Disc brake

Abstract

The invention relates to a disc brake (1) comprising a brake disc (2), two brake pads (3) facing each other, each brake pad (3) comprising a backing plate (4) and a lining material (5), each brake pad (3) comprising an input side (Si) and an output side (So), and a clamping unit comprising the brake pads (3) and a brake caliper (8), according to the invention, the brake caliper comprises a tensioning strut (9) which connects a portion (10) supporting one of the two brake pads (3) and a portion supporting the other of the two brake pads (3), the tensioning strut (9), the portion (10) and at least one of the two brake pads (3) are configured to deform during braking such that an application point of a resultant reaction force (FRes) from the brake disc (2) to the brake pads (3) is closer to the input side (Si) than to the output side (So).

Description

Technical Field

[0001] The present invention relates to a disc brake, in particular to a disc brake for a vehicle. Background Art

[0002] When disc brakes are used to brake a vehicle, the brake discs and, in particular, the brake pads of disc brakes wear over time. The problem is that the wear is uneven and there is a taper. The taper leads to an undefined pressure point until maximum braking effect can no longer be achieved.

[0003] Figure 1 A schematic diagram of a disc brake 1 according to the prior art is shown. The disc brake 1 includes a brake disc 2, a brake pad 3, and a brake caliper (not shown). When the vehicle moves forward, the brake disc 2 rotates about an axis A in a direction indicated by an arrow R, and the brake pad 3 includes a back plate 4 and a lining material 5, the back plate 4 is configured to be supported on a brake caliper (not shown) of the disc brake 1, and the lining material 5 is attached to the back plate 4. The lining material 5 includes a friction surface 6, and when the brake pad 3 is pressed against the brake disc 2 by a braking force F, the friction surface applies a friction force F to the rotating brake disc 2. R , through the friction force F R and the lever h between the friction surface 6 and the support area of ​​the brake pad 3, where the brake pad 3 is supported on the brake caliper of the disc brake 1, a moment M is generated about the point P. Due to the elasticity of the brake pad 3 and the brake caliper, this moment causes the brake pad 3 to rotate about the point P, so that the wear at the end of the lining material 5 opposite the point P is greater than the wear of the lining material 5 at the point P. This effect is called conical wear.

[0004] Nowadays, in order to avoid conical wear, the point at which the braking force is applied to the brake pad is selected so that it generates a compensating torque, as shown for example in document EP 3245417 B1; however, in order to obtain a suitable effect, this point must be varied according to the wear of the brake pad.

[0005] On the other hand, the components of the disc brake are designed to be particularly strong and large in size in order to withstand the cone wear torque and thus avoid cone wear. However, this measure increases the weight and cost of the brake components. Summary of the invention

[0006] The object of the present invention is to solve the above mentioned problems and avoid the negative effects of cone wear.

[0007] This object is achieved by a disk brake according to claim 1 , advantageous further developments of the invention being contained in the dependent claims.

[0008] According to one aspect of the present invention, a disc brake comprises a brake disc, two brake pads facing each other, and a clamping unit, wherein the brake pads respectively comprise a back plate and a lining material, each brake pad comprises an input side and an output side, wherein the input side is the front side of the brake pad when the brake disc rotates in a rotation direction when the vehicle moves in a forward direction, and the output side is the front side of the brake pad in the rotation direction R of the brake disc and the output side is the input side S i On the opposite side, the clamping unit includes the brake pad and a brake caliper, the brake caliper including a tensioning strut, the tensioning strut connecting a portion supporting one of the two brake pads and a portion supporting the other of the two brake pads, wherein at least one of the "tensioning strut, the portions and the two brake pads" is configured to deform during braking so that a point of application of a resultant reaction force from the brake disc to the brake pad is closer to an input side than to an output side.

[0009] The resultant reaction force from the brake disc to the brake pad, which is closer to the input side than to the output side, generates a compensating moment in the direction opposite to the moment causing conical wear.

[0010] In an advantageous embodiment of the disc brake, the brake disc has an axis, and the lining material comprises an inner edge facing the axis and an outer edge facing away from the axis, and at least one of "the two brake pads and the brake caliper" is configured to deform during braking so that the point of application of the resultant reaction force from the brake disc to the brake pad is closer to the outer edge than to the inner edge.

