Electric drive system with hydraulic torque converter and forklift

Abstract

The invention relates to the technical field of electric driving systems, and discloses an electric driving system with a hydraulic torque converter and a forklift. The system comprises a driving motor, a hydraulic torque converter, a speed reducer and a vehicle control unit, wherein a lock-up clutch is integrated in the hydraulic torque converter; an output shaft of the driving motor is connected with a pump wheel input side of the hydraulic torque converter; a turbine output side of the hydraulic torque converter is connected with an input shaft of the speed reducer; the output end of the reducer is connected with a vehicle drive axle; when the vehicle is in the low-speed large-torque demand working condition, the lock-up clutch is controlled to be separated, so that the hydraulic torque converter works in the torque conversion working condition, and when the vehicle is in the low-speed large-torque demand working condition, the lock-up clutch is controlled to be separated; and when the vehicle is in a high-speed small-torque demand working condition, the lock-up clutch is controlled to be engaged, so that the pump wheel of the hydraulic torque converter is mechanically locked with the turbine, and the vehicle is in a coupler working condition. The power performance and the energy efficiency of the vehicle are improved, the cost of the electric drive system is reduced, and the economical efficiency and the NVH performance are improved.

Description

Technical Field

[0001] This invention relates to the field of electric drive system technology, and more specifically, to an electric drive system with a hydraulic torque converter and a forklift. Background Technology

[0002] Currently, industrial vehicles such as electric forklifts generally adopt a power system solution that combines a drive motor with a fixed speed ratio reducer. This solution has a simple structure, but it has significant shortcomings when facing complex and ever-changing operating conditions. Taking electric forklifts as an example, their operating cycle typically includes high-speed driving under no-load / full-load conditions, climbing hills under full load conditions, and low-speed micro-movement loading and unloading, resulting in drastic changes in the load and speed requirements of the drive system.

[0003] Fixed-ratio reducers cannot simultaneously optimize high-speed and low-speed, high-torque operation. To meet the vehicle's maximum speed and gradeability requirements, motors are forced to have a wide high-efficiency range and high peak torque and speed capabilities, leading to high costs for both the motor and the electronic control system. In actual operation, motors often operate in low-efficiency ranges, especially during low-speed, high-torque climbing or high-speed driving, resulting in low overall system efficiency. Furthermore, increasing the size and weight of the motor to meet high torque output, or increasing the speed to meet vehicle speed requirements, negatively impacts the system's noise, vibration, harshness (NVH) performance and economic efficiency. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of existing technologies where traditional drive motors and single-speed ratio reducers cannot simultaneously achieve the high efficiency range and high power output of electric drive systems, resulting in high system costs. This invention provides an electric drive system and forklift with a hydraulic torque converter, which improves the vehicle's power performance and energy efficiency, reduces the cost of the electric drive system, and improves economy and NVH performance.

[0005] To achieve the above objectives, the present invention provides an electric drive system with a hydraulic torque converter. This system includes a drive motor, a hydraulic torque converter, a reducer, and a vehicle controller. The hydraulic torque converter integrates a lock-up clutch. The output shaft of the drive motor is connected to the pump wheel input side of the hydraulic torque converter. The turbine output side of the hydraulic torque converter is connected to the input shaft of the reducer. The output end of the reducer is used to connect to the vehicle's drive axle. The vehicle controller is configured to control the engagement and disengagement of the lock-up clutch according to vehicle operating conditions. When the vehicle is in a low-speed, high-torque demand condition, the lock-up clutch is disengaged, allowing the torque converter to operate in torque conversion mode; when the vehicle is in a high-speed, low-torque demand condition, the lock-up clutch is engaged, mechanically locking the pump wheel and turbine of the torque converter, placing it in coupling mode.

[0006] Preferably, the lock-up clutch is a normally closed clutch.

[0007] Preferably, the lock-up clutch is controlled by a hydraulic drive mechanism, which is controlled by an electrical signal from the vehicle controller.

[0008] Preferably, the reducer is a multi-stage gear reduction mechanism, comprising three pairs of parallel shaft gears meshing sequentially to form a three-stage reduction.

