A boom energy recovery system and control strategy for a hydraulic excavator

Abstract

The present invention discloses a boom energy recovery system and a control strategy for a hydraulic excavator, which relates to the technical field of boom energy recovery of hydraulic excavators. The system includes an oil tank, an accumulator, a first energy recovery cylinder, an energy utilization cylinder, and a second energy recovery cylinder that are sequentially arranged below the boom and connected to the boom. The first energy recovery cylinder, the energy utilization cylinder, and the second energy recovery cylinder are connected to the oil tank and the accumulator through an oil delivery system. The oil delivery system includes a rod-end cylinder inlet and outlet oil pipe system, a rodless cylinder inlet oil pipe system of the energy recovery cylinder, a rodless cylinder inlet oil pipe system of the energy utilization cylinder, a rodless cylinder return oil pipe system of the energy utilization cylinder, and a rodless cylinder return oil pipe system of the energy recovery cylinder. By adopting the boom energy recovery system and the control strategy with the above structure, the present invention can reduce the back pressure of the return oil and the throttling loss, maintain the controllability of the whole machine, and improve the energy recovery efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of boom energy recovery for hydraulic excavators, and in particular to a boom energy recovery system and control strategy for hydraulic excavators. Background Art

[0002] The boom energy recovery system in the prior art is as Figure 2 shown. When the boom descends, the oil in the rodless chamber of the energy recovery cylinder is input and stored in the accumulator to realize the recovery of the boom potential energy. During the boom lifting process, the hydraulic oil stored in the accumulator is output and enters the rodless chamber of the energy utilization cylinder to realize the reuse of the recovered energy. Although this structure can use the accumulator to supply oil to the energy utilization cylinder to balance the weight of the working device itself during the boom rising process and reduce the load of the main pump. However, there are the following problems in use: In the load condition of the boom descending of the hydraulic excavator, theoretically, only a small throttling backpressure is required at the oil outlet of the boom cylinder to realize the speed control of the boom descending. However, in the existing single spool four-way slide valve control mode, the state of the oil outlet can only follow the state of the oil inlet for linkage, increasing the throttling loss. In addition, this energy recovery system adopts the traditional main spool linkage control. During the boom descending process, the hydraulic oil output by the energy utilization cylinder returns to the fuel tank through the boom main valve, which will inevitably generate a large oil return backpressure at the front end of the boom main valve. The combined action of this pressure and the accumulator backpressure will generate a greater oil return backpressure. Therefore, to maintain the overall machine controllability, it is necessary to further increase the output pressure of the main pump, which will affect the controllability to a certain extent and reduce the energy recovery effect at the same time.

[0003] To solve the above problems, a new type of boom energy recovery system for hydraulic excavators is needed. Summary of the Invention

[0004] The purpose of the present invention is to provide a boom energy recovery system and control strategy for hydraulic excavators, which reduce the oil return backpressure and throttling loss, maintain the overall machine controllability, and improve the energy recovery efficiency.

[0005] To achieve the above purpose, the present invention provides a boom energy recovery system for hydraulic excavators, including a fuel tank, an accumulator, and a first energy recovery cylinder, an energy utilization cylinder, and a second energy recovery cylinder that are sequentially arranged below the boom and connected to the boom. The first energy recovery cylinder, the energy utilization cylinder, and the second energy recovery cylinder are connected to the fuel tank and the accumulator through an oil delivery system. The oil delivery system includes a rod cylinder inlet and outlet pipe system, a rodless cylinder inlet pipe system of the energy recovery cylinder, a rodless cylinder inlet pipe system of the energy utilization cylinder, a rodless cylinder return pipe system of the energy utilization cylinder, and a rodless cylinder return pipe system of the energy recovery cylinder.

[0006] Preferably, the rod cylinder inlet and outlet oil pipe system includes a rod chamber oil pipe. One end of the rod chamber oil pipe is connected to the rod chamber oil ports at the tops of the first energy recovery cylinder, the energy utilization cylinder, and the second energy recovery cylinder respectively through three first branch pipes. The other end of the rod chamber oil pipe is connected to the first oil hole on the boom main valve. The second oil hole on the boom main valve is connected to the oil outlet hole of the fuel tank through the main pump. The third oil hole of the boom main valve is connected to the oil return hole of the fuel tank.

[0007] Preferably, the rodless cylinder inlet oil pipe system of the energy recovery cylinder includes a rodless chamber oil pipe of the energy recovery cylinder and an inlet oil pipe of the energy recovery cylinder. One end of the rodless chamber oil pipe of the energy recovery cylinder is connected to the rodless chamber oil ports of the first energy recovery cylinder and the second energy recovery cylinder respectively through two second branch pipes. The other end of the rodless chamber oil pipe of the energy recovery cylinder is connected to the first oil port on the energy control valve. The second oil port of the energy control valve is connected to the fourth oil hole of the boom main valve through the inlet oil pipe of the energy recovery cylinder;

[0008] When the right position of the boom main valve is opened, the first oil hole is connected to the second oil hole, and the third oil hole is connected to the fourth oil hole. The oil supplied by the main pump causes the boom to descend. When the left position of the boom main valve is opened, the second oil hole is connected to the fourth oil hole, and the first oil hole is connected to the third oil hole. The oil supplied by the main pump causes the boom to rise.

[0009] Preferably, the rodless cylinder inlet oil pipe system of the energy utilization cylinder includes a rodless chamber oil pipe of the energy utilization cylinder, an inlet oil pipe of the energy utilization cylinder, and an accumulator oil pipe. One end of the rodless chamber oil pipe of the energy utilization cylinder is connected to the rodless chamber oil port of the energy utilization cylinder. The other end of the rodless chamber oil pipe of the energy utilization cylinder is connected to the third oil port of the energy control valve through the inlet oil pipe of the energy utilization cylinder. The fourth oil port of the energy control valve is connected to the accumulator through the accumulator oil pipe;

[0010] When the right position of the energy control valve is opened, the first oil port and the fourth oil port on the energy control valve are connected, and the third oil port and the second oil port are not connected. When the left position of the energy control valve is opened, the first oil port and the second oil port on the energy control valve are connected, and the third oil port and the fourth oil port are connected.

