Abstract:
A decration sensor includes a pendulum which is suspended within an U-shaped bucket. The pendulum carries a permanent magnet which is adjacent to a Hall Effect device mounted upon the bucket. Both the pendulum and bucket are carried in an open ended housing which permits movement of the bucket relative to the pendulum to adjust for surface angles when the sensor is mounted upon a vehicle. Upon the deceleration of the vehicle, the pendulum move relative to the Hall Effect Device. As a result of the changing magnetic field, a voltage is generated by the Hall Effect Device which is directly proportional to the vehicle deceleration.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to controllers for electric trailer brakes and in particular to a deceleration sensor for an electric brake controller. 
     Towed vehicles, such as recreational and utility trailers adapted to be towed by automobiles and small trucks, are commonly provided with electric brakes. The electric brakes generally include a pair of brake shoes which, when actuated, frictionally engage a brake drum. An electromagnet is mounted on one end of a lever to actuate the brake shoes. When an electric current is applied to the electromagnet, the electromagnet is drawn against the rotating brake drum which pivots the lever to actuate the brakes. Typically, the braking force produced by the brake shoes is proportional to the electric current applied to the electromagnet. This electric current can be relatively large. For example, the electric brakes on a two wheeled trailer can draw six amperes of current when actuated and the electric brakes on a four wheeled trailer can draw 12 amperes of current. 
     Automotive industry standards require that electrically-actuated vehicle brakes be driven against the ground potential of the vehicle power supply. Accordingly, one end of each of the towed vehicle brake electromagnets is electrically connected to the towed vehicle ground and the towed vehicle ground is electrically connected to the towing vehicle ground. The other end of each of the brake electromagnets is electrically connected through an electric brake controller to the towing vehicle power supply. 
     Various electric brake controllers for towed vehicle electric brakes are known in the art. For example, a variable resistor, such as a rheostat, can be connected between the towing vehicle power supply and the brake electromagnets. The towing vehicle operator manually adjusts the variable resistor setting to vary the amount of current supplied to the brake electromagnets and thereby control the amount of braking force developed by the towed vehicle brakes. An example of such a controller is disclosed in U.S. Pat. No. 3,740,691. 
     Also known in the art are more sophisticated electric brake controllers which include electronics to automatically supply current to the brake electromagnets when the towing vehicle brakes are applied. Such electronic brake controllers typically include a sensing unit which generates a brake control signal corresponding to the desired braking effort. For example, the sensing unit can include a pendulum which is displaced from a rest position when the towing vehicle decelerates and an electronic circuit which generates a brake control signal which is proportional to the pendulum displacement. One such sensing unit is disclosed in U.S. Pat. No. 4,726,627. Alternately, the hydraulic pressure of the brake fluid in the towing vehicle&#39;s braking system or the pressure applied by the driver&#39;s foot to the towing vehicle&#39;s brake pedal can be sensed to generate the brake control signal. A pressure transducer for sensing the brake fluid pressure is disclosed in U.S. Pat. No. 4,279,162, while a brake pedal pressure sensor is disclosed in U.S. Pat. No. 4,380,002. 
     Known electronic brake controllers also usually include an analog pulse width modulator. The input of the pulse width modulator is electrically connected to the sensing unit and receives the brake control signal therefrom. The pulse width modulator is responsive to the brake control signal for generating an output signal comprising a fixed frequency pulse train. The pulse width modulator varies the duty cycle of the pulse train in proportion to the magnitude of the brake control signal. Thus, the duty cycle of the pulse train corresponds to the amount of braking effort desired. 
     Electronic brake controllers further include an output stage which is electrically connected to the output of the pulse width modulator. The output stage typically has one or more power transistors which are connected between the towing vehicle power supply and the towed vehicle brake electromagnets. The power transistors function as an electronic switch for supplying electric current to the towed vehicle brakes. 
     The output stage is responsive to the pulse width modulator output signal to switch the power transistors between conducting, or “on”, and non-conducting, or “off”, states. As the output transistors are switched between their on and off states in response to the modulator output signal, the brake current is divided into a series of pulses. The power supplied to the towed vehicle brakes and the resulting level of brake application are directly proportional to the duty cycle of the modulator generated output signal. A typical electronic brake controller is disclosed in U.S. Pat. No. 4,721,344. 
