Device and method for detecting stroke end point of piston of hydraulic system

Abstract

According to the detection device and method for the stroke end point of the piston of the hydraulic system, the internal space of a hydraulic cylinder is divided into a hydraulic cavity and a spring cavity through a piston, hydraulic drive is adopted in the stroke of liquid hydrogen compression, and spring drive is adopted in the stroke of liquid hydrogen suction. In the stroke of compressing the liquid hydrogen, when the pressure value of the hydraulic oil in the hydraulic cavity reaches the peak value, it can be indicated that the piston reaches the end point of the stroke, in the stroke of sucking the liquid hydrogen, when the difference value between the pressure value of the hydraulic oil in the hydraulic cavity and the normal pressure value of the oil tank is smaller than the difference threshold value, it can be indicated that the piston reaches the end point of the stroke, and on the basis, the piston is not in contact with the piston. According to the hydraulic cylinder, the pressure sensor is used for detecting an oil way connected with the hydraulic cavity, compared with a traditional contact switch, the pressure sensor has higher stability and longer service life, and due to the fact that the pressure sensor is installed outside, replacement and maintenance are easy.

Description

Technical Field

[0001] The present application relates to the field of hydraulic control technology, and in particular to a device and method for detecting an end point of a piston stroke in a hydraulic system. Background Art

[0002] In a high-pressure liquid hydrogen pump, liquid hydrogen (liquefied hydrogen gas) is stored in a container. The temperature of the liquid hydrogen container is ultra-low temperature (20K). At ultra-low temperatures, steel becomes brittle, the strength becomes weak, and there is a risk of hydrogen corrosion in hydrogen working conditions. Therefore, under current technology, the maximum pressure resistance value of its liquid hydrogen container is relatively low. Hydrogen refueling stations need to use high-pressure gas hydrogen to refuel vehicles loaded with compressed hydrogen. Therefore, it is necessary to use a high-pressure liquid hydrogen pump to compress liquid hydrogen to high pressure, and then vaporize it into high-pressure gas hydrogen for use by the hydrogen refueling machine. Hydrogen is a flammable and explosive dangerous gas with a very low lower explosion limit of only 4%, and its ignition energy is very low, only 0.02 millijoules, so liquid hydrogen is more dangerous than ordinary hydrocarbons. Therefore, the high-pressure liquid hydrogen pump uses hydraulic drive, and the hydraulic fluid can flow through the hydraulic pipeline to a certain distance away to transmit the pressure to the hydraulic piston. High-current electrical equipment such as motors can be kept away from liquid hydrogen and operated at a safe distance, which can more reliably achieve safety and explosion protection.

[0003] High-pressure liquid hydrogen pumps are generally submerged designs, that is, the liquid hydrogen pump is placed in a liquid hydrogen container, the drive end leaks out, and the hydraulic end is immersed in liquid hydrogen. Since hydraulic drive allows physical separation between the drive motor and the pump, it is more advantageous for high-pressure liquid hydrogen pumps to use hydraulic drive. Common hydraulic drives are often used as the power source of reciprocating pistons. The piston moves together with the piston rod, and the rear end of the piston rod is connected to the work machine to achieve the desired mechanical work. Because the forward and reverse forces (or resistance) of the machine connected to the rear end of the piston rod always exist and are relatively large, the output force of the hydraulic drive system is generally relatively large, so most of them use double-acting hydraulic cylinders, that is, both the extension stroke and the retraction stroke are driven by hydraulic means. When the hydraulic drive system is working, it is very critical to judge whether the piston has reached the end of the stroke. At present, it is mainly detected by setting a contact switch, that is, if the piston reaches the end of the stroke, the piston or the piston rod touches the contact switch so that the position switch sends a signal. However, contact switches are prone to failure after long-term use. Once a contact switch fails, the stop control will fail, causing the piston to contact the cylinder wall of the hydraulic cylinder with great force, causing noise and vibration, increasing fatigue, reducing the life of the hydraulic system, causing leakage and many other problems. In severe cases, it will cause direct damage to the equipment. Summary of the invention

[0004] The technical problem to be solved by the present application is that the determination of the end point of the piston stroke in the existing hydraulic system is prone to failure. To this end, the present application proposes a detection device and method for the end point of the piston stroke in the hydraulic system.

[0005] In response to the above technical problems, this application provides the following technical solutions:

[0006] In a first aspect, the technical solution of the present application provides a detection device for a piston stroke end point of a hydraulic system, wherein the hydraulic system comprises a hydraulic cylinder and a piston disposed in the hydraulic cylinder, wherein the piston divides the internal space of the hydraulic cylinder into a hydraulic chamber and a spring chamber, and a piston rod is disposed in the spring chamber; the detection device further comprises:

[0007] A spring is arranged outside the piston rod, one end of the spring abuts against the piston, and the other end of the spring abuts against the cylinder wall of the hydraulic cylinder;

[0008] An electrically controlled reversing valve, wherein a first port thereof is connected to the hydraulic chamber, a second port thereof is connected to the spring chamber, a third port thereof is connected to the oil tank via a hydraulic pump, and a fourth port thereof is connected to the oil tank;

[0009] A pressure sensor, used to detect the pressure value of the hydraulic oil in the hydraulic cavity;

[0010] A controller connected to the pressure sensor and the electrically controlled reversing valve;

[0011] The controller is used to control the state of the electronically controlled reversing valve to switch the moving direction of the piston; when the piston moves toward the spring chamber, whether the piston has reached the end of the stroke is determined based on whether the pressure value has reached a peak value; when the piston moves toward the hydraulic chamber, whether the piston has reached the end of the stroke is determined based on whether the difference between the pressure value and the normal pressure value of the oil tank is less than a difference threshold.