[0011] Preferably, the rodless cylinder return oil pipe system of the energy utilization cylinder includes the rodless chamber oil pipe of the energy utilization cylinder and a return oil pipe of the energy utilization cylinder. One end of the rodless chamber oil pipe of the energy utilization cylinder is connected to the rodless chamber oil port of the energy utilization cylinder. The other end of the rodless chamber oil pipe of the energy utilization cylinder is connected to the fuel tank through the return oil pipe of the energy utilization cylinder, and a throttle speed control valve is provided on the return oil pipe of the energy utilization cylinder.

[0012] Preferably, the rodless cylinder oil return pipeline system of the energy recovery cylinder includes the rodless cavity oil pipeline of the energy recovery cylinder and the accumulator oil pipeline.

[0013] Preferably, a first anti-overflow oil pipeline with a first anti-overflow valve is provided between the rod cavity oil pipeline and the fuel tank, and a second anti-overflow oil pipeline with a second anti-overflow valve is provided between the energy recovery cylinder inlet oil pipeline and the fuel tank.

[0014] A control strategy for the boom energy recovery of a hydraulic excavator: when the boom descends, the boom main valve maintains the maximum opening according to the signal value of the pilot pressure of the operating handle, and changes the opening of the throttle speed control valve through a pressure adaptive energy recovery control strategy based on load observation to achieve the control of the boom descending speed and the main pump output flow. The specific method includes the following steps:

[0015] Step 1: Use sensors to detect the required signal values and transmit them to the controller. The signal values include the boom movement speed collected by the speed sensor , the pilot pressure of the operating handle when the boom descends collected by the first pressure sensor , the target pressure of the rod cavity collected by the second pressure sensor , the actual load pressure of the rodless cavity of the energy utilization cylinder collected by the third pressure sensor and the load pressure at the output port of the main pump collected by the fourth pressure sensor . The controller includes a load observer module, a throttle valve target pressure solving module, and a spool opening solving module;

[0016] Step 2: Use the load observer module to calculate the equivalent load term , and the calculation method is as follows:

[0017]

[0018] Where is the equivalent load term, is the external force load, is the accumulator acting force, represents the area of the rodless cavity of the energy utilization cylinder, represents the area of the rodless cavity of the first energy recovery cylinder or the second energy recovery cylinder, is the pressure at the accumulator port;

[0019] Step 3: Use the throttle valve target pressure solving module to calculate the throttle valve target pressure :

[0020]

[0021] Where, It represents the sum of the rod-side chamber areas of the first energy recovery cylinder, the second energy recovery cylinder, and the energy utilization cylinder; is the target rod-side chamber pressure measured in Step 1; m represents the equivalent mass of the working device acting on the oil cylinder; is the boom movement speed measured in Step 1; represents acceleration, which is obtained by differentiating ; represents the viscosity coefficient; is the equivalent load term calculated in Step 2; represents the area of the rodless chamber of the energy utilization cylinder;

[0022] Step 4: Compare the target pressure of the throttle speed control valve obtained in Step 3 with the actual load pressure of the rodless chamber of the energy utilization cylinder measured in Step 1. If is equal to , then do not change the opening of the throttle speed control valve. If is not equal to , then proceed to the next Step 5;

[0023] Step 5: When the pressure difference between and is positive, decrease the opening of the throttle speed control valve, increase the throttle pressure difference, and reduce the main pump output flow to thus reduce the boom lowering speed; when the pressure difference between and is negative, increase the opening of the throttle speed control valve, reduce the throttle pressure difference, and increase the main pump output flow to thus increase the boom lowering speed;

[0024] In this control process, the spool opening area of the flow control speed valve is calculated according to the following formula:

[0025]

[0026]

[0027] where, is the spool flow coefficient of the proportional speed control valve, is the density of the hydraulic oil, is the actual load pressure of the rodless chamber of the energy utilization cylinder measured in Step 1, is the target flow of the throttle speed control valve, is the proportional constant between the boom target speed and the pilot pressure of the operating handle, is the error threshold of the pilot pressure signal of the operating handle;

[0028] In this control process, the main pump is in the constant power control mode. After the opening of the throttle speed control valve changes, the boom movement speed Change, the controller controls the output flow of the main pump to change until the load pressure at the output port of the main pump collected by the fourth pressure sensor reaches the target value, The calculation method of the target value is as follows:

[0029]

[0030] wherein, is the load pressure at the output port of the main pump; is the rated maximum displacement of the main pump; is the engine speed, is the target flow rate of oil inlet for the three rod-end chambers, The calculation method is as follows:

[0031]

[0032] wherein, is the proportional constant between the target speed of the boom lowering and the pilot control pressure, is the pilot pressure of the operating handle when the boom is lowered, is the error threshold of the pilot pressure signal of the operating handle, represents the sum of the rod-end areas of the first energy recovery cylinder, the second energy recovery cylinder and the energy utilization cylinder.