     Recently, microprocessors have been incorporated into electronic brake controllers. The microprocessor replaces the analog pulse width modulator described above. The microprocessor is connected directly to the controller output stage and switches the output transistors between their on and off states as a function of the brake control signal. Such a unit is disclosed in U.S. Pat. No. 5,620,236. 
     SUMMARY OF THE INVENTION 
     This invention relates to a deceleration sensor for an electric brake controller. 
     As described above, it is known to use a pendulum device to generate a brake control signal which is proportional to the deceleration of a towing vehicle. Because the pendulum rest position is determined by gravity, it is necessary to level the pendulum when the controller is mounted upon a vehicle dashboard in a nonhorizontal position. Accordingly, it would be desirable to provide a structure for supporting the pendulum that would allow a maximum amount of adjustment to compensate for a variety of mounting positions. 
     The present invention contemplates a device for sensing the deceleration of a vehicle which includes a housing adapted to be secured to the vehicle. The housing includes a pair of spaced apart supporting members with a U-shaped bucket suspended between the housing support members and pivotable about an axis. A pendulum is suspended within the bucket and also pivotable about the same axis. A positioning device is carried by the housing and connected to the bucket. In the preferred embodiment, the positioning device includes a crank which is connected to the bucket and operable to rotate the bucket relative to the housing. The positioning device is operable to rotate the bucket about the axis relative to the housing in either a forward or a rearward direction with the bucket being rotatable sufficiently in either the forward or rearward direction such that at least of portion of the bucket extends beyond both of housing supporting members. 
     At least one of the housing support members has a recess formed therein, the recess receiving a portion of the crank whereby the amount of rotation of the bucket about the pivot pin is increased over prior art sensor designs. The housing further includes a cross member supported by a pair of arms which extend from the housing support members. The cross member is urged by the arms against a portion of the bucket such that the bucket is frictionally retained in a particular position relative to the housing. 
     It is also contemplated that the device includes a carrier mounted upon the bucket, the carrier having a slot formed therein which slidingly receives and frictionally retains a Hall Effect Device. The end of the pendulum opposite from the pivot carries a permanent magnet. The permanent magnet cooperates with the Hall Effect Device upon movement of the pendulum to cause the Hall Effect Device to generate a voltage which is proportional to the deceleration of the vehicle. 
     In the preferred embodiment, the device is included in an electric brake controller installed upon a towing vehicle. The voltage generated by the Hall Effect Device upon deceleration of the towing vehicle is utilized by the brake controller as a brake control signal for controlling a set of electric wheel brakes mounted upon a towed trailer. The electric brake controller can have an outer housing with the device mounted inside the outer housing. In such a case, the outer housing has an aperture formed therethrough with an end of the crank extending through the outer housing aperture. An adjustment lever is formed upon the extended end of the crank. A vehicle operator can manipulate the adjustment lever to move the bucket relative to the housing in order to position of the Hall Effect Device relative to the pendulum magnet. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is schematic diagram illustrating an electric trailer brake system which includes an electronic trailer brake controller. 
     FIG. 2 is a perspective view of a pendulum assembly in accordance with the invention and which is included in the brake controller shown in FIG.  1 . 
     FIG. 3 is a sectional view of the pendulum assembly shown in FIG. 2 taken along line  3 — 3  in FIG.  2 . 
     FIG. 4 is a sectional view of the pendulum assembly shown in FIG. 2 taken along line  4 — 4  in FIG.  3 . 
     FIG. 5 is an exploded view of the pendulum assembly shown in FIG.  1 . 
     FIG. 6 is a perspective view of an alternative embodiment of the housing included in the pendulum assembly shown in FIG.  2 . 
     FIG. 7 is a sectional view illustrating the attachment of the housing shown in FIG. 6 to a printed circuit board. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is shown in FIG. 1 a schematic diagram illustrating an electric brake system for a towed vehicle (not shown), shown generally at  10 , which utilizes an electronic brake controller  11 . The brake controller  11  is typically located in a towing vehicle (not shown), usually being mounted beneath the towing vehicle dashboard. When actuated, the controller  11  functions to supply an electric current through line  12  to energize electric brakes  13  and  14  which brake the wheels of the towed vehicle (not shown). 
