Electric Excavator

Abstract

An excavator with a boom comprises a main electrical drive system with an electrical power storage unit. The excavator comprises an electrical drive configured to actuate movement of the boom to raise and/or lower part of the boom. The excavator comprises a separate fluid-operated, auxiliary actuation system for storing potential energy of the part of the boom during lowering thereof and for using the stored potential energy to support raising of the part of the boom. The auxiliary actuation system is configured to store the potential energy and to support raising the part of the boom autonomously without interaction with the main electrical drive system.

Claims

1. An excavator including a boom, comprising: a main electrical drive system including an electrical power storage unit and an electrical drive configured to actuate movement of the boom to raise and/or lower part of the boom with a pivoting movement; and a separate fluid-operated auxiliary actuation system for storing potential energy of the part of the boom during lowering thereof and for using the stored potential energy to support raising of the part of the boom, wherein the auxiliary actuation system is configured to store the potential energy and to support raising the part of the boom autonomously without interaction with the main electrical drive system.

2. The excavator according to claim 1, wherein the auxiliary actuation system comprises an auxiliary actuator coupled to the boom and at least one accumulator, and wherein the auxiliary actuator and the at least one accumulator are coupled such that lowering of the part of the boom pressurizes the at least one accumulator and such that raising of the part of the boom is supported by potential energy stored in the at least one accumulator.

3. The excavator according to claim 2, further comprising a main hydraulic system including a hydraulic actuator for moving the part of the boom and a hydraulic pump for actuating the hydraulic actuator, wherein the hydraulic pump is powered by the main electrical drive system.

4. The excavator according to claim 3, wherein the hydraulic actuator of the main hydraulic system and the auxiliary actuator of the auxiliary actuation system are arranged in parallel to each other.

5. The excavator according to claim 3, wherein the auxiliary actuator of the auxiliary actuation system is arranged above the main hydraulic system.

6. The excavator according to claim 3, wherein the main hydraulic system has a higher maximum power output than the auxiliary actuation system.

7. The excavator according to claim 2, wherein the auxiliary actuator is attached at one end to an upper carriage of the excavator, and wherein the auxiliary actuator is attached to a side surface of the boom, the side surface facing away from an operator's cab of the excavator.

8. The excavator according to claim 1, wherein the auxiliary actuation system is passively controlled during the storing of potential energy and the lifting of the part of the boom.

9. The excavator according to claim 1, wherein the auxiliary actuation system comprises an accumulator and a valve for filling and/or emptying the accumulator with a fluid and a control unit for controlling the valve.

10. The excavator according to claim 9, wherein the control unit is configured to open the valve to release pressure from the accumulator when the excavator is turned off.

11. The excavator according to claim 9, wherein the excavator includes a main hydraulic system, wherein the valve is fluidly connected to the main hydraulic system, and wherein the control unit is configured to open the valve to fill the accumulator with fluid from the main hydraulic system and/or equalize pressure in both the main-electrical drive system and the auxiliary actuation system when the excavator is turned on.

12. The excavator according claim 1, wherein the auxiliary actuation system is configured to be pressurized from storage of potential energy during lowering of the part of the boom.

13. The excavator according to claim 2, wherein the at least one accumulator and the auxiliary actuator of the auxiliary actuation system are pneumatically operated.

14. The excavator according to claim 2, wherein the auxiliary actuator of the auxiliary actuation system is hydraulically operated and the at least one accumulator comprises a gas acting as a compression medium for storing potential energy.

15. The excavator according to claim 3, wherein the hydraulic actuator is larger than the auxiliary actuator.

16. The excavator according to claim 2, wherein the auxiliary actuator is attached to an upper carriage of the excavator within 60% of forward extension of the auxiliary actuator.

17. The excavator according to claim 2, wherein the auxiliary actuator does not cross or overlap an operator's cab of the excavator in a direction orthogonal to a forward-backward direction of the excavator.

18. The excavator according to claim 2, wherein the auxiliary actuator is at least partially arranged in a same vertical plane extending in a forward-backward direction as a main hydraulic actuator.

19. The excavator according to claim 2, wherein a rod end of the auxiliary actuator is attached to the boom of the excavator and a cylinder end of the auxiliary actuator is attached to an upper carriage of the excavator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 shows in a schematic side view an excavator with a moveable boom.

[0035] FIG. 2 illustrates in a schematic side view the excavator according to FIG. 1 with an auxiliary actuation system and its boom in a raised position according to an embodiment.

[0036] FIG. 3 illustrates the embodiment according to FIG. 2 with the boom in a lowered position.

[0037] FIG. 4 schematically illustrates the auxiliary actuation system of the embodiment according to FIG. 2.

[0038] FIG. 5 illustrates in a schematic perspective view the excavator according to FIG. 1 with an auxiliary actuation system and its boom in the raised position according to a further embodiment.