[0033] A control strategy for energy recovery of the boom of a hydraulic excavator: When the boom rises, the opening of the proportional pressure reducing valve is changed through an energy reuse control strategy based on flow following. The specific method includes the following steps:

[0034] Step 1: Calculate the target flow rate of the oil inlet: A proportional pressure reducing valve is set on the control oil path between the operating handle and the boom main valve. The proportional pressure reducing valve is connected to the controller. The controller is provided with an oil inlet target flow rate operation module, a rodless chamber target pressure solving module and a proportional pressure reducing valve control signal solving module. The pilot pressure of the operating handle when the boom rises is collected by the first pressure sensor , and is input into the oil inlet target flow rate operation module to obtain the oil inlet target flow rate , and then is sent to the proportional pressure reducing valve control signal solving module, The calculation method is as follows:

[0035]

[0036] wherein, is the proportional constant between the target speed of the boom and the pilot pressure of the operating handle, is the error threshold of the pilot pressure signal of the operating handle, represents the rodless chamber area of the first energy recovery cylinder or the second energy recovery cylinder;

[0037] Step 2: Determine whether to adjust the proportional pressure reducing valve: Use the sixth pressure sensor to collect the actual pressure of the rodless chamber of the energy recovery cylinder at the oil pipe of the rodless chamber of the energy recovery cylinder , use the seventh pressure sensor to collect the load pressure at the output port of the main pump , the target pressure solving module for the rodless chamber receives , and the target flow rate at the inlet port output by the inlet port target flow rate operation module in Step 1 , and calculate the target flow rate at the inlet port of the rodless chamber of the energy recovery cylinder by the following method :

[0038]

[0039] Among them, is the flow coefficient of the boom main spool valve, is the opening area of the boom main valve spool under the control of the proportional pressure reducing valve;

[0040] Compare with . If is equal to , the judgment result is "do not adjust the proportional pressure reducing valve". If is not equal to , the judgment result is "adjust the proportional pressure reducing valve", and the inlet port target flow rate operation module transmits the judgment result to the proportional pressure reducing valve control signal solving module;

[0041] Step 3: Solve the proportional pressure reducing valve control signal: When the judgment result received by the proportional pressure reducing valve control signal solving module is "do not adjust the proportional pressure reducing valve", the proportional pressure reducing valve control signal solving module has no signal output, does not change the output of the proportional pressure reducing valve, and thus does not cause the displacement of the boom main valve spool, so as to avoid the increase of the throttling loss at the boom main valve port, and the system outputs the main pump flow rate according to the current constant power control mode; when the judgment result received by the proportional pressure reducing valve control signal solving module is "adjust the proportional pressure reducing valve", the proportional pressure reducing valve control signal solving module uses the received and the negative flow feedback pressure of the boom main valve detected by the fifth pressure sensor to solve the proportional pressure reducing valve control signal , and the controller controls the proportional pressure reducing valve to output a decrease or an increase according to . When the output of the proportional pressure reducing valve decreases, the spool displacement of the boom main valve decreases, and the flow rate of the boom main valve increases, resulting in the negative flow feedback pressure of the boom main valve detected by the fifth pressure sensor When it increases and the output of the proportional pressure reducing valve increases, the spool displacement of the boom main valve increases, and the flow rate of the boom main valve decreases, resulting in the negative flow feedback pressure of the boom main valve detected by the fifth pressure sensor decreases, and the system adjusts the main pump output flow rate according to the negative flow feedback pressure of the boom main valve until the main pump output flow rate and the negative flow feedback pressure of the boom main valve form a balance, where The calculation method is:

[0042]

[0043] where is the fitting function of the mapping relationship between the main pump negative flow signal and the main pump output flow rate

[0044] Therefore, the hydraulic excavator boom energy recovery system and control strategy with the above structure of the present invention have the following beneficial effects:

[0045] 1. By using the rodless cylinder inlet and outlet pipe systems, the rodless cylinder inlet pipe system of the energy recovery cylinder, the rodless cylinder inlet pipe system of the energy utilization cylinder, the rodless cylinder return pipe system of the energy utilization cylinder, and the rodless cylinder return pipe system of the energy recovery cylinder, the inlet and outlet oil can be controlled by two groups of spools respectively, and the positions of each spool can be adjusted according to the system state to realize the boom movement control. At the same time, the return oil back pressure and throttling loss are reduced, the main pump energy output is reduced, the controllability of the whole machine is maintained, and the energy recovery efficiency is improved;

[0046] 2. By using the pressure adaptive energy recovery control strategy based on independent inlet and outlet, the opening of the throttle speed control valve is changed to realize the control of the boom lowering speed and the main pump output flow rate, effectively reducing the inlet oil throttling loss of the boom main valve;

[0047] 3. By using the energy reuse control strategy based on flow following to control the opening of the proportional pressure reducing valve, the active control of the spool opening of the boom main valve and the negative flow feedback pressure of the boom main valve is realized, thereby changing the main pump output flow rate and maintaining the controllability of the whole machine.

[0048] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Brief Description of the Drawings

[0049] Figure 1 is a schematic diagram of an embodiment of the boom energy recovery system of the hydraulic excavator of the present invention;

[0050] Figure 2 is the boom energy recovery system of the hydraulic excavator in the prior art;

[0051] Figure 3 is a schematic diagram of an embodiment of the pressure adaptive energy recovery control strategy based on load observation of the present invention;

[0052] Figure 4 This is a schematic diagram of an embodiment of the energy reuse control strategy based on flow following of the present invention.

[0053] Reference numerals

[0054] 1. Fuel tank; 2. Accumulator; 3. Boom; 4. First energy recovery cylinder; 5. Energy utilization cylinder; 6. Second energy recovery cylinder; 7. Rod chamber oil pipe; 8. First branch pipe; 9. Boom main valve; 10. Rodless chamber oil pipe of energy recovery cylinder; 11. Inlet oil pipe of energy recovery cylinder; 12. Second branch pipe; 13. Energy control valve; 14. Rodless chamber oil pipe of energy utilization cylinder; 15. Inlet oil pipe of energy utilization cylinder; 16. Accumulator oil pipe; 17. Cartridge valve; 18. Pressure control valve; 19. Return oil pipe of energy utilization cylinder; 20. Throttle speed control valve; 21. First anti-overflow valve; 22. First anti-overflow oil pipe; 23. Second anti-overflow valve; 24. Second anti-overflow oil pipe; 25. Main pump; 26. Speed sensor; 27. First pressure sensor; 28. Second pressure sensor; 29. Third pressure sensor; 30. Fourth pressure sensor; 31. Control oil circuit; 32. Proportional pressure reducing valve; 33. Fifth pressure sensor; 34. Sixth pressure sensor; 35. Seventh pressure sensor. Detailed implementation manners

[0055] The technical solution of the present invention will be further described below with reference to the drawings and embodiments.

