Systems and methods for calibrating electrohydraulic valves

Abstract

Calibration circuit, operable for calibrating an electro-hydraulic control valve in a hydraulic system, wherein the hydraulic system comprises a pump configured for supplying fluid to a supply line and at least one consumer, wherein the electro-hydraulic control valve comprises at least one working port in fluid communication with the at least one consumer, wherein the calibration circuit comprises: a calibration line configured to be isolated from the supply line; a first calibration port configured to provide a fluid connection between the calibration line and the fluid source; a second calibration port arranged in series with the first calibration port;wherein the second calibration port is arranged on a coil of the electrohydraulic control valve and is configured to selectively provide a fluid connection between the calibration line and a low-pressure source; and a pressure sensor configured to measure a pressure in the calibration line between the first calibration port and the second calibration port, wherein the second calibration port is configured to be isolated from the at least one working port of the electrohydraulic control valve.

Description

CROSS-REFERENCE TO RELATED REGISTRATIONS The present invention is based on, claims priority from and, in its entirety, encompasses by reference the United States Provisional Patent Application No. 62 / 305,315, which was filed on March 8, 2016, under the name “Valve Calibration Core for Spool Position vs. Command”. FINDINGS REGARDING PUBLICLY FUNDED RESEARCH Not applicable. BACKGROUND The present disclosure relates generally to hydraulic systems for use in mobile machinery and, in particular, to systems and methods for calibrating electrohydraulic valves. Electrohydraulic valves are used in hydraulic systems in mobile machinery to provide a variety of flow control functions based on an electrical input signal from a controller. For example, electrohydraulic valves can be used to direct pressurized fluid to a consumer in the mobile machine, to provide a fluid connection between a consumer in the mobile machine and a reservoir, and / or to regulate fluid pressure. In hydraulic systems with electrohydraulic valves, calibration is commonly required to try to eliminate the effect of component tolerances on the performance of the overall system. SUMMARY OF THE INVENTION The present disclosure provides systems and methods for calibrating electrohydraulic valves. In one aspect, the present disclosure provides a calibration circuit operable for calibrating an electrohydraulic control valve in a hydraulic system. The hydraulic system comprises a pump configured for supplying a fluid to a supply line and at least one consumer. The electrohydraulic control valve comprises at least one working port in fluid communication with the at least one consumer. The calibration circuit comprises a calibration line configured to be insulated from the supply line, a first calibration port configured to provide a fluid connection between the calibration line and a fluid source, and a second calibration port arranged in series with the first calibration port.The second calibration port is located on a coil of the electrohydraulic control valve and is configured to selectively provide a fluid connection between the calibration line and a low-pressure source. The calibration circuit further includes a pressure sensor for measuring the pressure in the calibration line between the first and second calibration ports. The second calibration port is isolated from the at least one working port of the electrohydraulic control valve. In one aspect, the present disclosure provides a hydraulic system operable for calibrating an electrohydraulic control valve. The hydraulic system comprises a pump configured for supplying fluid to a supply line, at least one consumer, an electrohydraulic control valve with at least one working port in fluid communication with the at least one consumer, a calibration supply line configured for receiving a flow from a calibration source, and a calibration line. The hydraulic system further comprises a first calibration port configured for selectively providing a fluid connection between the calibration supply line and the calibration line, and a second calibration port arranged in series with the first calibration port.The second calibration port is located on a coil of the electrohydraulic control valve and is configured to selectively provide a fluid connection between the calibration line and a low-pressure source. The hydraulic system further includes a pressure sensor designed to measure the pressure in the calibration line located upstream of the second calibration port. The calibration line and the second calibration port are isolated from the at least one consumer. In one aspect, the disclosure provides a method for calibrating an electrohydraulic control valve in a hydraulic system. The hydraulic system comprises a pump configured to supply fluid to a supply line and at least one consumer. The electrohydraulic control valve comprises at least one working port in fluid communication with the at least one consumer. The method includes supplying a flow through a first calibration port into a calibration line. The calibration line is isolated from the supply line. The method further comprises controlling the electrohydraulic control valve to supply a fluid connection through a second calibration port from the calibration line to a low-pressure source.The second calibration port is arranged on a coil of the electrohydraulic control valve and is insulated from the at least one consumer. The method further comprises monitoring the pressure in the calibration line while the electrohydraulic control valve is being controlled, determining when the pressure in the calibration line exceeds a predetermined value, detecting the control command applied to the electrohydraulic control valve when the pressure in the calibration line exceeds the predetermined pressure value, and calibrating a position of the electrohydraulic control valve to the control command applied thereto. The foregoing and other aspects and advantages of the invention can be derived from the description below. The description refers to the accompanying drawings, which form part of this document and illustrate a preferred embodiment of the invention. However, such an embodiment does not necessarily represent the full scope of the invention; therefore, reference is made to the accompanying claims for an interpretation of the scope of the invention. DESCRIPTION OF THE DRAWING The invention is better understood, and features, aspects, and advantages other than those described above become clear when considering the following detailed description of the invention. The detailed description refers to the following drawings: Fig. 1 shows a schematic representation of a calibration circuit that can be operated to