Patent Grant
9315968
The present disclosure relates generally to a hydraulic control system and, more particularly, to a hydraulic control system for a machine.
Swing-type excavation machines, for example hydraulic excavators and front shovels, require significant hydraulic pressure and flow to transfer material from a dig location to a dump location. These machines direct the high-pressure fluid from an engine-driven pump through a swing motor to accelerate a loaded work tool at the start of each swing, and then restrict the flow of fluid exiting the motor at the end of each swing to slow and stop swinging of the work tool.
In order to improve the efficiency of this type of hydraulic arrangement, one or more accumulators are provided in fluid communication with the swing motor. Based on an operating state of the swing motor, the accumulators are charged or discharged. For example, the accumulators may be discharged to assist an acceleration of the swing motor. Further, the accumulators may be charged by fluid exiting the swing motor during a deceleration of the swing motor.
However, charging of the accumulators by fluid from the swing motor may reduce fluid pressure at an input port of the swing motor. This may result in cavitation, thereby damaging the swing motor and adjoining components.
U.S. Patent Publication 2011/0020146 discloses a variable displacement hydraulic pump supplying pressure oil to a hydraulic actuator, a pressure detector detecting a pump discharge pressure from the hydraulic pump, a control valve controlling a supply of the pressure oil to the hydraulic actuator, a controller controlling a pump displacement of the hydraulic pump, a hydraulic motor rotating an upper structure of the construction machine, a swing relief valve defining a relief pressure of the hydraulic motor, and a control lever switching a control valve for the hydraulic motor. The controller includes: an adjuster that, when a pump discharge pressure detected by the pressure detector exceeds a first set value, conducts an adjustment to reduce the pump displacement; and a canceller that cancels the adjustment when the pump discharge pressure falls below a second set value. The second set value is equal to or larger than the first set value.
One aspect of the present disclosure is directed to a hydraulic control system. The hydraulic control system includes a pump configured to pressurize a fluid, and a swing motor selectively driven by pressurized fluid from the pump. The swing motor is configured to move a part of a machine. The hydraulic control system also includes a controller in communication with the pump. The controller is configured to receive an input indicative of a difference between a desired speed and an actual speed of the swing motor, and determine if the swing motor is accelerating, decelerating, or operating at neutral mode based on the difference between the desired and actual speeds. The controller is also configured to determine an amount of return fluid from an actuator of the machine that is available as makeup fluid for the swing motor if the swing motor is operating at neutral mode. The controller is further configured to receive an input indicative of a swing speed of the part of the machine, and control the pump based on at least the swing speed and the amount of return fluid.
Another aspect of the present disclosure is directed to a method of operating a hydraulic control system. The method includes pressurizing a fluid with a pump and selectively directing the pressurized fluid from the pump to a swing motor to move a part of a machine. The method also includes receiving an input indicative of a difference between a desired speed and an actual speed of the swing motor. The method also includes determining of the swing motor is accelerating, decelerating, or operating at neutral mode. The method further includes determining an amount of return fluid from an actuator of the machine that is available as makeup fluid for the swing motor if the swing motor is operating at neutral mode, and receiving an input indicative of a swing speed of the part of the machine. The method also includes controlling the pump based on at least the swing speed and the amount of return fluid.
The implement system 14 may include a linkage structure acted on by fluid actuators to move the work tool 16. Specifically, the implement system 14 may include a boom 24 that is vertically pivotal relative to a work surface 26 by a pair of adjacent, double-acting, hydraulic cylinders 28 (only one shown in
Numerous different work tools 16 may be attachable to the single machine 10 and controllable via the operator station 22. The work tool 16 may include any device used to perform a particular task such as, for example, a bucket, a fork arrangement, a blade, a shovel, a crusher, a shear, a grapple, a grapple bucket, a magnet, or any other task-performing device known in the art. Although connected in the embodiment of
The operator station 22 may be configured to receive input from a machine operator indicative of a desired work tool movement. Specifically, the operator station 22 may include one or more operator input devices 48 embodied, for example, as single or multi-axis joysticks located proximal an operator seat (not shown). The operator input devices 48 may be proportional-type controllers configured to position and/or orient the work tool 16 by producing work tool position signals that are indicative of a desired work tool speed and/or force in a particular direction. The position signals may be used to actuate any one or more of the hydraulic cylinders 28, 36, 38 and/or the swing motor 49. It is contemplated that different input devices may alternatively or additionally be included within the operator station 22 such as, for example, wheels, knobs, push-pull devices, switches, pedals, and other operator input devices known in the art.