[0056] Embodiment

[0057] As Figure 1 shown, a boom energy recovery system of a hydraulic excavator includes a fuel tank 1, an accumulator 2, and a first energy recovery cylinder 4, an energy utilization cylinder 5, and a second energy recovery cylinder 6 that are sequentially arranged below the boom 3 and connected to the boom 3. The first energy recovery cylinder 4, the energy utilization cylinder 5, and the second energy recovery cylinder 6 are connected to the fuel tank 1 and the accumulator 2 through an oil delivery system. The oil delivery system includes a rod cylinder inlet and outlet oil pipe system, a rodless cylinder inlet oil pipe system of the energy recovery cylinder, a rodless cylinder inlet oil pipe system of the energy utilization cylinder 5, a rodless cylinder return oil pipe system of the energy utilization cylinder 5, and a rodless cylinder return oil pipe system of the energy recovery cylinder.

[0058] The rod cylinder inlet and outlet oil pipe system includes a rod chamber oil pipe 7. One end of the rod chamber oil pipe 7 is respectively connected to the rod chamber oil ports at the tops of the first energy recovery cylinder 4, the energy utilization cylinder 5, and the second energy recovery cylinder 6 through three first branch pipes 8. The other end of the rod chamber oil pipe 7 is connected to the first oil hole on the boom main valve 9. The second oil hole on the boom main valve 9 is connected to the oil outlet hole of the fuel tank 1 through the main pump 25. The third oil hole of the boom main valve 9 is connected to the oil return hole of the fuel tank 1.

[0059] The rodless cylinder inlet pipeline system of the energy recovery cylinder includes the rodless cavity oil pipe 10 of the energy recovery cylinder and the inlet oil pipe 11 of the energy recovery cylinder. One end of the rodless cavity oil pipe 10 of the energy recovery cylinder is connected to the rodless cavity oil ports of the first energy recovery cylinder 4 and the second energy recovery cylinder 6 respectively through two second branch pipes 12. The other end of the rodless cavity oil pipe 10 of the energy recovery cylinder is connected to the first oil port on the energy control valve 13. The second oil port of the energy control valve 13 is connected to the fourth oil hole of the boom main valve 9 through the inlet oil pipe 11 of the energy recovery cylinder;

[0060] When the right position of the boom main valve 9 is opened, the first oil hole is connected to the second oil hole, and the third oil hole is connected to the fourth oil hole. The oil supplied by the main pump 25 causes the boom 3 to descend. When the left position of the boom main valve 9 is opened, the second oil hole is connected to the fourth oil hole, and the first oil hole is connected to the third oil hole. The oil supplied by the main pump 25 causes the boom 3 to rise.

[0061] The rodless cylinder inlet pipeline system of the energy utilization cylinder 5 includes the rodless cavity oil pipe 14 of the energy utilization cylinder, the inlet oil pipe 15 of the energy utilization cylinder, and the accumulator oil pipe 16. One end of the rodless cavity oil pipe 14 of the energy utilization cylinder is connected to the rodless cavity oil port of the energy utilization cylinder 5. The other end of the rodless cavity oil pipe 14 of the energy utilization cylinder is connected to the third oil port of the energy control valve 13 through the inlet oil pipe 15 of the energy utilization cylinder. The fourth oil port of the energy control valve 13 is connected to the accumulator 2 through the accumulator oil pipe 16;

[0062] When the right position of the energy control valve 13 is opened, the first oil port and the fourth oil port on the energy control valve 13 are connected, and the third oil port and the second oil port are not connected. When the left position of the energy control valve 13 is opened, the first oil port and the second oil port on the energy control valve 13 are connected, and the third oil port and the fourth oil port are connected. In use, when the energy control valve 13 is in the right position, the oil in the rodless cavities of the first energy recovery cylinder 4 and the second energy recovery cylinder 6 can enter the accumulator 2 through the energy control valve 13 and the accumulator oil pipe 16. When the energy control valve 13 is in the left position, the oil in the accumulator 2 can enter the energy utilization cylinder 5 through the energy control valve 13, and the oil in the inlet oil pipe 11 of the energy recovery cylinder can enter the rodless cavities of the first energy recovery cylinder 4 and the second energy recovery cylinder 6 through the energy control valve 13, causing the boom 3 to rise.

[0063] The accumulator oil pipe 16 is provided with a cartridge valve 17. The accumulator oil pipe 16 includes a front section connected to the energy control valve 13 and a rear section connected to the accumulator 2. The A port of the cartridge valve 17 is connected to the front end, and the B port of the cartridge valve 17 is connected to the rear section. The X port of the cartridge valve 17 is connected to the oil tank 1 through a pressure control valve 18. The left position of the pressure control valve 18 is a first check valve, and the flow direction of the first check valve is from the oil tank 1 to the X port. The right position of the pressure control valve 18 is a blocking valve. The pressure control valve 18 is connected to the rear section through a control oil pipe with a second check valve, and the flow direction of the second check valve is from the second oil pipe to the pressure control valve 18. The combined use of the cartridge valve 17 and the pressure control valve 18 enables the oil in the accumulator 2 to flow in and out smoothly.

[0064] The rodless cylinder oil return system of the energy utilization cylinder 5 includes the rodless cavity oil pipe 14 of the energy utilization cylinder and the oil return pipe 19 of the energy utilization cylinder. One end of the rodless cavity oil pipe 14 of the energy utilization cylinder is connected to the rodless cavity oil port of the energy utilization cylinder 5, and the other end of the rodless cavity oil pipe 14 of the energy utilization cylinder is connected to the oil tank 1 through the oil return pipe 19 of the energy utilization cylinder, and a throttle speed control valve 20 is provided on the oil return pipe 19 of the energy utilization cylinder.

[0065] The rodless cylinder oil return system of the energy recovery cylinder includes the rodless cavity oil pipe 10 of the energy recovery cylinder and the accumulator oil pipe 16. When the boom 3 descends and the energy control valve 13 is in the right position, the rodless cylinder oil return system of the energy recovery cylinder enables the oil in the first energy recovery cylinder 4 and the second energy recovery cylinder 6 to return to the accumulator 2.

