Abstract:
An electric drum brake comprises a back plate. Shoes are operatively mounted to the backplate and displaceable to a deployed condition against a wheel drum from a retracted condition. An electrically powered actuation mechanism is adapted to convert electric power to a movement of the shoes to the deployed condition. A safety actuation mechanism comprises a lever having a first end adapted to receive a mechanical force. A joint configuration connects the lever to at least one of the shoes to convert movements of the lever to movements of at least one of the shoes between the deployed condition and the retracted condition without said electric power. A biasing member produces a biasing action against at least one of the lever and the joint configuration to maintain the shoes in the deployed condition, the mechanical force being against the biasing action to maintain the shoes in the retracted condition.

Description:
FIELD OF THE APPLICATION 
     The present application relates to trailers such as domestic trailers and, more particularly, to a safety brake system used when trailers are unhitched or accidentally detached from a vehicle to block the wheels of the trailer. 
     BACKGROUND OF THE ART 
     Large trailers, such as those used in the freight industries, are equipped with braking systems in order to ensure that the tractor and trailer combination has enough braking power to safely transit on roads. Some trailers are commonly equipped with air brakes that are actuated from the tractor, which air brakes automatically lock the wheels of the trailer when the latter is unhitched. 
     Smaller trailers, for instance domestic trailers or trailers used to tow recreational vehicles (e.g., boat, motorcycle, ATV, etc.) may have brake systems. For instance, electric drum brakes are commonly used in smaller trailers. In a drum brake, shoes (a.k.a., pads) press against a rotating drum-shaped part called a brake drum. The brake drum rotates, as part of the wheel. In order to apply the braking power to the drum brake, an electromagnetic magnet is powered to activate a displacement of the shoes into contact with the drum. 
     Accordingly, an electric current must be supplied to the electric drum brake to apply the brakes. When the trailer is unhitched, the electric drum brake may often be disconnected from the power source of the vehicle. Accordingly, random masses (e.g., log, plank, rock) are often wedged behind the wheels of the trailer so as to block movement of the trailer. This action of wedging is hazardous. Moreover, if the operator forgets to wedge a mass behind the wheels, the trailer might start moving if it is on a slope. With the inertia of the trailer and its contents, a moving trailer is hard to stop and may cause severe damages and/or injuries. 
     Hence, a safety brake system has been developed to address this issue, and is described in PCT application publication no. WO 2010/096934. The safety brake system detects an unhitched condition of the trailer and produces a mechanical force to apply the brakes in response thereto. However, in electric drum brakes, an electric current must be supplied to apply the brakes, which electric current may not be available due to the unhitching of the trailer from the vehicle. Moreover, electric drum brakes may not be configured to receive electric current for an extended period (e.g., parked trailer). This would require a continuous supply of power and batteries of suitable capacity. 
     SUMMARY OF THE APPLICATION 
     It is therefore an aim of the present disclosure to provide a safety brake system that addresses issues associated with the prior art. 
     Therefore, in accordance with the present application, there is provided an electric drum brake comprising: a back plate; shoes operatively mounted to the backplate and displaceable to a deployed condition against a wheel drum from a retracted condition; an electrically powered actuation mechanism adapted to convert electric power to a movement of the shoes to the deployed condition; and a safety actuation mechanism comprising a lever having a first end adapted to receive a mechanical force, a joint configuration connecting the lever to at least one of the shoes to convert movements of the lever to movements of at least one of the shoes between the deployed condition and the retracted condition without said electric power, and a biasing member producing a biasing action against at least one of the lever and the joint configuration to maintain the shoes in the deployed condition, the mechanical force being against the biasing action to maintain the shoes in the retracted condition. 
     Further in accordance with the present disclosure, the joint configuration comprises a shaft integrally connected to a second end of the lever on a rear side of the back plate to move therewith, the shaft passing through a hole in the back plate for the joint configuration to connect to at least one of the shoes and transmit movements of the lever to at least one of the shoes. 
     Still further in accordance with the present disclosure, the joint configuration comprises a cam link integrally connected to the shaft, the cam link being connected to a first one of the shoes by an interface link, the interface link being rotatably connected to the cam link and the shoe. 
