BATTERY PACK

Abstract

Battery pack which includes the following: a battery module (1) comprising a plurality of cells (11 to 15) and a first housing (50) in which the cells are arranged; a connection module (2) comprising busbars (70 to 76) connected to electrode terminals (10g, 10h) of the cells, and a second housing (60) to which the busbars are secured; Screws (90) that fasten the first housing and the second housing together to position the busbars close to the electrode terminals; and a multitude of cell stacks (10i, 10j), each of which has two or more of the cells stacked in a vertical direction, wherein the cell stacks are arranged adjacent to each other in a lateral direction perpendicular to the vertical direction, wherein the cells of one of the cell stacks have a first cell, the cells of another of the cell stacks have a second cell, and one of the busbars connecting the electrode terminals of the first and second cell has a punched section (72d, 74d) passing through the thickness of the busbar in a longitudinal direction which is a direction in which the first case and the second case are adjacent to each other, and wherein sections (50c, 60c) of the first housing and the second housing which are aligned with the punched section, and sections (50d, 50e, 60d, 60e) of the first housing and the second housing which are adjacent to the cell stacks in the lateral direction have screw holes (61 to 65) in which the screws are tightened.

Description

BACKGROUND 1. Technical field

[0001] The present invention generally relates to a battery pack equipped with a plurality of electrical cells. 2. State of the art

[0002] Japanese patent JP 6015174 B2 discloses an assembled battery module equipped with a plurality of cells, a battery case in which the cells are stacked, and an insulating cover secured to the cell case.

[0003] The insulating cover has a plurality of openings formed therein, aligned with the positive and negative terminals of the cells. The insulating cover is attached to the battery case with the cell terminals inserted into the openings. A plurality of bus bars are secured to the insulating cover to block the openings. Recently, there has been a trend toward increasing cell size with an increase in battery pack output. Such an increase in cell size will result in an increase in cell volume, resulting in undesirable cell swelling. Accordingly, new mechanisms are required to minimize cell swelling.

[0004] The battery module, as taught in the preceding publication, has protrusions at the ends of the battery casing and the insulating cover. The connection of the battery casing and the insulating cover is achieved by holding the protrusions together using clips.

[0005] It is difficult to completely suppress cell swelling using clips. Cell swelling will result in instability of the joint between the battery casing and the insulating cover, which can lead to reduced reliability in the electrical connection between the cells and the busbars.

[0006] Screws can be used alternately to firmly connect the battery case and the insulating cover. In particular, the screws hold the cells tightly to prevent cell swelling.

[0007] The assembled battery module disclosed in the preceding publication has a stack of a plurality of thin cuboid-shaped cells. Specifically, the cells are stacked with their main surfaces facing each other. To press the cells together, screws may be arranged on the cell stack in a vertical direction. However, this results in an undesirable increase in the overall height of the battery pack.

[0008] The screws can alternatively be arranged on the sides of the cell stack. The battery module in the previous publication is designed to have two stacks of battery cells arranged adjacent to each other in the lateral direction of the battery module. The busbars are located between the cell stacks. The screws must therefore be arranged on the sides of an assembly of the laterally aligned cell stacks. The distance between the screws that laterally hold the cell stack assembly increases with an increase in the number of cell stacks, which may lead to insufficient suppression of cell swelling. This results in instability of the electrical connection between the cells and the busbars. SUMMARY OF THE INVENTION

[0009] It is an object of the invention to provide a battery pack having a reduced height and designed to ensure the stability of an electrical connection between the electrical cells and the busbars.

[0010] According to one aspect of the invention, there is provided a battery pack comprising: (a) a battery module having a plurality of cells and a first casing in which the cells are arranged; (b) a connection module having bus bars connected to electrode terminals of the cells and a second casing to which the bus bars are secured; (c) screws that tighten or fix the first casing and the second casing together to place the bus bars close to the electrode terminals; and (d) a plurality of cell stacks, each of which has two or more of the cells stacked in a height direction.

[0011] The cell stacks are arranged adjacent to each other in a lateral direction perpendicular to the height direction.

[0012] The cells of one of the cell stacks include a first cell. The cells of another of the cell stacks include a second cell. One of the busbars connecting the electrode terminals of the first and second cells has a punched portion penetrating through the thickness of the busbar in a longitudinal direction, which is a direction in which the first housing and the second housing are arranged adjacent to each other.

[0013] Portions of the first housing and the second housing aligned with the punched portion and portions of the first housing and the second housing located adjacent to the cell stacks in the lateral direction have screw holes formed therein in which the screws are secured.

[0014] The busbar connecting the electrode terminals of the first and second cells, as described above, has a punched section. One of the screw holes is located between the cell stacks. These arrangements allow the interval between the screws arranged in the lateral direction to be minimized despite an increase in the number of cell stacks, thereby minimizing cell swelling and ensuring the stability of the electrical connection between the cells and the busbars.

[0015] The screws can be located within a range between the top and bottom ends of the cell stacks in the vertical direction. This minimizes the size of the battery pack in the vertical direction.

[0016] In this disclosure, symbols in parentheses represent a correspondence relationship between terms in claims and terms described in embodiments discussed later, but are not limited merely to parts referred to in the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be more fully understood from the detailed description given hereinafter and from the accompanying drawings of the preferred embodiments of the invention, which, however, are not to be used to limit the invention to the specific embodiments, but are for purposes of illustration and understanding only.

[0018] In the drawings: Fig. 1 is a block diagram illustrating an electrical power system according to an embodiment of the invention; Fig. 2 is a perspective view illustrating a power supply module according to an embodiment of the invention; Fig. 3 is an exploded perspective view showing the power supply module in Fig. 2 represents; Fig. 4 is a front view of a first housing of the power supply module in Fig. 3; Fig. 5 is a front view of a second housing of the power supply module in Fig. 3; Fig. 6 is a front view of a power supply module; Fig. 7 is a front view of a power supply module; Fig. Figure 8 is a sectional view taken along the line VIII-VIII in Fig. 7 is taken; Fig. Figure 9 is a sectional view taken along the line IX-IX in Fig. 7 is taken; Fig. 10 is a perspective view illustrating a bus bar connecting cell stacks and attached to the power supply module in Fig. 6 is secured; Fig. 11 is a front view showing a modification of a power supply module; Fig. 12 is a front view showing a modification of a power supply module; Fig. 13(a), Fig. 13(b) and Fig. 13(c) are views illustrating modifications of a connection module; and Fig. 14(a) and Fig. 14(b) are views illustrating modifications of busbars connecting between cell stacks. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Embodiments are described below with reference to the drawings. FIRST EMBODIMENT

[0020] The battery pack 100 and the electric power system 200 including the battery pack 100 according to the first embodiment will be described below with reference to Fig. 1 to 10 described. POWER SYSTEM

[0021] The power system 200 is mounted in a vehicle, such as an automobile. The power system 200 includes a plurality of in-vehicle devices mounted in the vehicle and the battery pack 100. One of the in-vehicle devices is the lead-acid battery 110. The battery pack 100 is equipped with the lithium battery 10. The power system 200 forms a dual power system consisting of the lead-acid battery 110 and the lithium battery 10.

[0022] One of the in-vehicle devices is the engine 140, such as an internal combustion engine. The vehicle in which the power system 200 is installed is equipped with an idle stop mode (also called an automatic engine stop and restart mode) that stops the engine 140 when a predetermined engine stop condition is met and restarts the engine 140 when a predetermined engine restart condition is met. The power system 200 is, as shown in Fig. 1, the vehicle is further equipped with the starter motor 120, the electric rotating machine 130, the electrical loads 150, the main ECU (host ECU) 160, and the MGECU 170, in addition to the lead-acid battery 110 and the engine 140. The lead-acid battery 110, the starter motor 120, and the electrical loads 150 are electrically connected to the battery pack 100 through the first wiring harness 201. The electric rotating machine 130 is electrically connected to the battery pack 100 through the second wiring harness 202.

[0023] The main ECU 160 and the MGECU 170 are electrically connected to the lead-acid battery 110 and the battery pack 100 by electrical conductors not shown. Similarly, other types of ECUs (Electronic Control Units) are electrically connected to the lead-acid battery 110 and the battery pack 100 by electrical conductors not shown.

[0024] The power system 200, as described above, is provided as a dual-power system having two electrical power supplies: the lead-acid battery 110 and the battery pack 100 (i.e., the lithium battery 10). The electrical loads 150 include the general load 151 and the protective load 152. The general load 151 is, for example, an in-vehicle device, such as a seat heater, a blower fan, an electric compressor, a room light, or a headlight, to which constant electrical power does not necessarily need to be supplied. The protective load 152 is, for example, an in-vehicle device, such as an electric shift position sensor, an electric power steering system (EPS), an anti-lock braking system (ABS), a door locking system, a navigation system, or an audio system, to which constant electrical power must always be supplied.The protective load 152 generally comprises an in-vehicle device that is more relevant to driving the vehicle than the general load 151.

[0025] Each of the main ECU 160 and the MGECU 170 is one of the ECUs installed in the vehicle. The ECUs are electrically connected to each other using a bus bar 161 to develop an in-vehicle network. The ECUs operate in a coordinated manner to control fuel combustion in the engine 140 and a power generation mode or motor mode of the electric rotary machine 130. The main ECU 160 operates to control operation of the battery pack 100. The MGECU 170 operates to control operation of the electric rotary machine 130.

[0026] Although not shown, the power system 200 also includes sensors used to measure a physical quantity, such as a voltage or an electric current, and to obtain vehicle information regarding an accelerator pedal position or a throttle valve opening position. Outputs from such sensors are transmitted to the ECUs. BATTERY PACK

[0027] The battery pack 100 is described below. The battery pack 100 is, as shown in Fig. 1, is equipped with the lithium battery 10, the circuit board 20 and the sensor unit 40. The battery pack 100, as shown in Fig. 2, comprises the first housing 50 and the second housing 60.

[0028] The circuit board 20 includes the wiring substrate 21, the switches 22, and the BMU (Battery Management Unit) 23 mounted on the wiring substrate 21 to function as an electrical circuit to which the lithium battery 10 and the sensor unit 40 are electrically connected. The electrical circuit is electrically connected to external connection terminals, as indicated by double circles in Fig. 1. The connections of the electrical circuit to the external connection terminals are achieved using conductors manufactured by machining metallic conductors, such as copper plates.