[0066] A first anti-overflow oil pipe 22 with a first anti-overflow valve 21 is provided between the rodless cylinder oil pipe 7 and the oil tank 1. The first anti-overflow oil pipe 22 can prevent the oil delivered by the main pump 25 from flowing back to the oil tank 1 through the first anti-overflow valve 21 when the boom 3 jams during the descent of the boom 3, instead of continuously delivering oil to the energy utilization cylinder 5, the first energy recovery cylinder 4, and the second energy recovery cylinder 6 and causing damage to the cylinder block. A second anti-overflow oil pipe 24 with a second anti-overflow valve 23 is provided between the energy recovery cylinder inlet oil pipe 11 and the oil tank 1. The second anti-overflow oil pipe 24 can prevent the oil delivered by the main pump 25 from flowing back to the oil tank 1 through the second anti-overflow valve 23 when the boom 3 jams during the ascent of the boom 3, instead of continuously delivering oil to the first energy recovery cylinder 4 and the second energy recovery cylinder 6 and causing damage to the cylinder block.

[0067] During operation, when the boom 3 descends, the main boom valve 9 and the energy control valve 13 are both in the right-position open state, the throttle speed control valve 20 is in the open state, and the main pump 25 causes the hydraulic oil in the fuel tank 1 to pass through the main boom valve 9, the rod-side cavity oil pipe 7, and the first branch pipe 8 in sequence and enter the rod-side cavities of the energy utilization cylinder 5, the first energy recovery cylinder 4, and the second energy recovery cylinder 6. The hydraulic oil in the rodless cavities of the first energy recovery cylinder 4 and the second energy recovery cylinder 6 passes through the second branch pipe 12, the rodless cavity oil pipe 10 of the energy recovery cylinder, the energy control valve 13, and the accumulator oil pipe 16 in sequence and enters the accumulator 2. The hydraulic oil in the rodless cavity of the energy utilization cylinder 5 returns to the fuel tank 1 through the return oil pipe 19 of the energy utilization cylinder; when the boom 3 ascends, the main boom valve 9 and the energy control valve 13 are both in the left-position open state, the throttle speed control valve 20 is in the closed state, and the main pump 25 causes the hydraulic oil in the fuel tank 1 to pass through the main boom valve 9, the oil pipe 11 for the energy recovery cylinder, the energy control valve 13, the rodless cavity oil pipe 10 of the energy recovery cylinder, and the second branch pipe 12 in sequence and enter the rodless cavities of the first energy recovery cylinder 4 and the second energy recovery cylinder 6. The hydraulic oil in the accumulator 2 passes through the accumulator oil pipe 16, the energy control valve 13, the oil pipe 15 for the energy utilization cylinder, and the rodless cavity oil pipe 14 of the energy utilization cylinder in sequence and enters the rodless cavity of the energy utilization cylinder 5. The hydraulic oil in the rod-side cavities of the energy utilization cylinder 5, the first energy recovery cylinder 4, and the second energy recovery cylinder 6 passes through the first branch pipe 8, the rod-side cavity oil pipe 7, and the main boom valve 9 and returns to the fuel tank 1 in sequence.

[0068] As Figure 3 shown, an energy recovery control strategy for the boom 3 of a hydraulic excavator: when the boom 3 descends, the main boom valve 9 maintains the maximum opening according to the signal value of the pilot pressure of the operating handle, and changes the opening of the throttle speed control valve 20 through a pressure adaptive energy recovery control strategy based on load observation to achieve the control of the descending speed of the boom 3 and the output flow of the main pump 25. The specific method includes the following steps:

[0069] Step 1: Use sensors to detect the required signal values and transmit them to the calculation module of the controller. The signal values include the movement speed of the boom 3 collected by the speed sensor 26 , the pilot pressure of the operating handle when the boom 3 descends collected by the first pressure sensor 27 , the target pressure of the rod-side cavity collected by the second pressure sensor 28 , the actual load pressure of the rodless cavity of the energy utilization cylinder 5 collected by the third pressure sensor 29 , and the load pressure at the output port of the main pump collected by the fourth pressure sensor 30 . The calculation module includes a load observer module, a target pressure solving module for the speed control valve, and a spool opening solving module;

[0070] Step 2: Use the load observer module to calculate the equivalent load term , the calculation method is as follows:

[0071]

[0072] Among them is the equivalent load term, is the external force load, is the force of the accumulator 2, represents the area of the rodless cavity of the energy utilization cylinder 5, represents the area of the rodless cavity of the first energy recovery cylinder 4 or the second energy recovery cylinder, is the pressure at the port of the accumulator 2;

[0073] Step 3: Calculate the target pressure of the throttle speed control valve 20 using the throttle speed control valve target pressure solving module :

[0074]

[0075] Among them, represents the sum of the areas of the rod chambers of the first energy recovery cylinder 4, the second energy recovery cylinder 6 and the energy utilization cylinder 5; is the target pressure of the rod chamber measured in Step 1; m represents the equivalent mass of the working device acting on the oil cylinder; is the moving speed of the boom 3 measured in Step 1; represents the acceleration, obtained by differentiating ; represents the viscosity coefficient; is the equivalent load term calculated in Step 2; represents the area of the rodless cavity of the energy utilization cylinder 5;

[0076] Step 4: Compare the target pressure of the throttle speed control valve 20 obtained in Step 3 with the actual load pressure of the rodless cavity of the energy utilization cylinder 5 measured in Step 1. If is equal to , then the opening of the throttle speed control valve 20 remains unchanged. If is not equal to , then proceed to the next Step 5;

[0077] Step 5: When and the pressure difference is positive, decrease the opening of the throttle speed control valve 20, increase the throttling pressure difference, and reduce the output flow of the main pump 25 to thus reduce the lowering speed of the boom 3; when and the pressure difference is negative, increase the opening of the throttle speed control valve 20, reduce the throttling pressure difference, and increase the output flow of the main pump 25 to thus increase the lowering speed of the boom 3;