As illustrated in
The swing motor 49 may include a housing 62 at least partially forming a first and a second chamber (not shown) located to either side of an impeller 64. When the first chamber is connected to an output of the pump 58 (e.g., via a first chamber passage 66 formed within the housing 62) and the second chamber is connected to the tank 60 (e.g., via a second chamber passage 68 formed within the housing 62), the impeller 64 may be driven to rotate in a first direction (shown in
The swing motor 49 may include built-in makeup and relief functionality. In particular, a makeup passage 70 and a relief passage 72 may be formed within the housing 62, between the first chamber passage 66 and the second chamber passage 68. A pair of opposing check valves 74 and a pair of opposing relief valves 76 may be disposed within the makeup and relief passages 70, 72, respectively. A low-pressure passage 78 may be connected to each of the makeup and relief passages 70, 72 at locations between the check valves 74 and between the relief valves 76. Based on a pressure differential between the low-pressure passage 78 and the first and second chamber passages 66, 68, one of the check valves 74 may open to allow fluid from the low-pressure passage 78 into the lower-pressure one of the first and second chambers. Similarly, based on a pressure differential between the first and second chamber passages 66, 68 and the low-pressure passage 78, one of the relief valves 76 may open to allow fluid from the higher-pressure one of the first and second chambers into the low-pressure passage 78. A significant pressure differential may generally exist between the first and second chambers during a swinging movement of the implement system 14.
The pump 58 may be configured to draw fluid from the tank 60 via an inlet passage 80, pressurize the fluid to a desired level, and discharge the fluid to the first and second circuits 52, 54 via a discharge passage 82. A check valve 83 may be disposed within the discharge passage 82, if desired, to provide for a unidirectional flow of pressurized fluid from the pump 58 into the first and second circuits 52, 54. The pump 58 may embody, for example, a variable displacement pump (shown in
The tank 60 may constitute a reservoir configured to hold a low-pressure supply of fluid. The fluid may include, for example, a dedicated hydraulic oil, an engine lubrication oil, a transmission lubrication oil, or any other fluid known in the art. One or more hydraulic systems within the machine 10 may draw fluid from and return fluid to the tank 60. It is contemplated that the hydraulic control system 50 may be connected to multiple separate fluid tanks or to a single tank, as desired. The tank 60 may be fluidly connected to the swing control valve 56 via a drain passage 88, and to the first and second chamber passages 66, 68 via the swing control valve 56 and the first and second chamber conduits 84, 86, respectively. The tank 60 may also be connected to the low-pressure passage 78. A check valve 90 may be disposed within the drain passage 88, if desired, to promote a unidirectional flow of fluid into the tank 60.
The swing control valve 56 may have elements that are movable to control the rotation of the swing motor 49 and corresponding swinging motion of the implement system 14. Specifically, the swing control valve 56 may include a first chamber supply element 92, a first chamber drain element 94, a second chamber supply element 96, and a second chamber drain element 98 all disposed within a common block or housing 97. The first and second chamber supply elements 92, 96 may be connected in parallel with the discharge passage 82 to regulate filling of their respective chambers with fluid from the pump 58, while the first and second chamber drain elements 94, 98 may be connected in parallel with the drain passage 88 to regulate draining of the respective chambers of fluid. A makeup valve 99, for example a check valve, may be disposed between an outlet of the first chamber drain element 94 and the first chamber conduit 84 and between an outlet of the second chamber drain element 98 and the second chamber conduit 86.
To drive the swing motor 49 to rotate in a first direction (shown in
The supply and drain elements 92-98 of the swing control valve 56 may be solenoid-movable against a spring bias in response to a flow rate and/or position command issued by a controller 100. In particular, the swing motor 49 may rotate at a velocity that corresponds with the flow rate of fluid into and out of the first and second chambers and with a torque that corresponds with a pressure differential across the impeller 64. To achieve an operator-desired swing torque, a command based on an assumed or measured pressure drop may be sent to the solenoids (not shown) of the supply and drain elements 92-98 that causes them to open an amount corresponding to the necessary fluid flow rates and/or pressure differential at the swing motor 49. This command may be in the form of a flow rate command or a valve element position command that is issued by the controller 100.
