Electric machine with permanent magnet rotor

Abstract

An electric machine (1) having: a shaft (2); a rotor (4) having: a magnetic core (6) consisting of a series of laminations (12, 13) stacked together and having a plurality of axially oriented seats (10, 11); a plurality of magnetic poles (7), each having two permanent magnets (8); and a stator (5). The magnetic core (6) consists of alternating first laminations (12) and second laminations (13) different from the first laminations (12) such that at least ten second laminations (13) are interposed between two first laminations (12). For each seat (10), each first lamination (12) has two first fixed blades (14) which are parallel to each other, are arranged on the same side of the first seat (10) and are bent 90 DEG against the same larger side wall of the corresponding permanent magnet (8). For each seat (10), each first lamination (12) has a second fixed blade (15) oriented perpendicular to the corresponding first fixed blade (14) and bent 90 DEG against the smaller side wall of the corresponding first permanent magnet (8). Each of the second laminations (13) is entirely free of fixed blades bent against the corresponding permanent magnet (8).

Description

[0001] Cross-reference to related applications

[0002] This patent application claims priority to Italian Patent Application No. 102024000018064, filed on August 1, 2024, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to an electric motor with a permanent magnet rotor. Existing technology

[0004] Patent application EP4243249A1 describes a synchronous motor with a rotor having permanent magnets (i.e., arranged inside the rotor), primarily used in the automotive industry. In this motor, the rotor includes a magnetic core consisting of a series of stacked laminations and multiple permanent magnets embedded within the magnetic core; specifically, the magnetic core includes a series of axially arranged seats into which the permanent magnets are inserted. To ensure that the permanent magnets remain within the seats even when subjected to stresses generated by the rotor rotating at high speeds (which can even reach 30,000 rpm), the permanent magnets are attached to the inner wall of the seats by adhesive. However, adhesive bonding of the permanent magnets within the seats involves increased production costs, a (slight) increase in weight, and may also involve an increase in rotor imbalance (because the adhesive, subjected to the thrust of the permanent magnets during axial insertion, is typically distributed irregularly within the seats). That is, securing the permanent magnets with adhesive can lead to the development of imbalances within the rotor because it is difficult to achieve a uniform distribution of the adhesive within the seats.

[0005] Other examples of synchronous motors with permanent magnet rotors are described in patent applications US2008007131A1 and WO2006003244A2.

[0006] Patent application FR3129792A1 describes a rotor for a rotating electric motor, comprising: a permanent magnet having a long side and a short side in a cross-section perpendicular to the rotor's axis of rotation; and a magnetic core consisting of a series of stacked laminations and provided with a plurality of axially oriented seats containing the permanent magnets. In each seat, at least one lamination includes at least one tab extending within the seat to contact a corresponding permanent magnet and push the permanent magnet against an opposing surface of the seat.

[0007] Patent CN115378204B describes a method for manufacturing a laminated magnetic core for the rotor of a rotating electric machine. Detailed Implementation

[0008] The purpose of this invention is to provide a motor with a permanent magnet rotor that does not have the aforementioned disadvantages, and is also easy and cost-effective to manufacture.

[0009] According to the present invention, as claimed in the appended claims, an electric motor having a permanent magnet rotor is provided.

[0010] The claims describe preferred embodiments of the invention that form an integral part of this description. Attached Figure Description

[0011] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting exemplary embodiments of the invention, wherein:

[0012] · Figure 1 This is a schematic longitudinal sectional view of an electric motor with a permanent magnet rotor manufactured according to the present invention, wherein some parts have been removed for clarity.

[0013] · Figure 2 yes Figure 1 A partial exploded perspective view of the rotor core of the motor, with some parts removed for clarity;

[0014] · Figure 3 It constitutes Figure 1 A plan view of the first type of laminated rotor core of the electric motor;

[0015] · Figure 4 and Figure 5 They are Figure 3 Two magnified views of a seat without and with corresponding permanent magnets;

[0016] · Figure 6 and Figure 7 They are Figure 3 Two magnified views of a separate seat with and without corresponding permanent magnets;

[0017] · Figure 8 It constitutes Figure 1 A plan view of the second type of laminations of the rotor core of the motor;

[0018] · Figure 9 and Figure 10 They are Figure 8 Two magnified views of a seat without and with corresponding permanent magnets;

[0019] · Figure 11 and Figure 12 They are Figure 8 Two magnified views of the other seat, one without and one with corresponding permanent magnet laminations; and

[0020] · Figures 13 to 16 yes Figure 1 A schematic diagram showing the corresponding details of the rotor core of the motor, and in particular, Figure 13It is a sectional view along line XIII-XIII, and Figure 14 It is a sectional view along line XIV-XIV.