[0078] During this control process, the spool opening area of the flow control throttle valve is calculated according to the following formula:

[0079]

[0080]

[0081] where is the flow coefficient of the spool of the proportional throttle valve, is the density of the hydraulic oil, is the actual load pressure of the rodless chamber of the energy utilization cylinder 5 measured in step 1, is the target flow rate of the throttle valve 20, is the proportional constant of the target speed of the boom 3 and the pilot pressure of the operating handle, is the error threshold of the pilot pressure signal of the operating handle;

[0082] During this control process, the main pump 25 is in the constant power control mode. After the opening of the throttle valve 20 changes, the movement speed of the boom 3 collected by the speed sensor 26 changes, and the controller controls the output flow rate of the main pump 25 to change until the load pressure at the output port of the main pump collected by the fourth pressure sensor 30 reaches the target value, The calculation method of the target value of

[0083]

[0084] where is the load pressure at the output port of the main pump; is the rated maximum displacement of the main pump 25; is the engine speed, is the target flow rate of the oil inlet of the three rod chambers, The calculation method of

[0085]

[0086] where is the proportional constant of the target descending speed of the boom 3 and the pilot control pressure, is the pilot pressure of the operating handle when the boom 3 descends, is the error threshold of the pilot pressure signal of the operating handle, represents the sum of the rod chamber areas of the first energy recovery cylinder 4, the second energy recovery cylinder 6 and the energy utilization cylinder 5.

[0087] Such as Figure 4As shown in the figure, an energy recovery control strategy for the boom 3 of a hydraulic excavator: when the boom 3 rises, the opening degree of the proportional pressure reducing valve 32 is changed through an energy reuse control strategy based on flow following to control the rising speed of the boom 3 and the output flow of the main pump 25. The specific method includes the following steps:

[0088] Step 1: Calculate the target flow rate at the inlet port: A proportional pressure reducing valve 32 is set on the control oil circuit 31 between the operation handle and the boom main valve 9. The proportional pressure reducing valve 32 is connected to the controller. The controller is provided with an inlet port target flow rate operation module, a rodless chamber target pressure solving module, and a proportional pressure reducing valve control signal solving module. The first pressure sensor 27 is used to collect the pilot pressure of the operation handle when the boom 3 rises , and is input into the inlet port target flow rate operation module to obtain the inlet port target flow rate . Subsequently, is transported to the proportional pressure reducing valve control signal solving module, and the calculation method is as follows:

[0089]

[0090] Among them, is the proportional constant between the target speed of the boom 3 and the pilot pressure of the operation handle, is the error threshold of the pilot pressure signal of the operation handle, represents the rodless chamber area of the first energy recovery cylinder 4 or the second energy recovery cylinder 6;

[0091] Step 2: Determine whether to adjust the proportional pressure reducing valve: The sixth pressure sensor 34 is used to collect the actual pressure of the rodless chamber of the energy recovery cylinder at the rodless chamber oil pipe 10 of the energy recovery cylinder , and the seventh pressure sensor 35 is used to collect the load pressure at the output port of the main pump . The rodless chamber target pressure solving module receives , and the output by the inlet port target flow rate operation module in Step 1, and uses the following method to calculate the target flow rate at the inlet port of the rodless chamber of the energy recovery cylinder :

[0092]

[0093] Among them, is the flow coefficient of the boom main valve spool, is the opening area of the boom main valve spool under the control of the proportional pressure reducing valve;

[0094] Compare with . If is equal to , the judgment result is "do not adjust the proportional relief valve". If is not equal to , the judgment result is "adjust the proportional relief valve", and the inlet port target flow calculation module sends the judgment result to the proportional relief valve control signal solving module;

[0095] Step 3: Solve the proportional relief valve control signal: When the judgment result received by the proportional relief valve control signal solving module is "do not adjust the proportional relief valve", the proportional relief valve control signal solving module has no signal output, does not change the output of the proportional relief valve 32, and thus will not cause the displacement of the spool of the boom main valve 9, so as to avoid the increase of the throttling loss at the valve port of the boom main valve 9, and the system outputs the flow of the main pump 25 according to the current constant power control mode; When the judgment result received by the proportional relief valve control signal solving module is "adjust the proportional relief valve", the proportional relief valve control signal solving module uses the received and the negative flow feedback pressure of the boom main valve detected by the fifth pressure sensor 33 to solve the proportional relief valve control signal , and the controller controls the output of the proportional relief valve 32 to decrease or increase according to . When the output of the proportional relief valve 32 decreases, the spool displacement of the boom main valve 9 decreases, and the flow of the boom main valve 9 increases, resulting in an increase in the negative flow feedback pressure of the boom main valve detected by the fifth pressure sensor 33 . When the output of the proportional relief valve 32 increases, the spool displacement of the boom main valve 9 increases, and the flow of the boom main valve 9 decreases, resulting in a decrease in the negative flow feedback pressure of the boom main valve detected by the fifth pressure sensor 33 . The system adjusts the output flow of the main pump 25 according to the negative flow feedback pressure of the boom main valve until the output flow of the main pump 25 and the negative flow feedback pressure of the boom main valve form a balance. Among them, The calculation method of is:

[0096]

[0097] Among them, is the fitting function of the mapping relationship between the negative flow signal of the main pump 25 and the output flow of the main pump 25.

