阅读说明：本技术 一种电静液储能单元 (Electro-hydrostatic energy storage unit ) 是由 王峰 林梓畅 徐兵 于 2021-09-02 设计创作，主要内容包括：本发明公开了一种电静液储能单元。本发明包括液压油箱、蓄电池、电机控制器、电机和液压泵马达；蓄电池通过电机控制器与电机电连接,电机的输出轴与液压泵马达的输出轴同轴连接,液压泵马达设置有两个进出油口,液压泵马达的第一进出油口与液压油箱连通,液压泵马达的第二进出油口作为电静液储能单元的进出油口。电储能具有高能量密度,与传统的液压蓄能器储能相比,本发明可实现高能量密度的液压储能,同时通过对电机速度转矩的控制,可以实现主动的液压压力流量控制。(The invention discloses an electro-hydrostatic energy storage unit. The invention comprises a hydraulic oil tank, a storage battery, a motor controller, a motor and a hydraulic pump motor; the battery passes through the machine controller and is connected with the motor electricity, and the output shaft of motor and hydraulic pump motor's output shaft coaxial coupling, hydraulic pump motor are provided with two business turn over hydraulic fluid ports, and hydraulic pump motor's first business turn over hydraulic fluid port and hydraulic tank intercommunication, hydraulic pump motor's second business turn over hydraulic fluid port is as the business turn over hydraulic fluid port of electricity hydrostatic energy storage unit. The electric energy storage has high energy density, compared with the energy storage of the traditional hydraulic energy accumulator, the hydraulic energy storage of high energy density can be realized, and meanwhile, the active hydraulic pressure flow control can be realized by controlling the speed and the torque of the motor.)

1. An electro-hydrostatic energy storage unit, characterized in that: comprises a hydraulic oil tank (1), a storage battery (2), a motor controller (3), a motor (4) and a hydraulic pump motor (5);

the storage battery (2) is electrically connected with the motor (4) through the motor controller (3), the output shaft of the motor (4) is coaxially connected with the output shaft of the hydraulic pump motor (5), a first oil inlet and outlet of the hydraulic pump motor (5) is communicated with the hydraulic oil tank (1), and a second oil inlet and outlet of the hydraulic pump motor (5) serves as an oil inlet and outlet of the electro-hydrostatic energy storage unit.

2. An electro-hydrostatic energy storage unit according to claim 1, characterized in that: when the electro-hydrostatic energy storage unit outputs energy, oil output from the hydraulic oil tank (1) is boosted by a hydraulic pump motor (5) driven by the motor (4) and then is output from an oil inlet and an oil outlet of the electro-hydrostatic energy storage unit; when the electro-hydrostatic energy storage unit stores energy, oil input from an oil inlet and an oil outlet of the electro-hydrostatic energy storage unit is input into the hydraulic oil tank (1) after being reduced in pressure by the hydraulic pump motor (5).

3. An electro-hydrostatic energy storage unit according to claim 1, characterized in that: the hydraulic pump motor (5) is a fixed displacement hydraulic pump motor or an electronic proportional control variable displacement hydraulic pump motor; the hydraulic pump motor (5) is a single hydraulic pump motor or a combination of two or more hydraulic pump motors.

4. An electro-hydrostatic energy storage unit according to claim 1, characterized in that: the storage battery (2) is a battery pack or a super capacitor.

5. An electro-hydrostatic energy storage unit according to claim 1, characterized in that: the flow of the electro-hydrostatic energy storage unit, the rotating speed of the motor (4) and the displacement of the hydraulic pump motor (5) satisfy the following relations:

Q＝ω*D

q is the input and output flow of the electro-hydrostatic energy storage unit, omega is the rotating speed of the motor (4), and D is the displacement of the hydraulic pump motor (5).

