JPH017873Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a wheel cylinder of a drum brake that presses a brake shoe against a brake drum that rotates together with a wheel, and in particular, the present invention relates to a wheel cylinder for a drum brake that presses a brake shoe against a brake drum that rotates together with a wheel. This relates to a wheel cylinder equipped with an automatic gap adjustment function that maintains appropriate clearance with the wheel cylinder.

Prior Art A drum brake wheel cylinder as described above generally includes a cylinder body fixed to a bucking plate and a piston slidably fitted to the cylinder body and engaged with a brake shoe. When the piston is pushed out by hydraulic pressure, the brake shoe is pressed against the brake drum to achieve a braking action.

Since the brake shoe (strictly speaking, the brake lining) gradually wears out due to repeated braking operations, the clearance between the brake shoe and the brake drum when not braking increases accordingly. Regardless of the wear of the brake shoes, it is necessary to keep the above clearance constant. This can be achieved, for example, by gradually shifting the rearward movement end position of the piston of the wheel cylinder toward the front as the brake shoe wears.

Conventionally, it has been known to incorporate such an automatic gap adjustment device into the wheel cylinder of a drum brake and adjust the gap using the amount of advance of the piston during braking as a parameter. When the brake fluid pressure is extremely high, it is inevitable that the brake components will be elastically deformed to some extent, such as compressive deformation of the brake lining, expansion deformation of the brake drum, and bending deformation of the brake shoe. Even after the clearance between the brake drum and the brake shoe disappears during operation, the piston is usually pushed out further, albeit slightly, due to the above-mentioned elastic deformation. Therefore, if the appropriate clearance is set in advance during non-braking and the piston's retreating end position is defined based on it, the piston's retreating end position tends to be too close to the forward side, which may cause the braking This was one of the causes of drag in the shoe.

Purpose of the invention With this background in mind, the present invention is capable of always maintaining an appropriate clearance between the brake drum and the brake shoe when not braking, without causing the dragging phenomenon of the brake shoe. This was made for the purpose of providing a wheel cylinder.

Structure of the invention In order to achieve such an objective, the gist of the invention is that the wheel cylinder of the drum brake described above is configured to include the following structural requirements (a) to (f). It is.

That is, (a) Adjustment member ◇ Provided movably in the moving direction of the piston.

◇ It is operatively connected to the piston through a gap that allows a predetermined amount of relative movement in the axial direction. Note that this gap corresponds to the appropriate clearance between the brake shoe and the brake drum when braking is not applied.

(b) Locking member ◇ The locking member is attached to the adjustment member in a state that allows relative movement in the movement direction of the locking member.

(c) First spring ◇ When the adjustment member is moved forward following the piston, it biases the locking member in a direction to advance together with the adjustment member.

(d) Rotating tooth member ◇ Rotatably attached to the cylinder body around a rotation axis perpendicular to the moving direction of the adjusting member.

◇ A plurality of engaging teeth are formed along a pitch line whose distance from the rotation axis gradually increases, and the engaging teeth are engaged with the locking member.

(e) Second spring ◇ A state in which the rotating tooth member is biased in the forward direction in which the distance between the engagement position with respect to the locking member and the rotation axis increases, thereby preventing the locking member from retreating. to maintain the engaged state between the rotating tooth member and the locking member.

◇ However, the rotating tooth member is allowed to rotate in the opposite direction, allowing the adjusting member and the locking member to move forward integrally following the piston.

(f) Lock member ◇ Provided on the cylinder body so as to be able to approach and separate from the rotating tooth member.

◇ It is a member to which hydraulic pressure of the same magnitude as the hydraulic pressure applied to the piston is applied.

◇ Normally, the third spring biases the rotating tooth member to the non-operating position, allowing the rotating tooth member to rotate in the opposite direction.

◇ However, when the hydraulic pressure exceeds a predetermined level, the hydraulic pressure overcomes the biasing force of the third spring and moves it to the operating position, causing the rotating tooth member to be directly or indirectly connected to the third spring. The rotating tooth member is prevented from rotating in the opposite direction, and the rotating tooth member prevents movement of the locking member regardless of the advancement of the adjustment member.