[0029] The external connection terminals include the first external connection terminal 100a, the second external connection terminal 100b, the third external connection terminal 100c, the fourth external connection terminal 100d, and the fifth external connection terminal 100e. The first external connection terminal 100a, the fourth external connection terminal 100d, and the fifth external connection terminal 100e are electrically connected to the lead-acid battery 110, the starter motor 120, and the electrical loads 150 through the first wiring harness 201. The second external connection terminal 100b is electrically connected to the electric rotary machine 130 through the second wiring harness 202. The third external connection terminal 100c is attached to a body of the vehicle using a screw.The screw inserted into the third external connection terminal 100c serves as a fixture to connect the battery pack 100 and the body of the vehicle, thereby grounding the battery pack 100.

[0030] The first case 50, as clearly shown in Fig. 3, has the lithium battery 10 disposed therein to form the battery module 1. The second housing 60 has bus bars 70 and power connection wires 80 secured thereto, which will be described in detail later, thereby forming the connection module 2. The battery module 1 and the connection module 2 are coupled together to form the power supply module 3, which will be described in detail later.

[0031] The battery pack 100 is equipped with a housing (not shown). The housing is made of cast aluminum and has the lithium battery 10, the circuit board 20, the sensor unit 40, the first housing 50, and the second housing 60 arranged therein.

[0032] The casing also serves as a heat sink to dissipate heat generated by the lithium battery 10 and the circuit board 20. The casing is located below a seat in the vehicle. The above-described third external connection terminal 100c is implemented through a hole formed in the casing. The casing has an opening closed by a resin cover or a metallic cover, thereby protecting the electrical circuit and the lithium battery 10 from water. The casing (i.e., the battery pack 100) can alternatively be arranged in a space between a rear seat and a luggage compartment, or between a driver's seat and a passenger seat in the vehicle. ELECTRICAL CIRCUIT IN THE BATTERY PACK

[0033] The electrical circuit of the battery pack 100 is described below. The circuit board 20, as already described, includes the wiring substrate 21, the switches 22, and the BMU 23.

[0034] The circuit substrate 21 is a printed circuit board made of an insulating substrate on which conductive circuit patterns are formed. The circuit patterns include the first lead 24, the second lead 25, the third lead 26, and the fourth lead 27, which are formed at least in or on the insulating substrate.

[0035] The wiring substrate 21 has terminals arranged thereon that are electrically connected to the external connection terminals. Specifically, the terminals include the first internal terminal 28a, the second internal terminal 28b, the third internal terminal 28c, the fourth internal terminal 28d, and the fifth internal terminal 28e. These internal terminals are electrically connected to the external terminals by the conductors described above.

[0036] Specifically, the first internal terminal 28a is electrically connected to the first external connection terminal 100a. The second internal terminal 28b is electrically connected to the second external connection terminal 100b. The third internal terminal 28c is electrically connected to the third external connection terminal 100c. The fourth internal terminal 28d is electrically connected to the fourth external connection terminal 100d. The fifth internal terminal 28e is electrically connected to the fifth external connection terminal 100e.

[0037] The first internal terminal 28a and the second internal terminal 28b are electrically connected to each other by the first lead line 24. The first lead line 24 and the third internal terminal 28c are electrically connected to each other by the second lead line 25. The first lead line 24 and the second lead line 25 are electrically connected to each other by the third lead line 26. The fourth internal terminal 28d and the first lead line 24 are electrically connected to each other by the fourth lead line 27. The first lead line 24 and the third lead line 26 are electrically connected to each other by the fourth lead line 27. The third lead line 26 and the fifth internal terminal 28e are electrically connected to each other by the fourth lead line 27.

[0038] The switches or switching elements 22 include the first switch 29, the second switch 30, the third switch 31, the fourth switch 32, the fifth switch 33 and the sixth switch 34. Each of the first switch 29 to the fourth switch 32 comprises semiconductor switches, i.e. MOSFETs (metal oxide semiconductor field effect transistors), more precisely N-channel MOSFETs.

[0039] Each of the first switch 29 to the fourth switch 32 has at least one on-off switch made of two MOSFETs connected in series. Specifically, the two MOSFETs have sources connected to each other and gates electrically isolated from each other. The MOSFETs have a parasitic diode. The parasitic diodes of the MOSFETs have anodes connected to each other.

[0040] The first switch 29 and the second switch 30 each have a plurality of on-off switches having sources electrically connected to each other.

[0041] The third switch 31 has a single on / off switch. The fourth switch 32 has a plurality of on / off switches connected in series.

[0042] Fig. 1 represents the first switch 29 and the second switch 30, each of which is equipped with two on-off switches connected in parallel. Fig. Figure 1 also shows the fourth switch 32, which is equipped with two on-off switches connected in series. The number of on-off switches is not limited to the one shown in Fig. 1, but can be determined depending on the amount or magnitude of an electric current flowing through the on-off switches.

[0043] The first switch 29 is arranged in the first supply line 24. The electrical connection between the first internal terminal 28a and the second internal terminal 28b is therefore controlled by opening or closing the first switch 29. In other words, an electrical connection between the lead-acid battery 110 and the electric rotary machine 130 is controlled by opening or closing the first switch 29.

[0044] The second switch 30 is installed in the second supply line 25. The electrical connection between the third internal terminal 28c and the second internal terminal 28b is therefore controlled by opening or closing the second switch 30. In other words, an electrical connection between the lithium battery 10 and the electric rotary machine 130 is controlled by opening or closing the second switch 30.

[0045] The third switch 31 and the fourth switch 32 are installed in the third supply line 26. In particular, the third switch 31 is arranged between connections of the third supply line 26 to the first supply line 24 and the fourth supply line 27. The fourth switch 32 is arranged between connections of the third supply line 26 to the fourth supply line 27 and the second supply line 25.

[0046] The electrical connection between the first internal terminal 28a and the fifth internal terminal 28e is therefore controlled by opening or closing the third switch 31. In other words, an electrical connection between the lead-acid battery 110 and the protective load 152 is blocked or achieved by opening or closing the third switch 31.

[0047] The electrical connection between the third internal terminal 28c and the fifth internal terminal 28e is controlled by opening or closing the fourth switch 32. In other words, an electrical connection between the lithium battery 10 and the protective load 152 is blocked or achieved by opening or closing the fourth switch 32.

[0048] Each of the fifth switch 33 and the sixth switch 34 is implemented by a mechanical relay. Specifically, each of the fifth switch 33 and the sixth switch 34 is constructed of a normally closed electromagnetic relay and a normally closed electromagnetic relay, respectively.

[0049] The fifth switch 33 and the sixth switch 34 are installed in the fourth supply line 27. Specifically, the fifth switch 33 is arranged between connections of the fourth supply line 27 to the fourth internal terminal 28d and the first supply line 24. The sixth switch 34 is arranged between connections of the fourth supply line 27 to the first supply line 24 and the third supply line 26.

[0050] The electrical connection between the fourth internal terminal 28d and the second internal terminal 28b is therefore controlled by opening or closing the fifth switch 33. In other words, an electrical connection between the lead-acid battery 110 and the electric rotary machine 130 is blocked or achieved by opening or closing the fifth switch 33.

[0051] The electrical connection between the fifth internal terminal 28e and the second internal terminal 28b is controlled by opening or closing the sixth switch 34. In other words, an electrical connection between the protective load 152 and the rotary electric machine 130 is blocked or achieved by opening or closing the sixth switch 34.

[0052] As described above, the sensor unit 40 is electrically connected to the electrical circuit fabricated on the circuit board 20. The sensor unit 40 is equipped with sensor devices that operate to measure conditions of the lithium battery 10 and the switches 22. The sensor devices of the sensor unit 40 include a temperature sensor, an electrical current sensor, and a voltage sensor.

[0053] The sensor unit 40 serves to measure the temperature, electric current, and voltage of the lithium battery 10 and outputs these in the form of status signals to the BMU 23. The sensor unit 40 also serves to measure the temperature, electric current flowing through, and voltage at the switches 22 and outputs these in the form of status signals to the BMU 23.

[0054] The sensor unit 40 as shown in Fig. 2, further includes the water damage sensor 41. The water damage sensor 41 is equipped with a capacitor made of the first counter electrode 42 and the second counter electrode 43. If there is water between the first counter electrode 42 and the second counter electrode 43, this will result in a change in permittivity (i.e., capacitance) of the capacitor. The sensor unit 40 outputs such a change in permittivity in the form of a status signal to the BMU 23. The BMU 23 monitors whether or not a change in permittivity of the water damage sensor 41 continues for a predetermined period of time to determine whether or not the battery pack 100 is immersed in water.

[0055] The BMU 23 operates to control the operations of the switches 22 in response to the status signals from the sensor unit 40 and / or control command signals from the main ECU 160. The BMU 23, as described above, serves as a battery management unit.

[0056] The BMU 23 analyzes the state signals from the sensor unit 40 to calculate the state of charge (SOC) of the lithium battery 10 and diagnose the operations of the switches 22. The BMU 23 outputs signals indicating the calculated value of the state of charge of the lithium battery 10 and the diagnosis of the switches 22 to the main ECU 160.

[0057] The main ECU 160 analyzes the outputs from the BMU 23 and vehicle information input from the ECUs to determine how to control the operations of the switches 22. The main ECU 160 outputs control command signals, including control signals for the switches 22, to the BMU 23. The BMU 23 is receptive to the control command signals from the main ECU 160 to control the operations of the switches 22.

[0058] When it is determined that the battery pack 100 is immersed in water using the state signal output from the water damage sensor 41, the BMU 23 itself decides that the control signals are to be stopped from being output to the switches 22, and then actually stops outputting the control signals to the switches 22. POWER SUPPLY MODULE

[0059] The structure of the power supply module 3 formed by coupling the battery module 1 of the battery pack 100 and the connection module 2 together will be described below. In the following discussion, three directions perpendicular to each other are referred to as a lateral direction, a longitudinal direction, and a height direction. A side where the bottom of the case is located in the height direction is also referred to as a lower side. A side where a cover that closes the opening of the case is located in the height direction is also referred to as an upper side. In this embodiment, the length direction is a direction in which the vehicle travels forward or backward. The lateral direction is a horizontal direction of the vehicle. The height direction is a vertical direction of the vehicle.

[0060] In the battery module 1 is the lithium battery 10 as shown in Fig. 3, is arranged in the first housing 50. In the connection module 2, the busbars 70 and the voltage measuring wires 80 are mechanically connected to the second housing 60. The battery module 1 and the connection module 2 are mechanically connected to each other by tightening the first housing 50 and the second housing 60 using screws. The battery module 1 and the connection module 2 are electrically connected to each other by joining the lithium battery 10 and the busbars 70 by laser welding. This forms the power supply module 3. BATTERY MODULE

[0061] The lithium battery 10 is as shown in Fig. 3, is equipped with a plurality of electrical cells connected in series. The cells are secondary cells. Specifically, the cells are lithium-ion cells that develop a voltage in an electrochemical reaction to generate a current flow through the cells. This will generate heat, so the cells typically expand.