The controller 100 may be in communication with the different components of the hydraulic control system 50 to regulate operations of the machine 10. For example, the controller 100 may be in communication with the elements of the swing control valve 56 in the first circuit 52 and with the elements of control valves (not shown) associated with the second circuit 54. Based on various operator input and monitored parameters, as will be described in more detail below, the controller 100 may be configured to selectively activate the different control valves in a coordinated manner to efficiently carry out operator requested movements of the implement system 14.
The controller 100 may include a memory, a secondary storage device, a clock, and one or more processors that cooperate to accomplish a task consistent with the present disclosure. Numerous commercially available microprocessors can be configured to perform the functions of the controller 100. It should be appreciated that the controller 100 could readily embody a general machine controller capable of controlling numerous other functions of the machine 10. Various known circuits may be associated with the controller 100, including signal-conditioning circuitry, communication circuitry, and other appropriate circuitry. It should also be appreciated that the controller 100 may include one or more of an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a computer system, and a logic circuit configured to allow the controller 100 to function in accordance with the present disclosure.
The operational parameters monitored by the controller 100, in one embodiment, may include a pressure of fluid within the first and/or second circuits 52, 54. For example, one or more pressure sensors 102 may be strategically located within the first chamber and/or second chamber conduits 84, 86 to sense a pressure of the respective passages and generate a corresponding signal indicative of the pressure directed to the controller 100. It is contemplated that any number of the pressure sensors 102 may be placed in any location within the first and/or second circuits 52, 54, as desired. It is further contemplated that other operational parameters such as, for example, speeds, temperatures, viscosities, densities, etc. may also or alternatively be monitored and used to regulate operation of the hydraulic control system 50, if desired.
The hydraulic control system 50 may be fitted with an energy recovery arrangement 104 that is in communication with at least the first circuit 52 and configured to selectively extract and recover energy from waste fluid that is discharged from the swing motor 49. The energy recovery arrangement (ERA) 104 may include, among other things, a recovery valve block (RVB) 106 that is fluidly connectable between the pump 58 and the swing motor 49, a first accumulator 108 configured to selectively communicate with the swing motor 49 via the RVB 106, and a second accumulator 110 (shown in dotted lines) also configured to selectively and directly communicate with the swing motor 49. In the disclosed embodiment, the RVB 106 may be fixedly and mechanically connectable to one or both of the swing control valve 56 and the swing motor 49, for example directly to the housing 62 and/or directly to the housing 97. The RVB 106 may include an internal first passage 112 fluidly connectable to the first chamber conduit 84, and an internal second passage 114 fluidly connectable to the second chamber conduit 86. The first accumulator 108 may be fluidly connected to the RVB 106 via a conduit 116, while the second accumulator 110 may be fluidly connectable to the low-pressure and drain passages 78 and 88, in parallel with the tank 60, via a conduit 118. The conduit 118 is connected to the return line 53.
The RVB 106 may house a selector valve 120, a charge valve 122 associated with the first accumulator 108, and a discharge valve 124 associated with the first accumulator 108 and disposed in parallel with the charge valve 122. The selector valve 120 may automatically fluidly communicate one of the first and second passages 112, 114 with the charge and discharge valves 122, 124 based on a pressure of the first and second passages 112, 114. The charge and discharge valves 122, 124 may be selectively movable in response to commands from the controller 100 to fluidly communicate the first accumulator 108 with the selector valve 120 for fluid charging and discharging purposes.
The selector valve 120 may be a pilot-operated, 2-position, 3-way valve that is automatically movable in response to fluid pressures in the first and second passages 112, 114 (i.e., in response to a fluid pressures within the first and second chambers of the swing motor 49). In particular, the selector valve 120 may include a valve element 126 that is movable from a first position (shown in
The charge valve 122 may be a solenoid-operated, variable position, 2-way valve that is movable in response to a command from the controller 100 to allow fluid from the passage 128 to enter the first accumulator 108. In particular, the charge valve 122 may include a valve element 134 that is movable from a first position (shown in
The discharge valve 124 may be substantially identical to the charge valve 122 in composition, and movable in response to a command from the controller 100 to allow fluid from the first accumulator 108 to enter the passage 128 (i.e., to discharge). In particular, the discharge valve 124 may include a valve element 138 that is movable from a first position (not shown) at which fluid flow from the first accumulator 108 into the passage 128 is inhibited, toward a second position (shown in
An additional pressure sensor 102 may be associated with the first accumulator 108 and configured to generate signals indicative of a pressure of fluid within the first accumulator 108, if desired. In the disclosed embodiment, the additional pressure sensor 102 may be disposed between the first accumulator 108 and the discharge valve 124. It is contemplated, however, that the additional pressure sensor 102 may alternatively be disposed between the first accumulator 108 and the charge valve 122 or directly connected to the first accumulator 108, if desired. Signals from this additional pressure sensor 102 may be directed to the controller 100 for use in regulating operation of the charge and/or discharge valves 122, 124.
