A device and method for detecting the end of stroke of a hydraulic system piston

Abstract

The application discloses a kind of detection device and method of hydraulic system piston stroke end, utilize piston to divide the internal space of hydraulic cylinder into hydraulic chamber and spring chamber, adopt hydraulic drive in the stroke of compressed liquid hydrogen, and adopt spring drive in the stroke of inhaled liquid hydrogen.In the stroke of compressed liquid hydrogen, when the pressure value of hydraulic oil in hydraulic chamber reaches peak value, then it can be illustrated that piston reaches stroke end, in the stroke of inhaled liquid hydrogen, when the difference between the pressure value of hydraulic oil of hydraulic chamber and the normal pressure value of oil tank is less than difference threshold value, then it illustrates that piston reaches stroke end, on this basis, only need to detect the oil line connected with hydraulic chamber using pressure sensor, compared with traditional contact switch, it has higher stability and longer service life, and because it is installed outside, easy to replace and maintain.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydraulic control, in particular to a detection device and method for the end of stroke of a piston of a hydraulic system. BACKGROUND

[0002] In a high-pressure liquid hydrogen pump, liquid hydrogen (liquefied hydrogen gas) is stored in a container, and the temperature of the liquid hydrogen container is ultralow (20K). At the ultralow temperature, the steel material becomes brittle and weak, and there is a risk of hydrogen corrosion under the hydrogen working condition. Therefore, under the current technology, the maximum pressure resistance value of the liquid hydrogen container is relatively low. The hydrogen filling station needs to use high-pressure gaseous hydrogen to fill the compressed hydrogen gas into the vehicle. Therefore, a high-pressure liquid hydrogen pump is needed to compress the liquid hydrogen to high pressure, and then vaporize it into high-pressure gaseous hydrogen for use in the hydrogen filling machine. Hydrogen is a flammable and explosive dangerous gas, with a very low lower explosive limit of only 4%, and a very low ignition energy of only 0.02 millijoules. Therefore, liquid hydrogen is more dangerous than ordinary carbon hydrogen compounds. Therefore, the high-pressure liquid hydrogen pump is driven by hydraulic pressure, and the hydraulic fluid can flow to a certain distance outside through the hydraulic pipeline to transmit pressure to the hydraulic piston. The large-current electrical equipment such as the motor can be operated at a safe distance from the liquid hydrogen, and the safety explosion-proof can be more reliably achieved.

[0003] The high-pressure liquid hydrogen pump is generally designed as a submerged type, that is, the liquid hydrogen pump is placed in the liquid hydrogen container, the driving end is exposed, and the liquid end is immersed in the liquid hydrogen. Since the hydraulic drive allows physical separation between the driving motor and the pump, the high-pressure liquid hydrogen pump has more advantages when using hydraulic drive. The common hydraulic drive is often used as the power source for reciprocating motion of the piston. The piston moves together with the piston rod, and the rear end of the piston rod is connected to a mechanical device to perform work, thereby achieving the desired mechanical work. Because of the mechanical device connected to the rear end of the piston rod, the forward and reverse forces (or resistances) always exist and are relatively large. Therefore, the output force of the hydraulic drive system is generally relatively large, so most of them use double-acting hydraulic cylinders, that is, the extension stroke and the retraction stroke are driven by hydraulic means. When the hydraulic drive system is working, it is very important to determine whether the piston has reached the end of stroke. At present, a contact switch is mainly used to detect whether the piston has reached the end of stroke, that is, if the piston reaches the end of stroke, the piston or the piston rod touches the contact switch to make the position switch send a signal. However, the contact switch is prone to failure after long-term use. Once the contact switch fails, the stop control will be invalid, which will cause the piston to contact the cylinder wall with a large force, causing noise and vibration, increasing fatigue, reducing the service life of the hydraulic system, causing leakage and many other problems, and even causing direct damage to the equipment. SUMMARY

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

[0005] In order to solve the above technical problems, the present application provides the following technical solutions.

