Working machine

A working machine comprises a direct voltage source (301), a first power converter (302) for transferring energy from the direct voltage source to electric machines (303a, 303b) driving actuators of the working machine, an electric connector system (304) for electrically connecting to an external power grid, a second power converter (305) for transferring energy from the external power grid to the direct voltage source, and alternating current electric machines (306a, 306b) driving auxiliary devices of the working machine. The electric connector system is suitable for connecting the alternating current electric machines to receive alternating voltage of the external power grid, and the second power converter is suitable for transferring energy from the direct voltage source to the alternating current electric machines. Thus, the electric machines driving the auxiliary devices can be energized directly by the external power grid when the working machine is connected to the external power grid.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority benefits under U.S.C. § 119 to European Patent Application No. EP17201772.5 filed on Nov. 15, 2017, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to a method for driving one or more auxiliary devices of a working machine. An auxiliary device can be, for example but not necessarily, a hydraulic pump, a blower, a compressor, or a coolant circulating pump. Furthermore, the disclosure relates to a working machine.

BACKGROUND

In many cases, a working machine comprises one or more electrically driven actuators. The working machine can be, for example, a mobile working machine having wheels and/or chain tracks. A mobile working machine can be for example a tractor, a bucket charger, a road drag, an excavator, or a bulldozer. It is also possible that the working machine is for example a stone crusher or a wood chipping machine that is not necessarily provided with means for moving the working machine. Each actuator can be for example a wheel, a chain track, a cutter of a wood chipping machine, or some other actuator of a working machine. A working machine of the kind described above comprises typically a direct voltage source and a power converter for transferring electric energy from the direct voltage source to one or more electric machines for driving the one or more actuators. The direct voltage source may comprise for example a battery element and/or a capacitor element. It is also possible that the direct voltage source comprises a generator, a combustion engine for driving the generator, and a power converter for converting the voltage of the generator into suitable direct voltage.

Typically, a working machine of the kind described above further comprises auxiliary devices for enabling and/or assisting the operation of the actuators of the working machine. An auxiliary device can be for example a hydraulic pump, a blower, a compressor, a coolant circulating pump, a heating system, or a cooling system. In a working machine having electrically driven actuators, also the auxiliary devices are typically electrically driven. A working machine may comprise for example one or more power converters for converting direct voltage of a direct voltage source, such as e.g. battery element, into voltages suitable for electric machines driving the auxiliary devices. Thus, a working machine of the kind described above may comprise many power converters which need room, cooling capacity, and maintenance. Furthermore, the need for many power converters increases the manufacturing costs of a working machine.

SUMMARY

In accordance with the invention, there is provided a new working machine that can be, for example but not necessarily, a tractor, a bucket charger, a road drag, an excavator, a bulldozer, a stone crusher, or a wood chipping machine. A working machine according to the invention comprises:a direct voltage source,at least one first power converter for transferring electric energy from the direct voltage source to one or more electric machines for driving one or more actuators of the working machine,an electric connector system for electrically connecting to an external alternating current power grid,a second power converter for transferring electric energy from the external alternating current power grid to the direct voltage source, andone or more alternating current electric machines for driving one or more auxiliary devices for enabling and/or assisting the operation of the actuators of the working machine.

The electric connector system is suitable for connecting the one or more alternating current electric machines to receive alternating voltage of the external alternating current power grid. Thus, the alternating current electric machines driving the auxiliary devices can be energized directly by the external alternating current power grid when the working machine is connected to the external alternating current power grid. The above-mentioned second power converter is suitable for transferring electric energy from the direct voltage source to the one or more alternating current electric machines. Therefore, the second power converter has two functionalities: i) transfer electric energy from the external alternating current power grid to the working machine when the working machine is connected to the external alternating current power grid, and ii) energize the alternating current electric machines driving the auxiliary devices when the working machine is disconnected from the external alternating current power grid. The above-described arrangement reduces the complexity of a power electronic system of a working machine and thereby savings can be achieved in cooling capacity, maintenance, room requirement, and costs.

In accordance with the invention, there is provided also a new method for driving one or more auxiliary devices of a working machine of the kind described above. A method according to the invention comprises:controlling, in response to a situation in which the working machine has been disconnected from the external alternating current power grid, the second power converter to transfer electric energy from the direct voltage source to the one or more alternating current electric machines driving the one or more auxiliary devices, andconnecting, in response to a situation in which the working machine has been connected to the external alternating current power grid, the one or more alternating current electric machines to receive the alternating voltage of the external alternating current power grid.

Various exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Furthermore, it is to be understood that lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated.

FIG. 1shows a schematic illustration of a powering system of a working machine according to an exemplifying and non-limiting embodiment of the invention. The working machine comprises a direct voltage source101. In this exemplifying case, the direct voltage source101comprises a battery element108and a capacitor element109. The capacitor element109may comprise for example an electric double layer capacitor “EDLC” in order to increase the energy storing capacity of the capacitor element109. An EDLC is sometimes called a “super capacitor”. Furthermore, the direct voltage source101comprises a generator110, a combustion engine111for driving the generator, and a power converter112for converting the voltage of the generator110into suitable direct voltage. The combustion engine111can be for example a diesel engine, an Otto-cycle engine, or a turbine engine. It is, however, also possible that the working machine is a full-electric working machine which does not comprise a combustion engine.

