Hydraulic system for the dampening of inertia load

Abstract: A hydraulic system is provided with a pump (42) supplying pressurized hydraulic fluid through a first supply line (44) to a closed center control valve (40). From the control valve (40) the fluid is directed through work lines (46, 48) to a hydraulic motor (36). Exhausted hydraulic fluid from the hydraulic motor (36) is directed through the control valve (40) to an exhaust line (50) having a back pressure check valve (52) set at a first pressure level. The hydraulic motor (36) is provided with a pressure relief valve (56, 58) and an anti-cavitation valve (60, 62) that are mounted in parallel with one another. The anti-cavitation valve (60, 62) is hydraulically coupled to the exhaust line (50). To keep the exhaust line (50) fully charged a second supply line (70) extends between the first supply line (44) and the exhaust line (50). The second supply line (70) is provided with a pressure reducing valve (72) that is set at a second pressure level. The second pressure level of the pressure reducing valve (72) is less than the first pressure level of the back pressure check valve (52).

Description: The invention is directed to an hydraulic system according the precharacterizing part of claim one. The invention is further directed to a backhoe with such a hydraulic system. Hydraulic motors in the form of linear hydraulic cylinders and rotary motors are used to move large bodies resulting in large inertial forces when the bodies are stopped. As the load is quickly stopped, oil on one side of the motor is forced over relief, and oil on the other side of the motor experiences cavitation. Fluid is directed to the cavitating side through anti-cavitation valves. In systems having closed center control valves there may be insufficient fluid to supply the cavitating side of the motor resulting in oscillation of the load as it is stopped. One example of a machine that may experience this oscillation problem is a backhoe. A backhoe is provided with a pivotal boom which is attached to the vehicle by a swing frame. The swing frame is provided with a vertical pivot for pivoting the backhoe about a vertical axis relative to the vehicle. As the boom is quickly swung and stopped the boom will oscillate . This oscillation is caused by return fluid from the hydraulic swing cylinders being forced over the relief valves at high pressure as the closed center control valve closes. At the same time the supply side of the hydraulic swing cylinders experience a loss of fluid or cavitation. The high pressure developed on the return fluid side of the hydraulic swing cylinder now forces the boom back towards the cavitated side now building up pressure in that side. The newly generated pressure then pushes the hydraulic swing cylinders. This oscillating movement continues until the swing energy is dissipated and the boom oscillating motion stops. From the US-A-5,159,813 a slewing control device for a hydraulic slewing crane is known which is adapted for applying a discharge oil from a hydraulic pump through a slewing control valve to a slewing motor and for controlling a rotational direction and a rotational speed of the slewing motor. The slewing control device includes a brake pressure control valve for variably controlling a discharge pressure of the slewing motor, an acceleration pressure control valve for variably controlling a suction pressure of the slewing motor, and a controller for outputting to both pressure control valves a pressure control signal to be determined according to an operational condition of the crane. The acceleration pressure control valve comprises a variable main relief valve which is coupled between the hydraulic pump and a tank. The relief valve is controlled by a three-position selector valve which is adapted to select one of three set pressures corresponding to the operational conditions. A similar backpressure control circuit for a hydraulic drive device is disclosed by the US-A-6,112,521 where the circuit is adapted for reducing the losses in drive power and for suppressing cavitation. The control circuit includes a pilot valve for taking a pressure on a drive side of a hydraulic motor as a pilot pressure upon receipt of a signal from an operating lever, and a variable throttle valve for changing a backpressure to a low pressure or to a high pressure upon receipt of a pilot pressure from the pilot valve. A relief valve is positioned between the pump and the variable throttle valve which conducts a relieving operation when the pressure exceeds the highest drive pressure set for driving the hydraulic motor. The US-A-5,513,551 relates to a hydraulic control system for a tractor with a backhoe implement. Two slew cylinders are controlled by an electromagnetic proportional control valve. This valve has an exhaust line connected through oil lines having check valves to oil lines extending to the hydraulic cylinders. With this construction pressure oil is supplemented from the exhausting oil line through the further oil lines, as necessary, to avoid cavitation. It is an object of the present invention to provide an inertial load hydraulic dampening system and a backhoe with such a hydraulic system for dampening the high inertial forces generated by a body being driven by a hydraulic motor. This object is solved according to the invention by the teaching of one of the claims 1 and 7. Further advantageous arrangements and developments of the invention appear from the dependent claims. It is a feature of the invention that pressurized hydraulic fluid is directed to the exhaust line through a pressure reducing valve to assure that the anti-cavitation circuit of the hydraulic motor is adequately supplied. The hydraulic circuit for this system is provided with a source of pressurized hydraulic fluid that is directed through a first supply line to a control valve. From the control valve the fluid is directed to work lines to a hydraulic motor. In the example explained in the description below, the hydraulic motor is two hydraulic swing cylinders used to swing a boom on a backhoe. Exhausted hydraulic fluid from the hydraulic motor is directed through the control valve to an exhaust line having