     The electric brakes  13  and  14  each include a pair of brake shoes  15  and  16  which, when actuated by a lever  17 , are expanded into contact with a brake drum  18  for braking the wheels of the towed vehicle. A separate electromagnet  19  is mounted on an end of each of the brake actuating levers  17 . Each electromagnet  19  is positioned to abut the generally flat side of the brake drum  18 . As an electric current is passed through each of the electromagnets  19 , the electromagnets  19  are drawn into contact with the brake drums  18  and the resulting drag pivots the levers  17  to engage the brake shoes  15  and  16  in a conventional manner. It will be appreciated that, while FIG. 1 shows two sets of brakes  13  and  14 , the invention also can be applied to towed vehicles having more than two sets of brakes. 
     The towing vehicle typically includes a conventional hydraulic brake system  20  which is actuated when a brake pedal  21  is depressed by a vehicle driver. The brake pedal  21  is coupled to a brake light switch  22 . When the brake pedal  21  is depressed, the switch  22  is closed and power from a vehicle power supply  23 , shown as a storage battery in FIG. 1, is supplied to one or more towing vehicle brake lights  24  and one or more towed vehicle brake lights  25 . The vehicle power supply  23  is also connected by a first line  26  through a circuit breaker  27  to the controller  11 . Power is continuously supplied to the controller  11  through the first line  27 . It will be appreciated that, while circuit breaker  27  is shown in FIG. 1, a fuse or other overcurrent protection device can be used. A second line  28  connects the brake light side of the brake light switch  22  to the controller  11 . Thus, power also is supplied through the second line  28  to the controller  11  when the brake light switch  22  is closed. 
     The brake controller  11  is normally operated in an automatic mode with the towed vehicle brakes  13  and  14  being automatically actuated by the controller  11  when the towing vehicle brakes are actuated. The automatic mode is activated upon closure of the brake light switch  22 . The present invention contemplates that the controller  11  includes an improved pendulum assembly  30  which generates a brake control signal, that is directly proportional to the towing vehicle deceleration. The controller  11  is responsive to the brake control signal to supply an electric current through line  12  to actuate the towed vehicle brakes. Thus, electric current is directly proportional to the braking force applied to the towing vehicle. The pendulum assembly  30  is located within an outer housing  31  of the controller  11 . The pendulum assembly  30  includes a pendulum  32  which swings in response to the deceleration of the towing vehicle. As will be explained below, the brake control signal is proportional to the amount of pendulum swing. The pendulum assembly  30  also includes a leveling arm  34  which extends through a side wall of the controller outer housing  31 . 
     In some instances, it may be desirable to actuate only the towed vehicle brakes  13  and  14 . This may be desirable, for example, to stabilize the towed vehicle against vacillations or swinging caused by strong side winds. Therefore, the brake controller  11  also includes a manual mode of operation. Accordingly, a manual switch  36  is provided on the electronic controller  11  to allow the vehicle driver to actuate the towed vehicle brakes  13  and  14  without applying the towing vehicle brakes. Pressing the manual switch  36  initiates the manual mode of operation. The amount of electric current supplied to the towed vehicle brakes  13  and  14  is proportional to the displacement of the manual switch  36 . If the manual switch  36  is pressed while the brake pedal  21  is depressed, the manual operating mode overrides the automatic operating mode. 
     As shown in FIGS. 2 through 5, the pendulum assembly  30  includes an outer housing  40  formed from plastic. A plurality of stakes  41  extend from the bottom of the housing  40  and are received by corresponding apertures formed through a Printed Circuit Board (PCB)  44 , as shown in FIG.  4 . The ends of the stakes  41  are glued to the PCB  44  to secure the housing  40  to the PCB  44 . Alternately, the ends of the stakes  41  are heated and then peened against the bottom surface of the PCB  44 . The PCB  44  carries electronic components (not shown) which are responsive to the brake control signal to control the electric trailer brakes. The PCB  44  is mounted within the electronic brake controller outer housing  31 , which is shown in phantom in FIGS. 3 and 4. 
