JP5231910B2 - Vehicle power supply - Google Patents

Description

  The present invention relates to a vehicle power supply device provided in a vehicle such as an automobile, and more particularly to a device in which a plurality of capacitors are connected by a bus bar and safety at the time of breakage due to a collision is improved.

  In an automobile with an internal combustion engine such as a gasoline engine, the engine is automatically stopped when the vehicle is stopped and the engine is automatically restarted when the vehicle is started in order to reduce the amount of carbon dioxide generated by suppressing fuel consumption when the vehicle is stopped. It is known to provide an idle stop system (ISS). In the case of a vehicle equipped with such an idle stop system, since it is necessary to frequently drive a starter motor that starts an engine, an electric double layer capacitor (EDLC) is provided to assist a battery such as a lead storage battery. It has been proposed to connect the power supply device in parallel with the battery.

Such a power supply device can be considered to have a structure in which, for example, a pair of units each having an EDLC are accommodated in an integrated case, and conduction between each unit and between the unit and the battery is secured by a bus bar. The bus bar is a band plate-like member or rod-like member made of a conductor such as a metal constituting a part of the electric circuit.
As a power supply device having a plurality of power storage means, for example, in Patent Document 1, in a power supply module in which a plurality of power supply cells are housed in a case, the power supply cells are connected by a bus bar and are connected to each bus bar. It is described that a holding portion for holding and covering the conductive wire is formed to prevent breakage of the conductive wire due to vibration.
Patent Document 2 describes a power supply device having a plurality of batteries with different voltages, in which a high voltage battery and a low voltage battery are arranged adjacent to each other and connected via a bus bar.
JP 2006-40819 A JP 2007-253660 A

When a power supply device that is mounted on a vehicle and is always connected in parallel with a battery, for example, when collapsing due to a collision or the like, when an intermediate bus bar that connects each unit and a battery bus bar that connects the unit and the battery positive electrode come into contact with each other, While the positive electrode and the negative electrode of the positive unit are short-circuited, the negative unit is overcharged by the current from the battery. If such overcharge continues, there is a concern that smoke and fire may be generated from the unit, and some measures are required.
The subject of this invention is providing the power supply device for vehicles which improved the safety | security at the time of damage by collision etc.

The present invention solves the above-described problems by the following means.
The invention according to claim 1 is a vehicular power supply device connected in parallel to a battery that supplies electric power to a vehicle electrical component, wherein the first power storage means having a capacitor, the second power storage means, A battery bus bar that conducts between the positive electrode of the battery and the positive electrode of the first power storage means or between the negative electrode of the battery and the negative electrode of the second power storage means; and the negative electrode of the first power storage means An electrical connection between the positive electrode of the second power storage means and at least a part of the intermediate bus bar disposed adjacent to the battery bus bar, the adjacent portion of the intermediate bus bar with the battery bus bar is the A power supply device for a vehicle, wherein the power supply device is arranged to be shifted with respect to the battery bus bar when viewed from the input direction of a load caused by a collision.

According to a second aspect of the present invention, in the vehicle power supply device according to the first aspect, the portion of the intermediate bus bar adjacent to the battery bus bar is shifted in the vertical direction with respect to the battery bus bar. It is.
The invention according to claim 3 is characterized in that the intermediate bus bar is provided with a fragile portion that is more easily broken by the load than other parts at the intermediate portion thereof. Device.

The invention according to claim 4 is a vehicle power supply device connected in parallel to a battery for supplying electric power to electrical components of the vehicle, the first power storage means having a capacitor, the second power storage means, A battery bus bar that conducts between the positive electrode of the battery and the positive electrode of the first power storage means or between the negative electrode of the battery and the negative electrode of the second power storage means; and the negative electrode of the first power storage means Conducting between the positive electrode of the second power storage means and at least a part thereof is provided with an intermediate bus bar arranged adjacent to the battery bus bar, and the intermediate bus bar has another part due to a load caused by a collision at the intermediate part. A vehicular power supply device having a fragile portion that is more easily broken than a portion.
According to a fifth aspect of the present invention, in the vehicle power supply device according to the third or fourth aspect, the fragile portion includes a groove portion formed by recessing the bus bar.
According to a sixth aspect of the present invention, in the vehicle power supply device according to the third or fourth aspect, the fragile portion is a stitch having a plurality of small holes formed in a row. is there.
The invention according to claim 7 is characterized in that the intermediate bus bar is formed by joining at least a pair of bus bar members by spot welding having a joining strength that is broken by the load. It is a vehicle power supply device of description.
The invention according to claim 8 is a case for housing the first power storage means, the second power storage means, the battery bus bar, and the intermediate bus bar, and formed in the case. The vehicle power supply device according to any one of claims 1 to 7, further comprising a break portion that breaks an intermediate portion of the intermediate bus bar.