[0062] The cells can alternatively be implemented as nickel-hydrogen secondary cells or organic radical cells. In such a case, the name of the lithium battery 10 is changed to a nickel battery or a radical battery depending on the type of secondary cells used.

[0063] Each of the cells is of a square prism shape and accordingly has six faces. Specifically, each of the cells has the first main surface 10a and the second main surface 10b, which are opposite to each other in the height direction. Each of the cells also has the first side surface 10c and the second side surface 10d, which are opposite to each other in the lateral direction. Each of the cells also has the upper end surface 10e and the lower end surface 10f, which are opposite to each other in the height direction. The first main surface 10a and the second main surface 10b are larger in area than the first side surface 10c, the second side surface 10d, the upper end surface 10e, and the lower end surface 10f. Each of the cells is of a flat shape with a thickness between the first main surface 10a and the second main surface 10b.

[0064] Each of the cells has the positive terminal 10g and the negative terminal 10h, which are formed on the upper end surface 10e as electrode terminals. The positive terminal 10g and the negative terminal 10h are arranged away from each other in the lateral direction. The positive terminal 10g is located closer to the first side surface 10c, while the negative terminal 10h is located closer to the second side surface 10d.

[0065] Each of the positive terminal 10g and the negative terminal 10h is cuboid-shaped and protrudes from the upper end surface 10e in the longitudinal direction. Each of the positive terminal 10g and the negative terminal 10h has side surfaces covered with an annular plastic member 10k having an opening facing the longitudinal direction. Each of the positive terminal 10g and the negative terminal 10h has an end surface aligned in the longitudinal direction and exposed from the plastic member 10k. The exposed end surface is laser-welded to one of the busbars 70.

[0066] The seals 10l are arranged between the positive terminal 10g and the negative terminal 10h in the upper end surface 10e. Each of the seals 10l is annular in shape with an opening aligned in the longitudinal direction. The seals 10l each have a thickness greater than that of the positive terminal 10g and the negative terminal 10h in the longitudinal direction. Each of the seals 10l is held by one of the cells and the second housing 60, as described later.

[0067] The lithium battery 10 is equipped with the first cell 11, the second cell 12, the third cell 13, the fourth cell 14 and the fifth cell 15. The first cell 11, the fourth cell 14 and the fifth cell 15 are, as clearly shown in Fig. 3, are stacked upward in the height direction to form the first cell stack 10i. The second cell 12 and the third cell 13 are stacked upward in the height direction to form the second cell stack 10j. The first cell stack 10i and the second cell stack 10j are adjacent to each other in the lateral direction.

[0068] The first case 50, as it is in Fig. 3 and Fig. 4, has the first stack storage chambers 50a for the first cell stack 10i and the second stack storage chambers 50b for the second cell stack 10j. The first stack storage chambers 50a and the second stack storage chambers 50b are arranged adjacent to each other in the lateral direction. The first stack storage chambers 50a and the second stack storage chambers 50b each have an opening facing the longitudinal direction.

[0069] The first housing 50 also has intermediate flanges 50c that interconnect the first stack storage chambers 50a and the second stack storage chambers 50b. The intermediate flanges 50c are arranged between the first stack storage chambers 50a and the second stack storage chambers 50b in the lateral direction.

[0070] The first housing 50 also includes the first flange 50d, which is disposed adjacent to the intermediate flanges 50c through the first cell stack storage chamber 50a in the lateral direction. Furthermore, the first housing 50 includes the second flange 50e, which is disposed adjacent to the intermediate flanges 50c through the second cell stack storage chamber 50b in the lateral direction. The first flange 50d is located on a portion of an outer wall of the first cell stack storage chamber or the first cell stack storage 50a facing the lateral direction, close to the opening of the first cell stack storage 50a. Similarly, the second flange 50e is located on a portion of an outer wall of the second cell stack storage 50b facing the lateral direction, close to the opening of the second cell stack storage 50b.

[0071] As apparent from the foregoing discussion, the first housing 50 is designed to have the first flange 50d, the first cell stack bearing 50a, the intermediate flanges 50c, the second cell stack bearing 50b, and the second flange 50e, which are aligned substantially in this order in the lateral direction. Fig. 4 shows the intermediate flanges 50c, the first flange 50d and the second flange 50e enclosed by dashed lines for clarity of illustration.

[0072] Each of the intermediate flanges 50c, the first flange 50d, and the second flange 50e of the first housing 50 has screw holes extending in the longitudinal direction for connection to the second housing 60 using screws. In other words, the screw holes are located on the sides of the first cell stack support 50a that are opposite to each other in the lateral direction. Similarly, the screw holes are located on the sides of the second cell stack support 50b that are opposite to each other in the lateral direction.

[0073] The first housing 50 is equipped with screw tightening portions 50f for use in mechanically connecting the power supply module 3 to the housing. The screw tightening portions 50f are formed on outer side surfaces of the first cell stack bearing 50a and the second cell stack bearing 50b.

[0074] Each of the screw tightening portions 50f has a screw through-hole formed therein extending in the height direction. Connecting the power supply module 3 to the housing is achieved by inserting screws into the screw through-holes and tightening them to the housing.

[0075] The screw tightening portions 50f on the outer side surface of the first cell stack bearing 50a are arranged adjacent to the first flange 50d in the longitudinal direction. The screw tightening portions 50f on the outer side surface of the second cell stack bearing 50b are arranged adjacent to the second flange 50e in the longitudinal direction. More specifically, the screw tightening portions 50f on the outer side surface of the first cell stack bearing 50a are located in a projection plane of the first flange 50d in the longitudinal direction. Similarly, the screw tightening portions 50f on the outer side surface of the second cell stack bearing 50b are located in a projection plane of the second flange 50e in the longitudinal direction.

[0076] The first cell stack storage 50a, as it is in Fig. 3 and Fig. 5, has three insulated chambers in which the three cells are arranged. The second cell stack storage 50b has two insulated chambers in which the two cells are arranged.

[0077] Specifically, the first cell stack warehouse 50a includes the first storage chamber 51, the fourth storage chamber 54, and the fifth storage chamber 55, which are stacked upward in the height direction. The second cell stack warehouse 50b includes the second storage chamber 52 and the third storage chamber 53, which are stacked upward in the height direction.

[0078] The first storage chamber 51 and the second storage chamber 52 are arranged adjacent to each other by the intermediate flanges 50c in the lateral direction. The third storage chamber 53 and the fourth storage chamber 54 are arranged adjacent to each other by the intermediate flanges 50c in the lateral direction. With these arrangements, a space whose volume is substantially identical to those of the first to fifth storage chambers 51 to 55 is created above the third storage chamber 53. Although not shown, such a space has at least a portion of the circuit board 20 arranged therein. The circuit board 20 is at least partially aligned with the fifth storage chamber 55 in the lateral direction.

[0079] The first to fourth storage chambers 51 to 55 have openings facing the longitudinal direction. Each of the cells is inserted into one of the first to fifth storage chambers 51 to 55. Each of the cells is inserted into one of the first to fifth storage chambers 51 to 55 until the lower end surface 10f of the cell physically touches the inner wall of one of the first to fifth storage chambers 51 to 55. When each of the cells is completely disposed within one of the first to fifth storage chambers 51 to 55, the positive terminal 10g and the negative terminal 10h are placed outside of one of the first to fifth storage chambers 51 to 55.The first main surface 10a, the second main surface 10b, the first side surface 10c and the second side surface 10d of each of the cells have projections which are close to the upper end surface 10e and are exposed outside of a corresponding one of the first to fifth storage chambers 51 to 55.

[0080] The arrangements of the cells in the respective first to fifth storage chambers 51 to 55 are described below.

[0081] The first cell 11 is arranged in the first storage chamber 51 with the positive terminal 10g located close to the second cell stack bearing 50b so that the second main surface 10b of the first cell 11 faces the fourth storage chamber 54.

[0082] The second cell 12 is arranged in the second storage chamber 52 with the negative terminal 10h located close to the first cell stack bearing 50a, so that the negative terminal 10h of the second cell 12 and the positive terminal 10g of the first cell 11 are arranged adjacent to each other across the intermediate flanges 50c. The second main surface 10b of the second cell 12 faces the third storage chamber 53.

[0083] The third cell 13 is arranged in the third storage chamber 53 with the second main surface 10b facing the second main surface 10b of the second cell 12 in the height direction, so that the negative terminal 10h of the third cell 13 and the positive terminal 10g of the second cell 12 are arranged adjacent to each other in the height direction. The positive terminal 10g of the third cell 13 is located close to the first cell stack storage 50a.

[0084] The fourth cell 14 is arranged in the fourth storage chamber 54 with the second main surface 10b facing the second main surface 10b of the first cell 11, so that the negative terminal 10h of the fourth cell 14 is adjacent to the positive terminal 10g of the third cell 13 across the intermediate flanges 50c in the lateral direction. The positive terminal 10g of the fourth cell 14 is located farther away from the second cell stack storage 50b in the lateral direction. In other words, the positive terminal 10g of the fourth cell 14 is close to the first flange 50d in the lateral direction.

[0085] The fifth cell 15 is arranged in the fifth storage chamber 55 with the first main surface 10a facing the first main surface 10a of the fourth cell 14 in the height direction, so that the negative terminal 10h of the fifth cell 15 is arranged adjacent to the positive terminal 10g of the fourth cell 14 in the height direction.

[0086] With the foregoing arrangements, in each of the first cell stack storage 50a and the second cell stack storage 50b, the positive terminals 10g and the negative terminals 10h are arranged alternately in the height direction. CONNECTION MODULE

[0087] The connection module 2 is equipped with the second housing 60, the busbars 70, and the voltage measuring wires 80. The voltage measuring wires 80 function to measure the voltage developed at the cells and are therefore one of the components of the sensor unit 40.

[0088] The second housing 60 is, as clearly shown in Fig. 3, Fig. 5 and Fig. 6, is shaped to have a length extending in the lateral direction. The second housing 60 has a center recessed away from the first housing 50 in the longitudinal direction. The second housing 60 is mechanically coupled to the first housing 50 to close the openings of the first to fifth storage chambers 51 to 55 of the first housing 50 and to cover the portions of the cells protruding from the first to fifth storage chambers 51 to 55. In this assembly of the first housing 50 and the second housing 60, the second housing 60 lies within a projection plane of the first housing 50 in the longitudinal direction.