[0011] According to a further advantageous embodiment of the disk brake, the back plate has a non-uniform thickness and is thinner towards the output side than towards the input side.

[0012] In a further advantageous embodiment of the disk brake, the tensioning strut located closer to the input side has a different stiffness than the tensioning strut located closer to the output side.

[0013] According to a further advantageous embodiment of the disk brake, the tension struts are produced from the same material and the cross section of the tension struts closer to the input side differs from the cross section of the tension struts closer to the output side.

[0014] According to a further advantageous embodiment of the disk brake, the rigidity of the tensioning strut closer to the input side is greater than the rigidity of the tensioning strut closer to the output side.

[0015] In a further advantageous embodiment of the disc brake, the brake disc has an axis and the lining material comprises an inner edge facing the axis and an outer edge facing away from the axis, the inner edge of the respective tensioning strut being stiffer than the outer edge.

[0016] In another advantageous embodiment of the disc brake, the friction surface of the lining material is configured to apply friction to a rotating brake disc, the lining material comprising a groove in the friction surface extending toward the back plate, and in the plane of the friction surface, the groove has a width and a centerline of the width of the groove, and the friction surface has a centroid, the centerline of the width of the groove is located at a different position from the centroid, so that the centerline does not pass through the centroid.

[0017] In a further advantageous embodiment of the disk brake, the friction surface is designed to contact a rotating brake disk for braking, and the grooves are arranged in a direction perpendicular to a tangential direction of the rotational direction of the brake disk.

[0018] According to a further advantageous embodiment of the disk brake, the friction surface is designed to contact a rotating brake disk for braking, and the grooves are arranged in a direction parallel to a tangential direction of the rotational direction of the brake disk.

[0019] According to a further advantageous embodiment of the disk brake, the groove has a concave or rectangular cross section, in particular a U-shaped or V-shaped cross section.

[0020] In another advantageous embodiment of the disk brake, the side surfaces of the V-shaped groove respectively enclose different angles with the friction surface.

[0021] According to a further advantageous embodiment of the disk brake, the groove extends as far as the back plate.

[0022] In a further advantageous embodiment of the disk brake, the cross section of the recess changes in the direction along the friction surface.

[0023] The present invention will be described below by way of embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram showing a disc brake according to the prior art;

[0025] Figure 2 A schematic diagram showing a first embodiment of a disc brake according to the present invention in the axial direction of the brake disc;

[0026] Figure 3 Show Figure 2 A schematic diagram of a brake pad of an embodiment of the present invention in a direction perpendicular to the axis of the brake disc;

[0027] Figure 4 A schematic diagram showing a disc brake of a second embodiment;

[0028] Figure 5 A schematic diagram showing a brake pad for a disc brake of a second embodiment;

[0029] Figure 6 shows a cross-sectional view of a disc brake according to a third embodiment, wherein the brake caliper is cut in a cutting plane including the brake disc surface, so that the tensioning struts are also cut, and a top view of one of the brake pads is presented in the figure;

[0030] Figure 7 A schematic diagram showing a disc brake according to a fourth embodiment;

[0031] Figure 8 Show Figure 7 Schematic diagram of alternative disc brakes; and

[0032] Fig. 9 A principle diagram of a disc brake according to a fifth embodiment is shown. DETAILED DESCRIPTION

[0033] Figure 2 A schematic diagram showing a first embodiment of a disc brake 1 according to the invention in the direction of the axis A of the brake disc 2, and Figure 3 Show Figure 2 Schematic diagram of the brake pad 3 of the embodiment along a direction perpendicular to the axis A of the brake disc 2.

[0034] The disc brake 1 of the vehicle includes a brake disc 2 and a brake pad 3. When the vehicle moves in the forward direction, the brake disc 2 rotates in the rotation direction R. Further, the brake pad 3 includes a back plate 4 and a lining material 5. The back plate 4 is configured to be supported on the brake caliper ( Figure 2 and 3 The back plate 4 is not shown in the figure, and the lining material 5 is attached to the back plate 4. The lining material 5 includes a friction surface 6, which applies a friction force F to the rotating brake disc 2 when the brake pad 3 is pressed against the brake disc 2 by the braking force F. R .