Functions and effects of the invention In a wheel cylinder that includes the structural requirements (a) to (f) above, when the piston is pushed out with a stroke that exceeds the gap with the adjustment member, the clearance between the brake shoe and the brake drum As the adjustment member is moved forward following the piston, the locking member also rotates the rotary tooth member in the opposite direction by the amount necessary to overcome the engagement teeth of the rotary tooth member until The adjusting member is moved forward integrally with the adjustment member, and its retreat is prevented by the rotating tooth member. However, even after the clearance between the brake shoe and the brake drum disappears, in the process where the piston is pushed out while elastically deforming the brake shoe etc. due to the increasing hydraulic pressure, the locking member that receives the increasing hydraulic pressure is The locking member overcomes the biasing force of the spring and moves to the operating position to prevent the rotating tooth member from rotating in the opposite direction. cannot move, and displacement of the locking member in the elastic deformation region is prevented. Therefore, when the hydraulic pressure on the piston and locking member is released, the piston is retracted and the locking member returns to its non-operating position.
Further, the adjusting member is retracted and its retracted end position is defined by the locking member, and the retracted end position of the piston is determined by the adjusting member. As a result, the forward movement of the piston in the elastic deformation region of the brake shoe etc. is absorbed between the locking member and the adjustment member, and the backward movement of the piston is not affected by the elastic deformation mentioned above, and the brake Defined based on the actual clearance between the drum and brake shoe. This prevents so-called over-adjustment, in which the piston's retreating end position is too close to the front, and maintains an appropriate clearance between the brake shoe and the brake drum without causing any dragging. It is.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

The following embodiment is an example in which the present invention is applied to a wheel cylinder in a two-leading type drum brake.

FIG. 1 shows a simplified representation of such a drum brake. In the figure, 10 is a bucking plate fixed to a non-rotating member, and the bucking plate 10 includes a pair of brake shoes 1.
2 and 12 are supported in a floating state. Each of the brake shoes 12 is provided with a brake lining 14, and one end is brought into contact with anchors 16, 16 provided at symmetrical positions with respect to the center of the bucking plate 10, while the other end on the opposite side The wheel cylinders 18, 18 push and expand the portions in the diametrical direction, respectively. As a result, the brake lining 14 of the brake shoe 12
Usually, it is pressed against the drum inner peripheral surface 22 of the brake drum 20, which rotates together with the wheel in the direction of the arrow, and the rotation of the brake drum 20 is suppressed.

When the pressing action by the wheel cylinders 18, 18 is released, the pair of brake shoes 12, 1
2 is returned to the non-braking position by the return springs 24, 24, and as a result, a minute clearance C is created between the brake lining 14 and the inner peripheral surface of the drum 22. It is desirable to keep it as constant as possible regardless of the wear of the lining 14 so that the depression stroke of the brake pedal, etc. does not increase. The wheel cylinder 18 is
It is equipped with an automatic gap adjustment function for this purpose. One of the wheel cylinders 18 is shown enlarged in FIGS. 2 and 3.

As is clear from these figures, this wheel cylinder 18 includes a cylinder body 26.
The cylinder body 26 integrally has the anchor 16 and is fixed to the bucking plate 10, but the middle part is partitioned by a partition wall 28, so that a cylinder bore 30 and a working chamber are formed on both sides of the cylinder body 26. 32 are formed. A piston 34 is slidably fitted into the cylinder bore 30 and protrudes from its opening while being protected from dust by a dust boot 36, and is fitted into an engagement groove 38 formed at the protruding end. The brake shoe 12
The free ends of are engaged. The piston 34 and the inner circumferential surface of the cylinder bore 30 are airtight by the seal member 4.
0, a hydraulic pressure chamber 42 is formed between this seal member 40 and the bottom surface of the cylinder bore 30, and hydraulic fluid is supplied to this hydraulic pressure chamber 42 via a conduit 44. The piston 34 is pushed out by.

A connecting protrusion 46 is formed at the retreating end of the piston 34, and the engaging pin 4 is inserted from the inner peripheral surface of the connecting protrusion 46.
8 protrudes radially inward. This engagement pin 48 is connected to the adjustment rod 5 which functions as an adjustment member.
It is fitted into an engagement hole 52 formed at the tip of the 0. The engagement pin 48 and the engagement hole 52 are engaged with each other through a gap δ that allows relative movement between the piston 34 and the adjustment rod 50 in the axial direction of the piston 34, and this gap δ is This gap is predetermined to provide an appropriate clearance C between the shoe 12 and the brake drum 20 when braking is not being applied, and is determined corresponding to the clearance C. The adjustment rod 50 has a tip end connected to the connecting hole 4 of the piston 34.
6 and is slidably fitted to the partition wall 26.
The piston 34 is held so as to be slidable in the movement direction of the piston 34 while being sealed by an O-ring 54 and protruding toward the working chamber 32 .

