Brake resistor for electrically driven vehicle

Abstract

The invention relates to a brake resistor (8) of an electrically driven vehicle (2) having at least one traction battery (4) and at least one electric machine (6). During braking, the at least one electric machine generates electrical energy during operation of the generator, which electrical energy is fed into the braking resistor (8) when the traction battery (4) cannot be charged. The brake resistor (8) implemented in a modular structure (34) comprises an elastically deformable housing part (18, 20) that compensates for thermal expansion of the resistive element (22).

Description

Technical Field

[0001] The present invention relates to a brake resistor for an electrically driven vehicle having at least one traction battery and at least one electric motor. During braking, the at least one electric motor generates electrical energy in generator mode, which is fed into the brake resistor when the traction battery cannot be charged. Furthermore, the present invention relates to the use of the brake resistor for converting braking electrical energy into heat and dissipating it, as well as an electrically driven vehicle having such a brake resistor. Background Art

[0002] Electric vehicles use electric braking. Here, the electric motor operates as a generator, charging the traction battery. However, when the traction battery is cold or fully charged, the charging current is limited. In this case, friction brakes must be used to decelerate the vehicle, which is energy-inefficient.

[0003] The motor power of many electric drive vehicles can generally replace the friction brake at the drive axle. Due to the above reasons, friction brakes are still additionally required.

[0004] Braking resistors can provide a solution. If the traction battery cannot be charged, the energy generated during braking is diverted to the braking resistor. The braking resistor converts the braking energy generated in a generator-like manner into heat. This heat is then dissipated.

[0005] These components are used in industrial applications. These are typically large, stationary applications with a high thermal mass as a buffer. Heat is dissipated to the surrounding air, sometimes via forced ventilation. The housings of these components are usually stationary and designed to ensure good heat dissipation. Due to their high mass, the thermal expansion of the resistors used here is relatively low.

[0006] In mobile applications, brake resistors are often fully encapsulated. The generated heat is dissipated into the cooling water circuit. Due to the good cooling capabilities, the resistors do not heat up too high. Therefore, thermal expansion has a minimal impact. The disadvantages of these brake resistors are, on the one hand, their high mass and, on the other hand, the large volume required for installation. Summary of the Invention

[0007] According to the present invention, a brake resistor for an electrically driven vehicle is provided. The vehicle has at least one traction battery and at least one electric motor. During braking, the at least one electric motor generates electrical energy in generator mode. This electrical energy is fed into the brake resistor when the traction battery cannot be charged. The modular brake resistor includes an electrically deformable housing component that compensates for thermal expansion of the resistor element. This advantageously allows for a lightweight and relatively small brake resistor for mobile applications. The elastic housing substantially compensates for thermally induced expansion of the components. The lightweight brake resistor has a relatively low thermal mass and a small volume, and due to its dynamic properties, is capable of operation at high temperatures.

[0008] In an advantageous embodiment of the braking resistor proposed according to the invention, the housing of the braking resistor comprises a fixed housing part, a housing part that is movable relative to the fixed housing part, and an elastically deformable housing part that represents the preload element. To reduce weight, the housing is reduced to its essential components.

[0009] In an advantageous embodiment of the braking resistor proposed according to the invention, the linear resistor element extends between the fixed housing and the movable housing part. This offers the advantage that, in addition to heat absorption, it also enables electrical interconnection according to the required electrical wiring diagram.

[0010] In the braking resistor according to the present invention, the linear resistor elements are arranged at a distance from one another, viewed in the vertical direction. This ensures that heat can be dissipated by an airflow, such as the wind from an electric vehicle, and prevents short circuits due to the spacing between the tensioned linear resistor elements.

[0011] In the brake resistor according to the invention, the wire-shaped resistor elements are prestressed by an elastically deformable housing component, which represents the prestressing element. The inherent prestressing of the wire-shaped resistor elements ensures that the spacing between the individual wire-shaped resistor elements is maintained in all operating states of the brake resistor, and that no electrical short circuits occur.

[0012] In an advantageous embodiment of the braking resistor according to the invention, the movable housing part is displaced horizontally relative to the fixed housing part along the base part. This allows for continuous compensation of thermally induced elongations of the linear resistor element. This in turn contributes to a simple and largely maintenance-free design of the braking resistor according to the invention.

[0013] In an advantageous embodiment, in the cold state of the braking resistor, the wire-shaped resistance element has a first length between the housing parts, which first length depends on a first prestressing state of the housing part representing the prestressing element.

