Contact element, plug with a contact element and contact arrangement for contacting a bipolar stack

A contact element for contacting a bipolar plate of a fuel cell stack includes a contact body extending along a longitudinal axis. The contact body has a channel extending along the longitudinal axis and delimited by a pair of channel walls disposed opposite one another in a direction transverse to the longitudinal axis. The channel is adapted to receive a portion of the bipolar plate. The contact body has a contact spring on a first channel wall of the pair of channel walls. The contact spring protrudes into the channel and has a cutting edge directed toward a second channel wall of the pair of channels walls and adapted to contact the bipolar plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of German Patent Application No. 102018213688.2, filed on Aug. 14, 2018.

FIELD OF THE INVENTION

The present invention relates to a contact element and, more particularly, to a contact element for contacting a bipolar plate.

BACKGROUND

In a fuel cell stack, individual cells are layered above one another to form the stack, with each of them being separated by a bipolar plate. The bipolar plates are used to conduct operational media to electrodes of the fuel cells. In order to investigate the performance and/or failure of the fuel cell stack, for example in a vehicle, the bipolar plates between the cells are connected via a plug with a control circuit and the voltage in each cell is measured. A contact element is used to contact a bipolar plate of a fuel cell stack. The plug includes a plurality of the contact elements contacting a plurality of bipolar plates of the fuel cell stack.

In particular in vehicles, the plugs are exposed to heavy vibration loads and/or impact loads, as a result of which the contact elements can become detached from the bipolar plates. Vibrations and/or impacts can additionally generate fluctuating voltage values between the bipolar plate and the contact element, leading to an inaccurate assessment of the fuel cell stack.

SUMMARY

A contact element for contacting a bipolar plate of a fuel cell stack includes a contact body extending along a longitudinal axis. The contact body has a channel extending along the longitudinal axis and delimited by a pair of channel walls disposed opposite one another in a direction transverse to the longitudinal axis. The channel is adapted to receive a portion of the bipolar plate. The contact body has a contact spring on a first channel wall of the pair of channel walls. The contact spring protrudes into the channel and has a cutting edge directed toward a second channel wall of the pair of channels walls and adapted to contact the bipolar plate.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, the invention is described in greater detail by way of example using exemplary embodiments with reference to the attached figures. In the figures, elements which correspond to one another in structure and/or function are provided with the same reference symbols.

The combination of features shown and described in the individual exemplary embodiments serves solely for the purposes of explanation. It is possible to dispense with a feature of an exemplary embodiment if its technical effect is of no importance in a particular application. Conversely, a further feature can be added in an exemplary embodiment if its technical effect is meant to be advantageous or necessary for a particular application.

A contact element1according to an embodiment is shown inFIGS. 1 and 2. A Cartesian coordinate system is used in the description, with a longitudinal direction x, a transverse direction y, and a depth direction z.

The contact element1, as shown inFIGS. 1 and 2, has a contact body2extending along a longitudinal axis L. The longitudinal axis L is substantially parallel to the longitudinal direction x. The contact body2has a substantially U-shaped cross-section in a plane spanned by the transverse direction y and depth direction z. A pair of limbs4,6of the contact body2are spaced apart from one another in the depth direction z transverse to the longitudinal axis L. The limbs4,6are arranged substantially parallel to a plane spanned by the longitudinal direction x and transverse direction y. The limbs4,6delimit a channel8in the depth direction z, and the limbs4,6function as channel walls10,12. The channel8is delimited on one side in the transverse direction y by a base14connecting the channel walls10,12. The channel8is open at the end opposite from the base14. The channel8forms a receiving region15, in which a portion of a bipolar plate can be received. In this case, the contact body2can encompass the portion of the bipolar plate, wherein the channel walls10,12cover the portion.

The contact body2, as shown inFIGS. 1 and 2, has a plug-in portion16, which extends in the longitudinal direction x and is arranged at an end18. A width20of the channel walls10,12of the plug-in portion16in the transverse direction y, in the shown embodiment, is smaller than a width22of the channel walls10,12in the receiving region15, and can be introduced into a plug-in aperture of an electrical conductor, such as a printed circuit board for example. In an embodiment, the plug-in portion16is coated with a tin coating, so that the plug-in portion can be attached for example with a solder joint in the plug-in aperture of the electrical conductor.