A fixed tooth wheel 58 is provided at the rear end of the adjustment rod 50 via a sliding member 56. The sliding body 56 is slidably fitted into a guide hole formed in the axial direction at the rear end of the adjustment rod 50, and is fitted into the sliding body 56 via a mounting shaft 60 that protrudes in the radial direction of the adjustment rod 50. A fixed tooth wheel 58 is non-rotatably mounted. Therefore, the fixed tooth wheel 58 and the adjusting rod 50 are
Relative movement in the movement direction of 0 is allowed, but
The first springs 62 are biased toward each other by the first springs 62 so that when the adjustment rod 50 is advanced in the direction indicated by the arrow, the first springs 62 are biased toward moving the fixed tooth wheel 58 forward with the adjustment rod 50. A biasing force acts.

This fixed tooth wheel 58 functions as a locking member, and has a gear-like form in which engaging teeth 64 are formed over the entire circumference of the outer circumferential surface of the fixed tooth wheel 58. A pair of rotating sectors 66 are provided which function as moving tooth members. These rotational sectors 66 are connected to the cylinder body 26 by the shaft 6.
8, 68 and their shafts 68
are provided in parallel to the axis 60 at mutually symmetrical positions with respect to the axis 60, in other words, perpendicular to the moving direction of the piston 34, and the pair of rotation sectors 66 are located at the axis of the axis 68 (hereinafter referred to as the rotation axis O). ) can be rotated within the same plane. A plurality of engagement teeth 70 are formed on the periphery of the free end side of these rotational sectors 66 along a pitch line in which the distance from the rotational axis O gradually increases toward the direction B in FIG. These engaging teeth 70 are connected to the engaging teeth 6 of the fixed tooth wheel 58.
It is designed to be able to mesh with 4.

Both rotation sectors 66 are attached by second springs 72, 72 in the forward direction (direction A in the figure) in which the distance between the meshing position with respect to the fixed tooth wheel 58 and each rotation axis O increases. in a state in which the fixed tooth wheel 58 is biased to narrow the fixed tooth wheel 58 from both sides and prevent the fixed tooth wheel 58 from retreating (movement to the left in the figure).
The state of engagement with the fixed tooth wheel 58 is always maintained. However, those second springs 72, 72
For fixed-tooth wheel 58 to move forward (movement to the right in the figure), each rotational sector is rotated by the amount of rotation necessary for fixed-tooth wheel 58 to overcome engagement teeth 70 of rotational sectors 66, 66. It is permissible to rotate 66 by a small angle (reverse rotation) in the direction B in the figure. A locking member 74 is provided further behind these rotating sectors 66, 66. This locking member 74 includes a base plate 76 housed in the working chamber 32 in a posture perpendicular to the moving direction of the adjustment rod 50, and a piston portion 78 integrally protruding from the center of the back surface of the base plate 76. A piston portion 78 is slidably fitted into a cylinder bore 80 formed in the cylinder body 26, and working protrusions 82, 82 are protruded from the surface of the base plate 76 opposite to the piston portion 78. There is.
On the other hand, arm portions 8 extending toward the opposite side of the engagement teeth 70 with respect to the rotation axis O are provided in both rotation sectors 66.
4 is formed, and the second spring 72
is disposed between the arm portion 84 of these rotating sectors 66 and the working protrusion 82 of the locking member 74 with a predetermined preload applied thereto.

And the locking member 74 is connected to the third spring 86.
The working protrusion 82 is urged away from the arm part 84 by the piston part 78, and is normally placed in the non-working position where the base plate 76 is seated on the wall surface where the cylinder bore 80 opens. The application of hydraulic pressure that overcomes the preload of the third spring 86 causes the locking member 74 to advance and compress the second springs 72, 72 until their coils are substantially in intimate contact and the actuating projections 82, 82 are moved forward. The second springs 72, 72 indirectly abut the arms 84, 84 of the rotating sectors 66, 66. When the locking member 74 is moved to such an operating position, the pair of rotating sectors 66 are prevented from rotating in the direction B, and therefore the front of the fixed tooth wheel 58 that is meshed with them is prevented. When the adjustment rod 50 is moved forward following the piston 34 in such a state that the adjustment rod 50 is not allowed to be true, only the adjustment rod 50 moves forward as the first spring 62 expands.