6. An electro-hydrostatic energy storage unit according to claim 1, characterized in that: the high-low pressure difference of the electro-hydrostatic energy storage unit, the torque of the motor (4) and the displacement of the hydraulic pump motor (5) satisfy the following relations:

T＝Δp*D

wherein, Δ p is the pressure difference of the oil inlet and the oil outlet of the hydraulic pump motor (5), T is the torque of the motor (4), and D is the displacement of the hydraulic pump motor (5).

7. An electro-hydrostatic energy storage unit according to claim 1, characterized in that: the hydraulic circuit of the hydraulic pump motor (5) is a closed hydraulic circuit or an open hydraulic circuit.

Technical Field

The invention relates to a hydraulic energy storage unit, in particular to an electro-hydrostatic energy storage unit.

Background

The hydraulic energy storage unit is widely applied to the fields of engineering machinery, vehicles, ocean energy utilization and the like, wherein the most common hydraulic energy storage unit is a hydraulic energy accumulator which has high power density but has the following defects: 1) the energy density is low, the energy storage capacity is small, and the long-time energy release can not be realized; 2) the output hydraulic pressure of the hydraulic accumulator is quickly reduced to be below the pressure required by the system along with the release of the stored energy, so that the working stability of the system is influenced; 3) the pressure and flow of the oil at the input and output can not be actively regulated. The electric energy storage technology mainly refers to the technology of electrochemical batteries, super capacitor energy storage and the like, and has higher energy storage energy density.

Disclosure of Invention

In order to solve the technical problems, the invention provides an electro-hydrostatic energy storage unit based on a battery and a motor pump, wherein a hydraulic pump motor driven by a motor is used as an electro-hydrostatic pump, and the electro-hydrostatic energy storage unit can be driven by the motor to work under a pumping working condition or work under a motor working condition to drag the motor to work as a generator to convert hydraulic energy and electric energy into each other. The electric energy storage has high energy density, and compared with the energy storage of the traditional hydraulic energy accumulator, the hydraulic energy storage with high energy density can be realized. Meanwhile, the active hydraulic pressure flow control can be realized by controlling the speed and the torque of the motor.

The technical scheme adopted by the invention is as follows:

the invention comprises a hydraulic oil tank, a storage battery, a motor controller, a motor and a hydraulic pump motor;

the battery passes through the machine controller and is connected with the motor electricity, and the output shaft of motor and hydraulic pump motor's output shaft coaxial coupling, hydraulic pump motor are provided with two business turn over hydraulic fluid ports, and hydraulic pump motor's first business turn over hydraulic fluid port and hydraulic tank intercommunication, hydraulic pump motor's second business turn over hydraulic fluid port is as the business turn over hydraulic fluid port of electricity hydrostatic energy storage unit.

When the electro-hydrostatic energy storage unit outputs energy, oil output from the hydraulic oil tank is boosted by a hydraulic pump motor driven by a motor and then is output from an oil inlet and an oil outlet of the electro-hydrostatic energy storage unit; when the electro-hydrostatic energy storage unit stores energy, oil input from an oil inlet and an oil outlet of the electro-hydrostatic energy storage unit is depressurized by a hydraulic pump motor and then input into a hydraulic oil tank.

The hydraulic pump motor is a fixed displacement hydraulic pump motor or a variable displacement hydraulic pump motor controlled by an electronic proportion; the hydraulic pump motor is a single hydraulic pump motor, or a combination of two or more hydraulic pump motors.

The storage battery is a battery pack or a super capacitor.

The flow of the electro-hydrostatic energy storage unit, the rotating speed of the motor and the displacement of the hydraulic pump motor satisfy the following relations:

Q＝ω*D

q is the input and output flow of the electro-hydrostatic energy storage unit, omega is the rotating speed of the motor, and D is the displacement of the hydraulic pump motor.

The high-low pressure difference of the electro-hydrostatic energy storage unit, the torque of the motor and the displacement of the hydraulic pump motor satisfy the following relations:

T＝Δp*D

wherein, Δ p is the pressure difference of the oil inlet and the oil outlet of the hydraulic pump motor, T is the torque of the motor, and D is the displacement of the hydraulic pump motor.

