Energy recovery device and energy recovery method for forklift

Abstract

Provided are an energy recovery device (100) and an energy recovery method (S100) for a forklift (FL) including a fork (300). The energy recovery device includes a dynamotor (DN), a kinetic energy computation circuit (110), a conversion module (120), a control circuit (130), a speed regulation module (140), and an energy storage module (150). The kinetic energy computation circuit calculates a kinetic energy (EM) of the fork as it descends. The conversion module obtains a rotational speed (WS) and a torque (TQ) according to kinetic energy. The control circuit obtains optimal rotational speed (WO) of dynamotor corresponding to torque and highest efficiency of dynamotor, and provides speed regulation command (CMD) according to error (ERR) between current rotational speed (WD) and optimal rotational speed of dynamotor. Speed regulation module adjusts current speed to optimal speed according to speed regulation command, so that dynamotor provides dynamotor power (ED) to energy storage module.

Description

BACKGROUND Technical Field

[0001] The disclosure relates to an energy recovery device and an energy recovery method, and particularly relates to an energy recovery device and an energy recovery method for a forklift.Related Art

[0002] Generally, when a fork of a forklift descends from a high position, potential energy is converted into kinetic energy. The energy generated by the dynamotor of the forklift based on the kinetic energy of the fork may be stored. Therefore, how to optimally recover the above-mentioned energy is one of the research focuses for persons skilled in the art.SUMMARY

[0003] The disclosure provides an energy recovery device and an energy recovery method for a forklift, which can optimally recover energy.

[0004] In an embodiment of the disclosure, the energy recovery device of the disclosure is for a forklift. The forklift includes a fork. The energy recovery device includes a dynamotor, a kinetic energy computation circuit, a conversion module, a control circuit, a speed regulation module, and an energy storage module. The kinetic energy computation circuit calculates a kinetic energy of the fork as it descends. The conversion module is coupled to the kinetic energy computation circuit. The conversion module obtains a rotational speed and a torque according to the kinetic energy. The control circuit obtains an optimal rotational speed of the dynamotor corresponding to the torque and a highest efficiency of the dynamotor, and provides a speed regulation command according to an error between a current rotational speed and the optimal rotational speed of the dynamotor. The speed regulation module is coupled to the control circuit and the dynamotor. The speed regulation module adjusts the current speed to the optimal speed according to the speed regulation command, so that the dynamotor generates a dynamotor power according to the optimal rotational speed and the kinetic energy. The energy storage module is coupled to the dynamotor. The energy storage module stores the dynamotor power.

[0005] In an embodiment of the disclosure, the energy recovery method is for a forklift. The forklift includes a fork. The energy recovery method includes the following. A kinetic energy of the fork as it descends is calculated. A rotational speed and a torque are obtained according to the kinetic energy. A dynamotor is provided, an optimal rotational speed corresponding to the torque and a highest efficiency of the dynamotor is obtained, and a speed regulation command is provided according to an error between a current rotational speed of the dynamotor and the optimal rotational speed. The current rotational speed is adjusted to the optimal rotational speed according to the speed regulation command, so that the dynamotor generates a dynamotor power according to the optimal rotational speed and the kinetic energy. Also, the dynamotor power is stored.

[0006] Based on the above, the energy recovery device and the energy recovery method of the disclosure can enable the dynamotor to generate the dynamotor power according to the optimal rotational speed and the kinetic energy. Therefore, the dynamotor can generate the dynamotor power with the highest efficiency. In this way, the energy recovery device and the energy recovery method of the disclosure can optimally recover the energy generated based on the kinetic energy of the fork.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a schematic diagram of an energy recovery device according to an embodiment of the disclosure. FIG. 2 is a schematic diagram of a kinetic energy computation circuit according to an embodiment of the disclosure. FIG. 3 is a schematic diagram of a conversion module according to an embodiment of the disclosure. FIG. 4 is a schematic diagram of a lookup table according to an embodiment of the disclosure. FIG. 5 is an operational schematic diagram for obtaining an optimal rotational speed according to an embodiment of the disclosure. FIG. 6 is a schematic diagram of a speed regulation module according to an embodiment of the disclosure. FIG. 7 is a schematic diagram of an energy storage module according to an embodiment of the disclosure. FIG. 8A and FIG. 8B are schematic diagrams of energy recovery results according to an embodiment of the disclosure. FIG. 9 is a flowchart of an energy recovery method according to an embodiment of the disclosure. DESCRIPTION OF THE EMBODIMENTS