  The invention according to claim 9 is a vehicle power supply device connected in parallel to a battery for supplying electric power to electrical components of the vehicle, wherein the first power storage means having a capacitor, the second power storage means, A battery bus bar that conducts between the positive electrode of the battery and the positive electrode of the first power storage means or between the negative electrode of the battery and the negative electrode of the second power storage means; and the negative electrode of the first power storage means An intermediate bus bar that is electrically connected to the positive electrode of the second power storage means and at least a part of which is disposed adjacent to the battery bus bar, the first power storage means, the second power storage means, and the battery A vehicle comprising: a bus bar; a case that accommodates the intermediate bus bar; and a break portion that is formed in the case and breaks an intermediate portion of the intermediate bus bar using a load caused by a collision. A power supply unit.

According to the present invention, the following effects can be obtained.
(1) The intermediate bus bar adjacent to the battery bus bar is arranged so as to be shifted with respect to the battery bus bar when viewed from the input direction of the load due to the collision, so that the intermediate bus bar and the battery are destroyed when the device is collapsed due to a collision or the like. There is no contact with the bus bar, and a short circuit inside the apparatus can be prevented.
(2) Since the intermediate bus bar is broken at the intermediate portion of the intermediate bus bar so that the intermediate bus bar is more easily broken by the load caused by the collision, the intermediate bus bar breaks at the time of the collision. Can be prevented.
(3) Since the intermediate bus bar is ruptured at the time of collision by having a break portion that is formed in the case and breaks the intermediate portion of the intermediate bus bar using the load caused by the collision, overcharge from the battery to the power storage means occurs. Can be prevented.

  The present invention has a problem of providing a vehicle power supply device with improved safety at the time of breakage due to a collision or the like, in which a battery bus bar and an intermediate bus bar are arranged apart from each other in the vertical direction and the short circuit is prevented at the time of a collision. This was solved by breaking the intermediate bus bar and electrically disconnecting each power storage means.

A vehicle power supply device according to a first embodiment to which the present invention is applied will be described below.
The vehicle provided with the vehicle power supply device of the first embodiment is, for example, an automobile such as a passenger car. This vehicle includes an idle stop system (ISS) that automatically stops the engine when the vehicle stops and automatically starts the engine when the vehicle restarts.

FIG. 1 is a schematic diagram showing a system configuration of an electrical system of a vehicle.
The vehicle electrical system 1 includes a battery 10, an alternator 20, a starter 30, a vehicle load 40, a navigation / audio device 50, a sub power supply unit 60, a capacitor unit 100, and the like.

The battery 10 is a secondary battery that supplies power to the electrical system 1 of the vehicle. The battery 10 is, for example, a lead storage battery having a rated voltage of 12V. The positive terminal of the battery 10 is connected to each electrical component via a harness, and the negative terminal is grounded (grounded).
The alternator 20 is a power generation device driven by an engine (not shown). The positive electrode of the alternator 20 is connected to the positive terminal of the battery 10 and the positive electrodes of various electrical components via a harness, and the negative electrode is grounded.
The starter 30 includes a DC motor that starts the engine, a relay that controls on / off of power supplied from the battery 10 to the DC motor, and the like.
The vehicle load 40 includes, for example, various ECUs, lights, and other electrical components.
The navigation / audio device 50 includes a navigation device, an audio device, an LCD, an amplifier, a speaker, and the like as an output unit thereof.
The sub power supply unit 60 assists the power supply to the navigation / audio device 50. The sub power supply unit 60 is connected in parallel with the navigation audio apparatus 50 and includes a capacitor and a relay for storing electric power.