The hydraulic circuit of the hydraulic pump motor is a closed hydraulic circuit or an open hydraulic circuit.

The invention has the beneficial effects that:

the electro-static liquid pump is a hydraulic pump motor driven by a motor, and can work under the pumping working condition driven by the motor or work under the working condition of the motor to reversely drag the motor to operate as a generator, so that hydraulic energy and electric energy are converted into each other. The electric energy storage has high energy density, compared with the energy storage of the traditional hydraulic energy accumulator, the hydraulic energy storage of high energy density can be realized, and meanwhile, the active hydraulic pressure flow control can be realized by controlling the speed and the torque of the motor.

Drawings

Fig. 1 is a schematic diagram of an electro-hydrostatic energy storage unit.

Fig. 2 is a schematic diagram of a series hydraulic hybrid system of the present invention for wheel drive of a wheel loader.

Fig. 3 is a schematic diagram of a front parallel hybrid system of the gearbox for wheel type driving of the wheel loader.

Fig. 4 is a schematic diagram of the rear parallel hybrid system of the gearbox for wheel type driving of the wheel loader according to the invention.

FIG. 5 is a schematic diagram of a front parallel hybrid transmission system of the present invention when used in a truck powertrain.

FIG. 6 is a schematic diagram of a transmission rear parallel hybrid system of the present invention when used in a truck powertrain.

In the figure: 1. the hydraulic system comprises a hydraulic oil tank, 2, a storage battery, 3, a motor controller, 4, a motor, 5, a hydraulic pump motor, 6, an engine, 7, a main hydraulic pump, 8, a hydraulic motor, 9, a vehicle main speed reducer, 10, a meshing gear pair, 11, a hydraulic torque converter, 12, a gearbox, 13, a first clutch, 14 and a second clutch.

Detailed Description

The invention is described in further detail below with reference to the figures and the embodiments.

As shown in fig. 1, the present invention includes a hydraulic oil tank 1, a storage battery 2, a motor controller 3, an electric motor 4, and a hydraulic pump motor 5;

the battery 2 is connected with the motor 4 through the motor controller 3, the output shaft of the motor 4 is coaxially connected with the output shaft of the hydraulic pump motor 5, the hydraulic pump motor 5 is provided with two oil inlet and outlet ports, the first oil inlet and outlet port of the hydraulic pump motor 5 is communicated with the hydraulic oil tank 1, the second oil inlet and outlet port of the hydraulic pump motor 5 is used as the oil inlet and outlet port of the electro-hydrostatic energy storage unit, and in specific implementation, the oil inlet and outlet port of the electro-hydrostatic energy storage unit is communicated with the hydrostatic transmission loop.

When the electro-hydrostatic energy storage unit outputs energy in a high-pressure oil form, oil output from the hydraulic oil tank 1 is boosted by a hydraulic pump motor 5 driven by a motor 4 and then is output from an oil inlet and an oil outlet of the electro-hydrostatic energy storage unit; when the electro-hydrostatic energy storage unit stores energy, high-pressure oil input from an oil inlet and an oil outlet of the electro-hydrostatic energy storage unit is depressurized by the hydraulic pump motor 5 and then input into the hydraulic oil tank 1.

The hydraulic pump motor 5 is a fixed displacement hydraulic pump motor or an electronic proportional control variable displacement hydraulic pump motor; the hydraulic pump motor 5 is a single hydraulic pump motor, or a combination of two or more hydraulic pump motors.

The storage battery 2 is a battery pack or a super capacitor.

The flow of the electro-hydrostatic energy storage unit, the rotating speed of the motor 4 and the displacement of the hydraulic pump motor 5 satisfy the following relations:

Q＝ω*D

wherein, Q is the input/output flow of the electro-hydrostatic energy storage unit, ω is the rotation speed of the motor 4, and D is the displacement of the hydraulic pump motor 5.