[0014] The braking resistor proposed according to the invention is designed such that its wire-shaped resistance element exhibits a second length in the hot state, which is longer than the first length by an extension ΔL, the extension being dependent on a second prestressing state of the housing part representing the prestressing element. This ensures that, in the hot state, the wire-shaped resistance element remains tensioned due to the second prestressing state of the housing part representing the prestressing element, and that the extension of the wire-shaped resistance element is dependent on the thermal load, which in turn is dependent on the energy dissipated by the electric machine in its generator mode.

[0015] Furthermore, the braking resistor proposed according to the invention is characterized in that the housing part representing the preload element is designed as a bent sheet metal part. This embodiment variant of the braking resistor proposed according to the invention is a simple, efficient and economical embodiment option.

[0016] In the braking resistor proposed according to the invention, the thermally induced expansion of the linear resistor element is substantially permanently compensated by the housing part representing the preload element. The braking resistor proposed according to the invention therefore functions substantially maintenance-free and without the need for further components.

[0017] Furthermore, the present invention relates to the use of a braking resistor for converting electrical braking energy into heat energy and dissipating it from the braking resistor.

[0018] The invention further relates to an electrically driven vehicle having a braking resistor according to the invention and having at least one traction battery and at least one electric machine, which generates electrical energy in generator mode during braking, which energy can be fed into the braking resistor when the traction battery cannot be charged.

[0019] Advantages of the Invention The solution proposed according to the invention is characterized in that the braking resistor is of very simple construction and, ideally for mobile applications, has an extremely low weight and requires a relatively small installation space.

[0020] Compared to previously manufactured braking resistors, the braking resistor for mobile applications and its housing proposed according to the present invention have a relatively low thermal mass and low weight. This is achieved by utilizing a high application temperature while maintaining a low braking resistor weight. The braking resistor is passive, meaning it is cooled by the travel airflow. Because the thermal expansion of the linear resistor elements is compensated by the elastic housing or elastic housing parts, the individual linear resistor elements can be positioned at a small distance from one another. The essentially elastic housing of the braking resistor proposed according to the present invention enables a significantly smaller volume compared to previously known variants. If the linear resistor elements heat up due to the applied braking power during generator operation of the electric machine, they expand due to their higher temperature. The housing parts that are movable relative to one another and serve as prestressing elements are more cost-effective to construct than, for example, bent sheet metal parts, which apply prestress to the linear resistor elements. Since the plate-shaped housing parts are arranged so as to be movable relative to the fixed housing parts, the linear resistor elements become stressed due to the applied braking power when they heat up.

[0021] The braking resistor proposed in accordance with the present invention reacts quickly, so that the linear resistor elements are always tensioned and the individual linear resistor elements do not contact each other, thus effectively avoiding electrical short circuits.

[0022] The elastically designed housing or elastically deformable housing part and the compensation of thermal expansion function properly and continuously at all temperatures and also for different lengths of the wire-shaped resistance elements. When the wire-shaped resistance elements cool, they shorten, which causes the movable and fixed plates to be tensioned again, and the housing parts (e.g., designed as sheet metal) that prestress these plates once again exhibit a stronger prestress because they bend more strongly.

[0023] In addition to being able to compensate for the elongation of a linear resistor element, the solution proposed according to the invention can also compensate for the thermal expansion of other components. Elastic housings or elastic housing parts are suitable wherever clamping or prestressing of components is important.

[0024] The housing or housing parts of the braking resistor proposed according to the invention can be easily adjusted by varying the width of the sheet metal and are designed in particular in a modular and primarily lightweight manner, so that simple scaling (sizing) is possible.

[0025] In addition to compensating for thermally induced expansion, other expansion effects can also be compensated. For example, a component prone to creep can be permanently stressed, thereby preventing creep as long as the prestressing force can be maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention are explained in more detail with the aid of the drawings and the following description.

[0027] Figure 1 shows a schematic diagram of an electric drive vehicle and its components, Figure 2 shows a schematic diagram of a brake resistor in a cold state according to the present invention, and Figure 3 FIG. 4 is a schematic diagram showing a braking resistor according to the present invention in a hot state. DETAILED DESCRIPTION

[0028] In the following description of the embodiments of the present invention, identical or similar elements are denoted by the same reference numerals, wherein a repeated description of these elements is omitted in individual cases. The figures merely schematically illustrate the subject matter of the present invention.

[0029] Figure 1 An electrically driven vehicle and some components of its electric drive train are shown schematically.

[0030] The electric vehicle 2 comprises a front axle 3 and a rear axle 5. Figure 1 In the top view shown in FIG, the traction battery 4 is housed in the bottom of the electric vehicle 2. The traction battery 4 supplies electrical energy to the electric motor 6. The power electronics 7 are provided for controlling the electric motor 6. Figure 1 As shown in FIG, the electrically driven vehicle 2 further comprises a braking resistor 8 which is subjected to the driving wind of the electrically driven vehicle 2 when the electrically driven vehicle is traveling, for example.

