Patent Description:
An electric motor having an inverter is known for example from <CIT>, <CIT> and <CIT>. The electric motor comprises a rotor and a stator which electromagnetically interact with one another. Usually, the inverter comprises a capacitor board with capacitors, a transistor board with transistors and a control circuit board and converts the direct current into the three-phase current for the stator. In order to feed the direct current into the inverter, the same usually comprises battery terminals assigned to the positive pole and the negative pole. The design of the battery terminals is often highly complex as a result of which the manufacturing costs and the assembly expenditure are increased. <CIT>, <CIT>, <CIT>, <CIT> disclose battery terminals of a simple design. The battery terminals are here formed as one piece formed from electric conductive material.

The object of the invention therefore is to state an improved or at least alternative embodiment for an inverter of the generic type, with which the described disadvantages are overcome. The object of the invention also is to provide an electric motor having such an inverter.

According to the invention, these objects are solved through the subject of the independent claims. Advantageous embodiments are subject of the dependent claims.

An inverter is provided for an electric motor. The inverter comprises a capacitor board having multiple capacitors, multiple transistor boards each with multiple transistors and a control circuit board. The capacitor board, the respective transistor boards and the control circuit board lie axially on top of one another and are electrically interconnected with one another. For the negative pole and for the positive pole, the inverter comprises a battery terminal each which are connected to the capacitor board in an electrically conductive manner and axially project from the capacitor board. Advantageously, the battery terminals can be screwed to the capacitor board. According to the invention, the battery terminals are identical to one another and are each formed by a connector having an external dielectric casing and internal electrically conductive lines. The battery terminals according to the invention are advantageously of a simple design and because of this the manufacturing expenditure and the assembly expenditure of the battery terminals in the inverter reduced.

The terms "axial" and "radial" in connection with the present invention relate to a longitudinal centre axis of the inverter. The capacitor board, the control circuit board and the transistor boards orientated in the inverter perpendicularly to the longitudinal centre axis. The transistors are primarily MOSFET.

According to the invention, the capacitors are arranged annularly on the capacitor board. The battery terminals are then arranged between the capacitors and centrally on the capacitor board. According to the invention, the respective battery terminal comprises three pole contact for contacting to the capacitor board, wherein the pole contacts of the one battery terminal and the pole contacts of the other battery terminal are arranged in a circle on the capacitor board and alternately arranging one another in the circle. Advantageously, the pole contacts of the battery terminals can be arranged symmetrically in the centre of the capacitor board. Through the symmetry created on the capacitor board, negative effects and losses in the inverter can be minimised.

Advantageously, the respective battery terminal can comprise a bridge that is parallel to the capacitor board, which connects the central pole contact with a lateral pole contact in an electrically conductive manner. The respective battery terminal can additionally comprise a second bridge that is parallel to the capacitor board, which connects the central pole contact with the other lateral pole contact in an electrically conductive manner. The first bridge and the second bridge are axially offset to one another and orientated at an angle to one another. Advantageously, the first bridge of the one battery terminal in each case can bridge the second bridge of the other battery terminal, so that the pole contacts of the one battery terminal and the pole contacts of the other battery terminal are arranged in a circle and alternating one another in the circle. Because of this, the pole contacts of the negative pole and the pole contacts of the positive pole are also arranged alternately and in a circle. Through the created symmetry on the capacitor board, negative effects and losses in the inverter can be minimised.

Advantageously it can be provided that on one of the pole contacts of the respective battery terminal a contact connector is formed, which axially projects from the capacitor board and leads to the outside. By way of the contact connector, the pole contacts of the respective battery terminal are contactable towards the outside in an electrically conductive manner.