     Still further in accordance with the present disclosure, a brake shoe interface is rotatably mounted to the shaft and connected to a second one of the shoes by a rotational joint, and further wherein a dimension of the hole is selected to allow translation of the shaft relative to a plane of the back plate, a translation of the shaft causing said movement of the shoe by transmission via the brake shoe interface. 
     Still further in accordance with the present disclosure, said interface link and the rotational joint are positioned on generally opposite sides of the shaft. 
     Still further in accordance with the present disclosure, a support bracket is secured to a rear face of the back plate, the support bracket comprising a cable stop to form an abutment for a cable housing enclosing a cable adapted to be connected to the first end of the lever for transmitting the mechanical force, the mechanical force being a pull from said cable. 
     Still further in accordance with the present disclosure, the support bracket further comprises an abutment to which a first end of the biasing member is connected, a second end of the biasing member being connected to the lever. 
     Still further in accordance with the present disclosure, a support bracket is secured to a rear face of the back plate, the support bracket comprising lever stops positioned on opposite sides of the lever to delimit movements of the lever. 
     Still further in accordance with the present disclosure, the joint configuration and lever of the safety actuation mechanism are separate from the electrically powered actuation mechanism. 
     Still further in accordance with the present disclosure, the electrically powered actuation mechanism comprises an electromagnet connected to linkages to convert said electric power to the movement of the shoes to the deployed condition. 
     Still further in accordance with the present disclosure, a trailer comprises at least an axle; a wheel with a drum mounted to the axle to rotate therewith; and the electric drum brake as described above, wherein the axle passes through a hole in the back plate. 
     Still further in accordance with the present disclosure, a safety brake system has a cable applying the mechanical force when the trailer is in an unhitched condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an assembly view of an electric drum brake assembly with a safety actuation mechanism in accordance with the present disclosure; 
         FIG. 2  is a face view of a back plate of the electric drum brake with safety actuation mechanism of  FIG. 1 , with a shield thereon; 
         FIG. 3  is a face view of the back plate of the electric drum brake with safety actuation mechanism of  FIG. 2 , without the shield; 
         FIG. 4  is a face view of the electric drum brake with safety actuation mechanism of  FIG. 1 ; and 
         FIG. 5  is a face view of the safety actuation mechanism of  FIG. 1  relative to the back plate, with components of the electric drum brake remove. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, and more particularly to  FIG. 1 , there is illustrated an electric drum brake assembly at  10 . The electric drum brake assembly  10  comprises a safety actuation mechanism that actuates the drum brake when the trailer is in an unhitched condition. For example, the electric drum brake assembly  10  is connected to a safety brake system as described in PCT application publication no. WO 2010/096934, by the current applicant and incorporated herein by reference. This PCT application is one of many published applications by the current applicant, and the electric drum brake assembly  10  may be used with the safety brake systems of any one of the patent applications by the current applicant. Hence, a force in direction F1 is available at the electric drum brake assembly  10 , which force is for instance provided by a wire. 
     Referring to  FIGS. 1 and 4 , the electric drum brake assembly  10  comprises a back plate  11  (or frame, or structure). The back plate  11  is the structural component of the electric drum brake assembly  10  and hence is in a fixed relation relative to the trailer (i.e., it does not rotate with the wheel). The axle A is part of the trailer and extends through a hole in the back plate  11 . Accordingly, a drum of the wheel is secured to the end of the axle A (shown in  FIG. 1 ) projecting beyond the face of the back plate  11 . 
     Referring to  FIGS. 1 and 5 , shoes  12  are operatively mounted to the back plate  11 , and may therefore move outwardly in directions F2 and F3. The shoes  12  may also be known as brake pads and are configured to come in contact with an inner surface of the drum when moved to directions F2 and F3, and hence oppose friction forces against rotational movement of the drum, in a deployed condition. Among other accessories, the electric drum brake assembly  10  may comprise springs  14  ( FIG. 5 ) to bias the shoes  12  toward one another (i.e., brakes not being applied). The electric drum brake assembly  10  comprises an electromagnet  15  that receives an electric current from the towing vehicle or from a power source in the trailer. The electromagnet  15  is connected to a first end of a lever  16  ( FIG. 5 ), while a second end of the lever  16  is connected to a cam mechanism  17  ( FIG. 5 ) or like reciprocal mechanism that will convert a motion of the lever  16  to a movement of the shoes  12  in directions F2 and F3. Accordingly, when the electric current is applied to the electromagnet  15 , the lever  16  will be displaced, thereby causing the shoes  12  to move in directions F2 and F3, via mechanism  17 . 