The hydraulic pressure which moves the locking member 74 into the active position is directed into the cylinder bore 80 via line 88, which hydraulic pressure is of the same magnitude as the hydraulic pressure applied to said piston 34 and therefore When the load on cylinder 34 increases and the hydraulic pressure in hydraulic chamber 42 increases, the hydraulic pressure supplied to cylinder bore 80 also increases accordingly. and,. The preload force of the third spring 86 is such that the brake shoe 12 is pressed against the brake drum 20 by the extrusion of the piston 34, and the brake shoe 12,
The locking member 74 is sized to maintain the locking member 74 in the non-operating position against the hydraulic pressure until the piston 34 is moved forward to a significant extent by elastic deformation of the brake component such as the brake lining 14.

Wheel cylinder 18 configured as above
When brake fluid pressure is supplied to the hydraulic pressure chamber 42, the piston 34 is pushed out and presses the brake shoe 12 against the drum inner peripheral surface 22. However, while the brake lining 14 of the brake shoe 12 is new, the piston 34 The amount of extrusion (advance amount) of the piston 34 is substantially equal to the clearance δ with the adjusting rod 50, so the adjusting rod 50 does not move. However, as the brake lining 14 wears, the piston 34 moves forward. When the amount exceeds δ,
The engagement pin 48 of the piston 34 comes into contact with the end of the engagement hole 52 of the adjustment rod 50, and the adjustment rod 50 follows the piston 34 and advances a short distance by an amount of advance exceeding δ. At this time, brake shoe 1
Clearance C between 2 and the brake drum 20
Until this disappears, the hydraulic pressure acting on the piston 34 is relatively low, and therefore the hydraulic pressure acting on the locking member 74 is also the same, and the locking member 74 is moved to the non-acting position by the third spring 86. Therefore, when the adjusting rod 50 moves forward, the fixed tooth wheel 58 is pulled by the first spring 62 and rotates the pair of rotary sectors 66 slightly in the direction B, and the engaging teeth 70 If we can overcome one of these and move forward as one, and once we are able to move forward,
Retraction is not possible based on the engagement with the rotational sectors 66, 66.

However, even after the clearance C disappears, the piston 34 is still moved forward with elastic compression deformation of the brake lining 14, elastic bending deformation of the brake shoe 12, etc., and the brake lining 14 is moved inside the drum. When pressing strongly against the circumferential surface 22, the piston portion 78 of the locking member 74 increases as the hydraulic pressure applied to the piston 34 increases.
The hydraulic pressure acting on the third spring 86 is also increased, and the locking member 74 is moved to the operating position by overcoming the biasing force of the third spring 86, so that the operating protrusion 82 of the rotating sector 66 is moved through the second spring 72 in close contact with the locking member 74. It comes into contact with the arm portion 84 and prevents both rotating sectors 66 from rotating in the B direction. As a result, the fixed tooth wheel 58 is no longer allowed to move forward and the adjustment rod 50 follows the piston 34.
Despite being moved forward, the first spring 62 only stretches and the position of the fixed tooth wheel 58 does not change in any way.

Thereafter, when the hydraulic pressure on the piston 34 is released, the piston 34 is moved back based on the biasing force of the return spring 24, and the adjustment rod 50 is also moved back and comes into contact with the fixed tooth wheel 58 via the sliding body 56. This defines the retracted end position. Further, since the hydraulic pressure on the locking member 74 is also released, it is returned to the non-acting position by the third spring 86, but even in this state, the fixed tooth wheel 58 is prevented from retreating as described above. Therefore, the fixed tooth wheel 58 defines the rearward end position of the adjustment rod 50, and the engagement hole 52 of the adjustment rod 50
The retracted end position of the piston 34 is defined by the engagement pin 48 coming into contact with the end of the piston 34 .

As is clear from the above explanation, the piston 34
In the latter half of the forward movement region where the brake component is advanced with elastic deformation, the forward movement is absorbed between the adjusting rod 50 and the fixed tooth wheel 58.
Since the substantial amount of advancement of the adjustment rod 50 is given by the amount of advancement of the fixed tooth wheel 58, the retreating end position of the piston 34 is moved forward little by little without being affected by the elastic deformation of the brake component. As a result, an appropriate clearance C can be maintained between the brake shoe 12 and the brake drum 20 during non-braking without causing so-called over-adjustment. In other words, if the adjusting rod 50 and the fixed tooth wheel 58 were to be moved forward together in the latter half of the forward movement region of the piston 34, the backward end position of the piston 34 would be too close to the front, causing the brake shoe 12 and brake drum to move forward. 2
0 tends to be smaller than a predetermined size, which tends to cause the brake shoe to drag, but in the case of this embodiment, the clearance is influenced by the amount of advance of the piston 34 in the elastic deformation region. Since the rearward end position is sequentially adjusted to the front side without any adjustment, over-adjustment (excessive adjustment) can be prevented and an appropriate clearance C can be maintained.

