controls the operation of the load. Fluid flow to and from the cylinder 26 can be controlled proportional control valves 50, 52. In one aspect of the system, the proportional control valves are solenoid-controlled, but any proportional control valve can be used in the system as well.

In one embodiment, a first proportional control valve 50 controls fluid flow to and from the rod chamber 26a and a second proportional control valve 52 controls fluid flow to and from the head chamber 26b. The first and second proportional control valves 50, 52 are operable to be connected to the supply line 18 or the independent tank line 43 In one aspect of the system, the first and second control valves 50, 52 operate according to one of three scenarios: (1) one control valve 50, 52 is connected to the supply line 18 and the other control valve 50, 52 is connected to the tank 20, (2) both control valves 50, 52 are open to the tank, and (3) both control valves 50, 52 are open to the supply line 18. A first pressure gauge 54 may monitor the pressure at the rod side 26a of the cylinder 26, and a second pressure gauge 56 may monitor the pressure at the head side 26b of the cylinder 26.

A third proportional control valve 58 may control fluid flow from the independent tank line 43 to the tank 20. In other words, the third control valve 58 controls the fluid pressure in the independent tank line 43. A third pressure gauge 59 may be disposed at the output of the third proportional control valve 58 to monitor the fluid pressure at the independent tank line 43. The control valves 50, 52, 58 may be solenoid-operated valves that respond according to input signals from a controller 60.

The control valves 50, 52 regulate fluid flow between the supply line 18 and the cylinder 26 based on signals from the controller 60. As can be seen in FIG. 1, the control valves 50, 52 for the cylinder 26 can receive fluid from both the supply line 18 and the independent tank line 43. A check valve 62 may control fluid flow from the independent thank line 43 to the supply line 18. In one embodiment, the check valve 62 is closed when the pressure in the supply line 18 is higher than the pressure in the independent tank line 43 to prevent flow from the supply line 18 to the independent tank line 43, and the check valve 62 is open when the pressure in the supply line 18 is equal to or lower than the pressure in the independent tank line 43 to allow free flow to the supply line 18. The check valve 62 allows fluid to flow back to the supply line 18 so that the fluid can be used for another function 14, 16.

The controller 60 itself controls operation of the system 10 by receiving input signals from the pressure sensors 24, 54, 56, 59 and other input devices (not shown) and outputting signals to actuate solenoids in the control valves 50, 54, 58 to carry out a desired function. The controller 60 also monitors the pressure sensors 24, 54, 56, 59 to ensure the system 10 is properly operating.

As explained above, regeneration generally involves supplying fluid exhausted from one portion of the actuator 26 into another portion of the actuator 26 in a given function 12 or to an actuator 28 in a different function 14 altogether. Regeneration reduces or eliminates the amount of fluid that must be supplied from the tank 20 to the actuator 26 to carry out a given function. This reduces the amount of energy needed to pressurize the fluid and also reduces the time needed for the fluid to reach its operational pressure, therefore improving system 10 performance. The examples below describe possible regeneration processes that can be carried out by the system 10.

In one operation, one or more functions 12 may recirculate fluid from one side of the actuator 26 to the other within a single function. Although the example below focuses on a single function that involves sending fluid from the head side 26b of the cylinder 26 to the rod side 26a of the cylinder 26 for simplicity in explanation, the fluid may be recirculated in other directions and/or within other functions 14, 16 without departing from the scope of the invention. This operation generally corresponds to known recirculation functions.

Note that in one aspect of the system, the check valve 62 does not play a role in single-function regeneration because the check valve 62 is used to isolate the functions 12, 14, 16 from each other. Since single-function regeneration focuses on a single function, there is no need for the check valve 62 to isolate the functions.

To initially raise the load 38, the pump 22 increases the fluid pressure in the supply line 18, and the second control valve 52 is adjusted (e.g., via control of the solenoid current by the controller 60) to control the fluid velocity though the valve 52. This fluid velocity controls the velocity at which the load is raised 38. The first control valve 50 is opened to minimize fluid flow restriction back to the tank 20. The third control valve 58 is completely open to minimize the pressure drop across the valve 58 and allow fluid in the rod side 26a to drain easily into the tank 20 without creating any fluid pressure that could fight against the pressure buildup in the head side 26b needed to raise the load 38.

