Hydraulic hybrid power system of engineering vehicle and control method of hydraulic hybrid power system

Abstract

The invention discloses an engineering vehicle hydraulic hybrid power system and a control method thereof, belongs to the field of engineering machinery, and aims to solve the problems that in the prior art, vehicle power output is adjusted only depending on motor displacement changes, so that a motor is large in size, cost is greatly increased, and installation is difficult. Stepped automatic speed change is realized by adopting a transmission mode of combining a combined power source and a stepped variable displacement motor, multiple driving modes under different working conditions are realized by utilizing arrangement and control of a reversing valve group, and different requirements are met; meanwhile, the working point of the engine can be adjusted to work in a high-efficiency area, and the fuel economy is improved.

Description

Technical Field

[0001] The present invention belongs to the field of construction machinery, and particularly relates to a hydraulic hybrid system for engineering vehicles and a control method thereof. Background Art

[0002] When an engineering vehicle is operating, it needs to start and stop frequently and move back and forth. Frequent braking wastes a large amount of kinetic energy. The wasted energy is consumed in the form of heat, which will cause the oil temperature to rise, shorten the service life of components, deteriorate the working environment of the machine, increase the failure rate. At the same time, frequent starting will cause the engine to often be in an inefficient area, and the service brakes of the vehicle are used frequently and wear quickly.

[0003] The currently common transmission method for engineering vehicles is hydrodynamic transmission. The matching versatility is poor. Machinery with different traction characteristics needs to select different types of torque converters, and the matching conditions between the torque converter and engines with different characteristics are also relatively harsh. It often requires special machine matching and is not very suitable for use in small-batch manufactured complete machines. Moreover, the hydrodynamic torque converter has low transmission efficiency, which is not conducive to energy conservation, reducing displacement and reducing noise. The steady-state efficiency of hydrodynamic transmission is relatively low, and a separate cooling system needs to be set up, and a mechanical gearbox and a reverse gear mechanism must be configured at the same time. Hydraulic transmission has higher efficiency than hydrodynamic transmission, is flexible and convenient to arrange. The input and output components can be connected by flexible pipes. Variable pump / motor volume speed regulation can achieve continuous stepless speed change, but the structure is relatively complex, the cost is high, it is difficult to control, and the reliability is poor. The core technology of variable pumps is controlled by foreign countries.

[0004] The Chinese patent publication number is CN102141040B, the publication date is December 14, 2016, and the invention name is "Multi-fixed pump stepped variable system". The applicant is Jilin University. This patent uses multiple ordinary switching valves to logically control multiple fixed pump / motors to form a stepped variable system to replace the plunger type variable element, solving problems such as high price, difficult control, and susceptibility to contamination. However, new problems have also arisen. The stepped jump of the displacement will cause pipeline impact and system chatter, deteriorating the comfort.

[0005] The Chinese patent publication number is CN201310065366.2, and the invention title is "Hybrid vehicle drive device based on transformer, hydraulic pump and multi-connected motor". The applicant is Beijing Institute of Technology. This patent greatly improves the power performance and transmission efficiency of hydraulic hybrid vehicles through a hydraulic transformer, fixed-displacement multi-connected hydraulic motors and fixed-displacement pumps. The Chinese patent publication number is CN204716962U, and the invention title is "Stepped variable speed system of multiple fixed-displacement pumps in series with multiple fixed-displacement motors based on logic control". The applicant is Jilin University. This patent realizes stepped variable speed by connecting multiple coaxial fixed-displacement pumps with different displacements in series with multiple coaxial fixed-displacement motors with different displacements. However, these two patents have a common drawback: adjusting the vehicle power output solely by changing the motor displacement will make the motor bulky, the cost increase sharply, and the installation difficult. Summary of the Invention

[0006] In view of the technical problems existing in the prior art, the present invention provides a hydraulic hybrid system for engineering vehicles and its control method. The technical solution of the present invention is as follows:

[0007] A hydraulic hybrid system for engineering vehicles, the system includes: a hydraulic working device 1 for engineering vehicles, a first two-position two-way directional control valve 2, a first accumulator 3, a second accumulator 4, a second two-position two-way directional control valve 5, a three-position four-way directional control valve group 8, a torque continuously adjustable coupler 9, a rear axle 10, a stepped variable motor 11, a clutch 12, a check valve group 13, a combined power source 14, a hydraulic oil tank 15, an engine 16, a front axle 17, a two-position three-way directional control valve group 18 and a flow priority valve 19;

[0008] Wherein, the engine 16 is coaxially connected to the input shaft of the combined power source 14, the output shaft of the combined power source 14 is connected to the input end of the stepped variable motor 11 through the clutch 12, the output end of the stepped variable motor 11 is connected to the power input end of the torque continuously adjustable coupler 9, and the power output end of the torque continuously adjustable coupler 9 is respectively connected to the power input ends of the rear axle 10 and the front axle 17; the torque continuously adjustable coupler 9 has the function of continuously variable speed and torque increase;

[0009] The two-position three-way directional control valve group 18 is an integrated valve block, including a plurality of two-position three-way directional control valves. The A ports of the two-position three-way directional control valves are connected to each other and the external outputs are ports A1 and A2; the B ports of the two-position three-way directional control valves are connected to each other and the external output is port B1, and each two-position three-way directional control valve is provided with a P port;

[0010] The combined power source 14 consists of multiple fixed-displacement pumps connected coaxially or by a power take-off box. Each fixed-displacement pump has a separate oil inlet and oil outlet. The oil inlet of the combined power source 14 is connected to the hydraulic oil tank 15, and the oil outlet is successively connected to the oil inlets of the corresponding valves of the check valve group 13. The oil outlets of the check valve group 13 are respectively connected to the P ports of the respective directional control valves in the two-position three-way directional control valve group 18. The A1 port of the two-position three-way directional control valve group 18 is connected to the P port of the flow priority valve 19, and the B1 port of the two-position three-way directional control valve group 18 is connected to the hydraulic oil tank 15.

[0011] The three-position four-way directional control valve group 8 is an integrated valve block, including multiple three-position four-way directional control valves. Inside the integrated valve block, the A ports of the respective three-position four-way directional control valves are interconnected and output to the outside as the A port; the B ports are also interconnected and output to the outside as the B port; each three-position four-way directional control valve is respectively provided with a P port and a T port.

[0012] The A port of the flow priority valve 19 is connected to the hydraulic working device 1 of the engineering vehicle, and at the same time, it is connected to the A port of the first two-position two-way directional control valve 2 through a bypass. The B port of the first two-position two-way directional control valve 2 is connected to the first accumulator 3 and is connected to the hydraulic oil tank 15 through a bypass; the A port of the second two-position two-way directional control valve 5 is connected to the B port of the flow priority valve 19, and the B port of the second two-position two-way directional control valve 5 is connected to the second accumulator 4 and is connected to the hydraulic oil tank 15 through a bypass.

[0013] The stepped variable motor 11 is composed of multiple fixed-displacement motors connected coaxially. Each fixed-displacement motor has a separate oil inlet and oil outlet. The B port of the flow priority valve 19 is connected to the A port of the three-position four-way directional control valve group 8. The P ports of the respective directional control valves in the three-position four-way directional control valve group 8 are respectively connected to the B ports of the corresponding motors in the stepped variable motor 11, and the T ports of the respective directional control valves in the three-position four-way directional control valve group 8 are respectively connected to the A ports of the corresponding motors in the stepped variable motor 11. The B port of the three-position four-way directional control valve group 8 is connected to the hydraulic oil tank 15.

[0014] Preferably, the system further includes a bypass relief valve 24. The bypass relief valve 24 is arranged on the bypass of the two-position three-way directional control valve group 18. The A2 port of the two-position three-way directional control valve group 18 is connected to the inlet of the bypass relief valve 24 through a bypass, and the outlet of the bypass relief valve 24 is connected to the hydraulic oil tank 15.

[0015] Preferably, a first pressure reducing valve 20 and a first throttle valve 21 are successively connected between the A port of the flow priority valve 19 and the hydraulic working device 1 of the engineering vehicle.

[0016] Preferably, a working device safety valve 7 is arranged on the bypass between the B port of the first two-position two-way directional control valve 2 and the hydraulic oil tank 15.