perform a calibration of an electrohydraulic valve according to one aspect of the present disclosure. Fig. 2 shows a schematic representation of another calibration circuit that can be operated to perform a calibration of an electrohydraulic valve according to one aspect of the present disclosure. Fig. 3 shows a schematic representation of a hydraulic system that can be operated to perform a calibration of an electrohydraulic valve according to one aspect of the present disclosure.Figure 4 shows a flowchart illustrating the steps for performing an offset calibration for an electrohydraulic valve according to one aspect of the present disclosure. Figure 5 shows a flowchart illustrating the steps for performing various calibrations for an electrohydraulic valve according to one aspect of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION The terms "downstream" and "upstream" used herein refer to the direction of flow of a liquid. "Downstream" refers to the direction of flow, while "upstream" refers to the opposite direction of flow. Fig. 1 shows an example of a calibration circuit 10, which does not limit the scope of the invention and is operable for performing a calibration of one or more electrohydraulic control valves according to one aspect of the present disclosure. The calibration circuit 10 can comprise a pressure source 12, which is in fluid communication with a calibration supply line 14 and is configured to supply the calibration supply line 14 with pressurized fluid. A valve 16 can be arranged downstream of the fluid source 12 on the calibration supply line 14 and can be selectively movable between at least two positions and comprise at least two ports 18 and 20. In a first position of the valve, the valve 16 can be configured to block fluid communication between the at least two ports 18 and 20.In a second position of the valve, the valve 16 can be configured to provide a fluid connection between the at least two ports 18 and 20 in order to connect the calibration supply line 14 and a calibration line 22 through a first calibration opening 24. In some examples, which do not limit the scope of the invention, the valve 16 can be adjusted electrohydraulically between the first and second positions of the valve. A consumer control valve 26 can be connected to a consumer 28 (e.g., a hydraulic actuator or motor load) via one or more working ports 30. The consumer control valve 26 can be configured to selectively provide a fluid connection from the fluid source 12, or from another fluid source separate from the fluid source 12, to the consumer 28, and from the consumer 28 to a fluid reservoir (not shown). In addition to the one or more working ports 30, the consumer control valve 26 can include at least two additional ports 32 and 34, which are configured to be isolated from the consumer 28 (i.e., isolated from the one or more working ports 30). The consumer control valve 26 can be selectively movable between at least two positions.In a first position of the consumer valve, the consumer control valve 26 can be configured to block fluid flow between the at least two additional ports 32 and 34. In a second position of the consumer valve, the consumer control valve 26 can be configured to provide fluid flow between the at least two additional ports 32 and 34 in order to connect the calibration line 22 to a low-pressure source 36 through a second calibration port 38. In some examples, which do not limit the scope of the invention, the consumer control valve 26 can be activated electrohydraulically between the first and second positions of the consumer valve. In some examples, which do not limit the scope of the invention, the low-pressure source 36 can be a line connected to a liquid container or reservoir, or a line connected to a tank. In the illustrated example, which does not limit the scope of the invention, the first calibration opening 24 can be a fixed opening and the second calibration opening 38 a variable opening. In some examples, which do not limit the scope of the invention, the first calibration opening 24 can be a permanent opening located on either the calibration supply line 14 or the calibration line 22 and upstream of and in series with the second calibration opening 38. In some examples, which do not limit the scope of the invention, the first calibration opening 24 can be significantly smaller than the second calibration opening 38.This means that a minimum constraint defined by the second calibration opening 38 can be less than a constraint defined by the first calibration opening 24. This can ensure that the pressure in the calibration supply line 14 generally remains constant while the calibration line 22 is connected to the low-pressure source 36 via the second calibration opening 38. A pressure sensor 40 can be arranged on the calibration line 22 downstream of the first calibration opening 24 and upstream of the second calibration opening 38. As described below, the calibration circuit enables 10 different calibrations of the consumer control valve 26 to be performed. For example, the series arrangement of the first calibration port 24 and the second calibration port 38, as well as the connection of the calibration line 22 to the low-pressure source 36, allows the pressure sensor 40 to detect a pressure drop in the calibration line 22 as soon as the connection between the calibration line 22 and the low-pressure source 36 is established via the second calibration port 38. In this way, calibration of the position of the consumer control valve 26 as a consumer of the control command input to the consumer control valve 26 can be provided. Fig. 2 shows another example of a calibration circuit 50 according to one aspect of the present disclosure, which does not limit the scope of the invention. The calibration circuit 50 from Fig. 2 can be similar to the calibration circuit 10 from Fig. 1, except for the features described below or apparent from the figures. Similar components are provided with similar reference numerals. As shown in Fig. 2, the bypass control valve 16 may not be required at all. Instead, the first calibration opening 24 can be a fixed opening arranged to provide a fluid connection between the calibration supply line 14 and the calibration line 22.The electro-hydraulic control valve 26 can generally be biased into a first position 52, in which the consumer control valve 26 can be configured to provide a fluid connection between the at least two additional ports 32 and 34 in order to connect the calibration line 22 to a low-pressure source 36 through the second calibration port 38. In a second position 54, the consumer control valve 26 can be configured to restrict a fluid connection between the at least two additional ports 32 and 34. The calibration circuit 10 enables various calibrations of the consumer control valve 26 to be performed. Fig. 3 shows an example of the calibration circuit 10, which does not limit the scope of the invention, and