Technical Field

The present invention relates in general to center brakes, in particular, for middle- or large-sized automobiles such as trucks or buses used for keeping temporary parking of the automobiles with the engine set going or for reliably keeping the braked state of long time parked automobiles with the engine shut down.

Background Art

As well known to those skilled in the art, the brakes of automobiles are used not only for reducing the speed of automobiles and stopping the automobiles but also for keeping the braked state of parked automobiles. The brakes typically generate frictional force and convert the kinetic energy of the automobiles into thermal energy and evolve the thermal energy to the atmosphere and thereby braking the automobiles. Typically, each of small-sized automobiles has two types of brakes, that is, a foot brake and a hand brake. The foot brake is for braking the running automobile by foot in order for reducing the speed or stopping the automobile, while the hand brake (otherwise stated, side brake or parking brake) is for manually braking the rear wheels of the automobile, in particular, during parking of the automobile.

Differently from the small-sized automobiles, middle- or large-sized automobiles such as trucks or buses also have their center brakes besides the above two types of brakes. ^■ The center brake is a kind of hand brake which is adapted for braking a propeller shaft of the automobile.

Both the center brake and the hand brake are used for prevention of possible slip of the automobile during parking of the automobile on a slope. The center brake is preferably used, in particular, when temporarily parking the automobile while setting the engine going.

For example, the fire engines or the fire trucks should be parked with the engine set going when putting out a fire in a fire spot. That is, the engine of a fire truck in a fire spot should be set going in order for continuously generating water pumping force. The gross weight of a fire truck charged with much water is very heavy so that the parked state of the fire truck in the fire spot may be unstable when the truck is braked by the hand brake exclusively. Therefore, the center brake should be operated and cooperate with the hand brake for stably braking and parking the fire truck with the engine set going in the fire spot.

However, there may be a problem when parking the fire truck with the engine set going on a slope. That is, when the parking place of the fire truck in a fire spot is a slope, only a good center brake can stably brake the fire

truck. However, when the center brake of the fire truck has a trouble caused, for example, by abrasion of brake lining, the parked truck with the engine set going and with much water may slide down on the slope due to its gross weight and cause a terrible accident.

Of course, the above problem caused by a trouble of the center brake may occur in another middle- or large- sized automobile, such as a cargo truck or a bus, besides the fire trucks. The typical brakes are generally classified into two types, that is, drum brakes and disk brakes. In a typical drum brake, two arcuate brake shoes fitted with heat- and water-resistant linings are forced against inner or outer surface of a rotating drum. The drum brake in which the shoes are forced against the inner surface of the drum is referred to simply as internal forcing type brake, while the drum brake in which the shoes are forced against the outer surface of the drum is referred to simply as external forcing brake. In a typical disk brake, disks attached to a fixed frame are pressed, using hydraulic pressure, against disks attached to a rotating axle or against the inner surfaces of a rotating housing. In the above brakes, the linings or pads used as. braking means are typically made of asbestos which is noted to be very injurious to human health, in particular, to function of hearts and lungs of users so that use of the asbestos for the linings or pads can not help being limited. The above

brakes has another problem that they can not achieve desired braking force which is the soul of the brakes.

Still another problem of the above brakes is resided in that as the lining or pad of the brake should be fixed to the brake shoe using a plurality of rivets so that production of the brakes should be accompanied with somewhat difficulty and this increases cost of the brakes. Furthermore, it is noted that the brakes of the same performance are scarcely produced in mass production.

Disclosure of the Invention

It is, therefore, a primary object of the present invention to provide a center brake for automobiles in which the above problems can be overcome and which is provided with a plurality of triangular or trapezoidal braking teeth integrally formed on the outer surfaces of the brake shoes and on the inner surface of the brake drum, thus to let perfect braking action and to prevent possible safety accident caused by bad braking action of the brake.

It is another object of the present invention to provide a center brake for automobiles which does not use harmful material, such as asbestos, for braking means, thus to prevent the braking means not only from causing functional diseases of hearts and lungs of users and but also from causing environmental pollution.

It is still another object of the present invention

to provide a center brake for automobiles which reliably carries out its returning action even in the case of malfunction of return springs and of freeze of the brake in the winter season, thus to remarkably improve the operational reliability of the center brake.

It is a further object of the present invention to provide a center brake for automobiles which can be handled by a switch without handling a lever when operating or releasing the center brake, thus to facilitate handling of the center brake.