[0021] Preferred embodiments of the present invention

[0022] exist Figure 1 In this context, reference numeral 1 generally indicates a reversible synchronous motor for use in the automotive industry (i.e., one that can operate as both an electric motor that absorbs electrical energy and generates mechanical torque, and a generator that absorbs mechanical energy and generates electrical energy). The motor 1 includes a shaft 2 mounted to rotate about a central rotation axis 3; a permanent magnet rotor 4 having a cylindrical shape and keyed to the shaft 2 for rotation with the shaft 2; and a stator 5 having a cylindrical tubular shape arranged around the rotor 4 to surround the rotor 4.

[0023] according to Figure 2 As shown, the rotor 4 includes a magnetic core 6 and multiple magnetic poles 7, which are composed of permanent magnets 8 and 9 embedded in the magnetic core 6.

[0024] according to Figure 2 Additionally, each magnetic pole 7 includes two permanent magnets 8, which are axially positioned within the magnetic core 6 at corresponding seats 10 (in... Figure 3 and Figure 8 In a preferred embodiment, two permanent magnets 8 are arranged adjacent to each other at a certain distance from each other in each magnetic pole 7, such that the two permanent magnets 8 form a "V" shape (with an obtuse angle at the apex); that is, in each magnetic pole 7, two permanent magnets 8 are arranged adjacent to each other and tilted to form an obtuse angle in a corresponding pair of spaced-apart seats 10, such that between the two seats 10, the magnetic core 6 has a radial orientation and a bridge spanning the two permanent magnets 8. Furthermore, each magnetic pole 7 includes two permanent magnets 9, which are axially positioned within the magnetic core 6 at corresponding seats 11 (in... Figure 3 and Figure 8 In a preferred embodiment, two permanent magnets 9 are arranged adjacent to each other at a certain distance from each other in each magnetic pole 7, such that the two permanent magnets 9 form a "V" shape (with an obtuse angle at the apex); that is, in each magnetic pole 7, two permanent magnets 9 are arranged adjacent to each other and are inclined to form an obtuse angle in a corresponding pair of spaced-apart seats 11, such that between the two seats 11, the magnetic core 6 has a radial orientation and a bridge spanning the two permanent magnets 9. In particular, in each magnetic pole 7, the two permanent magnets 9 are smaller than the two permanent magnets 8, are arranged more radially outside the two permanent magnets 8, and are arranged in the region defined by the two permanent magnets 8.

[0025] It is important to remember that an obtuse angle is a convex angle, with a width greater than 90° (corresponding to a right angle) and less than 180° (corresponding to a straight angle); in other words, an obtuse angle is greater than a right angle (i.e., greater than 90°) and less than a straight angle (i.e., less than 180°).

[0026] According to the preferred embodiment shown in the accompanying drawings, in each magnetic pole 7, the obtuse angle formed between the two permanent magnets 8 is smaller than the obtuse angle formed between the two permanent magnets 9. Specifically, in each magnetic pole 7, the obtuse angle formed between the two permanent magnets 8 is equal to 110°, and the obtuse angle formed between the two permanent magnets 9 is equal to 120°.

[0027] According to the preferred embodiment shown in the accompanying drawings, in each magnetic pole 7, a first distance exists between the proximal ends (i.e., the two ends closest to each other) of the two permanent magnets 8, which is greater than a second distance exists between the proximal ends (i.e., the ends closest to each other) of the two permanent magnets 9. Similarly, in each magnetic pole 7, a third distance exists between the proximal ends (i.e., the two ends closest to each other) of the two seats 10, which is greater than a fourth distance exists between the proximal ends (i.e., the two ends closest to each other) of the two seats 11.