[0012] The detection device for the end point of the hydraulic system piston stroke described in some embodiments also includes:

[0013] A flow meter, used to detect the flow value of the hydraulic oil flowing out of the hydraulic chamber;

[0014] The controller is connected to the flow meter;

[0015] When the piston moves toward the hydraulic chamber, the controller is further used to determine whether the piston reaches the end of the stroke according to whether the flow value detected by the flow meter is lower than a set threshold.

[0016] Some schemes describe a detection device for the end point of a hydraulic system piston stroke, wherein the piston is provided with a piston valve stem and a valve seat; the hydraulic chamber is input with hydraulic oil pumped by the hydraulic pump, and the piston valve stem moves toward the valve seat under the action of the hydraulic oil and is sealed with the valve seat; the end of the piston valve stem extends to the outside of the piston.

[0017] In some schemes, the detection device for detecting the end point of the piston stroke of the hydraulic system is formed with a first limiting portion at the piston rod outlet portion of the spring chamber, the caliber of the first limiting portion is smaller than the caliber of the spring chamber, and the end surface of the first limiting portion is suitable for abutting against the piston valve stem when the piston reaches the end point of the stroke.

[0018] In some embodiments, the detection device for the end point of the piston stroke of the hydraulic system is provided, wherein a boss is formed on one end of the piston located in the hydraulic cavity;

[0019] A concave cavity matching the boss is formed on the cylinder wall of the hydraulic chamber at a position corresponding to the boss.

[0020] In some schemes, the detection device for the end point of the piston stroke of the hydraulic system is described, wherein the pressure sensor is arranged between the hydraulic chamber and the first port of the electronically controlled reversing valve.

[0021] In a second aspect, the technical solution of the present application provides a method for detecting an end point of a piston stroke of a hydraulic system, the method being applied to a device for detecting an end point of a piston stroke of a hydraulic system as described in any one of the solutions of the first aspect, comprising:

[0022] Controlling the action of the electrically controlled reversing valve so that the first port and the third port of the electrically controlled reversing valve are in communication;

[0023] Controlling the hydraulic pump to start, the hydraulic pump delivers the hydraulic oil in the oil tank to the hydraulic chamber of the hydraulic cylinder through the electronically controlled reversing valve;

[0024] receiving the pressure value of the hydraulic oil in the hydraulic cavity sent by the pressure sensor, determining whether the pressure value has reached a peak value, and taking the time when the pressure value reaches the peak value as the time when the piston reaches the end of the stroke of the compressed liquid hydrogen;

[0025] Controlling the hydraulic pump to shut down, and controlling the electric control reversing valve to move, disconnecting the passage between the first port and the third port of the electric control reversing valve, and connecting the first port with the fourth port;

[0026] receiving the pressure value of the hydraulic oil in the hydraulic cavity sent by the pressure sensor;

[0027] It is determined whether the difference between the pressure value and the normal pressure value of the fuel tank is less than a difference threshold, and the time when the difference between the pressure value and the normal pressure value of the fuel tank is less than the difference threshold is used as the time when the piston reaches the end of the stroke of inhaling liquid hydrogen.

[0028] The method for detecting the end point of the piston stroke of the hydraulic system described in some embodiments also includes:

[0029] receiving a flow value of the hydraulic oil flowing out of the hydraulic chamber sent by a flow meter;

[0030] Determine whether the flow value is lower than the set threshold, and take the moment when the flow value is lower than the set threshold as the moment when the piston reaches the end of the stroke of inhaling liquid hydrogen.

[0031] For the method of detecting the end of the piston stroke of the hydraulic system described in some solutions, determine whether the pressure value reaches the peak value in the following way:

[0032] Determine the control parameter B1 of the pressure value change rate according to the pressure value change rate at historical moments;

[0033] Obtain the pressure value change rate B2 at the current moment;

[0034] If B2 < [B1 - β1], it is determined that the pressure value reaches the peak, where β1 represents the redundancy coefficient.

[0035] For the method of detecting the end of the piston stroke of the hydraulic system described in some solutions, determine whether the pressure value reaches the peak value in the following way:

[0036] Obtain the piston displacement value X at the current moment and the pressure value change rate B2 at the current moment;

[0037] Determine the control parameter B1 of the pressure value change rate according to the pressure value change rate at historical moments;

[0038] If B2 < [B1 - β1], and X1 - β2 < X < X1 + β2, it is determined that the pressure value reaches the peak, where β1 and β2 represent the redundancy coefficients, and X1 represents the pre - stored control parameter for the end of the stroke.

[0039] For the method of detecting the end of the piston stroke of the hydraulic system described in some solutions:

[0040] The determination of the control parameter B1 of the pressure value change rate according to the pressure value change rate at historical moments includes:

[0041] Obtain the average pressure value change rate at historical moments where (n - 1) represents that there are (n - 1) historical moments before the current moment, i represents the i - th historical moment, p represents the real - time detected value of the pressure value, and t represents time;

[0042] Take the average pressure value change rate as the control parameter of the pressure value change rate; or,

[0043] Obtain the median of the pressure value change rates at historical moments, and take the median of the pressure value change rates as the control parameter of the pressure value change rate; or,

[0044] The redundancy coefficient β1 is equal to the control parameter B1;

[0045] Use the median of the end point of the compressed liquid hydrogen stroke as the reference parameter for the pre-stored stroke end point.