[0009] Preferably, the three pairs of parallel shaft gear pairs include a first gear pair formed by a first gear and a sixth gear, a second gear pair formed by a second gear and a fifth gear, and a third gear pair formed by a third gear and a fourth gear.

[0010] Preferably, the system further includes a differential and a pair of drive half-shafts, the housing of the differential is connected to the final output gear of the reducer, and the two output ends of the differential are respectively connected to the drive half-shafts.

[0011] Preferably, the drive motor, hydraulic torque converter and reducer are integrated into one housing.

[0012] Preferably, the drive motor, hydraulic torque converter, and reducer are arranged coaxially along the power transmission direction.

[0013] A second aspect of the present invention provides a forklift equipped with an electric drive system with a hydraulic torque converter as described above.

[0014] Preferably, the forklift is an electric forklift.

[0015] According to the above technical solution, the torque amplification function of the hydraulic torque converter can multiply the drive torque under low-speed, heavy-load conditions, greatly improving the vehicle's climbing and starting capabilities, while ensuring high-speed performance during lock-up. In the more prevalent medium-to-high-speed, light-load conditions, the lock-up clutch engages, and the system transmission efficiency approaches that of a direct mechanical connection, avoiding the efficiency dips of traditional hydraulic transmissions in these conditions. This allows the motor to operate more within its high-efficiency range, reducing overall vehicle energy consumption. Furthermore, because the hydraulic torque converter provides additional torque amplification, the peak torque and maximum speed requirements of the drive motor can be appropriately reduced, allowing for the selection of lower-cost, smaller motors. Simultaneously, the reduced input speed of the reducer also helps improve gear noise and vibration, enhancing overall vehicle NVH performance and fuel economy. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall principle structure of an electric drive system with a hydraulic torque converter provided by the present invention; Figure 2 This is a schematic diagram of the structural principle of the hydraulic torque converter in an electric drive system with a hydraulic torque converter according to the present invention; Figure 3This is a schematic diagram of the three-stage reduction mechanism of the reducer in an electric drive system with a hydraulic torque converter provided by the present invention. Figure 4 This is a flowchart illustrating the working principle of an electric drive system with a hydraulic torque converter provided by the present invention.

[0017] Explanation of reference numerals in the attached figures 1-Drive motor, 2-Hydraulic torque converter, 21-Power input shaft, 22-Lock-up clutch, 23-Torque converter housing, 24-Pump wheel, 25-Power output shaft, 26-Guide wheel, 27-Turbine, 3-Box housing, 4-Reducer, 41-First gear, 42-Second gear, 43-Third gear, 44-Fourth gear, 45-Fifth gear, 46-Sixth gear, 5-Differential, 6-Drive half-shaft. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0019] In this invention, unless otherwise stated, directional terms such as "inner," "outer," "left," and "right" included in the terminology represent only the orientation of the term in its normal use or are common terms understood by those skilled in the art, and should not be regarded as limitations on the term.

[0020] See Figure 1 This invention provides an electric drive system with a hydraulic torque converter, comprising a drive motor 1, a hydraulic torque converter 2, a reducer 4, and a vehicle controller. The hydraulic torque converter 2 integrates a lock-up clutch 22. The output shaft of the drive motor 1 is connected to the input side of the pump impeller 24 of the hydraulic torque converter 2. The output side of the turbine 27 of the hydraulic torque converter 2 is connected to the input shaft of the reducer 4. The output end of the reducer 4 is used to connect to the vehicle's drive axle. The vehicle controller is configured to control the engagement and disengagement of the lock-up clutch 22 according to vehicle operating conditions. When the vehicle is in a low-speed, high-torque demand condition, the lock-up clutch 22 is disengaged, so that the torque converter 2 operates in a torque-changing condition; when the vehicle is in a high-speed, low-torque demand condition, the lock-up clutch 22 is engaged, so that the pump wheel 24 and turbine 27 of the torque converter 2 are mechanically locked, and the system is in a coupling condition.