[0028] Each permanent magnet 8 or 9 has a parallelepiped shape, which is externally defined by two larger sidewalls and two smaller sidewalls, the two larger sidewalls being parallel to and opposite to each other, and the two smaller sidewalls being parallel to and opposite to each other and perpendicular to the larger sidewalls; obviously, the two larger sidewalls have a larger extension (area) than the two smaller sidewalls.

[0029] The magnetic core 6 consists of a series of stacked laminations 12 and 13 (different from each other, as will be explained below) and has a plurality of spaced-apart axial seats 10 and 11 into which permanent magnets 8 and 9 are inserted (as previously described). In particular, laminations 12 and laminations 13 (different from laminations 12, as will be explained below) alternate, such that at least ten laminations 13 are inserted between two laminations 12; in particular, at least fifteen, and preferably at least twenty, laminations 13 are inserted between two laminations 12 (in a preferred embodiment, between twenty and thirty laminations 13 are inserted between two laminations 12).

[0030] according to Figure 4 and Figure 5As shown, for each seat 10, each lamination 12 has two and only two fixing blades 14, which are parallel to each other, arranged on the same side of the seat 10, and bent 90° against the same larger sidewall of the corresponding permanent magnet 8 housed in the seat 10 (according to different embodiments not shown, for each seat 10, each lamination 12 has at least two fixing blades 14, i.e., more than two fixing blades 14 may be provided for each seat 10). Furthermore, for each seat 10, each lamination 12 has a single fixing blade 15, which is oriented perpendicular to the corresponding fixing blade 14 and bent 90° against the smaller sidewall of the corresponding permanent magnet 8 housed in the seat 10 (according to different embodiments not shown, for each seat 10, each lamination 12 has two or more fixing blades 15).

[0031] According to different embodiments not shown, the number of fixing blades 14 in each seat 10 varies, ranging from a minimum of two to a maximum of four or five; similarly, according to different embodiments not shown, the number of fixing blades 15 in each seat 10 varies, ranging from a minimum of one to a maximum of two or three. Generally, the number of fixing blades 14 and 15 is determined based on the dimensions (length and width) of the fixing blades 14 and 15, the dimensions (length and width) of each permanent magnet 8, and the desired retaining force that the fixing blades 14 and 15 must apply to each permanent magnet 8.

[0032] According to a preferred embodiment, each seat 10 has a flat wall 16 opposite to two fixed blades 14, and the two fixed blades 14 push the corresponding permanent magnet 8 housed in the seat 10 against the flat wall; that is, the corresponding permanent magnet 8 is stacked between the two fixed blades 14 and the flat wall 16 of the seat 10, and is pushed against the flat wall 16 of the seat 10 by the two fixed blades 14.

[0033] According to a preferred embodiment, each seat 10 has a tooth 17 that protrudes into the seat 10 and is oriented perpendicular to the wall 16, and a fixing blade 15 pushes a corresponding permanent magnet 8 housed in the seat 10 against the tooth; that is, the corresponding permanent magnet 8 is stacked between the fixing blade 15 and the tooth 17 of the seat 10 and is pushed against the tooth 17 of the seat 10 by the fixing blade 15.

[0034] according to Figure 6 and Figure 7As shown, for each seat 11, each lamination 12 has a single retaining blade 18, which is bent 90° relative to the larger sidewall of the corresponding permanent magnet 9 housed in the second seat 11; furthermore, for each seat 11, each lamination 12 has a single retaining blade 19, which is oriented perpendicular to the corresponding retaining blade 18 and bent 90° relative to the smaller sidewall of the corresponding permanent magnet 9 housed in the seat 11. According to different embodiments not shown, the number of retaining blades 18 in each seat 11 varies, ranging from a minimum of one to a maximum of two or three; similarly, according to different embodiments not shown, the number of retaining blades 19 in each seat 11 varies, ranging from a minimum of one to a maximum of two or three. Generally, the number of retaining blades 18 and 19 is determined based on the dimensions (length and width) of the retaining blades 18 and 19, the dimensions (length and width) of each permanent magnet 9, and the desired holding force that the retaining blades 18 and 19 must apply to each permanent magnet 9.

[0035] According to a preferred embodiment, each seat 11 has a flat wall 20 opposite to a fixed blade 19, and the fixed blade 19 pushes the corresponding permanent magnet 9 housed in the seat 11 against the flat wall; that is, the corresponding permanent magnet 9 is stacked between the fixed blade 19 and the flat wall 20 of the seat 11, and is pushed against the flat wall 20 of the seat 11 by the fixed blade 19.