The first and second accumulators 108, 110 may each embody pressure vessels filled with a compressible gas that are configured to store pressurized fluid for future use by the swing motor 49. The compressible gas may include, for example, nitrogen, argon, helium, or another appropriate compressible gas. As fluid in communication with the first and second accumulators 108, 110 exceeds predetermined pressures of the first and second accumulators 108, 110, the fluid may flow into the accumulators 108, 110. Because the gas therein is compressible, it may act like a spring and compress as the fluid flows into the first and second accumulators 108, 110. When the pressure of the fluid within conduits 116, 118 drops below the predetermined pressures of the first and second accumulators 108, 110, the compressed gas may expand and urge the fluid from within the first and second accumulators 108, 110 to exit. It is contemplated that the first and second accumulators 108, 110 may alternatively embody membrane/spring-biased or bladder types of accumulators, if desired.
In the disclosed embodiment, the first accumulator 108 may be a larger (i.e., about 5-20 times larger) and higher-pressure (i.e., about 5-60 times higher-pressure) accumulator, as compared to the second accumulator 110. Specifically, the first accumulator 108 may be configured to accumulate up to about 30-100 L of fluid having a pressure in the range of about 200-315 bar, while the second accumulator 110 may be configured to accumulate up to about 10 L of fluid having a pressure in the range of about 5-30 bar. In this configuration, the first accumulator 108 may be used primarily to assist the motion of the swing motor 49 and to improve machine efficiencies, while the second accumulator 110 may be used primarily as a makeup accumulator to help reduce a likelihood of voiding at the swing motor 49. It is contemplated, however, that other volumes and pressures may be accommodated by the first and/or second accumulators 108, 110, if desired.
The second accumulator 110 may be an optional component of the hydraulic control system 50. In an embodiment, the second accumulator 110 may have a reduced capacity. However, in various other embodiments, the second accumulator 110 may not be present.
The controller 100 may be configured to selectively cause the first accumulator 108 to charge and discharge, thereby improving performance of the machine 10. In particular, a typical swinging motion of the implement system 14 instituted by the swing motor 49 may consist of segments of time during which the swing motor 49 is accelerating a swinging movement of the implement system 14, and segments of time during which the swing motor 49 is decelerating the swinging movement of the implement system 14. The acceleration segments may require significant energy from the swing motor 49 that is conventionally realized by way of pressurized fluid supplied to the swing motor 49 by the pump 58, while the deceleration segments may produce significant energy in the form of pressurized fluid that is conventionally wasted through discharge to the tank 60. Both the acceleration and the deceleration segments may require the swing motor 49 to convert significant amounts of hydraulic energy to swing kinetic energy, and vice versa. The fluid passing through the swing motor 49 during deceleration, however, still contains a large amount of energy. The fluid passing through the swing motor 49 may be pressurized during deceleration as a result of restrictions to the flow of the fluid exiting the swing motor 49. If the fluid passing through the swing motor 49 is selectively collected within the first accumulator 108 during the deceleration segments, this energy can then be returned to (i.e., discharged) and reused by the swing motor 49 during the ensuing acceleration segments. The swing motor 49 can be assisted during the acceleration segments by selectively causing the first accumulator 108 to discharge pressurized fluid into the higher-pressure chamber of the swing motor 49 (via the discharge valve 124, the passage 128, the selector valve 120, and the appropriate one of the first and second chamber conduits 84, 86), alone or together with high-pressure fluid from the pump 58, thereby propelling the swing motor 49 at the same or greater rate with less pump power than otherwise possible via the pump 58 alone. The swing motor 49 can be assisted during the deceleration segments by selectively causing the first accumulator 108 to charge with fluid exiting the swing motor 49, thereby providing additional resistance to the motion of the swing motor 49 and lowering a restriction and cooling requirement of the fluid exiting the swing motor 49.
