The present invention is related to a loader of a construction apparatus such as front-end wheel loader or an agricultural tractor. Specifically, the present invention is related to a control system for a loader.
Typically, conventional front-end loaders for construction machinery such as wheel loaders and agricultural tractor loaders may be articulated by a hydraulic system. Loaders may be added to existing tractors or may be the principal implement of a track driven or wheel loader. Typically, loaders include a large bucket to scoop material such as coal, dirt, and stone and load the material into a trailer or dump truck. Some loaders may also be used to dig holes.
Most loader hydraulic systems include a hydraulic pump and at least one hydraulic cylinder adapted to articulate a loader boom and/or a bucket. An operator may use any of a plurality of controls located in a cab of the machinery or elsewhere to control the hydraulic system to articulate loader boom and bucket assembly. Some common features of the control system for the boom and bucket assembly include raising and lowering the boom and rotating the bucket fore and aft to load or dump the bucket. Another common feature of the control system is a float feature. The float feature allows the bucket to “float” on the ground for backgrading or leveling operations, for example leveling a gravel-based parking lot. When the bucket is floated, only the weight of the boom and bucket assembly is applied to the ground. This allows the bucket to float over the material being leveled and create a smooth, even leveled area free of large depressions or bumps.
One embodiment of the present invention includes a control system for a loader on a construction apparatus including a frame and a hydraulic pump, the loader including a boom, a bucket, and a hydraulic cylinder including at least three chambers, the cylinder operably coupled between the boom and the frame, the control system including a variable input configured to accept an operator instruction to one of raise, lower, and float the bucket, the variable input configured to output a signal corresponding to the operator instruction, a control valve, an accumulator adapted to receive and store pressurized hydraulic fluid from at least one of three chambers of the hydraulic cylinder when the boom is lowered and supply pressurized hydraulic fluid to at least one of the three chambers of the hydraulic cylinder when the bucket is raised, a plurality of pressure sensors adapted to measure a hydraulic pressure in each the three chambers of the hydraulic cylinder and output a plurality of corresponding signals, and a controller configured to receive the signal from the variable input and control the control valve and the hydraulic pump to one of raise, lower, and float the bucket based on the signal from the variable input, the controller further configured to determine a first force applied to one of the chambers of the cylinder by the accumulator and control the pump and the plurality of control valves to supply pressurized hydraulic fluid to another chamber of the cylinder to overcome the first force when the float instruction is received by the variable input.
Another embodiment of the present invention includes a method of controlling a loader of a construction apparatus including a frame, a hydraulic pump, a hydraulic cylinder including a plurality of chambers, a plurality of pressure sensors, an accumulator, a control valve, an input, a bucket, and a boom operably coupled between the bucket and the frame, the method including the steps of receiving operator input corresponding to a command to float the bucket, measuring a pressure in each of the chambers of the hydraulic cylinder, calculating a first force of the hydraulic cylinder acting on the boom to move the boom upward, and controlling the hydraulic pump and the control valve to supply hydraulic pressure to at least one of the chambers of the hydraulic cylinder to prevent the boom from moving upward.
The detailed description of the drawings particularly refers to the accompanying figures in which:
Referring initially to
Referring now to
Referring now to
Three chambered boom cylinder 42 includes housing 63, piston 43, flange 49, internal sleeve 47, and first, second, and third chambers 44, 46, and 48. Flange 49 extends outwardly from piston 43 and forms a seal around housing 63 to separate second chamber 46 from third chamber 48. Flange 49 separates second chamber 46 from third chamber 48. First chamber 44 is formed by internal sleeve 47 and piston 43. First chamber 44 is coupled to line 54 and is not in fluid communication with either second chamber 46 or third chamber 48. Hydraulic line 54 is coupled between accumulator 66 and first chamber 44. When boom cylinder 42 is retracted, i.e. boom 26 is lowered, hydraulic fluid flows out of second chamber 46 through line 58 while simultaneously, hydraulic fluid is pulled into third chamber 48 by suction created by flange 49. At the same time, hydraulic fluid in first chamber 44 is compressed or pressurized by piston 43 and pushed through line 54 to accumulator 66. The pressurized fluid stored by accumulator 66 provides a positive or extending force on the lower portion of piston 43 present in first chamber 44. To extend piston 43, pump 62 provides pressurized hydraulic fluid to second chamber 46 through line 58. This pressurized fluid acts on flange 49 of piston 43 to extend piston 43 out of housing 63. The pressurized hydraulic fluid present in first chamber 44 and accumulator 66 also acts to extend piston 43 thereby reducing the pressure of hydraulic fluid needed in second chamber 46 to extend piston 43.
Pressure sensor 56 is positioned in line 54 to measure the pressure of the hydraulic fluid in first chamber 44 of cylinder 42. Second chamber 46 is coupled to control valve 61 by line 58. Pressure sensor 60 is positioned in line 58 to measure the pressure of the hydraulic fluid in second chamber 46. Third chamber 48 is coupled to control valve 64 by line 51. Pressure sensor 52 is positioned in line 51 to measure the pressure of the hydraulic fluid in third chamber 48. Pressure sensors 52, 56, and 60 provide output signals corresponding the pressure of the respective chamber of cylinder 42 to controller 45 of hydraulic system 41.
Hydraulic pump 62 and control valves 61 and 64 may be controlled by controller 45 to operate cylinder 42. In this embodiment, control valves 61 and 64 are solenoid actuated spring return valves, however any suitable control valve may be used. Hydraulic line 53 couples pump 62 to control valve 61. Pump 62 is also coupled to control valve 64 by hydraulic line 50. Pump 62 receives hydraulic fluid from reservoir 68. An input such as input 36, as shown in
Hydraulic system 41 also includes accumulator 66, check valve 70, and safety valve 72. Accumulator 66 is in fluid communication with first chamber 44 of cylinder 42 via line 54. When piston 43 of cylinder 42 is extended, for example when the boom is raised, pressurized fluid from accumulator 66 flows into first chamber 44 of cylinder 42 to provide additional energy. When piston is retracted, for example when the boom is lowered, pressurized fluid from first chamber 44 flows into accumulator 66 and is stored under pressure. Accumulator 66 conserves some the pressure or energy generated in first chamber 44 when piston 43 is retracted. In this embodiment, accumulator 66 includes a flexible bladder positioned between a compressed gas and the hydraulic fluid received from first chamber 44. It should be noted that any suitable accumulator such as a raised weight, spring type, or gas charged accumulator may be used.
Referring now to
As an example, control scheme 74 is described using hydraulic system 41, as shown in
In step 84, the force error is calculated by the controller. The force error is equal to the difference between the net force acting on the cylinder and the reference force. In step 86, the controller calculates the appropriate pump command that will move the force error closer to zero. In step 88, the pump is activated with the calculated pump command of step 86. After step 88, the scheme returns to step 78 and repeats as long the float function is activated in step 76. Control scheme 74 measures the pressure in each chamber 44, 46, and 48 of cylinder 42 and controls pump 62 so the net force acting on cylinder 42 is equal to zero to provide an automated float function for a loader.
Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the spirit and scope of the invention as described and defined in the following claims.
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