Electronic unit cooling

Abstract

A power unit for a vehicle may control the flow of power between batteries and a motor of a vehicle and the unit may include capacitors 205, buss bars 207 and switching components 206 etc. that produc

Description

This invention relates to a power unit for a vehicle. The Electric Drive Unit (EDU) of an electric vehicle comprises three main parts: the power electronics, the gearbox and the electric motor. The power electronics primarily process and control the flow of electrical energy in the vehicle, enabling power to be delivered to the road surface. They control the speed of the motor, and the torque it produces. They may also convert and distribute electrical power to other vehicle systems. The power electronics may be contained within a power unit. The power unit typically includes some form of casing to surround and protect the power electronics during operation of the vehicle. The power electronics will often get hot during use, which heats up the inside of the power unit. Some power units incorporate a cold plate to cool the power unit. This separate component is usually bolted to the casing, increasing the overall bulk of the unit. Therefore, there is a need for an improved power unit for electric vehicles. According to a first embodiment of the invention, there is provided a power unit for a vehicle, comprising a casing configured to contain one or more electrical components; and a channel formed integrally with the casing that is configured to carry a coolant for reducing a temperature inside the casing. The power unit may comprise a thermal path configured to conduct heat between the one or more electrical components and coolant in the channel. The thermal path may comprise a thermal transfer material that physically connects one or more of the electrical components to the casing and / or to a wall of the channel. The casing may form a wall of the channel. A chassis of the vehicle may form a wall of the channel. The channel may comprise a cooling plate configured to, when there is coolant in the channel, conduct heat from inside the casing to the coolant, thereby cooling the inside of the casing via conduction and / or convection. The cooling plate may form a wall of the casing. The inside of the casing may form an enclosure for containing the electrical components, and the cooling plate forms a wall of that enclosure. The cooling plate may be capable of, when there is coolant in the channel and the vehicle is in operation, keeping the temperature inside the casing lower than a relatively high temperature outside of the casing. The channel may comprise an inlet and an outlet, and is configured such that coolant can flow between the inlet and the outlet. The casing may be configured to form an airtight seal around the electrical components. The power unit may comprise one or more bus bars, the bus bars having a reduced volume as a consequence of the cooling provided to the inside of the casing by coolant flowing through the channel. The channel may be welded to the casing. The channel may be welded to the casing via friction stir welding. The casing may be formed from a metal, a metal alloy or a polymer. The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings: Figure 1 shows an example of a power unit; Figure 2 shows an example of another power unit; and Figure 3 shows an example of a further power unit. An example of a power unit is shown at 101 in Figure 1. The power unit is designed for use in a vehicle. It comprises a casing 102. The casing is configured to hold one or more electrical components, shown at 103, 104. The casing is designed to keep the electrical components physically separate from the environment external to the power unit, which may be at a relatively high temperature. The casing comprises a channel 105. The channel is configured to carry a coolant for cooling the inside of the casing. The channel is formed integrally with the casing. They are not readily separable. The connection between them is such that they essentially form one unit, as they cannot be easily dismantled without damaging one (or both) of the casing or the channel. The channel and the casing are thus attached to each other without requiring additional attachment means such as screws or bolts. The connection between them may additionally be airtight. This airtight connection is innate and does not require additional seals. This reduces the number of components, enabling simpler, cheaper production. It also significantly reduces the height of the power unit by reducing the need for screws or bolts. Another example of a power unit is shown in Figure 2. The power unit comprises a casing 201. In this example the casing includes a closure plate 202 that can be fastened across the side walls of the casing to form an isolated interior enclosure 203 that is physically separate from the higher temperature external environment 204. The plate may be fastened to the walls of the casing via any suitable attachment means, such as screws, bolts etc. An advantage of having the closure plate readily separable from the walls of the casing is that the electrical components within the casing are then accessible, e.g. in the case of malfunction or repair. The casing preferably forms an airtight seal around the electrical components so that a lower temperature can be maintained in the enclosure than outside of the casing. A seal (not shown) may be provided between the closure plate and the walls of the casing to ensure that there is no airflow between the enclosure and the external environment. The power unit 201 comprises a number of electrical components, including a capacitor bank 205 and SMT (Surface Mount Technology) components 206. The power unit also comprises a bus bar 207. The electrical components generate a thermal load. They also benefit from operating in a lower ambient temperature, which can increase their reliability. The power unit 201 comprises a channel 208 for carrying coolant. In this example the channel comprises an inlet 209 and an outlet 210 that enable coolant to flow through the channel. This enables continuous replenishment of the coolant adjacent to the enclosure, enabling it to retain its temperature differential with the enclosure as warmed coolant is replaced by the flow of new coolant into the channel. The flow of coolant through the channel cools plate 213, which in turn cools the air in enclosure 203. The electrical components are cooled by convection into the cooler air. This is represented in Figure 2 by the arrows exiting capacitor bank 205 and busbar 207 into the air of the enclosure. Figure 2 represents a cross section through the power unit 201. The channel 208 preferably extends the full length (as shown) and width of the power unit, but there could be applications in which the channel extends over only part of the width of the power unit and / or applications in which it is useful or expedient to have multiple individual channels across the width of the power unit. The individual channels may join together, at a point inside or outside the walls of the casing, and may be fed from a single inlet and / or feed a single outlet. The power unit 201 also comprises one or more thermal paths. These are physical pathways through the power unit that are capable of cooling the electrical components via conduction. These pathways may be formed of parts of the casing and / or the channel, together with other solid components comprised within the power unit. These thermal paths provide a conduction route from one or more of the electrical components to the cooling plate 213. This is represented in Figure 2 by the arrows exiting through the power module 214 and through the base of SMT components 206. Preferably the cooling of plate 213 via the flow of coolant through the channel keeps the temperature of enclosure 203 below that of the relatively high temperature outside of the casing. The channel 208 is formed integrally with the casing 201. In this example a wall of the casing 213 also forms a wall of the channel. The channel may be bonded to the at 211,212. The lower wall 214 of the casing may be provided by the chassis of the vehicle jSpecifically designing the vehicle so that chassis provides a cooling plate for the power unit enables a much smaller product. This is beneficial in applications such as electric vehicles, where space and weight are at a premium. In some implementations it might be desirable to configure the chassis to accommodate the power unit. For example, in the same way that the power unit is configured to hold particular power electronics, the chassis may have to be configured to accommodate a particular shape of power unit. Equally the chassis may have to be adapted to accommodate particular requirements regarding the provision of cooling to the enclosure, such as the location and number of cooling ports, connector locations etc. Figure 3 shows a further example of a power unit. In this example extra thermal paths have been added to the power unit by adding solid material with good thermal conductivity to join one or more of the electrical components to an existing thermal path, e.g. a thermal path provided by the casing and / or the cooling plate. The solid material is suitably a thermal transfer material such as gap filler. In Figure 3, this additional filler material is shown at 301 joining capacitor bank 304 to casing 305, at 302 joining busbar 306 to cooling plate 307 and at 303 joining SMT components 308 to cooling plate 307. The electrical busbars 207, 306 are conductors for collecting electric power and locally distributing it. Their material composition and cross-sectional size determines the maximum current they can safely carry. Carrying a current beyond this maximum may cause the busbars to overheat, threatening their structural integrity. The cooling channel described herein provides a means of cooling the busbars by convection into the cooler air of the enclosure and / or conduction into the casing / cooling plate. The cooling effect may be beneficially employed to optimise the bus bars for the overall application. For example, for a given current requirement and without the cooling channel, the bus bars may need to have a first cross-sectional area. For that same current requirement, but with the cooling effect of the cooling channel, the bus bars may be able to have a second, smaller cross-sectional area. This may save weight and / or space, both of which are at a premium in vehicular applications. The cooling effect may also make it possible to substitute one material of the bus bars for another, lighter weight material, while still achieving the same maximum current for a given size of busbar. The join between the casing and the channel may be achieved via any means capable of forming a connection that is strong enough to meet vehicle safety standards. This includes a range of fusion techniques, such as standard welding, resistance welding, solid state welding etc, and any glues capable of forming a strong enough bond. One specific technique solid state technique that may be employed is Friction Stir Welding. In this welding technique the components to be joined together are not melted. Instead, heat is generated between a rotating tool and the components, leading to a softened region. The tool intermixes material from the two components as it is moved along the joint line. This technique produces a very high weld strength, avoids distortion in the substrates and requires minimal to no further processing. Conventionally, it is not a standard technique for high volume manufacturing, possibly due to process control for monitoring weld quality. In this application, however, it has been found that minimal modifications are required to accommodate Friction Stir Welding other than providing sufficient weld surfaces between the two substates to provide a seam weld around the profile of the casing, which is achievable given the size and shape of a typical power unit. The technique used to join the casing and the channel is dictated by vehicle safety standards but also the respective materials that the casing and channel are made from. These components may be made from any materials having the requisite properties of strength, durability and weight. This encompasses, for example, metals, metal alloys and polymers. The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. 17 09 24