In an embodiment, the present invention provides a center brake for automobiles comprising: a brake drum fixed to a propeller shaft of the automobile and adapted for braking the propeller shaft using frictional force generated by a pair of brake shoes; a housing fitted to and closing the drum and used as a mount for varieties of parts of the brake; the pair of shoes of the single-action two-leading type pivoted to the housing by their anchor pins such that the shoes are selectively turned about their anchor pins by action of a cam and forced against the inner surface of the drum at a given frictional force; the cam fixedly mounted to a shaft of an operating lever at the top ends of the shoes and adapted for biasing the top ends of the shoes outward and opening the shoes in the drum, the operating lever being selectively operated by a brake lever; a plurality of return springs for elastically returning the operating lever and the shoes

to their original positions when the brake lever is free from outside force; an adjuster disposed between the bottom ends of the shoes and adapted for controlling a gap between the shoes; a compression coil spring extending between the bottom ends of the shoes about the adjuster and adapted for preventing separation of the adjuster from the shoes; and a plurality of braking teeth integrally formed on the inner surface of the drum and on the outer surfaces of the shoes, the braking teeth of the shoes engaging with the braking teeth of the drum during a braking action of the brake.

In another embodiment, the present invention provides a center brake for automobiles comprising:a brake drum fixed to a propeller shaft of the automobile and adapted for braking the propeller shaft using frictional force generated by a pair of brake shoes; a housing fitted to and closing the drum and used as a mount for varieties of parts of the brake; the pair of shoes of the double-action two-leading type disposed in the drum such that the shoes are moved outward and opened by action of a pair of cams and forced against the inner surface of the drum at a given frictional force; the cams fixedly mounted to a shaft of an operating lever at the opposed ends of the shoes and adapted for biasing the opposed ends of the shoes outward and for opening the shoes in the drum in order for forcing the shoes against the inner surface of the drum; a plurality of return springs for elastically

returning the shoes to their original positions when releasing the brake lever; and a plurality of braking teeth integrally formed on the inner surface of the drum and on the outer surfaces of the shoes, the braking teeth of the shoes engaging with the braking teeth of the drum during a braking action of the brake.

The center brake of this invention lets perfect braking action, prevents its braking means from causing functional diseases of hearts and lungs of users and from causing environmental pollution, lets reliable returning motion of the brake shoes and facilitates handling of the brake.

Brief Description of Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is an exploded perspective view of a center brake having a pair of single-action two-leading shoes in accordance with a primary embodiment of the present invention;

Fig. 2 is a front view of the center brake of Fig. 1, after assembling the parts into the brake; Figs. 3A and 3B are partially enlarged views of center brakes of the primary embodiment of the invention respectively, in which:

Fig. 3A shows the center brake having a plurality of triangular braking teeth formed on the brake shoes and on the brake drum; and

Fig. 3B shows the center brake having a plurality of trapezoidal braking teeth formed on the brake shoe and on the brake drum;

Figs. 4A and 4B are sectional view showing operation of the internal forcing brake having the single-action two-leading shoes with the triangular braking teeth of the invention;

Figs. 5A and 5B are sectional view showing operation of an internal forcing brake having a pair of double- action two-leading shoes in accordance with another embodiment of the invention; Fig. 6 is a partial view of the center brake provided with air booster or solenoid used as return means in accordance with the invention; and

Fig. 7 is a partial view of the center brake provided with solenoid and air booster used as braking means and return means of the brake respectively in accordance with the invention.

Best Mode for Carrying Out the Invention With reference to Figs. 1 and 2, there is shown a center brake for automobiles in accordance with a primary embodiment of the present invention.

As shown in the drawings, the center brake of the

internal forcing type includes a brake drum 10, which drum 10 is directly fixed to a propeller shaft (not shown) of an automobile and adapted for braking the propeller shaft using frictional force generated by a pair of brake shoes 31. The drum 10 is fitted into and closed by a housing 20, which housing 20 forms an internal space in cooperation with the drum 10 and is used as a mount for varieties of parts of the brake. The brake also includes the pair of single-action two-leading shoes 31, which shoes 31 are provided, on their outer surfaces, with braking teeth 311 and pivoted to the housing 20 by their anchor pins 21 such that the shoes 31 are selectively turned about their anchor pins 21 by action of a cam 40 and forced against the toothed inner surface of the drum 10 at a given frictional force. The cam 40 is fixedly mounted to a shaft of an operating lever 60 at the top ends of the shoes 31, thus to bias the top ends of the shoes 31 outward and to open the shoes 31 in order for causing the shoes 31 be forced against the inner surface of the drum 10. The operating lever 60 is selectively operated by a brake lever. The brake also includes a plurality of return springs 50 which are provided for the operating lever 60 and for the shoes 31 and adapted for elastically returning the operating lever 60 and the shoes 31 to their original positions when the brake lever such as a flexible wire is free from outside force. In the brake of this invention, the gap between the shoes 31 can

be adjusted by a gap adjuster 70, which adjuster 70 is disposed between the bottom ends of the shoes 31. A compression coil spring 55 is connected between the bottom ends of the shoes 31 about the adjuster 70 and prevents possible sudden separation of the adjuster 70 from the shoes 31.