[0006] In the first aspect, the present application provides a device for detecting the stroke end of a piston in a hydraulic system, the hydraulic system comprising a hydraulic cylinder and a piston arranged in the hydraulic cylinder, the piston dividing the space inside the hydraulic cylinder into a hydraulic chamber and a spring chamber, and a piston rod arranged in the spring chamber; the device further comprising:

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

[0008] an electrically controlled reversing valve, a first port of the electrically controlled reversing valve being connected to the hydraulic chamber, a second port of the electrically controlled reversing valve being connected to the spring chamber, a third port of the electrically controlled reversing valve being connected to an oil tank through a hydraulic pump, and a fourth port of the electrically controlled reversing valve being connected to the oil tank;

[0009] a pressure sensor for detecting the pressure value of the hydraulic oil in the hydraulic chamber;

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

[0011] the controller being configured to control the state of the electrically controlled reversing valve to switch the moving direction of the piston, and determine whether the piston reaches the stroke end according to whether the pressure value reaches a peak value when the piston moves towards the spring chamber, and determine whether the piston reaches the stroke end according to whether the difference between the pressure value and the normal pressure value of the oil tank is less than a difference threshold value when the piston moves towards the hydraulic chamber.

[0012] In some embodiments, the device for detecting the stroke end of a piston in a hydraulic system further comprises:

[0013] a flow meter for detecting the flow value of the hydraulic oil flowing out of the hydraulic chamber;

[0014] the controller being connected to the flow meter;

[0015] the controller being further configured to determine whether the piston reaches the stroke end according to whether the flow value detected by the flow meter is lower than a set threshold value when the piston moves towards the hydraulic chamber.

[0016] In some embodiments, the device for detecting the stroke end of a piston in a hydraulic system further comprises a piston valve rod and a valve seat arranged on the piston; the hydraulic chamber is supplied with hydraulic oil pumped by the hydraulic pump, the piston valve rod moves towards the valve seat under the action of the hydraulic oil and is in sealing connection with the valve seat; and the end of the piston valve rod extends to the outside of the piston.

[0017] In some embodiments, the detection device for the end of stroke of the hydraulic system piston, the piston rod outlet portion of the spring cavity is formed with a first limiting portion, the diameter of the first limiting portion is smaller than the diameter of the spring cavity, and the end face of the first limiting portion is adapted to abut against the piston valve rod when the piston reaches the end of stroke.

[0018] In some embodiments, the detection device for the end of stroke of the hydraulic system piston, the piston is formed with a boss at one end in the hydraulic cavity;

[0019] The cylinder wall of the hydraulic cavity is formed with a concave cavity corresponding to the boss.

[0020] In some embodiments, the detection device for the end of stroke of the hydraulic system piston, the pressure sensor is arranged between the hydraulic cavity and the first port of the electrically controlled reversing valve.

[0021] In a second aspect, the technical scheme of the present application provides a method for detecting the end of stroke of the hydraulic system piston, which is applied to the detection device for the end of stroke of the hydraulic system piston according to any one of the first aspect, and comprises the following steps:

[0022] Controlling the electrically controlled reversing valve to act, so that the first port of the electrically controlled reversing valve is in communication with the third port;

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

[0024] Receiving the pressure value of the hydraulic oil in the hydraulic cavity sent by the pressure sensor, judging whether the pressure value reaches 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 stroke of compressing liquid hydrogen;

[0025] Controlling the hydraulic pump to stop, and controlling the electrically controlled reversing valve to act, so that the communication between the first port and the third port of the electrically controlled reversing valve is disconnected, and the first port is in communication with the fourth port;

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

[0027] Judging whether the difference between the pressure value and the normal pressure value of the oil tank is less than a difference threshold value, and taking the time when the difference between the pressure value and the normal pressure value of the oil tank is less than the difference threshold value as the time when the piston reaches the end of stroke of sucking liquid hydrogen.

[0028] In some embodiments, the method for detecting the end of stroke of the hydraulic system piston further comprises the following steps:

[0029] Receiving the flow value of the hydraulic oil flowing out of the hydraulic cavity sent by the flow meter;

[0030] determining whether the flow value is lower than a set threshold value, and taking the time point when the flow value is lower than the set threshold value as the time point when the piston reaches the stroke end of the suction liquid hydrogen.

[0031] In some embodiments, the method for detecting the stroke end of the piston of the hydraulic system comprises determining whether the pressure value reaches a peak value by the following method:

[0032] determining a comparison parameter B1 of the pressure value change rate according to the pressure value change rate at the historical time point;

[0033] obtaining the pressure value change rate B2 at the current time point;

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

[0035] In some embodiments, the method for detecting the stroke end of the piston of the hydraulic system comprises determining whether the pressure value reaches a peak value by the following method:

[0036] obtaining the piston displacement value X at the current time point and the pressure value change rate B2 at the current time point;

[0037] determining a comparison parameter B1 of the pressure value change rate according to the pressure value change rate at the historical time point;

[0038] if B2 < [B1-β1] and X1-β2 < X < X1+β2, it is determined that the pressure value reaches a peak value, wherein β1 and β2 represent redundancy coefficients, and X1 represents a pre-stored stroke end comparison parameter.