In an alternative embodiment, the controller 100 may be configured to selectively control charging of the first accumulator 108 with fluid exiting the pump 58, as opposed to fluid exiting the swing motor 49. That is, during a peak-shaving or economy mode of operation, the controller 100 may be configured to cause the first accumulator 108 to charge with fluid exiting the pump 58 (e.g., via the control valve 56, the appropriate one of the first and second chamber conduits 84, 86, the selector valve 120, the passage 128, and the charge valve 122) when the pump 58 has excess capacity (i.e., a capacity greater than required by the circuits 52, 54 to move the work tool 16 as requested by the operator). Then, during times when the pump 58 has insufficient capacity to adequately power the swing motor 49, the high-pressure fluid previously collected from the pump 58 within the first accumulator 108 may be discharged in the manner described above to assist the swing motor 49.
The controller 100 may be configured to regulate the charging and discharging of the first accumulator 108 based on a current or ongoing segment of the excavation, material handling, or other work cycle of the machine 10. In particular, based on input received from one or more performance sensors 141, the controller 100 may be configured to partition a typical work cycle performed by the machine 10 into a plurality of segments. A typical work cycle may be partitioned, for example, into a dig segment, a swing-to-dump acceleration segment, a swing-to-dump deceleration segment, a dump segment, a swing-to-dig acceleration segment, and a swing-to-dig deceleration segment, as will be described in more detail below. Based on the segment of the excavation work cycle currently being performed, the controller 100 may selectively cause the first accumulator 108 to charge or discharge, thereby assisting the swing motor 49 during the acceleration and deceleration segments.
One or more maps and/or dynamic elements relating signals from the sensor(s) 141 to the different segments of the excavation work cycle may be stored within the memory of the controller 100. Each of these maps may include a collection of data in the form of tables, graphs, and/or equations. The dynamic elements may include integrators, filters, rate limiters, and delay elements. In one example, threshold speeds, cylinder pressures, and/or operator input (i.e., lever position) associated with the start and/or end of one or more of the segments may be stored within the maps. In another example, threshold forces and/or actuator positions associated with the start and/or end of one or more of the segments may be stored within the maps. The controller 100 may be configured to reference the signals from the sensor(s) 141 with the maps and filters stored in memory to determine the segment of the excavation work cycle currently being executed, and then regulate the charging and discharging of the first accumulator 108 accordingly. The controller 100 may allow the operator of the machine 10 to directly modify these maps and/or to select specific maps from available relationship maps stored in the memory of the controller 100 to affect segment partitioning and accumulator control, as desired. It is contemplated that the maps may additionally or alternatively be automatically selectable based on modes of machine operation, if desired.
The sensor(s) 141 may be associated with the generally horizontal swinging motion of the work tool 16 imparted by the swing motor 49 (i.e., the motion of the frame 42 relative to the undercarriage member 44). For example, the sensor 141 may embody a rotational position or speed sensor associated with the operation of the swing motor 49, an angular position or speed sensor associated with the pivot connection between the frame 42 and the undercarriage member 44, a local or global coordinate position or speed sensor associated with any linkage member connecting the work tool 16 to the undercarriage member 44 or with the work tool 16 itself, a displacement sensor associated with movement of the operator input device 48, or any other type of sensor known in the art that may generate a signal indicative of a swing position, speed, force, or other swing-related parameter of the machine 10. The signal generated by the sensor(s) 141 may be sent to and recorded by the controller 100 during each excavation work cycle. It is contemplated that the controller 100 may derive a swing speed based on a position signal from the sensor 141 and an elapsed period of time, if desired.
Alternatively or additionally, the sensor(s) 141 may be associated with the vertical pivoting motion of the work tool 16 imparted by the hydraulic cylinders 28 (i.e., associated with the lifting and lowering motions of the boom 24 relative to the frame 42). Specifically, the sensor 141 may be an angular position or speed sensor associated with a pivot joint between the boom 24 and the frame 42, a displacement sensor associated with the hydraulic cylinders 28, a local or global coordinate position or speed sensor associated with any linkage member connecting the work tool 16 to the frame 42 or with the work tool 16 itself, a displacement sensor associated with movement of the operator input device 48, or any other type of sensor known in the art that may generate a signal indicative of a pivoting position or speed of the boom 24. It is contemplated that the controller 100 may derive a pivot speed based on a position signal from the sensor 141 and an elapsed period of time, if desired.