In the above center brake, the inner surface of the drum 10 and the outer surface of each shoe 31 are provided with triangular or trapezoidal braking teeth 11 and 311, which teeth 11 and 311 are integrally formed on their associated surfaces of the drum 10 and of the shoe 31. In this primary embodiment, the braking teeth 311 of the shoes 31 are partially formed on the outer surfaces of the shoes 31 such that the teeth 311 are exclusively formed in a portion of each shoe 31 from a turning center of each shoe 31 to about the top end or the cam contact end of the shoe 31. The center brake further includes a pair of connectors 80 which connect the opposed ends of the cam 40 to the top ends of the shoes 31 respectively. The connectors 80 are adapted for smoothing the returning motion of the shoes 31 when releasing the brake.

As shown in Fig. 6, an air booster 91 or a solenoid 92 as means for forcibly returning the operating lever 60, the cam 40 and the shoes 31 to their original positions in the case of release of the center brake is provided for the operating lever 60.

Please noted that the air booster 91 may be

preferably used as the forcible returning means of a brake used in a large-sized automobile, while the solenoid 92 is preferably used as the forcible returning means of a brake used in a small- or middle-sized automobile. Fig. 7 shows the braking means and the returning means of the center brake in accordance with another embodiment of the invention. In this embodiment, the operating lever 60 is provided with both a switch-operated one touch solenoid 92, used as the braking means, and an air booster 92 used as the returning means. The air booster 92 is supplied with air at the same time of release of the one touch solenoid 91, thus to return the operating lever 60, the cam 40 and the shoes 31 to their original positions and to release the center brake. The present invention may be adapted for an internal forcing center brake having a pair of double-action two- leading shoes as shown in Figs. 5A and 5B. In this embodiment, the center brake includes a brake drum 10 which is directly fixed to a propeller shaft of an automobile and adapted for braking the propeller shaft using frictional force generated by a pair of brake shoes 32. The drum 10 is fitted into and closed by a housing 20, which housing 20 forms an internal space in cooperation with the drum 10 and is used as a mount for varieties of parts of the brake. The brake also includes the pair of double-action two-leading shoes 32, which shoes 32 can be moved outward and opened by action of a

pair of cams 40 and forced against the inner surface of the drum 10 at a given frictional force. The cams 40 are mounted to a shaft of an operating lever 60 at the opposed ends of the shoes 32, thus to bias the opposed ends of the shoes 32 outward and to open the shoes 32 in the drum 10 in order for forcing the shoes 32 against the inner surface of the drum 10. The brake also includes a plurality of return springs 50 which are provided for the operating lever 60 and for the shoes 32 and adapted for elastically returning the operating lever 60 and the shoes 32 to their original positions when the brake lever such as a flexible wire is released. In this center brake, the inner surface of the drum 10 and the outer surface of each shoe 32 are provided with triangular or trapezoidal braking teeth 11 and 321, which teeth 11 and 321 are integrally formed on their associated surfaces. Differently from the brake of the primary embodiment of Figs. 4A and 4B, the braking teeth 321 of the shoes 32 of this embodiment are nearly totally formed on the outer surfaces of the shoes 32.

The operational effect of the center brake of the invention will be given hereinbelow.

When forming the drum 10 and the single-action two- leading shoes 31 of the center brake according to the primary embodiment of the invention, the braking teeth 11 and 311 are integrally formed, using given molds, on the inner surface of the drum 10 and on the outer surfaces of

the shoes 31 respectively.

That is, differently from typical center brakes, the center brake of this invention has no lining on the outer surfaces ^• of the shoes but has the triangular or trapezoidal braking teeth 11 and 311 integrally formed on the inner surface of the drum 10 and on the outer surfaces of the shoes 31. The braking teeth 11 and 311 are preferably made of cast iron. With the braking teeth 11 and 311, the brake of this invention is free from post- machining and remarkably saves the cost and simplifies assembling and disassembling process of the center brake. In the present invention, the braking teeth 11 and 311 have either the triangular shape or the trapezoidal shape as shown in Figs. 3A and 3B. Please noted that it is preferred to let the braking teeth 11 and 311 of the brake for a small- or middle-sized automobile have the triangular shape of Fig. 3A, while it is preferred to let the braking teeth 11 and 311 of the brake for a large- sized automobile have the trapezoidal shape of Fig. 3B as the teeth of the trapezoidal shape can achieve stronger tooth engaging force.