[0039] In some embodiments, the method for detecting the stroke end of the piston of the hydraulic system comprises:

[0040] The comparison parameter B1 of the pressure value change rate is determined according to the pressure value change rate at the historical time point, and comprises:

[0041] obtaining the average pressure value change rate at the historical time point wherein (n-1) represents (n-1) historical time points before the current time point, i represents the i-th historical time point, p represents the real-time detection value of the pressure value, and t represents time;

[0042] the average pressure value change rate is taken as the comparison parameter of the pressure value change rate; or

[0043] the median of the pressure value change rate at the historical time point is obtained, and the median of the pressure value change rate is taken as the comparison parameter of the pressure value change rate; or

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

[0045] The median of the end point of the compression liquid hydrogen stroke is taken as the pre-stored end point reference parameter.

[0046] In some schemes, the method for detecting the end point of the hydraulic system piston stroke includes:

[0047] The piston displacement value X at the current time and the pressure value P at the current time are obtained.

[0048] The total amount L1 of hydraulic oil released from the hydraulic cavity to the oil tank is obtained.

[0049] The piston displacement value X at the current time is obtained.

[0050] 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 oil tank and the flow value is below the set threshold value; wherein P1 is the normal pressure value of the oil tank, L is the volume of the cylinder, X2 is the median of the end point of the liquid hydrogen suction stroke, F is the flow value, and β3, β4, β5, and β6 are redundancy coefficients.

[0051] The technical scheme of the present application has the following technical effects relative to the prior art:

[0052] The hydraulic system piston stroke end point detection device and method provided by the present application divides the internal space of the hydraulic cylinder into a hydraulic cavity and a spring cavity by using a piston, so that hydraulic driving can be used in the liquid hydrogen compression stroke, and spring driving can be used in the liquid hydrogen suction stroke. In the liquid hydrogen compression stroke, 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 liquid hydrogen suction stroke, when the difference between the pressure value of the hydraulic oil in the hydraulic cavity and the normal pressure value of the oil tank is less than the difference threshold value, it can be indicated that the piston reaches the end point of the stroke. On this basis, only the oil line connected to the hydraulic cavity needs to be detected by using a pressure sensor. Compared with a traditional contact type switch, the pressure sensor has higher stability and longer service life, and because it is installed externally, it is easy to replace and maintain. BRIEF DESCRIPTION OF DRAWINGS

[0053] The preferred embodiments of the present application will be described in detail below with the help of the accompanying drawings, which will help to understand the purposes and advantages of the present application, in which:

[0054] Figure 1 The structure diagram of the hydraulic system piston stroke end point detection device according to an embodiment of the present application;

[0055] Figure 2 The structure diagram of the hydraulic system piston stroke end point detection device according to another embodiment of the present application;

[0056] Figure 3 Flow chart of the method for detecting the end of the piston stroke of the hydraulic system according to an embodiment of the present application;

[0057] Figure 4 Flow chart of the method for detecting the end of the piston stroke of the hydraulic system according to another embodiment of the present application. DETAILED DESCRIPTION

[0058] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall 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" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0060] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication between the two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the 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 embodiments of the present application provide a kind of detection device for the end of the piston stroke of the hydraulic system, such as Figure 1As shown in the figure, the hydraulic system comprises a hydraulic cylinder 101 and a piston arranged in the hydraulic cylinder 101, the piston divides the space inside the hydraulic cylinder 101 into a hydraulic chamber 102 and a spring chamber, and a piston rod 103 is arranged in the spring chamber; the detection device further comprises a hydraulic pump 104, an electrically controlled 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 electrically controlled reversing valve 105 is connected with the hydraulic chamber 102 at a first port, connected with the spring chamber at a second port, connected with the oil tank 107 through the hydraulic pump 104 at a third port, and connected with the oil tank 107 at a fourth port. 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 with the pressure sensor 106 and the electrically controlled reversing valve 105. The controller 200 is used to control the state of the electrically controlled reversing valve 105 to switch the moving direction of the piston; when the piston moves in the direction of the spring chamber, it is determined whether the piston reaches the end of stroke according to whether the pressure value reaches a peak value; when the piston moves in the direction of the hydraulic chamber 102, it is determined whether the piston reaches the end of stroke according to whether the difference between the pressure value and the normal pressure value of the oil tank 107 is less than a difference threshold value.

