A bus bar is often used for electrically connecting terminals of electrical parts such as a bipolar battery. A terminal of an electrical part and a bus bar is mainly connected by ultrasonic welding or thread-tightening. Conventional art relating to such connection of electrical parts or connection of a terminal of an electrical part and a bus bar is disclosed in Japanese Patent Application Laid Open No. 2008-140624 (hereinafter referred to as Patent literature 1), Japanese Patent Application Laid Open No. 2005-327677 (hereinafter referred to as Patent literature 2), and Japanese Patent Application Laid Open No. 2005-268029 (hereinafter referred to as Patent literature 3). Also, research on contact of two conductors has been conducted for many years, and an example of a research report relating to current density distribution in a contact portion is Isao Minowa, Mitsunobu Nakamura, “Simulation for the Current Density Distribution in a Contact Spot”, Journal of the Institute of Electronics, Information and Communication Engineers, C-II, Vol. J76-C-II, No. 10, pp. 637-643, October, 1993 (hereinafter referred to as Non-patent literature 1).
Patent literature 1 shows a connecting structure in which a current-collecting body of a battery is clamped with a spring metal plate. However, it is difficult to achieve a sufficiently low contact resistance in a connection between flat surfaces with merely a spring force of a leaf spring.
In Patent literature 2, connection is made by ultrasonic welding after a protrusion section is inserted into a through hole. With this method, normal pressure load at the time of the ultrasonic welding between flat surfaces is reasonably small since an ultrasonic horn is applied to a protrusion (engagement) of a terminal. However, this does not increase strength after joining. Also, detachment cannot be made after joining.
A conductive member in Patent literature 3 is provided with numerous protrusions or grooves on both upper and lower surfaces of a washer-shaped member. By thread-tightening of the conductive member sandwiched between a terminal and a bus bar, a portion of the protrusion removes a contamination layer on the surface of the terminal to obtain a favorable connection. However, Patent literature 3 does not describe the shape or arrangement of the protrusion in detail. To obtain a favorable connection resistance, approximately the same clamp load as in a simple conventional thread-tightening is necessary depending on the shape of the protrusion, and it is necessary to control the tightening torque. Also, the disclosed conductive member can only be manufactured through cutting work or forging. Cutting work is likely to increase processing cost and is considered difficult for practical application. In the case of manufacturing by forging, the processing cost also increases, although to a lesser extent than the cutting work. Also, in the case of manufacturing by forging, it is difficult to make a protrusion with a sharp tip. Thus, it is difficult to remove an oxide with the protrusion, whereby application of considerable load is presumably necessary.
A toothed washer is a conventional art similar to the conductive member in Patent literature 3. The material is steel or phosphor bronze for a spring. The toothed washer has a gear-shaped cutout on an outer circle and an inner circle and the teeth are contorted. The purpose is to prevent a thread from loosening. Specifically, the contorted teeth are flattened by the tightening force of the thread, and the reaction force to regain a contorted state prevents the thread from loosening. However, since the contortion angle of the teeth is small, entering inside a terminal or a bus bar is not feasible even through insertion between the terminal and the bus bar. Thus, a favorable electrical connection with small load is difficult.