which is applied in a hydraulic system 100 according to one aspect of the disclosure. The hydraulic system 100 comprises a pump 102, a reservoir 104, and a control valve arrangement 106. In the example shown, which does not limit the scope of the invention, the pump 102 can be a fixed-displacement pump. In other examples, which do not limit the scope of the invention, the pump 102 can be a variable-displacement pump. The pump 102 can be configured to draw a liquid, such as oil, from a reservoir 104 and deliver the liquid under increased pressure to a pump outlet 108. The pump outlet 108 can be in fluid communication with a supply line 110, which extends into and through the control valve assembly 106. A return line 112 can extend through the control valve assembly 106 and be in fluid communication with the reservoir 104. The control valve arrangement 106 can comprise a bypass control valve 114 and a consumer control valve 116. The consumer control valve 116 can be configured to control flow between a consumer 118 and the pump 102 and the reservoir 104. It should be noted that the number of consumers and corresponding consumer control valves shown in the hydraulic system 100 does not in any way limit the scope of the invention, and that in other examples not limiting the scope of the invention, the hydraulic system 100 may comprise more than one consumer 18 and a corresponding number of consumer control valves 116. The control valve arrangement 106 can comprise a single, one-piece body or physically separate valve sections connected side by side. The bypass control valve 114 may include a bypass coil 120 movable between three positions. In other examples, which do not limit the scope of the invention, the bypass coil 120 may be movable between more than three or fewer than three positions. The bypass control valve 114 may include a bypass input port 122, a bypass output port 124, a bypass calibration input port 126, and a bypass calibration output port 128. It should be noted that the number of ports on the bypass control valve 114 is in no way intended to be limiting. In other examples, which do not limit the scope of the invention, the bypass control valve 114 may be configured to include more than two or fewer than two ports in addition to the bypass calibration input port 126 and the bypass calibration output port 128. The bypass inlet port 122 can be in fluid connection with the supply line 110, and the bypass outlet port 124 can be in fluid connection with the return line 112. The bypass calibration inlet port 126 can be in fluid connection with a calibration supply line 130. The calibration supply line 130 can extend through the control valve assembly 106 and be separate from the supply line 110. The bypass calibration outlet port 128 can be in fluid connection with a calibration line 132. The calibration line 132 can extend through the control valve assembly 106 and be separate from the supply line 110. In the illustrated example, which does not limit the scope of the invention, a fluid connection between the bypass input port 122 and the bypass output port can be provided when the bypass coil 120 is in a first bypass position 134, and a fluid connection between the bypass calibration input port 126 and the bypass calibration output port 128 can be blocked. When the bypass coil 120 is moved to a second bypass position 136, the fluid connection between the bypass input port 122 and the bypass output port 124, and between the bypass calibration input port 126 and the bypass calibration output port 128, can be blocked.When the bypass coil 120 is adjusted to a third bypass position 138, a fluid connection between the bypass inlet port 122 and the bypass outlet port 124 can be provided through a bypass opening 140, and a fluid connection between the bypass calibration inlet port 126 and the bypass calibration outlet port 128 can be provided through a bypass calibration opening 142. In some examples, which do not limit the scope of the invention, the bypass calibration opening 142 can be a fixed opening. It should be noted that the specific arrangement of the bypass positions 134, 136, and 138 is in no way intended to be considered limiting, and that the bypass positions 134, 136, and 138 can be arranged on the bypass coil 120 in any order.In the illustrated example, which does not restrict the scope of the invention, the connection between the bypass calibration input port 126 and the bypass calibration output port 128 is formed independently of other connections simplified by the bypass control valve 114. The bypass control valve 114 can generally be biased into the first bypass position 134 by a bypass spring 144. The bypass control valve 114 can be electro-hydraulically activated by a bypass pilot coil 146, which is in electrical communication with a controller 148. During operation, an electrical signal (e.g., an electric current) can be selectively applied to the bypass pilot coil 146 by the controller 148. In response to receiving the electrical signal from the controller 148, the bypass pilot coil 146 can provide a pilot signal to the bypass control valve 114, which in turn can adjust the bypass coil 120 from the first bypass position 134 towards the third bypass position 138 in relation to the magnitude of the electrical signal.Therefore, the magnitude of the electrical signal supplied by the control unit 148 can correspond proportionally to an adjustment position of the bypass coil 120 between the first bypass position 134 and the third bypass position 138. In other examples, which do not limit the scope of the invention, the bypass control valve 114 can be activated by a solenoid engaged with the bypass coil 120 instead of the bypass pilot coil 146. The consumer control valve 116 can include a consumer coil 150 movable between three positions. In other examples, which do not limit the scope of the invention, the consumer coil 150 can have more or fewer than three positions. The consumer control valve 116 can include a consumer input port 152, a first consumer output port 154, a second consumer output port 156, a consumer calibration input port 158, a consumer calibration output port 160, a first working port 162, and a second working port 164. It should be noted that the number of ports on the consumer control valve 116 is in no way intended to be limiting.In other examples, which do not limit the scope of the invention, the consumer control valve 116 may be configured to include more than or fewer than five ports in addition to the consumer calibration input port 158 ​​and the consumer calibration output port 160. The consumer inlet port 152 can be in fluid connection with the supply line 110. The first consumer outlet port 154 and the second consumer outlet port 156 can each be in fluid connection with the return line 112. The consumer calibration inlet port 158 ​​can be in fluid connection with the calibration line 132, and the consumer calibration outlet port 160 can