Heavy-current charging cable for charging an electric vehicle

Technical Field

The invention relates to a heavy-current charging cable for charging an electric ve hicle, comprising a central heavy-current wire configured for serving as ground, the central wire comprising a central conductor and extending in a longitudinal direction, and a plurality of heavy-current power wires configured for conducting positive and negative direct current, DC, each of said power wires comprising a power conductor and a power wire insulation surrounding said power conductor, the power wires sur rounding and extending parallel to the central wire. The invention further relates to an electric vehicle supply equipment comprising the heavy-current charging cable and a cooling unit, as well as to a respective method for cooling a heavy-current charging cable.

Background Art

A liquid cooled charging cable for high power charging of electric vehicles, EVs, with more than 250 A consists typically of a cable arrangement, including a plurality of conductors with the charging cable and a charging connector, wherein power con tacts are located. The coolant loop in the charging cable is generally designed to remove heat generated by Joule effect both in the charging cable and in the charg ing connector. The liquid cooled charging cable is connected to a cooling unit, gen erally located inside a charge post, where the heat provided to the coolant by Joule effect is preferably dissipated to the surrounding ambient air.

Such liquid cooling is necessary for high-current fast EV chargers, mainly because the liquid cooling avoids other necessary use of bulky charging conductors which would make the charging cable very difficult to handle. Non-cooled charging cable are typically used for charging current up to 250 A as otherwise the charging cable becomes too large, heavy and stiff for the user. Thus, active liquid cooling is essen tial, by using a coolant fluid such as for example oils, water/glycol or water/salts mixtures, halogenated hydrocarbon compounds, etc., and said cooling unit for con veying and respective cooling of the liquid coolant.

In a conservative approach, the electrical metallic conductors present in the charg ing cable, typically Cu, are electrically insulated to prevent shorts between the con ductors or to ground through the liquid coolant. In this case, non-insulating coolants, like water/glycol mixtures, can be used, which bring some advantages. First, these mixtures exhibit chemical compatibility with a variety of materials, including rubber like polymeric materials to be used for electrical insulation, for example silicone rub bers or thermoplastic elastomers. Such materials remain soft even at low tempera ture. Furthermore, some water-based mixtures have low viscosity even below - 30°C, so a heating system and/or a large pump are generally not required to enable a proper operation of the charge post at low temperatures. On the other hand, cool ing performance is penalized due to the presence of insulating, and poor thermally conducting, layers between the conductors and the liquid coolant, limiting maximum allowed power rating of the liquid cooled charging cable.

In more advanced solutions known from prior art, the liquid coolant flows directly around the bare and thus uninsulated conductors providing more efficient cooling. In this case, insulating liquids have to be used, like synthetic oils or halogenated hydrocarbon compounds, with drawbacks in terms of their low temperature perfor mance due to increased viscosity and their environmental friendliness, respectively. Many dielectric fluids become very viscous at temperatures below -20°C. It is worth to mention that data available on chemical compatibility between synthetic oils and plastic materials is scarce and unreliable, raising also questions with regards to long term stability.

Existing liquid cooled charging cable solutions suffer drawbacks in terms of safety, reliability and/or performance. For instance, one known solution shows poor perfor mance at low temperatures such as below -20°C because of excessive pressure drop and problematic material compatibility between the liquid coolant (synthetic oil) and the polymeric material used for flow channels. Another known solution adopts an indirect cooling approach with a water/glycol mixture flowing in separate ducts. The charging cable-to-electric vehicle contacts are well thermally controlled but the heat generated in the conductors is not dissipated effectively. As a consequence, a higher cross section of copper conductors is adopted thus making the cable heavier and a nominal current of 500 A can be reached at 40°C ambient, only if a cooling unit with a refrigerant loop is used. In addition, both solutions are considered weak in terms of reliability since during normal operation, materials temperature very limit is reached.

Furthermore, in existing solutions, coolant flow can be easily blocked as an example by inner clogging or pipe crushing. This represents potentially a safety issue, espe cially during a charging session because the thermal runaway can be extremely fast and the interlock system in the charge post may only intervene with a certain delay.

Summary of invention

It is therefore an object of the invention to provide a charging cable and respective charge post solution for high power charging at power ratings equal or greater to 500kW increasing reliability and safety standards.

The object of the invention is solved by the features of the independent claims. Pre ferred embodiments are detailed in the dependent claims.