In an advantageous embodiment of the inverter it can be provided that the inverter comprises a hollow-cylindrical carrier with a centre axis. Then, the carrier carries the capacitor board, the transistor boards and the control circuit board and encases these in the circumferential direction towards the outside. In the carrier, an annular rear ring that is orientated transversely to the centre axis is additionally integrally formed. The carrier ring is formed annularly, so that an opening located in the centre is formed in the carrier ring. Advantageously it can be provided that the battery terminals project through the opening of the annular carrier ring to the outside. By way of this, the inverter is designed in a particularly compact manner. The term "carry" in the context with the present invention means that the capacitor board, the transistor boards and the control circuit board are aligned in the right position to each other via the carrier. A pressure plate is firmly connected to a cooling plate, so that an elastically deformable foam pad, the capacitor board, the carrier ring, and the transistor boards are pressed together i.e. are sandwiched between the pressure plate and the cooling plate. The inverter forms a contiguous assembly unit with the carrier, the capacitor board, the transistor boards, the cooling plate and the control circuit board ready for assembly. By way of this, the inverter can be finish-assembled independently of further elements of the electric motor. Because of this, both the effort and also the costs can be reduced. In addition, the inverter can be tested for its functionality even prior to the assembly on further elements of the electric motor.

The carrier is preferentially formed from plastic and not electrically conductive. The carrier protects the capacitor board, the transistor boards and the control circuit board towards the outside and aligns the same relative to one another. The capacitor board, the transistor boards and the control circuit board are arranged in the carrier sandwich-like on top of one another and axially spaced apart from one another, wherein the capacitor board is preferentially arranged between the control circuit board and the transistor boards. The centre axis of the carrier coincides with the longitudinal centre axis of the inverter, so that accordingly the capacitor board, the transistor boards and the control circuit board are arranged perpendicularly to the centre axis.

In addition it can be provided that the transistor boards are fastened on the annular carrier ring, facing away from the capacitor board and circulating about the centre axis in a distributed and clamping manner. The carrier ring divides an interior space of the carrier into two axially adjacent regions, wherein in the first region the transistor boards and in the second axial region the capacitor board and the control circuit board are received and fixed. In other words, the capacitor board and the transistor boards are separated from one another and electrically insulated by the carrier ring.

Advantageously, multiple slots can be formed in the carrier ring in which a contact bus bar each is received. The respective contact bus bar is then compressed between the respective transistor board and the capacitor board and because of this the transistor boards are electrically contacted with the capacitor board. By way of the foam board and the pressure plate, the respective contact bus bar is securely fixed between the capacitor board and the respective transistor board. By way of the foam pad, an adequately high pressure force can be generated between the respective transistor board and the capacitor board. Practically, the contact bus bar comprises electrically conductive paths or is completely formed from an electrically conductive material.

For fixing the transistor boards on the support ring it can be provided that on the support ring at least one undercut fixing element and at least one clip for the respective transistor board are formed. The respective transistor board is then fastened on the carrier ring in a clamping manner by means of the at least one fixing element and the at least one clip. Practically, the at least one fixing element and the at least one clip are arranged located opposite one another or the at least one fixing element is assigned to a side and the at least one clip to a side of the respective transistor board located opposite. Then, the respective transistor board can be guided under the at least one fixing element and clipped onto the carrier ring by way of the at least one clip. Preferentially, two fixing elements and two clips for the respective transistor board are formed on the carrier ring so that a tilting of the respective transistor board on the carrier ring is prevented.

Advantageously it can be provided that multiple contact pins are cast into the carrier ring of the carrier. The contact pins are orientated axially from the transistor boards to the control circuit board and arranged circulating about the centre axis. The respective transistor board is electrically contacted with the respective assigned contact pin via an electrically conductive wire, which is wire bonded to the respective transistor board and to the respective contact pin. Further, the respective contact pin has a thickened portion on the end side in each case towards the control circuit board and the control circuit board comprises a receiving opening for the respective thickened portion. The respective thickened portion engages in the respective receiving opening and by way of this the contact pin is fastened in the control circuit board in a clamping manner and electrically contacted with the control circuit board.

Practically, the carrier and thus the carrier ring are formed from plastic and not electrically conductive. For example, the respective contact pin can be metallic. It is to be understood that at least some regions of the respective contact pin are not cast into the carrier ring or are open towards the outside and serve for a contacting with the control circuit board and the respective transistor board. It is to be understood in addition that the respective transistor board can also be assigned multiple contact pins. Through the cast-in contact pin its position in the carrier is predefined so that the contacting of the respective transistor board with the control circuit board can take place in a simplified and automated manner.