[0017] Preferably, an auxiliary brake circuit safety valve 6 is arranged on the bypass between the B port of the second two-position two-way directional control valve 5 and the hydraulic oil tank 15.

[0018] Preferably, a second pressure reducing valve 22 and a second throttle valve 23 are sequentially connected to the B port of the flow dividing priority valve 19, and then are respectively connected to the A port of the three-position four-way reversing valve group 8 and the A port of the second two-position two-way reversing valve 5.

[0019] Preferably, the displacement combination mode adopted by the combined power source 14 and the stepped variable motor 11 is one of equal value combination, arithmetic progression combination, Fibonacci sequence combination and geometric progression combination.

[0020] The present invention also provides a control method for the hydraulic hybrid power system of the engineering vehicle. The system is divided into an idle charging mode, a low-load starting mode, a driving charging mode, an engine single driving mode and a hybrid driving mode under driving conditions;

[0021] Wherein, when the engine 16 is warm or temporarily stopped, and the pressure in the second accumulator 4 is lower than the set maximum working pressure, the system enters the idle charging mode. The control method in the idle charging mode is:

[0022] The clutch 12 is in a disengaged state, the left position of the flow dividing priority valve 19 is energized and works in the left position, the second two-position two-way reversing valve 5 is energized and works in the left position, the first two-position two-way reversing valve 2 is de-energized and disconnected, and the three-position four-way reversing valve group 8 is de-energized and works in the middle position; adjust the displacement of the combined power source 14 to make the engine 16 work in the fuel-efficient area. The engine 16 drives the combined power source 14 to rotate, and the oil in the hydraulic oil tank 15 is charged to the second accumulator 4 through the combined power source 14. At this time, the stepped variable motor 11 does not work;

[0023] When the required power of the engineering vehicle is less than the lower limit of the fuel-efficient area of the engine 16, and the pressure in the second accumulator 4 is higher than the set minimum working pressure, the system enters the low-load starting mode. The control method in the low-load starting mode is:

[0024] The clutch 12 is in a disengaged state, the flow dividing priority valve 19 is de-energized and works in the middle position, the engine 16 and the combined power source 14 do not work, the second two-position two-way reversing valve 5 is energized and works in the left position, determine the displacement of the stepped variable motor 11 according to the vehicle power performance requirements, and then control the number of reversing valves in the right position of the three-position four-way reversing valve group 8; at this time, the high-pressure oil in the second accumulator 4 enters the stepped variable motor 11 through the second two-position two-way reversing valve 5 and the AT oil circuit in the three-position four-way reversing valve group 8, driving it to work in the motor condition, and the power is transmitted to the front axle 17 and the rear axle 10 of the vehicle through the torque infinitely adjustable coupler 9;

[0025] When the required power of the engineering vehicle is lower than the lower limit of the fuel-efficient area power of the engine 16, and the pressure in the second accumulator 4 is lower than the set maximum working pressure, the system enters the driving charging mode. The control method in the driving charging mode is:

[0026] Disconnect the clutch 12. The flow dividing priority valve 19 is de-energized and operates in the middle position. The second two-position two-way directional control valve 5 is energized and operates in the left position. The first two-position two-way directional control valve 2 is disconnected. Adjust the displacement of the combined power source 14 and the stepped variable motor 11 to make the engine 16 operate in the fuel-efficient area. The engine 16 drives the combined power source 14 to rotate. The hydraulic oil in the hydraulic oil tank 15 is divided into two paths, namely path A and path B, through the combined power source 14, the one-way valve group 13, the two-position three-way directional control valve group 18, and the flow dividing priority valve 19. Path A enters the hydraulic working device 1 of the engineering vehicle; path B charges the second accumulator 4 through the second two-position two-way directional control valve 5, and at the same time drives the stepped variable motor 11 through the three-position four-way directional control valve group 8. The power output by the stepped variable motor 11 is transmitted to the front axle 17 and the rear axle 10 respectively through the torque continuously adjustable coupler 9;

[0027] When the required power of the engineering vehicle is in the fuel-efficient area of the engine 16, or when the required power of the engineering vehicle is higher than the upper limit of the fuel-efficient area of the engine 16 and the pressure of the second accumulator 4 is lower than the set minimum working pressure value, the system enters the engine single drive mode. The control method in the engine single drive mode is as follows:

[0028] Disconnect the clutch 12. The flow dividing priority valve 19 is de-energized and operates in the middle position. The second two-position two-way directional control valve 5 and the first two-position two-way directional control valve 2 are disconnected. Adjust the displacement of the combined power source 14 and the stepped variable motor 11 to make the engine 16 operate in the fuel-efficient area. The engine 16 drives the combined power source 14 to rotate. The hydraulic oil in the fuel tank 15 is divided into two paths, namely path A and path B, through the combined power source 14, the one-way valve group 13, the two-position three-way directional control valve group 18, and the flow dividing priority valve 19. Path A enters the hydraulic working device 1 of the engineering vehicle, and path B drives the stepped variable motor 11 through the three-position four-way directional control valve group 8. The power output by the stepped variable motor 11 is transmitted to the front axle 17 and the rear axle 10 respectively through the torque continuously adjustable coupler 9;

[0029] When the engineering vehicle starts or climbs with a high load, the required power is greater than the upper limit of the fuel-efficient area of the engine 16, and the pressure of the second accumulator 4 is higher than the set minimum working pressure value, the system enters the hybrid drive mode. The control method in the hybrid drive mode is as follows:

[0030] Disconnect the clutch 12. The shunt priority valve 19 is de-energized and works in the middle position. The second two-position two-way directional valve 5 is energized and works in the left position. The first two-position two-way directional valve 2 is disconnected. Adjust the displacement of the combined power source 14 and the stepped variable motor 11 so that the engine 16 operates in the fuel-efficient area. The engine 16 drives the combined power source 14 to rotate. The oil in the hydraulic oil tank 15 passes through the combined power source 14, the check valve group 13, the two-position three-way directional valve group 18, and the shunt priority valve 19 and is divided into two paths, A and B. Path A enters the hydraulic working device 1 of the engineering vehicle; Path B drives the stepped variable motor 11 through the three-position four-way directional valve group 8. At the same time, the high-pressure oil in the second accumulator 4 is discharged through the second two-position two-way directional valve 5 and drives the stepped variable motor 11 through the three-position four-way directional valve group 8. The power output by the stepped variable motor 11 is transmitted to the front axle 17 and the rear axle 10 respectively through the torque continuously adjustable coupler 9;

[0031] When the pressure in the first accumulator 3 is higher than the working pressure of the hydraulic working device 1 of the engineering vehicle, the first two-position two-way directional valve 2 is energized and works in the right position. The auxiliary combined power source 14 provides an oil source for the hydraulic working device 1 of the engineering vehicle; The oil output from the first accumulator 3 enters the hydraulic working device 1 of the engineering vehicle through the first two-position two-way directional valve 2 in sequence.

[0032] In the braking condition of this system, it is divided into a light braking mode and a heavy braking mode;

[0033] When the required braking force is less than the set value of the braking force, the system enters the light braking mode. The control method in the light braking mode is:

[0034] Disconnect the clutch 12. The shunt priority valve 19 is energized and works in the right position. The second two-position two-way directional valve 5 is energized and works in the left position. Adjust the displacement of the combined power source 14 so that the engine 16 operates in the fuel-efficient area. The engine 16 drives the combined power source 14 to rotate. The oil in the hydraulic oil tank 15 passes through the combined power source 14, the check valve group 13, the two-position three-way directional valve group 18, and the shunt priority valve 19 and enters the hydraulic working device 1 of the engineering vehicle;

[0035] The braking energy from the front axle 17 and the rear axle 10 drives the stepped variable motor 11 through the torque continuously adjustable coupler 9 to make it work in the pump condition. The stepped variable motor 11 in the pump condition sucks oil from the hydraulic oil tank 15 through the BT oil circuit of the three-position four-way directional valve group 8 and charges the second accumulator 4 again through the PA oil circuit of the three-position four-way directional valve group 8;

[0036] When the required braking force is greater than or equal to the set value of the braking force, it is in the heavy braking mode. The control method in the heavy braking mode is:

[0037] At this time, the original vehicle braking and the regenerative braking system work together.