a back pressure check valve set at a first pressure level. The back pressure check valve maintains a specified amount of hydraulic pressure in the exhaust line adjacent to the control valve as directed by the set pressure level of the valve. The hydraulic motor is provided with a pressure relief valve and an anti-cavitation valve that are mounted in parallel with one another. The anti-cavitation valve is hydraulically coupled to the exhaust line. With a closed center control valve pressurized hydraulic fluid is not continually passing through the exhaust line, as such the back pressure set by the back pressure check valve may be much less than the pressure dictated by this valve. To keep the exhaust line fully charged a second supply line extends between the first supply line and the exhaust line. The second supply line is provided with a pressure reducing valve that is set at a second pressure level. The second pressure level of the pressure reducing valve is less than the first pressure level of the back pressure check valve. In the preferred embodiment the hydraulic system is a PCLS (Pressure Compensated Load Sensing) system having a variable displacement pump used to supply pressurized hydraulic fluid. The hydraulic motor is a double acting hydraulic cylinder. In addition, the pressure reducing valve can be located in the valve stack for controlling the various operations of a machine. The invention and further advantageous developments and arrangements of the invention will now be described and explained in more detail by way of example and with reference to the accompanying drawings in which: Fig. 1 is a rear perspective view of a self propelled backhoe loader and Fig. 2 is a hydraulic schematic of the present inertial load hydraulic dampening system. Fig. 1 illustrates a backhoe 10, having a supporting frame 12 to which are mounted ground engaging wheels 14 for supporting and propelling the frame. Although the current invention is illustrated as being mounted on a wheeled work vehicle, it can also be mounted on a tracked work vehicle having conventional steel or rubber tracks. The front of the backhoe 10 is provided with a loader bucket 16 having a suitable loader bucket linkage 17 for manipulating the loader bucket relative to the supporting frame 12. The rear of the supporting frame 12 is provided with a swing frame 18. A boom 20 is pivotally coupled to the swing frame 18, a dipperstick 22 is pivotally connected to the boom and a bucket 26 is pivotally connected to the dipperstick 22. A bucket actuating hydraulic cylinder 28 manipulates the bucket 26 through a bucket linkage. The backhoe loader is also provided with two stabilizers 30. The operation of the vehicle is controlled from operator's station 32. The swing frame 18 is pivotally coupled to the vehicle frame 12 by a vertical pivot in a conventional manner. Hydraulic cylinders 36 pivot the swing frame 18 relative to the supporting frame 12 about a vertical axis defined by the vertical pivot. The position of the swing frame 18 relative to the supporting frame 12 is controlled by a three position control valve 40. The control valve 40 has a right swing position, a left swing position, and a stationary position. Pressurized hydraulic fluid from a source of pressurized hydraulic fluid 42 is coupled to the control valve 40 by supply line 44. In the illustrated embodiment the source of pressurized hydraulic fluid is a variable displacement pump. The control valve 40 in turn is hydraulically coupled to the hydraulic swing cylinders 36 by first and second work lines 46 and 48. Pressurized and exhausted hydraulic fluid passes through the work lines 46 and 48. Exhausted hydraulic fluid from swing cylinders 36 passes through the control valve 40 to exhaust line 50. The exhaust line 50 is provided with a back pressure check valve 52 which has a first pressure level. In one example the back pressure check valve is set at 110 psi (1 pound per square inch = 6,8947 kPa). If the pressure is less that 110 psi the valve is closed. If the pressure exceeds this first pressure level of 110 psi the valve opens and hydraulic fluid is exhausted through an oil cooler, not shown, back to tank 54 where it is returned to the pump 42. Each of the swing cylinders 36 are also provided with a pressure relief valve 56 and 58 and an anti-cavitation valve 60 and 62. The pressure relief valve 56 is coupled in parallel with anti-cavitation valve 60. Both of these valves 56 and 60 are hydraulically positioned between work line 46 and exhaust line 50. Similarly, the pressure relief valve 58 is coupled in parallel with anti-cavitation valve 62. Again, both of these valves are hydraulically positioned between work line 48 and exhaust line 50. The above discussed swing cylinder hydraulic configuration is typical of the prior art for a backhoe having a PCLS hydraulic system. The present invention is different from the prior art in providing a second supply line 70 and a pressure reducing valve 72. The second supply line 70 extends between the first supply line 44 and the exhaust line 50. The flow of pressurized hydraulic fluid through this short circuit path is controlled by pressure reducing valve 72 that is hydraulically positioned in the second supply line 70 and which is set at a second pressure level that is less than the first pressure level of the back pressure check valve 52. In the example discussed above the pressure reducing valve 72 is set at 100 psi which is 10 pounds less than the 110 psi setting of the back pressure check valve 52. In this way the exhaust line 50 between the back pressure check valve 52 and the control valve 40 is maintained at a minimum pressure of 100 psi and at a maximum maintained pressure of 110 psi. Therefore, the back pressure on the anti-cavitation valves 60 and 62 is at the same pressure level in the exhaust line 50, and additional fluid from the exhaust line 50 can be supplied to the cavitating side of a hydraulic cylinder 36. By supplying the fluid to the cavitating side in a rapid manner the oscillation is dampened when stopping a large body abruptly. The invention should not be limited to the above described embodiment, but should be limited solely to the claims that follow.