[0036] According to a preferred embodiment, each seat 11 has a tooth 21 that protrudes into the seat 11 and is oriented perpendicular to the wall 20, and the fixing blade 19 pushes the corresponding permanent magnet 9 housed in the seat 11 against the tooth; that is, the corresponding permanent magnet 9 is stacked between the fixing blade 19 and the tooth 21 of the seat 11 and is pushed against the tooth 21 of the seat 11 by the fixing blade 19.

[0037] according to Figures 8 to 11 As shown, unlike the stack 12 with fixed blades 14 and 15, the stack 13 has no fixed blades bending against the permanent magnets 8 and 9. That is, fixed blades 14-15 and 18-19 are not present in each stack 12 or 13, but only in the stack 12, such that there is a certain axial distance between the fixed blades 14-15 or 18-19 and the subsequent fixed blades 14-15 or 18-19 (equal to the thickness of the stack 13 inserted between two subsequent stacks 12), such as... Figures 13 to 16 As shown.

[0038] Generally speaking, the number of laminations 13 inserted between the two laminations 12 is determined based on the dimensions (length and width) of the fixing blades 14-15 and 18-19, the dimensions (length and width) of the permanent magnets 8 and 9, the number of permanent magnets 8 and 9 present inside the magnetic core 6, and the desired holding force that the fixing blades 14-15 and 18-19 must apply to the permanent magnets 8 and 9.

[0039] according to Figures 13 to 15 In the preferred embodiment shown, each seat 10 in all the stacked pieces 13 has three recesses 22 (shown in...). Figure 9 and Figure 10 (in the middle), these three recesses are arranged in the regions of the three fixed blades 14 and 15 of the laminate 12 and create corresponding empty spaces for the curved portions of the fixed blades 14 and 15, and similarly, each seat 11 has two recesses 23 (shown in the middle). Figure 11 and Figure 12 In the middle), these two recesses are arranged in the regions of the two fixed blades 18 and 19 of the lamination 12 and create corresponding empty spaces for the curved portions of the fixed blades 18 and 19. In other words, all the laminations 13 are identical to each other, and therefore, in all the laminations 13, each seat 10 has a recess 22 and each seat 11 has a recess 23.

[0040] exist Figures 13 to 16 The space left by the recesses 22 of the fixing blades 14 and 15 is schematically shown, while the space left by the recess 23 of the fixing blade 18 is exactly similar and therefore requires no further explanation (relative to...). Figure 11 and Figure 12 The content already shown is supplementary.

[0041] according to Figure 16In the alternative embodiment shown, only in a set of laminations 13 arranged to contact the corresponding laminations 12, each seat 10 has three recesses 22 arranged in the regions of the three fixing blades 14 and 15 of the lamination 12 and creating corresponding empty spaces for the curved portions of the fixing blades 14 and 15, and each seat 11 has two recesses 23 arranged in the regions of the two fixing blades 18 and 19 of the lamination 12 and creating corresponding empty spaces for the curved portions of the fixing blades 18 and 19; conversely, the remaining laminations 13 have no recesses 22 and 23. That is, in this embodiment, there are two types of laminations 13: a first type of lamination 13, in which each seat 10 has a recess 22 and each seat 11 has a recess 23; and a second type of lamination 13, in which the seat 10 has no recess 22 and the seat 11 has no recess 23. The first type of laminations 13 (with recesses 22 and 23) are arranged in the region where the fixed blades 14-15 and 18-19 bent against the permanent magnets 8 and 9 are engaged (i.e., the region where the fixed blades 14-15 and 18-19 bent against the permanent magnets 8 and 9 are arranged), while the other groups of the second type of laminations 13 (without recesses 22 and 23) are arranged in the region where the fixed blades 14-15 and 18-19 not bent against the permanent magnets 8 and 9 are not engaged (i.e., the region where the fixed blades 14-15 and 18-19 bent against the permanent magnets 8 and 9 are not present). Therefore, the groups of the first type of laminations 13 alternate with the groups of the second type of laminations 13 (e.g., ...). Figure 16 (As shown).

[0042] The embodiments described herein can be combined with each other without departing from the scope of protection of this invention.