[0039] FIG. 6 schematically illustrates the auxiliary actuation system of the embodiment according to FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0040] FIG. 1 shows an excavator 10 with a movable boom 12. In the given example, the boom 12 comprises a first arm 14 and a second arm 16 that are pivotably attached to each other. The excavator 10 comprises an under carriage 18 and an upper carriage 20. The under carriage 18 comprises tracks 201 which allow the excavator to move over terrain. The upper carriage 20 is pivotably attached to the under carriage 18 so that they may turn relatively to each other around a vertical axis. The under carriage 18 supports the upper carriage 20. The upper carriage 20 may also be referred to as the turret of the excavator 10. The upper carriage 20 provides the platform for supporting the boom 12 and a cab 38 for the operator or driver of the excavator 10. Specifically, the proximal end of the first arm 14 is pivotably attached to the upper carriage 20. Furthermore, an opposite distal end of the first arm 14 is preferably connected with a proximal end of the second arm 16. The opposite distal end of the second arm 16 and the tool 22 of the boom 12 are also pivotably attached to each other. In the present example, the tool 22 is a bucket.

[0041] The excavator 10 comprises a main electrical drive system 24 with an electrical power unit 26 in the form of a battery and an electrical drive 28, e.g. an electric motor. The necessary power to operate the excavator 10 and in particular the electrical drive 28 is only provided by the electrical power unit 26. In particular, no combustion engine is provided. The main electrical drive system 24 is configured to actuate movement of the boom 12 to raise and lower at least part of the boom 12. In particular, as can be taken from FIG. 1, the boom 12 comprises several actuation cylinders 30 that may allow to move each of the first and second arm 14, 16 as well as the tool 22. Each cylinder 30 may be actuated by the main electrical drive system 24. In one embodiment, the excavator 10 comprises a main hydraulic actuation system 40, which is powered by the main electrical drive system 24. In that case, the electrical drive 28 powers a hydraulic pump 41 that generates hydraulic pressure to activate hydraulic cylinders 30 via hydraulic lines 42. Alternatively, the electrical drive 28 may also directly actuate each of the movable parts of the boom 12. Furthermore, the main electrical drive system 24 may also pivot or swivel the upper carriage 20 relatively to the under carriage 18 and/or drive the tracks 201 to move the excavator 10.

[0042] Raising at least a part of the boom 12 increases the potential energy in said part of the boom 12. Such a movement may also be called lifting of the boom 12. Accordingly, raising the boom 12 requires more power than lowering of the boom 12. In particular, lowering the boom 12 may not even require any energy at all but is just caused by gravity. Breaking during lowering of the boom 12 may be controlled by a hydraulic valve in its actuation system. During lowering of the boom 12, the potential energy of the raised position is freed and thus available for recuperation.

[0043] This freed potential energy may therefore be recuperated to increase the overall efficiency of the excavator 10. For that purpose, the excavator 10 comprises an auxiliary fluid-operated actuation system 32, of which one embodiment is shown in FIG. 2 and another in FIG. 5. In the present examples, a hydraulic oil is used as the fluid and the auxiliary actuation system 32 will henceforth be called the auxiliary hydraulic actuation system 32, although the system 32 could also be designed as an auxiliary pneumatic actuation system 32 using gas as the fluid. The auxiliary hydraulic actuation system 32 does not comprise or use a power supply for actuation. Instead, the auxiliary hydraulic actuation system 32 is configured to store potential energy freed during lowering of at least part of the boom 12 and to use the stored energy to support raising of at least part of the boom 12 independent of a power source during its operation. The auxiliary actuation system 32 is configured to store the energy and to support raising the part of the boom 12 completely autonomous without any interaction with main electrical drive system 24.

[0044] For that purpose, the embodiment of the auxiliary hydraulic actuation system 32 comprises an auxiliary hydraulic cylinder 34 and an accumulator 36. To illustrate the working principal of the auxiliary hydraulic actuation system 32, FIG. 2 shows a raised position of the boom 12 (only the first arm 14 of the boom being shown) and FIG. 3 shows a lowered position of the boom 12 (also only the first arm 14 of the boom being shown). As can be seen from a comparison of FIG. 2 and FIG. 3 with FIG. 1, only the first arm 14 is counterbalanced with the auxiliary actuation system 32 for recuperation during lowering and support during raising. Similar systems and/or components could be provided to other arms of the boom 12 as well. Alternatively, the boom 12 shown in said embodiment could also comprise just a single arm and would thus be less complex then the boom 12 shown in FIG. 1. However, the overall working principal of the recuperation is the same, regardless of which part of the boom 12 is raised or lowered and/or connected to an auxiliary actuation system.