In an advantageous embodiment of the inverter it is provided that the inverter comprises an annular cooling plate through which a cooling liquid can flow. The pressure plate is fastened to the cooling plate and the transistor boards lie against the cooling plate in a heat-transferring manner. The capacitors of the capacitor board are then axially guided between the transistor boards and through an opening of the annular cooling plate and lie radially against the cooling plate in a heat-transferring manner. Then, the battery terminals project between the transistor boards and between the capacitors axially through an opening of the annular cooling plate towards the outside. By way of the cooling plate, the transistors and the capacitors can be particularly effectively cooled. In order to increase the cooling performance, fins can be formed in a cooling passage of the cooling plate that can be flowed through. The cooling liquid can for example be water.

The invention also relates to an electric motor. The electric motor comprises a rotor that is rotatable about an axis of rotation and a stator which electromagnetically interact with one another. The stator comprises multiple stator coils, wherein at least some of the stator coils are directly electrically contacted with three electric phases via their coil wires. The electric motor comprises at least one electrically conductive phase terminal which is provided for the receptive phase and is connected with the assigned coil wire in an electrically conductive manner. According to the invention, the electric motor comprises the inverter described above. The inverter is fastened on the stator facing the phase terminals, wherein the phase terminals engage in the inverter and are electrically contacted with the transistor boards. Besides the stator coils, the stator can comprise a stator housing and/or a coil carrier, so that the formulation "on the stator" also includes the formulation "on the stator housing" and/or "on the coil carrier".

Advantageously it can be provided by the respective phase terminal lies radially outside of the assigned coil wire and because of this the assigned coil wire radially engages in the respective phase terminal. Between the respective phase terminals and the stator, an elastically deformable support each is arranged and the respective phase terminals are pressed against the stator by means of a pressure ring and because of this fastened on the stator. By way of the pressure ring, a pressure force is advantageously generated by way of which the phase terminals are securely fixed on the stator. The pressure ring can for example be screwed to the stator.

Further important features and advantages of the invention are obtained from the subclaims, from the drawings and from the assigned figure description by way of the drawings.

It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention.

Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference characters relate to same or similar or functionally same components.

<FIG> shows an exploded view of an inverter <NUM> according to the invention for an electric motor <NUM>. The inverter <NUM> comprises a carrier <NUM> with a centre axis <NUM>. The carrier <NUM> has a wall <NUM> and an annular carrier ring <NUM>. The wall <NUM> circulates about the centre axis <NUM> and is orientated axially. The carrier ring <NUM> is integrally formed on the wall <NUM> and orientated radially to the inside. The carrier ring <NUM> divides the carrier <NUM> into a first region 6a and into a second region 6b, which are axially adjacent. In the first region 6a, multiple transistor boards <NUM> with transistors <NUM>, a cooling plate <NUM> and a cover <NUM> of the inverter <NUM> are mounted. In the second region 6b, a capacitor board <NUM> with capacitors <NUM>, two battery terminals <NUM>, a foam pad <NUM>, a pressure plate <NUM>, a control circuit board <NUM> and multiple iron cores <NUM> are mounted. The transistor boards <NUM> are electrically contacted with the capacitor board <NUM> by means of multiple contact bus bars <NUM> passing through the carrier ring <NUM>. On the carrier <NUM>, a connection <NUM> for the control circuit board <NUM> is additionally formed. Furthermore, the inverter <NUM> comprises a screw assembly 10a for the cover <NUM>, a screw assembly 13a for the battery terminals <NUM>, a screw assembly 15a for the pressure plate <NUM> and a screw assembly 16a for the control circuit board <NUM>. The further construction of the inverter <NUM> is explained in more detail by way of <FIG>.

<FIG> show views of the assembled inverter <NUM> from a side facing the first region 6a of the carrier <NUM>. In the inverter <NUM>, the carrier <NUM> carries all further elements of the inverter <NUM>, so that the inverter <NUM> forms a contiguous assembly unit ready for assembly. In other words, the inverter <NUM> can be assembled independently of further elements of the electric motor <NUM> - see also <FIG> in this regard. As is evident in <FIG>, the two battery terminals <NUM> - which are practically assigned to the positive pole and the negative pole - project out of the cover <NUM>. The cooling plate <NUM> can be flowed through by a cooling liquid - for example water - and comprises an inlet 9a and an outlet 9b for the cooling liquid. On the cooling plate <NUM>, multiple screw openings <NUM> which are provided for fixing the inverter <NUM> in the electric motor <NUM> are additionally provided - see <FIG> in this regard.