be in fluid connection with a sump line 166. In other examples, which do not limit the scope of the invention, the consumer calibration outlet port 160 can be in fluid connection with the return line 112. As shown in Fig. 3, neither the consumer calibration inlet port 158 ​​nor the consumer calibration outlet port 160 is connected to either the first working port 162 or the second working port 164.Therefore, any flow between the consumer calibration input port 158 ​​and the consumer calibration output port 160 can be configured to be isolated from the consumer 18. The first working port 162 can be in fluid communication with a first consumer port 168 of the consumer 18, and the second working port 164 can be in fluid communication with a second consumer port 170 of the consumer 18. In the illustrated example, which does not limit the scope of the invention, the consumer 18 is a hydraulic actuator. In other examples, which do not limit the scope of the invention, the consumer 18 can be another device that must be driven by a fluid controlled by the consumer control valve 116 (e.g., a motor). In the illustrated example, which does not limit the scope of the invention, a fluid connection between the consumer input port 152 and the second working port 164 can be provided when the consumer coil 150 is in a first position 172, and a fluid connection between the first working port 162 and the second consumer output port 156 can be provided. Furthermore, in the first position 172, a fluid connection between the consumer calibration input port 158 ​​and the consumer calibration output port 160 can be provided through a consumer calibration port 174. When the consumer coil 150 is in a second position 176, a fluid connection between all ports 152, 154, 156, 158, 160, 162, and 164 can be blocked.When the consumer coil 150 is adjusted to a third position 178, a fluid connection can be provided between the consumer inlet port 152 and the first working port 162, and a fluid connection can be provided between the second working port 164 and the first consumer outlet port 154. Furthermore, in the third position 178, a fluid connection can be provided through the consumer calibration port 174 between the consumer calibration inlet port 158 ​​and the consumer calibration outlet port 160. It should be noted that the consumer coil 150 can include two identical consumer calibration ports 174, or, in some examples not limiting the scope of the invention, the consumer coil 150 can define different consumer calibration ports 174 on different sides of a groove (or cuts) on the consumer coil 150.Nevertheless, the consumer calibration openings 174 function similarly during the calibration procedure, regardless of their specific limiting characteristics. In some examples, which do not limit the scope of the invention, the consumer calibration port 174 can be a variable port. A restriction provided by the bypass calibration port 142 can be significantly less than the restriction provided by the consumer calibration port 174. Additionally, the bypass calibration port 142 and the consumer calibration port 174 can be arranged in series. In this way, the pressure in the calibration supply line 132 can remain largely constant when a fluid connection between the calibration supply line 130 and the calibration line 132 is provided by the bypass calibration port 142, and the pressure in the calibration line 132 can decrease when the calibration line 132 is connected to the sump line 166 via the consumer calibration port 174. The consumer control valve 116 can typically be biased into the second position 176 by a first spring 180 and a counteracting second spring 182. In other examples, which do not limit the scope of the invention, the consumer control valve 116 can typically be biased into the first position 172 or into the third position 178. The consumer control valve 116 can be electro-hydraulically activated by a first pilot coil 184 and a second pilot coil 186. The first pilot coil 184 and the second pilot coil 186 can be in electrical communication with the control unit 148. During operation, an electrical signal (e.g., an electric current) can be selectively applied by the control unit 148 to either the first pilot coil 184 or the second pilot coil 186.If the consumer coil 150 is moved towards the first position 172, the control unit 148 can provide an electrical signal to the first pilot coil 184. In response, the first coil 184 can provide a pilot signal to the consumer control valve 116, which in turn can adjust the consumer coil 150 towards the first position 172 in proportion to the magnitude of the electrical signal. Conversely, if the consumer coil 150 is moved towards the third position 178, the control unit 148 can provide an electrical signal to the second pilot coil 186. In response, the second pilot coil 186 can provide a pilot signal to the consumer control valve 116, which in turn can adjust the consumer coil 150 towards the third position 178 in proportion to the magnitude of the electrical signal.Therefore, the magnitude of an adjustment position of the consumer coil 150 provided by the control 148 to the first pilot coil 184 or the second pilot coil 186 can correspond proportionally to the first position 172 or the third position 178. In other examples, which do not limit the scope of the invention, the consumer control valve 116 can be adjusted by one or more solenoids engaged with the consumer coil 150 instead of the first and second pilot coils 184 and 186. A calibration pressure sensor 188 can be arranged downstream of the bypass calibration port 142 and upstream of the consumer calibration port 174 on the calibration line 132. In the illustrated example, which does not limit the scope of the invention, a calibration source 190 can be in fluid communication with an inlet 192 of the calibration supply line 130. The calibration source 190 can be in the form of a pump arranged outside the pump 102. The calibration source 190 can be configured to selectively introduce a pressurized fluid (e.g., oil) into the calibration supply line 130. In other examples, which do not limit the scope of the invention, the hydraulic system 100 may not include a calibration source 190, and instead the pump 102 may be configured to selectively introduce a pressurized fluid into the calibration supply line 130.A pump pressure sensor 194 can be located downstream of the pump outlet 108 and upstream of the bypass inlet port 122 on the supply line 110. It should be noted that the pump pressure sensor 194 is not required to perform the calibration procedures described in this document. The hydraulic system 100 can be operated to perform a calibration of the consumer control valve 116 in order to eliminate the influence of component tolerances on the performance of the entire system. In particular, the series connection of the bypass calibration port 142 and the consumer calibration port 174 along the calibration line 132, as