[0038] When in special circumstances, such as when the engineering vehicle needs to travel at high speed or when the hydraulic system fails and needs to be transferred to a suitable place for repair, the clutch 12 engages and the vehicle is driven only by the engine 16.

[0039] When the boom descends, the first two-position two-way directional control valve 2 is energized and works in the right position, recovering the potential energy of the boom and storing it in the first accumulator 3.

[0040] Calculation methods for the displacement sizes of the combined power source 14 and the stepped variable motor 11 required by the system:

[0041] 1) Calculation method for the displacement size of the combined power source 14 required by the system:

[0042]

[0043] In the formula: M E0 (n E ) is the torque value on the engine's economic curve;

[0044] V p_max is the maximum displacement value of the combined power source 14;

[0045] p is the working pressure of the system;

[0046] 2) Calculation method for the displacement size of the stepped variable motor 11 required by the system:

[0047]

[0048] In the formula: M K (t) is the load torque of the engine 16;

[0049] K is the transmission coefficient of the torque continuously adjustable coupler;

[0050] p is the working pressure of the system;

[0051] V m_max is the maximum displacement value of the stepped variable motor 11.

[0052] Compared with the prior art, the beneficial effects of the present invention are:

[0053] 1. The hydraulic hybrid power system of the engineering vehicle described in the present invention can recover and reuse braking energy, adjust the engine operating point to make it work in the efficient area, and improve fuel economy.

[0054] 2. The hydraulic hybrid power system of the engineering vehicle described in the present invention adopts a transmission method combining a combined power source and a stepped variable motor to achieve stepped automatic transmission, replacing the torque converter, avoiding the problem of low transmission efficiency of the torque converter, and at the same time replacing the traditional variable pump and variable motor, reducing costs, being easier to control, having a fast response, etc.

[0055] 3. In the hydraulic hybrid system of the engineering vehicle described in the present invention, the torque continuously adjustable coupler has the function of speed change and torque increase, which can reduce the installed displacement of the stepped variable motor. A smaller displacement can be used to achieve a larger driving and braking effect at the wheel end, reducing the volume, cost and installation difficulty of the stepped motor. At the same time, it can ensure that the stepped variable motor operates in the high-efficiency area, improving the working efficiency.

[0056] 4. In the hydraulic hybrid system of the engineering vehicle described in the present invention, the combined power source is directly connected to the engine. Since the working speed of the engine roughly corresponds to the high-efficiency speed of the hydraulic pump, the hydraulic pump can operate within the high-efficiency range throughout the process, avoiding the difficulty of speed matching.

[0057] 5. In the hydraulic hybrid system of the engineering vehicle described in the present invention, the braking energy recovery system and the hydraulic working system of the engineering vehicle share the combined power source, saving costs, reducing the installation space and reducing the vehicle body weight.

[0058] 6. In the hydraulic hybrid system of the engineering vehicle described in the present invention, the series connection of the first pressure reducing valve and the first throttle valve, and the second pressure reducing valve and the second throttle valve converts the stepped variable into a continuous variable, making the flow more smooth. At the same time, the accumulator can absorb the impact and shock generated during the stepped variable process.

[0059] 7. In the hydraulic hybrid system of the engineering vehicle described in the present invention, a clutch is used to connect the combined power source and the motor. When the hydraulic system is damaged, it can be converted to mechanical drive and can move to a convenient area for maintenance by itself without the need to tow with great effort.

[0060] 8. The hydraulic hybrid system of the engineering vehicle described in the present invention can recover and reuse the potential energy of the boom in the working device. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is the schematic diagram of the hydraulic hybrid system of the engineering vehicle described in the present invention;

[0062] Figure 2 is the power transmission route diagram of the hydraulic hybrid system of the engineering vehicle described in the present invention under idle charging;

[0063] Figure 3 is the power transmission route diagram of the hydraulic hybrid system of the engineering vehicle described in the present invention under pure hydraulic drive mode;

[0064] Figure 4 is the power transmission route diagram of the hydraulic hybrid system of the engineering vehicle described in the present invention under driving charging;

[0065] Figure 5 is the power transmission route diagram of the hydraulic hybrid system of the engineering vehicle described in the present invention under the engine single drive mode;

[0066] Figure 6 It is the power transmission route diagram of the hydraulic hybrid system of the engineering vehicle described in the present invention in the hybrid drive mode;

[0067] Figure 7 It is the power transmission route diagram of the hydraulic hybrid system of the engineering vehicle described in the present invention in the regenerative braking mode;

[0068] Figure 8 It is the schematic diagram of the integrated valve block of the two-position three-way directional control valve group 18 described in the present invention;

[0069] Figure 9 It is the schematic diagram of the integrated valve block of the three-position four-way directional control valve group 8 described in the present invention;

[0070] Figure 10 It is the working condition discrimination diagram of the control method of the hydraulic hybrid system of the engineering vehicle described in the present invention;

[0071] Figure 11 It is the driving condition discrimination diagram of the control method of the hydraulic hybrid system of the engineering vehicle described in the present invention;

[0072] Figure 12 It is the braking condition discrimination diagram of the control method of the hydraulic hybrid system of the engineering vehicle described in the present invention;

[0073] Figure 13 It is the special condition discrimination diagram of the control method of the hydraulic hybrid system of the engineering vehicle described in the present invention.

[0074] The above-mentioned drawings use the following markings: 1. Hydraulic working device of the engineering vehicle, 2. First two-position two-way directional control valve, 3. First accumulator, 4. Second accumulator, 5. Second two-position two-way directional control valve, 6. Safety valve for the auxiliary braking circuit, 7. Safety valve for the working device, 8. Three-position four-way directional control valve group, 801. First three-position four-way directional control valve group, 802. Second three-position four-way directional control valve group, 803. Third three-position four-way directional control valve group, 9. Torque continuously adjustable coupler, 10. Rear axle, 11. Step variable motor, 12. Clutch, 13. Check valve group, 14. Combined power source, 15. Hydraulic oil tank, 16. Engine, 17. Front axle, 18. Two-position three-way directional control valve group, 1801. First two-position three-way directional control valve group, 1802. First two-position three-way directional control valve group, 1803. First two-position three-way directional control valve group, 19. Flow dividing priority valve, 20. First pressure reducing valve, 21. First throttle valve, 22. Second pressure reducing valve, 23. Second throttle valve, 24. Bypass overflow valve. Detailed implementation manners

[0075] The technical solution of the present invention will be further explained and described below with reference to the drawings in the specification.

[0076] Refer to Figure 1 , the hydraulic hybrid system of the construction vehicle includes a hydraulic working device 1 of the construction vehicle, a first two-position two-way directional control valve 2, a first accumulator 3, a second accumulator 4, a second two-position two-way directional control valve 5, a safety valve 6 for the auxiliary braking circuit, a safety valve 7 for the working device, a three-position four-way directional control valve group 8, a torque continuously adjustable coupler 9, a rear axle 10, a stepped variable motor 11, a clutch 12, a check valve group 13, a combined power source 14, a hydraulic oil tank 15, an engine 16, a front axle 17, a two-position three-way directional control valve group 18, a flow priority valve 19, a first pressure reducing valve 20, a first throttle valve 21, a second pressure reducing valve 22, a second throttle valve 23, and a bypass overflow valve 24.

[0077] Refer to Figure 1 , Figure 8 , Figure 9 , wherein, the two-position three-way directional control valve group 18 is an integrated valve block, including three two-position three-way directional control valves 1801, 1802 and 1803. It has six interfaces, namely A1, A2, B1, P1, P2, P3. Inside the integrated valve block, the A port of the two-position three-way directional control valve 1801 is connected to the A ports of the two-position three-way directional control valves 1802 and 1803, and the external outputs are the A1 and A2 ports; the B port of the two-position three-way directional control valve 1801 is connected to the B ports of the two-position three-way directional control valves 1802 and 1803, and the external output is the B1 port; the P1, P2, P3 ports of the integrated valve block are respectively the P ports of the two-position three-way directional control valves 1801, 1802, 1803. The three-position four-way directional control valve group 8 is an integrated valve block, including three-position four-way directional control valves 801, 802, 803. It has eight interfaces, namely A, B, P1, P2, P3, T1, T2, T3. Inside the integrated valve block, the A port of the three-position four-way directional control valve 801 is connected to the A ports of the three-position four-way directional control valves 802 and 803, and the external output is the A port; the B port of the three-position four-way directional control valve 801 is connected to the B ports of the three-position four-way directional control valves 802 and 803, and the external output is the B port; the P1, P2, P3 ports of the integrated valve block are respectively the P ports of the three-position four-way directional control valves 801, 802, 803, and the T1, T2, T3 ports are respectively the T ports of the three-position four-way directional control valves 801, 802, 803.