[0063] Preferably, as Figure 2 As shown in the figure, the device further comprises a flow meter 110 used to detect the flow value of the hydraulic oil flowing out of the hydraulic chamber 102; the controller 200 is connected with the flow meter 110; when the piston moves in the direction of the hydraulic chamber 102, the controller 200 is further used to determine whether the piston reaches the end of stroke according to whether the flow value detected by the flow meter 110 is lower than a set threshold value.

[0064] As a preferred scheme, a piston valve rod 108 and a valve seat are arranged on the piston; the hydraulic chamber 102 inputs the hydraulic oil pumped by the hydraulic pump 104, the piston valve rod 108 moves to the valve seat under the action of the hydraulic oil and is in sealed connection with the valve seat; the end of the piston valve rod 108 extends to the outside of the piston.

[0065] As shown in the figure, the hydraulic pump 104, the electrically controlled reversing valve 105 and the pressure sensor 106 are all connected with the controller 200, the hydraulic pump 104 is connected between the oil tank 107 and the hydraulic chamber 102, and the hydraulic pump 104 delivers the hydraulic oil in the oil tank 107 to the hydraulic chamber 102. As shown in Fig. 1, when the hydraulic chamber 102 on the left side of the piston is injected with high-pressure hydraulic oil, under the pushing of the hydraulic oil, the piston valve rod 108 is pressed to the right to the valve seat, and the valve is closed. As shown in the figure, because the spring chamber on the right side of the piston is connected with the oil tank 107, the pressure is very low, so the pressure difference between the two sides of the piston is large, and the piston is subjected to a large rightward pushing force under the action of the large pressure difference, and the piston moves to the right. When the piston reaches the end of the stroke, because the piston valve rod 108 extends out of the piston by a small part, the piston valve rod 108 will first contact the cylinder wall to stop moving, and at this time, when the piston continues to move to the right, the sealing surface on the piston valve rod 108 will be separated from the valve seat on the piston, and the valve is opened. The hydraulic oil on the left side of the piston flows to the right side of the piston through the flow channel opened by the piston valve rod, the pressure on the two sides of the piston is balanced, the piston loses the pushing force under the action of the pressure difference, and the piston stops.

[0066] In the above-mentioned hydraulic driving stroke of 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, and because the spring 109 in the spring chamber on the right side is subjected to extrusion, the reaction force of the spring 109 increases continuously, and the pressure signal of the hydraulic oil also increases continuously. When the piston reaches the end of the stroke, the piston valve rod 108 is opened, 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 rises, the pressure on the left side is relieved, the pressure difference between the two sides of the piston decreases suddenly, and the piston stops moving. By monitoring the pressure change, the peak moment of the pressure value of the hydraulic oil in the hydraulic chamber 102 can be clearly judged, and the moment is the last moment before the piston valve rod 108 is opened. Subsequently, the pressure of the hydraulic oil in the hydraulic chamber 102 decreases rapidly, which shows the pressure relief condition after the piston valve rod 108 is opened. The present scheme is to judge the compression of liquid hydrogen according to this principle.

[0067] When the controller 200 determines that the piston stops 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 having a constant pressure value, so that the high pressure in the hydraulic oil in the hydraulic chamber 102 is released. The piston immediately moves to the left under the elastic force of the spring 109. At this time, the hydraulic oil in the hydraulic chamber 102 starts to flow to the oil tank 107 under the pushing of the piston, and the flow rate thereof is determined by the pressure acting on the hydraulic oil after the elastic force of the spring 109 is transmitted to the piston, which is much smaller than the high pressure in the hydraulic driving stroke due to the small flow resistance of the hydraulic oil. At the same time, in the preferred embodiment, the controller 200 monitors the flow rate of the hydraulic oil at any time through the flow meter 110 (which can be a vortex flow meter). During this process, the pressure of the hydraulic oil is continuously reduced, and the flow rate of the hydraulic oil is continuously reduced, and as the piston stops moving, the pressure reaches a static pressure in the oil tank 107, i.e. the pressure value of the hydraulic oil is consistent with the constant pressure value of the oil tank, and at the same time, since there is no more hydraulic oil flowing in the hydraulic chamber, the flow rate value detected by the flow meter 110 also reaches almost zero point. Therefore, at least one of the pressure value and the flow rate value can be selected to determine the end of the stroke, and the present application determines the end of the stroke of the piston based on this feature.