Thus, the object is solved by a heavy-current charging cable for charging an electric vehicle, comprising:

a central heavy-current wire configured for serving as ground, the central wire comprising a central conductor and extending in a longitudinal direction,

a plurality of heavy-current power wires configured for conducting positive and negative direct current, DC, each of said power wires comprising a power con ductor and a power wire insulation surrounding said power conductor, the power wires extending parallel to the central wire, a liquid tight inner hose extending in the longitudinal direction and surround ing the central wire and the power wires thereby defining a first hollow area com prising liquid coolant to flow between the central wire and the power wires along the longitudinal direction, and

a liquid tight outer hose extending in the longitudinal direction and surround ing the inner hose thereby defining a second hollow area comprising liquid coolant to flow between the inner hose and the outer hose along the longitudinal direction.

The proposed solution provides a heavy-current charging cable suitable for High Power Charging, HPC, of Electrical Vehicles, EV. The solution enables charging at 500A and 1000V, meeting today’s standards for fast DC charging, in particular al lowing 100 km of driving within 3 to 5 min charging, and can be also adapted to evolving future requirements towards higher ratings such as charging with 600 A at 1500 V i.e. at 900 kW. Compared to prior art solution, the proposed solution provides improved thermal and mechanical performance, and ease in manufacturing and as sembly. As revealed by thermal simulations, with a commonly used material for the power wire insulation respectively core wire insulation described below, a maximum temperature of the respective conductors remains below 90°C when a current of 500 A is flowing at ambient temperature up to 50°C. As compared to existing solu tion as known from prior art, the maximum temperature of conductors at 500 A is reduced by 20 to 25°C.

The simple preferably cylindrical design of all components of the cable provides ease during manufacturing of all components and also in assembling the final liquid cooled cable. The core part of the cable comprised of the conductor wires and the inner hose can be easily assembled together or purchased in a ready cable form from an external cable manufacturer. At a second step the aforementioned assem bly is inserted into the outer hose. Thus, the proposed solution is readily scalable towards higher power ratings by suitably modifying the dimensions of the conduc tors, of the inner and outer hose as well as the flow rate of the liquid coolant.

The cable can be part of an electric vehicle supply equipment, EVSE, also referred to as electric vehicle, EV, charging station, electric recharging point, charging point, charge point, charge post or electronic charging station, ECS. The EVSE is an ele ment in an infrastructure that supplies electric energy for recharging of electric ve hicles, including electric cars, neighbourhood electric vehicles and plug-in hybrids, via said charging cable and a charging connector to the EV. EVSEs usually comply with standards for electric vehicle fast charging, such as the so-called Combined Charging System, CCS, protocol according to IEC 61851 -23 and SAE J1772 stand ard for charging electric vehicles both in the US and in the European Union, EU. The Combined Charging System, CCS, protocol is a fast charging method for charg ing electric vehicles delivering high-voltage direct current via a charging connector derived from SAE J1772 standard (IEC Type 1 ) or IEC Type 2 connector. Automo bile manufactures that support CCS include Jaguar, Volkswagen, General Motors, BMW, Daimler, Ford, FCA, Tesla and Flyundai. The CSS standard is controlled by the so called CharIN consortium. Besides other protocols such as, for example, CFIAdeMO, as abbreviation of CFIArge de Move, or GB/T, in particular according to 20234.3-201 1 standard. The proposed solution can be advantageously used with even higher charging currents such as more than 500A and/or in combination with newer standards not yet defined requiring higher currents.

Preferably the inner hose, the outer hose and/or the arrangement of the power wires surrounding the central wire comprise a cylindrical or cylindrical-like shape respec tively design. The first hollow area and/or the second hollow area shall preferably be understood as an‘empty space’ through which the liquid coolant can be con veyed respectively flow. The inner hose and/or the outer hose can be provided as a cooling jacket and/or as an annular, integral jacket which is extruded on and in which defines the respective hollow chamber. The term heavy-current shall be understood that the conductors and the respective insulation is configured for conveying total currents equal to or greater than 500 A. In a further implementation the cable may comprise a plurality of core wires.

The central wire may comprise a central wire insulation surrounding the central con ductor or is non-insulated, and/or the power wires surrounding the central wire. The term surrounding shall be understood that, in a sectional view, the central wire is encompassed by the power wires respectively the power wires and the core wires are encompassed by the inner hose.