[0021] In practical use, if the clutch is designed to be normally open, the torque converter will always be in a hydraulic transmission state under normal conditions, resulting in continuous hydraulic losses. This contradicts the fundamental goal of high energy efficiency in electric systems. Therefore, in this embodiment, the lock-up clutch 22 is preferably a normally closed clutch. In this way, under default conditions, without a control signal, the clutch remains engaged. This ensures that the pump impeller and turbine of the torque converter are rigidly locked for most of the operating time, and the power transmission path becomes a near 100% efficient mechanical direct connection. This completely avoids the power losses caused by oil turbulence and slippage in the coupled condition of the torque converter, directly maximizing the average operating efficiency of the system and reducing energy consumption.

[0022] The normally closed clutch described above relies on spring force to maintain engagement, requiring a large operating force to overcome the spring clamping force and achieve rapid and reliable disengagement. Therefore, in this embodiment, the lock-up clutch 22 is preferably controlled by a hydraulic drive mechanism, which is controlled by an electrical signal from the vehicle controller. In this way, the hydraulic system utilizes Pascal's principle to easily generate a large linear thrust or torque on the hydraulic piston using a small flow of high-pressure oil, making it very suitable for providing high-power, high-torque linear or rotary drives.

[0023] In this invention, the hydraulic torque converter is mainly responsible for stepless speed change and torque amplification in the low-speed range, but its inherent transmission efficiency characteristics determine that it is not suitable for undertaking the main fixed deceleration task. Therefore, the system still needs a mechanical reducer with a large speed ratio and high load-bearing capacity as the final amplifier of torque output. Therefore, in this embodiment, preferably, the reducer 4 is a multi-stage gear reduction mechanism, including three pairs of parallel shaft gears meshing in sequence, forming a three-stage reduction. In this way, the three-stage reduction can multiply the speed ratio of the single stage, easily achieving a total transmission ratio as high as 15:1 to over 100:1, perfectly meeting the needs of low-speed, high-torque drive of forklifts. At the same time, the huge output torque is distributed across the three pairs of gears, avoiding a single gear bearing the entire load, making the force on each gear more reasonable, and improving the overall reliability and lifespan. Among them, the parallel shaft gears have a large contact area and high tooth root bending strength, making them particularly suitable for transmitting large torques.

[0024] Specifically, in one embodiment, the three pairs of parallel shaft gear pairs include a first gear pair formed by a first gear 41 and a sixth gear 46, a second gear pair formed by a second gear 42 and a fifth gear 45, and a third gear pair formed by a third gear 43 and a fourth gear 44.

[0025] During vehicle operation, any dual-axle drive wheeled vehicle must be able to rotate at different speeds when turning. If the vehicle lacks a differential, the two drive wheels are rigidly connected, and the inner wheel will be forced to slip due to its shorter travel distance, while the outer wheel will slip due to its longer travel distance. This will lead to abnormal tire wear, difficulty in steering, and poor handling. Therefore, in this embodiment, the system preferably also includes a differential 5 and a pair of drive half-shafts 6. The housing of the differential 5 is connected to the final output gear of the reducer 4, and the two output ends of the differential 5 are respectively connected to the drive half-shafts 6. In this way, the differential 5, through a planetary gear mechanism, allows the left and right half-shafts 6 to rotate at different speeds, while evenly distributing the torque from the reducer 4 to both wheels, perfectly solving the problem of speed difference during steering.

[0026] In this embodiment, the drive motor 1, hydraulic torque converter 2, and reducer 4 are preferably integrated into a single housing 3. This integrated housing, as a large, continuous, rigid structure, can withstand and distribute the enormous torque reaction force and impact load generated by the entire drive system under heavy loads, impacts, and sudden starts and stops. This avoids the fretting, deformation, and wear of the connecting surfaces that may occur with separate structures connected by bolts, significantly improving the system's dynamic response characteristics, NVH performance, and fatigue life.

