Abstract:
A system for actuating brakes in a towed vehicle in response to actuation of brakes in a towing vehicle comprising a cylinder including an inner cylindrical wall attached to a brake pedal in the towed vehicle and an outer cylindrical wall attached to the firewall in the towed vehicle. An air line supplies positive airflow from the towing vehicle to the cylinder and to a venturi to create a vacuum in response to the airflow. The vacuum is supplied to a brake booster in the towed vehicle while the airflow is supplied to the air cylinder to move the brake pedal in the towed vehicle in proportion to the amount of braking is the towing vehicle.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   Provisional Application for Patent No. 60/736,403, filed Nov. 12, 2005, with the title, “Towed Vehicle Brake System” which is hereby incorporated by reference. Applicant claims priority pursuant to 35 U.S.C. Par. 119(e)(i). 

   STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   Not applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to towed vehicle brake actuator assemblies. 
   2. Background Information 
   Applicant is co-inventor of Schuck et al, “Towed Vehicle Brake Actuator Assembly” Ser. No. 11/096,083 filed Mar. 31, 2005. 
   Existing towed vehicle brake actuating systems lack a means of applying proportionate braking effort to a towed vehicle using air pressure. 
   A mechanical vacuum pump is used to create a vacuum in the towed vehicle&#39;s power brake system. 
   As will be seen in the subsequent description of the preferred embodiments of the present invention, the present invention overcomes shortcomings of prior art. 
   SUMMARY OF THE INVENTION 
   The present invention in the preferred embodiment comprises a venturi that generates vacuum from a towing vehicle&#39;s compressed air brake system, an air valve in communication with a vacuum sensor that controls the level of vacuum generated by the venturi, an air cylinder that applies a towed vehicle&#39;s brakes, and a bracket for attaching the air cylinder to a brake pedal arm. The vacuum is supplied to the towed vehicle brake booster making the power brakes of the towed vehicle operate as if the engine were running. 
   The air cylinder comprises an inner wall that serves as a stationary mandrel, an outer wall that serves as the cylinder body, at least one return spring between the inner and outer walls, a DELRIN washer used as a separator if more than one return spring is used, a pull rod attached to the outer wall, and a cable attached to the pull rod. 
   The cylinder inner wall is attached to the bracket, which is attached to the brake pedal arm in the towed vehicle. As the towing vehicle brakes are applied, compressed air from the towing vehicle air brake system enters into the air cylinder which forces the outer wall of the cylinder away from the inner wall. The pull rod, being attached to the outer wall, with a cable attached to the pull rod and to the towed vehicle&#39;s firewall, as the outer wall, which is free to be displaced, is displaced with respect to the inner wall by compressed air pressure, the compressed air forces the outer wall of the cylinder away from the brake pedal. The inner wall is attached to the brake pedal by means of the bracket, so, as the outer wall is forced away from the brake pedal, the pull rod cable, which is in mechanical communication with the outer wall, pulls on the towed vehicle&#39;s firewall, forcing the brake pedal, which is in mechanical communication with the brake pedal, towards the firewall, applying the towed vehicle&#39;s brakes. 
   As the air input is from the towing vehicle&#39;s compressed air brake system, the present invention will apply truly proportionate braking in the towed vehicle. 
   Air from the towed vehicle&#39;s air system is directed, in parallel, to both the cylinder and the venturi. The vacuum created by the venturi is routed to the towed vehicle&#39;s vacuum booster of the power brake system of the towed vehicle&#39;s brake system creating vacuum assisted brakes without the means of a mechanical vacuum pump. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of the preferred embodiment of the present invention, a towed vehicle brake system 
       FIGS. 2 and 2A  are views of the cylinder and mounting bracket. 
       FIGS. 3 and 3A  are cross section views of the cylinder. 
       FIGS. 4 and 4A  illustrate cylinder function. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , the preferred embodiment of the present invention, a towed vehicle brake actuator assembly  10 , comprises an air input  100 , a venturi  102 , such as is obtainable from PIAB, which is known to the trade, a vacuum line  105  which is attached to a vacuum brake booster  107  located in a towed vehicle (not shown), a vacuum sensor such as vacuum switch  125 , an air valve  104 , and a cylinder  110 . 
   Air input  100 , from a towing vehicle (not shown), is applied to the venturi  102  as well as to an actuator such as the cylinder  110 , the venturi  102  and the cylinder  110  being in parallel. As the air passes through the venturi  102 , a vacuum is created in the vacuum line  105  and the vacuum brake booster  107 . Vacuum is communicated through the vacuum line  105  through the vacuum switch  125  that senses the vacuum level in the vacuum brake booster  107 . A brake booster  107  in a vehicle often uses a vacuum booster to enhance the activation of hydraulic brakes in the vehicle for example. Vacuum for the booster is typically supplied by the motor of the vehicle but when the vehicle is being towed normally the engine would not be operating. The air valve  104  opens as more vacuum is required for the vacuum brake booster  107 , which allows input air  100  to pass through the valve  104  to the venturi  102 . As air enters venturi  102 , a vacuum is created in the line  105  from a vacuum port  111  in the venturi  102  which results in vacuum in the power brake booster  107 . Excess air is vented through an exhaust port  112  of the venturi  102 . Vacuum switch  125  is in electrical communication with the air valve  104  through an electrical connection  130 . Vacuum switch  125  is powered by a 12 volt power source  135 , in the preferred embodiment of the present invention. 
   The venturi  102  serves the purpose of creating vacuum without the use of a mechanical vacuum pump. 