In a preferred implementation the cable comprises six power wires, each three of the power wires conducting positive and negative DC and arranged alternately around the central heavy-current core. Alternatively, the conductors conducting pos itive current are arranged on one side on the central heavy-current core and the conductors conducting negative current are arranged on the other side on the cen tral heavy-current core. According to a further preferred implementation the central wire and the power wires are arranged such that the packing factor is 0.777. The packing factor is preferably defined as per DIN EN 60317-1 1 and/or as conductor area, of all conductors, divided total area, used by all conductors preferably within the inner hose. Usage of seven wires, three power wires for DC+ respectively power plus, three power wires for DC- respectively power minus and one core wire for grounding, is a favourable topology since it allows a high packing factor as 0.777. Furthermore, the total current and the total heat losses due to Joule effect can be divided into six conductors, thus reducing the heat flux on each conductor and min imizing the effect of the insulation layer on the total thermal resistance.

Generally cross sections of the power wires and of the core wire, thickness of the power wire insulation and of the outer hose and/or of the inner hose and/or cable length can be arbitrarily chosen, preferably provided that sufficient dielectric strength is assured between conductors. According to a preferred implementation a cross section of the power wires is 16 mm ² , a cross section of the core wire is 25 mm ² , a thickness of the power wire insulation is in a range of 0.5 to 2.0 mm, the outer hose and/or the inner hose comprises a thickness in a range of 2 to 10 mm, and/or the cable comprises a length of 6 m. Such parameters allow charging at 500 A DC and 1000 V DC. Such wise the term heavy-current shall be understood that a total cur rent greater or equal 500 A is meant respectively can be conducted by the respec tive conductors or wires. According to a preferred implementation the liquid coolant comprises oil, a water and glycol mixture, a water and salt mixture, and /or halogenated hydrocarbon com pounds. As coolant liquid a non-insulating fluid such as for example water/glycol mixtures can be used since the proposed solution is compatible with indirect cooling approach. According to numerical calculations, with a preferred coolant having a kinematic viscosity at -40°C lower than 470 cSt, a maximum pressure drop in a 6 m long cable is of 4 bar, at a flow rate below 1 I/m in, and such wise suitable for thermal control of the cable’s conductors.

Inner hose and/or outer hose can be generally provided from an ordinary but pref erably insulating material. Preferably inner hose and/or outer hose are provided as a tube and/or as a sleeving. In a preferred implementation the inner hose and/or the outer hose comprise a polymer-based material and/or extruded polymer layers. Most preferably, inner hose and/or outer hose comprise polyamide.

In another preferred implementation the outer hose comprises a flexible metal tube arranged between the inner hose and the outer hose and whereby the outer hose is extruded on the flexible metal tube. In an alternative implementation the flexible metal tube is arranged on the outer hose thereby encompassing the outer hose. Such flexible metal tube provides enhanced safety and mechanical robustness for the cable. In particular, in case of a damage in the outer hose the user of the cable is still protected to any exposure to the high voltage cable by both the flexible metal hose, which is preferably also provided water tight, and the inner hose. Furthermore, the flexible metal hose provides required mechanical protection in the event an elec tric vehicle drives over the liquid cooled cable. Therefore, the flexible metal tube is preferably configured to comprise a lateral crushing strength in the range of 65.5 kN/m. The metal tube may comprise, in cross-section, a strip-wound hose made from galvanic steel, for example cut of carcass wall. Most preferably the metal tube is made of steel, galvanized steel or aluminum, preferably comprising strip-wound profiles to provide necessary flexibility and/or having a bending radius below 300 mm, preferably below 150 mm. Generally, the central conductor and/or the power conductors may comprise an ar bitrary conducting material. According to a preferred implementation the central con ductor and/or the power conductors comprise copper and/or aluminium wires and/or wire strands. The proposed cable can be simply and thus cost efficient manufac tured, whereby in particular the usage of Aluminium instead of Copper conductors result in significant cost reduction. Aluminium has about 60% of the conductivity of copper but has only 30% of the weight of copper. That means that a bare wire of aluminium weighs half as much as a bare wire of copper that has the same electrical resistance. Thus, by keeping constant the total weight per meter of the cable, usage of Aluminium advantageously results in about half the Ohmic losses as compared to Copper. Special aluminium alloys, such as for example AA-8000 series, exhibit similar to copper creep and elongation properties, meeting the requirements of ASTM B800 for electrical purposes. Thus, thermal performance can be further im proved by using Aluminium instead of Copper wires respectively conductors.

According to a further preferred implementation the central wire, the power wires and/or the inner hose are arranged distant from each other and/or comprising wire spacers to arrange the central wire, the power wires and/or the inner hose distant from each other. In another preferred implementation the inner hose and the outer hose are arranged distant from each other and/or comprising hose spacers to ar range the inner hose and the outer hose distant from each other. The wire spacers and/or the hose spacers can be provided as plastic spacers and/or are preferably arranged in a regular pattern. The distance respectively size of the wire spacers and/or the hose spacers can be for example 2, 3 or 5 mm such that sufficient liquid coolant can flow in the respective hollow area.