[0078] Refer to Figure 1, in this embodiment, the combined power source 14 is a coaxial triple fixed-displacement pump or connected by a power take-off box, which is an integrated component that cancels, combines, and integrates intermediate components together, rather than a simple input and output shaft connection. Each fixed-displacement pump has a separate oil inlet and oil outlet; the stepped variable motor 11 is a coaxial connection of multiple fixed-displacement motors, which is an integrated component of multiple fixed-displacement motors that cancels, combines, and integrates intermediate components together, rather than a simple input and output shaft connection. Each fixed-displacement motor has a separate oil inlet and oil outlet. The displacement combination methods that the combined power source 14 and the stepped variable motor 11 can adopt include: equal-value combination, arithmetic progression combination, Fibonacci sequence combination, and geometric progression combination. The displacement of the combined power source 14 is controlled by the on-off combination form of the two-position three-way valve group 18; the displacement of the stepped variable motor 11 is controlled by the combination form of the working positions of the three-position four-way valve group 8.

[0079] In the hydraulic hybrid system of the engineering vehicle, the braking energy recovery system and the hydraulic working device 1 of the engineering vehicle share the combined power source 14.

[0080] The mechanical structure connection method of the hydraulic hybrid system of the engineering vehicle is as follows: the engine 16 is coaxially connected to the input shaft of the combined power source 14, the output shaft of the combined power source 14 is connected to the input end of the stepped variable motor 11 through the clutch 12, the output end of the stepped variable motor 11 is connected to the power input end of the torque continuously adjustable coupler 9, and the power output end of the torque continuously adjustable coupler 9 is respectively connected to the power input ends of the rear axle 10 and the front axle 17; the torque continuously adjustable coupler 9 has the function of continuously variable speed and torque increase.

[0081] The hydraulic circuit connection mode of the hydraulic hybrid system of the construction vehicle is as follows: The oil inlet of the combined power source 14 is connected to the hydraulic oil tank 15, and the oil outlet is sequentially connected to the oil inlets of the corresponding valves of the check valve group 13. The oil outlets of the check valve group 13 are sequentially connected to the P1, P2, and P3 ports of the two-position three-way directional valve group 18. The A1 port of the two-position three-way directional valve group 18 is connected to the P port of the flow dividing priority valve 19, and the A2 port of the two-position three-way directional valve group 18 is connected to the inlet of the bypass overflow valve 24; the B1 port of the two-position three-way directional valve group 18 is connected to the hydraulic oil tank 15. The A port of the flow dividing priority valve 19 is connected to the inlet of the first pressure reducing valve 20 and the A port of the first two-position two-way directional valve 2. The outlet of the first pressure reducing valve 20 is connected to the inlet of the first throttle valve 21, the spring side control port of the first pressure reducing valve 20 is connected to the outlet of the first throttle valve 21, and the outlet of the first throttle valve 21 is connected to the hydraulic working device 1 of the construction vehicle. The B port of the flow dividing priority valve 19 is connected to the inlet of the second pressure reducing valve 22, the outlet of the second pressure reducing valve 22 is connected to the inlet of the second throttle valve 23, the spring side control port of the second pressure reducing valve 22 is connected to the outlet of the second throttle valve 23, and the outlet of the second throttle valve 23 is connected to the A port of the second two-position two-way directional valve 5 and the A port of the three-position four-way directional valve group 8. The B port of the first two-position two-way directional valve 2 is respectively connected to the oil inlet of the first accumulator 3 and the oil inlet of the working device safety valve 7; the B port of the second two-position two-way directional valve 5 is respectively connected to the oil inlet of the second accumulator 4 and the oil inlet of the auxiliary braking circuit safety valve 6.

[0082] The B port of each motor in the stepped variable motor 11 is sequentially connected to the P1, P2, and P3 ports of the directional valves in the three-position four-way directional valve group 8, and the A port of each motor in the stepped variable motor 11 is sequentially connected to the T1, T2, and T3 ports of the directional valves in the three-position four-way directional valve group 8. The outlet of the bypass overflow valve 24, the outlets of the auxiliary braking circuit safety valve 6 and the working device safety valve 7, and the B port of the three-position four-way directional valve group 8 are all connected to the hydraulic oil tank 15.

[0083] Refer to Figure 10 , Figure 11 , Figure 12 , Figure 13 , the control method of the present invention is as follows:

[0084] During the actual operation of the construction vehicle, it should first ensure the normal operation of the working device. The combined power source 14 supplies oil to the hydraulic working device 1 of the construction vehicle through the flow dividing priority valve 19 preferentially, and then supplies oil to the braking energy recovery circuit, that is, the stepped variable motor 11. The energy source of the first accumulator 3 is the potential energy of the boom descending in the working device.

[0085] 1. Driving condition: Refer to Figure 2 .

[0086] 1.1 Idle charging mode: When the engine 16 is warm or temporarily stopped and the pressure in the second accumulator 4 is lower than the set maximum working pressure, the system enters the idle charging mode. The clutch 12 is in the disengaged state. The left position of the shunt priority valve 19 is energized and works in the left position. The second two-position two-way directional control valve 5 is energized and works in the left position. The first two-position two-way directional control valve 2 is de-energized and disconnected. The three-position four-way directional control valve group 8 is de-energized and works in the neutral position. Adjust the displacement of the combined power source 14 so that the engine 16 operates in the fuel-efficient zone. The engine 16 drives the combined power source 14 to rotate. The oil in the fuel tank 15 passes through the combined power source 14, the check valve group 13, the two-position three-way directional control valve group 18, the shunt priority valve 19, the second pressure reducing valve 22, the second throttle valve 23, and the second two-position two-way directional control valve 5 to charge the second accumulator 4. At this time, the stepped variable motor 11 does not work. The oil flow of the combined power source 14 in the figure is taken as an example for one section.

[0087] 1.2 Low-load start: (Pure hydraulic drive mode): Refer to Figure 3 .

[0088] When the required power of the engineering vehicle is less than the lower limit of the fuel-efficient zone of the engine 16 and the pressure in the second accumulator 4 is higher than the set minimum working pressure, the clutch 12 is disengaged. The shunt priority valve 19 is de-energized and works in the neutral position. The engine 16 and the combined power source 14 do not work. The second two-position two-way directional control valve 5 is energized and works in the left position. Determine the displacement of the stepped variable motor 11 according to the vehicle dynamic performance requirements, and then control the number of directional control valves in the right position of the three-position four-way directional control valve group 8. At this time, the high-pressure oil in the second accumulator 4 enters the stepped variable motor 11 through the second two-position two-way directional control valve 5 and the AT oil circuit in the three-position four-way directional control valve group 8, driving it to work in the motor condition. The power is transmitted to the front axle 17 and the rear axle 10 of the vehicle through the torque continuously adjustable coupler 9. The oil flow of the stepped variable motor 11 in the figure is taken as an example for one section.

[0089] 1.3 Driving charging mode: Refer to Figure 4 .

[0090] When the required power of the construction vehicle is lower than the lower limit of the power in the fuel-efficient zone of the engine 16 and the pressure in the second accumulator 4 is lower than the set maximum working pressure, the system enters the driving and pressurizing mode. The clutch 12 is in the disengaged state. The flow priority valve 19 is de-energized and works in the middle position. The second two-position two-way directional control valve 5 is energized and works in the left position. The first two-position two-way directional control valve 2 is disconnected. The displacements of the composite power source 14 and the stepped variable motor 11 are adjusted to make the engine 16 work in the fuel-efficient zone. The engine 16 drives the composite power source 14 to rotate. The oil in the fuel tank 15 is divided into two paths, namely path A and path B, through the composite power source 14, the check valve group 13, the two-position three-way directional control valve group 18, and the flow priority valve 19. Path A enters the hydraulic working device 1 of the construction vehicle through the first pressure reducing valve 20 and the first throttle valve 21. Path B charges the second accumulator 4 through the second pressure reducing valve 22, the second throttle valve 23, and the second two-position two-way directional control valve 5. At the same time, it drives the stepped variable motor 11 through the three-position four-way directional control valve group 8. The power output by the stepped variable motor 11 is transmitted to the front axle 17 and the rear axle 10 respectively through the torque continuously adjustable coupler 9. In the figure, the oil flow of the composite power source 14 and the stepped variable motor 11 takes one section as an example.