[0089] The second housing 60 has five screw holes formed therein for coupling to the first housing 50. The screw holes extend through surfaces 60a and 60b of the second housing 60, which oppose each other across a thickness of the second housing 60. Surface 60a faces the first housing 50.

[0090] Surface 60b is further away from surface 60a. The screw holes of the second housing 60 are aligned with the screw holes formed in the intermediate flanges 50c, the first flange 50d, and the second flange 50e of the first housing 50. Specifically, the second housing 60 has the flange 60c facing the intermediate flanges 50c in the longitudinal direction, the first flange 60d facing the first flange 50d in the longitudinal direction, and the second flange 60e facing the second flange 50e in the longitudinal direction. The flange 60c, the first flange 60d, and the second flange 60e of the second housing 60 have screw holes formed therein. The flange 60c, the first flange 60d and the second flange 60e are also referred to as a counter flange, a first counter flange and a second counter flange 60e respectively. Fig. 5 and Fig. 6, the mating flange 60c, the first mating flange 60d, and the second mating flange 60e are enclosed by dashed lines. The surface 60b is also referred to as a front surface or a first surface. The surface 60a is also referred to as a rear surface or a second surface.

[0091] When the second housing 60 is attached to the first housing 50 to close the openings of the first housing 50, the five screw holes of the second housing 60 are all aligned with the screw holes of the first housing 50 in the longitudinal direction. Each of the housing tightening members 90 made of screws is tightened into the two aligned screw holes of the first housing 50 and the second housing 60, thereby mechanically coupling the first housing 50 and the second housing 60 to each other.

[0092] Fig. Figure 8 is a sectional view taken along the alternate long and short dashed line VIII-VIII in Fig. 7. The housing collar 90a is, as shown in Fig. 8, fitted into each of the screw holes of the second housing 60. Each of the housing tightening members 90 has a portion protruding from the screw hole and to which the housing nut 90b is fitted. Dashed lines in Fig. 8 represent boundaries between sections of the alternate long and short dashed line extending in the height direction and sections of the alternate long and short dashed line extending in the lateral direction in Fig. 7 extends. Fig. 7 is used only to show the alternate long and short dashed line and the alternate long and short dashed short line, and accordingly, reference numerals are omitted.

[0093] Five combinations of the aligned screw holes of the first housing 50 and the second housing 60 are hereinafter referred to as the first screw hole 61, the second screw hole 62, the third screw hole 63, the fourth screw hole 64, and the fifth screw hole 65, respectively. In some of the drawings, such reference numerals are assigned to each of the first housing 50 and the second housing 60.

[0094] Portions of the first screw hole 61 to the fifth screw hole 65 formed in the first housing 50 each have an internal thread formed therein. Portions of the first screw hole 61 to the fifth screw hole 65 formed in the second housing 60 may be designed to have no internal thread.

[0095] Each of the first screw hole 61 and the second screw hole 62 is formed in both the first flange 50d and the first counter flange 60d. The first screw hole 61 and the second screw hole 62 are adjacent to each other in the height direction. The first screw hole 61 is located adjacent to the first bearing chamber 51 in the lateral direction. The second screw hole 62 is located adjacent to the fifth bearing chamber 55 in the lateral direction.

[0096] Each of the third screw hole 63 and the fourth screw hole 64 is formed in both the second flange 50e and the second mating flange 60e. The third screw hole 63 and the fourth screw hole 64 are adjacent to each other in the height direction. The third screw hole 63 is adjacent to the second bearing chamber 52 in the lateral direction. The fourth screw hole 64 is adjacent to the third bearing chamber 53 in the lateral direction.

[0097] The fifth screw hole 65 is formed in each of the intermediate flange 50c and the counter flange 60c. The center of the fifth screw hole 65 is located between the center of the first bearing chamber 51 and the center of the fourth bearing chamber 54 in the height direction. The center of the fifth screw hole 65 is also located between the center of the second bearing chamber 52 and the center of the third bearing chamber 53 in the height direction. The fifth screw hole 65 is located between the first bearing chamber 51 and the second bearing chamber 52 in the lateral direction. The fifth screw hole 65 is also located between the third bearing chamber 53 and the fourth bearing chamber 54 in the lateral direction.

[0098] With the foregoing arrangements, the first cell stack support 50a is disposed between each of the first screw hole 61 and the second screw hole 62 and the fifth screw hole 65. The second cell stack support 50b is disposed between each of the third screw hole 63 and the fourth screw hole 64 and the fifth screw hole 65. In other words, the first cell stack 10i is disposed between each of the first screw hole 61 and the second screw hole 62 and the fifth screw hole 65. The second cell stack 10j is disposed between each of the third screw hole 63 and the fourth screw hole 64 and the fifth screw hole 65. The distance between each of the first screw hole 61 and the second screw hole 62 and the fifth screw hole 65 in the lateral direction is set equal to that between each of the third screw hole 63 and the fourth screw hole 64 and the fifth screw hole 65 in the lateral direction.

[0099] The housing tightening members 90 are tightened into the corresponding first to fifth screw holes 61 to 65. The front surface 60b of the second housing 60 has seating surfaces formed thereon, on which the housing tightening members 90 are seated. The housing tightening members 90 are tightened or tightened in the first to fifth screw holes 61 to 65 from the second housing 60 to the first housing 50 in the longitudinal direction.

[0100] Tightening the housing tightening members 90 causes the seals 10l placed on the upper end surfaces 10e of the cells 11 to 15 to be compressed in the longitudinal direction between the cells 11 to 15 and the second housing 60. This will cause the seals 10l to generate a restoring force oriented away from the seals 10l in the longitudinal direction, thereby urging the cells 11 to 15 in the longitudinal direction. Specifically, the cells 11 to 15 are firmly held between the seals 10l and the walls of the first to fifth storage chambers 51 to 55 of the first housing 50, thereby stopping the cells 11 to 15 from moving in the longitudinal direction and also minimizing the swelling of the cells 11 to 15 in the longitudinal direction. The seals 10l can be alternately omitted in order to have the cells 11 to 15 placed in direct contact with the second housing 60.

[0101] The second housing 60 has a plurality of openings formed therein for use in electrically connecting the first cell 11 to the fifth cell 15 to the busbars 70. The openings extend from the rear surface 60a to the front surface 60b of the second housing 60 in the longitudinal direction. The openings are aligned with the positive terminals 10g and the negative terminals 10h of the cells 11 to 15, which reach electrical series circuits of the cells 11 to 15 and from which power is output from the cells 11 to 15.

[0102] Specifically, the openings formed in the second housing 60 include the first opening 66a, the second openings 66b, the third openings 66c, the fourth openings 66d, the fifth openings 66e, and the sixth opening 66f. The first opening 66a is formed in the second housing 60 in alignment with the negative terminal 10h of the first cell 11 in the longitudinal direction when the first housing 50 is coupled to the second housing 60. The second openings 66b are formed in the second housing 60 in alignment with the positive terminal 10g of the first cell 11 and the negative terminal 10h of the second cell 12 in the longitudinal direction when the first housing 50 is coupled to the second housing 60.

[0103] The third openings 66c are formed in the second housing 60 in alignment with the positive terminal 10g of the second cell 12 and the negative terminal 10h of the third cell 13 in the longitudinal direction. The fourth openings 66d are formed in the second housing 60 in alignment with the positive terminal 10g of the third cell 13 and the negative terminal 10h of the fourth cell 14 in the longitudinal direction.

[0104] The fifth openings 66e are formed in the second housing 60 in alignment with the positive terminal 10g of the fourth cell 14 and the negative terminal 10h of the fifth cell 15 in the longitudinal direction. The sixth opening 66f is formed in the second housing 60 in alignment with the positive terminal 10g of the fifth cell 15 in the longitudinal direction.

[0105] The busbars 70 installed on the connection module 2 include the first busbar 71, the second busbar 72, the third busbar 73, the fourth busbar 74, the fifth busbar 75, and the sixth busbar 76. The first busbar 71 to the sixth busbar 76 are arranged on the front surface 60b of the second housing 60. Each of the first to sixth busbars 71 to 76 faces one or more of the openings 66a to 66f.

[0106] Specifically, the first bus bar 71 is mechanically connected to the front surface 60b of the second housing 60 to close the first opening 66a. The first bus bar 71 has a portion located within the first opening 66a and mechanically and electrically connected to the negative terminal 10h of the first cell 11 using laser welding techniques. The first bus bar 71 has formed therein the negative connection terminal 71a extending in the longitudinal direction, that is, a direction from the rear surface 60a to the front surface 60b. The negative connection terminal 71a functions as a negative output terminal of the battery pack 100. The first bus bar 71 is connected to the ground.

[0107] The second busbar 72 is mechanically connected to the front surface 60b of the second housing 60 to close the second opening 66b. The second busbar 72 has a length that extends in the lateral direction. The second busbar 72 has portions that lie within the second openings 66b and are mechanically and electrically connected to the positive terminal 10g of the first cell 11 and the negative terminal 10h of the second cell 12 using laser welding techniques. This creates a series connection of the first cell 11 and the second cell 12 using the second busbar 72.

[0108] The third busbar 73 is mechanically connected to the front surface 60b of the second housing 60 to close the third openings 66c. The third busbar 73 has a length that extends in the height direction. The third busbar 73 has portions located in the third openings 66c and are mechanically and electrically connected to the positive terminal 10g of the second cell 12 and the negative terminal 10h of the third cell 13 using laser welding techniques. This creates a series connection of the second cell 12 and the third cell 13 using the third busbar 73.

[0109] The fourth busbar 74 is mechanically connected to the front surface 60b of the second housing 60 to close the fourth openings 66d. The fourth busbar 74 has a length that extends in the lateral direction. The fourth busbar 74 has portions that lie within the fourth openings 66d and are mechanically and electrically connected to the positive terminal 10g of the third cell 13 and the negative terminal 10h of the fourth cell 14 using laser welding techniques. This creates a series connection of the third cell 13 and the fourth cell 14 using the fourth busbar 74.

[0110] The fifth busbar 75 is mechanically connected to the front surface 60b of the second housing 60 to close the fifth openings 66e. The fifth busbar 75 has a length that extends in the height direction. The fifth busbar 75 has portions located in the fifth openings 66e and are mechanically and electrically connected to the positive terminal 10g of the fourth cell 14 and the negative terminal 10h of the fifth cell 15 using laser welding techniques. This creates a series connection of the fourth cell 14 and the fifth cell 15 using the fifth busbar 75.