described below, simplifies the calibration of the consumer control valve 116. However, it should be noted that the specific design of the components within the hydraulic system 100 should in no way be considered limiting. This means that the systems and procedures for calibrating valves described in this document can be applied to any hydraulic system with one or more electrohydraulic valves connected to control flow to a consumer. The operation of the hydraulic system 100 during the execution of various calibration procedures is described below with reference to Figures 2, 3 to 4. It should be noted that the calibration systems and procedures can also be applied to the calibration circuit 10 from Figures 1 and 2, or to any other hydraulic system configured using the features and techniques described in this document. In some examples, which do not limit the scope of the invention, the control unit 148 can be configured to provide instructions to the bypass control valve 114 and the consumer control valve 116, to monitor the pressure detected by the calibration pressure sensor 188, and / or to perform the calibration calculation procedures described in this document. Fig. 4 shows an example, not limiting the scope of the invention, of the steps for performing an offset calibration for the consumer control valve 116 according to one aspect of the present disclosure. When the offset calibration is to begin, in step 200 the calibration source 190 can be connected to the calibration line 132. This can be simplified by instructing the bypass control valve 114 to move to the third position 138. In the third bypass position 138, the bypass control valve 114 provides a fluid connection from the calibration supply line 130 to the calibration line 132 through the bypass calibration port 142. As described above, in other examples not limiting the scope of the invention, the pump 102 can be configured to supply a pressurized fluid to the calibration supply line 130 instead of to the external calibration source 190. Since the calibration source 190 provides flow through the bypass calibration port 142 into the calibration line 132, a calibration supply pressure can be measured in step 202. The calibration supply pressure can correspond to the pressure measured by the calibration pressure sensor 188 when no control command is provided to the consumer control valve 116 (i.e., the consumer control valve 116 is in the second position 176, in which the flow from the calibration line 132 through the consumer control valve 116 is restricted). The calibration supply pressure measured in step 202 can be used as a reference pressure during calibration and, once acquired, stored by the controller 148. Once the calibration supply pressure has been acquired, the consumer control valve 116 can be controlled in step 204 (i.e.,, the control 148 can apply an electrical signal that causes the consumer coil 150 to move from the second position 176 towards the first position 172 or the third position 178). While the consumer control valve 116 is being controlled in step 204, the calibration pressure sensor 188 can be monitored in step 206. In this way, the pressure in the calibration line 132 can be monitored as a consumer of the control command (e.g., an electrical signal from the controller 148) supplied to the consumer control valve 116. While the consumer coil 150 changes its position during the control command to the consumer control valve 116, the connection between the calibration line 132 and the sump line 166 can be continuously maintained through the consumer calibration port 174. The sump line 166 can have a significantly lower pressure than the calibration line 132, and thus the pressure detected by the calibration pressure sensor 188 can drop while the consumer control valve 116 is being controlled. While the calibration pressure sensor 188 monitors the pressure in the calibration line 132, step 208 can determine whether the pressure value monitored in the calibration line 132 exceeds a predetermined pressure value in step 202. For example, step 208 can determine when the pressure in the calibration line 132 drops to a predetermined ratio of the calibration supply pressure. This predetermined ratio can be set to indicate when the consumer control valve 116 begins to "open a gap" or when flow is directed through it. Alternatively or additionally, it can be determined when the pressure in the calibration line 132 exceeds a known pressure, for example, a known pressure of the sump line 166.This means that the pressure in the calibration line 132 can be monitored by the calibration pressure sensor 188 and it can be determined when the monitored pressure exceeds a known pressure value (either from a pressure value below the known pressure value to a pressure value above the known value or vice versa). Electrohydraulic control valves can define a known or predetermined relationship between a constraint across the control valve and the control command applied to the control valve. However, the constraint, as a consumer of the control command, must be calibrated to account for variations and tolerances within the hydraulic system. Therefore, finding or defining a known point on the constraint / pressure / position relative to the control command curve allows for defining the remaining curve and / or the x-intercept of the curve. If, in step 208, it is determined that the pressure in the calibration line 132 exceeds the predetermined pressure value, the control command value supplied to the consumer control valve 116 can be detected at this point of exceedance, and a control command offset can be calculated in step 210. The control command offset in step 210 can be calculated by comparing the detected control command value with an output control command value, where the output control command value should correspond to the consumer control valve 116 beginning to allow fluid to flow through it. Therefore, the relationship between the control command supplied to the consumer control valve 116 and the corresponding position of the consumer coil 150 can be calibrated. Since the calibration circuit (i.e.,Since the calibration supply line 130, the calibration line 132, the bypass calibration port 142, and the consumer calibration port 174 are isolated from the consumer 118, the offset calibration procedure can be safely started at any time during the operation of the hydraulic system 100. Therefore, the offset control command for the consumer control valve 116 can be continuously checked and improved. Fig. 5 shows an example, not limiting the scope of the invention, of the steps for carrying out various calibration procedures for the consumer control valve 116 according to one aspect of the present disclosure. When the calibration procedure is to begin, the calibration source 190 can be connected to the calibration line 132 in step 300. This can be simplified by directing the bypass control valve 114 to move to the