[0091] 1.4. Engine single drive mode: Refer to Figure 5 。

[0092] When the required power of the construction vehicle is within the fuel-efficient zone of the engine 16, or when the required power of the construction vehicle is higher than the upper limit of the fuel-efficient zone of the engine 16 and the pressure of the second accumulator 4 is lower than the set minimum working pressure value, the system enters the engine single drive mode. The clutch 12 is in the disengaged state. The flow priority valve 19 is de-energized and works in the middle position. The second two-position two-way directional control valve 5 and the first two-position two-way directional control valve 2 are disconnected. The displacements of the composite power source 14 and the stepped variable motor 11 are adjusted to make the engine 16 work in the fuel-efficient zone. The engine 16 drives the composite power source 14 to rotate. The oil in the fuel tank 15 is divided into two paths, namely path A and path B, through the composite power source 14, the check valve group 13, the two-position three-way directional control valve group 18, and the flow priority valve 19. Path A enters the hydraulic working device 1 of the construction vehicle through the first pressure reducing valve 20 and the first throttle valve 21. Path B drives the stepped variable motor 11 through the second pressure reducing valve 22, the second throttle valve 23, and the three-position four-way directional control valve group 8. The power output by the stepped variable motor 11 is transmitted to the front axle 17 and the rear axle 10 respectively through the torque continuously adjustable coupler 9. In the figure, the oil flow of the composite power source 14 and the stepped variable motor 11 takes one section as an example.

[0093] 1.5. Hybrid drive mode: Refer to Figure 6 。

[0094] When the construction vehicle starts or climbs a slope under high load, the required power is greater than the upper limit of the fuel-efficient area of the engine 16, and the pressure of the second energy accumulator 4 is higher than the set minimum working pressure value, the system enters the hybrid drive mode. The clutch 12 is in the disengaged state, the flow priority valve 19 is de-energized and works in the middle position, the second two-position two-way directional control valve 5 is energized and works in the left position, the first two-position two-way directional control valve 2 is disconnected, and the displacements of the combined power source 14 and the stepped variable motor 11 are adjusted to make the engine 16 work in the fuel-efficient area. The engine 16 drives the combined power source 14 to rotate. The oil in the fuel tank 15 is divided into two paths A and B through the combined power source 14, the one-way valve group 13, the two-position three-way directional control valve group 18, and the flow priority valve 19. Path A enters the hydraulic working device 1 of the construction vehicle through the first pressure reducing valve 20 and the first throttle valve 21; Path B drives the stepped variable motor 11 through the second pressure reducing valve 22, the second throttle valve 23, and the three-position four-way directional control valve group 8; at the same time, the high-pressure oil in the second energy accumulator 4 is discharged through the second two-position two-way directional control valve 5 and drives the stepped variable motor 11 through the three-position four-way directional control valve group 8. The power output by the stepped variable motor 11 is transmitted to the front axle 17 and the rear axle 10 respectively through the torque continuously adjustable coupler 9. When the pressure in the first energy accumulator 3 is higher than the working pressure of the hydraulic working device 1 of the construction vehicle, the first two-position two-way directional control valve 2 is energized and works in the right position, and the auxiliary combined power source 14 provides an oil source for the hydraulic working device 1 of the construction vehicle. The oil output by the first energy accumulator 3 enters the hydraulic working device 1 of the construction vehicle through the first two-position two-way directional control valve 2, the first pressure reducing valve 20, and the first throttle valve 21. In the figure, the oil flow of the combined power source 14 and the stepped variable motor 11 takes one series as an example.

[0095] 2. Braking condition: Refer to Figure 7 。

[0096] 2.1 Light braking: Regenerative braking mode.

[0097] When the required braking force is less than the set value of the braking force, it is in the light braking mode. At this time, the clutch 12 is in the disengaged state, the right position of the flow priority valve 19 is energized and works in the right position, the second two-position two-way directional control valve 5 is energized and works in the left position, and the displacement of the combined power source 14 is adjusted to make the engine 16 work in the fuel-efficient area. The engine 16 drives the combined power source 14 to rotate. The oil in the fuel tank 15 enters the hydraulic working device 1 of the construction vehicle through the combined power source 14, the one-way valve group 13, the two-position three-way directional control valve group 18, the flow priority valve 19, the first pressure reducing valve 20, and the first throttle valve 21.

[0098] The braking energy from the front axle 17 and the rear axle 10 drives the stepped variable motor 11 through the torque continuously adjustable coupler 9 to make it work in the pump condition. The stepped variable motor 11 in the pump condition sucks oil from the hydraulic oil tank 15 through the BT oil circuit of the three-position four-way valve group 8, and then charges the second accumulator 4 through the PA oil circuit of the three-position four-way valve group 8. In the figure, the oil flow of the combined power source 14 and the stepped variable motor 11 takes one series as an example.

[0099] 2.2 Heavy braking: It is a combination of the original vehicle braking and the regenerative braking modes.

[0100] When the required braking force is greater than or equal to the braking force setting value, it is in the heavy braking mode. At this time, the original vehicle braking and the regenerative braking systems work together.

[0101] In case of special circumstances, when the engineering vehicle needs to travel at high speed or the hydraulic system fails and needs to be transferred to a suitable place for repair, the clutch 12 engages and the vehicle is only driven by the engine 16.

[0102] When the boom descends, the first two-position two-way directional valve 2 is energized and works in the right position, recovering the potential energy of the boom and storing it in the first accumulator 3.

[0103] Calculation method for the displacement sizes of the required combined power source 14 and the stepped variable motor 11 in the system:

[0104] The power balance equation of the hydraulic drive vehicle is:

[0105]

[0106] In the formula: M E (n E ) is the output torque of the engine 16;

[0107] n E is the rotational speed of the engine 16;

[0108] n p is the rotational speed of the combined power source 14;

[0109] V p is the displacement of the combined power source 14;

[0110] p is the working pressure of the system;

[0111] V m is the displacement of the stepped variable motor 11;

[0112] n m is the rotational speed of the stepped variable motor 11;

[0113] n K is the rotational speed of the wheel;

[0114] K is the transmission coefficient of the torque continuously adjustable coupler;

[0115] M K (t) is the load torque of the engine 16.

[0116] Calculation method for the displacement size of the required combined power source 14 of the system:

[0117]

[0118] In the formula: M E0 (n E ) is the torque value on the economic curve of the engine;

[0119] V p_max is the maximum displacement value of the combined power source 14.

[0120] Calculation method for the displacement size of the required stepped variable motor 11 of the system:

[0121]

[0122] In the formula: V m_max is the maximum displacement value of the stepped variable motor 11.