Capacitor unit 100 is connected in parallel with battery 10 and accumulates electric power during normal vehicle operation, and cooperates with battery 10 when using starter 30 to supply electric power to starter 30 to reduce the burden on battery 10. This is a vehicle power supply device.
FIG. 2 is a schematic diagram illustrating the configuration of the capacitor unit 100.
FIG. 3 is a partial cross-sectional perspective view of the capacitor unit 100.
As shown in FIG. 2, the capacitor unit 100 includes a first unit 110, a second unit 120, a plus terminal 130, a minus terminal 140, a battery plus bus bar 150, a cell plus bus bar 160, a relay 170, a battery minus bus bar 180, and an intermediate bus bar. 190, a case 200, and the like.

  The first unit 110 and the second unit 120 are power storage means in which three cells of electric double layer capacitors (EDLC) are connected in series and packed. The first unit 110 and the second unit 120 are connected in series by connecting the negative electrode of the first unit 110 and the positive electrode of the second unit 120 via the intermediate bus bar 190. The first unit 110 and the second unit 120 are arranged side by side substantially along the width direction of the capacitor unit 100.

The plus terminal 130 and the minus terminal 140 are input / output portions of the capacitor unit 100, and are connected to the plus terminal and the minus terminal of the battery 10, respectively.
The plus terminal 130 and the minus terminal 140 are provided so as to protrude from the upper surface of the capacitor unit 100 and are arranged in the width direction of the capacitor unit 100.

The battery plus bus bar 150 is a bus bar connected to the plus terminal 130.
The cell plus bus bar 160 is a bus bar connected to the positive electrode of the first unit 110.
The relay 170 is provided between the battery plus bus bar 150 and the cell plus bus bar 160, and electrically connects and disconnects the capacitor unit 100 and the battery 10 by switching between conduction and interruption between them.

The battery minus bus bar 180 is a bus bar that is connected to the negative electrode of the second unit 120 and the minus terminal 140 and conducts between them.
The intermediate bus bar 190 is a bus bar that is connected to the negative electrode of the first unit 110 and the positive electrode of the second unit 120 and conducts between them. Attached to the intermediate bus bar 190 is a negative electrode tab T of the first unit 110.
The case 200 is a box-shaped container in which, for example, a resin material is injection-molded, and accommodates each component of the capacitor unit 100 described above.

FIG. 4 is a perspective view showing the arrangement of peripheral components of the capacitor unit 100. FIG.
Capacitor unit 100 is arranged along the rear surface of battery 10 (the vehicle rear side surface).
The battery 10 and the capacitor unit 100 are disposed, for example, at the left front end of an engine room provided at the front of the vehicle body. The battery 10 and the capacitor unit 100 are mounted on the upper part of the front side frame 310 and are fixed by a common battery holder 320. A headlamp unit 330 is provided in front of the battery 10. A fuse box 340 is provided behind the capacitor unit 100, and a strut tower 350 is arranged behind the fuse box 340. Further, a front fender 360 is disposed on the outer side of the battery 10 and the capacitor unit 100 in the vehicle width direction.
In such an arrangement, when the vehicle has a frontal collision, for example, the capacitor unit 100 may be sandwiched between the battery 10 and the fuse box 340 and receive a load in the front-rear direction and may be crushed.

FIG. 5 is a schematic diagram showing the positional relationship between the battery plus bus bar 150 and the intermediate bus bar 190 as seen from the direction of action of the load due to the collision with the capacitor unit 100 (front-rear direction).
The battery plus bus bar 150 and the intermediate bus bar 190 are formed so as to extend substantially along the width direction, respectively, and a part of the battery plus bus bar 150 and the intermediate bus bar 190 are arranged adjacent to each other with the positions in the width direction of the capacitor unit 100 overlapping. In this adjacent location, the intermediate bus bar 190 is disposed on the front side (battery 10 side) of the battery plus bus bar 150. Further, in this adjacent portion, the upper end portion 191 of the intermediate bus bar 190 is arranged with a gap G so as to be spaced apart in the vertical direction so as to be lower than the lower end portion 151 of the battery plus bus bar 150. . This gap G is set to about 3 to 5 mm, for example.
As a result, in this adjacent portion, the battery plus bus bar 150 and the intermediate bus bar 190 are arranged so as not to overlap each other when viewed from the acting direction (front-rear direction) of the load caused by the collision.