Claims

1. A power unit for a vehicle, comprising:a casing configured to contain one or more electrical components; and a channel formed integrally with the casing that is configured to carry a coolant for reducing a temperature inside the casing,wherein a chassis of the vehicle forms a wall of the channel.

2. A power unit as claimed in claim 1, wherein the power unit comprises a thermal path configured to conduct heat between the one or more electrical components and coolant in the channel.

3. A power unit as claimed in claim 2, wherein the thermal path comprises a thermal transfer material that physically connects one or more of the electrical components to the casing and / or to a wall of the channel.

4. A power unit as claimed in any preceding claim, wherein the casing forms a wall of the channel.

5. A power unit as claimed in any preceding claim, wherein the channel comprises a cooling plate configured to, when there is coolant in the channel, conduct heat from inside the casing to the coolant, thereby cooling the inside of the casing via conduction and / or convection.

6. A power unit as claimed in claim 6, wherein the cooling plate forms a wall of the casing.

7. A power unit as claimed in claim 5 or 6, wherein the inside of the casing forms an enclosure for containing the electrical components, and the cooling plate forms a wall of that enclosure.

8. A power unit as claimed in any preceding claim, wherein the cooling plate is capable of, when there is coolant in the channel and the vehicle is inoperation, keeping the temperature inside the casing lower than a relatively high temperature outside of the casing.

9. A power unit as claimed in any preceding claim, wherein the channel comprises an inlet and an outlet, and is configured such that coolant can flow between the inlet and the outlet.

10. A power unit as claimed in any preceding claim, wherein the casing is configured to form an airtight seal around the electrical components.

11. A power unit as claimed in any preceding claim, wherein the power unit comprises one or more bus bars, the bus bars having a reduced volume as a consequence of the cooling provided to the inside of the casing by coolant flowing through the channel.

12. A power unit as claimed in any preceding claim, wherein the channel is welded to the casing.

13. A power unit as claimed in any preceding claim, wherein the channel is welded to the casing via friction stir welding.

14. A power unit as claimed in any preceding claim, wherein the casing is formed from a metal, a metal alloy or a polymer.

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