     Referring concurrently to  FIGS. 1 to 4 , the safety actuation mechanism is used to convert the force from the safety brake system in direction F1 into motion of the shoes  12  in directions F2 and F3. The safety actuation mechanism has a lever assembly. The lever assembly comprises a lever  20  that is positioned on the backside of the back plate  11  (i.e., in the back of the face shown in  FIG. 1 ). A free end  21  of the lever  20  is connected to the safety brake system, illustrated by cable housing W applying force F1. The cable housing W typically encloses a wire of the safety brake system that extends all the way from a trailer tongue to the free end  21  of the lever  20  and therefore transmits/releases a pulling force in direction F1, as described in PCT application publication no. WO 2010/096934. 
     The opposite end of the lever  20  is connected to a shaft  22 . The shaft  22  may be spaced apart from a longitudinal axis of the lever  20  by a bent in the lever  20 . The bent may be provided to distance the lever  20  from components projecting from the backside of the back plate  11  (e.g., bolts, etc.). In an embodiment, the lever  20  is connected to the shaft  22  by way of a sleeve  23  receiving the shaft  22  to rotate therewith (e.g., by an appropriate set screw). Thus, the lever  20  and the shaft  22  are integrally connected, so as to move concurrently. The shaft  22  passes through a hole  24  made in the back plate  11 . The hole  24  is sized to allow some movement of the shaft  22 , in addition to rotational movement, as discussed hereinafter. 
     Referring concurrently to  FIGS. 2 and 3 , a support bracket  25  is connected to the back plate  11 , and comprises a cable stop  25 A for cable housing W. The bracket  25  further comprises an abutment  25 B, to which an end of biasing member  26  is connected. The biasing member  26  is illustrated as being a torsion spring will bias the lever  20  to apply a pull on the wire in the cable housing W, by being connected at a second end to the lever  20 . Hence, the spring  26  pressures the free end of the lever  20  away from the cable stop  25 A, thereby applying the brakes, as described hereinafter. 
     Another support bracket  27  is also connected to the back plate  11 . The support bracket  27  comprises lever stops  27 A and  27 B to delimit the range of movements of the lever  20 . As shown in  FIG. 2 , a shield  28  may be used to cover the various components described above, and prevent tampering with the safety actuation mechanism. 
     Referring to  FIGS. 1 and 4 , the front face of the back plate  11  is shown. A link  29  is integrally connected to a free end of the shaft  22  so as move therewith, and will act as a cam to cause movement of one of the brake pads, as described hereinafter. It is observed that a rotational axis of the lever assembly relative to the back plate  11  is that of the shaft  22 . It is also observed that the rotational axis of the lever assembly is not fixed relative to the back plate  11 , as the shaft  22  may translate relative to the hole  24 . 
     A brake shoe interface  30  is integrally connected to one of the shoes  12 . According to an embodiment, the brake shoe interface  30  may be bolted, welded or fastened in any appropriate way to the shoe  12 , but with a rotational joint being formed. In the illustrated embodiment, screw holes are provided on both the shoe  12  and the brake shoe interface  30 . The brake shoe interface  30  comprises a tube  31 . The tube  31  has an inner diameter sized so as to rotatingly receive therein the shaft  22 . Hence, a rotational joint is formed between the tube  31  and the shaft  22 . An end of the tube  31  abuts against an end of the sleeve  23 , with either one of the sleeve  23  and the tube  31  being within the hole  24  in the back plate  11 . As mentioned previously, the hole  24  is bigger in dimensions than the sleeve  23  and the tube  31 , to allow translational movement of the shaft  22  in a plane of the back plate  11  (e.g., X and Y axes in  FIGS. 4 and 5 ), as well as rotational movement about a longitudinal axis of the shaft  22 , for two translational degrees of freedom and one rotational degree of freedom. 