The high-low pressure difference of the electro-hydrostatic energy storage unit, the torque of the motor 4 and the displacement of the hydraulic pump motor 5 satisfy the following relations:

T＝Δp*D

wherein Δ p is a pressure difference between an oil inlet and an oil outlet of the hydraulic pump motor 5, T is a torque of the motor 4, and D is a displacement of the hydraulic pump motor 5.

The electro-hydrostatic energy storage unit can realize the energy output and input storage in the form of high-pressure oil. When energy is output in a high-pressure oil form, oil can be output after being boosted by a hydraulic pump motor 5 driven by a motor 4 from a hydraulic oil tank 1, electric energy stored in a storage battery drives the motor to rotate and is converted into high-pressure hydraulic energy, and the output flow is controlled and adjusted through the rotating speed of the motor; when energy is stored, high-pressure oil flows into the hydraulic oil tank 1 through the hydraulic pump motor 5, the hydraulic pump motor 5 drives the motor 4 to serve as a generator to generate electricity, high-pressure hydraulic energy is converted into electric energy to be stored in the storage battery 2, and the input flow is controlled and adjusted through the rotating speed of the motor.

The embodiment of the invention used for different power systems and the implementation working process thereof are as follows:

example 1

Fig. 2 is a schematic diagram of a series hydraulic hybrid system for a wheel loader travel drive of the present invention. The wheel loader is widely applied engineering machinery, a common hydrostatic transmission system for walking and driving of small and medium-sized wheel loaders is applied to the hydrostatic transmission system of the wheel loader.

The hydrostatic transmission system comprises an engine 6, a main hydraulic pump 7, a hydraulic motor 8 and a vehicle main speed reducer 9, an output shaft of the engine 6 is coaxially connected with an output shaft of the main hydraulic pump 7, two oil inlet and outlet ports of the main hydraulic pump 7 are respectively communicated with two oil inlet and outlet ports of the hydraulic motor 8, the main hydraulic pump 7 and the hydraulic motor 8 form a hydrostatic transmission loop, the output shaft of the hydraulic motor 8 is connected with the vehicle main speed reducer 9 through a transmission shaft, and an oil pipe connected between the main hydraulic pump 7 and the hydraulic motor 8 is communicated with a first oil inlet and outlet port of an electro-hydraulic energy storage unit. The hydraulic circuit of the hydraulic pump motor 5 of the electro-hydraulic energy storage unit in this embodiment is an open hydraulic circuit.

The main power source is an engine 6, drives a main hydraulic pump 7, drives a hydraulic motor 8 through a hydrostatic transmission circuit, drives a vehicle main speed reducer 9 through the hydraulic motor 8, and finally drives vehicle wheels to run through the vehicle main speed reducer 9. The electro-hydrostatic energy storage unit can ensure that the hydraulic pressure of the hydrostatic transmission loop is in a relatively stable level on one hand by controlling the hydraulic pressure of the oil inlet and the oil outlet and the flow of the oil inlet and the oil outlet, and reduce system vibration caused by sudden pressure change; on the other hand, the power matching of the engine and the load can be adjusted through energy charging and discharging, the problem that the power matching of the engine and the load is poor when the load speed changes too fast so that the working condition of the engine is worsened is solved, and the main power source can work stably. Meanwhile, the electro-hydrostatic energy storage unit can recover braking energy and provide auxiliary power, and the engine works in a higher efficiency range in a mode of energy storage and reutilization.

Example 2

Fig. 3 is a schematic diagram of a front parallel hybrid system of a gearbox for a wheel loader travel drive according to the present invention. For medium and large wheel loaders, the common drive train is hydrodynamic drive + gear shifting.