[0031] During braking, the electric machine 6 can generate electrical energy in generator mode, which is fed into the traction battery 4. If the traction battery 4 cannot be charged due to its state of charge or its temperature, the electrical energy generated by the electric machine 6 in generator mode is fed into the braking resistor 8.

[0032] Figure 2 The brake resistor 8 and its main components are shown in a cold state 44 .

[0033] From the basis Figure 2 As can be seen from the diagram, the brake resistor 8 is composed of a plurality of housing parts 9. The housing part 9 of the brake resistor 8 comprises a base element 10 extending essentially in the horizontal direction. A fixed housing part 12 is accommodated on the base element, as well as a housing part 14 which is movable in the horizontal direction 16 relative to the fixed housing part. In addition, according to Figure 2 The housing part 9 of the brake resistor 8 comprises a first preload element 18 and a second preload element 20 arranged in parallel with the first preload element, and the first preload element and the second preload element also belong to the housing part 9 of the brake resistor 8. Figure 2In the cold state 44 shown in FIG, the housing parts 18 and 20 representing the prestressing element assume the first prestressing state 40. The housing parts 18, 20 representing the prestressing element are preferably made of sheet metal components. They can be elastically deformed and assume their first prestressing state 40 in the cold state 44, as shown in FIG. Figure 2 As shown in .

[0034] A plurality of linear resistor elements 22 extend between a fixed housing part 12, which is designed, for example, in the form of a plate, and a housing part 14, which is also designed in the form of a plate and is movable relative to the fixed housing part 12. These resistor elements are acted upon with braking energy, for example, by a braking energy feed 30 connected to the fixed housing part 12. This braking energy is applied in accordance with Figure 1 4 , ie at low external temperatures to which the electric vehicle 2 may be subjected.

[0035] If excess braking energy is generated during generator operation of the electric motor 6 of the electrically driven vehicle 2, which cannot be introduced into the traction battery 4, this braking energy is introduced into the braking resistor 8 via the feed-in 30. This heats up a plurality of linear resistor elements 22 extending between the fixed housing part 12 and the movable housing part 14. The individual linear resistor elements 22 are arranged at a distance 24 from each other in the vertical direction. Due to the housing parts 18 and 20, which are arranged between the fixed housing part 12 and the movable housing part 14 and serve as prestressing elements, the linear resistor elements 22 are tensioned in a first prestressing state 40 and do not touch each other. The prestressing is thus maintained and the individual linear resistor elements 22 do not touch each other. As soon as the braking energy is fed in at the feed-in 30, the plurality of linear resistor elements 22 heat up, which causes them to expand, i.e., to stretch. In the cold state 44, as in Figure 2 As shown in FIG, the linear resistor element 22 has a first length 26 thereof.

[0036] Figure 3 The brake resistor 8 proposed according to the invention is shown in a hot state.

[0037] From the braking resistor 8 proposed by the present invention Figure 2 Starting from the cold state 44 shown in FIG, when the resistance elements 22 extending parallel to one another in the form of lines are heated, they expand beyond the first length 26, as shown in FIG. Figure 2 As shown in .

[0038] During thermally induced expansion of the wire-shaped resistor elements 22, they assume a second length 28. Figure 2In the cold state 44, the second length 28 is longer than the first length 26 by an extension ΔL48. Simultaneously with the extension ΔL48, the housing components serving as preload elements 18, 20 assume a second length 28 that is longer than the first length 26 by an extension ΔL48. Depending on the braking energy applied to the brake resistor 8, the braking energy is converted into heat, which is transported away along the path of the heat dissipation 38 via the air flow 36 and the wind of the electric vehicle 2. Figure 3 The transition of the brake resistor 8 from the cold state 44 to the hot state 46 is accompanied by a change from the first preloaded state 40 (as shown in FIG. Figure 2 44 in the cold state) transitions to the second preloaded state 42 (as shown in FIG. Figure 3 (The thermal state 46 of the brake resistor 8 is present). During the expansion ΔL48 of the linear resistor element 22, the movable housing part 14 of the brake resistor 8 is continuously displaced on the substantially horizontally extending base element 10, while the fixed housing part 12 maintains its position on the base element 10. The expansion ΔL48 of the linear resistor element 22 occurs continuously in the horizontal direction 16 due to heat dissipation 38. Because the prestressing force applied by the housing parts 18, 20, which serve as prestressing elements, acts uniformly on the movable housing part 14, the vertically extending spacing 24 between the individual linear resistor elements 22 remains substantially constant. The airflow 36 through the free space between the individual linear resistor elements 22 ensures heat dissipation 38.