Further, as will be described below, the intermediate bus bar 190 is provided with a fragile portion that is broken by a load caused by a collision at the intermediate portion.
FIG. 6 is a schematic diagram illustrating the configuration of the weakened portion of the intermediate bus bar 190. 6A is a view from above (a view taken along the line bb in FIG. 6B), and FIG. 6B is a view from the front (a in FIG. 6A). -A section arrow view) (same in FIG. 7 described later).
The intermediate bus bar 190 is divided into two parts in the longitudinal direction. That is, the intermediate bus bar 190 is formed by joining the first member 192 and the second member 193 by spot welding using, for example, laser, ultrasonic waves or the like. This joint location is a fragile portion having a low breaking strength against a load caused by a collision with respect to other portions.

According to the first embodiment described above, the following effects can be obtained.
(1) The upper end portion 191 of the intermediate bus bar 190 adjacent to the battery plus bus bar 150 is disposed below the lower end portion 151 of the battery plus bus bar 150 and is intermediate when viewed from the input direction of the load due to the collision. By arranging the bus bar 190 and the battery plus bus bar 150 so as not to overlap with each other, the intermediate bus bar 190 and the battery plus bus bar 150 do not come into contact with each other when the capacitor unit 100 is crushed due to a collision or the like. A short circuit can be prevented.
(2) Since a weakened portion that is more easily broken than other parts by a load due to a collision is provided in an intermediate portion of the intermediate bus bar 190, the intermediate bus bar 190 is broken at the time of the collision. Overcharge can be prevented from occurring.

Next, a vehicle power supply device according to a second embodiment to which the present invention is applied will be described. In each of the embodiments described below, portions that are substantially the same as those of the previous embodiment are denoted by the same reference numerals, description thereof is omitted, and differences are mainly described.
In the vehicle power supply device of the second embodiment, the weak portion is formed by forming the intermediate bus bar 190 integrally and forming the groove portion 194.
FIG. 7 is a schematic diagram showing a weakened portion of the intermediate bus bar 190.
The groove part 194 has a substantially V-shaped cross section formed by cutting out and recessing the rear surface (surface on the side opposite to the battery 10) of the intermediate bus bar 190. The groove 194 extends along the height direction of the intermediate bus bar 190.
Also in the second embodiment described above, the same effects as those of the first embodiment described above can be obtained.

Next, a third embodiment of the vehicle power supply device to which the present invention is applied will be described.
In the power supply device for a vehicle according to the third embodiment, the weak portion is formed by forming the intermediate bus bar 190 integrally and forming the stitch 195.
FIG. 8 is a schematic diagram showing a weakened portion of the intermediate bus bar 190.
The stitch 195 is formed by arranging a plurality of small holes formed through the intermediate bus bar 190 along the height direction of the intermediate bus bar 190.
Also in the third embodiment described above, the same effect as in the first embodiment described above can be obtained.

Next, a fourth embodiment of the vehicle power supply device to which the present invention is applied will be described. In Examples 4 to 7 described below, the case 200 is provided with a fracture portion described below instead of the weakened portion of the intermediate bus bar 190 of Examples 1 to 3.
The break portion is formed in the case 200 and breaks the intermediate portion of the intermediate bus bar 190 using a load caused by a collision. In addition, although such a fracture | rupture part may be formed integrally with case 200, you may comprise by another component.
FIG. 9 is a schematic diagram showing the configuration of the fracture portion, and shows a state seen from above.
The fracture portion includes a pair of pressing portions 201 and 202 that sandwich the intermediate bus bar 190 in the thickness direction (front-rear direction). The pressing part 201 contacts the front surface of the intermediate bus bar 190, and the pressing part 202 contacts the rear surface of the intermediate bus bar 190. The pressing part 201 and the pressing part 202 are arranged offset in the lateral direction, and the edge inside the vehicle width direction of the pressing part 201 and the edge outside the vehicle width direction of the pressing part 202 are substantially the same position in the lateral direction. It is arranged to become.
When a load due to a collision is applied, the pressing portions 201 and 202 press in the direction in which the intermediate bus bar 190 is sandwiched, and at this time, shear stress concentrated on the intermediate bus bar 190 is generated at a location where the edges of the pressing portions 201 and 202 are adjacent. The intermediate bus bar 190 is broken.
Also in the fourth embodiment described above, the same effects as those of the first embodiment described above can be obtained.