[0111] The sixth busbar 76 is mechanically connected to the front surface 60b of the second housing 60 to close the sixth opening 66f. The sixth busbar 76 has a portion located within the sixth opening 66f and is mechanically and electrically connected to the positive terminal 10g of the fifth cell 15 using laser welding techniques. The sixth busbar 76 has the positive connection terminal 76a extending in the longitudinal direction, that is, a direction from the rear surface 60a to the front surface 60b. The positive connection terminal 76a serves as a positive output terminal of the battery pack 100.

[0112] As apparent from the foregoing discussion, each of the second busbar 72 to the fifth busbar 75 serves to connect adjacent two of the cells 11 to 15 in series. Specifically, the fifth busbar 75 connects the fourth cell 14 and the fifth cell 15 of the first cell stack 10i in series. The third busbar 73 connects the second cell 12 and the third cell 13 of the second cell stack 10j in series. Therefore, each of the fifth busbar 75 and the third busbar 73 is shaped to have a length extending in the height direction, that is, a direction in which the cells 11 to 15 or the cells 12 and 13 are stacked.

[0113] The second bus bar 72 serves to connect the first cell 11 of the first cell stack 10i and the second cell 12 of the second cell stack 10j in series. The fourth bus bar 74 serves to connect the third cell 13 of the second cell stack 10j and the fourth cell 14 of the first cell stack 10i in series. Therefore, each of the second bus bar 72 and the fourth bus bar 74 is shaped to have a length extending in the lateral direction, that is, a direction in which the first cell stack 10i and the second cell stack 10j are adjacent to each other. The second bus bar 72 and the fourth bus bar 74 are larger in size than the third bus bar 73 and the fifth bus bar 75.

[0114] The second openings 66b, which are closed by the second busbar 72, are, as in Fig. 3 and Fig. 5, are arranged adjacent to each other on opposite sides of the mating flange 60c in the lateral direction. Similarly, the fourth openings 66d, which are closed by the fourth busbar 74, are arranged adjacent to each other on opposite sides of the mating flange 60c in the lateral direction.

[0115] The second busbar 72 and the fourth busbar 74 are designed to have a shape as shown in Fig. 10, which depends on the configuration or locations of the second opening 66b and the fourth opening 66d. Specifically, the second busbar 72 is provided with the first end portion 72a, the second end portion 72b, and the intermediate portion 72c. The first end portion 72a is electrically connected to the positive terminal 10g of the first cell 11. The second end portion 72b is electrically connected to the negative terminal 10h of the second cell 12. The intermediate portion 72c couples the first end portion 72a and the second end portion 72b to each other.

[0116] The second busbar 72 has bends between the first end portion 72a and the intermediate portion 72c, and between the second end portion 72b and the intermediate portion 72c. The bends (i.e., boundary regions) between the first end portion 72a and the intermediate portion 72c, and between the second end portion 72b and the intermediate portion 72c, extend parallel to each other in the longitudinal direction. This layout of the bends between the first end portion 72a and the intermediate portion 72c, and between the second end portion 72b and the intermediate portion 72c, orients the first end portion 72a and the second end portion 72b to be closer to the rear surface 60a of the second housing 60 than the intermediate portion 72c.

[0117] The fourth busbar 74 is equipped with the first end portion 74a, the second end portion 74b, and the intermediate portion 74c. The first end portion 74a is electrically connected to the positive terminal 10g of the third cell 13. The second end portion 74b is electrically connected to the negative terminal 10h of the fourth cell 14. The intermediate portion 74c couples the first end portion 74a to the second end portion 74b.

[0118] The fourth busbar 74 has bends between the first end portion 74a and the intermediate portion 74c, and between the second end portion 74b and the intermediate portion 74c. The bends (i.e., boundary regions) between the first end portion 74a and the intermediate portion 74c, and between the second end portion 74b and the intermediate portion 74c, extend parallel to each other in the longitudinal direction. This layout of the bends between the first end portion 74a and the intermediate portion 74c, and between the second end portion 74b and the intermediate portion 74c, orients the first end portion 74a and the second end portion 74b to be closer to the rear surface 60a of the second housing 60 than the intermediate portion 74c.

[0119] The intermediate portion 72c of the second busbar 72 and the intermediate portion 74c of the fourth busbar 74 are disposed on the mating flange 60c of the second housing 60. The intermediate portions 72c and 74c have punched portions that correspond to the fifth screw hole 65. Specifically, the intermediate portion 72c of the second busbar 72 has an upper end portion whose thickness is punched in a semicircular shape to form the punched portion 72d. Similarly, the intermediate portion 74c of the fourth busbar 74 has a lower end portion whose thickness is punched in a semicircular shape to form the punched portion 74d.In other words, the punched portions 72d and 74d are formed by punching the thicknesses of the second bus bar 72 and the fourth bus bar 74 in the longitudinal direction, that is, a direction in which the first housing 50 and the second housing 60 are adjacent to each other. The punched portions 72d and 74d are adjacent to each other in the height direction to form a circular opening aligned with the fifth screw hole 65 in the longitudinal direction.

[0120] The mating flange 60c of the second housing 60 has formed thereon the protrusion 67, which is contoured to correspond to the shapes of the punched portions 72d and 74d (i.e., the circular opening defined by the punched portions 72d and 74d). The protrusion 67 is of a hollow cylindrical shape. The protrusion 67 extends in the longitudinal direction, that is, a direction from the rear surface 60a to the front surface 60b. The protrusion 67 is shaped to have an outer diameter substantially equal to an inner diameter of the circular opening defined by the punched portions 72d and 74d.

[0121] The front surface 60b of the second housing 60 has the fifth screw hole 65 formed in a portion thereof surrounded by the protrusion 67. Specifically, the protrusion 67 is located around an edge of the opening of the fifth screw hole 65 in the front surface 60b (i.e., the first surface of the second housing 60). Therefore, the protrusion 67 is located between the housing tightening member 90 and the second busbar 72, and between the housing tightening member 90 and the fourth busbar 74 when the housing tightening member 90 is inserted into the fifth screw hole 65.

[0122] The formation of the punched portion 72d results in the formation of a thin portion of the intermediate portion 72c of the second busbar 72. However, the intermediate portion 72c (that is, a portion of the intermediate portion 72c equipped with the punched portion 72d) is designed to have a minimum width (that is, a minimum dimension in a direction perpendicular to its length, that is, in the height direction) that is closer to or equal to one-half of a maximum width of the intermediate portion 72c. Similarly, the intermediate portion 74c of the fourth busbar 74 is also designed to have a minimum width in the direction perpendicular to its length that is more than or equal to one-half of a maximum width of the intermediate portion 74c.The minimum width of each of the intermediate portions 72c and 74c is selected to be substantially equal to the width of the third busbar 73 and the fifth busbar 75 (that is, a dimension in a direction perpendicular to the length thereof). The thin portions of the intermediate portions 72c and 74c of the second busbar 72 and the fourth busbar 74 having the minimum width have a resistance value per unit length in the direction in which the second busbar 72 and the fourth busbar 74 extend, and therefore are substantially equal to those of the third busbar 73 and the fifth busbar 75 in the direction in which the third busbar 73 and the fifth busbar 75 extend.

[0123] The positive terminal 10g and the negative terminal 10h of each of the cells 11 to 15 are, as described above, separated from each other in the lateral direction. The positive terminal 10g and the negative terminal 10h of each of the cells 11 to 15 are connected to discrete two of the bus bars 70, respectively, so that a clearance is created between a portion of the upper end surface 10e of each of the cells 11 to 15 between the positive terminal 10g and the negative terminal 10h (also referred to as a first portion) and a portion of the second housing 60 (also referred to as a second portion) facing the first portion of the upper end surface 10e. In other words, clearances are formed between each two of the openings 66a to 66f of the second housing 60 at which the bus bars 70 are arranged.

[0124] At a portion of the second housing 60 facing the first cell stack 10i, a clearance, as described in detail later, is created between an array of the first opening 66a and the fifth openings 66e and an array of the second opening 66b, the fourth opening 66d, and the sixth opening 66f. At a portion of the second housing 60 facing the second cell stack 10j, a clearance is created between an array of the second opening 66b and the fourth opening 66d and an array of the third openings 66c. The voltage sensing wires 80 are placed at the foregoing clearances.

[0125] In the following discussion, the preceding clearance at the portion of the second housing 60 facing the first cell stack 10i will also be referred to as the first clearance 60f. The preceding clearance at the portion of the second housing 60 facing the second cell stack 10j will also be referred to as the second clearance 60g. Fig. 5 and Fig. 6, the first clearance 60f and the second clearance 60g are indicated by a line with alternating long and short dashes.

[0126] Each of the voltage measuring wires 80 is made of an insulated conductor covered with an insulating film. Each of the voltage measuring wires 80 has a terminal 80a connected to one end thereof for electrical connection to one of the busbars 70. Each of the terminals 80a has a through-hole penetrating through its thickness (i.e., in the longitudinal direction). The terminals 80a also have ends that are collected and connected to the plug 80b. The plug 80b is coupled to a plug of the circuit board 20, which is arranged above the third storage chamber 53. Fig. 3 and Fig. In Figure 7, the connector 80b is shown to be located above the first cell stack 10i, but it may alternatively be located above the second cell stack 10j, over which the circuit board 20 is mounted. The location of the connector 80b may be determined depending on the total length of the voltage sensing wires 80 connected to the connector 80b.

[0127] The voltage measuring wires 80 of the connection module 2 comprise the first voltage measuring line 81, the second voltage measuring line 82, the third voltage measuring line 83, the fourth voltage measuring line 84, the fifth voltage measuring line 85 and the sixth voltage measuring line 86.

[0128] The first voltage measuring line 81 serves to measure an electrical potential (i.e., ground potential) at the negative terminal 10h of the first cell 11. The second voltage measuring line 82 serves to measure an electrical potential between the first cell 11 and the second cell 12. The third voltage measuring line 83 serves to measure an electrical potential between the second cell 12 and the third cell 13.

[0129] The fourth voltage measuring line 84 serves to measure an electrical potential between the third cell 13 and the fourth cell 14. The fifth voltage measuring line 85 serves to measure an electrical potential between the fourth cell 14 and the fifth cell 15. The sixth voltage measuring line 86 serves to measure an electrical potential (i.e., the highest potential) at the positive terminal 10g of the fifth cell 15.

[0130] The busbars 70 are, as shown in Fig. 3 and Fig. 6, are equipped with connecting terminals 70a coupled to terminals 80a of the voltage measuring wires 80. Each of the connecting terminals 70a has a through-hole formed therein, passing through a thickness thereof in the longitudinal direction. The connecting terminals 70a are mounted on the front surface 60b in the first clearance 60f or the second clearance 60g.