[0098] Therefore, the boom energy recovery system and control strategy of the hydraulic excavator with the above structure are adopted in the present invention, which can realize that the oil inlet and outlet are controlled by two groups of valve cores respectively through the rodless cylinder inlet pipe system of the rod cylinder, the rodless cylinder inlet pipe system of the energy recovery cylinder, the rodless cylinder inlet pipe system of the energy utilization cylinder, the rodless cylinder return pipe system of the energy utilization cylinder and the rodless cylinder return pipe system of the energy recovery cylinder. And it can adjust the positions of each valve core according to the system state to control the boom movement. At the same time, it can reduce the oil return back pressure and throttling loss, reduce the energy output of the main pump, maintain the controllability of the whole machine, and improve the energy recovery efficiency; By using the pressure adaptive energy recovery control strategy based on independent inlet and outlet, the opening of the throttle speed control valve is changed to realize the control of the boom lowering speed and the main pump output flow, effectively reducing the throttling loss of the oil inlet of the boom main valve; By using the energy reuse control strategy based on flow following, the opening of the proportional pressure reducing valve is controlled to realize the active control of the valve core opening of the boom main valve and the negative flow feedback pressure of the boom main valve, thereby changing the main pump output flow and maintaining the controllability of the whole machine.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A hydraulic excavator boom energy recovery system, characterized in that: It comprises an oil tank, an accumulator, and a first energy recovery cylinder, an energy utilization cylinder, and a second energy recovery cylinder which are sequentially arranged below the boom and connected to the boom, wherein the first energy recovery cylinder, the energy utilization cylinder, and the second energy recovery cylinder are connected to the oil tank and the accumulator via an oil delivery system, and the oil delivery system comprises an oil inlet and outlet pipe system of a rod cylinder, an oil inlet pipe system of a rodless cylinder of an energy recovery cylinder, an oil inlet pipe system of a rodless cylinder of an energy utilization cylinder, an oil return pipe system of a rodless cylinder of an energy utilization cylinder, and an oil return pipe system of a rodless cylinder of an energy recovery cylinder; The rod cylinder oil inlet and outlet pipe system includes a rod chamber oil pipe, one end of the rod chamber oil pipe is respectively connected to the rod chamber oil ports on the top of the first energy recovery cylinder, the energy utilization cylinder and the second energy recovery cylinder through three first branch pipes, the other end of the rod chamber oil pipe is connected to the first oil hole on the boom main valve, the second oil hole on the boom main valve is connected to the oil outlet hole of the oil tank through the main pump, and the third oil hole of the boom main valve is connected to the oil return hole of the oil tank; The rodless cylinder oil inlet pipe system of the energy recovery cylinder includes an energy recovery cylinder rodless chamber oil pipe and an energy recovery cylinder oil inlet pipe, one end of the energy recovery cylinder rodless chamber oil pipe is respectively connected to the rodless chamber oil ports of the first energy recovery cylinder and the second energy recovery cylinder through two second branch pipes, the other end of the energy recovery cylinder rodless chamber oil pipe is connected to the first oil port on the energy control valve, and the second oil port of the energy control valve is connected to the fourth oil hole of the boom main valve through the energy recovery cylinder oil inlet pipe; When the boom main valve is opened to the right, the first oil hole is connected to the second oil hole, the third oil hole is connected to the fourth oil hole, and the oil supplied by the main pump causes the boom to descend; when the boom main valve is opened to the left, the second oil hole is connected to the fourth oil hole, the first oil hole is connected to the third oil hole, and the oil supplied by the main pump causes the boom to ascend; The rodless cylinder oil inlet pipe system of the energy utilization cylinder includes an energy utilization cylinder rodless chamber oil pipe, an energy utilization cylinder oil inlet pipe and an accumulator oil pipe, one end of the energy utilization cylinder rodless chamber oil pipe is connected to the rodless chamber oil port of the energy utilization cylinder, the other end of the energy utilization cylinder rodless chamber oil pipe is connected to the third oil port of the energy control valve through the energy utilization cylinder oil inlet pipe, and the fourth oil port of the energy control valve is connected to the accumulator through the accumulator oil pipe; When the right position of the energy control valve is opened, the first oil port and the fourth oil port on the energy control valve are connected, and the third oil port and the second oil port are not connected; when the left position of the energy control valve is opened, the first oil port and the second oil port on the energy control valve are connected, and the third oil port and the fourth oil port are connected; The rodless cylinder oil return pipe system of the energy utilization cylinder includes the energy utilization cylinder rodless chamber oil pipe and the energy utilization cylinder oil return pipe, one end of the energy utilization cylinder rodless chamber oil pipe is connected to the rodless chamber oil port of the energy utilization cylinder, the other end of the energy utilization cylinder rodless chamber oil pipe is connected to the oil tank through the energy utilization cylinder oil return pipe, and a throttling speed regulating valve is provided on the energy utilization cylinder oil return pipe; The hydraulic excavator boom energy recovery control strategy of the hydraulic excavator boom energy recovery system is: When the boom is lowered, the boom main valve maintains the maximum opening according to the signal value of the pilot pressure of the operating handle, and changes the opening of the throttling speed regulating valve through the pressure adaptive energy recovery control strategy based on load observation to control the boom lowering speed and the output flow of the main pump. The specific method includes the following steps: Step 1: Use the sensor to detect the required signal value and transmit it to the controller, where the signal value includes the actual movement speed of the boom collected by the speed sensor , the pilot pressure of the operating handle when the boom is lowered is collected by the first pressure sensor , the rod cavity target pressure collected by the second pressure sensor , using the energy collected by the third pressure sensor to use the actual load pressure of the cylinder rodless chamber and the load pressure at the main pump outlet collected by the fourth pressure sensor , the controller includes a load observer module, a speed control valve target pressure solving module and a valve core opening solving module; Step 2: Use the Load Observer module to calculate the equivalent load term , the calculation method is as follows: ； in is the equivalent load term, is the external load, is the accumulator force, Indicates the energy utilization cylinder rodless cavity area, represents the rodless cavity area of ​​the first energy recovery cylinder or the second energy recovery cylinder, is the pressure at the accumulator port; Step 3: Use the speed control valve target pressure solving module to calculate the throttling speed control valve target pressure : ； in, represents the sum of the rod cavity areas of the first energy recovery cylinder, the second energy recovery cylinder and the energy utilization cylinder; is