[0008] Some embodiments of the disclosure will now be described in detail with reference to the accompanying drawings. In the following description, when the same reference numerals appear in different drawings, the reference numerals will be regarded as the same or similar components. These embodiments are merely a part of the disclosure and do not disclose all possible implementations of the disclosure. More precisely, these embodiments are merely examples within the scope of the appended claims of the disclosure.

[0009] Please refer to FIG. 1, which is a schematic diagram of an energy recovery device according to an embodiment of the disclosure. In this embodiment, an energy recovery device 100 is for a forklift FL. The forklift FL includes a fork 300. The energy recovery device 100 includes a dynamotor DN, a kinetic energy computation circuit 110, a conversion module 120, a control circuit 130, a speed regulation module 140, and an energy storage module 150. The kinetic energy computation circuit 110 calculates a kinetic energy EM generated as the fork 300 descends. The conversion module 120 is coupled to the kinetic energy computation circuit 110. The conversion module 120 obtains a rotational speed WS and a torque TQ according to the kinetic energy EM.

[0010] The control circuit 130 is coupled to the conversion module 120. The control circuit 130 obtains an optimal rotational speed WO of the dynamotor DN. The optimal rotational speed WO is the rotational speed corresponding to the torque TQ and a highest efficiency of the dynamotor DN. In other words, when the torque TQ is known, the optimal rotational speed WO is the rotational speed corresponding to the highest efficiency of the dynamotor DN. In addition, the control circuit 130 provides a speed regulation command CMD according to an error ERR between the current rotational speed WD and the optimal rotational speed WO of the dynamotor DN.

[0011] In this embodiment, the speed regulation module 140 is coupled to the control circuit 130 and the dynamotor DN. The speed regulation module 140 adjusts the current rotational speed WD of the dynamotor DN to the optimal rotational speed WO according to the speed regulation command CMD. Therefore, the dynamotor DN generates the dynamotor power ED according to the optimal rotational speed WO and the kinetic energy EM. The speed regulation module 140 generates the error ERR according to the current rotational speed WD and the optimal rotational speed WO, and provides the error ERR to the control circuit 130. The energy storage module 150 is coupled to the dynamotor DN. The energy storage module 150 stores the dynamotor power ED.

[0012] It is worth mentioning here that the energy recovery device 100 may enable the dynamotor DN to generate the dynamotor power ED according to the optimal rotational speed WO and the kinetic energy EM. The optimal rotational speed WO is generated based on the highest efficiency of the dynamotor DN. Therefore, the dynamotor DN can generate the dynamotor power ED with the highest efficiency. In this way, the energy recovery device 100 can optimally recover energy generated based on the kinetic energy EM of the fork 300.

[0013] In this embodiment, the forklift FL may be an electric forklift. However, the disclosure is not limited thereto. In some embodiments, the forklift FL has hybrid power. For example, the forklift FL may be an electric and internal combustion forklift.

[0014] The implementation details of the kinetic energy computation circuit 110, the conversion module 120, the control circuit 130, the speed regulation module 140, and the energy storage module 150 will be described below.

[0015] Please refer to FIG. 1 and FIG. 2, in which FIG. 2 is a schematic diagram of a kinetic energy computation circuit according to an embodiment of the disclosure. In this embodiment, the kinetic energy computation circuit 110 may obtain the kinetic energy EM according to an upward support force F2, a downward distance S, and a mass of cargo m of the fork 300.