[0043] The aforementioned motor 1 has many advantages.

[0044] First, in the aforementioned motor 1, permanent magnets 8 and 9 are firmly fixed in their respective seats 10 and 11 without the use of adhesive; therefore, the production cost of the aforementioned motor 1 is reduced, and the rotor 4 is more balanced.

[0045] Furthermore, the aforementioned motor 1 is easy and cost-effective to manufacture because the fixed blades 14-15 and 18-19 can be easily obtained during the shearing of the lamination 12 without increasing production costs, and similarly, the recesses 22 and 23 can also be easily obtained during the shearing of the lamination 13 without increasing production costs.

[0046] List of reference numerals in the attached figures

[0047] 1 motor

[0048] 2-axis

[0049] 3. Rotation axis

[0050] 4 rotors

[0051] 5 stators

[0052] 6 magnetic cores

[0053] 7 magnetic poles

[0054] 8 permanent magnets

[0055] 9 permanent magnets

[0056] 10 seats

[0057] 11 seats

[0058] 12 stacks

[0059] 13 stacked pieces

[0060] 14 Fixed blades

[0061] 15 fixed blades

[0062] 16 walls

[0063] 17 teeth

[0064] 18 fixed blades

[0065] 19 Fixed blades

[0066] 20 walls

[0067] 21 teeth

[0068] 22 Recessed area

[0069] 23 Recessed area

Claims

1. An electric motor (1), the electric motor comprising: Shaft (2), which is mounted to rotate about a central rotation axis (3); The rotor (4), carried by the shaft (2), has: a magnetic core (6) consisting of a series of stacked laminations (12, 13) and having a plurality of axially oriented seats (10, 11); and a plurality of magnetic poles (7), each magnetic pole comprising two first permanent magnets (8) and two second permanent magnets (9), the two first permanent magnets being arranged adjacent to each other and inclined to form a first obtuse angle in a corresponding pair of spaced-apart first seats (10), and the two second permanent magnets being arranged adjacent to each other and inclined to form a second obtuse angle in a corresponding pair of spaced-apart second seats (11); as well as Stator (5), the stator being arranged around the rotor (4) to surround the rotor (4); Each of the first permanent magnets or the second permanent magnets (8,9) has a parallelepiped shape, which is defined externally by two larger sidewalls and by two smaller sidewalls, the two larger sidewalls being parallel to and opposite to each other, and the two smaller sidewalls being parallel to and opposite to each other and perpendicular to the larger sidewalls. In each magnetic pole (7), the two second permanent magnets (9) are smaller than the two first permanent magnets (8), are arranged more radially outward than the two first permanent magnets (8), and are arranged in the region defined by the two first permanent magnets (8); The magnetic core (6) is composed of alternating first laminations (12) and second laminations (13) different from the first laminations (12), such that at least ten second laminations (13) are inserted between two first laminations (12); The motor (1) is characterized in that: For each first seat (10), each first stack (12) has at least two first fixed blades (14), which are parallel to each other, arranged on the same side of the first seat (10), and bent at 90° against the same larger sidewall of the corresponding first permanent magnet (8) housed in the first seat (10). For each first seat (10), each first stack (12) has at least one second fixed blade (15) oriented perpendicular to the corresponding first fixed blade (14) and bent 90° against the smaller sidewall of the corresponding first permanent magnet (8) housed in the first seat (10). For each second seat (11), each first lamination (12) has at least one third fixed blade (18), which is bent 90° against the larger sidewall of the corresponding second permanent magnet (9) housed in the second seat (11); and For each second seat (11), each first lamination (12) has at least one fourth fixing blade (19), said at least one fourth fixing blade being oriented perpendicular to the corresponding third fixing blade (18) and bent 90° against the smaller sidewall of the corresponding second magnet (9) housed in the second seat (11); and Each second stack (13) has no fixed blades that bend against the first permanent magnet and the second permanent magnet (8,9).

2. The motor (1) according to claim 1, wherein each first seat (10) has a flat wall (16) opposite to the two first fixed blades (14), and the two first fixed blades (14) push the corresponding first permanent magnet (8) housed in the first seat (10) against the flat wall.

3. The motor (1) according to claim 1 or 2, wherein each first seat (10) has a first tooth (17) protruding into the first seat, and the second fixing blade (15) pushes the corresponding first permanent magnet (8) housed in the first seat (10) against the first tooth.