the rod chamber target pressure measured in step 1; m represents the equivalent mass of the working device acting on the cylinder; is the boom movement speed measured in step 1; Represents acceleration, which is represented by Differentiate to get; represents the viscosity coefficient; is the equivalent load term calculated in step 2; Indicates the rodless cavity area of ​​the energy utilization cylinder; Step 4: Set the throttle speed regulating valve target pressure obtained in step 3 to The energy measured in step 1 is compared with the actual load pressure of the cylinder rodless chamber Compare, if equal , the opening of the throttling speed regulating valve does not change. Not equal to , then proceed to the next step 5; Step 5: When and When the pressure difference is positive, the throttling speed regulating valve opening is reduced, the throttling pressure difference is increased, the output flow of the main pump is reduced, and the boom lowering speed is reduced; when and When the pressure difference is negative, increase the opening of the throttling speed regulating valve, reduce the throttling pressure difference, increase the output flow of the main pump, and thus increase the boom lowering speed; During this control process, the valve core opening area of ​​the flow control speed regulating valve Calculated as follows: ； ； in, is the flow coefficient of the proportional speed control valve core, is the density of hydraulic oil, The energy measured in step 1 is the actual load pressure of the rodless chamber of the cylinder. is the target flow rate of the throttling speed regulating valve, is the proportional constant between the boom target speed and the pilot pressure of the operating handle, It is the error threshold of the pilot pressure signal of the operating handle; During this control process, the main pump is in constant power control mode. After the throttle speed regulating valve opening changes, the boom movement speed collected by the speed sensor The controller controls the output flow of the main pump to change until the load pressure at the output port of the main pump collected by the fourth pressure sensor changes. Reach the target value, The target value is calculated as follows: ； in, The load pressure of the main pump output port; The maximum rated displacement of the main pump; is the engine speed, The target flow rate of the three rod chamber oil ports is: The calculation method is as follows: ； in, is the proportional constant between the boom lowering target speed and the pilot control pressure, It is the pilot pressure of the operating handle when the boom is lowered. is the error threshold of the pilot pressure signal of the operating handle, represents the sum of the rod cavity areas of the first energy recovery cylinder, the second energy recovery cylinder and the energy utilization cylinder; When the boom rises, the opening of the proportional pressure reducing valve is changed by an energy recycling control strategy based on flow following. The specific method includes the following steps: Step 1: Calculate the target flow rate of the oil inlet: A proportional pressure reducing valve is set on the control oil line between the operating handle and the boom main valve. The proportional pressure reducing valve is connected to the controller. The controller is equipped with an oil inlet target flow calculation module, a rodless cavity target pressure solution module and a proportional pressure reducing valve control signal solution module. The first pressure sensor is used to collect the pilot pressure of the operating handle when the boom rises. ,Will Input into the oil inlet target flow calculation module to obtain the oil inlet target flow , and then Sent to the proportional pressure reducing valve control signal solution module, The calculation method is as follows: ； in, is the proportional constant between the boom target speed and the pilot pressure of the operating handle, is the error threshold of the pilot pressure signal of the operating handle, represents the rodless cavity area of ​​the first energy recovery cylinder or the second energy recovery cylinder; Step 2: Determine whether to adjust the proportional pressure reducing valve: Use the sixth pressure sensor to collect the actual pressure of the energy recovery cylinder rodless cavity at the energy recovery cylinder rodless cavity oil pipe. , use the seventh pressure sensor to collect the load pressure at the main pump output port , the rodless cavity target pressure solution module receives , and the output of the oil inlet target flow calculation module in step 1 , and use the following method to calculate the target flow rate of the oil inlet of the energy recovery cylinder rodless chamber : ； in, is the flow coefficient of the boom main valve core, The proportional pressure reducing valve controls the valve core opening area of ​​the lower boom main valve; Will and For comparison, if equal , the judgment result is "do not adjust the proportional pressure reducing valve", if Not equal to , the judgment result is "adjust the proportional pressure reducing valve", and the oil inlet target flow calculation module transmits the judgment result to the proportional pressure reducing valve control signal solution module; Step 3: Solve the proportional pressure reducing valve control signal: When the judgment result received by the proportional pressure reducing valve control signal solving module is "do not adjust the proportional pressure reducing valve", the proportional pressure reducing valve control signal solving module has no signal output, does not change the output of the proportional pressure reducing valve, and thus does not cause the displacement of the boom main valve spool, so as to avoid the increase of throttling loss of the boom main valve port. The system outputs the main pump flow according to the current constant power control mode; When the judgment result received by the proportional pressure reducing valve control signal solving module is "adjust the proportional pressure reducing valve", the proportional pressure reducing valve control signal solving module uses the received and the negative flow feedback pressure of the boom main valve detected by the fifth pressure sensor Solving the proportional pressure reducing valve control signal , the controller is based on Control the proportional pressure reducing valve output to decrease or increase. When the proportional pressure reducing valve output decreases, the valve core displacement of the boom main valve decreases, and the flow of the boom main valve increases, resulting in the boom main valve negative flow feedback pressure detected by the fifth pressure sensor. When the proportional pressure reducing valve output increases, the valve core displacement of the boom main valve increases, and the flow of the boom main valve decreases, resulting in the boom main valve negative flow feedback pressure detected by the fifth pressure sensor. The system responds to the negative flow feedback pressure of the boom main valve. Adjust the main pump output flow until the main pump output flow is equal to the negative flow feedback pressure of the boom main valve. A balance is formed, in which The calculation method is: ； in, It is the fitting function of the mapping relationship between the negative flow signal of the main pump and the output flow of the main pump.

2. The hydraulic excavator boom energy recovery system according to claim 1, characterized in that: The rodless cylinder oil return pipe system of the energy recovery cylinder includes the energy recovery cylinder rodless chamber oil pipe and the accumulator oil pipe.

3. The hydraulic excavator boom energy recovery system according to claim 2, characterized in that: A first anti-overflow pipe with a first anti-overflow valve is provided between the rod cavity oil pipe and the oil tank, and a second anti-overflow pipe with a second anti-overflow valve is provided between the energy recovery cylinder oil inlet pipe and the oil tank.

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