third bypass position 138. In the third bypass position 138, the bypass control valve 114 provides a fluid connection from the calibration supply line 130 to the calibration line 132 through the bypass calibration port 142. As described above in other examples not limiting the scope of the invention, the pump 102 can be configured to supply pressurized fluid to the calibration supply line 130 instead of the external calibration source 190. Since the calibration source 190 provides flow through the bypass calibration port 142 into the calibration line 132, a calibration supply pressure can be measured in step 302. The calibration supply pressure can be the pressure measured by the calibration pressure sensor 188 when no control command is provided to the consumer control valve 116 (i.e., the consumer control valve 116 is in the second position 176, in which flow through the consumer control valve 116 from the calibration line 132 is restricted). The calibration supply pressure measured in step 302 can be used as a reference pressure during calibration and, once acquired, stored by the controller 148. Once the calibration supply pressure is acquired, a minimum value of a control command to the consumer control valve 116 can be replaced by a maximum value in step 304 (i.e.,The control unit 148 can replace a minimum value of an electrical signal supplied to the consumer control valve 116 with a maximum value, causing the consumer coil 150 to move from the second position 176 to the first position 172 or the third position 178. While the consumer coil 150 is changing position as the consumer control valve 116 is being controlled from the minimum value to the maximum value, the connection between the calibration line 132 and the sump line 166 can be continuously maintained through the consumer calibration port 174. The sump line 166 can have a significantly lower pressure than the calibration line 132, and therefore the pressure detected by the calibration pressure sensor 188 can drop while the calibration line 132 is connected to the sump line 166. While the consumer control valve 116 is controlled from a minimum control command to a maximum control command in step 304, the pressure in the calibration line 132 can be monitored by the calibration pressure sensor 188 in step 306. In this way, the pressure in the calibration line 132 can be monitored as a consumer of the control command (e.g., an electrical signal from the controller 148) supplied to the consumer control valve 116. Based on the monitored pressure in the calibration line 132, one or more calibration sequences can be performed. For example, a control command offset calibration can be calculated in steps 308 and 310. The control command offset calibration calculated in steps 308 and 310 can be similar to the procedure described above with reference to steps 208 and 210 in Fig. 4. Alternatively or additionally, in step 312, a multi-point calibration map can be generated based on the pressure in the calibration line 132, while a minimum of the control command to the consumer control valve 116 is replaced by a maximum. In some examples, which do not limit the scope of the invention, the multi-point calibration map can calibrate a relationship between the control command to the consumer control valve 116 and the corresponding position of the consumer coil 150. To simplify the generation of the multi-point calibration map, a constraint provided by the consumer calibration port 174 can define a known relationship to the position of the consumer coil 150. The relationship between the constraint of the consumer calibration port 174 and the position of the consumer coil 150 can take any form (e.g., linear, exponential, parabolic, polynomial, etc.) as long as the relationship is known or defined.The multi-point calibration map can be generated in step 312 using the known relationship between the restriction of the consumer calibration orifice 174, the position of the consumer coil 150, and the pressure in the calibration line 132 measured by the calibration pressure sensor 188. For example, the pressure measured by the calibration pressure sensor 188 can be monitored to determine when the pressure in the calibration line 132 exceeds at least two different expected pressures based on known characteristics of the consumer coil 150 as a consumer of the control command. The corresponding control command values ​​applied to the consumer control valve 116, which occur when the at least two expected pressure values ​​are exceeded, can be recorded.Based on the recorded control command values ​​that occur when the pressure in the calibration line 132 exceeds at least two expected pressure values, the predetermined characteristics of the consumer coil 150 can be compensated for to calibrate the consumer control valve 116. This means that a multi-point calibration map can be generated for the consumer control valve 116. It should be noted that the consumer control valve 116 does not need to be controlled from a minimum control command to a maximum control command to simplify the generation of a multi-point calibration map. The control command value can be recorded when at least two different expected pressure values ​​are exceeded. These two expected pressure values ​​can occur at any time within the range of control commands applied to the consumer control valve 116. Changing the control command to the consumer control valve 116 from a minimum value to a maximum value can alter the pressure in the calibration line 132 to enable the calibration offset to be calculated in step 310 and / or the multi-point calibration map to be generated in step 312. Additionally, hysteresis can be further calibrated by changing the control command to the consumer control valve 116 from the maximum value back to the minimum value in step 314. Here, too, the known relationship between the restriction of the consumer calibration orifice 174 and the position of the consumer coil 150, as well as the pressure in the calibration line 132 measured by the calibration pressure sensor 188, can be used to generate another multi-point calibration map of the control command to the consumer control valve 116 compared to a position of the consumer coil 150.The multi-point calibration map generated when the consumer control valve 116 was controlled from a minimum to a maximum can be compared in step 316 with the multi-point calibration map generated when the consumer control valve 116 was controlled from a maximum to a minimum to calculate a hysteresis map as a consumer of the control command to the consumer control valve 116. It should be noted that controlling the consumer control valve 116 from a minimum control command to a maximum control command and back to a minimum control command is only one example of generating hysteresis calibration data that does not limit the scope of the invention.In other examples, which do not limit the scope of the invention, the consumer control