   This is a simpler more effective way to actuate a brake pedal than prior art. The towed vehicle brakes are applied in proportion to input air from the towing vehicle. The input air is typically, but not limited to, the air used in a towing vehicle&#39;s brake system as in the case with a diesel powered towing vehicle with air brakes. No standard air cylinders were available. No systems marketed today incorporate a venturi to create vacuum. The applicant&#39;s air cylinder is considerably smaller than a comparable vacuum cylinder. 
   The preferred embodiments of the present invention only require 20 PSI air pressure from the towing vehicle. 
   Referring to  FIGS. 2 and 2A , the cylinder  110  comprises an air input port  200 , an outer cylindrical wall  210 , an inner cylindrical wall  250 , a mounting assembly  260 , mounting plate  240 , mounting bolts  230  and mounting nuts  235 . 
   The mounting assembly  260  is affixed to the towed vehicles brake pedal arm  420 . 
   Referring to  FIGS. 3 and 3A , the cylinder  110  comprises a bushing  300 , a flexible cable  302 , at least one return spring  315 , a DELRIN washer  316  if more than one return spring  315  is used, the outer wall  210 , the inner wall  250 , a pull rod  340 , the air input port  200 , and a retaining ring  360 , retaining the pull rod  340  to the outer wall  210 . The cable  302  is attached to the pull rod  340  through the bushing  300  which is bronze in the preferred embodiment, and the retaining ring  360  retains the pull rod  340  to the outer wall  210 . The cable is attached to a fixed point  308 , such as on a firewall  309 . This can be done with a firewall attachment bracket  306 . 
   As air pressure is applied to the air input port  200 , the outer wall  210  is forced to extend away from the firewall  309 . The pull rod  340  is attached to the outer wall  210 , so as the outer wall  210  is extended against the at least one return spring  315 , thereby tightening the cable  302  against the fixed point  308 . Since the inner wall  250  is affixed to the brake pedal arm  420  of the towed vehicle, the towed vehicle&#39;s brakes are applied. In the preferred embodiment, the cable  302  is a coated flexible cable known to the trade. 
   Referring to  FIGS. 2 and 4 , the air cylinder  110  is mounted to the brake pedal arm  420  of the towed vehicle using the mounting plate  260  and mounting bolts  230  and mounting nuts  225 . As input air is applied to the air input port  200 , the cable  302  is tightened against the mounting point  308 . The inner wall  250  is secured to brake pedal arm  420 , as air is applied to the air cylinder  110 , the outer wall  210  is extended away from the firewall  309  thereby applying the towed vehicle&#39;s brakes as indicated in  FIG. 4A . 
   In operation, positive air pressure and flow is provided from a towing vehicle brake system to inlet line  100 . Air pressure in proportion to brake pressure in the towing vehicle is provided to cylinder  110  to apply the brakes in the towed vehicle in proportion to the braking in said towing vehicle. Air flow and pressure from line  100  also flows to the valve  104 . The air valve  104  is a solenoid operated valve, spring biased to normally closed as shown in  FIG. 1 , in the preferred embodiment of the present invention. A signal from vacuum switch  125  can call for pressure to be supplied when the vacuum in brake booster  107  of the towed vehicle gets low. When air pressure from the towed vehicle passes through valve  104  it is supplied to venturi  102  and the positive flow of air through the venturi  102  creates a vacuum in line  105  that is supplied to booster  107  through vacuum switch  125 . When the vacuum switch  125  senses that the vacuum in booster  107  is sufficient it will switch solenoid valve  104  to the closed position to shut off the flow of air and thereby the vacuum supplied by venturi  102 . Referring to  FIG. 2 , the bracket  260  can be used to bolt the cylinder  110  to the brake pedal arm  420 . Referring to  FIG. 3  a bracket  306  can be attached to the towed vehicle fire wall at  308  and thereafter the cable  302  can be quickly attached to the bracket  306  so that the cylinder  110  can be quickly attached for repeated use. The cylinder normally stays in place once it is mounted, this is the advantage of the smaller cylinder and one of the advantages of this system. 
   Referring to  FIG. 3  when air pressure is supplied to cylinder  110  air flows in through port  200  and fills inner wall  250  as air continues to flow the pressure in inner wall  250  will drive the inner wall  250  axially out from the outer wall  210  against the return spring  315  extending the overall length of the cylinder from the position shown in  FIG. 4  to that shown in  4 A. The movement of the outer wall  210  relative to the inner wall  250  actuates the brake pedal  420 . The cable  302  maintains the outer wall  210  in a fixed location relative to the firewall of the towed vehicle so as the cylinder  110  expands in length the inner wall  250  moves toward the firewall  309  of the towed vehicle and takes the bracket  260  and brake pedal  420  with it. Because the venturi operates the power brakes of the towed vehicle, the cylinder  110  can be much smaller in diameter than would otherwise be possible. This is important as it takes up less space under the dash board of the towed vehicle. 
   This is a simpler, effective way to actuate a brake pedal than prior art. The towed vehicle brakes are applied in proportion to input air. The input air is typically, but not limited to, the air used in a towing vehicle&#39;s brake system as in the case with a diesel powered towing vehicle with air brakes. As no air cylinders were available to serve the function of the present invention, and no systems marketed today incorporate a venturi to create vacuum, applicant came up with the present invention. A venturi eliminates the need for a source of vacuum, usually a battery powered vacuum pump, typically used in towed vehicle brake actuating systems. Another big advantage of a venturi is that there are no moving parts to wear out. The venturi  102  can generate vacuum at a low supply air pressure, less than 20 PSI. 
   Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. It will be understood that the towed vehicle could be a car, truck or trailer for example. 
   It will be obvious to those skilled in the art that modifications may be made to the embodiments described above without departing from the scope of the present invention. 
   Thus the scope of the invention should be determined by the appended claims in the formal application and their legal equivalents, rather than by the examples given.