More particularly, the first control valve 50 is connected to the independent tank line 43 and the second control valve 52 and connected to the supply line 18. The fluid pressure in the supply line 18 through the second control valve 52 causes the head side 26b of the cylinder 26 to fill with pressurized fluid, actuating the piston 32 and forcing fluid out of the rod side 26a back through the first control valve 50 into the tank 20.

To lower the load 38 and recirculate the fluid within the function 12, the controller 60 adjusts the solenoid currents to the first and second control valves 50, 52 so they are both closed to the supply line 18 and both connected to the independent tank line 43. The third control valve 58 is restricted to generate pressure in the independent tank line 43 and force some fluid to flow back to the rod side 26a. Connecting the control valves 50, 52 to the independent tank line 43 and restricting the third control valve 58 redirects fluid from the head side 26b to the rod side 26a while still allowing excess fluid to drain into the tank 20.

When the load 38 drops (e.g., when gravity pulls the load downward), the piston 32 lowers, forcing fluid out of the head side 26b. The second control valve 52 may be metered, if desired, to control the rate at which fluid drains from the head side 26b, thereby controlling the rate at which the load 38 lowers. Since the control valves 50, 52, 58 restrict fluid from flowing to the tank 20, the fluid from the head side 26b creates a pressure differential that pushes fluid through the second control valve 52, through the independent tank line 43, and through the first control valve 50 into the rod side 26a. In other words, the fluid exhausted from the head side 26b is recirculated and sent to the rod side 26a instead of drained to the tank 20, thereby allowing the potential energy to be used to fill the rod side 26a.

In another operation, cross-functional regeneration may be desired, allowing energy captured from lowering one load 38 to be used to raise or otherwise operate one or more other loads 40, 42 in the system 10. To do this, the first control valve 50 is opened to connect the rod side 26a of the cylinder 26 to the independent tank line 43 and the second control valve 52 is opened to connect the head side 26b to the independent tank line 43. The third control valve 58 is closed or partially closed to control the pressure in the independent tank line 43 at a desired level.

When fluid exhausts out of the head side 26b, it flows though the open second control valve 52 to the independent tank line 43. If the pressure in the supply line 18 is lower than the pressure in the independent tank line 43, the check valve 62 opens to connect the independent tank line 43 with the supply line 18. This allows the exhausted fluid to flow into the supply line 18 and raise the supply line 18 pressure. The increased supply line 18 pressure makes the energy from the exhausted fluid available to power loads in any of the other functions 14, 16 (assuming the load pressures in functions 14 and 16 are lower than the load pressure in function 12) because the supply line 18 is connected to all of the functions 12, 14, 16. Thus, loads 40 and 42 can be raised or otherwise operated using the increased fluid pressure in the supply line 18 created by the lowered load 38. If the supply line 18 already has sufficient operating pressure, the pump 22 does not need to be operated to raise the loads 40, 42.

In yet another operation, fluid is recirculated in one function while the pump is activated to lift loads in other functions. This is possible in the inventive system 10 because the independent tank lines 43, 44, 45 allow each function 12, 14, 16 to operate independently, with its own associated fluid pressures, without affecting the operation of the other functions 12, 14, 16 in the system 10. More particularly, in one example, fluid may recirculate in function 12 in the manner described above. The check valve 62 isolates the function 12 from the supply line 18 and the other functions 14, 16. The check valves in the other functions 14, 16 isolate their corresponding functions 14, 16 as well.

With respect to function 12, when the pressure in the supply line 18 is higher than the pressure in the independent tank line 43, the check valve 62 closes to isolate the function 12 from the supply line 18. As in the previous example, recirculation pressure may be generated when fluid exhausts from the head side 26b. If the third control valve 58 operates so that the pressure in the independent tank line 43 is the same as or greater than the supply line 18 pressure, the check valve opens and connects the independent tank line 43 to the supply line 18. Once this connection occurs, function 12 is connected to the other functions, and the increased supply line pressure may power the other functions 14, 16 or cross-functional regeneration.