The power transmission system comprises a hydraulic motor 8, a vehicle main speed reducer 9, an engine 6, a hydraulic torque converter 11, a gearbox 12 and a meshing gear pair 10;

two oil inlets and outlets of the hydraulic motor 8 are respectively communicated with the oil inlet and outlet of the electro-hydraulic hybrid energy storage unit and the first oil inlet and outlet of the hydraulic pump motor 5, and the first oil inlet and outlet of the hydraulic pump motor 5 is not communicated with the hydraulic oil tank, namely, the hydraulic circuit of the hydraulic pump motor 5 is a closed hydraulic circuit. The hydraulic pump motor 5 and the hydraulic motor 8 constitute a hydrostatic transmission circuit.

Two gears of the meshing gear pair 10 are meshed to form a gear pair, an output shaft of the hydraulic motor 8 is coaxially connected with one gear of the meshing gear pair 10, the other gear of the meshing gear pair 10 is respectively coaxially connected with an output shaft of the hydraulic torque converter 11 and an input shaft of the gearbox 12, the hydraulic torque converter 11 and the gearbox 12 are respectively arranged on two sides of the meshing gear pair 10, the input shaft of the hydraulic torque converter 11 is coaxially connected with an output shaft of the engine 6, the output shaft of the gearbox 12 is coaxially connected with the vehicle main speed reducer 9, and the output shaft of the hydraulic torque converter 11 and the input shaft of the gearbox 12 which are coaxially connected with the meshing gear pair 10 are both used as transmission shafts of the power transmission system.

The hydraulic energy of the electro-hydrostatic energy storage unit can be converted into mechanical energy through the hydraulic motor 8 and then the mechanical energy is converged into the transmission shaft, and the redundant mechanical energy output by the engine 6 can be converted into hydraulic energy which is stored in the electro-hydraulic hybrid energy storage unit. When the power of the engine is smaller than the power required by wheel driving, the storage battery 2 supplies power to the motor 4, the motor controller 3 controls the motor to rotate to drive the hydraulic pump motor 5 to work as a pump, and the output high-pressure hydraulic oil drives the hydraulic motor 8 to rotate to drive the main speed reducer 9 of the vehicle; when the output power of the engine is greater than the power required by wheel driving, the redundant output power of the engine drives the hydraulic motor 8 to work as a pump through the meshing gear pair 10, the output high-pressure hydraulic oil drives the hydraulic pump motor 5 to rotate as a motor, and then drives the motor 4 to generate electricity as a generator, the motor controller 3 controls the rotating speed of the motor 4, and further controls the power absorbed by the engine, and the obtained electric energy is stored in the storage battery 2. On one hand, the working point of the engine can be adjusted to a high-efficiency working area through the storage and release of energy, the fuel economy is improved, and the exhaust emission is reduced; on the other hand, the hydraulic motors 8 connected in parallel can be used as auxiliary power, and can play a role in starting, stopping, accelerating, decelerating and other working conditions by utilizing the characteristics of quick response and high power density of the hydraulic power, so that the power performance and the manipulation performance of the wheel loader are improved.

Example 3

Fig. 4 is a schematic diagram of the rear parallel hybrid system of the gearbox for the wheel loader travel drive of the present invention. The main difference from embodiment 2 is that the position of the hydraulic motor 8 connected in parallel to the main drive shaft is different, and the operating conditions are also different. Compared with the parallel hybrid before the gearbox, the rotating speed of the parallel after the gearbox is lower and the torque requirement is higher, the rotating speed of the hydraulic motor 8 is lower.

The power transmission system comprises a hydraulic motor 8, a vehicle main speed reducer 9, an engine 6, a hydraulic torque converter 11, a gearbox 12 and a meshing gear pair 10;

two oil inlets and outlets of the hydraulic motor 8 are respectively communicated with the oil inlet and outlet of the electro-hydraulic hybrid energy storage unit and the first oil inlet and outlet of the hydraulic pump motor 5, and the first oil inlet and outlet of the hydraulic pump motor 5 is not communicated with the hydraulic oil tank, namely, the hydraulic circuit of the hydraulic pump motor 5 is a closed hydraulic circuit. The hydraulic pump motor 5 and the hydraulic motor 8 constitute a hydrostatic transmission circuit.