In the embodiment described above, two rotating sectors 6
6 were each biased by a dedicated second spring 72, but as shown in FIG.
0 can also be stretched with a tensile preload.
In this case, the operating protrusion 82 of the locking member 74
Direct contact with the arm portion 84 of the rotating sector 66
This will prevent rotation in the direction. Further, instead of providing two rotating sectors 66 and narrowing the fixed tooth wheel 58 from the outer circumferential side, even if only one rotating sector 66 is provided on one side, substantially the same result as in the previous embodiment can be achieved. Effects can be obtained.

Furthermore, the engagement teeth to be formed on the rotating sector 66 are not limited to the serrated engagement teeth 70, but may also include, for example, fine serrations or minute irregularities formed on the pear surface by shot peening. They can also function as engaging teeth. In that case, it is desirable to form similar irregularities on the fixed tooth wheel 58, but if the pair of rotating sectors 66 narrow the fixed tooth wheel 58 as shown in FIG. When the locking member 74 is moved to the operating position to prevent the toothed wheel 58 from advancing, it can apply a force that pushes both rotary sectors 66 in the direction A, so that the locking member 74 is in contact with the fixed toothed wheel 58. As the frictional force increases, it is not very difficult to prevent its advance.

Furthermore, in the previous embodiments, a gear-shaped fixed tooth wheel 58 was used as a locking member, but this was done to facilitate processing by rolling, etc., and the wheel did not rotate all the way around. Engaging teeth may be formed only in the portion that engages with the sector 66. Furthermore, it is also possible to employ a locking member that has only one engagement tooth and has the form of a locking pawl.

Although other details will not be described in detail, it goes without saying that the present invention can be embodied in various modifications and improvements based on the knowledge of those skilled in the art without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of a drum brake including a wheel cylinder, which is an embodiment of the present invention. FIG. 2 is an enlarged front view showing the wheel cylinder. FIG. 3 is a cutaway view of the bottom view of FIG. 2. FIG. 4 is a simplified diagram showing the main parts of another embodiment of the present invention. 10: Bucking plate, 12: Brake shoe, 14: Brake lining, 18: Wheel cylinder, 20: Brake drum, 26: Cylinder body, 34: Piston, 50: Adjustment rod (adjustment member), 58: Fixed tooth wheel (locking member),
62: First spring, 66: Rotating sector (rotating tooth member), 70: Engaging tooth, 72, 90: Second spring, 74: Lock member, 86: Third spring, δ: Predetermined gap .

Claims (1)

[Claim for Utility Model Registration] A piston that receives a predetermined hydraulic pressure is slidably fitted into the cylinder body fixed to the packing plate, and the piston engages with the brake shoe and rotates it together with the wheels. A wheel cylinder configured to be pressed against a brake drum, which is movable in the direction of movement of the piston, and is actuated through a gap that allows a predetermined amount of relative movement in the axial direction with respect to the piston. an adjusting member that is connected to the adjusting member; a locking member that is attached to the adjusting member such that it is allowed to move relative to the adjusting member in a moving direction; and when the adjusting member is moved forward following the piston, the locking member a first spring that biases the locking member in a direction to move the locking member forward together with the adjustment member; A rotating tooth member comprising a plurality of engaging teeth formed along a pitch line whose distance from a moving axis gradually increases, and the engaging teeth are engaged with the locking member; and the rotating tooth member. is biased in a forward direction in which the distance between the engagement position with respect to the locking member and the rotation axis increases, thereby preventing the rotation tooth member and the locking member from retreating. a second spring that maintains an engaged state while allowing the rotating tooth member to rotate in the opposite direction so that the adjusting member and the locking member move forward integrally following the piston; , a member that is provided in the cylinder body so as to be able to approach and separate from the rotating tooth member, and to which a hydraulic pressure of the same magnitude as the hydraulic pressure applied to the piston is applied, and is usually a member of the third spring. However, when the hydraulic pressure exceeds a predetermined level, the hydraulic pressure overcomes the biasing force of the third spring and moves the spring to the non-operating position, and the rotation The locking member contacts the rotating tooth member directly or indirectly through another member to prevent the rotating tooth member from rotating in the opposite direction, and the locking member is attached to the rotating tooth member regardless of the advancement of the adjustment member. A wheel cylinder for a drum brake, comprising a locking member for preventing movement of the drum brake.