<FIG> shows a view of the carrier <NUM> from a side facing the first region 6a of the carrier <NUM>. Here, the contact bus bars <NUM> are already received in the carrier ring <NUM> of the carrier <NUM>. For this purpose, multiple slots are formed in the carrier ring <NUM> in which the contact bus bars <NUM> are received and axially orientated.

<FIG> shows a view of the carrier <NUM> with the transistor boards <NUM> from a side facing the first region 6a of the carrier <NUM>. The transistor boards <NUM> are arranged circulating and distributed about the centre axis <NUM> and fixed to the carrier ring <NUM> in a clamping or force-fit manner. For this purpose, two undercut fixing elements <NUM> and two clips <NUM> each are formed on the carrier ring <NUM> for the respective transistor board <NUM>. The respective fixing elements <NUM> are arranged radially outside and the respective clips <NUM> are arranged radially inside. During the fixing of the respective transistor board <NUM>, the same is slid with one side under the fixing elements <NUM> and on a side located opposite clipped to the carrier ring <NUM> via the clips <NUM>.

<FIG> now shows a view of the carrier <NUM> with the transistor boards <NUM> from a side facing the second region 6b of the carrier <NUM>. <FIG> shows an enlarged extract from <FIG>. The carrier ring <NUM> comprises a contact opening <NUM> for the respective transistor board <NUM> so that contact points of the respective transistor board <NUM> are accessible from a side of the carrier ring <NUM> facing the second region 6b. Furthermore, the inverter <NUM> comprises multiple electrically conductive contact pins <NUM> which are cast into the carrier ring <NUM>. The contact pins <NUM> are arranged about the contact opening <NUM> and electrically contacted with contact points of the respective transistor board <NUM> via an electrically conductive wire <NUM> each. Here, the respective wire is wire bonded to the assigned contact point and the assigned contact pin <NUM>. The respective contact pin <NUM> is L-shaped and extends in regions axially from the carrier ring <NUM> to the control circuit board <NUM>. On the respective pin <NUM>, a thickened portion <NUM> facing the control circuit board <NUM> is formed, which then engages in a receiving opening <NUM> of the control circuit board <NUM> - see also <FIG> in this regard - and fixes the contact pin <NUM> in the control circuit board <NUM> in a clamping manner. The contact bus bars <NUM> arranged in the slots of the carrier ring <NUM> are electrically contacted with the circuit boards <NUM>.

<FIG> shows an exploded view and <FIG> shows a view of the assembled state of the capacitor board <NUM>, of the battery terminals <NUM> and of the screw assembly 13a. The battery terminals <NUM> are formed identically to one another and fastened in the centre on the capacitor board <NUM> by way of the screw assembly 13a. The respective battery terminal <NUM> is formed by a connector with a dielectric casing and electrically conductive lines located inside. The respective battery terminal <NUM> comprises altogether three pole contacts <NUM> which are electrically contacted with the capacitors <NUM> of the capacitor board <NUM> by means of an assigned screw of the screw assembly 13a each and via electrically conductive lines. The pole contacts <NUM> of the battery terminals <NUM> are arranged in a circle and centrally on the capacitor board <NUM>. The capacitors <NUM> surround the pole contacts <NUM> of the battery terminals and are arranged symmetrically on the capacitor board <NUM>. The one battery terminal <NUM> is assigned to the negative pole and the other battery terminal <NUM> is assigned to the positive pole.

<FIG> now shows a view of the individual battery terminal <NUM>. <FIG> show views of the battery terminals <NUM>. The respective battery terminal <NUM> comprises a first bridge <NUM> that is parallel to the capacitor board <NUM> and a second bridge 29b that is parallel to the capacitor board <NUM>. The first bridge 29a and the second bridge 29b are formed axially offset to one another. The respective bridge 29a or 29b connects two of the pole contacts <NUM> of the receptive battery terminal <NUM> to one another in an electrically conductive manner. As is evident in <FIG>, the first bridge 29a of the one battery terminal <NUM> bridges the second bridge 29b of the other battery terminal <NUM>, so that the pole contacts <NUM> of the battery terminals <NUM> are arranged in a circle and alternating one another in the circle.