[0039] Figure 3 The position of the movable housing part 14 is shown in FIG. Figure 3 The initial position 50 , shown by the dashed line, transitions into a horizontally displaced position 52 in order to compensate for the thermally induced elongation ΔL 48 of the linear resistor element 22 .

[0040] Figure 2 and 3 The brake resistor 8 shown in the figure in different states, namely in the cold state 44 and in the hot state 46, reacts quickly so that when the braking energy is fed in 30, the linear resistor elements 22 are always tensioned and do not come into contact with each other. This reliably prevents short circuits. The elastic housing part 9 and the compensation of thermal expansion when the electrical energy is fed in 30 are continuously effective at all temperatures and therefore even when the linear resistor elements 22 are designed with different lengths. When cooling, i.e. when the brake resistor 8 is stretched from the braking resistor 8 according to the braking resistor 8, the braking resistor 8 is continuously stretched. Figure 3 The thermal state 46 transitions to Figure 2 In the cold state 44, the linear resistor element 22 shortens accordingly and pulls the movable housing part 14 against the fixed housing part 12 on the base element 10 again. Figure 2 and 3The prestressed state 40 or 42 shows that the housing parts 18, 20, which are preferably constructed as sheet metal components and serve as prestressed elements, are bent more in the first prestressed state 40 than in the Figure 3 The second preload state 42 shown in FIG is even stronger.

[0041] In addition to the linear resistor element 22, thermal expansion of other components can also be compensated. The elastic housing part 9 of the housing of the brake resistor 8 is suitable wherever prestressing or clamping of components is important. The elastic housing part 9 of the housing of the brake resistor 8 can be easily adjusted by varying the width of the sheet metal component, is modular in design, and is thus designed in a simple, scalable manner.

[0042] In addition to thermal expansion, other expansion effects can also be compensated. Components prone to creep are an example here. These components can be permanently maintained at a prestressing level that prevents creep, such as in Figure 2 and 3 As shown in .

[0043] The invention is not limited to the embodiments described herein and the aspects emphasized therein. Rather, within the scope of the claims, numerous modifications are possible which are within the purview of a person skilled in the art.

Claims

1. A braking resistor (8) for an electrically driven vehicle (2), the electrically driven vehicle having at least one traction battery (4) and at least one electric motor (6), wherein the at least one electric motor generates electrical energy in generator mode during braking, the electrical energy being fed into the braking resistor (8) when the traction battery (4) cannot be charged, characterized in that A braking resistor (8) embodied in a modular structure (34) comprises elastically deformable housing parts (18, 20) which compensate for thermal expansion of the resistor element (22).

2. The brake resistor (8) according to claim 1, characterized in that The housing of the brake resistor (8) comprises a fixed housing part (12), a movable housing part (14) movable relative to the fixed housing part, and elastically deformable housing parts (18, 20) representing preload elements.

3. The braking resistor (8) according to claim 2, characterized in that The linear resistor element (22) extends between the fixed housing part (12) and the movable housing part (14).

4. The braking resistor (8) according to claim 1 or 3, characterized in that The linear resistor elements (22) are arranged at a distance (24) from one another, viewed in the vertical direction.

5. Braking resistor (8) according to claims 1 to 4, characterized in that The linear resistor element (22) is prestressed by elastically deformable housing parts (18, 20) representing prestressing elements.

6. Braking resistor (8) according to claims 2 to 5, characterized in that The movable housing part (14) is movable relative to the fixed housing part (12) along the base part (10) in a horizontal direction (16).

7. Braking resistor (8) according to claims 1 to 6, characterized in that In a cold state (44), the linear resistor element (22) between the housing parts (12, 14) has a first length (26), which depends on a first prestressing state (40) of the housing parts (18, 20) representing the prestressing element.

8. Braking resistor (8) according to claims 1 to 7, characterized in that In the hot state (46), the linear resistor element (22) between the housing parts (12, 14) has a second length (28), namely the first length (26) plus an elongation ΔL (48), which depends on the second prestressing state (42) of the housing parts (18, 20) representing the prestressing element.

9. Braking resistor (8) according to claims 1 to 8, characterized in that The housing parts (18, 20) representing the prestressing elements are designed as bent sheet metal.

10. Braking resistor (8) according to claims 1 to 9, characterized in that The elongation ΔL (48) of the linear resistor element (22) is continuously compensated by the housing part (18, 20) representing the prestressing element.

11. Use of the braking resistor (8) according to any one of claims 1 to 10 for converting braking electrical energy into heat and dissipating it.

12. An electrically driven vehicle (2) having a braking resistor (8) according to any one of claims 1 to 10, and having at least one traction battery (4) and at least one electric machine (6), which generates electrical energy in generator mode during braking, which electrical energy can be fed into the braking resistor (8) when the traction battery cannot be charged.

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