[0046] In some embodiments, the method for detecting the end point of the piston stroke of the hydraulic system includes determining whether the pressure value is consistent with the atmospheric pressure value of the fuel tank and whether the flow rate value is lower than the set threshold, and includes:

[0047] Obtain the piston displacement value X at the current moment and the pressure value P at the current moment;

[0048] Obtain the total amount of hydraulic oil L1 released from the hydraulic chamber to the fuel tank;

[0049] Obtain the piston displacement value X at the current moment;

[0050] If P < P1 + β3, L + β4 < L1 < L + β4, and X2 - β5 < X < X2 + β5, F < β6, then it is determined that the pressure value is consistent with the atmospheric pressure value of the fuel tank and whether the flow rate value is the set threshold; where P1 is the atmospheric pressure value of the fuel tank, L is the volume of the oil cylinder, X2 is the median of the end point of the suction liquid hydrogen stroke, F is the flow rate value, and β3, β4, β5, and β6 are redundancy coefficients.

[0051] The technical solution of the present application has the following technical effects compared with the prior art:

[0052] The detection device and method for the end point of the piston stroke of the hydraulic system provided by the present application use the piston to divide the internal space of the hydraulic cylinder into a hydraulic chamber and a spring chamber, so that it can be realized that hydraulic drive is used during the compression of liquid hydrogen, and spring drive is used during the suction of liquid hydrogen. During the compression of liquid hydrogen, when the pressure value of the hydraulic oil in the hydraulic chamber reaches the peak value, it can be explained that the piston reaches the end point of the stroke. During the suction of liquid hydrogen, when the difference between the pressure value of the hydraulic oil in the hydraulic chamber and the atmospheric pressure value of the fuel tank is less than the difference threshold, it indicates that the piston reaches the end point of the stroke. On this basis, it is only necessary to use a pressure sensor to detect the oil circuit connected to the hydraulic chamber. Compared with the traditional contact switch, the pressure sensor has higher stability and longer service life, and because it is installed outside, it is easy to replace and repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The following will describe in detail the preferred embodiments of the present application through the drawings, which will help to understand the purpose and advantages of the present application, where:

[0054] Figure 1 It is a schematic structural diagram of the detection device for the end point of the piston stroke of the hydraulic system according to an embodiment of the present application;

[0055] Figure 2 It is a schematic structural diagram of the detection device for the end point of the piston stroke of the hydraulic system according to another embodiment of the present application;

[0056] Figure 3 This is a flow chart of a method for detecting an end point of a piston stroke in a hydraulic system according to an embodiment of the present application;

[0057] Figure 4 This is a flow chart of a method for detecting an end point of a piston stroke in a hydraulic system according to another embodiment of the present application. DETAILED DESCRIPTION

[0058] The technical solution of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0059] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0060] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0061] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0062] The present application embodiment provides a device for detecting the end point of a piston stroke in a hydraulic system, such as Figure 1As shown, the hydraulic system includes a hydraulic cylinder 101 and a piston arranged in the hydraulic cylinder 101, wherein the piston divides the space inside the hydraulic cylinder 101 into a hydraulic chamber 102 and a spring chamber, wherein a piston rod 103 is arranged in the spring chamber; the detection device also includes a hydraulic pump 104, an electric control reversing valve 105, a pressure sensor 106, an oil tank 107, a spring 109 and a controller 200. The spring 109 is arranged outside the piston rod 103, one end of the spring 109 abuts against the piston, and the other end abuts against the cylinder wall of the hydraulic cylinder 101. The electric control reversing valve 105 has a first port connected to the hydraulic chamber 102, a second port connected to the spring chamber, a third port connected to the oil tank 107 via the hydraulic pump 104, and a fourth port connected to the oil tank 107. The pressure sensor 106 is used to detect the pressure value of the hydraulic oil in the hydraulic chamber 102. The controller 200 is connected to the pressure sensor 106 and the electric control reversing valve 105. The controller 200 is used to control the state of the electric control reversing valve 105 to switch the moving direction of the piston; when the piston moves toward the spring chamber, it is determined whether the piston has reached the end of the stroke according to whether the pressure value reaches the peak value; when the piston moves toward the hydraulic chamber 102, it is determined whether the piston has reached the end of the stroke according to whether the difference between the pressure value and the normal pressure value of the oil tank 107 is less than the difference threshold.

[0063] Preferably, if Figure 2 As shown, the device also includes a flow meter 110 for detecting the flow value of the hydraulic oil flowing out of the hydraulic chamber 102; the controller 200 is connected to the flow meter 110; when the piston moves toward the hydraulic chamber 102, the controller 200 is also used to determine whether the piston has reached the end of the stroke based on whether the flow value detected by the flow meter 110 is lower than a set threshold.

[0064] As a preferred solution, a piston valve stem 108 and a valve seat are provided on the piston; the hydraulic chamber 102 is input with hydraulic oil pumped by the hydraulic pump 104, and the piston valve stem 108 moves toward the valve seat under the action of the hydraulic oil and is sealed with the valve seat; the end of the piston valve stem 108 extends to the outside of the piston.