[0131] The first busbar 71, as in Fig. 6, has the connection terminal 70a located in the first clearance 60f. The second busbar 72 has the connection terminal 70a extending from the second end portion 72b and located in the second clearance 60g. The third busbar 73 has the connection terminal 70a located in the second clearance 60g.

[0132] Similarly, the fourth busbar 74 has the connecting terminal 70a extending from the second end portion 74b and located in the first clearance 60f. The fifth busbar 75 has the connecting terminal 70a located in the first clearance 60f. The sixth busbar 76 has the connecting terminal 70a located in the first clearance 60f.

[0133] The connecting terminals 70a of the first busbar 71, the fourth busbar 74, the fifth busbar 75, and the sixth busbar 76 are arranged on the front surface 60b within the first clearance 60f. The connecting terminals 70a of the second busbar 72 and the third busbar 73 are arranged on the front surface 60b within the second clearance 60g.

[0134] The layout of the connection terminals 70a is not limited to the one described above. For example, the second bus bar 72 may be configured to have the connection terminal 70a extending from the first end portion 72a to lie within the first clearance 60f. The fourth bus bar 74 may alternatively be configured to have the connection terminal 70a extending from the first end portion 74a to lie within the second clearance 60g. In such a case, the connection terminal 70a of the second bus bar 72 is arranged on the front surface 60b within the first clearance 60f. The connection terminal 70a of the fourth bus bar 74 is arranged on the front surface 60b within the second clearance 60g. The layout of the connection terminals 70a may be different depending on areas.Areas of the first clearance 60f and the second clearance 60g, the layout of the voltage measuring wires 80 or sensor devices arranged in the first and second clearances 60f and 60g.

[0135] The second housing 60 has screw holes, as described in detail later, formed within the first clearance 60f and the second clearance 60g for securing the busbars 70 and the voltage sensing wires 80 thereto. The screw holes open at the front surface 60b and extend in the longitudinal direction, which is a direction from the front surface 60b to the rear surface 60a. The screw holes do not completely penetrate a thickness of the second housing 60.

[0136] Specifically, the foregoing screw holes include the first screw hole 68a, the second screw hole 68b, the third screw hole 68c, the fourth screw hole 68d, the fifth screw hole 68e, and the sixth screw hole 68f. The first screw hole 68a, the fourth screw hole 68d, the fifth screw hole 68e, and the sixth screw hole 68f are formed within the first clearance 60f. The second screw hole 68b and the third screw hole 68c are formed within the second clearance 60g.

[0137] The connection terminals 70a of the busbars 70 and the terminals 80a of the voltage sensing wires 80 are connected to each other using fasteners 91. Specifically, the connection terminal 70a of the first busbar 71 and the terminal 80a of the first voltage sensing line 81 are secured to the first screw hole 68a using the fastener 91. The connection terminal 70a of the second busbar 72 and the terminal 80a of the second voltage sensing line 82 are secured to the second screw hole 68b using the fastener 91. The connection terminal 70a of the third busbar 73 and the terminal 80a of the third voltage sensing line 83 are secured to the third screw hole 68c using the fastener 91.

[0138] The connection terminal 70a of the fourth busbar 74 and the terminal 80a of the fourth voltage sensing line 84 are secured to the fourth screw hole 68d using the fastener 91. The connection terminal 70a of the fifth busbar 75 and the terminal 80a of the fifth voltage sensing line 85 are secured to the fifth screw hole 68e using the fastener 91. The connection terminal 70a of the sixth busbar 76 and the terminal 80a of the sixth voltage sensing line 86 are secured to the sixth screw hole 68f using the fastener 91.

[0139] Each of the fasteners 91 has a head with a washer and a shaft extending from the washer. Each of the terminals 80a and one of the connecting terminals 70a are, as shown in Fig. 3 and Fig. 9, are stacked on top of each other on the shank of the fastener 91. The terminal 80a is located closer to the head of the fastener 91, while the connecting terminal 70a is located farther from the head of the fastener 91. The terminal 80a and the connecting terminal 70a are designed to overlap each other in the axial direction of the fastener 91 (i.e., the longitudinal direction). The nut 92 is tightened onto each of the fasteners 91 to hold the terminals 80a and the connecting terminals 70a between the washer of the fastener 91 and the nut 92, thereby achieving overlap or contact between the terminal 80a and the connecting terminal 70a.The fastener 91 with the terminal 80a and the connection terminal 70a is screwed into a corresponding one of the screw holes 68a to 68f, thereby placing the terminal 80a of the voltage measuring wire 80 and the connection terminal 70a of the bus bar 70 on the front surface 60b of the second housing 60. Specifically, the terminal 80a and the connection terminal 70a are designed to overlap each other on the front surface 60b of the second housing 60. The fastener 91 and the nut 92 constitute a fastening member. A washer may be used instead of the nut 92. The fastener 91 may be used without the nut 92 and / or a washer. A dashed line in . Fig. 9 represents an intersection point between sections of the line with alternating long and two short lines extending in the elevation direction and the lateral direction in Fig. 7 extends.

[0140] In the manner described above, each of the busbars 70 and one of the voltage measuring wires 80 are electrically connected to the front surface 60b of the second housing 60 and also mechanically secured to the second housing 60. After the busbars 70 and the voltage measuring wires 80 are attached to the second housing 60, the busbars 70 and the cells 11 to 15 are laser welded together. Each of the busbars 70, as shown in Fig. 3 has the tiny hole(s) 70b formed therein. A laser is emitted onto a portion of each of the busbars 70 around the tiny hole 70b, thereby achieving an electrical and mechanical connection between each of the busbars 70 and one of the electrode terminals of the cells 11 to 15. Such a connection may be established before or after the first housing 50 and the second housing 60 are mechanically coupled to each other using the housing tightening members 90.

[0141] In order to reduce electrical resistance of connections between the busbars 70 and the voltage measuring wires 80, the connecting terminals 70a and the terminals 80a may be held between the fasteners 91 and the nuts 92 and then soldered together.

[0142] The second housing 60, as shown in Fig. 3 and Fig. 5, has formed therein the first discrete groove 69a to the sixth discrete groove 69f, which are located in the first clearance 60f or the second clearance 60g and in which the first voltage sensing line 81 to the sixth voltage sensing line 86 are arranged, respectively. Each of the first discrete groove 69a to the sixth discrete groove 69f has a depth extending from the front surface 60b to the rear surface 60a of the second housing 60. Specifically, each of the first discrete groove 69a to the sixth discrete groove 69f is defined by a side wall and a bottom wall formed on the front surface 60b. The first screw hole 68a to the sixth screw hole 68f are formed in the bottom walls of the first discrete groove 69a to the sixth discrete groove 69f.The terminals 80a of the first voltage measuring line 81 to the sixth voltage measuring line 86 are surrounded by the side walls of the first discrete groove 69a to the sixth discrete groove 69f.

[0143] Within the first clearance 60f and the second clearance 60g, a plurality of common grooves are formed in communication with the first discrete groove 69a through the sixth discrete groove 69f. Each of the common grooves has a depth extending from the front surface 60b to the rear surface 60a of the second housing 60.

[0144] Specifically, the common grooves include the first common groove 69g and the second common groove 69h. The first common groove 69g communicates with the first discrete groove 69a, the fourth discrete groove 69d, the fifth discrete groove 69e, and the sixth discrete groove 69f in the first clearance 60f. The second common groove 69h communicates with the second discrete groove 69b and the third discrete groove 69c in the second clearance 60g.

[0145] A collection of center portions of the first voltage measuring line 81, the fourth voltage measuring line 84, the fifth voltage measuring line 85, and the sixth voltage measuring line 86 are arranged in the first common groove 69g. A collection of center portions of the second voltage measuring line 82 and the third voltage measuring line 83 are arranged in the second common groove 69h.

[0146] The water damage sensor 41 is, as shown in Fig. 6, is arranged in the first clearance 60f. The first clearance 60f has the first electrode groove 69i and the second electrode groove 69j formed therein. The first counter electrode 42 of the water damage sensor 41 is arranged in the first electrode groove 69i. The second counter electrode 43 of the water damage sensor 41 is arranged in the second electrode groove 69j. Each of the first electrode groove 69i and the second electrode groove 69j has a depth extending from the front surface 60b to the rear surface 60a in the longitudinal direction.

[0147] The first counter electrode 42 is mechanically attached to the bottom of the first electrode groove 69i using a screw. Similarly, the second counter electrode 43 is mechanically attached to the bottom of the second electrode groove 69j using a screw. A side wall is located between the first counter electrode 42 and the second counter electrode 43 and acts as a stopper to prevent the first counter electrode 42 and the second counter electrode 43 from moving, thereby maintaining a constant distance therebetween.

[0148] Each of the first electrode groove 69i and the second electrode groove 69j communicates with the first common groove 69g along with the first discrete groove 69a, the fourth discrete groove 69d, the fifth discrete groove 69e, and the sixth discrete groove 69f. Insulated conductors are connected to the first counter electrode 42 and the second counter electrode 43. The insulated conductors have center portions arranged in the first common groove 69g along with center portions of the first voltage sensing line 81, the fourth voltage sensing line 84, the fifth voltage sensing line 85, and the sixth voltage sensing line 86. Specifically, the center portions of the insulated conductors, the first voltage sensing line 81, the fourth voltage sensing line 84, the fifth voltage sensing line 85, and the sixth voltage sensing line 86, are gathered within the first common groove 69g.The insulated conductor extending from the first counter electrode 42 and the second counter electrode 43 has ends connected to the plug 80b together with the ends of the voltage measuring wires 80.

[0149] Although not shown, a temperature sensor, such as a thermistor, installed in the sensor unit 40 may be arranged in the first clearance 60f or the second clearance 60g. In the foregoing manner, the conductors and / or the sensors are gathered in the first clearance 60f or the second clearance 60g to allow the second housing 60 to be placed within a projection plane of the first housing 50 in the longitudinal direction. BENEFICIAL BENEFITS

[0150] The beneficial advantages offered by the battery pack 100 in this embodiment are described below. CONNECTION MODULE

[0151] The busbars 70 and the voltage sensing wires 80 are electrically connected to each other as described above. The busbars 70 and the voltage sensing wires 80 are mechanically connected to the second housing 60. The connecting terminals 70a of the busbars 70 and the terminals 80a of the voltage sensing wires 80 are stacked in direct contact with each other on the front surface 60b of the second housing 60.