     The housing  40  includes left and right side walls, or members,  42  and  43 , respectively, which are spaced apart by upper and lower cross members,  44  and  45 , respectively. Thus, the rear of the housing  40  is open. As best seen in FIG. 5, a notch  46  is formed in the front surface of the right side wall  43 , the purpose for which will be explained below. A pair of cantilevered arms,  48  and  49 , extend from the upper portion of the side walls  42  and  43 . A clamp bar  50  extends across the top of the housing  40  between the ends of the cantilevered arms  48  and  49 . As best seen in FIG. 5, the upper portion of each of the housing side walls  42  and  43  extends forward to form a pair of pendulum supports  52 . A semi-cylindrical pivot pin seat  54  is formed transversely across the upper surface of each of the pendulum supports  52 . A pair of retaining hoops  56  are formed in the pendulum supports  52  adjacent to the outer ends of the seats  54 . 
     The pendulum  32  is supported for swinging movement relative to the housing  40  by a pivot pin  60 . The pivot pin  60  has a first end  62  formed at a right angle to the axis of the pin  60 . The first end  62  of the pivot pin  60  is received in a slot  64  formed in the leveling arm  34  to secure the pivot pin  60  to the leveling arm  34 . The pivot pin  60  extends through the retaining hoops  56  and is supported by the pivot pin seats  54  formed in the housing pendulum supports  52 . The pivot pin  60  is retained upon the housing  40  by an annular retaining clip  66  which is pressed onto the end of the pivot pin  60  opposite from the first end  62 . 
     The upper end of the pendulum  32  includes a pair of spaced apart bushings  68  which slidingly receive the pivot pin  60 . In the preferred embodiment, the pivot pin  60  has a plated surface which is very smooth to minimize frictional forces between the pin  60  and the pendulum bushings  68 . Accordingly, the pendulum  32  is free to rotate about the pivot pin  60 . Additionally, while one retaining clip  66  is shown in FIG. 3, it will be appreciated that the invention also can be practiced utilizing two retaining clips (not shown). The two retaining clips cooperate with one another to assure that the retaining clips do not slide in an axial direction upon the pivot pin  60 . Thus, the pendulum  32  is retained in the correct position relative to the other components of the pendulum assembly  30 . The lower end of the pendulum  32  carries a pendulum permanent magnet  70 . 
     The pendulum assembly  30  further includes a U-shaped bucket  72  formed from a ferromagnetic material. The bucket  72  includes an arcuate shaped lower wall  74  connected to a pair of spaced apart triangular shaped side walls  76  and  77 . The side walls  76  and  77  have apertures formed in the upper ends thereof for receiving the pivot pin  60 . The bucket  74  also has recesses  78  formed in the leading edge of each of the bucket side walls  76  and  77  immediately below the pivot pin apertures. The purpose for the recesses  78  will be explained below. The upper ends of the bucket sidewalls  76  and  77  are rounded. As best seen in FIG. 3, the pendulum  32  is suspended within the bucket  72  and the bucket  72  is, in turn, suspended between the housing sidewalls  42  and  43 . It has been found that the magnetic attraction between the bucket  72  and the pendulum magnet  70  dampen movement of the pendulum  32  when the pendulum assembly  30  is subjected to road shocks. 
     A positioning aperture  79  is formed through the right side wall  77 . The positioning aperture  79  receives the end of a crank  80  formed upon the leveling arm  34 . As will be explained below, the crank  80  cooperates with the positioning aperture  79  to level the pendulum assembly  30 . The clamp bar  50  is urged against the upper ends of the bucket side walls  76  and  77  by the cantilevered arms  48  and  49 . Accordingly, the bucket  72  is frictionally retained in position relative to the housing  40  by the clamp bar  50 . The pendulum bushings  68  have a smaller outside diameter than upper ends of the bucket sidewalls  76  and  77 . Accordingly, the pendulum  32  does not contact the clamp bar  50 , allowing the pendulum  32  to swing freely within the bucket  72 . 
     A plastic carrier  82  is mounted upon the upper surface of the lower bucket wall  74 . The carrier  82  includes an arcuate shaped base portion  83  which terminates in a cylindrical bracket  84 . The bracket  84  receives and retains a permanent restoring magnet  85 . The restoring magnet  85  repels the pendulum magnet  70  to urge the pendulum  32  toward its resting position. The restoring force increases in magnitude as the pendulum  32  swings further from its resting position. The quality of the restoring magnet  85  has been increased to make it more resistant to demagnetization. According the combination of the magnetic attraction between the restoring magnet  85  and the ferromagnetic bucket  72  and the frictional retaining force of the carrier bracket  84  is sufficient to retain the restoring magnet  85  in position. Accordingly, the need to apply an adhesive to the magnet  85 , as was required to secure the magnet in prior art devices, is eliminated. 