In yet an additional embodiment, the sensor(s) 141 may be associated with the tilting force of the work tool 16 imparted by the hydraulic cylinder 38. Specifically, the sensor 141 may be a pressure sensor associated with one or more chambers within the hydraulic cylinder 38 or any other type of sensor known in the art that may generate a signal indicative of a tilting force of the machine 10 generated during a dig and dump operation of the work tool 16.
With reference to
The controller 100 may selectively cause the first accumulator 108 to charge and to discharge based on the current or ongoing segment of the excavation work cycle. For example,
The controller 100 may be instructed by the operator of the machine 10 that the exemplary mode of operation is currently in effect (e.g., that truck loading is being performed) or, alternatively, the controller 100 may automatically recognize operation in the exemplary mode based on performance of the machine 10 monitored via the sensor(s) 141. For example, the controller 100 could monitor swing angle of the implement system 14 between stopping positions (i.e., between the dig and dump locations 18, 20) and, when the swing angle is repeatedly greater than a threshold angle, for instance greater than about 150°, the controller 100 may determine that the exemplary mode of operation is in effect. In another example, manipulation of the operator input device 48 could be monitored via the sensor(s) 141 to detect “harsh” inputs indicative of the exemplary mode operation. In particular, if the input is repeatedly moved from below a low threshold (e.g., about 10% lever command) to above a high threshold level (e.g., about 100% lever command) within a short period of time (e.g., about 2 sec or less), the input device 48 may be considered to be manipulated in a harsh manner, and the controller 100 may responsively determine that the exemplary mode of operation is in effect. In a final example, the controller 100 may determine that the first mode of operation is in effect based on a cycle and/or value of pressures within the first accumulator 108, for example when a threshold pressure is repetitively reached. In this final example, the threshold pressure may be about 75% of a maximum pressure.
There may be different modes of operation (not shown) in addition to the exemplary mode illustrated in
The curve 302 illustrates a rapid actuation of the swing lever from below a low threshold level (E.g., from a non-actuating level) to above a high threshold level (e.g., about 100% lever command) within a short period of time thereby initiating the swing-to-dump segment. The high threshold and the non-actuating levels of the swing lever may coincide with two displacement positions of the swing lever. Further, the swing lever may be retained at the high threshold level for a period. Consequently, the swing motor 49 accelerates to a maximum as illustrated by the curve 304. During acceleration of the swing motor 49, the first accumulator 108 (shown in
As illustrated in
Referring to
As shown in
Referring to
The disclosed hydraulic control system may be applicable to any excavation or other work-performing machine that performs a substantially repetitive work cycle, which involves swinging movements of a work tool. The machine may be a hydraulic excavator, a backhoe, a front shovel, a dragline excavator, or another similar machine. The disclosed hydraulic control system includes a swing motor configured to move a part of the machine. A first accumulator may selectively charge or discharge based on an operation of the swing motor.
Referring to
The controller 100 may then determine if the desired speed is about equal to (i.e., within a threshold amount of) the actual speed (Step 410). In the disclosed embodiment, the pressure gradient across the swing motor 49 may be directly related to a difference between the desired and actual speeds of the swing motor 49. In particular, when the pressure gradient is large, the swing motor 49 may either be undergoing a significant acceleration or a significant deceleration (depending on the sign or direction of the pressure gradient), which corresponds with a significant difference between the desired and actual speeds of the swing motor 49. In contrast, when the pressure gradient is less than a threshold amount, the swing motor 49 may not be significantly accelerating or decelerating and the difference between the desired and actual speeds is accordingly small. Alternatively, the signals from the sensors 102 and 141 may be utilized to determine the difference between the desired and actual speeds.
When the difference between the desired speed and the actual speed is small (e.g., equal to or less than a low threshold amount), the controller 100 may conclude that use of the first accumulator 108 is unwarranted (i.e., that charging or discharging of the first accumulator 108 would either not be possible or would be inefficient) and follow the normal mode of swing operation using pump pressure to move the work tool 16 (Step 420). In the normal mode of operation, the controller 100 may utilize the drain and supply elements 92-98 in a conventional manner to regulate flows of fluid from the pump 58 to the swing motor 49 and from the swing motor 49 to the tank 60 (Step 430). If already using the first accumulator 108 to move the work tool 16, the controller 100 may transition to the normal mode of operation in step 420.