[0068] The above scheme of the present embodiment divides the internal space of the hydraulic cylinder 101 into the hydraulic chamber 102 and the spring chamber by the piston, so that the hydraulic driving can be used in the compression stroke of the liquid hydrogen, and the spring 109 driving can be used in the suction stroke of the liquid hydrogen. In the compression stroke of the liquid hydrogen, when the pressure value of the hydraulic oil in the hydraulic chamber 102 reaches the peak value, it can be indicated that the piston reaches the end of the stroke, and in the suction stroke of the liquid hydrogen, when the flow rate of the hydraulic oil flowing out of the hydraulic chamber 102 is lower than the set threshold value and the pressure value of the hydraulic oil in the hydraulic chamber 102 is consistent with the constant pressure value of the oil tank 107, it can be indicated that the piston reaches the end of the stroke, and on this basis, only the oil line connected to the hydraulic chamber needs to be detected by the flow meter and the pressure sensor 106, and the pressure sensor 106 has higher stability and longer service life compared with the traditional contact switch, and since it is installed far away from the pump body on the hydraulic driving system, its maintenance and replacement are very easy. Therefore, the present scheme can improve the accuracy and reliability of the detection result of the end of the piston stroke.

[0069] Preferably, the piston rod outlet portion of the spring cavity is formed with a first limiting portion, the caliber of the first limiting portion is smaller than that of the spring cavity, and the end face of the first limiting portion is adapted to abut against the piston valve rod 108 when the piston reaches the stroke end. Through this design, it can be ensured that when the piston valve rod 108 abuts against the cylinder wall, there is enough space in the spring cavity to receive the hydraulic oil from the hydraulic cavity 102, so that the sum of the pressure of the spring 109 in the spring cavity and the pressure of the hydraulic oil is balanced with the pressure in the hydraulic cavity 102.

[0070] Further preferably, as shown in Figure 1 and Figure 2 , the piston is formed with a boss at one end in the hydraulic cavity 102, and the cylinder wall of the hydraulic cavity 102 is formed with a concave cavity corresponding to the boss. In this way, when the piston driven by the spring 109 approaches the left end of the hydraulic cavity 102, the spring force of the spring 109 becomes very small, and the speed of the piston slows down. Before the piston contacts the left cylinder wall, the boss and the concave cavity act as a buffer. The boss has an outer diameter slightly smaller than that of the concave cavity, and when the boss is pressed into the concave cavity, the hydraulic oil in the concave cavity is squeezed out through the gap between the boss and the concave 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 scheme, the pressure sensor 106 and the flow meter 110 are arranged between the hydraulic cavity 102 and the first port of the electrically controlled reversing valve 105. Through this design, the pressure value of the hydraulic oil flowing into the hydraulic cavity 102 and the flow value of the hydraulic oil flowing out of the hydraulic cavity 102 can be accurately detected.

[0072] The embodiments of the present application also provide a detection method for the stroke end of a piston of a hydraulic system, which is applied to the detection device for the stroke end of a piston of a hydraulic system in any one of the above embodiments, as shown in Figure 3 , the method comprises the following steps:

[0073] S10: Control the electrically controlled reversing valve to act, so that the first port of the electrically controlled reversing valve communicates with the third port.

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

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

[0076] After the hydraulic pump 104 starts, the hydraulic oil in the oil tank can be pumped to the hydraulic cavity 102.

[0077] S30: receiving the pressure value of the hydraulic oil in the hydraulic chamber sent by the pressure sensor, judging whether the pressure value reaches a peak value (which can be used as a PX judgment condition), and taking the time when the pressure value reaches the peak value as the time when the piston reaches the stroke end point of compressing the liquid hydrogen.

[0078] The pressure value between the pressure sensor 106 and the hydraulic chamber 102 should have a consistent relationship, so the pressure sensor 106 is arranged on the passage communicating with the hydraulic chamber 102 to detect the pressure value of the hydraulic chamber 102. In combination with the foregoing piston movement process, when the piston reaches the stroke end point, the piston valve rod 108 is pushed away, the piston valve rod 108 opens the passage between the hydraulic chamber and the spring chamber, the hydraulic oil flows from the hydraulic chamber into the spring chamber, so that the pressure value of the hydraulic chamber changes from a state of continuously rising to a state of falling, so the time when the piston reaches the stroke end point can be determined by detecting the peak value of the pressure value.