[0123] In this embodiment, the displacement combination control mode of the combined power source 14:

[0124] When 1DT, 2DT, and 3DT are all de-energized, the oil discharged by the three groups of fixed-displacement pumps flows back to the hydraulic oil tank 15 through the two-position three-way valve group 18. At this time, the displacement of the combined power source 14 is 0;

[0125] When 1DT is energized and 2DT and 3DT are de-energized, the oil discharged by the fixed-displacement pump with a displacement of V p1 enters the system, and the other two pumps are in the unloading state. At this time, the displacement of the combined power source 14 is equivalent to V p1 ;

[0126] When 2DT is energized and 1DT and 3DT are de-energized, the oil discharged by the fixed-displacement pump with a displacement of 2V p1 enters the system, and the other two pumps are in the unloading state. At this time, the displacement of the combined power source 14 is equivalent to 2V p1 ;

[0127] When 1DT and 2DT are energized and 3DT is de-energized, the oil discharged by the fixed-displacement pumps with displacements of V p1 and 2V p1 enters the system, and the other pump is in the unloading state. At this time, the displacement of the combined power source 14 is equivalent to V p1 +2V p1 =3V p1 ;

[0128] When 3DT is powered on and 1DT and 2DT are not powered on, the displacement is 4V p1 The oil discharged by the fixed-displacement pump with a displacement of p1 enters the system, and the other two pumps are in the unloading state. At this time, the displacement of the combined power source 14 is equivalent to 4V p1 ;

[0129] When 1DT and 3DT are powered on and 2DT is not powered on, the displacement is V p1 and 4V p1 The oil discharged by the fixed-displacement pumps with displacements of p1 and p1 enters the system, and the other pump is in the unloading state. At this time, the displacement of the combined power source 14 is equivalent to V p1 +4V p1 =5V p1 ;

[0130] When 2DT and 3DT are powered on and 1DT is not powered on, the displacement is 2V p1 and 4V p1 The oil discharged by the fixed-displacement pumps with displacements of p1 and p1 enters the system, and the other pump is in the unloading state. At this time, the displacement of the combined power source 14 is equivalent to 2V p1 +4V p1 =6V p1 ;

[0131] When 1DT, 2DT, and 3DT are all powered on, the displacement is V p1 and 2V p1 and 4V p1 The oil discharged by the fixed-displacement pumps with displacements of p1 , p1 , and p1 enters the system. At this time, the displacement of the combined power source 14 is equivalent to V p1 +2V p1 +4V p1 =7V p1 ;

[0132] In this embodiment, the displacement combination control method of the stepped variable motor 14:

[0133] Regarding the description of forward and reverse rotation: When 2YA, 4YA, and 6YA are powered on, that is, when the corresponding reversing valves in the three-position four-way reversing valve group 8 are in the right position, the stepped variable motor 14 rotates forward. On the contrary, when 1YA, 3YA, and 5YA are powered on, that is, when the corresponding reversing valves in the three-position four-way reversing valve group 8 are in the left position, the stepped variable motor 14 rotates in reverse.

[0134] When 1YA, 2YA, 3YA, 4YA, 5YA, and 6YA are all not powered on, the stepped variable motor 14 idles at this time.

[0135] Taking forward rotation (vehicle forward) as an example, the step change process of the displacement of the stepped variable motor 14 is described:

[0136] When 2YA is powered on and 1YA, 3YA, 4YA, 5YA, and 6YA are all not powered on, the high-pressure oil of the system enters the displacement of Vm1 For the port A of the fixed-displacement motor, the oil discharged from port B of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other two motors are in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 ;

[0137] When 4YA is energized and 1YA, 2YA, 3YA, 5YA, and 6YA are all de-energized, the high-pressure oil of the system enters the port A of the fixed-displacement motor with a displacement of 2V m1 For the port A of the fixed-displacement motor, the oil discharged from port B of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other two motors are in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to 2V m1 ;

[0138] When 2YA and 4YA are energized and 1YA, 3YA, 5YA, and 6YA are all de-energized, the high-pressure oil of the system enters the port A of the fixed-displacement motors with displacements of V m1 , 2V m1 For the port A of the fixed-displacement motor, the oil discharged from port B of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other motor is in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 +2V m1 =3V m1 ;

[0139] When 6YA is energized and 1YA, 2YA, 3YA, 4YA, and 5YA are all de-energized, the high-pressure oil of the system enters the port A of the fixed-displacement motor with a displacement of 4V m1 For the port A of the fixed-displacement motor, the oil discharged from port B of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other two motors are in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to 4V m1 ;

[0140] When 2YA and 6YA are energized and 1YA, 3YA, 4YA, and 5YA are all de-energized, the high-pressure oil of the system enters the port A of the fixed-displacement motors with displacements of V m1 , 4V m1 For the port A of the fixed-displacement motor, the oil discharged from port B of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other motor is in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 +4V m1 =5V m1 ;

[0141] When 4YA and 6YA are energized and 1YA, 2YA, 3YA, and 5YA are all de-energized, the high-pressure oil of the system enters the port A of the fixed-displacement motors with displacements of 2V m1 , 4V m1 For the port A of the fixed-displacement motor, the oil discharged from port B of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other motor is in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to 2V m1 +4V m1 =6V m1;

[0142] When 2YA, 4YA, and 6YA are energized and 1YA, 3YA, and 5YA are all de-energized, the high-pressure oil of the system enters port A of the fixed-displacement motor with a displacement of V m1 , 2V m1 , 4V m1 . The oil discharged from port B of the fixed-displacement motor flows back to the hydraulic oil tank 15. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 + 2V m1 + 4V m1 = 7V m1 ;

[0143] Similarly for reverse (vehicle moving backward), the specific implementation is as follows:

[0144] When 1YA is energized and 2YA, 3YA, 4YA, 5YA, and 6YA are all de-energized, the high-pressure oil of the system enters port B of the fixed-displacement motor with a displacement of V m1 . The oil discharged from port A of the fixed-displacement motor flows back to the hydraulic oil tank 15. The other two motors are in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 ;

[0145] When 3YA is energized and 1YA, 2YA, 4YA, 5YA, and 6YA are all de-energized, the high-pressure oil of the system enters port B of the fixed-displacement motor with a displacement of 2V m1 . The oil discharged from port A of the fixed-displacement motor flows back to the hydraulic oil tank 15. The other two motors are in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to 2V m1 ;

[0146] When 1YA and 3YA are energized and 2YA, 4YA, 5YA, and 6YA are all de-energized, the high-pressure oil of the system enters port B of the fixed-displacement motors with displacements of V m1 , 2V m1 . The oil discharged from port A of the fixed-displacement motors flows back to the hydraulic oil tank 15. The other motor is in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 + 2V m1 = 3V m1 ;

[0147] When 5YA is energized and 1YA, 2YA, 3YA, 4YA, and 6YA are all de-energized, the high-pressure oil of the system enters port B of the fixed-displacement motor with a displacement of 4V m1 . The oil discharged from port A of the fixed-displacement motor flows back to the hydraulic oil tank 15. The other two motors are in the unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to 4V m1 ;

[0148] When 1YA and 5YA are energized, and 2YA, 3YA, 4YA, and 6YA are all de-energized, the high-pressure oil of the system enters port B of the fixed-displacement motor with a displacement of V m1 , 4V m1 . The oil discharged from port A of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other motor is in a unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 + 4V m1 = 5V m1 ;

[0149] When 3YA and 5YA are energized, and 1YA, 2YA, 4YA, and 6YA are all de-energized, the high-pressure oil of the system enters port B of the fixed-displacement motor with a displacement of 2V m1 , 4V m1 . The oil discharged from port A of the fixed-displacement motor flows back to the hydraulic oil tank 15, and the other motor is in a unloading state. At this time, the displacement of the stepped variable motor 11 is equivalent to 2V m1 + 4V m1 = 6V m1 ;

[0150] When 1YA, 3YA, and 5YA are energized, and 2YA, 4YA, and 6YA are all de-energized, the high-pressure oil of the system enters port B of the fixed-displacement motors with displacements of V m1 , 2V m1 , 4V m1 . The oil discharged from port A of the fixed-displacement motors flows back to the hydraulic oil tank 15. At this time, the displacement of the stepped variable motor 11 is equivalent to V m1 + 2V m1 + 4V m1 = 7V m1 ;

[0151] During braking energy recovery, the stepped variable motor 11 operates in the pump state at this time.

[0152] When 1YA, 2YA, 3YA, 4YA, 5YA, and 6YA are all de-energized, the stepped variable motor 14 idles at this time.