If a given function does not need additional fluid flow however, the check valves 62 in each function 12, 14, 16 can continue to isolate the independent tank line 43, 44, 45 for each function from the supply line 18. For example, to lower the first load 38 and raise one or both of the other loads 40, 42, it is desirable to drain the independent tank line corresponding to the load(s) to be lifted 40, 42 during a lifting operation. Draining ensures that the fluid pressure in the independent tank line(s) 44, 45 is minimized, which optimizes energy efficiency and generates maximum load lifting capacity. Draining the independent tank line 44, 45 may be achieved by fully opening the third control valve 58 of functions 14 and 16.

When load 38 is lowered, the third control valve 58 of function 12 is restricted to raise the pressure at the independent tank line 43 and the supply line 18. However, since the third control valves 58 in the other functions 14, 16 are still fully open, the pressure in the independent tank lines 44, 45 is lower than the pressure in independent tank line 43, allowing cross-functional regeneration to occur.

Thus, the independent tank lines 43, 44, 45, check valves 62, and third control valves 58 in each function 12, 14, 16 allow selective connection and isolation of the functions 12, 14, 16 from each other. More particularly, the check valve 62 connects or isolates a given function 12, 14, 16 to or from the supply line 18, while the third control valve 58 controls the pressure in the independent tank line 43, 44, 45 to open or close the check valve 62 depending on the relative pressures of the supply line 18 and the independent tank line 43, 44, 45. The system 10 therefore can provide cross-function regeneration to reuse energy that would ordinarily be wasted.

FIG. 2 illustrates an alternative embodiment of the hydraulic system 10. In this embodiment, the third control valves 58 in each function 12, 14, 16 are replaced with pressure-controlled check valves 70. The check valve 70 maintains pressure in the independent tank line 43 at a single predetermined level. based on the difference between the pressure in the supply line 18 and the pressure in the tank 20.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

Claims

1. A hydraulic system, comprising:

a tank for hydraulic fluid;

a supply line connected to the tank;

a plurality of hydraulic functions connected to the supply line, each hydraulic function including an actuator that is connectable to a load, wherein the actuator has a first side and a second side; a first control valve connected to the first side, a second control valve connected to the second side, an independent tank line, wherein the first and second control valves are connected to the supply line and the independent tank line, a third control valve connected between the independent tank line and the tank, and a check valve connected between the supply line and the independent tank line.

2. The hydraulic system of claim 1, wherein the actuator is a cylinder, the first side is a rod side and the second side is a head side, and wherein the system further comprises a piston disposed within the cylinder and separating the rod side and the head side.

3. The hydraulic system of claim 1, further comprising a controller, and wherein at least one of the first and second control valves are controlled by the controller.

4. The hydraulic system of claim 4, wherein the first and second control valves are solenoid-operated valves.

5. The hydraulic system of claim 4, wherein the third control valve is a solenoid-operated valve controlled by the controller.

6. The hydraulic system of claim 4, wherein the third control valve is a pressure-controlled valve.

7. The hydraulic system of claim 1, wherein the check valve is a pressure-operated valve.

8. The system of claim 1, further comprising a pump connected between the tank and the supply line.

9. The system of claim 1, further comprising a first pressure sensor that monitors pressure at the first side of the actuator and a second pressure sensor that monitors pressure at the second side of the actuator.

10. A hydraulic system, comprising:

a tank for hydraulic fluid;

a controller;

a supply line connected to the tank;

a pump connected between the tank and the supply line;

a plurality of loads; and

a plurality of hydraulic functions, each hydraulic function connected to one of said plurality of loads and connected to the supply line, wherein each hydraulic function includes a cylinder and a piston disposed within the cylinder, wherein the piston is connected to the load and divides the piston into a rod side and a head side, a first operated control valve connected to the rod side and responsive to a first signal from the controller, a second control valve connected to the head side and responsive to a second signal from the controller, an independent tank line, wherein the first and second control valves are connected to the supply line and the independent tank line, a third control valve connected between the independent tank line and the tank, a pressure-operated check valve connected between the supply line and the independent tank line, a first pressure sensor that monitors pressure at the rod side of the cylinder, a second pressure sensor that monitors pressure at the head side of the cylinder, and a third pressure sensor that monitors pressure in the independent tank line.

11. The hydraulic system of claim 10, further comprising a controller, and wherein at the first and second control valves are solenoid-operated valves.

12. The hydraulic system of claim 10, wherein the third control valve is a solenoid-operated valve controlled by the controller.

13. The hydraulic system of claim 10, wherein the third control valve is a pressure-operated valve.