<FIG> shows a view of the carrier <NUM> with the transistor boards <NUM> and the cooling plate <NUM> from a side facing the second region 6b of the carrier <NUM>. As is noticeable here, the annular cooling plate <NUM> lies in the first region 6a of the carrier <NUM> against the transistor boards <NUM> in a heat-transferring manner. <FIG> shows a view of the cooling plate <NUM> with transistors <NUM> of the respective transistor boards <NUM>. Here, the transistor boards <NUM> are shown transparently for the sake of clarity.

<FIG> shows a view of the cooling plate <NUM> from a side facing the carrier <NUM> and <FIG> shows a view of the cooling plate <NUM> from a side facing away from the carrier <NUM>. As already explained above, the cooling plate <NUM> comprises the inlet 9a and the outlet 9b and can be flowed through by the cooling liquid. In <FIG> and <FIG>, a circumferential groove <NUM> is additionally evident, in which the wall <NUM> of the carrier <NUM> is received in a form-fit and non-displaceable manner.

<FIG> shows a view of the carrier <NUM> with the foam pad <NUM> and <FIG> shows a view of the carrier <NUM> with the pressure plate <NUM> from a side facing the second region 6b of the carrier <NUM>. Here, the pressure plate <NUM> is connected to the cooling plate <NUM> through the carrier ring <NUM> by way of the screw assembly 15a and presses the foam pad <NUM> against the capacitor board <NUM> and the capacitor board <NUM> against contact bus bars <NUM>. Because of this, the contact bus bars <NUM> are compressed between the transistor boards <NUM> and the capacitor board <NUM> and interconnect the transistor boards <NUM> and the capacitor board <NUM> in an electrically conductive manner. As is evident in <FIG>, the iron cores <NUM> are arranged in receptacles <NUM> of the carrier ring <NUM>. The receptacles <NUM> are provided for receiving phase terminals <NUM> of the electric motor <NUM>.

<FIG> shows a view of the carrier <NUM> with the control circuit board <NUM> from a side facing the second region 6b of the carrier <NUM>. The thickened portions <NUM> of the contact pins <NUM> engage in the receiving openings <NUM> of the control circuit board <NUM>, as a result of which the contact pins <NUM> are fixed in the control circuit board <NUM> in a force-fit manner. By way of the screw assembly 16a, the control circuit board <NUM> is screwed to the pressure plate <NUM>.

<FIG> shows a view of the inverter <NUM> without the cover <NUM> and <FIG> shows a view of the inverter <NUM> with the cover <NUM> from a side facing the first region 6a of the carrier <NUM>. As is evident in <FIG>, the battery terminals <NUM> project through the carrier ring <NUM> and the cooling plate <NUM> axially to the outside and the capacitors <NUM> are arranged on the capacitor board <NUM> symmetrically about the battery terminals <NUM>. In <FIG> it is noticeable that the cover <NUM> is screwed to the cooling plate <NUM> by means of the screw assembly 10a and the battery terminals <NUM> project through the cover <NUM> to the outside.

<FIG> shows a sectional view of the inverter <NUM>. The capacitor board <NUM> lies against the carrier ring <NUM> in the second region 6b of the carrier <NUM> and the capacitors <NUM> of the capacitor board <NUM> project through an opening of the carrier ring <NUM> into the first region 6a of the carrier <NUM>. The pressure plate <NUM> is firmly connected to the cooling plate <NUM>, so that the foam pad <NUM>, the capacitor board <NUM>, the contact bus bars <NUM>, and the transistor boards <NUM> are pressed together i.e. are sandwiched between the pressure plate <NUM> and the cooling plate <NUM>. Here, the capacitor board <NUM> is pressed against the contact bus bars <NUM> by the foam pad <NUM> and the pressure plate <NUM>. The transistor boards <NUM> are fixed on the carrier ring <NUM> in the first region 6a of the carrier <NUM> and distributed about the opening of the carrier ring <NUM> and thus about the capacitors <NUM>. The contact bus bars <NUM> are compressed between the capacitor board <NUM> and the transistor boards <NUM> and because of this the transistor boards <NUM> and the capacitor board <NUM> are electrically contacted with one another. The battery terminals <NUM> are fastened centrally on the capacitor board <NUM> and project through the opening of the carrier ring <NUM> out of the second region 6b into the first region 6a of the carrier <NUM>. Furthermore, the battery terminals are led through the cover <NUM> of the inverter axially to the outside. The control circuit board <NUM> is arranged in the second region 6b of the carrier <NUM> and screwed to the pressure plate <NUM>. By way of the contact pins <NUM> in the carrier <NUM>, the control circuit board <NUM> is electrically contacted with the transistor boards <NUM>.