In a further preferred implementation, the cable comprises at least a sensor wire extending in the longitudinal direction and arranged within the inner hose and/or between the inner hose and the outer hose. The first hollow area and/or the second hollow area between the electrical conductors as well as the space between the two hoses can host in particular thin wires used, for example, for sensing of various parameters such as temperature, humidity, light, acceleration, electrical resistance, etc. either in the charging connector or the liquid cooled cable as such. In a preferred implementation, the sensor wire comprises a Proximity Pilot, PP, wire for pre-inser tion signalling and/or a Control Pilot, CP, wire for post-insertion signalling, in partic ular as per SAE J1772 and/or IEC 61851 standard. Most preferably, the sensor wire or a plurality thereof is arranged between the inner hose and the outer hose. Such way safety is also improved by early detection of damages in the outermost layers by placing the Control Pilot and/or Proximity Pilot wire in said hollow second area between the inner and outer hoses.

The object is further solved by an electric vehicle supply equipment, EVSE, com prising the charging cable as described before, a cooling unit and a charging con nector, whereby

the charging cable is connected between the cooling unit and the charging connector,

the cooling unit is configured for conveying the liquid coolant from the cooling unit between the inner hose and the outer hose towards the charging connector and the charging connector is configured for returning the liquid coolant through the inner hose towards the cooling unit.

Compared to prior art solution, the proposed solution provides improved thermal and mechanical performance, and ease in manufacturing and assembly. The cool ing unit is preferably configured for conveying a coolant having a kinematic viscosity at -40°C lower than 470cSt having a maximum pressure drop in a 6 m long cable of 4 bar at a flow rate below 1 l/min. The cooling unit preferably comprises means for storing, cooling and/or conveying the liquid coolant across the entire extension of the cable. Cooling unit, cable and charging connector are preferably provided as closed cooling circuit, in particular by means of the inner hose and the outer hose.

In a preferred implementation the EVSE is configured to charge the electric vehicle with a current rating equal to or greater than 500 A DC and/or a voltage rating equal to or greater than 1000 V DC. The EVSE may comprise a transformer and/or a converter for connecting to respectively receiving electrical energy from an AC grid, which is transformed and/or converted to DC for being supplied via the charging cable to the electric vehicle connected thereto via the charging connector. The object is even further solved by a method for liquid cooling a heavy-current charging cable for charging an electric vehicle, the cable comprising

a central heavy-current wire configured for serving as ground, the central wire comprising a central conductor and extending in a longitudinal direction,

a plurality of heavy-current power wires configured for conducting positive and negative direct current, DC, each of said power wires comprising a power con ductor and a power wire insulation surrounding said power conductor, the power wires extending parallel to the central wire,

a liquid tight inner hose extending in the longitudinal direction and surround ing the central wire and the power wires thereby defining a first hollow between the central wire and the power wires along the longitudinal direction, and

a liquid tight outer hose extending in the longitudinal direction and surround ing the inner hose thereby defining a second hollow area between the inner hose and the outer hose along the longitudinal direction, the method comprising the step of:

Conveying liquid coolant through the first hollow area and the second hollow area.

Further embodiments and advantages of the method are directly and unambigu ously derived by the person skilled in the art from the cable as described before.

Brief description of drawings

These and other aspects of the invention will be apparent from and elucidated with reference to the implementations described hereinafter.

In the drawings:

Fig. 1 shows a heavy-current charging cable according to a preferred implementa tion in a sectional view, Fig. 2 shows a heavy-current charging cable according to another preferred imple mentation in a sectional view,

Fig. 3 shows a flexible metal tube of the heavy-current charging cable according to Fig. 2 in two sectional views,

Fig. 4 shows an electric vehicle supply equipment comprising the cable of Figs. 1 or 2 according to a preferred implementation in a schematic view.

Description of embodiments

Figs. 1 and 2 each show a heavy-current charging cable 1 for charging an electric vehicle according to preferred embodiments in a sectional view. The cable 1 com prises one central heavy-current wire 2 serving as ground which comprises a central conductor 3 extending in a longitudinal direction orthogonal to the figure layer and a central wire insulation 4 surrounding the central conductor 3. While not shown, the central conductor 2 can be provided non-insulated. The central conductor 2 com prises a cross section of 25 mm ² , while the central wire insulation 3 comprises thick ness of 0.5 to 2 mm.