The working machine comprises at least one first power converter102for transferring electric energy from the direct voltage source101to at least one electric machine103for driving one or more actuators of the working machine. Each actuator can be for example a wheel, a chain track, a hydraulic pump, a cutter of a wood chipping machine, or some other actuator of a working machine. In the exemplifying case illustrated inFIG. 1, the electric machine103is arranged to drive an actuator113that is a wheel of the working machine. The working machine comprises an electric connector system104for electrically connecting to an external alternating current “AC” power grid114. The working machine comprises a second power converter105for transferring electric energy from the external AC power grid to the direct voltage source101so that the battery element108and the capacitor element109can be charged from the AC power grid. The working machine comprises alternating current “AC” electric machines106a,106b, and106cfor driving auxiliary devices107a,107b, and107cof the working machine. The auxiliary devices107a-107cmay comprise for example a hydraulic pump, a blower, a compressor, a coolant circulating pump, a heating system, and/or a cooling system.

The above-mentioned electric connector system104is suitable for connecting the AC electric machines106a-106cto receive the alternating voltage of the external AC power grid114. Thus, the AC electric machines106a-106cdriving the auxiliary devices107a-107ccan be energized directly by the external AC power grid114when the working machine is connected to the external AC power grid114. The above-mentioned power converter105is suitable for transferring electric energy from the direct voltage source101to the AC electric machines106a-106c. Therefore, the power converter105has two functionalities: i) transfer electric energy from the external AC power grid114to the working machine when the working machine is connected to the external AC power grid114, and ii) energize the AC electric machines106a-106cdriving the auxiliary devices107a-107cwhen the working machine is disconnected from the external AC power grid114. In a working machine according to an exemplifying and non-limiting embodiment, the power converter105is suitable for changing the frequency of the alternating voltage supplied to the AC electric machines106a-106cwhen the working machine is disconnected from the external AC power grid114. In this exemplifying case, the frequency of the alternating voltage supplied by the power converter105can be e.g. lower than the frequency of the alternating voltage of the external AC power grid114when the power of the auxiliary devices107a-107ccan be lower.

FIG. 2shows a flowchart of a method according to an exemplifying and non-limiting embodiment of the invention for driving one or more auxiliary devices of a working machine that comprises:a direct voltage source,at least one first power converter for transferring electric energy from the direct voltage source to one or more electric machines for driving one or more actuators of the working machine,an electric connector system for connecting to an external alternating current power grid, anda second power converter for transferring electric energy from the external alternating current power grid to the direct voltage source.

The method comprises the following actions:action201: controlling, in response to a situation in which the working machine has been disconnected from the external alternating current power grid, the second power converter to transfer electric energy from the direct voltage source to one or more alternating current electric machines driving the one or more auxiliary devices, andaction202: connecting, in response to a situation in which the working machine has been connected to the external alternating current power grid, the one or more alternating current electric machines to receive alternating voltage of the external alternating current power grid.

FIG. 3shows a schematic illustration of a working machine320according to an exemplifying and non-limiting embodiment of the invention. In this exemplifying case, the working machine320is a bucket charger but the working machine could as well be a tractor, a road drag, a bulldozer, a stone crusher, or a wood chipping machine or any other working machine. The working machine320comprises a direct voltage source301. In this exemplifying case, the direct voltage source301comprises a battery element, a capacitor element, a generator, a combustion engine for driving the generator, and a power converter for converting the voltage of the generator into suitable direct voltage. The working machine320comprises electric machines at the hubs of wheels of the working machine. InFIG. 3, two of these electric machines are denoted with references303aand303band two of the wheels of the working machine are denoted with references313aand313b. The working machine320comprises a first power converter302for transferring electric energy between the electric machines303aand303band the direct voltage source301. The power converter302is arranged to produce voltages having amplitudes and frequencies suitable for the electric machines303aand303b. The power converter302may comprise a separate and independently controlled output stage for each of the electric machines at the hubs of the wheels. In this case, these electrical machines can be controlled independently of each other. It is, however, also possible that the electrical machines at the hubs of the wheels are parallel connected to a same output stage of the power converter302and thus these electric machines are controlled as a group.

The working machine320comprises an electric connector system304for attaching an electric cable321mechanically to the working machine and for electrically connecting to an external alternating current “AC” power grid314through the electric cable321. In a working machine according to another embodiment of the invention, the electric connector system comprises a pantograph for electrically connecting to electric conductors. The working machine320comprises a second power converter305for transferring electric energy from the external AC power grid314to the direct voltage source301so that the battery element and the capacitor element of the direct voltage source301can be charged from the AC power grid314. The working machine comprises alternating current “AC” electric machines306aand306bfor driving auxiliary devices of the working machine. In the exemplifying case illustrated inFIG. 3, the AC electric machine306ais arranged drive a hydraulic pump of a hydraulic system of the working machine320and the AC electric machine306bis arranged drive a coolant circulating pump of a cooling system of the working machine. The electric connector system304is suitable for connecting the AC electric machines306aand306bto receive the alternating voltage of the external AC power grid314. The working machine320may further comprise one or more soft-starters for reducing starting currents of the electric machines306aand/or306b. The soft-starters are not shown inFIG. 3.

The above-mentioned power converter305is suitable for transferring electric energy from the direct voltage source301to the AC electric machines306aand306c. Thus, the AC electric machines306aand306bdriving the auxiliary devices can be energized by the direct voltage source301when the working machine is disconnected from the external AC power grid314. The power converter305can be suitable for changing the frequency of the alternating voltage supplied to the AC electric machines306aand306cwhen the working machine320is disconnected from the external AC power grid314.

The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.