For contacting a portion of a bipolar plate inserted into the channel8, the contact element1has, on a channel wall10, two contact springs24shown inFIGS. 1 and 2which protrude into the channel8and which are each provided with a cutting edge26directed towards the opposite channel wall12. The contact springs24are spaced apart from one another in the longitudinal direction x and extend away from the base14in the transverse direction y. The contact springs24are elastically deflectable about a pivot axis S on the base14, which pivot axis S is arranged substantially parallel to the longitudinal axis L. The contact springs24are connected to the channel wall10and are pre-tensioned in the direction of the opposite channel wall12, such that the contact springs24can be deflected in the direction of the channel wall10upon insertion of the portion of the bipolar plate. The contact spring24is spaced from the opposite channel wall12by a spacing smaller than a material thickness of the bipolar plate.

The cutting edge26is formed at a free end30of the contact spring24remote from the base14, as shown inFIG. 2. The free end30is bent in the direction of the opposite channel wall12, so that the cutting edge26extends parallel to the longitudinal axis L and is arranged at an angle between approximately 60° and approximately 120° to a plane spanned by the longitudinal direction x and the transverse direction y. The surface of the inserted portion of the bipolar plate is arranged parallel to the plane spanned by the longitudinal direction x and transverse direction y. Thus, it can be ensured that the cutting edge26has good contact with the surface of the bipolar plate.

The cutting edge26can be arranged closer to the opposite channel wall12than to the channel wall10, away from which the contact spring24extends. Because the bipolar plate used with the contact element1shown inFIGS. 1 and 2is contacted on one side, a spring path around which the contact spring24can deflect elastically must be taken into account only on the channel wall10, which is provided with the contact springs24. Thus, a particularly compact contact element1can be manufactured.

As shown inFIG. 1, the channel wall10has plurality of windows32which each allow access to a contact spring24. Each contact spring24is arranged in one window32and extends away from a frame34facing the base14in the transverse direction y of the base14. In an embodiment, the cutting edge26can be arranged closer to the open end of the channel8than to the base14. As a result, incorrect stacking of stacked bipolar plates in the depth direction z can be compensated, because a broad clearance arises between cutting edge26and base14, into which the portion of the bipolar plate can be inserted. The depth to which the portion of a bipolar plate is inserted into the channel8in the transverse direction y can vary, with the result that, during plugging-in, a plug can be plugged with an accurate fit into a receptacle of a bipolar plate stack of a fuel cell stack, even in the case of incorrect stacking.

By way of the window32, the elastic deflection of the contact spring24can be prevented from influencing, and likewise deflecting, the channel wall10. During the deflection, the contact spring24does not press against the channel wall10and thus does not push the channel wall10away from the opposite channel wall12. Thus, the spacing between the channel walls10,12does not change even when the bipolar plate is inserted.

As shown inFIGS. 1 and 2, the contact spring24tapers further from the base14, such that a length36in the longitudinal direction x decreases with an increasing spacing from the base14up to the cutting edge26. The cutting edge26can, in an embodiment, extend in the longitudinal direction x with a length of approximately 0.4 mm, for example. As a result, a contact force acting through the spring force of the contact spring24can be concentrated on a small contact area. In an embodiment, the cutting edge26has a higher strength than the bipolar plate, and the cutting edge26can have a greater hardness than the bipolar plate.

In an embodiment, the contact element1can be molded from a stainless steel, such as a chromium-nickel alloy or a titanium alloy. The contact element1can be a monolithic component38, which can be manufactured simply and inexpensively in a single production process, for example by stamping and bending. The material thickness of the metal sheet can be approximately 0.1 mm thick, for example, wherein the normal force per spring24, which acts upon the surface of the portion of the bipolar plate, can be between approximately 1.8 N and 3.5 N, such that the plugging force of a contact element1adds up to approximately 5 N.

The contact element1, as shown inFIGS. 1 and 2, has an insertion chamfer42at its end40opposite the plug-in portion16, so that when the contact element1is plugged onto a portion of the bipolar plate, the insertion of the portion into the channel8is facilitated, and the contact element1is prevented from being damaged during insertion of the bipolar plate into the channel8, for example by the sharp edges of the bipolar plate that car arise from laser cutting or stamping of the bipolar plate.

The depth of the channel8in the depth direction z increases in the region of the insertion chamfer42, as shown inFIGS. 1 and 2. The insertion chamfer42can be formed, for example, at the corners of the channel walls10,12which are remote from the base14, wherein the corners are bent in the direction away from one another. As a result, the insertion chamfer42acts both during insertion of the bipolar plate in the longitudinal direction x and also in the transverse direction y. The channel8is opened at both ends in the longitudinal direction x, so that the depth in the longitudinal direction x to which the portion of the bipolar plate can be inserted is not limited, and can vary, thus it is possible to compensate an incorrect positioning of the bipolar plates in the longitudinal direction x.