     The carrier  82  also includes a side portion  86  which extends from the base portion  83  and has a notch  87  formed therein. The carrier side portion  86  is adjacent to the bucket left side wall  76 . The notch  87  slidingly receives a Hall Effect Device  30  (HED)  88 . The side carrier portion  86  cooperates with the bucket left side wall  76  to frictionally retain the HED  88  in the notch  87 . A plurality of electrical leads  88 A extend from the HED  88 . Each of the leads  88 A extends through a cylindrical length of electrically insulative material  88 B which is heat shrunk onto the lead  88 A. The insulative material  88 B insulates the HED leads  88 A from the bucket  72  and thereby prevents a short circuit. Use of the insulative material  88 B eliminates the need to position a strip of insulative material between the HED leads  88 A and the bucket, as was the practice with prior art pendulum assemblies. Thus, the assembly of the device is simplified. A pendulum stop post  89  extends from the rear of the carrier  82  to prevent rearward motion of the pendulum  32 . 
     As the pendulum  32  swings from its resting position when the towing vehicle decelerates, the HED  88  generates a voltage proportional to the amount of pendulum movement. In order to achieve proper operation, it is necessary that the resting position of the pendulum  32  relative to the center of the HED  88  be adjusted, or “leveled”, after the brake controller casing  31  has been securely mounted within the towing vehicle. Typically, the brake controller  11  is mounted upon, or under, the towing vehicle dashboard. The mounting location usually is not horizontal. Once the controller is mounted, the pendulum position is adjusted by moving the leveling arm  34 . As explained above, movement of the leveling arm moves the bucket  74  relative to the pendulum assembly housing  40 . Since the HED  88  is held against the left bucket wall  76  by the carrier  82 , movement of the bucket  74  also moves the HED  88  relative to the pendulum  32 . Typically the controller  11  includes a feedback device to assist the operator in leveling the controller after it is installed in the towing vehicle. For example, the controller  11  can include a light which is illuminated when the pendulum magnet  70  is positioned correctly relative to the HED  88 , 
     The notch  46  formed in the left side of the pendulum assembly housing  40  provides for additional travel of the crank  80  while the open rear end of the housing  40  provides for additional travel of the bucket  74  in the rearward direction over prior art pendulum assemblies. Thus, a brake controller  11  which includes the improved pendulum assembly  30  can be installed over a greater range of mounting surface angles than prior art brake controllers. Furthermore, the recesses  78  formed in the leading edges of the bucket side walls  76  and  77  receive the clamp bar  50  and thereby increase the amount of bucket travel relative to the housing  40  in the forward direction. Additionally, as described above, the clamp bar  50  frictionally retains the bucket  72  in the leveled position. Thus, the magnet/HED relationship is maintained. Because the slot  87  in the carrier side portion  86  frictionally retains the HED  88 ; a step of gluing the HED  88  in place, which was required in the assembly of prior art pendulum assemblies, is eliminated. 
     An alternate embodiment of the pendulum assembly housing is shown in FIG. 6 where the stakes  41  shown in the preceding figures have been replaced by clips  90  which terminate in barbs  92 . The ends of the clips  90  are arcuate shaped. As shown in FIG. 7, the clips  90  are received by corresponding slots  94  (one shown) formed through the PCB  44 . As the clips  90  are pressed into the PCB slots  94 , the clips  90  are urged in an inward direction by their arcuate shaped ends. Once the barbs  92  have passed through the slots  94 , the resiliency of the plastic forming the housing urges the clips  90  in an outward direction causing the barbs  92  to engage the lower surface of the PCB  44  and thereby retain the housing and pendulum assembly upon the PCB  44 . Thus, the alternate embodiment of the housing simplifies installation of the pendulum assembly in the brake controller  11  by eliminating the steps of gluing or heating and peening. 
     Further details concerning operation of the pendulum assembly  30  and the associated electronic brake controller are included in the above mentioned U.S. Pat. Nos. 4,721,344, 4,726,627 and 5,620,236, which are incorporated herein by reference. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. For example, while the invention has been illustrated and described as being utilized with an electric trailer brake controller, it will be appreciated that the invention also can be practiced with other devices. For example, the pendulum assembly can be utilized to measure vehicle deceleration for input to anti-lock and vehicle stability systems.