Abstract:
A line-locking brake system consists of a brake pressure generator which, in conjunction with a brake fluid solenoid isolates the front brake circuit from the master cylinder while maintaining a precise brake pressure in the front brake hydraulic system. The brake pressure generator consists of a pressure amplifier having a high pressure chamber located in the flow path from the master cylinder to the front brake cylinders and a low pressure chamber in fluid communication with a regulated gas pressure source. When activated, the brake pressure generator applies a pressure to the front brake circuit that is directly proportional to the pressure of the regulated gas and therefore is precisely controllable irrespective of wear on parts, driver fatigue or other variables.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to drag racing equipment and in particular to methods and apparatus for locking the hydraulic braking system on drag racing vehicles. 
     In the sport of automotive racing, the race is begun by a starting system consisting of a series of lights of various numbers, commonly called “Christmas tree” lights. Typically, there are one to five warning lights of amber color, one green colored light to indicate the start of the race and one red light to indicate a foul start. 
     Before the Christmas tree is activated, the vehicles must be “staged” into the starting area. This is typically accomplished using a “line lock” device in cooperation with the vehicle&#39;s transmission brake. A line lock device typically consists of a solenoid valve that isolates the front brake hydraulic system from the master cylinder. The line lock is activated by a line lock button, usually mounted on the steering wheel, which opens and closes the solenoid, activating the line lock. In use, the vehicle driver presses on the brake pedal to apply the brakes, then engages the line lock to maintain pressure in the front brake circuit after the brake pedal is released. Locking the front brakes in such a manner allows the driver to spin the rear tires to heat them up as well as assisting in staging as discussed hereinafter. 
     The transmission brake, or transbrake, is a mechanism that selectively places the transmission in first and reverse gears simultaneously, effectively holding the car stationary. It is used on vehicles with automatic transmissions that employ a torque converter, where it is beneficial to build up pressure in the torque converter before the vehicle is launched. The transbrake is activated by the driver activating a solenoid in the transmission. With the transbrake engaged (transmission locked), the engine throttle can be increased to in preparation for launch without the car creeping forward. Milliseconds before the green light illuminates on the Christmas tree the transbrake is released. The power from the engine is then instantly transmitted to the wheels through first gear. This results in extremely quick acceleration of the vehicle. 
     Typically, a drag race car is staged by engaging the line lock device, then using the transbrake to bump the car into the starting box right before the start. Unfortunately, because the line lock device relies on the driver&#39;s foot pressure to set the initial stopping force on the front tires, the brake stopping force may not be consistent from race to race. If the stopping force is too little, the car may creep forward too quickly, leading to a false start. If the stopping force is too much, the car will not creep forward to the starting box and/or momentary release of the transbrake will cause the vehicle suspension to load up, altering the vehicle from its optimum attitude at the start. 
     Various methods and apparatus have been suggested for improving consistency in the operation of line locks and launch control. Published US Application US 20110175438 discloses a Vehicle Line-Locking Braking System and Method incorporating a computer that performs various status checks before enabling the line locking device. US Patent Application 20140129107 discloses a brake system for a vehicle that includes a wheel hold mode in which the wheel brake pressure is maintained at the wheels of the non-driven axle alternatively by depressing the brake pedal or by engaging the Antilock Brake System (ABS) pump. The prior art solutions add significant complexity with concomitant reduction in reliability. 
     What is needed, therefore, is a method and apparatus for applying a consistent, repeatable, brake pressure to the front brakes of a vehicle equipped with a line locking device, without adding significant weight or complexity to the brake system. 
     SUMMARY OF THE INVENTION 
     The present invention solves the foregoing need by providing a brake pressure generator which, in conjunction with a line-locking device used to isolate the front brake circuit from the master cylinder, maintains a precise brake pressure in the front brake hydraulic system. According to one embodiment of the invention, the brake pressure generator comprises a pressure amplifier consisting of a low pressure chamber, a high pressure chamber and a dual-diameter piston. The high pressure chamber of the brake pressure generator is located in the flow path from the master cylinder to the front brake cylinders between the line-locking device and the front brake cylinders. The low pressure chamber of the brake pressure generator is in fluid communication with a pressure regulator that receives pressurized air, carbon dioxide or other stored gas used to operate the vehicle air shifter, parachute mechanism or other auxiliary systems. An air solenoid selectively allows or prevents the pressurized gas from reaching the low pressure chamber of the brake modulator. The air solenoid is preferably actuated by the same electrical trigger as the line locking device. 