[0035] In addition, the lining 5 has a groove 7 in the friction surface 6 extending toward the back plate 4. The groove 7 divides the friction surface 6 into two partial friction surfaces 6', 6'' of the entire friction surface 6. In the plane of the friction surface 6, the groove 7 has a width 7w and a center line 7c along the friction surface 6 of the width 7w. Without considering the groove 7, the entire friction surface 6 is defined as the friction surface 6 of the lining 5. The entire friction surface 6 has a centroid C, and the groove 7 is located at a position different from the centroid so that it does not pass through the centroid C. In particular, the groove 7 is offset from the centroid so that when the brake disc 2 rotates in the rotation direction R when the vehicle moves in the forward direction, it is located on the input side S of the brake disc 2. i The surface area of ​​the friction surface 6' of the part of the brake pad 3 is larger than that of the part of the brake pad 3 on the output side S o (It is in the rotation direction R of the brake disc 2 and the entry side Si The groove 7 is arranged in a direction perpendicular to the tangential direction of the rotation direction R of the brake disc 2, and is therefore arranged radially along the brake disc 2.

[0036] In cross section, the groove 7 has a V-shape, wherein the sides 7', 7" of the V-shaped groove 7 respectively enclose different angles with the friction surface 6. In alternative embodiments, the groove 7 has a U-shape, a V-shape with the sides 7', 7" enclosing the same angle with the friction surface 6, a concave shape or a rectangle.

[0037] The groove 7 extends as far as the backing plate 4. In an alternative embodiment, the groove 7 does not extend to the backing plate 4, but its depth is less than the thickness of the backing material 5.

[0038] The cross section of the groove 7 is the same in the direction along the friction surface 6 . In an alternative embodiment, the cross section of the groove varies in the direction along the friction surface 6 .

[0039] For braking, the friction surface 6 contacts the rotating brake disc 2, and the groove 7 is arranged along the friction surface 6 in a direction perpendicular to the tangent direction of the rotation direction R of the brake disc 2. In alternative embodiments, alternatively or additionally, the groove 7 is arranged along the friction surface 6 in a direction parallel to the tangent direction of the rotation direction R of the brake disc 2; the groove 7 encloses another angle with the tangent direction of rotation of the brake disc 2 along the friction surface 6; or the groove 7 is concentric with the brake disc 2.

[0040] In use, the torque M that may cause taper wear is determined by the compensation torque M comp The compensation moment is caused by different reaction forces F1 and F2 acting in the respective centroids of the partial friction surfaces 6', 6'' of the friction surface 6. The pressure generated by the braking force F on the friction surface 6 is uniform, and therefore, the different sizes of the parts 6', 6'' of the friction surface 6 lead to different reaction forces F1 and F2.

[0041] Figure 4 A schematic diagram showing a disc brake 1 according to a second embodiment, Figure 5 A schematic diagram of a brake pad 3 of a disc brake 1 according to a second embodiment is shown.

[0042] The disc brake 1 comprises a brake disc 2, two brake pads 3 facing each other and a brake caliper 8. The brake pads 3 each comprise a back plate 4 and a lining material 5. Each brake pad 3 comprises an input side S i and output side S oThe brake caliper 8 and the brake pad 3 are configured so that the brake pad 3 is supported on the brake caliper 8. In particular, the brake caliper 8 includes a tensioning strut 9 connecting a portion 10 of the brake caliper 8 supporting one of the two brake pads 3 and a portion 10 of the brake caliper 8 supporting the other of the two brake pads 3. At least one of the “brake caliper 8 and the two brake pads 3” is configured to deform during braking so that the resultant reaction force F from the brake disc 2 to the brake pad 3 is Res The application point is S away from the input side i Ratio to the output side S o The brake lining 3 , which in each case comprises a backing plate 4 and a lining material 5 , and the brake caliper 8 , which comprises a tensioning strut 9 and a section 10 , are components of a clamping unit.

[0043] The back plate 4 has a non-uniform thickness, and the thickness toward the output side is smaller than the thickness toward the input side. Due to this characteristic, the back plate 4 and thus the brake pad 3 toward the output side S o The rigidity of the back plate 4 and thus the brake pad 3 toward the input side S i This makes the output side S from the brake disc 2 to the brake pad 3 o The reaction force of Res The application point is S away from the input side i Ratio output side S o Closer. Due to the resultant reaction force F Res The application point is located closer to the input side S i , thus generating a compensation torque M comp , and thus the conical wear of the lining material 5 in the tangential direction of the brake disc 2 can be reduced or eliminated.