[0016] Furthermore, the kinetic energy computation circuit 110 includes calculation circuits 111 to 115. In this embodiment, a downward gravitational force F1 may be obtained from the mass of cargo m. The calculation circuit 111 subtracts the upward support force F2 from the downward gravitational force F1 to obtain a downward net force FG. The calculation circuit 111 may obtain the downward net force FG according to Formula (1). The upward support force F2 may be obtained from the specifications of the forklift FL. FG = F 1 − F 2

[0017] The calculation circuit 112 receives the downward net force FG and the mass of cargo m. The calculation circuit 112 divides the downward net force FG by the mass of cargo m to obtain a downward acceleration a. The calculation circuit 112 may obtain the downward acceleration a according to Formula (2). FG = m × a

[0018] The calculation circuit 113 receives the downward acceleration a and the downward distance S, and obtains a downward time t of the fork 300 according to the downward acceleration a and the downward distance S. The calculation circuit 113 may obtain the downward time t according to Formula (3). The downward distance S may be the moving distance required for the fork 300 to descend to the target height. The downward time t may be the time required for the fork 300 to descend to the target height. S = V 0 × t + 1 2 a × t 2

[0019] "V0" is the initial downward velocity. Generally, the initial downward velocity is equal to 0.

[0020] The calculation circuit 114 receives the downward acceleration a and the downward time t, and obtains a velocity V of the fork 300 at a position when it descends to the target height according to the downward acceleration a and the downward time t. The calculation circuit 114 may obtain the velocity V according to Formula (4). V = V 0 + a × t

[0021] The calculation circuit 115 receives the mass of cargo m and the velocity V, and obtains the kinetic energy EM of the fork 300 at the position when it descends to the target height according to the mass of cargo m and the velocity V. The calculation circuit 115 may obtain the kinetic energy EM according to Formula (5). EM = 1 2 m × V 2

[0022] Please refer to FIG. 1 and FIG. 3, in which FIG. 3 is a schematic diagram of the conversion module according to an embodiment of the disclosure. In this embodiment, the conversion module 120 includes a transmission gear 121 and a speed and torque calculation circuit 122. The fork 300 drives the transmission gear 121 when descending. The transmission gear 121 drives the dynamotor DN. Further, the transmission gear 121 drives the dynamotor DN according to the kinetic energy EM.

[0023] The speed and torque calculation circuit 122 obtains the rotational speed WS and the torque TQ according to a gear mass M of the transmission gear 121, a gear radius R of the transmission gear 121, the downward time t of the fork 300, and the kinetic energy EM. In this embodiment, the speed and torque calculation circuit 122 includes calculation circuits 1221, 1222. The calculation circuit 1221 receives the gear mass M of the transmission gear 121 and the gear radius R of the transmission gear 121, and obtains a moment of inertia I of the transmission gear 121 according to the gear mass M and the gear radius R. The calculation circuit 1221 may obtain the moment of inertia I according to Formula (6). I = 1 2 M × R 2

[0024] The calculation circuit 1222 receives the moment of inertia I, the downward time t, and the kinetic energy EM. In this embodiment, the calculation circuit 1222 is coupled to the calculation circuit 1221 to receive the moment of inertia I. The calculation circuit 1222 is coupled to the calculation circuit 113 in FIG. 2 to receive the downward time t. The calculation circuit 1222 is coupled to the calculation circuit 115 in FIG. 2 to receive the kinetic energy EM.

[0025] In this embodiment, the calculation circuit 1222 divides the kinetic energy EM by the downward time t to obtain a power PG. The calculation circuit 1222 may obtain the power PG according to Formula (7). PG = EM ÷ t

[0026] The calculation circuit 1222 obtains the rotational speed WS according to the kinetic energy EM and the moment of inertia I. The calculation circuit 1222 may obtain the rotational speed WS according to Formula (8) and Formula (9). EM = 1 2 I × WS 2 WS = 2 × EM I

[0027] In addition, the calculation circuit 1222 obtains the torque TQ according to the rotational speed WS and the power PG.

[0028] The calculation circuit 1222 may obtain the torque TQ according to Formula (10). TQ = PG ÷ WS

[0029] The rotational speed WS is the rotational speed of the transmission gear 121 when the kinetic energy EM is generated. The torque TQ is the torque when the kinetic energy EM is generated.

[0030] Please refer to FIG. 1 and FIG. 4, in which FIG. 4 is a schematic diagram of a lookup table according to an embodiment of the disclosure. In this embodiment, the control circuit 130 includes a lookup table LT. The lookup table LT stores multiple rotational speeds corresponding to multiple torques and multiple efficiencies. The control circuit 130 finds the optimal rotational speed WO corresponding to the highest efficiency of the dynamotor DN from the lookup table LT according to the torque TQ received.