     In operation, prior to staging, the driver engages the line lock (with or preferably without applying foot pressure to the brake system). The solenoid valve of the line lock isolates the front brake circuit from the master cylinder. Simultaneously, the air solenoid opens to allow pressurized gas to enter the low pressure chamber of the brake pressure generator. Pressurized gas acting on the piston in the low pressure chamber then pressurizes the isolated front brake system to a hydraulic pressure that is precisely equal to the gas pressure leaving the regulator multiplied by the area ratio between the two diameters of the dual-diameter piston. This ensures that the hydraulic pressure in the front brake system is precisely controlled and repeatable race after race without the added cost or complexity of computer controls, electronic timers, ABS pumps, or other cumbersome apparatus of the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which: 
         FIG. 1  is an illustration of a vehicle equipped with a hydraulic braking system incorporating features of the present invention; 
         FIG. 2  is a diagram of a brake hydraulic system incorporating features of the present invention; 
         FIG. 3  is a cross-sectional view of a brake pressure generator used in connection with the hydraulic braking system incorporating features of the present invention in a deactivated state; and 
         FIG. 4  is a cross-sectional view of the brake pressure generator of  FIG. 3  in an activated state. 
     
    
    
     DETAILED DESCRIPTION 
     The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention. 
     With reference to the drawing figures and in particular,  FIG. 1 , a typical drag race car  10  is equipped with a brake system  12  consisting of a brake master cylinder  14  and at least one brake piston at each wheel  16 ,  18 ,  20 ,  22 , each brake piston operating on the rotor of a disk brake to apply a stopping force to the wheel. Typically brake master cylinder  14  has two independent hydraulic circuits. The front hydraulic circuit  24  operates the front brake pistons  16 ,  18  and the rear hydraulic circuit  26  operates the rear brake pistons  20 ,  22 . Typically, the car  10  is also equipped with a pressurized gas bottle  28 , which provides a source of gas to operate the parachute pack  30 , air shifter  32  or other vehicle auxiliary systems. 
     With additional reference to  FIG. 2 , a line-lock apparatus  34  incorporating features of the present invention comprises a brake fluid solenoid (line lock)  36  and a brake pressure generator  38 . Brake fluid solenoid  36  is operatively attached to the front hydraulic circuit  24 . When activated, brake fluid solenoid  36  closes to isolate front brake pistons  16 ,  18  from master cylinder  14 . 
     With additional reference to  FIG. 3 , brake pressure generator  38  comprises a hydraulic amplifier  44  which consists of a lower body  46  having a high pressure chamber  48  and a low pressure chamber  50 . A dual-diameter piston  52  is disposed within lower body  46  so that the small piston surface  54  is disposed in high pressure chamber  48  and large piston surface  56  is disposed in low pressure chamber  50 . Sealing rings  58 ,  60  seal piston  52  to chambers  48  and  50 , respectively. High-pressure chamber  48  includes a pair of fluid ports  62  and  64 . 
     Brake pressure generator  38  further comprises an upper body  66  which is attached to lower body  46  by means of a conventional snap ring engaging a groove  68  formed in lower body  46  and sealed to lower body by means of a sealing ring  70 . Inlet housing  72 , which includes air inlet port  74  is similarly attached to upper body  66  by means of a conventional snap ring and a sealing ring  76 . Upper body  66  includes a plurality of exhaust apertures  78  which vent inner chamber  80  to the outside, and a plurality of longitudinal passageways  82  which provide fluid communication between inner chamber  80  and low pressure chamber  50 . A sealing member  84  is disposed within inner chamber  80 . Sealing member  84  comprises an axisymmetric resilient member, preferably made from Nitrile, Fluorocarbon or other elastomer, having a “batwing” profile consisting of a substantially conical raised center portion  86  and a substantially cup-shaped perimeter portion  88 . Sealing member  84  is disposed within inner chamber  80  oriented so that the concave surface of the cup-shaped perimeter portion  88  and the raised portion face toward valve seat  90 . 
     With reference again to  FIG. 2 , fluid port  62  of brake pressure generator  38  is operatively attached to one of the common fluid ports  94 ,  96 ,  98  of brake fluid solenoid  36 , with the remainder of common fluid ports  94 ,  96 ,  98  connected to front hydraulic circuit  24 . A bleed screw  92  is attached to fluid port  64  to enable high pressure chamber  48  of brake pressure generator  38  to be bled of any residual air using master cylinder  14  as the source of fluid (via brake fluid solenoid  36 , which in its inactive position simply acts as a manifold). Alternatively, if brake pressure generator is mounted in a vertical orientation, bleed screw  92  is attached to fluid port  62 , while fluid port  64  is operatively attached to brake fluid solenoid  36 . 