[0044] The brake disc 2 has an axis A, and the lining material 5 comprises an inner edge E facing the axis A. i and the outer edge E facing away from the axis A o At least one of the “brake caliper 8 and the two brake pads 3” is configured to deform during braking so that the resultant reaction force F from the brake disc 2 to the brake pad 3 Res The distance from the application point to the outer edge E o Than inner edge E i By means of this characteristic, the conical wear of the lining material 5 in the radial direction of the brake disk 2 can be reduced or eliminated.

[0045] In an alternative embodiment, the brake caliper 8 and the two brake pads 3 are not both configured to deform during braking, so that the resultant reaction force F from the brake disc 2 to the brake pads 3 Res The distance from the application point to the outer edge E o Than inner edge E iCloser.

[0046] Although not shown in the drawings of this embodiment, the groove 7 of the first embodiment may alternatively be provided in the brake pad 3 of the second embodiment.

[0047] Figure 6 A cross-sectional view of a disc brake 1 according to a third embodiment is shown, wherein the brake caliper 8 is cut in a cutting plane including the surface of the brake disc 2 , so that the tensioning struts 9 are also cut, and a top view of one of the brake pads 3 is presented.

[0048] The brake caliper 8 comprises a tensioning strut 9, which connects a portion 10 of the brake caliper 8 supporting one of the two brake pads 3 and a portion of the brake caliper 8 supporting the other of the two brake pads 3. The portion 10 supporting the brake pad 3 and the tensioning strut 9 are formed in one piece, so that the portion supporting the brake pad 3 and in particular the tensioning strut 9 are made of the same material. In an alternative embodiment, the brake caliper 8 is composed of a plurality of parts composed of different materials.

[0049] Closer to the input side S of the brake pad 3 i The tensioning strut 9 has an output side S closer to the brake pad 3. o In particular, in the embodiment with the brake caliper 8 formed in one piece from the same material, the tensioning strut 9 closer to the input side S i The cross section of the tensioning strut 9 differs from that closer to the output side S o The cross section of the tensioning strut 9.

[0050] In particular, closer to the input side S i The stiffness of the tensioning strut 9 is greater than that closer to the output side S o The stiffness of the tensioning strut 9.

[0051] This feature enables Figure 5 Similar effect as shown. Due to the closer to the input side S i The tensioning strut 9 is closer to the output side S o The tensioning struts 9 have different stiffnesses, especially when closer to the input side S i The stiffness of the tensioning strut 9 is greater than that closer to the output side S o The stiffness of the tensioning strut 9 is such that the resultant reaction force F is achieved. Res A similar displacement of comp , and reduce or eliminate taper wear.

[0052] Also in this embodiment, the lining material 5 comprises an inner edge E facing the axis A. i and the outer edge E facing away from the axis Ao The stiffness of the tension struts 9 is distributed so that the stiffness of one of the tension struts 9 closer to the inner edge is greater than that of the other closer to the outer edge. o This is achieved by choosing the shape of the cross section in an appropriate way. In order to reduce or eliminate the i To the outer edge E o The conical wear in the radial direction is accordingly set in each tensioning strut 9 .

[0053] In an alternative embodiment, both brake pads 3 and brake caliper 8 are not all configured to deform during braking, so that the resultant reaction force F from brake disc 2 to brake pad 3 is Res The distance from the application point to the outer edge E o Than inner edge E i Closer.

[0054] Although not shown in the drawings of this embodiment, the groove 7 of the first embodiment may alternatively be provided in the brake pad 3 of the third embodiment.

[0055] Figure 7 A principle diagram of a disc brake 1 according to a fourth embodiment is shown.

[0056] The disc brake 1 comprises a brake disc 2, two brake pads 3 facing each other, wherein the brake pads 3 each comprise a back plate 4 and a lining material 5. Each brake pad 3 comprises an input side S i and output side S o The lining material 5 has a thickness towards the brake disk 2 which increases from the output side S o To the input side S i The disc brake 1 further comprises a brake caliper 8, the brake caliper 8 and the brake pad 3 being configured such that the brake pad 3 is supported on the brake caliper 8, and the brake caliper 8 is configured to be supported on the bracket 11 of the vehicle in a rotatable manner. o On the other hand, the back plate 4 of each brake pad 3 is configured to be rotatably supported by the bracket 11 .