[0153] When 1YA is energized, and 2YA, 3YA, 4YA, 5YA, and 6YA are all de-energized, the hydraulic oil tank 15 enters port A of the fixed-displacement motor with a displacement of V m1 to make it operate in the pump state. The oil discharged from port B enters the second accumulator 4 to charge the accumulator. The other two motors are in a unloading state. At this time, the stepped variable motor 11 is equivalent to a pump with a displacement of V m1 ;

[0154] When 3YA is energized, and 1YA, 2YA, 4YA, 5YA, and 6YA are all de-energized, the hydraulic oil tank 15 enters port A of the fixed-displacement motor with a displacement of 2V m1The A port of the fixed-displacement motor is made to work in the pump state, and the oil discharged from the B port enters the second accumulator 4 to charge the accumulator. The other two motors are in the unloading state. At this time, the stepped variable motor 11 is equivalent to a pump with a displacement of 2V. m1 displacement pump;

[0155] When 1YA and 3YA are energized and 2YA, 4YA, 5YA, and 6YA are not energized, the hydraulic oil tank 15 enters the A port of the fixed-displacement motor with a displacement of V m1 , 2V m1 The A port of the fixed-displacement motor is made to work in the pump state, and the oil discharged from the B port enters the second accumulator 4 to charge the accumulator. Another motor is in the unloading state. At this time, the stepped variable motor 11 is equivalent to a pump with a displacement of V m1 + 2V m1 = 3V m1 displacement pump;

[0156] When 5YA is energized and 1YA, 2YA, 3YA, 4YA, and 6YA are not energized, the hydraulic oil tank 15 enters the A port of the fixed-displacement motor with a displacement of 4V m1 The A port of the fixed-displacement motor is made to work in the pump state, and the oil discharged from the B port enters the second accumulator 4 to charge the accumulator. The other two motors are in the unloading state. At this time, the stepped variable motor 11 is equivalent to a pump with a displacement of 4V m1 displacement pump;

[0157] When 1YA and 5YA are energized and 2YA, 3YA, 4YA, and 6YA are not energized, the hydraulic oil tank 15 enters the A ports of the fixed-displacement motors with displacements of V m1 , 4V m1 The A ports of the fixed-displacement motors are made to work in the pump state, and the oil discharged from the B ports enters the second accumulator 4 to charge the accumulator. Another motor is in the unloading state. At this time, the stepped variable motor 11 is equivalent to a pump with a displacement of V m1 + 4V m1 = 5V m1 displacement pump;

[0158] When 3YA and 5YA are energized and 1YA, 2YA, 4YA, and 6YA are not energized, the hydraulic oil tank 15 enters the A ports of the fixed-displacement motors with displacements of 2V m1 , 4V m1 The A ports of the fixed-displacement motors are made to work in the pump state, and the oil discharged from the B ports enters the second accumulator 4 to charge the accumulator. Another motor is in the unloading state. At this time, the stepped variable motor 11 is equivalent to a pump with a displacement of 2V m1 + 4V m1 = 6V m1 displacement pump;

[0159] When 1YA, 3YA, and 5YA are energized and 2YA, 4YA, and 6YA are not energized, the hydraulic oil tank 15 enters the A port of the fixed-displacement motor with a displacement of V m1 , 2V m1, 4V m1 The port A of the fixed-displacement motor m1 is made to work in the pump state, and the oil discharged from port B enters the second accumulator 4 to charge the accumulator. At this time, the stepped variable motor 11 is equivalent to a pump with a displacement of m1 +2V m1 +4V m1 =7V m1 displacement.

Claims

1. A hydraulic hybrid power system for an engineering vehicle, characterized in that: The system comprises: an engineering vehicle hydraulic working device (1), a first two-position two-way reversing valve (2), a first accumulator (3), a second accumulator (4), a second two-position two-way reversing valve (5), a three-position four-way reversing valve group (8), a torque stepless adjustable coupler (9), a rear axle (10), a step variable motor (11), a clutch (12), a one-way valve group (13), a combined power source (14), a hydraulic oil tank (15), an engine (16), a front axle (17), a two-position three-way reversing valve group (18) and a diversion priority valve (19); The engine (16) is coaxially connected to the input shaft of the combined power source (14); the output shaft of the combined power source (14) is connected to the input end of the step variable motor (11) through the clutch (12); the output end of the step variable motor (11) is connected to the power input end of the stepless variable torque coupler (9); the power output end of the stepless variable torque coupler (9) is respectively connected to the power input ends of the rear axle (10) and the front axle (17); the stepless variable torque coupler (9) has the function of stepless speed change and torque increase; The two-position three-way reversing valve group (18) is an integrated valve block, comprising a plurality of two-position three-way reversing valves, wherein the A ports of the two-position three-way reversing valves are connected to each other, and the outputs to the outside are ports A1 and A2; the B ports of the two-position three-way reversing valves are connected to each other, and the output to the outside is port B1, and each two-position three-way reversing valve is respectively provided with a P port; The combined power source (14) is composed of a plurality of quantitative pumps connected coaxially or by a transfer case, each quantitative pump having a separate oil inlet and oil outlet; the oil inlet of the combined power source (14) is connected to a hydraulic oil tank (15), the oil outlet is sequentially connected to the oil inlet of the corresponding valve of the one-way valve group (13), the oil outlet of the one-way valve group (13) is respectively connected to the P port of each reversing valve in the two-position three-way electromagnetic reversing valve group (18), the A1 port of the two-position three-way reversing valve group (18) is connected to the P port of the diversion priority valve (19), and the B1 port of the two-position three-way reversing valve group (18) is connected to the hydraulic oil tank (15); The three-position four-way reversing valve group (8) is an integrated valve block, comprising a plurality of three-position four-way reversing valves; inside the integrated valve block, the A ports of the three-position four-way reversing valves are interconnected, and the output to the outside is port A; the B ports are also interconnected, and the output to the outside is port B; each three-position four-way reversing valve is respectively provided with a P port and a T port; The A port of the diverter priority valve (19) is connected to the hydraulic working device (1) of the engineering vehicle, and is connected to the A port of the first two-position two-way reversing valve (2) through a bypass. The B port of the first two-position two-way reversing valve (2) is connected to the first accumulator (3) and is connected to the hydraulic oil tank (15) through a bypass. The A port of the second two-position two-way reversing valve (5) is connected to the B port of the diverter priority valve (19), and the B port of the second two-position two-way reversing valve (5) is connected to the second accumulator (4) and is connected to the hydraulic oil tank (15) through a bypass. The step variable motor (11) is a plurality of fixed-displacement motors coaxially connected, and each fixed-displacement motor has a separate oil inlet and an oil outlet; the B port of the diversion priority valve (19) is connected to the A port of the three-position four-way reversing valve group (8); the P port of each reversing valve in the three-position four-way reversing valve group (8) is respectively connected to the B port of the corresponding motor in the step variable motor (11); the T port of each reversing valve in the three-position four-way reversing valve group (8) is respectively connected to the A port of the corresponding motor in the step variable motor (11); and the B port of the three-position four-way reversing valve group (8) is connected to the hydraulic oil tank (15); The system further comprises a bypass relief valve (24), wherein the bypass relief valve (24) is arranged on a bypass of a two-position three-way reversing valve group (18), wherein an A2 port of the two-position three-way reversing valve group (18) is connected to an inlet of the bypass relief valve (24) via a bypass, and an outlet of the bypass relief valve (24) is connected to a hydraulic oil tank (15); a first pressure reducing valve (20) and a first throttle valve (21) are connected in sequence between an A port of the diversion priority valve (19) and a hydraulic working device (1) of the engineering vehicle.

2. The hydraulic hybrid power system for an engineering vehicle according to claim 1, characterized in that: A working device safety valve (7) is provided on a bypass between the B port of the first two-position two-way reversing valve (2) and the hydraulic oil tank (15).

3. The hydraulic hybrid power system for an engineering vehicle according to claim 1, characterized in that: An auxiliary brake circuit safety valve (6) is provided on a bypass between the B port of the second two-position two-way reversing valve (5) and the hydraulic oil tank (15).

4. The hydraulic hybrid power system for an engineering vehicle according to claim 1, characterized in that: The B port of the flow diversion priority valve (19) is connected to the second pressure reducing valve (22) and the second throttle valve (23) in sequence, and is then connected to the A port of the three-position four-way reversing valve group (8) and the A port of the second two-position two-way reversing valve (5) respectively.

5. The hydraulic hybrid power system for an engineering vehicle according to claim 1, characterized in that: The displacement combination mode adopted by the combined power source (14) and the step variable motor (11) is one of an equal value combination, an arithmetic progression combination, a Fibonacci sequence combination and a geometric sequence combination.