As shown inFIGS. 1 and 2, the contact element1is provided, on the channel wall8opposite the contact spring24, with a latching tab44deflected in the direction away from the channel8. With the latching tab44, the contact element1can latch in a contact chamber of a housing of a plug and the contact element1can thus be fitted securely into the contact chamber.

A plug46according to an embodiment is shown inFIG. 3. The plug46is shown plugged on a stack of bipolar plates47of a fuel cell stack49inFIGS. 4 and 5.

The plug46, as shown inFIGS. 3 and 4, has a housing48, which is traversed by a plurality of contact chambers50in the longitudinal direction x. The housing48is electrically insulating and can be manufactured by an injection molding method, for example. The contact chambers50are spaced apart from one another in the depth direction z, wherein a first group of contact chambers50is arranged in a first row52and a second group of contact chambers50in a second row54. The first and second rows52,54are spaced apart from one another in the transverse direction y and are arranged offset in relation to one another in the depth direction z by a spacing56, shown inFIG. 4, between the contact chambers50in a row52,54. The spacing56corresponds to the spacing between the bipolar plates47arranged behind one another.

As shown inFIG. 3, the first row52of contact chambers50adjoins a first side wall58, which is traversed by slots60, in order to make it possible to insert a portion of a bipolar plate47into the contact chamber50. Similarly, the second row54of contact chambers50adjoins a second side wall62opposite the first side wall58. The second side wall62is likewise traversed by slots60. The slots60are each arranged on a plane perpendicular to the depth direction z with an adjoining contact chamber50.

As shown inFIGS. 3 and 4, contact elements1are fitted in an alternating manner, so that every second contact chamber50in a row52,54is provided with a contact element1. Since the rows52,54are offset in relation to one another, the contact elements1are not arranged in a common plane spanned by the longitudinal direction x and the transverse direction y. The contact elements1are arranged in the rows52,54in such a way that the channel8opens in the transverse direction y relative to the adjoining side wall58,62.

As shown inFIGS. 3 and 5, the plug-in portions16protrude out of the contact chamber50in the longitudinal direction x and are inserted, and firmly soldered, into insertion apertures63of an electrical conductor64, for example a flexible printed circuit board66.

The bipolar plate47has edge portions74, shown inFIG. 5, which flank the cutout72and can be inserted into the channel8in the transverse direction y and the longitudinal direction x. The depth to which the edge portion74can be inserted into the channel8in the transverse direction y can vary by a length76in the transverse direction y by which the cutting edge26is spaced apart from the base14. The edge portion74can be inserted at most until it comes to a stop on the base14in the transverse direction y. In the longitudinal direction x, the edge portion74can even be inserted until it comes to a stop at the closed end of the slot60of the housing48.

When the edge portion74is inserted into the channel8, the contact springs24are deflected elastically by the edge portion74about a pivot axis S shown inFIG. 1aligned substantially parallel to the longitudinal axis L, in the direction of the channel wall10on which the contact springs24are arranged. The cutting edge26cuts into a surface76, facing the channel wall10provided with the contact springs24, of the edge portion74of the bipolar plate47. The surface76is coated, wherein the cutting edge26traverses the coating and presses against the surface76with great force between approximately 1.8 N and approximately 3.5 N. Since the cutting edge26cuts into the surface76, secure contacting in the contact arrangement70can be created, which withstands heavy loads, for example impact loads and/or vibration loads. Thus, the fluctuation in the measurement results during the journey can be reduced.

InFIG. 5, two contact arrangements70are shown, wherein the contact arrangements70are stacked behind one another and the bipolar plates47are arranged offset in relation to one another by an offset in the longitudinal direction x and the transverse direction y. The contact elements1are fitted in a plug46and can be plugged into the cutout72, so that an edge portion74of the front bipolar plate47in the channel8of the front contact element1and the opposite edge portion74of the rear bipolar plate47in the depth direction z are arranged in the channel8of the rear contact element. The high tolerance of the contact element1in the longitudinal direction x and the transverse direction y makes it possible for the plug46to be pluggable with an accurate fit into the cutout72, without bending the bipolar plates47out of shape and/or damaging them.