[0057] The back plate 4 includes a fixed bearing member to support the back plate 4 on the bracket 11 in a rotatable manner via the fixed bearing.

[0058] In operation, when a braking force F is applied to the brake pad 3, the brake pad 3 rotates about the fixed bearing, so that the cone wear effect is automatically taken into account when the lining material 5 is worn by changing the thickness of the lining material 5, so as to avoid the problems usually caused by cone wear. The desired wear distribution can be achieved by the position of the braking force application point at an optimal predetermined distance relative to the fixed bearing.

[0059] Figure 8 Show Figure 7 Schematic diagram of an alternative solution of a disc brake 1, Figure 8 Only one brake pad 3 is shown, however, the disc brake 1 comprises Figure 7 Two brake pads 3 are shown.

[0060] The disc brake 1 and Figure 7 The difference between the disc brake 1 in FIG. 1 and FIG. 2 is the type of fixed bearing. In this embodiment, the fixed support comprises a component of a half-shell bearing. By using a half-shell bearing to support the brake pad 3 on the carrier 11 (which is possible due to the small rotation angle of the brake pad 3 relative to the carrier 11), the rotation point can be closer to the brake disc 2, so that a more compact design is achieved and the lining material 5 can be better utilized. In addition, assembly is made easier.

[0061] Although not shown in the drawings of this embodiment, the groove 7 of the first embodiment may be provided in the brake pad 3 of the fourth embodiment instead.

[0062] Fig. 9 A principle diagram of a disc brake 1 according to a fifth embodiment is shown.

[0063] The disc brake 1 according to the fifth embodiment is Figure 7 The difference of the disc brake 1 is that the back plate 4 is not fixed by the bearing but by the output side S of the brake pad. o The movable bearing on the back plate 4 is supported on the bracket 11. Therefore, the back plate 4 and the bracket 11 respectively include components of the movable bearing to support the back plate 4 on the bracket 11.

[0064] In addition, on the input side S of the brake pad 3 i On the top, the back plate 4 and the brake caliper 8 (as shown in the bracket) respectively include components for fixing the bearing to support the back plate 4 through the brake caliper 8.

[0065] Although not shown in the drawings of this embodiment, the groove 7 of the first embodiment may be provided in the brake pad 3 of the fifth embodiment instead.

[0066] In operation, the effect of the considered taper wear can be determined by the input side S i The brake pad 3 is supported on the carrier 11 by a fixed bearing on the carrier 11 (about which the brake pad 3 can rotate) and a rotatable brake caliper 8, and in addition, in order to achieve a defined wear of the lining material 5, the brake pad 3 is supported on the carrier 11 by a movable bearing. The position of the application point of the braking force F can be defined at an optimal predetermined distance from the fixed bearing.

[0067] Although the present invention has been shown and described in detail in the drawings and the description above, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention defined in the claims is not limited to the disclosed embodiments. Other modifications will be apparent to those skilled in the art by reading this disclosure. Such modifications may involve other features known in the art, which may be used to replace or supplement the features described herein, and in particular, these features may be combined. In the claims, the expression "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality of cases.

[0068] Reference numerals list

[0069] 1 Disc brake

[0070] 2 brake discs

[0071] 3 Brake pads

[0072] 4 Back Panel

[0073] 5 Lining material

[0074] 6 Friction surface

[0075] 6', 6'' Partial friction surface

[0076] 7 grooves

[0077] 7', 7'' (groove) side

[0078] 7w groove width

[0079] 7c The width of the groove at the center line

[0080] 8 Brake calipers

[0081] 9 Tensioning struts

[0082] 10 parts (of brake calipers)

[0083] 11 Bracket

[0084] A axis

[0085] E i Inner Edge

[0086] E o Outer Edge

[0087] FBrake force

[0088] F R Friction

[0089] F1, F2 force

[0090] M torque (caused by friction)