[0031] In this embodiment, the lookup table LT may be an efficiency contour map. The vertical axis is the torque. The horizontal axis is the rotational speed. When the torque TQ is known, the control circuit 130 may find multiple rotational speeds corresponding to the highest efficiency of the dynamotor DN in the area corresponding to the torque TQ in the contour map, and select one of the multiple rotational speeds as the optimal rotational speed WO. For example, the control circuit 130 receives the rotational speed WS and uses a rotational speed closest to the rotational speed WS among the above-mentioned multiple rotational speeds as the optimal rotational speed WO, but the disclosure is not limited thereto.

[0032] Please refer to FIG. 1 and FIG. 5, in which FIG. 5 is an operational schematic diagram for obtaining the optimal rotational speed according to an embodiment of the disclosure. When the lookup table LT is not obtained, the control circuit 130 may use a gradient method to obtain the optimal rotational speed WO.

[0033] For example, the control circuit 130 obtains a first efficiency of the dynamotor DN according to the torque TQ and a first rotational speed. The control circuit 130 obtains a second efficiency of the dynamotor DN according to the torque TQ and a second rotational speed. The control circuit 130 generates a slope based on an efficiency difference between the first efficiency and the second efficiency and a rotational speed difference between the first rotational speed and the second rotational speed. The control circuit 130 fine-tunes the first rotational speed and the second rotational speed to change the slope, and obtains the optimal rotational speed WO according to a minimum absolute value of the slope.

[0034] Taking FIG. 5 as an example, the vertical axis is the reciprocal of the efficiency. The horizontal axis is the rotational speed. The slope may be obtained by Formula (11). SL = EF 1 − EF 2 W 1 − W 2

[0035] "SL" is the slope. "EF1" is the reciprocal of the first efficiency. "EF2" is the reciprocal of the second efficiency. "W1" is the first rotational speed. "W2" is the second rotational speed.

[0036] In the initial stage of the gradient method, the first rotational speed is the old rotational speed. The second rotational speed is the new rotational speed. After calculating the second rotational speed, the second rotational speed becomes the old rotational speed, and a new rotational speed may be calculated again. The new rotational speed may be generated by Formula (12) and Formula (13). Wnew = Wold − k × SL Wnew = Wold + k × SL

[0037] "Wnew" is the new rotational speed. "Wold" is the old rotational speed. "k" is a learning rate. When the slope is greater than 0, the new rotational speed may be generated by Formula (12). When the slope is less than 0, the new rotational speed may be generated by Formula (13). For example, when a working point is at a position PO1, the slope at the position PO1 (that is, the tangent slope) is greater than 0. Therefore, applying Formula (12), the first rotational speed is decreased. Thus, the working point moves leftward from the position PO1 on an operation curve CV to PO2. When the working point is at the position PO2, the slope at the position PO2 (that is, the tangent slope) is greater than 0. Therefore, continuing to apply Formula (12), the second rotational speed is also decreased. Thus, the working point continues to move leftward, and so on. When the slope approaches 0, the new rotational speed is the optimal rotational speed WO.

[0038] In this embodiment, the control circuit 130 may divide the optimal rotational speed WO by the current rotational speed WD to generate a speed ratio, and generate the speed regulation command CMD according to the speed ratio. The control circuit 130 may also provide the speed regulation command CMD according to the error ERR. For example, the control circuit 130 may first use the speed ratio to generate the speed regulation command CMD, thereby making the current rotational speed WD approach the optimal rotational speed WO. Next, the control circuit 130 may also provide the speed regulation command CMD according to the error ERR, thereby ensuring that the current rotational speed WD continues to approach the optimal rotational speed WO.

[0039] Based on the optimal rotational speed WO and the same torque TQ, the dynamotor DN can provide the dynamotor power ED with the highest efficiency.