[0045] As can be seen in FIG. 2, in the position in which the auxiliary hydraulic actuation cylinder 34 is fully retracted, the boom 12 is raised. In that position, the accumulator 36 and the overall auxiliary hydraulic actuation system 32 is not pressurized, in particular relative to an ambient pressure. When lowering the boom 12, the auxiliary hydraulic cylinder 34 is extended. Due to this extension, there is a pressure increased in the auxiliary hydraulic actuation system 32, which stores the freed potential energy during lowering of the boom 12 in the accumulator 36. When lifting the boom 12 from the lowered position shown in FIG. 3 to the raised position of FIG. 2, the thus stored potential energy may be used to retract the auxiliary hydraulic cylinder 34, thus supporting raising of the boom 12. Therefore, overall required power output to raise the boom 12 may be reduced. The operation of the main hydraulic actuator 30 shown in FIGS. 2 and 3 during raising of the boom 12 is supported by the auxiliary hydraulic cylinder 34.

[0046] FIG. 4 illustrates in a schematic view the connection of the auxiliary hydraulic cylinder 34 with accumulator 36. As can also be taken from FIG. 4, the auxiliary hydraulic actuation system 32 does not necessarily require an active control and/or any valves. Accordingly, the system is simple, easy to service and cost-effective. However, a valve 50 and optionally also a control unit 53 could be added to provide depressurization of the auxiliary actuation system 32 after shutdown of the excavator 10. Alternatively or additionally, the valve 50 and control unit 53 could also serve to initially pressurize the auxiliary actuation system 32 via the hydraulic pump 41, which was described above, and a fluid connection line 51. A similar configuration could also be provided for the other embodiment. Specifically, when turning on the excavator 10, the control unit 53 might be configured to open the valve 50, thereby pressurizing the auxiliary actuation system with hydraulic fluid from the main hydraulic system 40, i.e. via the hydraulic pump 41. Once pressurized, the control unit 53 is configured to close the valve 50 and keep it closed during operation of the auxiliary actuation system. Likewise, when the excavator 10 is turned off, the control unit 53 may be configured to open the valve 50 again to de-pressurize the auxiliary actuation system.

[0047] FIG. 5 and FIG. 6 illustrate another embodiment of the auxiliary hydraulic actuation system 32. Here, the auxiliary hydraulic cylinder 34 is supporting raising of the boom 12 with the main hydraulic actuator 30 during extension of the auxiliary hydraulic actuator 34. Correspondingly, during lowering of the boom 12, the auxiliary hydraulic actuator 34 is compressed, thus pressurizing the auxiliary hydraulic actuation system 32 and in particular the accumulator 36 to store the freed potential energy. The system shown in FIG. 6 may also comprise a valve 50, a fluid line 51 and a control unit 53, which may be configured and connected to the main hydraulic system 40 as described in connection with FIG. 4.

[0048] In both embodiments, the auxiliary hydraulic actuators 34 are attached with their rod end, which is their distal end, to the boom 12 and a cylinder end, which is the proximal end, of the auxiliary hydraulic actuator 34 is attached to the upper carriage 20 of the excavator.

[0049] Besides the working direction of the auxiliary hydraulic actuator 34 in each of the embodiments shown in FIG. 2 and FIG. 5, the attachment position of the auxiliary hydraulic actuators 34 to the upper carriage 20 and the boom 12 is also different. FIG. 5 illustrates an embodiment where the auxiliary hydraulic actuator 34 is arranged in parallel to the main hydraulic actuator 30. Both ends of each the main hydraulic actuator 30 and the auxiliary hydraulic actuator 34 are mounted to the same respective shaft to be pivotably connected with one end each to the upper carriage 20 and the boom 12. In particular, the design of the auxiliary hydraulic actuator 34 and the main hydraulic actuator 30 is identical in this embodiment, allowing the use of more identical parts.

[0050] By comparison, in the embodiment of the auxiliary hydraulic actuation system 32 shown in FIG. 2 and FIG. 3, the auxiliary hydraulic actuator 34 is arranged above the main hydraulic actuator 30. Due to this arrangement, the auxiliary hydraulic actuator 34 may be smaller and less powerful than the main hydraulic actuator 30. This also allows the auxiliary hydraulic actuator 34 to be arranged at essentially the same position in the left right direction of the excavator 10 as the main hydraulic actuator 30. Due to this arrangement, the vision for the driver of the excavator 10 may be obstructed less.

REFERENCE SIGNS

[0051] 10 excavator [0052] 12 boom [0053] 14 first arm [0054] 16 second arm [0055] 18 under carriage [0056] 20 upper carriage [0057] 22 tool [0058] 24 main electrical drive system [0059] 26 electrical power storage unit [0060] 28 electrical drive [0061] 30 main hydraulic actuator [0062] 32 auxiliary hydraulic actuation system [0063] 34 auxiliary hydraulic actuator [0064] 36 accumulator [0065] 38 cab [0066] 40 main hydraulic system [0067] 41 hydraulic pump [0068] 42, 51 hydraulic line [0069] 50 valve [0070] 53 control unit