Next, a fifth embodiment of the vehicle power supply device to which the present invention is applied will be described.
FIG. 10 is a schematic diagram showing the configuration of the fracture portion, and shows a state seen from above.
The fracture portion has a protrusion 203 that is pressed against the front surface of the intermediate portion of the intermediate bus bar 190 by a load caused by a collision. The projection 203 has a substantially triangular shape when viewed from above, and its tip is formed as a sharp edge. When a load due to a collision is applied, the tip portion of the protrusion 203 presses the intermediate bus bar 190 to generate concentrated shear stress, and the intermediate portion of the intermediate bus bar 190 is broken.
Also in the fifth embodiment described above, the same effects as those of the first embodiment described above can be obtained.

Next, a sixth embodiment of the vehicle power supply device to which the present invention is applied will be described.
FIG. 11 is a schematic diagram illustrating the configuration of the fracture portion, and is a diagram illustrating a state viewed from above.
The fracture portion has a clamping portion 204 that clamps only one side in the lateral direction from a predetermined planned fracture location of the intermediate bus bar 190. When a load due to the collision acts, stress concentration occurs in the intermediate bus bar 190 at the end of the sandwiching portion 204, and the intermediate bus bar 190 is broken. Such a rupture portion can be formed by forming a groove portion as the holding portion 204 when the case 200 is molded, and press-fitting the intermediate bus bar 190 into the groove portion.
Also in the sixth embodiment described above, the same effect as in the first embodiment described above can be obtained.

Next, a seventh embodiment of the vehicle power supply device to which the present invention is applied will be described.
FIG. 12 is a schematic diagram illustrating the configuration of the fracture portion, and is a diagram illustrating a state viewed from the lateral direction (longitudinal direction of the intermediate bus bar 190).
The fracture portion has an inclined surface portion 205 that twists the intermediate bus bar 190 by applying an oblique force to the intermediate portion of the intermediate bus bar 190 and cuts the intermediate bus bar 190. The inclined surface portion 205 is provided on the rear side of the intermediate bus bar 190 adjacent to a predetermined scheduled breakage point of the intermediate bus bar 190. The inclined surface portion 205 is in contact with the lower end portion of the intermediate bus bar 190 and is inclined so as to gradually increase toward the vehicle rear side. When a load due to a collision is applied, the region of the intermediate bus bar 190 that comes into contact with the inclined surface portion 205 is twisted as indicated by a broken line, and the intermediate bus bar 190 is broken so as to be cut off.
Also in the seventh embodiment described above, the same effect as in the first embodiment described above can be obtained.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) The structure and configuration of the vehicle power supply device are not limited to those of the above-described embodiments, and can be changed as appropriate. For example, the present invention can also be applied to an apparatus having three or more power storage means. In addition, the shape and arrangement of each bus bar are not particularly limited. For example, the adjacent portions of the battery bus bar and the intermediate bus bar may be separated in the horizontal direction instead of being separated in the vertical direction as in the embodiment. Good.
(2) You may use combining the intermediate bus bar which has a weak part like Examples 1 thru | or 3, and the case which has a fracture | rupture part like Examples 4 thru | or 7.