[0040] Please refer to FIG.1 and FIG.6, in which FIG.6 is a schematic diagram of the speed regulation module according to an embodiment of the disclosure. In this embodiment, the speed regulation module 140 includes a speed regulation gear 141 and an error calculator 142. The speed regulation gear 141 is coupled to the dynamotor DN. The speed regulation gear 141 adjusts the current rotational speed WD of the dynamotor DN according to the speed regulation command CMD, thereby making the current rotational speed WD of the dynamotor DN substantially equal to the optimal rotational speed WO. The error calculator 142 is coupled to the speed regulation gear 141 and the control circuit 130. The error calculator 142 detects the current rotational speed WD of the dynamotor DN, and generates the error ERR according to the current rotational speed WD and the optimal rotational speed WO. The error calculator 142 provides the error ERR to the control circuit 130.

[0041] In this embodiment, the speed regulation gear 141 may be implemented by a planetary gear, but the disclosure is not limited thereto. The error calculator 142 may be implemented by a proportional-integral-derivative (PID) controller, but the disclosure is not limited thereto.

[0042] Please refer to FIG.1 and FIG.7, in which FIG.7 is a schematic diagram of the energy storage module according to an embodiment of the disclosure. In this embodiment, the energy storage module 150 includes a battery module 151 and a power converter 152. The power converter 152 is coupled to the dynamotor DN and the battery module 151. The power converter 152 converts the dynamotor power ED into a battery power EB, and charges the battery module 151 using the battery power EB. In this embodiment, the battery module 151 may be an aluminum-ion battery or other types of power storage components.

[0043] For example, the dynamotor power ED may be alternating current power. The battery power EB may be direct current power. Therefore, the power converter 152 may be an AC-DC power converter.

[0044] Please refer to FIG.1, FIG.8A, and FIG.8B, in which FIG.8A and FIG.8B are schematic diagrams of energy recovery results according to an embodiment of the disclosure. In this embodiment, in FIG.8A, a curve CV1 shows the trend of the downward time of the fork 300 in relation to the mass of cargo. A curve CV2 shows the trend of the torque TQ in relation to the mass of cargo. In the test, the downward time of the fork 300 shortens as the mass of cargo increases. The torque TQ increases as the mass of cargo increases.

[0045] In FIG.8B, a curve CV3_1 shows the trend of the optimal rotational speed WO of the dynamotor DN in relation to the mass of cargo. A curve CV3_2 shows the trend of rotational speed in the related art in relation to the mass of cargo. In this embodiment, the optimal rotational speed WO of the curve CV3_1 corresponds to the torque TQ of the curve CV2 and the highest efficiency of the dynamotor DN.

[0046] A curve CV4_1 shows the trend of the efficiency of the dynamotor DN in relation to the mass of cargo. A curve CV4_2 shows the trend of efficiency in the related art in relation to the mass of cargo. It should be noted that, based on the torque TQ and the optimal rotational speed WO, the efficiency of the curve CV4_1 is the highest efficiency in relation to the mass of cargo. Therefore, the efficiency of the curve CV4_1 is higher than the efficiency of the curve CV4_2.

[0047] A curve CV5_1 shows the trend of the dynamotor power ED of the dynamotor DN in relation to the mass of cargo. A curve CV5_1 is related to the curve CV4_1. A curve CV5_2 shows the trend of the dynamotor power ED of the dynamotor DN in the related art in relation to the mass of cargo. The curve CV5_2 is related to the curve CV4_2. It should be noted that, in the curve CV5_1, the dynamotor power ED is generated based on the highest efficiency. In the curve CV5_2, the dynamotor power ED is not generated based on the highest efficiency. Therefore, the dynamotor power ED of the curve CV5_1 is higher than the dynamotor power ED of the curve CV5_2.

[0048] Please refer to FIG.1 and FIG.9, in which FIG.9 is a flowchart of an energy recovery method according to an embodiment of the disclosure. In this embodiment, an energy recovery method S100 is applicable to the forklift FL. The energy recovery method S100 includes Steps S110 to S150. In Step S110, the kinetic energy computation circuit 110 calculates a kinetic energy EM generated as the fork 300 descends. In Step S120, the conversion module 120 obtains a rotational speed WS and a torque TQ according to the kinetic energy EM. In Step S130, the dynamotor DN is provided. The control circuit 130 obtains the optimal rotational speed WO of the dynamotor corresponding to the torque TQ and the highest efficiency of the dynamotor DN, and provides the speed regulation command CMD according to the error ERR between the current rotational speed WD and the optimal rotational speed WO of the dynamotor DN. In Step S140, the speed regulation module 140 adjusts the current rotational speed WD of the dynamotor DN to the optimal rotational speed WO according to the speed regulation command CMD. Therefore, the dynamotor DN in Step S140 generates the dynamotor power ED according to the optimal rotational speed WO and the kinetic energy EM. In Step S150, the energy storage module 150 stores the dynamotor power ED. The implementation details of Steps S110 to S150 are clearly described in multiple embodiments from FIG.2 to FIG.7, so details will not be repeated here.