[0152] The foregoing arrangements therefore serve to prevent separation of the bus bars 70 and the voltage sensing wires 80 from each other when the second housing 60 expands or contracts due to a change in ambient temperature, thereby ensuring stability in the electrical connection between the bus bars 70 and the voltage sensing wires 80.

[0153] Each of the connecting terminals 70a of the busbars 70 and one of the terminals 80a of the voltage measuring wires 80 are fitted to the shaft of a corresponding one of the fasteners 91 and then held between the washer of the fastener 91 and the nut 92. The fastener 91 is screwed into the non-through hole opening on the front surface 60b of the second housing 60 and having a length extending from the front surface 60b to the rear surface 60a of the second housing 60.

[0154] With the above arrangements, the busbars 70 and the voltage sensing wires 80 are pressed by the fasteners 91 against the front surface 60b of the second housing 60 in a direction from the front surface 60b toward the rear surface 60a. In other words, the mechanical contact between each of the busbars 70 and a corresponding one of the voltage sensing wires 80 is stably maintained by the fastener 91 and the nut 92, thereby minimizing a risk that the electrical connection between the busbar 70 and the voltage sensing wire 80 becomes unstable due to swelling of the cells 11 to 15 to press the busbars 70 and the voltage sensing wires 80 in a direction from the rear surface 60a toward the front surface 60b.Furthermore, the foregoing arrangements result in a reduction in the number of parts of the battery pack 100 when compared with a conventional structure equipped with first connecting members that electrically connect the bus bars 70 and the voltage sensing wires 80 and the second connecting members that mechanically connect the bus bars 70 and the voltage sensing wires 80.

[0155] The second housing 60 has the first discrete groove 69a through the sixth discrete groove 69f formed therein, in each of which one of the first voltage sensing lines 81 through the sixth voltage sensing line 86 is arranged. The terminals 80a of the first voltage sensing line 81 through the sixth voltage sensing line 86 are each surrounded by the side walls defining the first discrete groove 69a through the sixth discrete groove 69f. This minimizes unwanted movement of the voltage sensing wires 80, thereby ensuring stability in an electrical connection between the voltage sensing wires 80 and the busbars 70.

[0156] The voltage measuring wires 80 are made of insulated conductors. The second housing 60 also has the first common groove 69g and the second common groove 69h formed therein. The first common groove 69g communicates with the first discrete groove 69a, the fourth discrete groove 69d, the fifth discrete groove 69e, and the sixth discrete groove 69f. The second common groove 69h communicates with the first common groove 69g, the second discrete groove 69b, and the third discrete groove 69c.

[0157] The foregoing arrangements enable the first voltage sensing line 81, the fourth voltage sensing line 84, the fifth voltage sensing line 85, and the sixth voltage sensing line 86 to be bundled or tightened together and placed in contact with each other within the first common groove 69g. Similarly, the second voltage sensing line 82 and the third voltage sensing line 83 are also enabled to be bound together and placed in contact with each other within the second common groove 69h.

[0158] Each of the cells 11 to 15 has the positive terminal 10g and the negative terminal 10h, which are separated from each other, in other words, are arranged away from each other in the lateral direction (that is, a direction perpendicular to the thickness of the cells 11 to 15). The second housing 60 is therefore designed to have two discrete chambers: the first clearance 60f and the second clearance 60g. Some of the voltage sensing wires 80 are arranged in the first clearance 60f. The other voltage sensing wires 80 are arranged in the second clearance 60g. This makes it possible to greatly reduce the size of the second housing 60 compared to a conventional structure by arranging the voltage sensing wires 80 outside of cavities in the second housing 60.

[0159] The conductors or sensors are collected in the first clearance 60f and the second clearance 60g to position the second housing 60 within a projection plane of the first housing 50 in the longitudinal direction. This makes it possible to reduce the overall size of the battery pack 100.

[0160] After the busbars 70 and the voltage sensing wires 80 are electrically connected to each other using the fasteners 91, the busbars 70 and the electrode terminals (i.e., the positive terminals 10g and the negative terminals 10h) of the cells 11 to 15 are welded together using a laser. This eliminates the application of stress, which results from electrical connection of the busbars 70 and the voltage sensing wires 80, to the junctions of the busbars 70 and the electrode terminals of the cells 11 to 15, unlike a structure in which the busbars 70 are laser-welded to the electrode terminals of the cells 11 to 15 after the busbars 70 are electrically connected to the voltage sensing wires 80. This ensures stability in the electrical connection of the busbars 70 and the cells 11 to 15.

[0161] The seals 10l and the fastening elements 91 are, as in Fig. 9, are arranged out of alignment with each other in the longitudinal direction, that is, a direction in which the fastening elements 91 are screwed into the second housing 60. This allows the size of the connection module 2 to be reduced in the longitudinal direction compared to when the seals 10l and the fastening elements 91 are aligned with each other in the longitudinal direction. BUSBARS

[0162] The second busbar 72 and the fourth busbar 74, which are electrically connected to the first cell stack 10i and the second cell stack 10j, as shown in Fig. 10, have central portions whose thicknesses are punched to form a circular hole that matches the fifth screw hole 65 of the second housing 60. The first cell stack 10i, as shown in Fig. 4 is clearly shown, is located between an array of the first screw hole 61 and the second screw hole 62 and the fifth screw hole 65. The second cell stack 10j is located between an array of the third screw hole 63 and the fourth screw hole 64 and the fifth screw hole 65.

[0163] As apparent from the foregoing discussion, the screw holes 61 to 65 are located on both sides of each of the first and second cell stacks 10i and 10j, which are opposite to each other in the lateral direction. Such a layout of the screw holes 61 to 65 minimizes the distance between the case tightening members 90 despite an increase in the number of cell stacks 10i and 10j. In this embodiment, the distance between two of the case tightening members 90 arranged adjacent to each other in the lateral direction can be selected to be substantially equal to the width of the cells 11 to 15, thereby minimizing the swelling of the cells 11 to 15 and ensuring stability in an electrical connection between the cells 11 to 15 and the busbars 70.

[0164] The case tightening members 90 are located within a range between an upper end and a lower end of each of the first and second cell stacks 10i and 10j in the height direction (i.e., the thickness direction of the first and second cell stacks 10i and 10j). This minimizes the size of the battery pack 100 in the height direction. The interval between each of the first screw hole 61, the second screw hole 62, and the fifth screw hole 65 in the lateral direction is selected to be equal to that between each of the third screw hole 63, the fourth screw hole 64, and the fifth screw hole 65 in the lateral direction. This minimizes the swelling of the cells 11, 14, and 15 of the first cell stack 10i and the swelling of the cells 12 and 13 of the second cell stack 10j to the same extent.

[0165] Typically, the locations of two of the cells 11 to 15 that are electrically connected to each other may be changed in the longitudinal direction due to manufacturing variation among the cells 11 to 15. In such a case, when the bus bar 70 is connected to the positive terminal 10g of one of the two cells and the negative terminal 10h of the other cell, the bus bar 70 needs to be elastically deformed in the longitudinal direction to achieve direct contact of the bus bar 70 with both the positive terminal 10g and the negative terminal 10h. The elastic deformation of the bus bar 70 is released after the positive terminal 10g and the negative terminal 10h are connected to the bus bars 70, so that the bus bar 70 elastically returns to its original shape.Such an elastic restoring force generated by the bus bar 70 is exerted on connections of the positive terminal 10g and the negative terminal 10h with the bus bar 70.

[0166] Each of the cells 11 to 15 usually swells due to aging, but the increase in the volume of the cells 11 to 15 resulting from swelling is not always constant. Such a variation in the swelling volume of the cells 11 to 15 can exert stress on the connections of the positive terminals 10g and the negative terminals 10h to the busbars 70.

[0167] To mitigate the above problem, the second busbar 72, as described above, is shaped to have the first end portion 72a connected to the positive terminal 10g of the first cell 11, the second end portion 72b connected to the negative terminal 10h of the second cell 12, and the intermediate portion 72c coupling the first end portion 72a and the second end portion 72b together. The second busbar 72 is also shaped to have bends between the first end portion 72a and the intermediate portion 72c and between the second end portion 72b and the intermediate portion 72c.

[0168] Similarly, the fourth busbar 74 is shaped to have the first end portion 74a connected to the positive terminal 10g of the third cell 13, the second end portion 74b connected to the negative terminal 10h of the fourth cell 14, and the intermediate portion 74c coupling the first end portion 74a and the second end portion 74b together. The fourth busbar 74 is also shaped to have bends between the first end portion 74a and the intermediate portion 74c and between the second end portion 74b and the intermediate portion 74c.

[0169] The foregoing structure of the second busbar 72 minimizes adverse effects of elastic deformation of one of the first end portion 72a and the second end portion 72b and elastic deformation of the intermediate portion 72c at the other of the first end portion 72a and the second end portion 72b. Similarly, the structure of the fourth busbar 74 minimizes adverse effects of elastic deformation of one of the first end portion 74a and the second end portion 74b and elastic deformation of the intermediate portion 74c at the other of the first end portion 74a and the second end portion 74b.

[0170] The intermediate portion 72c has the punched portion 72d formed therein. Similarly, the intermediate portion 74c has the punched portion 74d. This facilitates the ease with which the intermediate portions 72c and 74c are elastically deformed, thereby minimizing adverse effects of such elastic deformation on the connections of the second and fourth busbars 72 and 74 to the electrode terminals of the cells 11 to 14.

[0171] The foregoing arrangements minimize the application of stress to the junctions of the electrode terminals and the ends of the bus bars 70, thereby ensuring stability in an electrical connection of the cells 11 to 15 and the bus bars 70.

[0172] The intermediate portion 72c is, as described above, configured to have a portion in which the punched portion 72d is formed and which has a minimum width (i.e., a minimum dimension in a direction perpendicular to the length of the intermediate portion 72c) that is more than or equal to one half of a maximum width of a portion of the intermediate portion 72c other than the punched portion 72d in the direction perpendicular to the length of the intermediate portion 72c.Similarly, the intermediate portion 74c of the fourth bus bar 74 is configured to have a portion in which the punched portion 74d is formed and which has a minimum width (i.e., a minimum dimension in a direction perpendicular to the length of the intermediate portion 74c) that is more than or equal to one half of a maximum width of a portion of the intermediate portion 74c other than the punched portion 74d in the direction perpendicular to the length of the intermediate portion 74c.

[0173] The formation of the punched sections 72d and 74d results in a reduction in electrical resistance of the busbars 70.