When the difference between the desired speed and the actual speed is large (e.g., more than the low threshold amount), the controller 100 may determine whether the swing motor 49 is accelerating or decelerating (Step 440). The controller 100 may determine whether the swing motor 49 is accelerating or decelerating based on the pressure gradient across the swing motor 49, the desired speed of the swing motor 49, and the actual speed of the swing motor 49. For example, when the desired speed is in the same direction as and larger than the actual speed, and the pressure gradient across the swing motor 49 is large, the controller 100 may conclude that the swing motor 49 is accelerating (then to step 450). In contrast, when the desired speed is in the same direction as and less than the actual speed (or in a direction opposing the actual speed), and the pressure gradient is large, the controller 100 may conclude that the swing motor 49 is decelerating (then to step 470). It is contemplated that the controller 100 could alternatively utilize a direction of the pressure gradient to make the above determinations rather than the relative directions of the desired and actual speeds, if desired. Determination and/or confirmation of whether the swing motor 49 is accelerating or decelerating may also be performed by comparing actual speeds of the swing motor 49 at successive points in time, and calculating the change of speed per time elapsed.
When the controller 100 determines that the swing motor 49 is accelerating, the controller 100 may utilize pressurized fluid stored within the first accumulator 108 to assist the movement of the work tool 16. In particular, the controller 100 may at least partially close the appropriate one of the first and second chamber supply elements 92, 96 (depending on the desired rotational direction of the swing motor 49) to inhibit fluid flow from the pump 58 to the swing motor 49, and simultaneously open the discharge valve 124 to supply fluid from the first accumulator 108 to the swing motor 49 (Step 450). It should be noted that the closing of the first or second chamber supply elements 92, 96 may be coordinated with the opening of the discharge valve 124, such that a gradual reduction in flow provided by the pump 58 may be accommodated by a corresponding gradual increase in flow provided by the first accumulator 108. In this manner, the motion of the swing motor 49 may be continuous and substantially unaffected by the switch between supply sources.
While supplying fluid from the first accumulator 108 to the swing motor 49, the controller 100 may monitor the pressure of fluid within the first accumulator 108 and compare the monitored pressure to a one or more pressure thresholds (e.g., to a minimum pressure threshold during acceleration) (Step 460). If the pressure of fluid within the first accumulator 108 passes through the appropriate pressure threshold (e.g., when the pressure of the fluid within the first accumulator 108 reaches or falls below the minimum pressure threshold during acceleration), control may return to step 420 where operation will transition to the normal mode. In this situation, the capacity of the first accumulator 108 to provide fluid will have been nearly or completely exhausted, and the pump 58 should be used to continue the swinging motion of the work tool 16. Otherwise, control may loop back to step 410.
If at step 440, the controller 100 instead determines that the swing motor 49 is decelerating, the controller 100 may use the first accumulator 108 to slow the work tool 16 and to simultaneously capture otherwise wasted energy in the form of stored pressurized fluid. In particular, the controller 100 may at least partially close the appropriate one of the first and second chamber drain elements 94, 98 (depending on the desired rotational direction of the swing motor 49) to inhibit fluid flow from the swing motor 49 being directed into the tank 60, and simultaneously open the charge valve 122 to instead direct the pressurized fluid from the swing motor 49 into the first accumulator 108 for storage (Step 470). As the fluid enters the first accumulator 108, the pressure within the first accumulator 108 and in the passages leading back to the swing motor 49 may increase, thereby providing greater resistance to the rotation of the swing motor 49 and slowing the swing motor 49. It should be noted that the gradual closing of the first or second chamber drain elements 94, 98 may be coordinated with the gradual opening of the charge valve 122, such that the reduction in flow to the tank 60 may be accommodated by the increase in flow into the first accumulator 108. In this manner, the motion of the swing motor 49 may be continuous and substantially unaffected by the change in collection reservoirs.