[0049] In summary, when the fork of the forklift descends, the energy recovery device and the energy recovery method may utilize the dynamotor to generate the dynamotor power according to the optimal rotational speed and the kinetic energy. The optimal rotational speed is generated based on the highest efficiency of the dynamotor. Therefore, the dynamotor can generate the dynamotor power with the highest efficiency. In this way, the energy recovery device and the energy recovery method can optimally recover the energy generated based on the kinetic energy of the fork.

Claims

1. An energy recovery device (100) for a forklift (FL), wherein the forklift (FL) comprises a fork (300), and the energy recovery device (100) comprises: a dynamotor (DN); a kinetic energy computation circuit (110) configured to calculate a kinetic energy (EM) of the fork (300) as the fork (300) descends; a conversion module (120) coupled to the kinetic energy computation circuit (110), configured to obtain a rotational speed (WS) and a torque (TQ) according to the kinetic energy (EM); a control circuit (130) coupled to the conversion module (120), configured to obtain an optimal rotational speed (WO) corresponding to the torque (TQ) and a highest efficiency of the dynamotor (DN), and to provide a speed regulation command (CMD) according to an error (ERR) between a current rotational speed (WD) and the optimal rotational speed (WO) of the dynamotor (DN); a speed regulation module (140) coupled to the control circuit (130) and the dynamotor (DN), configured to adjust the current rotational speed (WD) to the optimal rotational speed (WO) according to the speed regulation command (CMD), so that the dynamotor (DN) generates a dynamotor power (ED) according to the optimal rotational speed (WO) and the kinetic energy (EM); and an energy storage module (150) coupled to the dynamotor (DN), configured to store the dynamotor power (ED).

2. The energy recovery device (100) as claimed in claim 1, wherein the conversion module (120) comprises: a transmission gear (121), wherein the fork (300) drives the transmission gear (121) when descending, and the transmission gear (121) drives the dynamotor (DN); and a speed and torque calculation circuit (122) configured to obtain the rotational speed (WS) and the torque (TQ) according to a gear mass (M) of the transmission gear (121), a gear radius (R) of the transmission gear (121), a downward time (t) of the fork (300), and the kinetic energy (EM).

3. The energy recovery device (100) as claimed in claim 1, wherein the control circuit (130) comprises: a lookup table configured to store a plurality of rotational speeds (WS) corresponding to a plurality of torques (TQ) and a plurality of efficiencies, wherein the control circuit (130) finds the optimal rotational speed (WO) corresponding to the highest efficiency from the lookup table according to the torque (TQ) received.

4. The energy recovery device (100) as claimed in claim 1, wherein the control circuit (130) obtains a first efficiency of the dynamotor (DN) according to the torque (TQ) and a first rotational speed, obtains a second efficiency of the dynamotor (DN) according to the torque (TQ) and a second rotational speed, generates a slope based on an efficiency difference between the first efficiency and the second efficiency and a rotational speed difference between the first rotational speed and the second rotational speed, and obtains a new rotational speed value using the slope and a learning rate, thereby obtaining the optimal rotational speed (WO).

5. The energy recovery device (100) as claimed in claim 1, wherein the speed regulation module (140) generates the error (ERR) according to the current rotational speed (WD) and the optimal rotational speed (WO), and provides the error (ERR) to the control circuit (130).

6. The energy recovery device (100) as claimed in claim 1, wherein the control circuit (130) divides the optimal rotational speed (WO) by the current rotational speed (WD) to generate a speed ratio, and generates the speed regulation command (CMD) according to the speed ratio.