The single-action two-leading shoes 31 of the center brake are pivoted to the housing 20 by the anchor pins 21 and selectively turned about their anchor pins 21 by action of the cam 40 and forced against the inner surface of the drum 10. In this case, the braking teeth 311 of the shoes 31 come into engagement with the teeth 11 of the

drum 10 in such a manner that the tooth engagement between the teeth 11 and 311 starts at the teeth 311 about the anchor pins 21. Therefore when the teeth 311 are totally formed on the outer surfaces of the shoes 31, the teeth 311 about the top ends of the shoes 31 will not engage with the teeth 11 but come off the teeth 11, thus to reduce the braking force of the center brake. Furthermore, when the braking teeth 311 are totally formed on the outer surfaces of the shoes 31, the teeth 311 come into forcible engagement with the teeth 11 so that the brake can not achieve desired smooth returning motion of the shoes 31 when releasing the brake.

In order to combat the above possible problem, the teeth 311 of each shoe 31 are partially formed on the outer surface of the shoe 31 within the range from the turning center of each shoe to the top end of the shoe. In addition, the thickness of the teeth 311 gradually increases in the direction from the turning center to the top end of each shoe 31. The teeth 311 of the shoes 31 thus substantially meet with the teeth 11 of the drum 10 as shown in Fig. 4B when the shoes 31 are opened outward by the cam 40.

The center brake having the single-action two-leading shoes 31 according to the invention achieves desired brake function for braking the propeller shaft of the automobile.

The center brake includes the connectors 80 which

connect the opposed ends of the cam 40, fixed to the operating lever 60, to the top ends of the shoes 31 respectively. As the connectors 80 pull the shoes 31 when the cam 40 returns to its original position in response to releasing of the brake, this brake achieves more smooth return motion of the shoes 31 in comparison with typical brakes having no means for connecting the cam 40 to the shoes 31.

The operating lever 60 of the center brake is provided with the air booster 91 or the solenoid 92, as shown in Fig. 6, giving consideration to possible malfunction of the return springs 50 and to possible freeze of interface between the shoes 31 and the drum 10 in the winter season. When releasing the brake in the case of malfunction of the springs 50 or of freeze of the interface, the air booster 91 or the solenoid 92 forcibly turns the operating lever 60, thus to forcibly return the cam 40 and the shoes 31, both cooperating with the lever 60, to their original positions. Therefore, this center brake can be reliably released even in the case of malfunction of the springs 50 or of freeze of the interface between the drum 10 and the shoes 31 in the winter season.

The air booster 91 is operated by the air exclusively applied thereto when setting the engine, and provides such large force that the booster 91 is preferably used in a brake for a large-sized automobile. Meanwhile, the

solenoid 92 is operated by a switch and preferred to be used in a brake for small- or middle-sized automobile.

The solenoid 92 is an one touch solenoid. When the solenoid -92 is turned on and operated once, the solenoid 92 can keep the previous state even when the engine is shut down and the power is cut off. The solenoid 92, having kept the previous state, returns to its original position at the same time of cutting off of the power when the engine is set going and the switch is turned off by release of the center brake.

Fig. 7 shows the braking means and the returning means of the center brake in accordance with another embodiment of the invention. In this embodiment, the switch-operated one touch solenoid 92 used as the braking means is coupled to a side of the operating lever 60, while the air booster 92 used as the returning means is coupled to the other side of the operating lever 60. The solenoid 92 is turned on in response to switch operation, thus to achieve the braking operation of the center brake, while the air booster 91 is operated when the solenoid 91 is turned off, thus to reliably return the operating lever 60 and the cam 40 and the shoes 31 to their original positions.

When the switch-operated one touch solenoid 92 and the air booster 91 are used as the braking means and the returning means of the center brake as described above, the center brake does not need to be operated by the brake

lever but is simply operated by switch operation so that it is possible to facilitate operation of the brake.