Two gears of the meshing gear pair 10 are meshed to form a gear pair, an output shaft of the hydraulic motor 8 is coaxially connected with one gear of the meshing gear pair 10, the other gear of the meshing gear pair 10 is respectively coaxially connected with an output shaft of the gearbox 12 and a connecting shaft of the vehicle main reducer 9, the vehicle main reducer 9 and the gearbox 12 are respectively arranged on two sides of the meshing gear pair 10, the engine 6 is coaxially connected with an input shaft of the gearbox 12 through a hydraulic torque converter 11, and the output shaft of the gearbox 12 and the connecting shaft of the vehicle main reducer 9 which are coaxially connected with the meshing gear pair 10 are both used as transmission shafts of a power transmission system.

The hydraulic energy of the electro-hydrostatic energy storage unit can be converted into mechanical energy through the hydraulic motor 8 and be gathered into the main power transmission shaft, and the redundant mechanical energy output by the engine 6 can be converted into hydraulic energy and stored into the electro-hydraulic hybrid energy storage unit. Similar to embodiment 2, when the power of the engine is smaller than the power required by wheel driving, the storage battery 2 supplies power to the motor 4, the motor controller 3 controls the motor to rotate, the hydraulic pump motor 5 is driven to work as a pump, and the output high-pressure hydraulic oil drives the hydraulic motor 8 to rotate to drive the vehicle main reducer 9; when the output power of the engine is greater than the power required by wheel driving, the redundant output power of the engine drives the hydraulic motor 8 to work as a pump through the meshing gear pair 10, the output high-pressure hydraulic oil drives the hydraulic pump motor 5 to rotate as a motor, and then drives the motor 4 to generate electricity as a generator, the motor controller 3 controls the rotating speed of the motor 4, and further controls the power absorbed by the engine, and the obtained electric energy is stored in the storage battery 2. On one hand, the working point of the engine can be adjusted to a high-efficiency working area through the storage and release of energy, the fuel economy is improved, and the exhaust emission is reduced; on the other hand, the hydraulic motors 8 connected in parallel can be used as auxiliary power, and can play a role in starting, stopping, accelerating, decelerating and other working conditions by utilizing the characteristics of quick response and high power density of the hydraulic power, so that the power performance and the manipulation performance of the wheel loader are improved.

Example 4

FIG. 5 is a schematic diagram of a front parallel hybrid transmission system of the present invention when used in a truck powertrain. Heavy-duty trucks also have a high demand on power performance, and particularly under the working conditions of starting, braking, ascending and the like, a power system needs to adapt to the low-speed working condition and the high-speed working condition of long-distance transportation at the same time, and the demands on an engine and a gearbox are high. Meanwhile, a large amount of braking energy is wasted when the truck is in a long-distance downhill, and an auxiliary heat dissipation device of a brake pad needs to be assembled.

The truck power system comprises a hydraulic motor 8, a vehicle main speed reducer 9, an engine 6, a gearbox 12, a meshing gear pair 10, a first clutch 13 and a first clutch 14;

two oil inlets and outlets of the hydraulic motor 8 are respectively communicated with the oil inlet and outlet of the electro-hydraulic hybrid energy storage unit and the first oil inlet and outlet of the hydraulic pump motor 5, and the first oil inlet and outlet of the hydraulic pump motor 5 is not communicated with the hydraulic oil tank, namely, the hydraulic circuit of the hydraulic pump motor 5 is a closed hydraulic circuit. The hydraulic pump motor 5 and the hydraulic motor 8 constitute a hydrostatic transmission circuit.