[0065] As shown in the figure, the hydraulic pump 104, the electric control reversing valve 105 and the pressure sensor 106 are all connected to the controller 200. The hydraulic pump 104 is connected between the oil tank 107 and the hydraulic chamber 102. The hydraulic pump 104 delivers the hydraulic oil in the oil tank 107 to the hydraulic chamber 102. As can be seen from Figure 1, when the hydraulic chamber 102 on the left side of the piston is injected with high-pressure hydraulic oil, the piston valve stem 108 is pushed to the right against the valve seat under the push of the hydraulic oil, and the valve is closed. As shown in the figure, because the right side of the piston, i.e., the spring chamber, is connected to the oil tank 107, the pressure is very low, so the pressure difference on both sides of the piston is very large. Under the action of the large pressure difference, the piston is subjected to a large rightward thrust, and the piston moves to the right. When the piston reaches the end of the stroke, since the piston valve stem 108 extends a small part of the piston, the piston valve stem 108 will first contact the cylinder wall to stop moving. At this time, when the piston continues to move to the right, the sealing surface on the piston valve stem 108 will separate from the valve seat on the piston, and the valve will open. The hydraulic oil on the left side of the piston flows to the right side of the piston through the flow channel after the piston valve stem is opened. The pressure on both sides of the piston is balanced, the piston loses the thrust under the action of the differential pressure, and the piston stops.

[0066] During the hydraulic drive stroke of the compressed liquid hydrogen, the pressure signal of the hydraulic oil in the hydraulic chamber 102 is input into the controller 200 in real time through the pressure sensor 106. Since the spring 109 in the right spring chamber is squeezed, the reaction force of the spring 109 continues to increase, and the pressure signal of the hydraulic oil also continues to increase. When the piston reaches the end point, the piston valve stem 108 opens, the hydraulic oil flows to the right side of the piston, the pressure on the left side is transmitted to the right side, the pressure on the right side increases, the pressure on the left side is relieved, the pressure difference on both sides of the piston decreases sharply, and the piston movement stops. By monitoring the pressure change, the peak moment of the hydraulic oil pressure value in the hydraulic chamber 102 can be clearly judged, which is the last moment before the piston valve stem 108 opens. Subsequently, the pressure of the hydraulic oil in the hydraulic chamber 102 decreases rapidly, showing the pressure relief after the piston valve stem 108 opens. This scheme is based on this principle to judge the stop of the stroke of the compressed liquid hydrogen of the piston movement.

[0067] When the controller 200 determines that the piston has stopped and continues to move according to the predetermined logic, the controller 200 cuts off the passage between the hydraulic pump 104 and the hydraulic chamber 102 through the electrically controlled reversing valve 105, and connects the hydraulic chamber 102 with the oil tank 107 with a normal pressure value, and the high pressure in the hydraulic oil in the hydraulic chamber 102 is released. The piston then moves to the left under the elastic force of the spring 109. At this time, the hydraulic oil in the hydraulic chamber 102 begins to flow to the oil tank 107 under the push of the piston, and its flow speed is determined by the pressure acting on the hydraulic oil after the elastic force of the spring 109 is transmitted to the piston. Since the flow resistance of the hydraulic oil is very small, the pressure of the hydraulic oil at this time is much smaller than the high pressure of the hydraulic drive stroke. At the same time, in the preferred embodiment, the controller 200 monitors the flow of the hydraulic oil at any time through the flow meter 110 (the existing vortex flow meter can be used). During this process, the pressure of the hydraulic oil is also decreasing, and the flow rate of the hydraulic oil is also decreasing. As the piston stops moving, the pressure reaches a static pressure in the oil tank 107, that is, the pressure value of the hydraulic oil is consistent with the normal pressure value of the oil tank. At the same time, since there is no hydraulic oil flowing in the hydraulic cavity, the flow value detected by the flow meter 110 is almost zero. Therefore, at least one of the pressure value and the flow value can be selected to judge the end of the stroke. The present application judges that the piston's stroke of absorbing liquid hydrogen stops based on this feature.

[0068] In the above scheme of this embodiment, the piston is used to divide the internal space of the hydraulic cylinder 101 into a hydraulic chamber 102 and a spring chamber, so that hydraulic drive can be used in the stroke of compressing liquid hydrogen, and spring 109 drive can be used in the stroke of inhaling liquid hydrogen. In the stroke of compressing liquid hydrogen, when the pressure value of the hydraulic oil in the hydraulic chamber 102 reaches the peak value, it can be said that the piston has reached the end of the stroke. In the stroke of inhaling liquid hydrogen, when the flow rate of the hydraulic oil flowing out of the hydraulic chamber 102 is lower than the set threshold and the pressure value of the hydraulic oil in the hydraulic chamber 102 is consistent with the normal pressure value of the oil tank 107, it means that the piston has reached the end of the stroke. On this basis, it is only necessary to use the flow meter and the pressure sensor 106 to detect the oil circuit connected to the hydraulic chamber. Compared with the traditional contact switch, the pressure sensor 106 and the flow meter have higher stability and longer service life, and because their installation position is far away from the pump body, in the hydraulic drive system, they are very easy to repair and replace. Therefore, this scheme can improve the accuracy and reliability of the detection result of the piston stroke end.

[0069] Preferably, a first limiting portion is formed at the piston rod outlet of the spring chamber, the caliber of the first limiting portion is smaller than the caliber of the spring chamber, and the end surface of the first limiting portion is suitable for abutting against the piston valve stem 108 when the piston reaches the end of the stroke. Through this design, it can be ensured that when the piston valve stem 108 abuts against the cylinder wall, there is enough space inside the spring chamber to receive the hydraulic oil from the hydraulic chamber 102, so as to achieve a balance between the sum of the pressure of the spring 109 in the spring chamber and the pressure of the hydraulic oil and the pressure value in the hydraulic chamber 102.