7. The energy recovery device (100) as claimed in claim 1, wherein the speed regulation module (140) comprises: a speed regulation gear (141) coupled to the dynamotor (DN), configured to adjust the current rotational speed (WD) of the dynamotor (DN) according to the speed regulation command (CMD); and an error calculator (142) coupled to the speed regulation gear (141) and the control circuit (130), configured to detect the current rotational speed (WD) of the dynamotor (DN), and to generate the error (ERR) according to the current rotational speed (WD) and the optimal rotational speed (WO).

8. The energy recovery device (100) as claimed in claim 1, wherein the energy storage module (150) comprises: a battery module (151); and a power converter (152) coupled to the dynamotor (DN) and the battery module (151), configured to convert the dynamotor power (ED) into a battery power (EB), and to charge the battery module (151) using the battery power (EB).

9. An energy recovery method (S100) for a forklift (FL), wherein the forklift (FL) comprises a fork (300), and the energy recovery method (S100) comprises: calculating a kinetic energy (EM) of the fork (300) as the fork (300) descends; obtaining a rotational speed (WS) and a torque (TQ) according to the kinetic energy (EM); providing a dynamotor (DN), obtaining an optimal rotational speed (WO) corresponding to the torque (TQ) and a highest efficiency of the dynamotor (DN), and providing a speed regulation command (CMD) according to an error (ERR) between a current rotational speed (WD) and the optimal rotational speed (WO) of the dynamotor (DN); adjusting the current rotational speed (WD) to the optimal rotational speed (WO) according to the speed regulation command (CMD), so that the dynamotor (DN) generates a dynamotor power (ED) according to the optimal rotational speed (WO) and the kinetic energy (EM); and storing the dynamotor power (ED).

10. The energy recovery method (S100) as claimed in claim 9, wherein obtaining the rotational speed (WS) and the torque (TQ) according to the kinetic energy (EM) comprises: providing a transmission gear (121), and causing the fork (300) to drive the transmission gear (121) when descending; causing the transmission gear (121) to drive the dynamotor (DN); and obtaining the rotational speed (WS) and the torque (TQ) according to a gear mass (M) of the transmission gear (121), a gear radius (R) of the transmission gear (121), a downward time (t) of the fork (300), and the kinetic energy (EM).

11. The energy recovery method (S100) as claimed in claim 9, wherein obtaining the optimal rotational speed (WO) corresponding to the torque (TQ) and the highest efficiency of the dynamotor (DN) comprises: providing a lookup table, wherein the lookup table stores a plurality of rotational speeds (WS) corresponding to a plurality of torques (TQ) and a plurality of efficiencies; and finding the optimal rotational speed (WO) corresponding to the highest efficiency from the lookup table according to the torque (TQ) received.

12. The energy recovery method (S100) as claimed in claim 9, wherein obtaining the optimal rotational speed (WO) corresponding to the torque (TQ) and the highest efficiency of the dynamotor (DN) comprises: obtaining a first efficiency of the dynamotor (DN) according to the torque (TQ) and a first rotational speed; obtaining a second efficiency of the dynamotor (DN) according to the torque (TQ) and a second rotational speed; generating a slope based on an efficiency difference between the first efficiency and the second efficiency and a rotational speed difference between the first rotational speed and the second rotational speed; and obtaining a new rotational speed value using the slope and a learning rate, thereby obtaining the optimal rotational speed (WO).

13. The energy recovery method (S100) as claimed in claim 9, further comprising: dividing the optimal rotational speed (WO) by the current rotational speed (WD) to generate a speed ratio; and generating the speed regulation command (CMD) according to the speed ratio.

14. The energy recovery method (S100) as claimed in claim 9, wherein adjusting the current rotational speed (WD) to the optimal rotational speed (WO) according to the speed regulation command (CMD) comprises: providing a speed regulation gear (141), and using the speed regulation gear (141) to adjust the current rotational speed (WD) of the dynamotor (DN) according to the speed regulation command (CMD).

15. The energy recovery method (S100) as claimed in claim 9, wherein storing the dynamotor power (ED) comprises: converting the dynamotor power (ED) into a battery power (EB), and charging a battery module (151) using the battery power (EB).

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