6. The control method of a hydraulic hybrid power system for an engineering vehicle as claimed in claim 1, characterized in that: Under driving conditions, the system is divided into idle charging mode, low load starting mode, driving charging mode, engine-only driving mode and hybrid driving mode; When the engine (16) is hot or temporarily stopped, the pressure in the second accumulator (4) is lower than the set maximum working pressure, and the system enters an idle charging mode. The control method in the idle charging mode is: The clutch (12) is in a disconnected state, the diverter priority valve (19) is powered on in the left position and works in the left position, the second two-position two-way electromagnetic reversing valve (5) is powered on and works in the left position, the first two-position two-way electromagnetic reversing valve (2) is powered off and disconnected, and the three-position four-way reversing valve group (8) is not powered on and works in the middle position; the displacement of the combined power source (14) is adjusted so that the engine (16) works in the fuel efficiency zone, the engine (16) drives the combined power source (14) to rotate, and the oil in the hydraulic oil tank (15) charges the second accumulator (4) through the combined power source (14), and the step variable motor (11) does not work at this time; When the required power of the engineering vehicle is less than the lower limit of the fuel efficiency zone of the engine (16), and the pressure in the second accumulator (4) is higher than the set minimum working pressure, the system enters a low-load starting mode. The control method in the low-load starting mode is: The clutch (12) is in a disconnected state, the diverter priority valve (19) is not electrically operated in the middle position, the engine (16) and the combined power source (14) are not operated, the second two-position two-way electromagnetic reversing valve (5) is electrically operated in the left position, the displacement of the step variable motor (11) is determined according to the power requirements of the whole vehicle, and then the number of reversing valves in the three-position four-way reversing valve group (8) operating in the right position is controlled; at this time, the high-pressure oil in the second accumulator (4) enters the step variable motor (11) through the second two-position two-way electromagnetic reversing valve (5) and the AT oil circuit in the three-position four-way reversing valve group (8), driving it to work in the motor working condition, and the power is transmitted to the front axle (17) and the rear axle (10) of the vehicle through the torque steplessly adjustable coupler (9); When the required power of the engineering vehicle is lower than the lower limit of the fuel efficiency zone power of the engine (16), and the pressure in the second accumulator (4) is lower than the set maximum working pressure, the system enters the driving charging mode. The control method in the driving charging mode is: The clutch (12) is in a disconnected state, the flow diversion priority valve (19) is not powered and works in the middle position, the second two-position two-way electromagnetic reversing valve (5) is powered and works in the left position, the first two-position two-way electromagnetic reversing valve (2) is disconnected, the displacement of the combined power source (14) and the stepped variable motor (11) is adjusted so that the engine (16) works in the fuel efficient area, the engine (16) drives the combined power source (14) to rotate, and the oil in the hydraulic oil tank (15) passes through the combined power source (14), the single The directional valve group (13), the two-position three-way electromagnetic reversing valve group (18), and the diversion priority valve (19) are divided into two paths, A and B. The path A enters the hydraulic working device (1) of the engineering vehicle; the path B charges the second accumulator (4) through the second two-position two-way electromagnetic reversing valve (5), and at the same time drives the step variable motor (11) through the three-position four-way reversing valve group (8); the power output by the step variable motor (11) is transmitted to the front axle (17) and the rear axle (10) respectively through the torque steplessly adjustable coupler (9); When the power demand of the engineering vehicle is within the fuel efficiency zone of the engine (16), or when the power demand of the engineering vehicle is higher than the upper limit of the fuel efficiency zone of the engine (16) and the pressure of the second accumulator (4) is lower than the set minimum working pressure value, the system enters the engine-only driving mode. The control method in the engine-only driving mode is: The clutch (12) is in a disconnected state, the diverter priority valve (19) is not electrically operated in the middle position, the second two-position two-way electromagnetic reversing valve (5) and the first two-position two-way electromagnetic reversing valve (2) are disconnected, the displacement of the combined power source (14) and the step variable motor (11) are adjusted so that the engine (16) operates in a fuel efficient area, the engine (16) drives the combined power source (14) to rotate, and the oil in the oil tank (15) is divided into two paths A and B through the combined power source (14), the one-way valve group (13), the two-position three-way electromagnetic reversing valve group (18), and the diverter priority valve (19). The path A enters the hydraulic working device (1) of the engineering vehicle, and the path B drives the step variable motor (11) through the three-position four-way reversing valve group (8). The power output by the step variable motor (11) is transmitted to the front axle (17) and the rear axle (10) respectively through the torque steplessly adjustable coupler (9); When the engineering vehicle starts or climbs a slope under high load, the required power is greater than the upper limit of the fuel efficiency zone of the engine (16), and the pressure of the second accumulator (4) is higher than the set minimum working pressure value, the system enters the hybrid drive mode, and the control method in the hybrid drive mode is: The clutch (12) is in a disconnected state, the diverter priority valve (19) is not electrically operated in the middle position, the second two-position two-way electromagnetic reversing valve (5) is electrically operated in the left position, the first two-position two-way electromagnetic reversing valve (2) is disconnected, the displacement of the combined power source (14) and the stepped variable motor (11) is adjusted so that the engine (16) operates in the fuel efficiency zone, the engine (16) drives the combined power source (14) to rotate, and the oil in the hydraulic oil tank (15) passes through the combined power source (14), the one-way valve group (13), the two-position three-way electromagnetic reversing valve (5), and the hydraulic oil tank (15). The reversing valve group (18) and the diversion priority valve (19) are divided into two paths, A and B. The path A enters the hydraulic working device (1) of the engineering vehicle; the path B drives the step variable motor (11) through the three-position four-way reversing valve group (8); at the same time, the high-pressure oil in the second accumulator (4) is discharged through the second two-position two-way electromagnetic reversing valve (5), and drives the step variable motor (11) through the three-position four-way reversing valve group (8); the power output by the step variable motor (11) is transmitted to the front axle (17) and the rear axle (10) respectively through the torque steplessly adjustable coupler (9); When the pressure in the first accumulator (3) is higher than the working pressure of the hydraulic working device (1) of the engineering vehicle, the first two-position two-way electromagnetic reversing valve (2) is energized to work in the right position, and the auxiliary combined power source (14) provides an oil source for the hydraulic working device (1) of the engineering vehicle; the output oil of the first accumulator (3) passes through the first two-position two-way electromagnetic reversing valve (2) in sequence and enters the hydraulic working device (1) of the engineering vehicle.

7. The control method of a hydraulic hybrid power system for an engineering vehicle as claimed in claim 1, characterized in that: Under braking conditions, the system is divided into light braking mode and heavy braking mode; When the required braking force is less than the set braking force, the system enters the light braking mode. The control method in the light braking mode is: The clutch (12) is in a disconnected state, the right position of the diverter priority valve (19) is energized to work in the right position, the second two-position two-way electromagnetic reversing valve (5) is energized to work in the left position, the displacement of the combined power source (14) is adjusted so that the engine (16) works in a fuel efficient area, the engine (16) drives the combined power source (14) to rotate, and the oil in the hydraulic oil tank (15) enters the engineering vehicle hydraulic working device (1) through the combined power source (14), the one-way valve group (13), the two-position three-way electromagnetic reversing valve group (18), and the diverter priority valve (19); The braking energy from the front axle (17) and the rear axle (10) drives the step variable motor (11) to operate in a pumping state via the torque steplessly adjustable coupler (9); the step variable motor (11) in the pumping state draws oil from the hydraulic oil tank (15) via the BT oil circuit of the three-position four-way reversing valve group (8), and charges the second accumulator (4) again via the PA oil circuit of the three-position four-way reversing valve group (8); When the required braking force is greater than or equal to the system force setting value, it is in the heavy braking mode. The control method in the heavy braking mode is: the original vehicle braking and the light braking mode work together.

8. The control method of a hydraulic hybrid power system for an engineering vehicle as claimed in claim 1, characterized in that: Method for calculating the displacement of the combined power source (14) and the step variable motor (11) required by the system: 1) Calculation method of the displacement size of the combined power source (14) required by the system: Where: M E0 (n E ) is the torque value on the engine economy curve; V p_max is the maximum displacement value of the combined power source (14); p is the working pressure of the system; 2) Calculation method for the displacement size of the step variable motor (11) required by the system: Where: M K (t) is the load torque of the engine (16); K is the transmission coefficient of the torque steplessly adjustable coupler; p is the working pressure of the system; V m_max is the maximum displacement value of the step variable motor (11).

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