JPS6224656B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a method for adjusting the shoe clearance (the gap between the brake shoe and the brake drum) to an appropriate value in response to an increase in shoe clearance (the gap between the brake shoe and the brake drum) due to the wear of the lining of a drum brake. This invention relates to improvements to auto adjuster devices.

[Problems to be solved by conventional technology and invention]

Conventionally, as this type of auto adjuster device, 2
The lining of the brake shoe is worn out and the shoe clearance exceeds the set value. When the clearance increases, a so-called mechanical adjustment mechanism is widely used in which the adjuster star lever pivots to rotate the adjuster steering gear to adjust the shoe clearance to an appropriate value.

However, in this mechanical auto-adjuster device, when the brake drum thermally expands due to frictional heat, the above-mentioned shoe clearance adjustment is performed excessively, so that drag torque is generated when the brake is not activated. There is a problem in that so-called over-adjustment tends to occur.

The present invention provides a strut nut disposed between two brake shoes, an adjustment screw screwed onto the strut nut, a motor for rotationally driving the adjustment screw via a worm gear, and a shoe clearance. This problem is solved by an electric auto-adjuster equipped with a motor control circuit for controlling the operation of the motor to maintain the same value.

[Means for Solving the Problem] That is, the electric auto adjuster of the present invention has a motor that is controlled and operated by a control circuit to prevent the increase in shoe clearance due to lining wear.
The adjustment screw is rotationally driven to obtain the set shu clearance, and this control circuit also incorporates a program to prevent overadjustment and a brake temperature detection circuit to prevent overadjustment caused by thermal expansion of the brake drum. It is characterized by having a function of interlocking the strike, thereby achieving the intended purpose.

[Effect]

According to the present invention, the temperature is detected by a thermistor attached to the brake shoe, and when the temperature is high (during thermal expansion of the drum), the adjustment function is locked to prevent overadjustment, and the motor used above is reversed. It also has the function of allowing clearance to be set by

[Examples and effects of the invention]

The present invention will be described below based on embodiments shown in the accompanying drawings.

Embodiment FIG. 1 is a partial sectional view of a drum brake incorporating an electric auto-adjuster according to the present invention.
A wheel cylinder 2 for expanding the brake shoes 1 and 1' is interposed between the brake shoes 1 and 1', and the other ends of both brake shoes 1 and 1' are in contact with an anchor 3.

Also, shoe return springs 4, 4 are installed between the brake shoes 1, 1', and the tips of a strut nut 5 and a strut 6 are fitted and supported in the notches 1b, 1b' of the brake shoes, respectively. A threaded portion 7a of an adjuster screw 7 is screwed into the strut nut 5, and this shaft portion 7b is supported in a hole in the strut 6.

Furthermore, as shown in FIG. 2, which is a cross-sectional view of FIG. It is configured like this.

As shown in FIG. 1, the screw gear 7c of the adjusting screw 7 has a sufficient width w in the axial direction.
This width w is designed to be greater than the corrected shoe clearance at the limit of lining wear, and the worm gear 10
The mesh is designed to prevent it from falling off.

The small motor 9 is configured to be operated under control by a motor control circuit (not shown).
If the shrew clearance reaches the set value or more due to lining wear, for example, if the operating switch of this control circuit is turned on in the driver's seat, the motor 9 will rotate forward and the adjuster screw 7 will be screwed into the strut nut 5. The motor 9 is rotated in the direction of extension until the brake shoes 1, 1' collide with a brake drum (not shown) and the shoe clearance becomes zero.

Next, using, for example, an electric torque limiter or the like, a program is programmed to detect the zero state of this shu clearance, stop the motor 9, and further reverse the rotation by a predetermined number of revolutions, thereby obtaining the set shu clearance. .

This predetermined number of rotations is set to a value that provides the optimum shoe clearance according to the size and structure of the drum brake, but as a control method, a mechanism for counting the number of reverse rotations described above is provided, and a predetermined number of counts is provided. Various methods can be considered, such as stopping the operation of the motor 9.

Furthermore, by incorporating a brake temperature detection circuit into the motor control circuit described above, it is also possible to interlock over-adjustment due to thermal expansion of the brake drum.

That is, for example, a thermistor is attached to the brake shoe, and this detects the temperature of the brake drum (almost the same temperature can be detected, although not directly), and the motor control circuit controls the operation according to the critical resistance change of this thermistor. It is preferable to configure the circuit so that the motor 9 cannot be operated even if the operating switch of this control circuit is turned on at the seat.

In this way, the critical temperature of the thermistor is set at an appropriate temperature below the temperature at which over-adjustment occurs due to thermal expansion of the brake drum, and when the brake drum is overheated to a temperature higher than that, the motor 9 does not operate and the present invention The electric auto adjuster will not work.

[Brief explanation of the drawing]

Fig. 1 is a partial sectional view showing a drum brake incorporating the electric auto adjuster of the present invention;
The figures each represent a - sectional view of FIG. 1. 5...Strut nut, 7...Adjustment screw, 9...Motor, 10...Worm gear.

Claims (1)

[Claims] 1. A strut nut disposed between two brake shoes, an adjusting screw screwed thereto, a motor for rotationally driving the adjusting screw via a worm gear, and a strut nut disposed between two brake shoes. A motor control circuit is provided to control the operation of the motor so as to maintain the U-clearance at a set value, and the motor control circuit is provided with a brake temperature detection circuit to interlock over-adjustment due to thermal expansion of the brake drum. An electric auto adjuster that is characterized by having the function of 2 The motor control circuit rotates the adjustment screw until the brake shoe collides with the brake drum by normal rotation of the motor, and when this shoe clearance becomes zero, reverses the motor by a predetermined number of rotations and sets the setting system. An electric auto-adjuster according to claim 1, which operates under control to obtain a u-clearance.