<FIG> shows an exploded view and <FIG> shows a sectional view of an electric motor <NUM> according to the invention. The electric motor <NUM> comprises a rotor <NUM> and a stator <NUM> which electromagnetically interact with one another. Here, the rotor <NUM> is rotatable about an axis of rotation <NUM> which coincides with the centre axis <NUM> of the carrier <NUM> or inverter <NUM>. The stator <NUM> comprises multiple coils <NUM> and a stator housing <NUM> which receives the coils <NUM>. The rotor <NUM> is arranged in the stator <NUM> so that the coils <NUM> and the stator housing <NUM> encase the rotor <NUM>. The inverter <NUM> is arranged axially to the stator <NUM> and connected to the stator housing <NUM> in a fixed manner by way of a screw assembly 36a. For this purpose, continuous screw openings <NUM> are provided in the cooling plate <NUM> of the inverter <NUM>. The stator <NUM> is electrically contacted with the inverter <NUM> via multiple phase terminals <NUM>, for the purpose of which the phase terminals <NUM> engage in the receptacles <NUM> of the inverter <NUM> and are connected to the transistor boards <NUM> of the inverter <NUM> in an electrically conductive manner. The phase terminals <NUM> are distributed symmetrically about the axis of rotation <NUM> and arranged on assigned coil wires <NUM> radially outside.

<FIG> shows a view of the electric motor <NUM> without the inverter <NUM>. <FIG> show views of the individual phase terminal <NUM> in the electric motor <NUM>. The phase terminals <NUM> are arranged on the assigned coil wires <NUM> radially outside and are connected to these in an electrically conductive manner. The respective coil wire <NUM> engages radially in the respective phase terminal <NUM>. The respective phase terminal <NUM> is L-shaped and, with a pressure ring <NUM>, pressed against the stator <NUM> or against the stator housing <NUM>. Between the respective phase terminal <NUM> and the stator <NUM> or the stator housing <NUM>, an elastically deformable support <NUM> each is arranged. As is particularly clearly noticeable in <FIG>, the pressure ring <NUM> for the respective phase terminal <NUM> has two position projections <NUM>. The position projections <NUM> engage in position openings <NUM> of the respective phase terminal <NUM>, as a result of which the phase terminals <NUM> are fixed, correctly positioned, on the stator <NUM>.

Claim 1:
An inverter (<NUM>) for an electric motor (<NUM>),
- wherein the inverter (<NUM>) comprises a capacitor board (<NUM>) having multiple capacitors (<NUM>), multiple transistor boards (<NUM>) each having multiple transistors (<NUM>) and a control circuit board (<NUM>),
- wherein the capacitor board (<NUM>), the respective transistor boards (<NUM>) and the control circuit board (<NUM>) lie axially on top of one another and are electrically interconnected with one another,
- wherein the inverter (<NUM>), for the negative pole and for the positive pole, comprises a battery terminal (<NUM>) each, which is connected to the capacitor board (<NUM>) in an electrically conductive manner and axially projects from the capacitor board (<NUM>),
- wherein the positive and negative pole battery terminals (<NUM>) are identical to one another and are formed by a connector each with an external dielectric casing formed by a cover (<NUM>) of the inverter (<NUM>) and electrically conductive lines located inside the inverter (<NUM>) and project out of the cover (<NUM>) to the outside of the inverter (<NUM>),
- wherein each the respective battery terminal (<NUM>) comprises three pole contacts (<NUM>) for contacting with the capacitor board (<NUM>),
- wherein the capacitors (<NUM>) are annularly arranged on the capacitor board (<NUM>), characterized in
- that the two said battery terminals (<NUM>) are arranged side by side between the capacitors (<NUM>) and centrally on the capacitor board (<NUM>), and
- that the pole contacts (<NUM>) of the one battery terminal (<NUM>) and the pole contacts (<NUM>) of the other battery terminal (<NUM>) are arranged on the capacitor board (<NUM>) in a circle and alternating one another in the circle.