During deceleration, because substantially all of the return flow of fluid from the swing motor 49 may be directed into the first accumulator 108, as opposed to being routed back to the low-pressure passage 78 (through the relief valves 76) and/or the drain passage 88 (through 94, 98) from where the flow could reach the opposite side of the swing motor 49 (through the check valves 74 and/or the makeup valves 99), the displacement of the pump 58 may naturally destroke since no flow is requested from the first and/or second circuit 52 and 54. In this situation, it may be possible for the swing motor 49 to be starved of makeup fluid and, if not accounted for, the swing motor 49 could be caused to cavitate during charging of the first accumulator 108. Accordingly, the controller 100 may be configured to determine an amount of return flow available to the swing motor 49 during a deceleration event (Step 480). In particular, the controller 100 may monitor the activities of other actuators of the machine 10 (e.g., the activities of actuators in the second circuit 54) and/or monitor the flow rate of fluid returning from the second circuit 54 back into the first circuit 52. The controller 100 may then compare the flow rate of return fluid from the second circuit 54 to an amount of makeup fluid required by the swing motor 49 to prevent voiding or cavitation (Step 490). When the amount of return fluid from the second circuit 54 is insufficient to prevent cavitation of the swing motor 49, the controller 100 may command the pump 58 to increase its displacement (i.e., to upstroke) and command the appropriate one of the first or second chamber supply elements 92, 96 to open and provide additional makeup fluid to the swing motor 49 (Step 500). Control may pass then from steps 490 and 500 to step 460.
While directing fluid into the first accumulator 108 from the swing motor 49 during deceleration, the controller 100 may monitor the pressure of fluid within the first accumulator 108 and compare the monitored pressure to one or more pressure thresholds (e.g., to a maximum pressure threshold during deceleration) (Step 460). If the pressure of fluid within the first accumulator 108 passes through the appropriate pressure threshold (e.g., when the pressure of the fluid within the first accumulator 108 reaches or exceeds the maximum pressure threshold during deceleration), control may return to step 420 where operation will transition to the normal mode. In this situation, the capacity of the first accumulator 108 to receive fluid will have been nearly or completely exhausted, and the tank 60 should be used to consume the return fluid and continue the swinging motion of the work tool 16. Otherwise, control may loop back to step 410.
If at step 440, the controller 100 determines that the swing motor 49 is operating in the neutral segment (neither accelerating or decelerating), the controller 100 may then compare a swing speed of the work tool 16 with the threshold speed at step 502. The threshold speed may be a low speed (E.g., about 2 rpm) which may coincide with a substantially zero speed during most of the dump or dig segments. In case, the swing speed is below the threshold speed, control may return to step 420 where operation will transition to the normal mode, as described above. In the normal mode, the pump 58 may be operated based on an actuation of the swing lever. Thus, step 502 may prevent a false potential voiding detection in case the swing speed is substantially zero. However, in case the swing speed is above the threshold speed, the controller 100 determines an amount of return flow in the return line 53 that is available as makeup flow to the swing motor 49 (step 504). In an embodiment, the return flow in the return line 53 may be provided by at least one of the second circuit 54 and the second accumulator 110. The second circuit 54 can include the hydraulic cylinders 28, 36 and 38. The hydraulic cylinders 28, 36 and 38 may be actuators of various components of the machine 10. However, in an alternative embodiment, when the second accumulator 110 is not present, the return flow may be provided by the second circuit 54 alone. The controller 100 then determines, at step 506, if the amount of return flow is sufficient to prevent a potential voiding of the swing motor 49 during the subsequent deceleration segment. Therefore, the controller 100 may be able to predict any potential voiding situation in the neutral segment before the start of the deceleration segment. The controller 100 may then proactive steps to prevent voiding in the deceleration segment as explained hereinafter.
In case, the amount of return flow is sufficient to prevent a potential voiding of the swing motor 49, control may return to step 420 where operation will transition to the normal mode. However, of the return flow is insufficient to prevent a potential voiding of the swing motor 49, the controller 100 may, at step 508, prevent a destroking of the pump 58 segment and maintain an upstroked position of the pump 58 despite an actuation of the swing lever to the non-actuating level. Any time lag (as shown in
After step 508, control may continue to step 510 where the operation will continue in the normal mode where the pump flow is used for operating the swing motor 49. Subsequently, control loops back to steps 430 and 400.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed hydraulic control system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed hydraulic control system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
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| Number | Date | Country | |
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| 20150075147 A1 | Mar 2015 | US |