valve 116 can be controlled in a first direction between a first control command value and a second control command value, and consequently in a second direction opposite to the first direction between the first control command value and the second control command value. The control command value when the monitored pressure in the calibration line 132 exceeds a predetermined value can be detected when the electrohydraulic control valve is controlled in the first and second directions. Hysteresis calibration can be calculated based on detected control command values ​​when the monitored pressure in the calibration line 132 exceeds the predetermined pressure while the electrohydraulic control valve is controlled in the first and second directions.The hysteresis calibration represents the required difference in the control command to achieve the same valve position (as indicated by the monitored pressure in the calibration line 132). It should be noted that one or more of the calibration procedures described with reference to Fig. 5 can be carried out independently or simultaneously. Furthermore, the sequence of the calibration procedures shown in Fig. 5 is in no way restrictive. For example, in some examples that do not limit the scope of the invention, the calibration pressure sensor 188 can continuously measure the pressure in the calibration line 132, and the consumer control valve 116 can be controlled from a minimum to a maximum and back to a minimum. Subsequently, a calibration offset, a multi-point calibration map, and / or a hysteresis map can be calculated based on the measured pressure in the calibration line 132. The systems and procedures described in this document provide various calibration methods for an electrohydraulic valve. For example, offset calculation can be used to calibrate a control valve command to a coil position, a multi-point map can be used to calibrate a control valve command to a coil position, and / or hysteresis calibration can be implemented as a consumer of a control command to a control valve. These calibration methods can reduce variations during operation where system calibration is required. The use of a calibration line isolated from the main supply line and a consumer control port isolated from the consumer enables the calibration procedures described in this document to be performed at a lower pressure (i.e., a significantly lower pressure than the pressure during normal operation). In some examples, not limiting the scope of the invention, the pressure required to perform the calibration procedures described in this document may be only that required to fully energize the consumer coil being calibrated. Additionally, isolating the calibration circuit from the main supply line and the consumer eliminates the need to move the consumer or for the system to be in a high-energy state during calibration.This is advantageous for the safe calibration of mobile machinery in practical use. Furthermore, the isolation of the calibration circuit ensures that the consumers and the main supply line do not allow any fluid to flow into the calibration line. In addition, the isolation of the calibration circuit from the main supply line and the consumer eliminates the need for a consumer to be connected to or in fluid contact with the electrohydraulic control valve being calibrated. This can, for example, allow the calibration procedures described in this document to be performed during assembly or for an auxiliary consumer without any additional components being installed. This document describes embodiments in such a way as to provide a clear and concise description, but it is intended and also noted that embodiments can be combined or separated in various ways without departing from the scope of the invention. For example, it is noted that all preferred features described in this document are applicable to all aspects of the invention described herein. Therefore, the invention is not necessarily limited to the specific embodiments and examples described in this document and includes a multitude of other embodiments, examples, uses, modifications, and other deviations of the embodiments, examples, and uses from the appended claims. The entire disclosure of each patent and publication cited in this document is included by reference thereto. Various features and advantages of the invention are set out in the following claims.

Claims

Calibration circuit, operable for calibrating an electro-hydraulic control valve in a hydraulic system, wherein the hydraulic system comprises a pump configured for supplying fluid to a supply line and at least one consumer, wherein the electro-hydraulic control valve comprises at least one working port in fluid communication with the at least one consumer, wherein the calibration circuit comprises: a calibration line configured to be isolated from the supply line; a first calibration port configured to provide a fluid connection between the calibration line and the fluid source; a second calibration port arranged in series with the first calibration port;wherein the second calibration port is arranged on a coil of the electrohydraulic control valve and is configured to selectively provide a fluid connection between the calibration line and a low-pressure source; and a pressure sensor configured to measure a pressure in the calibration line between the first calibration port and the second calibration port, wherein the second calibration port is configured to be isolated from the at least one working port of the electrohydraulic control valve. Calibration circuit according to claim 1, further comprising: a calibration supply line configured to receive a flow from the liquid source. Calibration circuit according to claim 2, wherein the liquid source is located outside the pump. Calibration circuit according to claim 2, wherein the liquid source is the pump. Calibration circuit according to one of claims 1 to 4, wherein the first calibration opening is a fixed opening. Calibration circuit according to one of claims 1 to 5, wherein the first calibration opening is configured to selectively provide a fluid connection between the calibration line and a liquid source. Calibration circuit according to one of claims 1 to 6, wherein the second calibration opening is a variable opening. Calibration circuit according to one of claims 1 to 7, wherein a minimum restriction defined by the second calibration opening is less than a restriction defined by the first calibration opening. Calibration circuit according to one of claims 1 to 8, further comprising: a bypass control valve which is selectively movable between a first position in which a fluid connection between the calibration supply line and the calibration line is inhibited, and a second position in which the fluid connection between the calibration supply line and the supply line is provided. Calibration circuit according to claim 9, wherein the first calibration opening is arranged on a