[0027] In this embodiment, the drive motor 1, hydraulic torque converter 2, and reducer 4 are preferably arranged coaxially along the power transmission direction. This way, power originates from the motor rotor centerline and, without any angular or parallel offset, passes directly along the same theoretical axis through the pump impeller and turbine of the hydraulic torque converter, finally entering the input shaft of the reducer. This eliminates all additional transmission elements used to change the power direction, thus avoiding frictional losses, meshing losses, and energy dissipation caused by these elements. Simultaneously, the axial forces generated by all rotating components can be effectively borne and managed by the bearing system along the same axis, reducing additional radial forces and bending moments caused by axis misalignment, further reducing bearing frictional losses.

[0028] Furthermore, another aspect of the present invention provides a forklift equipped with an electric drive system with a hydraulic torque converter as described above. More specifically, this forklift is an electric forklift. Thus, the vehicle controller determines the power demand of the drive system based on driver commands and the current state of the vehicle. If the vehicle is in a state that requires low speed and high torque output from the drive system, such as when it is fully loaded and climbing a hill, the lock-up clutch of the torque converter is disengaged. The torque converter amplifies the input torque from the motor and outputs it to the reducer and half shaft, which greatly improves the vehicle's climbing ability.

[0029] If the vehicle is traveling at high speed on flat ground, the power system does not require high torque. The lock-up clutch of the torque converter is engaged, and the torque converter is used as a coupling to avoid power loss and improve the energy efficiency of the electric drive system.

[0030] The following provides a specific embodiment to illustrate the present invention: The main components of the electric drive system with a hydraulic torque converter in this embodiment are integrated into a housing 3. The drive motor 1 is fixed to one end of the housing 3 by a flange and bolts. The hydraulic torque converter 2 is located inside the housing 3, and its input shaft 21 is directly connected to the output shaft of the drive motor 1 or connected through a short shaft.

[0031] See Figure 2 The hydraulic torque converter 2 includes a pump impeller 24, a turbine 27, a guide wheel 26, and an integrated lock-up clutch 22. The pump impeller 24 is connected to the input shaft 21 and the driving part of the clutch. The turbine 27 is connected to the output shaft 25 and the driven part of the clutch. The guide wheel 26 is fixed to the housing 3 via a one-way clutch or directly. When the lock-up clutch 22 is engaged under hydraulic pressure, the input shaft 21 and the output shaft 25 are rigidly connected, and power is directly transmitted. When the clutch is disengaged, power is transmitted from the pump impeller to the turbine via hydraulic oil, achieving continuously variable transmission and torque amplification.

[0032] like Figure 3 As shown, the output shaft 25 of the hydraulic torque converter 2 is connected to the first-stage drive gear 41 of the reducer 4. Power is sequentially reduced and increased in torque through three stages via gear pairs 41 / 46, 42 / 45, and 43 / 44. The third-stage driven gear 44 also serves as the housing of the differential 5, transmitting power to the differential 5, which then outputs power to the wheels via the left and right drive half-shafts 6 after differential operation.

[0033] Combination Figure 4 The control logic of this system is as follows: The vehicle controller continuously monitors accelerator pedal signals, load sensor signals, slope sensor signals, vehicle speed signals, etc.

[0034] When the controller determines that the vehicle is in a fully loaded hill-climbing or heavy-load start-up condition, it sends a disengagement command to the solenoid valve of the lock-up clutch 22 of the torque converter 2. The clutch disengages, and the torque converter 2 performs its torque conversion function, amplifying the motor torque to meet the vehicle's demand for high driving force.

[0035] When the controller determines that the vehicle is in a state of no-load / light-load high-speed driving, light-load micro-movement, or downhill, it sends an engagement command to the control solenoid valve. The lock-up clutch 22 engages, and the pump wheel and turbine of the hydraulic torque converter 2 are locked. Power is directly transmitted with near 100% efficiency. At this time, the system is equivalent to a system of electric motor direct drive reducer, operating in the high-efficiency range.

[0036] In summary, this system improves vehicle power performance: Traditional drive systems using electric motors and single-speed reducers require the power system to balance both low-speed, high-torque and high-speed, low-torque conditions, necessitating a compromise between maximum speed and climbing ability, resulting in insufficient vehicle power. This invention, however, amplifies the torque output of the power system through a hydraulic torque converter, significantly improving the vehicle's climbing ability. Simultaneously, with the clutch engaged, it meets the power demands of high-speed driving, increasing the vehicle's maximum speed.

