The invention is related to a sensor arrangement for determining an actual swashplate angle of a swashplate.
Variable displacement hydraulic pumps, such as axial piston variable displacement pumps, are widely used in hydraulic systems to provide pressurized hydraulic fluid for various applications. For example, hydraulic earthworking and construction machines, e.g., excavators, bulldozers, loaders, and the like, rely heavily on hydraulic systems to operate, and hence often use variable displacement hydraulic pumps to provide the needed pressurized fluid. These pumps are driven by a mechanical shaft, for example by an engine, and the discharge flow rate, and hence the pressure, is regulated by controlling the angle of a swashplate pivotally mounted to the pump. Operation of the pump, however, is subject to variations in pressure and flow output caused by variations in load requirements. It is desirable to maintain the discharge flow rate of the pumps in a consistent manner so that operation of the hydraulic systems is well behaved and predictable. Therefore, attempts have been made to set up a control process including a step of sensing the swash plate position by a rotative sensor sensing the swivelling angle of the swash plate that is related to the pump stroke and hence the discharge flow rate.
In U.S. Pat. No. 6,623,247 B2, a method and apparatus for controlling a variable displacement hydraulic pump having a swashplate pivotally attached to the pump is disclosed. The method and apparatus includes determining a desired swashplate angle as a function of a power limit of the pump, determining an actual swashplate angle, determining a value of discharge pressure of the pump, moving a servo valve spool to a desired position as a function of the desired swashplate angle, the actual swashplate angle and the discharge pressure, and responsively moving the swashplate to the desired swashplate angle position. A means for determining the actual swashplate angle is adapted to determine the angle of the swashplate using a swashplate angle sensor, for example, a resolver or a strain gauge.
An aspect of the invention provides a sensor arrangement arrangement for determining an actual swashplate angle of a swashplate pivotally attached to a variable displacement hydraulic pump, the arrangement comprising: a control piston operable to control an angle of the swashplate relative to the variable displacement pump; a position marker arranged on the control piston; and a sensor arranged along the control piston to detect a movement of the position marker.
The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:
In the prior art, a problem is incurred by the control loop including a proportional valve being actuated by a controller, the proportional valve moving a control piston, the control piston swivelling the swashplate via a position member and, finally, sensing the swivelling angle of the swash plate as a feedback signal to the controller, because the number of clearances in the control loop may cause instable operation of the control process.
An aspect of the present invention is directed to providing a more stable control of a variable displacement hydraulic pump.
An aspect of invention is related to a sensor arrangement for determining an actual swashplate angle of a swashplate pivotally attached to a variable displacement hydraulic pump, to a measurement method for determining an actual swashplate angle of a swashplate pivotally attached to a variable displacement hydraulic pump, to a controller for controlling the actuation of a control piston of a variable displacement hydraulic pump and to a variable displacement hydraulic pump.
The sensor arrangement for determining an actual swashplate angle of a swashplate pivotally attached to a variable displacement hydraulic pump, according to the invention, comprises a control piston operable to control an angle of the swashplate relative to the pump a position marker arranged on the control piston and a sensor arranged along the control piston to detect a movement of the position marker. By using such a sensor arrangement, all clearances in the control loop are advantageously eliminated. This allows for a more stable pump control compared to the existing design.
According to a preferred embodiment, the sensor is adapted to detect the movement of the position marker in a contactless manner. The contactless sensor arrangement advantageously provides a completely wear-free design.
Furthermore preferred, the sensor is arranged generally parallel or coaxially to a direction of movement of the control piston. In particular, the sensor is a linear magnetostrictive position sensor and the position marker is a magnet.
The measurement method for determining an actual swashplate angle of a swashplate pivotally attached to a variable displacement hydraulic pump, according to the invention, wherein a control piston is operable to control an angle of the swashplate relative to the pump, comprises the steps of detecting a position of a position marker arranged on the control piston by a sensor arranged along the control piston and determining a linear translation of the control piston from a shift of the position marker relative to the sensor. In particular, the actual swashplate angle of the swashplate is determined from the linear translation of the control piston. Preferably, a sensor arrangement according to the invention is used.
Another aspect of the invention refers to a controller for controlling the actuation of a control piston of a variable displacement hydraulic pump, the control piston being operable to control an angle of a swashplate relative to the pump, wherein an actual swashplate angle is determined with a sensor arrangement according the invention and/or by a method according to the invention. Preferably, the control piston is actuated by a proportional valve.
Yet another aspect of the invention refers to a variable displacement hydraulic pump, wherein a control piston is operable to control an angle of the swashplate relative to the pump, comprising a controller according to the invention.
More advantages and details will become apparent from an embodiment according to the invention which will be described with respect to the attached drawings.
Referring to the drawings, in
With particular reference to
Referring now to
A sensor arrangement according to the invention is now described with respect to
The preferred embodiment of the sensor arrangement of
Details of the sensor arrangement are now described with reference to the schematic illustration of
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B, and C” should be interpreted as one or more of a group of elements consisting of A, B, and C, and should not be interpreted as requiring at least one of each of the listed elements A, B, and C, regardless of whether A, B, and C are related as categories or otherwise. Moreover, the recitation of “A, B, and/or C” or “at least one of A, B, or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B, and C.
Number | Date | Country | Kind |
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1223048.8 | Dec 2012 | GB | national |
This application is a U.S. national stage application under 35 U.S.C. § 371 of International Application No. PCT/EP2013/077286, filed on Dec. 19, 2013, and claims benefit to British Patent Application No. 1 223 048.8, filed on Dec. 20, 2012. The International Application was published in English on Jun. 26, 2014, as WO 2014/096129 A1 under PCT Article 21(2).
Filing Document | Filing Date | Country | Kind |
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PCT/EP2013/077286 | 12/19/2013 | WO | 00 |