It is a figure which shows the system configuration | structure of the electrical system of the vehicle which has Example 1 of the vehicle power supply device to which this invention is applied. 3 is a schematic diagram illustrating a configuration of a capacitor unit of Example 1. FIG. 3 is a partial cross-sectional perspective view of the capacitor unit of Example 1. FIG. FIG. 3 is a perspective view showing an arrangement of peripheral components of the capacitor unit according to the first embodiment. It is a schematic diagram which shows the positional relationship of the battery plus bus bar and the intermediate | middle bus bar seen from the action direction of the load by the collision of the capacitor unit of Example 1. FIG. FIG. 3 is a schematic diagram illustrating a fragile portion of the intermediate bus bar according to the first embodiment. It is a schematic diagram which shows the weak part of the intermediate | middle bus-bar in Example 2 of the vehicle power supply device to which this invention is applied. It is a schematic diagram which shows the weak part of the intermediate | middle bus-bar in Example 3 of the vehicle power supply device to which this invention is applied. It is a schematic diagram which shows the fracture | rupture part in Example 4 of the vehicle power supply device to which this invention is applied. It is a schematic diagram which shows the fracture | rupture part in Example 5 of the vehicle power supply device to which this invention is applied. It is a schematic diagram which shows the fracture | rupture part in Example 6 of the vehicle power supply device to which this invention is applied. It is a schematic diagram which shows the fracture | rupture part in Example 7 of the power supply device for vehicles to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrical system 10 Battery 20 Alternator 30 Starter 40 Vehicle load 50 Navigation audio apparatus 60 Sub power supply unit 100 Capacitor unit 110 1st unit 120 2nd unit 130 Positive terminal 140 Negative terminal 150 Battery positive bus bar 151 Lower end part 160 Cell positive bus bar 170 Relay 180 Battery minus bus bar T Cell electrode tab 190 Intermediate bus bar 191 Upper end portion 192 First member 193 Second member 194 Groove portion 195 Stitch 200 Case 201, 202 Pressing portion 203 Protrusion 204 Holding portion 205 Inclined surface portion 310 Front side frame 320 Battery holder 330 Headlamp unit 340 Fuse box 350 Strut tower 360 Front fender

Claims (9)

A power supply device for a vehicle connected in parallel to a battery that supplies power to electrical components of the vehicle,
A first power storage means having a capacitor and a second power storage means;
A battery bus bar for conducting between the positive electrode of the battery and the positive electrode of the first power storage means, or between the negative electrode of the battery and the negative electrode of the second power storage means;
An electrical connection between the negative electrode of the first power storage means and the positive electrode of the second power storage means, and at least a part of the intermediate bus bar disposed adjacent to the battery bus bar,
The vehicular power supply device, wherein a portion of the intermediate bus bar adjacent to the battery bus bar is shifted from the battery bus bar when viewed from the input direction of a load caused by a collision. 2. The vehicle power supply device according to claim 1, wherein a portion of the intermediate bus bar adjacent to the battery bus bar is arranged so as to be vertically shifted with respect to the battery bus bar. The vehicular power supply device according to claim 1, wherein the intermediate bus bar is provided with a weakened portion that is more easily broken by the load than other portions in the intermediate portion. A power supply device for a vehicle connected in parallel to a battery that supplies power to electrical components of the vehicle,
A first power storage means having a capacitor and a second power storage means;
A battery bus bar for conducting between the positive electrode of the battery and the positive electrode of the first power storage means, or between the negative electrode of the battery and the negative electrode of the second power storage means;
An electrical connection between the negative electrode of the first power storage means and the positive electrode of the second power storage means, and at least a part of the intermediate bus bar disposed adjacent to the battery bus bar,
The vehicular power supply apparatus according to claim 1, wherein the intermediate bus bar is provided with a fragile portion that is more easily broken than other portions by a load caused by a collision. The vehicular power supply apparatus according to claim 3 or 4, wherein the fragile portion includes a groove formed by recessing the bus bar. The vehicular power supply device according to claim 3 or 4, wherein the fragile portion is a stitch having a plurality of small holes formed in a row. 5. The vehicle power supply device according to claim 3, wherein the intermediate bus bar is formed by joining at least a pair of bus bar members by spot welding having a joining strength that is broken by the load. A case for housing the first power storage means, the second power storage means, the battery bus bar, and the intermediate bus bar;
The vehicular power supply device according to any one of claims 1 to 7, further comprising a breakage portion formed in the case and for breaking an intermediate portion of the intermediate bus bar using a load caused by a collision. . A power supply device for a vehicle connected in parallel to a battery that supplies power to electrical components of the vehicle,
A first power storage means having a capacitor and a second power storage means;
A battery bus bar for conducting between the positive electrode of the battery and the positive electrode of the first power storage means, or between the negative electrode of the battery and the negative electrode of the second power storage means;
An intermediate bus bar that conducts between the negative electrode of the first power storage means and the positive electrode of the second power storage means, and at least a portion thereof is disposed adjacent to the battery bus bar;
A case for housing the first power storage means, the second power storage means, the battery bus bar, and the intermediate bus bar;
A power supply device for a vehicle, comprising: a break portion formed in the case and for breaking an intermediate portion of the intermediate bus bar using a load caused by a collision.

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