coil of the bypass control valve. Calibration circuit according to claim 10, wherein a connection through the first calibration opening in the bypass control valve is isolated from other connections thereby generated. Calibration circuit according to one of claims 1 to 11, further comprising: a control in electrical connection with the pressure sensor and the electro-hydraulic control valve. Calibration circuit according to claim 12, wherein the control is operable for the following: monitoring a pressure in the calibration line; controlling the electrohydraulic control valve to provide a fluid connection from the calibration line to a low-pressure source through a second calibration port; determining when the pressure in the calibration line exceeds a predetermined pressure value; detecting the control command applied to the electrohydraulic control valve when the pressure in the calibration line exceeds the predetermined pressure value; and calibrating a position of the electrohydraulic control valve to the control command applied thereto. A hydraulic system configured for calibrating an electrohydraulic control valve, comprising: a pump configured for supplying fluid to a supply line; at least one consumer; an electrohydraulic control valve with at least one working port in fluid communication with the at least one consumer; a calibration supply line configured for receiving a flow from a calibration source; a calibration line; a first calibration port configured for selectively providing a fluid connection between the calibration supply line and the calibration line; a second calibration port arranged in series with the first calibration port; wherein the second calibration port is arranged on a coil of the electrohydraulic control valve and is configured for selectively providing a fluid connection between the calibration line and a low-pressure source;and a pressure sensor designed to measure pressure in the calibration line arranged upstream of the second calibration opening, wherein the calibration line and the second calibration opening are isolated from the at least one consumer. Hydraulic system according to claim 14, further comprising: a bypass control valve which is selectable between a first position in which the fluid connection between the calibration supply line and the calibration line is inhibited, and a second position in which the fluid connection between the calibration supply line and the calibration line is provided. Calibration circuit according to claim 15, wherein the first calibration opening is arranged on a coil of the bypass control valve. Calibration circuit according to claim 16, wherein a connection through the first calibration opening in the bypass control valve is isolated from other connections thereby generated. Hydraulic system according to one of claims 14 to 17, further comprising: a control unit which is electrically connected to the pressure sensor and the electro-hydraulic control valve. Hydraulic system according to claim 18, wherein the control is operable for the following: monitoring a pressure in the calibration line; controlling the electro-hydraulic control valve to provide a fluid connection from the calibration line to a low-pressure source through a second calibration port; determining when the pressure in the calibration line exceeds a predetermined pressure value; detecting the control command applied to the electro-hydraulic control valve when the pressure in the calibration line exceeds the predetermined pressure value; and calibrating a position of the electro-hydraulic control valve to the control command applied thereto. A method for calibrating an electrohydraulic control valve in a hydraulic system, wherein the hydraulic system comprises a pump configured to supply fluid to a supply line and at least one consumer, wherein the electrohydraulic control valve comprises at least one working port in fluid communication with the at least one consumer, and wherein the method comprises: supplying a flow into a calibration line through a first calibration port, wherein the calibration line is configured to be insulated from the supply line; controlling the electrohydraulic valve to provide a fluid connection from the calibration line to a low-pressure source through a second calibration port, wherein the second calibration port is arranged on a coil of the electrohydraulic control valve and is configured to be insulated from the at least one consumer;Monitoring the pressure in the calibration line while the electro-hydraulic control valve is being controlled; determining when the pressure in the calibration line exceeds a predetermined pressure value; detecting the control command applied to the electro-hydraulic control valve when the pressure in the calibration line exceeds a predetermined pressure value; and calibrating a position of the electro-hydraulic control valve to the control command applied to it. The method of claim 20, wherein calibrating a position of the electrohydraulic control valve to the control command applied thereto comprises: comparing the detected control command with a predetermined control command and calculating a control command offset based on the difference between the detected control command and the predetermined control command. The method of claim 20 or 21, further comprising: detecting at least two control commands applied to the electrohydraulic valve when the pressure in the calibration line exceeds at least two expected pressure values, wherein the at least two expected pressures are based on predetermined properties of the electrohydraulic control valve; generating a multi-point calibration map corresponding to a position of the electrohydraulic control valve with a control command applied thereto. Method according to one of claims 20 to 22, further comprising: controlling the electrohydraulic control valve arranged between a first control command value and a second control command value in a first direction and controlling the electrohydraulic control valve arranged between the first control command value and the second control command value in a second direction opposite to the first direction. The method of claim 23, further comprising: detecting the control command value when the monitored pressure in the calibration line exceeds a predetermined value when the electro-hydraulic control valve is controlled in the first direction, and detecting the control command value when the monitored pressure in the calibration line exceeds a predetermined value when the electro-hydraulic control valve is controlled in the second direction. Method according to claim 24, further comprising: calculating a hysteresis calibration based on the detected control command values ​​when the monitored pressure in the calibration line exceeds the predetermined pressure while the electrohydraulic control valve is controlled in the first and second directions.

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