4. The motor (1) according to claim 1, 2 or 3, wherein, In each second stack (13), each first seat (10) has a first recess (22) arranged in the region of the fixed blades (14, 15) of the first stack (12) and creating a corresponding empty space for the curved portion of the fixed blades (14, 15).

5. The motor (1) according to claim 1, 2 or 3, wherein: A second stack (13) of the first type is provided, wherein each first seat (10) has a first recess (22) arranged in the region of the first fixed blade and the second fixed blade (14, 15) of the first stack (12), and creating a corresponding empty space for the curved portion of the first fixed blade and the second fixed blade (14, 15); A second type of second stack (13) is provided, wherein each first seat (10) does not have the first recess (22); and A group of the first type of laminations (13) is arranged in the region where the first fixed blade and the second fixed blade (14, 15) of the first lamination (12) are arranged against the first permanent magnet (8), and other groups of the second type of laminations (13) are arranged in the region where the first fixed blade and the second fixed blade (14, 15) of the first lamination (12) are not arranged against the first permanent magnet (8).

6. The motor (1) according to any one of claims 1 to 5, wherein each second seat (11) has a flat wall (20) opposite to the third fixed blade (18), and the third fixed blade (18) pushes the corresponding second permanent magnet (9) housed in the second seat (11) against the flat wall.

7. The motor (1) according to any one of claims 1 to 6, wherein each second seat (11) has a second tooth (21) protruding into the second seat (11), and the fourth fixing blade (19) pushes the corresponding second permanent magnet (9) housed in the second seat (11) against the second tooth.

8. The motor (1) according to any one of claims 1 to 7, wherein, In each second stack (13), each second seat (11) has a second recess (23) arranged in the region of the fixed blades (18, 19) of the first stack (12) and creating a corresponding empty space for the curved portion of the fixed blades (18, 19).

9. The motor (1) according to any one of claims 1 to 7, wherein: A second stack (13) of the first type is provided, wherein each second seat (11) has a second recess (23) arranged in the region of the third fixed blade and the fourth fixed blade (18, 19) of the first stack (12), and creating a corresponding empty space for the curved portion of the third fixed blade and the fourth fixed blade (18, 19); Provide a second type of second stack (13), wherein each second seat (11) does not have the second recess (23); and A group of the first type of laminations (13) is arranged in the region where the third and fourth fixed blades (18, 19) of the first laminations (12) are arranged against the second permanent magnet (9), and other groups of the second type of laminations (13) are arranged in the region where the third and fourth fixed blades (18, 19) of the first laminations (12) are not arranged against the second permanent magnet (8).

10. The motor (1) according to any one of claims 1 to 9, wherein: For each first seat (10), each first lamination (12) has two and only two first fixed blades (14) and a single second fixed blade (15); and For each second seat (11), each first stack (12) has a single third fixed blade (18) and a single fourth fixed blade (19).

11. The motor (1) according to any one of claims 1 to 10, wherein at least fifteen, and preferably at least twenty, second laminations (13) are inserted between two first laminations (12).

12. The motor (1) according to any one of claims 1 to 11, wherein each magnetic pole (7) comprises exactly two and only two first permanent magnets (8) arranged adjacent to each other and tilted to form an obtuse angle, and exactly two and only two second permanent magnets (9) arranged adjacent to each other and tilted to form an obtuse angle.

13. The motor (1) according to any one of claims 1 to 12, wherein, In each magnetic pole (7), the first obtuse angle formed between the two first permanent magnets (8) is smaller than the second obtuse angle formed between the two second permanent magnets (9).

14. The motor (1) according to any one of claims 1 to 13, wherein, In each magnetic pole (7), the first obtuse angle formed between the two first permanent magnets (8) is equal to 110°, and the second obtuse angle formed between the two second permanent magnets (9) is equal to 120°.

15. The motor (1) according to any one of claims 1 to 14, wherein: In each magnetic pole (7), a first distance exists between the proximal ends of the two first permanent magnets (8) greater than a second distance exists between the proximal ends of the two second permanent magnets (9); and In each magnetic pole (7), the third distance between the proximal ends of the two first seats (10) is greater than the fourth distance between the proximal ends of the two second seats (11).

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