The heavy-current charging cable 1 further comprises six heavy-current power wires 5, each configured for conducting positive and negative direct current, DC. The six heavy-current power wires 5 each extend parallel to the central wire 2 and are ar ranged around thereby surrounding the central heavy-current wire 2 such that alter nately one heavy-current power wire 5 conveys positive DC and the another, next heavy-current power wire 5 conveys negative DC. Each heavy-current power wire 5 comprises a power conductor 6 and a power wire insulation 7 surrounding said power conductor 6. Each power conductor 6 comprises a cross section of 16 mm ² , while the power wire insulation 7 comprises thickness of 0.5 to 2 mm. With such arrangement of the central wire 2 and the power wires 5 a packing factor is 0.777 for the cable 1 is achieved. The central conductor 3 and the power conductors 6 consists of copper, aluminium or a mixture thereof and/or comprise wire strands. Alternatively, the power conductors 5 conducting positive current are arranged on one side on the central heavy-current wire 2 and the power conductors 5 conducting negative current are arranged on the other side on the central heavy-current wire 2.

The cable 1 further comprise a liquid tight inner hose 8 and a liquid tight outer hose 9 made of a polymer-based material and/or comprising extruded polymer layers. Both the liquid tight inner hose 8 and the liquid tight outer hose 9 extend in the longitudinal direction, whereby the liquid tight inner hose 8 surrounds the central wire 2 and the power wires 5, thereby defining a first hollow area 10. In other words, the liquid tight inner hose 8 does not surround the central wire 2 and the power wires 5 such that said wires 2, 5 are arranged tight to each other and with the inner hose 8. Wire spacers 1 1 are arranged in regular pattern between the central wire 2, the power wires 5 and the inner hose 8 for facilitating such arrangement. In an analo gous manner the outer hose 9 surrounds the inner hose 8 thereby defining a second hollow area 12 between both hoses 8, 9. Hose spacers 13 are arranged in regular pattern between both hoses 8, 9 for facilitating such arrangement so that the hoses 8, 9 do not touch each other at any location. Inner hose 8 comprises an inner diam eter of 25 mm and an outer diameter of 29 mm, whereby the outer hose 9 comprises an inner diameter of 33 mm and an outer diameter of 40 mm.

First hollow area 10 and second hollow area 12 are each filled with a liquid coolant to flow between the central wire 2 and the power wires 5 along the longitudinal di rection within the inner hose 8 and thus around respectively in direct contact with each the central wire 2 and all power wires 5 and flow between the inner hose 8 and the outer hose 9. The liquid coolant comprises oil, a water and glycol mixture, a water and salt mixture, and /or halogenated hydrocarbon compounds. In addition to the liquid coolant, sensor wires 14 are provided in the hollow area 10 and second hollow area 12 extending in longitudinal direction for submitting, among others, con trol pilot, CP, and proximity pilot, PP, signals.

The implementation in Fig. 2 comprises in addition to the implementation of Fig. 1 a flexible metal tube 15, which is arranged between the inner hose 8 and the outer hose 9, whereby the outer hose 9 is extruded on the flexible metal tube 14. Fig. 3 shows the flexible metal tube 15 in two sectional views besides each other, on the left as semi-perspective view and on the right as sectional view.

Fig. 4 shows an electric vehicle supply equipment, EVSE, 16, which comprising the charging cable 1 and a charging connector 16. The EVSE 16 is connected via a transformer and/or a converter for receiving electrical energy from an AC grid, not shown, which is transformed and/or converted to DC for being supplied via the charging cable 1 having a length of 6 m to the electric vehicle connected thereto via the charging connector 17 to charge the electric vehicle with a current rating greater or equal than 500 A DC and a voltage rating greater or equal than 1000 V DC. The EVSE 16 comprises a cooling unit 18 having a liquid coolant reservoir, a coolant-to- air heat exchanger and a respective pump for circulating the liquid coolant from the cooling unit 18 between the inner hose 8 and the outer hose 9 towards the charging connector 17. The charging connector 17 is configured for returning the liquid cool ant through the inner hose 8 towards the cooling unit 18 such that thereby the liquid coolant circulates around the central wire 2 and all power wires 5 for cooling the respective central conductor 3 and the power conductors 6.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustra tive or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word“comprising” does not exclude other elements or steps, and the indefinite arti cle“a” or“an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope. Reference signs list

1 cable

2 central heavy-current wire

3 central conductor

4 central wire insulation

5 heavy-current power wire

6 power conductor

7 power wire insulation

8 inner hose

9 outer hose

10 first hollow area

11 wire spacer

12 second hollow area

13 hose spacer

14 sensor wire

15 metal tube

16 electric vehicle supply equipment

17 charging connector

18 cooling unit