Two gears of the meshing gear pair 10 are meshed to form a gear pair, an output shaft of the hydraulic motor 8 is coaxially connected with one gear of the meshing gear pair 10 through a first clutch 14, the other gear of the meshing gear pair 10 is respectively coaxially connected with an input shaft of a gearbox 12 and an output shaft of a first clutch 13, the first clutch 13 and the gearbox 12 are respectively arranged on two sides of the meshing gear pair 10, the engine 6 is coaxially connected with the input shaft of the first clutch 13, and the output shaft of the gearbox 12 is coaxially connected with a main speed reducer 9 of the vehicle; an input shaft of the transmission case 12 coaxially connected to the meshing gear pair 10 and an output shaft of the first clutch 13 both serve as transmission shafts of the power transmission system.

On one hand, under the low-speed working conditions of starting and stopping, accelerating and decelerating, ascending and the like, the second clutch 14 is connected, the parallel hydraulic motor 8 provides auxiliary power, the power performance and the operation performance of the truck are improved by utilizing the quick response and high power density characteristics of the hydraulic power, and under the high-speed working condition, the second clutch 14 is disconnected, so that the work of an engine is not influenced; on the other hand, under the working conditions of braking, long-distance downhill and the like, the second clutch 14 is switched on, braking energy is recovered while braking force is provided, mechanical energy on the transmission shaft is converted and stored into the electro-hydrostatic energy storage unit through the hydraulic motor 8, and the mechanical energy is released under the working conditions of auxiliary starting and the like, so that the energy efficiency is improved, and meanwhile, the heat generated by braking is reduced.

Example 5

FIG. 6 is a schematic diagram of a transmission rear parallel hybrid system of the present invention when used in a truck powertrain. The main difference from embodiment 4 is that the position of the hydraulic motor 8 connected in parallel to the main drive shaft is different, and the operating conditions are also different. Compared with the parallel hybrid operation before the gearbox, the rotating speed of the hydraulic motor 8 is lower and the torque requirement is higher.

The truck power system comprises a hydraulic motor 8, a vehicle main speed reducer 9, an engine 6, a gearbox 12, a meshing gear pair 10, a first clutch 13 and a first clutch 14;

two oil inlets and outlets of the hydraulic motor 8 are respectively communicated with the oil inlet and outlet of the electro-hydraulic hybrid energy storage unit and the first oil inlet and outlet of the hydraulic pump motor 5, and the first oil inlet and outlet of the hydraulic pump motor 5 is not communicated with the hydraulic oil tank, namely, the hydraulic circuit of the hydraulic pump motor 5 is a closed hydraulic circuit. The hydraulic pump motor 5 and the hydraulic motor 8 constitute a hydrostatic transmission circuit.

Two gears of the meshing gear pair 10 are meshed to form a gear pair, an output shaft of the hydraulic motor 8 is coaxially connected with one gear of the meshing gear pair 10 through a second clutch 15, the other gear of the meshing gear pair 10 is respectively and coaxially connected with an output shaft of the gearbox 12 and a connecting shaft of the vehicle main reducer 9, the vehicle main reducer 9 and the gearbox 12 are respectively arranged on two sides of the meshing gear pair 10, the engine 6 is coaxially connected with an input shaft of the gearbox 12 through a first clutch 14, and the output shaft of the gearbox 12 and the connecting shaft of the vehicle main reducer 9 which are coaxially connected with the meshing gear pair 10 are both used as transmission shafts of the power transmission system.

Similarly, on one hand, during low-speed working conditions such as start-stop, acceleration and deceleration, uphill and the like, the second clutch 14 is connected, the parallel hydraulic motor 8 provides auxiliary power, the power performance and the handling performance of the truck are improved by utilizing the characteristics of quick response and high power density of the hydraulic power, and the second clutch 14 is disconnected under the high-speed working condition without influencing the work of an engine; on the other hand, under the working conditions of braking, long-distance downhill and the like, the second clutch 14 is switched on, braking energy is recovered while braking force is provided, mechanical energy on the transmission shaft is converted and stored into the electro-hydrostatic energy storage unit through the hydraulic motor 8, and the mechanical energy is released under the working conditions of auxiliary starting and the like, so that the energy efficiency is improved, and meanwhile, the heat generated by braking is reduced.