     Air inlet port  74  is operatively attached to air solenoid  108 , which receives a flow of regulated air from gas bottle  28  via air pressure regulator  110 . Air pressure regulator  110  is adjustable to provide a precisely controlled gas pressure to air inlet port  74 . 
     In operation, the racecar driver operating drag race car  10  stages the car  10  by gently applying foot pressure to the brake pedal, which causes master cylinder  14  to pump brake fluid into front hydraulic circuit  24  and rear hydraulic circuit  26 , which causes brake pistons  16 ,  18 ,  20  and  24  to apply a braking force to the front and rear wheels. Alternatively, the car  10  can be staged without applying any foot pressure to the brake pedal at all, although the alternative operation will consume somewhat more of the vehicle&#39;s stored pressurized gas. The driver then activates the line lock apparatus  34 , typically by means of a button  102  located on steering wheel  104 , which sends an electrical signal through wire bundle  106 . This action immediately activates brake fluid solenoid  36  which moves from an open position to a closed position to isolate front brake pistons  16 ,  18  from master cylinder  14 . The driver can then release the foot pressure on the brake pedal (if the brake pedal was applied). 
     Simultaneously, or shortly thereafter, air solenoid  108  is activated and moves from a closed position to an open position to allow a flow of regulated air from gas bottle  28  to enter air inlet port  74  of hydraulic amplifier  44 . As shown in  FIG. 4 , gas pressure action on sealing member  84  causes it to move to close off valve seat  80 , thereby closing exhaust ports  78  so that the remaining gas pressure will pass through longitudinal passageways  82  and enter low pressure chamber  50 . The force of the gas acting on the large piston surface  56  of piston  52  applies a pressure on the brake fluid in high-pressure chamber  48  that is equal to the ratio of the area of large piston surface  56  divided by the area of small piston surface  54 . Preferably the hydraulic amplification is from 300% to 700%, however, in the illustrative in sample, the area of large piston surface  56  is five times the area of small piston surface  54  and therefore the hydraulic pressure in high pressure chamber  48  (and therefore in front hydraulic circuit  24 ) is five times the gas pressure in low pressure chamber  52  (500% hydraulic amplification). The invention is not, however, limited to a particular amplification ratio. Because the pressure of the regulated air from gas bottle  28  can be precisely controlled, the brake fluid pressure in high-pressure chamber  48  (and therefore front brake pistons  16 ,  18 ) can be precisely controlled race after race regardless of component wear, driver fatigue, or other variables that would lead to inconsistent brake force applied to the front wheels. With the brake force on the front wheels precisely controlled and repeatable, the driver is able to stage the car precisely using the transbrake without fear of over creeping, or loading the suspension prior to start. 
     When line lock apparatus  38  is released milliseconds before the start, air solenoid  108  and brake fluid solenoid  36  are deactivated. As air solenoid  108  begins to vent, the gas pressure in low pressure chamber  50  unseats sealing member  84  from valve seat  90 . This opens gas communication between inner chamber  80  and the atmosphere via exhaust apertures  78 , which are designed to have significantly more flow area than gas inlet port  74 . With exhaust apertures  78  open, gas pressure in low pressure chamber is vented almost instantaneously and is vented independent of such variables as the operational characteristics of air solenoid  108 , the length and/or diameter of the tubing between air solenoid  108  and brake pressure generator  38  or other factors that would cause the release time to vary. 
     Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the invention. For example, although in the illustrative embodiment the brake modulator has a hydraulic amplification of 500% other amplification ratios, greater or less than 100% are considered within the scope of the invention. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law. Additionally, as used herein, references to direction such as “up” or “down” are intend to be exemplary and are not considered as limiting the invention and, unless otherwise specifically defined, the terms “generally,” “substantially,” or “approximately” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater. As used herein, a step of “providing” a structural element recited in a method claim means and includes obtaining, fabricating, purchasing, acquiring or otherwise gaining access to the structural element for performing the steps of the method. As used herein, the claim terms are to be given their broadest reasonable meaning unless a clear disavowal of that meaning appears in the record in substantially the following form (“As used herein the term —————— is defined to mean —————— ”).