[0070] More preferably, if Figure 1 and Figure 2 As shown, a boss is formed at one end of the piston located in the hydraulic chamber 102; a cavity matching the boss is formed at a position corresponding to the boss on the cylinder wall of the hydraulic chamber 102. With such a design, when the piston driven by the spring 109 is about to reach the left end of the hydraulic chamber 102, the elastic force of the spring 109 has become very small, and the speed of the piston slows down. Before the piston contacts the left cylinder wall, the boss and the cavity act as a buffer for buffering. The outer diameter of the boss is slightly smaller than that of the cavity. When the boss is pressed into the cavity, the hydraulic oil in the cavity is squeezed out through the gap between the boss and the cavity, thereby generating a reaction force to stop and buffer the piston. Finally, the piston stops smoothly at the leftmost side of the hydraulic cylinder 101 under the buffering action.

[0071] In the above solution, the pressure sensor 106 and the flow meter 110 are arranged between the hydraulic chamber 102 and the first port of the electric control reversing valve 105. With this design, the pressure value of the hydraulic oil flowing into the hydraulic chamber 102 and the flow value of the hydraulic oil flowing out of the hydraulic chamber 102 can be accurately detected.

[0072] The present application also provides a method for detecting the end point of a piston stroke in a hydraulic system. The method is applied to the detection device for detecting the end point of a piston stroke in a hydraulic system described in any one of the above embodiments. Figure 3 As shown, the method comprises the following steps:

[0073] S10: controlling the operation of the electrically controlled reversing valve so that the first port and the third port of the electrically controlled reversing valve are in communication with each other.

[0074] Combination Figure 1 In the structure shown, when the electrically controlled reversing valve 105 is in the state shown in the figure, the hydraulic oil flows from the oil tank into the hydraulic chamber.

[0075] S20: Control the hydraulic pump to start, and the hydraulic pump delivers the hydraulic oil in the oil tank to the hydraulic chamber of the hydraulic cylinder through the electronically controlled reversing valve.

[0076] After the hydraulic pump 104 is started, the hydraulic oil in the oil tank can be pumped into the hydraulic chamber 102 .

[0077] S30: Receive the pressure value of the hydraulic oil in the hydraulic chamber sent by the pressure sensor, determine whether the pressure value has reached a peak value (which can be used as a PX judgment condition), and use the time when the pressure value reaches the peak value as the time when the piston reaches the end of the stroke of compressed liquid hydrogen.

[0078] The pressure values ​​between the pressure sensor 106 and the hydraulic chamber 102 should have a consistent relationship, so the pressure sensor 106 is set on the passage connected to the hydraulic chamber 102 to detect the pressure value of the hydraulic chamber 102. Combined with the aforementioned piston movement process, when the piston reaches the end of the stroke, the piston valve stem 108 is pushed open, and the piston valve stem 108 opens the passage between the hydraulic chamber and the spring chamber, and the hydraulic oil flows from the hydraulic chamber into the spring chamber, so that the pressure value of the hydraulic chamber changes from a rising state to a falling state, so by detecting the peak value of the pressure value, it is possible to determine the moment when the piston reaches the end of the stroke.

[0079] S40: Control the hydraulic pump to shut down, and control the electronically controlled reversing valve to operate, disconnect the passage between the first port and the third port of the electronically controlled reversing valve, and connect the first port with the fourth port.

[0080] As shown in the figure, when the hydraulic chamber 102 is connected to the fourth port of the electric control reversing valve 105, it can be connected to the oil tank. At this time, the spring force of the spring 109 causes the piston to move to the left, the space of the hydraulic chamber 102 is compressed, and the hydraulic oil inside it can be transported to the oil tank 107 along the passage.

[0081] S50: Receive the pressure value of the hydraulic oil in the hydraulic cavity sent by the pressure sensor.

[0082] The pressure sensor 106 is always connected to the hydraulic chamber 102, so the pressure value thereof can be measured.

[0083] S60: Determine whether the difference between the pressure value and the normal pressure value of the fuel tank is less than a difference threshold, and take the time when the difference between the normal pressure value of the fuel tank is less than the difference threshold as the time when the piston reaches the end of the stroke for inhaling liquid hydrogen.

[0084] As mentioned above, when the piston reaches the end point on one side of the hydraulic chamber, the hydraulic oil in the hydraulic chamber is almost zero, and the pressure value detected by the pressure sensor should be basically consistent with the normal pressure value of the oil tank. Theoretically, the pressure value should be equal to the normal pressure value. In practical applications, considering the error reasons, it can be considered that the piston has reached the end of the stroke when the difference between the pressure value and the normal pressure value is less than the difference threshold.

[0085] Preferably, the method further comprises: receiving the flow value of the hydraulic oil flowing out of the hydraulic chamber sent by the flow meter; judging whether the flow value is lower than a set threshold value, and taking the moment when the flow value is lower than the set threshold value as the moment when the piston reaches the end point of the stroke for inhaling liquid hydrogen. When the piston reaches the left end point, the hydraulic oil in the hydraulic chamber 102 returns to zero, so no more hydraulic oil flows out, so the flow value detected by the flow meter should theoretically return to zero. Considering the error reason, the situation where it is less than an appropriate threshold value can be used as the judgment basis for the piston reaching the end point of the stroke.