Turning to Figs. 4A and 4B, there is shown operation of the center brake having the single-action two-leading shoes 31 of the invention. As shown in the drawings, when the brake is released, the arcuate two leading shoes 31 in the brake drum 10 are biased inward by the spring force of the return springs 50 and turned inward about their anchor pins 21, thus to be closed as shown in Fig. 4A. In this case, there is a gap between the braking teeth 11 of the drum 10, fixed to the propeller shaft of the automobile, and the teeth 311 of the shoes 31 so that the propeller shaft is applied with no braking force but can free rotate. When the brake lever or the switch (not shown) is handled in order for braking and stopping the automobile, the operating lever 60 which is pivoted to the housing 20 and biased by the return spring 50 is forcibly turned at a given turning angle in the direction of arrow of Fig. 4A. Therefore, the cam 40 fixed to the operating lever 60 is also turned clockwise or in the turning direction of the lever 60.

The two-leading shoes 31, contacting with the cam 40 at their top ends, are thus turned outward about their anchor pins 21 by the clockwise turning motion of the cam 40, thus to be opened in the drum 10. Hence, the braking teeth 311 of the shoes 31 come into engagement with the

braking teeth 11 of the drum 10 as shown in Fig. 4B.

When the teeth 311 of the shoes 31 substantially engage with the teeth 11 of the drum 10 as shown in Fig. 4B, there is no slip between the shoes 31 and the drum 10 differently from the typical brake with brake linings so that the automobile with this center brake can be stably braked. In this regard, the center brake of the invention prevents possible safety accident caused by bad braking action of the brake. In the center brake of this invention, the braking teeth 11 and 311 made of cast iron have excellent consume resistance in comparison with the typical brake linings made of asbestos so that the teeth 11 and 311 are scarcely consumed and scarcely reduced in their braking function irrespective of long time use. Therefore, the center brake of this invention can be semi-permanently used.

When the brake lever or the switch is handled in order for letting the brake be out of the braking action, the solenoid 92 or the air booster 91 used as the returning means is operated and, at the same time, the arcuate two leading shoes 31 in the brake drum 10 are biased inward by the spring force of the return springs 50 and turned inward about their anchor pins 21, thus to be closed as shown in Fig. 4A and to release the propeller shaft of the automobile.

Of course, the present invention may be adapted for an internal forcing center brake having the double-action

two-leading shoes 32 as shown in Figs. 5A and 5B. In this case, the center brake will achieve the same operational effect as described for the brake having the single-action two-leading shoes 31. As the single-action two-leading shoes 32 are evenly biased outward by turning motion of the pair of cams 40 contacting with the opposed ends of the shoes 32, the braking teeth 321 of the same thickness are nearly totally formed on the outer surfaces of the shoes 32 differently from the teeth 311 of the shoes 31 of the primary embodiment.

In this second embodiment, the braking teeth 11 of the drum 10 and the braking teeth 321 of the shoes 32 may have either the triangular shape or the trapezoidal shape in the same manner as described for the primary embodiment having the single-action two-leading shoes 31.

The center brake of the second embodiment also has the pair of connectors 80 for connecting the opposed ends of each cam 40 to their associated ends of the shoes 32. The connectors 80 are adapted for smoothing the returning motion of the shoes 32. In the same manner as described for the primary embodiment, the center brake of this second embodiment may include a solenoid 92 or an air booster 91 which will be used as the returning means of the brake as shown in Fig. 6. Of course, it should be understood that the brake may be provided with the solenoid 92 and the air booster 91 which will be used as

the braking means and the returning means of the brake respectively as shown in Fig. 7.

Figs. 5A and 5B show operation of the center brake having the double-action two-leading shoes 32 of the invention. The operation of the center brake having the shoes 32 is equal to that of the brake having the shoes 31 except for the moving direction of the shoes 32 and further explanation for the operation of the brake having the shoes 32 is thus not deemed to be necessary. Differently from the typical center brake having asbestos linings, the center brake having the cast iron braking teeth 11, 311, 321 of the invention reliably brakes and stops the automobile and absolutely prevents starting of the automobile as long as the braked state of the automobile is not released. In this regard, the center brake prevents possible abrasion of the brake due to unskilled handling of the brake lever.

Industrial Applicability As described above, the present invention provides a center brake for automobiles which is provided with a plurality of triangular or trapezoidal braking teeth integrally formed on the outer surfaces of the brake shoes and on the inner surface of the brake drum, thus to let perfect braking action of the center brake and to prevent possible safety accident caused by bad braking action of the brake.

This center brake does not use harmful material, such as asbestos, for braking means of the brake but uses steel for the braking means, thus to prevent the braking means not only, from causing functional diseases of the hearts and lungs of users but also from causing environmental pollution.

This center brake also includes an air booster or a solenoid and reliably carries out its returning action even in the case of freeze of the brake in the winter season, thus to remarkably improve the reliability of the center brake.

The instant center brake can be handled by a switch without use of brake lever when operating or releasing the center brake, thus to facilitate handling of the brake. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.