[0079] S40: controlling the hydraulic pump to stop, and controlling the electrically controlled reversing valve to act, disconnecting the passage between the first port and the third port of the electrically controlled reversing valve, and making the first port communicate with the fourth port.

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

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

[0082] The pressure sensor 106 is always in communication with the hydraulic chamber 102, so the pressure value can be measured.

[0083] S60: judging whether the difference between the pressure value and the normal pressure value of the oil tank is less than a difference threshold value, and taking the time when the difference between the pressure value and the normal pressure value of the oil tank is less than the difference threshold value as the time when the piston reaches the stroke end point of sucking in the liquid hydrogen.

[0084] As mentioned before, if the piston reaches the end point on the 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. In theory, the pressure value should be equal to the normal pressure value, and in actual application, considering the error reason, the piston can be considered to have reached the stroke end point when the difference between the pressure value and the normal pressure value is less than the difference threshold value.

[0085] Preferably, the method further comprises: receiving a flow value of the hydraulic oil flowing out of the hydraulic chamber sent by the flow meter; determining whether the flow value is lower than a set threshold value, and taking the time when the flow value is lower than the set threshold value as the time when the piston reaches the stroke end of the suction of liquid hydrogen. When the piston reaches the left end, the hydraulic oil in the hydraulic chamber 102 is zero, so there is no longer any hydraulic oil flowing out, so the flow value detected by the flow meter should also be theoretically zero. Considering the error reasons, the case that it is less than a proper threshold value can be used as the judgment basis for the piston reaching the stroke end.

[0086] In the above scheme, the controller uses the PX judgment condition to detect and judge whether the piston reaches the end during the right movement of the piston to perform the stroke of compressing liquid hydrogen, and uses the PFX judgment condition to detect and judge whether the piston reaches the end during the left movement of the piston to perform the stroke of sucking liquid hydrogen, that is, the two judgment conditions are alternately used to determine two different strokes in one working cycle, which can be called alternating composite criterion, and has the effects of simplicity and accuracy.

[0087] Preferably, the data of two stroke processes and parameters at the end point are stored in the controller, the statistical analysis and calculation can be performed according to the parameter data, the movement position of the piston can be calculated, so that the judgment of whether the piston reaches the end point of the stroke is more accurate, and the control is more accurate. Specifically, the parameters can include the instantaneous flow of hydraulic oil F (which can be detected 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 detected by a pressure sensor), the normal pressure value P1 of the hydraulic oil storage tank (an empirical value, which can also be determined by real-time detection of the pressure sensor arranged in the tank), the liquid hydrogen container pressure P2 (an empirical value, which can also be determined by real-time detection of the pressure sensor arranged in the container), the liquid hydrogen liquid level static pressure P3 (an empirical value, which can also be determined by real-time detection of the pressure sensor arranged in the container), the hydraulic pump outlet pressure P4 (an empirical value, which can also be determined by real-time detection of the pressure sensor arranged at the outlet of the hydraulic pump), the pump outlet check valve pressure drop P5 (which can be determined by real-time detection of the pressure sensor arranged at the check valve), the tank pump jacket pressure P6 (which can be determined by real-time detection of the pressure sensor arranged at the jacket), the spring output force Fs (which is determined by calculation), the hydraulic piston area S1 (which is a known parameter and can be determined by the design parameters of the hydraulic cylinder), the cold end piston area S2 (which is a known parameter and can be determined by the design parameters of the hydraulic cylinder), the spring elastic coefficient K (which is a known parameter and can be determined by the design parameters of the hydraulic cylinder), the length X of the spring compression or stretching (which is determined by calculation), the median values of the two end positions of the piston are X1 and X2 (which can be determined by historical detection data), the spring force Fs (which is calculated), the compression stroke movement friction resistance Ff1 (which is a known parameter and can be determined by the design parameters of the hydraulic cylinder), the suction stroke movement friction resistance Ff2 (which is a known parameter and can be determined by the design parameters of the hydraulic cylinder), the total mass m of the piston linkage system (which is a known parameter and can be determined by the design parameters of the hydraulic cylinder), the piston speed V1 in the compression stroke of the liquid hydrogen (which is calculated), the piston speed V2 in the suction stroke of the liquid hydrogen (which is calculated), the time t, the coefficients β1, β2, β3, β4, β5, β6, β7, β8, β9, β 10 , β 11 , β 12 , β 13 The following relationships exist:

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

[0089] The displacement calculation formula of the piston in the compression stroke of the liquid hydrogen is X = [P × S1 + (P6 - P2 - P3 - P4 - P5 × β 13) x S2-β6 x V2-β7-m(dV / dt)] / K; here, the displacement calculation formula of the piston is mainly calculated by using the pressure value in the hydraulic cavity, in order to improve the accuracy of the piston displacement calculation, after obtaining the calculation result, the flow value detected by the flow meter can also be verified. Because the volume of the hydraulic cavity changes during the movement of the piston, because the volume change rate is changed, the hydraulic oil flow of the hydraulic cavity is also changed, the moving speed of the piston and the flow value have corresponding relationship, so the piston displacement also has corresponding relationship with the flow value. According to this principle, the piston displacement can be obtained by pressure value and flow value, and each other is checked, so that the obtained piston displacement is more accurate.

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

[0091] PX judgment condition when the piston valve rod is opened when the stroke of the piston compressing liquid hydrogen reaches the end point: dP / dt<[average(dP / dt)-β1], X1-β2<X<X1+β2;

[0092] PX judgment condition can also be written as follows: average dP / dt<0, X1-β2<X<X1+β2;

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

[0094] In the above scheme, whether the pressure value reaches the peak value is judged by 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 time.

[0096] S12: obtain the pressure value change rate B2 at the current time.

[0097] S13: if B2<[B1-β1], it is judged that the pressure value reaches the peak value, wherein β1 represents the redundancy coefficient.

[0098] Or:

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

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

[0101] S23: if B2 < [B1-β1] and X1-β2 < X < X1+β2, then determine that the pressure value reaches the peak value, wherein β1 and β2 represent redundancy coefficients, and X1 represents a pre-stored stroke end control parameter.

[0102] The control parameter B1 of the pressure value change rate is determined according to a pressure value change rate of a historical moment, and includes:

[0103] The average pressure value change rate of the historical moment is obtained Wherein, (n-1) represents a total of (n-1) historical moments before the current moment, i represents the i-th historical moment, p represents a real-time detection value of the pressure value, and t represents time; the average pressure value change rate is used as the control parameter of the pressure value change rate;

[0104] Or,

[0105] The median of the pressure value change rate of the historical moment is obtained, and the median of the pressure value change rate is used as the control parameter of the pressure value change rate;

[0106] Or,

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

[0108] The median of the stroke end of the compressed liquid hydrogen is used as the pre-stored stroke end control parameter.

[0109] In combination with Figure 4 As shown in the figure, P condition is to determine whether the pressure value change rate meets the condition, and X condition is to determine whether the piston displacement meets the condition.

[0110] Further, according to the above parameters, the stroke process of inhaling liquid hydrogen can also be calculated:

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

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

[0113] In 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 < 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 normal pressure value of the oil tank and whether the flow value is lower than the set threshold value includes:

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

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

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

[0121] S34: If P

[0122] In combination with Figure 4 Wherein, 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 compound criterion of the scheme can judge the specific position of the piston at any time. By using the above formula, the scheme can not only judge whether the piston reaches the stroke end point, but also can calculate the piston position at any position in the middle process of the stroke. When the number of cycles gradually increases, the above coefficients can be optimized to improve the detection accuracy. Compared with the piston stroke end point judgment structure of the prior art, the structure of the scheme is simpler, the piston valve rod is lighter in mass, smaller in size, shorter in opening and closing time, can improve the response speed of the hydraulic driving system, reduce the hysteresis, and improve the system response time.

[0123] Obviously, the above embodiments are only examples for clearly illustrating, and not limit the embodiments. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made. Here, all the embodiments need not and cannot be exhausted. The 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 piston stroke in a hydraulic system, the hydraulic system comprising a hydraulic cylinder and a piston disposed within the hydraulic cylinder, the piston dividing the internal space of the hydraulic cylinder into a hydraulic chamber and a spring chamber, the spring chamber containing a piston rod; characterized in that, The detection device further includes: A spring is disposed outside the piston rod, with one end of the spring abutting against the piston and the other end abutting against the cylinder wall of the hydraulic cylinder; An electrically controlled directional valve has a first port connected to the hydraulic chamber, a second port connected to the spring chamber, a third port connected to the oil tank via a hydraulic pump, and a fourth port connected to the oil tank. Pressure sensor is used to detect the pressure value of hydraulic oil in the hydraulic chamber; The controller is connected to the pressure sensor and the electrically controlled directional valve. The controller is used to control the state of the electronically controlled directional valve to switch the movement direction of the piston; when the piston moves towards the spring chamber, it is determined whether the piston has reached the end of its stroke based on whether the pressure value reaches the peak value; when the piston moves towards the hydraulic chamber, it is determined whether the piston has reached the end of its stroke based on whether the difference between the pressure value and the constant pressure value of the oil tank is less than the difference threshold.