Claims: A hydraulic system for dampening the high inertia forces generated by a body being driven by a hydraulic motor (36), the system comprising: a source (42) of pressurized hydraulic fluid; a first supply line (44) coupled to the source (42) of pressurized hydraulic fluid; a control valve (40) coupled to the first supply line (44); a work line (46, 48) extending from the control valve (40) to the hydraulic motor (36) ; an exhaust line (50) coupled to the control valve (40) and returning exhausted hydraulic fluid to a tank (54) ; a back pressure check valve (52) set at a first pressure level hydraulically located in the exhaust line (50); an anti-cavitation valve (60, 62) hydraulically positioned between the exhaust line (50) and the work line (46, 48); characterized in that a second supply line (70) extends between the first supply line (44) and the exhaust line (50); and a pressure reducing valve (72) is hydraulically located in the second supply line (70) and is set at a second pressure level, whereby the second pressure level is less than the first pressure level. A hydraulic system as defined by claim 1 wherein the source (42) of pressurized hydraulic fluid is a pump. A hydraulic system as defined by claim 1 or 2 wherein the control valve (40) is a closed center valve. A hydraulic system as defined by one of the claims 1 to 3 wherein a pressure relief valve (56, 58) is hydraulically mounted in parallel with the anti-cavitation valve (60, 62). A hydraulic system as defined by one of the claims 1 to 4 wherein the hydraulic motor (36) is a double acting hydraulic cylinder. A hydraulic system as defined by one of the claims 1 to 5 wherein the pump (42) is a variable displacement pump. A backhoe comprising: a supporting frame (12) ; a swing frame (18) pivotally mounted to the supporting frame (12) about a vertical pivot; a boom (20) pivotally mounted to the swing frame (18) ; a dipperstick (22) pivotally mounted to the boom (20) ; a work implement (26) pivotally mounted to the dipperstick (22); at least one hydraulic swing cylinder (36) extending between the supporting frame (12) and the swing frame (18) for pivoting the swing frame (18) about the vertical pivot; a hydraulic circuit hydraulically coupled to the hydraulic swing cylinder (36) and comprising a hydraulic system as defined by one of the claims 1 to 6, where the control valve is a swing control valve (40). A backhoe as defined by claim 7 comprising a first and a second hydraulic swing cylinder (36) wherein the second hydraulic swing cylinder (36) swings the swing frame (18) in conjunction with the first hydraulic swing cylinder (36), the second hydraulic swing cylinder (36) is also a double acting hydraulic cylinder, as such there is a second work line (48) extending between the swing control valve (40) and the second hydraulic swing cylinder (36), a second anti-cavitation valve (62) that is hydraulically positioned between the second work line (48) and the exhaust line (50), and a second pressure relief valve (58) is mounted in parallel with the second anti-cavitation valve (62). A backhoe as defined by claim 7 or 8 further comprising ground engaging means (14) extending from the supporting frame means for supporting and propelling the supporting frame (12). A backhoe as defied by one of the claims 7 to 9 wherein the supporting frame (12) is provided with an operators station (32) for controlling the operation of the backhoe. A backhoe as defined by one of the claims 7 to 10 wherein the swing frame (18) and boom (20) is located at the rear of the supporting structure and a loader bucket (16) and associated loader linkage (17) is located at the front of the supporting frame (12). A backhoe as defined by one of the claims 7 to 11 wherein the work implement is a bucket (26). A backhoe as defined by one of the claims 7 to 12 comprising a hydraulic circuit according one of the claims 1 to 6.

Inventors: GITTER RICHARD JOHN, GITTER, RICHARD JOHN
Applicants: DEERE & CO, DEERE & COMPANY
Application year: 2001
Main classification: E02F9
IPC codes: E02F3, E02F9, F15B11