[0174] The intermediate portion 72c of the second busbar 72 is configured to have an upper end portion punched in a semicircular shape to form the punched portion 72d. Similarly, the intermediate portion 74c of the fourth busbar 74 is configured to have a lower end portion punched in a semicircular shape to form the punched portion 74d. The punched portions 72d and 74d are arranged adjacent to each other in the height direction to form a circular opening.

[0175] The mating flange 60c of the second housing 60 has the projection 67 formed thereon, which is contoured to correspond to the shape of the circular opening defined by the punched portions 72d and 74d. The front surface 60b of the second housing 60 has the fifth screw hole 65 formed in a portion thereof surrounding the projection 67.

[0176] The foregoing structure of a combination of the second bus bar 72 and the fourth bus bar 74 results in a reduction in an electrical resistance thereof to minimize a loss of electric current flowing therethrough when compared with a structure in which the second housing 60 has screw holes formed therein, one for each of the bus bars 70.

[0177] The projection 67 also functions as a guide to facilitate the installation of the second busbar 72 and the fourth busbar 74 with the punched portions 72d and 74d on the second housing 60.

[0178] The front surface 60b of the second housing 60 has the fifth screw hole 65 formed in a portion thereof surrounding the protrusion 67. This prevents physical contact of each of the second busbar 72 and the fourth busbar 74 with the housing tightening member 90 when the housing tightening member 90 is inserted into the fifth screw hole 65. BATTERY MODULE

[0179] The screw tightening portions 50f on the outer side surface of the first cell stack support 50a are located in a projection plane of the first flange 50d in the longitudinal direction. Similarly, the screw tightening portions 50f on the outer side surface of the second cell stack support 50b are located in a projection plane of the second flange 50e in the longitudinal direction. This makes it possible to reduce the overall size of the battery pack 100.

[0180] While the present invention has been disclosed in terms of preferred embodiments to facilitate a better understanding thereof, it should be recognized that the invention may be embodied in various forms without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the illustrated embodiments that may be practiced without departing from the principle of the invention as defined in the attached drawings. FIRST MODIFICATION

[0181] The screw tightening portions or screw fastening portions 50f on the outer side surface of the first cell stack bearing 50a are located, as described above, within a projection plane of the first flange 50d in the longitudinal direction. Similarly, the screw tightening portions or screw fastening portions 50f on the outer side surface of the second cell stack bearing 50b are also located within a projection plane of the second flange 50e in the longitudinal direction. The screw tightening portions 50f can alternatively be formed as shown in Fig. 11, at least partially outside a projection plane of the first flange 50d in the longitudinal direction. Similarly, alternatively, the screw tightening portions 50f may be at least partially outside the projection plane of the second flange 50e in the longitudinal direction. SECOND MODIFICATION

[0182] The connecting terminals 70a of all the busbars 70 are arranged within the first clearance 60f and the second clearance 60g, however, the connecting terminals 70a may alternatively be arranged as shown in Fig. 12, may be arranged partially outside the first clearance 60f or the second clearance 60g of the second housing 60. Fig. 12 also illustrates the sensor device(s) of the sensor unit 40 installed outside the first clearance 60f or the second clearance 60g of the second housing 60. THIRD MODIFICATION

[0183] In the foregoing embodiment, the punched portion 72d of the second busbar 72 and the punched portion 74d of the fourth busbar 74 define, as shown in Fig. 13a, a circular opening. The projection 67 is also formed in the shape of a hollow cylinder. However, the configurations of the punched portion 72d and the punched portion 74d are not limited to those in Fig. 13(a). For example, the punched portion 72d and the punched portion 74d, as shown in Fig. 13(b), to define a square or rectangular opening. The projection 67 may also be formed in the shape of a square bar. Alternatively, the projection 67 may be formed as shown in Fig. 13(c), may be shaped to have projections 67a formed on its outer periphery. The punched portion 72d and the punched portion 74d may be shaped to have recesses 70c formed in correspondence with the projections 67a. Each of the bosses 67a and each of the projections 67a is fitted into one of the recesses 70c to ensure a relative position between the corresponding one of the second busbars 72 and the fourth busbars 74 and the projection 67. FOURTH MODIFICATION

[0184] The second bus bar 72 is, as described above, shaped to have the intermediate portion 72c and the first end portion 72a, as shown in Fig. 14(a), which are joined or connected to each other by the bend 72d, which is angled substantially perpendicular to the intermediate portion 72c and the first end portion 72a. In addition, the second busbar 72 has the intermediate portion 72c and the second end portion 72b, which are connected to each other by the bend 72d, which is angled substantially perpendicular to the intermediate portion 72c and the first end portion 72b. The fourth busbar 74 has the same structure as that of the second busbar 72. The bends 72d may alternatively be bent, as shown in Fig. 14(b) to form the intermediate portion 72c upwardly curved in a substantially C- or U-shape.

[0185] The second housing 60 can, as in Fig.14(a), may be shaped to have the guide 60h contacting a portion of the intermediate portion 72c facing the cells 11 to 15. The second housing 60 may also have an additional guide 60h contacting the fourth busbar 64. FIFTH MODIFICATION

[0186] The lithium battery 10 in the above embodiment is equipped with five cells: cells 11 to 15, but can alternatively be configured to have a plurality of cells. The number of cell stacks can be more than two. SIXTH MODIFICATION

[0187] The embodiment illustrates the battery pack 100 to which the lead-acid battery 110 is connected and which is equipped with the lithium battery 10. The embodiment is not limited to such arrangements of the lead-acid battery 110 and the lithium battery 10. For example, the battery pack 100 may be configured to include at least one of the lead-acid battery 110 and the lithium battery 10. Alternatively, the battery pack 100 may be configured to include neither the lead-acid battery 110 nor the lithium battery 10. In this case, the battery pack 100 is electrically connected to both the lead-acid battery 110 and the lithium battery 10. SEVENTH MODIFICATION

[0188] The embodiment illustrates the vehicle equipped with the electric power system 200 and configured to have an idle stop mode. However, the electric power system 200 may alternatively be installed in hybrid vehicles or electric vehicles. In such a case, a motor generator is used instead of a combination of the starter motor 120 and the electric rotating machine 130. EIGHTH MODIFICATION

[0189] The embodiment illustrates the switches 22 mounted on the wiring substrate 21, however, the switches 22 only need to be electrically connected to the wiring substrate 21; in other words, they do not need to be directly installed on the wiring substrate 21. For example, the switches 22 may be disposed on the casing of the battery pack 100 through an insulating film to establish thermal connection of the switches 22 with the casing. This causes the heat generated by the switches 22 to be transferred to the casing rather than to the wiring substrate 21, thereby facilitating dissipation of the heat generated by the switches 22 to the outside of the casing.

[0190] The switches 22 as described above include the first switch 29 through the sixth switch 34. Some of the switches 22 may be mounted on the wiring substrate 21, while the others may be arranged on or in the housing.

[0191] A battery pack includes a plurality of cells, a first casing in which the cells are arranged, bus bars connecting positive and negative terminals of the cells, a second casing to which the bus bars are attached, and casing tightening members threadably connecting and fastening the first and second casings. Cell stacks, each of which has the cells stacked in a height direction, are arranged adjacent to each other in a lateral direction. At least one of the bus bars connecting between the terminals of the cells in the cell stacks has a punched portion formed therein. The first and second casings have a flange aligned with the punched portion and flanges arranged adjacent to the cell stacks in the lateral direction. The flanges have screw holes formed therein into which the casing tightening members are tightened.These arrangements ensure the stability of an electrical connection between the cells and the busbars without increasing the size of the battery pack in the vertical direction.

Claims

[1] Battery pack comprising: a battery module (1) having a plurality of cells (11 to 15) and a first housing (50) in which the cells are arranged; a connection module (2) comprising busbars (70 to 76) connected to electrode terminals (10g, 10h) of the cells and a second housing (60) to which the busbars are secured; screws (90) securing the first housing and the second housing together to position the busbars close to the electrode terminals; and a plurality of cell stacks (10i, 10j), each having two or more of the cells stacked in a height direction, wherein the cell stacks are arranged adjacent to each other in a lateral direction perpendicular to the height direction, wherein the cells of one of the cell stacks comprise a first cell, the cells of another of the cell stacks comprise a second cell, and one of the busbars connecting the electrode terminals of the first and second cells has a punched portion (72d, 74d) passing through the thickness of the busbar in a longitudinal direction, which is a direction in which the first housing and the second housing are arranged adjacent to each other, and wherein portions (50c, 60c) of the first housing and the second housing aligned with the punched portion and portions (50d, 50e, 60d, 60e) of the first housing and the second housing located adjacent to the cell stacks in the lateral direction have screw holes (61 to 65) formed therein into which the screws are tightened. [2] The battery pack of claim 1, wherein the bus bar connecting the electrode terminals of the first and second cells includes first and second end portions (72a, 72b, 74a, 74b) and an intermediate portion (72c, 74c) coupling the first and second end portions together, and wherein the bus bar further includes a bend between each of the first and second end portions and the intermediate portion, and wherein the intermediate portion has the stamped portion formed therein. [3] The battery pack according to claim 1 or 2, wherein the bus bar connecting the electrode terminals of the first and second cells has a length extending in the lateral direction, wherein a portion of the intermediate portion of the bus bar provided with the punched portion has a minimum dimension in the height direction, the minimum dimension being more than or equal to one half of a maximum dimension of a portion of the bus bar other than the punched portion. [4] The battery pack according to any one of claims 1 to 3, wherein the cells of one of the cell stacks comprise first cells, the cells of the other of the cell stacks comprise second cells, the bus bars comprise a first bus bar and a second bus bar, each of which connects the electrode terminals of the first cell and the second cell, and the first bus bar and the second bus bar are arranged adjacent to each other in the height direction, each of the first bus bar and the second bus bar has the punched portion, and portions of the first case and the second case that are aligned with the punched portions of the first and second bus bars and have holes formed therein that are aligned define one of the screw holes. [5] The battery pack according to any one of claims 1 to 4, wherein the second housing has a first surface (60b) and a second surface (60a) opposite to each other in the longitudinal direction, the second housing having the screw holes extending in a direction from the first surface to the second surface, and the second housing having the bus bars disposed on the first surface, the second housing having a projection (67) disposed around an edge of an opening of the screw hole formed in the front surface of the second housing in alignment with the punched portion, the projection being contoured to conform to a shape of the punched portion. [6] The battery pack according to claim 5, wherein the projection is of a cylindrical shape. [7] A battery pack according to any one of claims 1 to 6, wherein an elastic member (10l) is disposed between the cells and the second casing, the elastic member being firmly held between the cells and the second casing by the screws tightening the first casing and the second casing together.

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