[0086] In the above scheme, the controller uses the PX judgment condition to detect and judge whether the piston has reached the end point when the piston moves to the right to compress liquid hydrogen, and uses the PFX judgment condition to detect and judge whether the piston has reached the end point when the piston moves to the left to inhale liquid hydrogen. That is, the two judgment conditions are used alternately in one working cycle to judge two different strokes respectively, which can be called an alternating composite judgment criterion, which has a simple and accurate effect.

[0087] Preferably, the controller stores data of various parameters during the two stroke processes and when reaching the end point, and can perform statistical analysis and calculation based on the parameter data, and can calculate the movement position of the piston, thereby making the judgment of whether the piston reaches the end point of the stroke more accurate and facilitating more precise control. Specifically, the parameters may include the instantaneous flow rate of hydraulic oil F (which can be obtained by detecting by a flow meter), the volume of the hydraulic cylinder L (which is a known parameter and can be determined according to the design parameters of the hydraulic cylinder), the hydraulic oil pressure value P (which can be obtained by detecting by a pressure sensor), the normal pressure value P1 of the hydraulic oil storage tank (an empirical value, which can also be determined by setting a pressure sensor in the tank for real-time detection), the pressure of the liquid hydrogen container P2 (an empirical value, which can also be determined by setting a pressure sensor in the container for real-time detection), the static pressure of the liquid hydrogen level P3 (an empirical value, which can also be determined by setting a pressure sensor in the container for real-time detection), the hydraulic pump outlet pressure P4 (an empirical value, which can also be determined by setting a pressure sensor in the hydraulic pump outlet for real-time detection), the pump outlet check valve pressure drop P5 (which can be determined by setting a pressure sensor in the check valve for real-time detection), the tank pump jacket pressure P6 (which can be determined by setting a pressure sensor in the jacket for real-time detection), the spring output force Fs (determined by calculation) fixed), hydraulic piston area S1 (existing parameters, which can be determined by hydraulic cylinder design parameters), cold end piston area S2 (existing parameters, which can be determined by hydraulic cylinder design parameters), spring elastic coefficient K (existing parameters, which can be determined by hydraulic cylinder design parameters), spring compression or extension length X (determined by calculation), the median values ​​of the two end positions of the piston are X1 and X2 respectively (which can be determined by historical detection data), spring force Fs (obtained by calculation), compression stroke motion friction resistance Ff1 (existing parameters, which can be determined by hydraulic cylinder design parameters), suction stroke motion friction resistance Ff2 (existing parameters, which can be determined by hydraulic cylinder design parameters), total mass m of piston linkage system (existing parameters, which can be determined by hydraulic cylinder design parameters), piston speed V1 of liquid hydrogen compression stroke (obtained by calculation), piston speed V2 of liquid hydrogen suction stroke (obtained by calculation), time t, coefficients β1, β2, β3, β4, β5, β6, β7, β8, β9, β10, β11, β12, β13, β14, β15, β16, β17, β18, β19, β20, β21, β22, β23, β24, β25, β26, β27, β28, β29, β30, β31 10 , β 11 , β 12 , β 13 , then we have the following relationship:

[0088] V=β 10 (dP / dt), Fs=-KX, Ff1=β6×V2+β7, Ff2=β8×V2+β1;

[0089] The displacement calculation formula of the piston during the process of compressing liquid hydrogen is: X = [P × S1 + (P6-P2-P3-P4-P5 × β 13)×S2 - β6×V2 - β7 - m(dV / dt)] / K; Here, the displacement calculation formula of the piston mainly uses the pressure value in the hydraulic chamber to calculate. To improve the accuracy of piston displacement calculation, after obtaining the calculation result, it can also be verified through the flow value detected by the flowmeter. Because during the piston movement, the volume in the hydraulic chamber changes, and since the volume change rate changes, the hydraulic oil flow in the hydraulic chamber also changes. There is a corresponding relationship between the piston movement speed and the flow value, so there is also a corresponding relationship between the piston displacement and the flow value. Based on this principle, the piston displacement can be obtained through the pressure value and the flow value, and they can be mutually verified, so that the obtained piston displacement is more accurate.

[0090] During the process of the piston compressing the liquid hydrogen stroke, the average pressure value change rate should satisfy: dP / dt > 0, and the piston displacement should satisfy: X > X1 + β1;

[0091] The PX judgment condition when the piston compresses the liquid hydrogen stroke reaches the end and the piston valve stem opens: dP / dt < [average(dP / dt) - β1], X1 - β2 < X < X1 + β2;

[0092] The PX judgment condition can also be written in the following form: average dP / dt < 0, X1 - β2 < X < X1 + β2;

[0093] The PX judgment condition can also be written in the following form: dP / dt < [median value(dP / dt) - β1], X1 - β2 < X < X1 + β2. Based on the above principle:

[0094] In the above scheme, the pressure value is judged whether it reaches the peak value in the following way:

[0095] S11: Determine the comparison parameter B1 of the pressure value change rate according to the pressure value change rate at the historical moment.

[0096] S12: Obtain the pressure value change rate B2 at the current moment.

[0097] S13: If B2 < [B1 - β1], then judge that the pressure value reaches the peak, where β1 represents the redundancy coefficient.

[0098] Or:

[0099] S21: Obtain the piston displacement value X at the current moment and the pressure value change rate B2 at the current moment.

[0100] S22: Determine the comparison parameter B1 of the pressure value change rate according to the pressure value change rate at the historical moment.