     A further brake shoe interface  40  is pivotally connected to the free end of the link  29  and to the other shoe  12 . As the brake shoe interface  40  is positioned one side of the axis of the shaft  22  while the free end  21  of the lever  20  is on the other side, a rotational movement of the free end lever  21  about the shaft  22  results in the brake shoe interface  40  rotating in the other direction, from a vectorial perspective. The brake shoe interface  40  is rotatably mounted to the link  29  and to the show  12 . 
     Now that the various components of the electric drum brake assembly  10  and safety actuation mechanism have been described, an operation thereof to activate the drum brake in a safety condition is set forth, with reference to  FIGS. 1-5 . 
     It is firstly assumed that the electric drum brake assembly  10  is not being actuated by electrical current on the electromagnet  15 . However, assuming that the trailer is hitched, the safety actuation mechanism does not apply the brakes. 
     The safety brake system, displaced to an actuation condition, causes a movement of the lever  20 . For illustrative purposes, the movement of the lever  20  is by the release of the pulling action of the cable (i.e., away from direction F1), toward a right-hand side of the page in  FIGS. 2 and 3 . In other words, the cable was pulling in direction F1 to disarm the brakes, but a release in cable tension will result in the spring  26  displacing the lever  20  to the right-hand side of the page for  FIGS. 2 and 3 . As a result of the movement of the free end  21  of the lever  20 , the shaft  22  rotates about its axis and moves in translation along the hole  24  also in the right-hand side of the page in  FIGS. 2 and 3 , but left-hand side of the page in  FIG. 4 . 
     As the tube  31  of the brake shoe interface  30  is on the shaft  22 , the brake shoe interface  30  will translate in the same direction as the shaft  22 . As the tube  31  forms a rotational joint with the shaft  22 , the movement will be transmitted to the brake shoe interface  30  in such a way that same will move the brake shoe  12  in normal unconstrained fashion, outwardly relative to the back plate  11 , in direction F2. 
     On the other hand, the brake shoe interface  40  will convert the rotational movement of the link  29  into a displacement of its respective shoe  12 , toward the right-hand side in  FIG. 4 . The rotational joints formed between the brake shoe interface  40  and both the link  29  and the shoe  12  allow the generally unconstrained transmission of movement from the link  29  to its respective shoe  12 , thereby moving the shoe  12  outwardly and into braking contact with the wheel drum. 
     Although one specific configuration has been shown in  FIGS. 1-5 , it is considered to use other mechanisms to transmit the force from the safety brake system to the shoes  12 . For instance, instead of being integrally connected to its respective shoe  12 , the brake shoe interface  30  may be offset from the axis of the shaft  22 , and may be pivotally connected to its respective shoe  12  and to the link  29  (e.g., diametrically opposed to the connection point between the link  25  and the brake shoe interface  40 ). Hence, by the release of the cable tension, the biasing forces provided by the spring  26  will apply the brakes (i.e., will deploy the brake pads  12  against the wheel drum), as the spring  26  biases the lever  20  to the braking position. 
     It is observed that the safety actuation mechanism described above applies the brakes by way of mechanical forces (i.e., the spring  26 ), without using electric power for the electromagnet  15 . Hence, the safety actuation mechanism will not deplete power sources when actuating the brakes. 
     In the illustrated embodiment, the safety actuation mechanism applies the brakes in a normal standby position, and a force must be applied against the safety actuation mechanism (e.g., F1) to release the brakes. As discussed above, the force F1 may be a pulling action (although a pushing action could also be used) that results in a safety brake system being displaced to a hitched position of a trailer. The release of the pulling action is hence an unhitched condition, or sectioning of the cable (e.g., in case of theft). 
     In another embodiment, it is considered to connect the safety brake system directly to the lever  16 . One or more of the trailer wheels may have the safety actuation mechanism as described herein. The safety actuation mechanism may be retrofitted onto existing electric drum brake assembly, with the necessary modifications being made to the assembly (e.g., hole in the back plate  11 , connection points in the shoes). Also, the safety brake system has no impact on the operation of the electric actuation system of the brake drum assembly  10 , as these systems operate independently from one another. It is also considered to have the safety actuation mechanism operate on a single one of the shoes  12 .