[0091] M comp Compensation torque

[0092] RRotation direction

[0093] S i Input side

[0094] S o Output side

Claims

1. A disc brake (1), in particular a disc brake for a vehicle, the disc brake (1) comprising: Brake disc (2), Two brake pads (3) facing each other, each of which comprises a back plate (4) and a lining material (5), each brake pad (3) comprising an input side (S i ) and the output side (S o ), the input side is the front side of the brake pad (3) when the brake disc (2) rotates in the rotation direction (R) when the vehicle moves in the forward direction, and the output side is the rotation direction (R) of the brake disc (2) and the input side S i the opposite side, and A clamping unit, comprising the brake pad (3) and a brake caliper (8), wherein the brake caliper comprises a tensioning strut (9), wherein the tensioning strut connects a portion (10) supporting one of the two brake pads (3) with a portion (10) supporting the other of the two brake pads (3), The tensioning strut (9), the parts (10) and at least one of the two brake pads (3) are configured to deform during braking so that a resultant reaction force (F Res ) is applied from the input side (S i ) than the distance to the output side (S o ) is closer.

2. The disc brake (1) according to claim 1, wherein: The brake disc (1) has an axis (A), and the lining material (5) comprises an inner edge (E) facing the axis (A). i ) and the outer edge (E) facing away from the axis (A) o ),and At least one of the two brake pads (3) and the brake caliper (8) is configured to deform during braking so that a resultant reaction force (F Res ) is applied at a distance from the outer edge (E o ) is greater than the distance to the inner edge (E i ) is closer.

3. The disc brake (1) according to claim 1 or 2, wherein: The back plate (4) has a non-uniform thickness and is disposed toward the output side (S o ) is smaller than the thickness towards the input side (S i ) thickness.

4. The disc brake (1) according to any one of claims 1 to 3, wherein: closer to the input side (S i ) of the tensioning strut (9) having a portion closer to the output side (S o ) of the tensioning struts (9) of different stiffness.

5. The disc brake (1) according to claim 4, wherein: Each tensioning strut (9) is made of the same material and is closer to the input side (S i ) has a different cross-section than that closer to the output side (S o ) of the cross section of the tensioning strut (9).

6. The disc brake (1) according to claim 4 or 5, wherein: closer to the input side (S i ) has a greater stiffness than the tensioning strut (9) closer to the output side (S o ) of the tensioning strut (9).

7. The disc brake (1) according to any one of claims 4 to 6, wherein: The brake disc (2) has an axis (A), and the lining material (5) comprises an inner edge (E) facing the axis (A). i ) and the outer edge (E) facing away from the axis (A) o ), The stiffness of the respective tensioning strut (9) is distributed so that closer to the inner edge (E i ) is greater in stiffness than that of the corresponding tensioning strut (9) closer to the outer edge (E o )’s stiffness.

8. Disc brake (1) according to any one of the preceding claims, wherein: The friction surface (6) of the lining material (5) is configured to apply a friction force (F R ), the lining material (5) comprises a groove (7) in the friction surface (6) extending towards the back plate (4), and in the plane of the friction surface (6), the groove has a width (7w) and a center line (7c) of the width (7w) of the groove (7), and the entire friction surface (6) has a centroid (C), The center line (7c) of the width (7w) of the groove (7) is located at a position different from the centroid (C).

9. The disc brake (1) according to claim 8, wherein: For braking, the friction surface (6) is designed to contact the rotating brake disk (2), and The groove (7) is arranged in a direction perpendicular to the tangential direction of the rotation direction (R) of the brake disc (2).

10. The disc brake (1) according to claim 8 or 9, wherein: For braking, the friction surface (6) is designed to contact the rotating brake disk (2), and The groove is arranged in a direction parallel to a tangential direction of a rotation direction (R) of the brake disc (2).

11. The disc brake (1) according to any one of claims 8 to 10, wherein: The groove (7) has a concave or rectangular cross section, in particular a U-shaped or V-shaped cross section.

12. The disc brake (1) according to claim 11, wherein: Each side surface (7', 7'') of the V-shaped groove forms a different angle with the friction surface.

13. The disc brake (1) according to any one of claims 8 to 12, wherein: The groove (7) extends to the back plate (4).

14. The disc brake (1) according to any one of claims 8 to 13, wherein: The cross section of the groove (7) changes in a direction along the friction surface (6).

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