[0101] S23: If B2 < [B1 - β1] and X1 - β2 < X < X1 + β2, it is determined that the pressure value reaches the peak value, where β1 and β2 represent redundancy coefficients, and X1 represents the control parameter for the end point of the pre-stored stroke.

[0102] Among them, the control parameter B1 for determining the pressure value change rate according to the pressure value change rate at the historical moment includes:

[0103] Obtain the average pressure value change rate at the historical moment Among them, (n - 1) represents that there are (n - 1) historical moments before the current moment, i represents the i-th historical moment, p represents the real-time detected value of the pressure value, and t represents time; use the average pressure value change rate as the control parameter for the pressure value change rate;

[0104] Or,

[0105] Obtain the median of the pressure value change rate at the historical moment, and use the median of the pressure value change rate as the control parameter for the pressure value change rate;

[0106] Or,

[0107] The redundancy coefficient β1 is equal to the control parameter B1.

[0108] Use the median of the end point of the compressed liquid hydrogen stroke as the control parameter for the pre-stored stroke end point.

[0109] Combined with Figure 4 As shown, where the P condition is to judge whether the pressure value change rate meets the condition, and the X condition is to judge whether the piston displacement meets the condition.

[0110] Furthermore, based on the above parameters, it is also possible to calculate during the stroke of inhaling liquid hydrogen:

[0111] During the stroke of inhaling liquid hydrogen, the piston displacement calculation formula: X = [P × S1 + (P6 - P2 - P3) × S2 + m(dV / dt) + β8 × V2 + β1] / K;

[0112] During the stroke of inhaling liquid hydrogen, the average dP / dt < 0, P > P1 + a, F > β 11 , X > X2 + β 10 ;

[0113] During the stroke of inhaling liquid hydrogen, the PFX judgment condition when the piston reaches the end point to the left is:

[0114] The average P < the average P1 + β5;

[0115] That is the calculated flow value.

[0116] X2 - β5 < X < X2 + β5, F < β6.

[0117] That is, the judgment of whether the pressure value is consistent with the atmospheric pressure value of the fuel tank and whether the flow value is lower than the set threshold includes:

[0118] S31: Obtain the piston displacement value X at the current moment and the pressure value P at the current moment;

[0119] S32: Obtain the total amount of hydraulic oil L1 released from the hydraulic chamber to the fuel tank;

[0120] S33: Obtain the piston displacement value X at the current moment;

[0121] S34: If P < P1 + β3, L + β4 < L1 < L + β4, and X2 - β5 < X < X2 + β5, F < β6, then it is determined that the pressure value is consistent with the atmospheric pressure value of the fuel tank and whether the flow value is the set threshold; where P1 is the atmospheric pressure value of the fuel tank, L is the volume of the oil cylinder, X2 is the median of the end point of the suction liquid hydrogen stroke, F is the flow value, and β3, β4, β5, and β6 are redundancy coefficients.

[0122] Combined with Figure 4 , where the P condition is to judge whether the pressure value change rate meets the condition, the X condition is to judge whether the piston displacement meets the condition, and the F condition is to judge whether the flow value and the total flow meet the condition. The alternating composite criterion of the solution of the present application can judge the specific position of the piston at any time. Using the above formula, in fact, this solution can not only judge whether the piston reaches the end point of the stroke, but also calculate the piston position at any position in the middle process of the stroke using the above formula. When the number of cycles gradually increases, the above various coefficients can also be optimized to improve the detection accuracy. Compared with the piston stroke end point judgment structure of the prior art, the structure of this solution of the present application is simpler, the piston valve rod has a lighter mass, a smaller volume, and shorter opening and closing times, which can improve the reaction speed of the hydraulic drive system, reduce hysteresis, and improve the system response time.

[0123] Obviously, the above embodiments are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A detection device for the end point of a piston stroke in a hydraulic system, wherein the hydraulic system comprises a hydraulic cylinder and a piston arranged in the hydraulic cylinder, wherein the piston divides the internal space of the hydraulic cylinder into a hydraulic chamber and a spring chamber, and a piston rod is arranged in the spring chamber; characterized in that: The detection device also includes: A spring is arranged outside the piston rod, one end of the spring abuts against the piston, and the other end of the spring abuts against the cylinder wall of the hydraulic cylinder; An electrically controlled reversing valve, wherein a first port thereof is connected to the hydraulic chamber, a second port thereof is connected to the spring chamber, a third port thereof is connected to the oil tank via a hydraulic pump, and a fourth port thereof is connected to the oil tank; A pressure sensor, used to detect the pressure value of the hydraulic oil in the hydraulic cavity; A controller connected to the pressure sensor and the electrically controlled reversing valve; The controller is used to control the state of the electronically controlled reversing valve to switch the moving direction of the piston; when the piston moves toward the spring chamber, whether the piston has reached the end of the stroke is determined based on whether the pressure value has reached a peak value; when the piston moves toward the hydraulic chamber, whether the piston has reached the end of the stroke is determined based on whether the difference between the pressure value and the normal pressure value of the oil tank is less than a difference threshold.

2. The detection device for the end point of the piston stroke of the hydraulic system according to claim 1, characterized in that: Also includes: A flow meter, used to detect the flow value of the hydraulic oil flowing out of the hydraulic chamber; The controller is connected to the flow meter; When the piston moves toward the hydraulic chamber, the controller is further used to determine whether the piston reaches the end of the stroke according to whether the flow value detected by the flow meter is lower than a set threshold.