[0037] Meanwhile, this system improves vehicle energy efficiency: Traditional drive systems using electric motors and single-speed reducers have a fixed speed ratio, making it difficult to adjust the motor's operating range according to changes in load. Under harsh conditions such as full-load climbing and high-speed driving, the motor operates in an inefficient range, resulting in low vehicle energy efficiency. This invention, however, adjusts the motor's operating range using a hydraulic torque converter, keeping it within the high-speed range and significantly improving vehicle energy efficiency.

[0038] Furthermore, this system reduces the cost of the electric drive system and improves economy and NVH performance: Traditional drive systems using electric motors and single-speed reducers rely primarily on the high speed and high torque output of the motor to meet the demands of high-speed driving and fully loaded hill climbing, placing high demands on the motor and reducer. This invention, however, increases the torque output of the power system through a hydraulic torque converter, reducing the power system's requirements for motor torque and high speed. Simultaneously, it lowers the input speed of the reducer, improves the NVH performance of the power system, reduces the overall cost of the power system, and enhances economy.

[0039] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An electric drive system with a hydraulic torque converter, characterized in that, The system includes a drive motor (1), a hydraulic torque converter (2), a reducer (4), and a vehicle controller. The hydraulic torque converter (2) integrates a lock-up clutch (22). The output shaft of the drive motor (1) is connected to the input side of the pump wheel (24) of the hydraulic torque converter (2). The output side of the turbine (27) of the hydraulic torque converter (2) is connected to the input shaft of the reducer (4). The output end of the reducer (4) is used to connect to the vehicle drive axle. The vehicle controller is configured to control the engagement and disengagement of the lock-up clutch (22) according to the vehicle operating conditions. When the vehicle is in a low-speed, high-torque demand condition, the lock-up clutch (22) is disengaged, so that the hydraulic torque converter (2) works in a torque conversion condition; when the vehicle is in a high-speed, low-torque demand condition, the lock-up clutch (22) is engaged, so that the pump wheel (24) and turbine (27) of the hydraulic torque converter (2) are mechanically locked, and the coupling is in a coupling condition.

2. The electric drive system with a hydraulic torque converter according to claim 1, characterized in that, The lock-up clutch (22) is a normally closed clutch.

3. The electric drive system with a hydraulic torque converter according to claim 1 or 2, characterized in that, The lock-up clutch (22) is controlled by a hydraulic drive mechanism, which is controlled by an electrical signal issued by the vehicle controller.

4. The electric drive system with a hydraulic torque converter according to claim 1, characterized in that, The reducer (4) is a multi-stage gear reduction mechanism, which includes three pairs of parallel shaft gears meshing in sequence to form a three-stage reduction.

5. The electric drive system with a hydraulic torque converter according to claim 4, characterized in that, The three pairs of parallel shaft gear pairs include a first gear pair formed by a first gear (41) and a sixth gear (46), a second gear pair formed by a second gear (42) and a fifth gear (45), and a third gear pair formed by a third gear (43) and a fourth gear (44).

6. The electric drive system with a hydraulic torque converter according to claim 5, characterized in that, The system also includes a differential (5) and a pair of drive half shafts (6), the housing of the differential (5) is connected to the final output gear of the reducer (4), and the two output ends of the differential (5) are respectively connected to the drive half shafts (6).

7. The electric drive system with a hydraulic torque converter according to claim 1, characterized in that, The drive motor (1), hydraulic torque converter (2) and reducer (4) are integrated into a housing (3).

8. The electric drive system with a hydraulic torque converter according to claim 7, characterized in that, The drive motor (1), hydraulic torque converter (2) and reducer (4) are arranged coaxially along the power transmission direction.

9. A forklift, characterized in that, The forklift is equipped with an electric drive system with a hydraulic torque converter as described in any one of claims 1 to 8.

10. The forklift according to claim 9, characterized in that, The forklift in question is an electric forklift.

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