2. The detection device for the end point of piston stroke in a hydraulic system according to claim 1, characterized in that, Also includes: A flow meter is used to detect the flow rate of hydraulic oil flowing out of the hydraulic chamber; The controller is connected to the flow meter; As the piston moves toward the hydraulic chamber, the controller is also configured to determine whether the piston has reached the end of its stroke based on whether the flow rate detected by the flow meter is lower than a set threshold.

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

4. The detection device for the end point of piston stroke in a hydraulic system according to claim 3, characterized in that: The piston rod outlet portion of the spring cavity is formed with a first limiting portion, the diameter of the first limiting portion being smaller than the diameter of the spring cavity, and the end face of the first limiting portion being adapted to abut against the piston valve rod when the piston reaches the end of its stroke.

5. The detection device for the end point of piston stroke in a hydraulic system according to any one of claims 1-4, characterized in that: The piston has a boss formed at one end located in the hydraulic chamber; The cylinder wall of the hydraulic chamber has a recessed cavity formed at a position corresponding to the boss, which matches the boss.

6. A method for detecting the end point of piston stroke in a hydraulic system, characterized in that, The method is applied to the detection device for the end point of piston stroke in a hydraulic system according to any one of claims 1-5, comprising: Control the operation of the electrically controlled directional valve to connect the first port and the third port of the electrically controlled directional valve; The hydraulic pump is started and pumps hydraulic oil from the tank to the hydraulic chamber of the hydraulic cylinder via the electronically controlled directional valve. The pressure value of the hydraulic oil in the hydraulic chamber is received from the pressure sensor, it is determined whether the pressure value has reached the peak value, and the moment when the pressure value reaches the peak value is taken as the moment when the piston reaches the end of the stroke of the compressed liquid hydrogen. The hydraulic pump is shut down, and the electrically controlled directional valve is activated to disconnect the passage between the first and third ports of the electrically controlled directional valve, thereby connecting the first port to the fourth port. Receive the pressure value of the hydraulic oil in the hydraulic chamber sent by the pressure sensor; Judge 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 piston stroke in 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 flowmeter; Judge 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 piston stroke in a hydraulic system according to claim 7, characterized in that, Judge whether the pressure value reaches the peak value by the following method: Determine the control 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 judged that the pressure value reaches the peak, where β1 represents the redundancy coefficient.

9. The method for detecting the end point of piston stroke in a hydraulic system according to claim 7, characterized in that, Judge whether the pressure value reaches the peak value by the following method: Obtain the piston displacement value X at the current moment and the pressure value change rate B2 at the current moment; Determine the control 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 judged that the pressure value reaches the peak, where β1 and β2 represent the redundancy coefficients, and X1 represents the pre-stored stroke end control parameter.

10. The method for detecting the end of the piston stroke of the hydraulic system according to claim 8 or 9, wherein: The determining the control parameter B1 of the pressure value change rate according to the pressure value change rate at the historical moment includes: Obtain the average rate of change of pressure values ​​at historical time points This indicates that there are (n-1) historical moments before the current moment, where i represents the i-th historical moment, p represents the real-time detected value of the pressure, and t represents time. Taking the average pressure value change rate as the control parameter of the pressure value change rate; or, Obtain the median of the pressure value change rate at the historical moment, and take the median of the pressure value change rate as the control parameter of the pressure value change rate; or, The redundancy coefficient β1 is equal to the control parameter B1; Taking the median of the end of the stroke of compressed liquid hydrogen as the pre-stored stroke end control parameter.

11. The method for detecting the end point of piston stroke in a hydraulic system according to claim 7, characterized in that, The judging 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: Obtain the piston displacement value X at the current moment and the pressure value P at the current moment; Obtain the total amount of hydraulic oil L1 released from the hydraulic chamber to the fuel tank; Obtain 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 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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