3. The detection device for the end point of the piston stroke of the hydraulic system according to claim 2, characterized in that: The piston is provided with a piston valve stem and a valve seat; the hydraulic chamber is input with hydraulic oil pumped by the hydraulic pump, and the piston valve stem moves toward the valve seat under the action of the hydraulic oil and is sealed with the valve seat; the end of the piston valve stem extends to the outside of the piston.

4. The detection device for the end point of the piston stroke of a hydraulic system according to claim 3, characterized in that: A first limiting portion is formed at the piston rod outlet portion of the spring chamber, the caliber of the first limiting portion is smaller than the caliber of the spring chamber, and the end surface of the first limiting portion is suitable for abutting against the piston valve stem when the piston reaches the end of the stroke.

5. The detection device for the end point of the piston stroke of a hydraulic system according to any one of claims 1 to 4, characterized in that: A boss is formed on one end of the piston located in the hydraulic chamber; A concave cavity matching the boss is formed on the cylinder wall of the hydraulic chamber at a position corresponding to the boss.

6. A method for detecting the end point of a piston stroke in a hydraulic system, characterized in that: The method is applied to the detection device for the end point of the piston stroke of the hydraulic system according to any one of claims 1 to 5, comprising: Controlling the action of the electrically controlled reversing valve so that the first port and the third port of the electrically controlled reversing valve are in communication; Controlling the hydraulic pump to start, the hydraulic pump delivers the hydraulic oil in the oil tank to the hydraulic chamber of the hydraulic cylinder through the electronically controlled reversing valve; receiving the pressure value of the hydraulic oil in the hydraulic cavity sent by the pressure sensor, determining whether the pressure value has reached a peak value, and taking the time when the pressure value reaches the peak value as the time when the piston reaches the end of the stroke of the compressed liquid hydrogen; Controlling the hydraulic pump to shut down, and controlling the electric control reversing valve to move, disconnecting the passage between the first port and the third port of the electric control reversing valve, and connecting the first port with the fourth port; receiving the pressure value of the hydraulic oil in the hydraulic cavity sent by the pressure sensor; Determine whether the difference between the pressure value and the normal pressure value of the fuel tank is less than the difference threshold, and take the moment when the difference between the pressure value and the normal pressure value of the fuel tank is less than the difference threshold as the moment when the piston reaches the end of the stroke of inhaling liquid hydrogen.

7. The method for detecting the end point of the piston stroke of a hydraulic system according to claim 6, characterized in that: It further includes: Receiving the flow value of the hydraulic oil flowing out of the hydraulic chamber sent by the flow meter; Determine whether the flow value is lower than the set threshold, and take the moment when the flow value is lower than the set threshold as the moment when the piston reaches the end of the stroke of inhaling liquid hydrogen.

8. The method for detecting the end point of the piston stroke of a hydraulic system according to claim 7, characterized in that: Judge whether the pressure value reaches the peak value in the following way: Determine the comparison parameter B1 of the pressure value change rate according to the pressure value change rate at the historical moment; Obtain the pressure value change rate B2 at the current moment; If B2 < [B1 - β1], it is determined that the pressure value reaches the peak value, where β1 represents the redundancy coefficient.

9. The method for detecting the end point of the piston stroke of a hydraulic system according to claim 7, characterized in that: Judge whether the pressure value reaches the peak value in the following way: Obtain the piston displacement value X at the current moment and the pressure value change rate B2 at the current moment; Determine the comparison parameter B1 of the pressure value change rate according to the pressure value change rate at the historical moment; If B2 < [B1 - β1], and X1 - β2 < X < X1 + β2, it is determined that the pressure value reaches the peak value, where β1 and β2 represent the redundancy coefficients, and X1 represents the pre-stored stroke end comparison parameter.

10. The method for detecting the end point of the piston stroke of the hydraulic system according to claim 8 or 9, characterized in that: The determining the comparison parameter B1 of the pressure value change rate according to the pressure value change rate at the historical moment includes: Get the average change rate of pressure value at historical moments It indicates that there are (n-1) historical moments before the current moment, i indicates the ith historical moment, p indicates the real-time detection value of the pressure value, and t indicates time; Taking the average pressure value change rate as the comparison parameter of the pressure value change rate; or, Obtaining the median of the pressure value change rate at the historical moment, and taking the median of the pressure value change rate as the comparison parameter of the pressure value change rate; or, The redundancy coefficient β1 is equal to the comparison parameter B1; Taking the median of the end point of the stroke of compressed liquid hydrogen as the pre-stored stroke end comparison parameter.

11. The method for detecting the end point of the piston stroke of a hydraulic system according to claim 7, characterized in that: The determining whether the pressure value is consistent with the normal pressure value of the fuel tank and whether the flow value is lower than the set threshold includes: Obtaining the piston displacement value X at the current moment and the pressure value P at the current moment; Obtaining the total amount of hydraulic oil L1 released from the hydraulic chamber to the fuel tank; Obtaining the piston displacement value X at the current moment; If P < P1 + β3, L + β4 < L1 < L + β4, and X2 - β5 < X < X2 + β5, F < β6, it is determined that the pressure value is consistent with the normal pressure value of the fuel tank and whether the flow value is the set threshold; where P1 is the normal pressure value of the fuel tank, L is the volume of the oil cylinder, X2 is the median of the end point of the stroke of inhaling liquid hydrogen, F is the flow value, and β3, β4, β5 and β6 are redundancy coefficients.

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