Abstract:
An apparatus connectable to a brake master cylinder for regulating pressure in a hydraulic brake system. The apparatus includes an outer casing housing a cylinder portion and a piston slidable therewithin. A pressure chamber forms between the cylinder wall and the piston. The piston includes a seal within an outer groove to prevent fluid leakage. The cylinder portion includes an inlet hole for hydraulic fluid flow into the cylinder and an air discharge valve. A fixing member having an extension with a concave portion is threadably attached to the lower end of the case, and a rod portion of the piston slidably fits into the concave portion. A spring providing a constant pre-pressure is located between a shoulder of the piston and a pressure controlling member abutting the fixing member, such that the end of the rod remains a fixed distance from the bottom of the concave portion.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus for regulating pressure in the hydraulic brake system for a vehicle via a brake master cylinder, and, more particularly, to an apparatus for regulating pressure in a hydraulic brake system, the apparatus causing the brake lining and brake shoe to approach each other, such that initial brake response time is reduced, braking efficiency is improved, the slip rate between the vehicle tires and the road is minimized, stopping distance is shortened, and the fluid in the brake master cylinder flows into the apparatus such that the pressure of the brake master cylinder is prevented from rapidly rising during emergency or other urgent application of the brakes. 
     BACKGROUND 
     As described in FIG. 1, in a typical vehicle hydraulic brake system, when the driver applies the brake pedal  1 , hydraulic pressure rises in the master cylinder  3 , which is typically a tandem master cylinder, and pressure is thereby transmitted to the wheel cylinder  7  through hydraulic line P. The brake shoe  9  is moveable so as to frictionally contact the brake drum  13  via pressure transmitted to the wheel cylinder  7 , producing a braking force. 
     The master cylinder  3  comprises a piston  4 , a piston cup  5 , a check valve V and a return spring S. A reservoir tank  10  is typically located in close proximity to and communicates with the master cylinder  3 , so as to provide a supply of brake fluid. In front of the piston  4  (to the left as viewed in FIG. 1) is located a rubber piston cup  5  to maintain the hydraulic pressure. In the rear (to the right as viewed in FIG. 1) of the piston  4  is located a piston packing  6  to prevent the leakage of brake fluid. If the pressure in the master cylinder  3  is sufficient to activate a check valve V, the check valve V opens and transmits pressure from the master cylinder to the wheel cylinder  7 . 
     If driver releases the brake pedal  1 , the piston  4  returns by virtue of return spring S. Upon such return, if the fluid pressure in the master cylinder  3  is sufficiently reduced, this pressure causes the check valve V to close, preventing return of brake fluid to the master cylinder  3 . At the front of the piston cup  5  (to the left as viewed in FIG.  1 ), the pressure drops temporarily during return, and fluid flows into the master cylinder  3  via hole H, which is formed in the piston  4  and about the circumference of the piston cup  5 , as described further with respect to FIG.  2 . The availability of this flow ensures that the return of the piston  4  is not prevented or impaired due to low pressure in the master cylinder  3 . 
     As the piston  4  returns, brake fluid is able to return to the reservoir tank  10  through the relief port  11  and the inlet port  12 . The check valve V remains closed until the pressure in the master cylinder  3  reaches the set-pressure. 
     Improving the handling of an automobile requires both good acceleration and good deceleration, in turn necessitating a hydraulic brake system having superior characteristics. Such superior characteristics are especially important with respect to safety. 
     The brake system for a typical vehicle provides a great deal of stopping force, which is utilized to stop the revolution of the vehicle&#39;s tires. However, this force can completely stop the vehicle&#39;s tire rotation without stopping the vehicle, resulting to slippage of the tires on the road (wheel lock). Such slippage occurs when the slippage force on the tires is less than the braking force. This slippage force is calculated by multiplying the frictional coefficient between the tire and the road by the weight applied to the road via the tire. 
     Namely, frictional coefficient μ, is extremely low on slippery road surfaces, as occur with the presence of ice or snow, while μ is much higher on, for example, dry concrete roads. In general, varying by motor vehicle model and road surface, the slip rate has a maximum, from which it quickly drops off. 
     The formula for the slip rate is expressible as follows:              Y   -   W     S     ×   100     =   v                          
     where: 
     V−W=the velocity of wheel; 
     S=the rate of slip; and 
     V=the velocity of vehicle. 
     In other words, when the driver applies the brake, it is advisable to maintain the wheels in a state such that the braking force is maximized and just less than the force that causes wheel lock. Safety is reduced and the rate of vehicle deceleration is reduced, resulting in longer stopping distances, when wheel revolution stops and wheel lock occurs. 
     To help achieve this condition in existing vehicles, hydraulic pressure in the brake system is typically reduced for the rear wheels relative to the front wheels, which prevents handling instability that would otherwise be caused by premature locking of the rear wheels. In existing vehicles, appropriate hydraulic pressure to maintain this condition is achieved through use of the following valves, which are installed on certain portions of tandem brake master cylinders to improve the braking efficiency: 
     Check valve—this valve improves braking efficiency by preventing return of pressure to the tandem brake master cylinder below a certain predetermined pressure, leaving any remaining pressure in the brake hydraulic lines. As a result, air osmosis is prevented and initial response time is shortened. 
     P valve (proportioning valve)—this valve is used to control the increase of hydraulic pressure and the triggering pressure point for activation of the brakes. This valve reduces the hydraulic pressure increase rate for the rear wheels as the brake force transmitted from the piston increases. 
     G valve—this valve controls the pressure of hydraulic fluid transmitted to the rear wheels. The G valve, which uses a ball valve that moves in accordance with a decrease in velocity of the vehicle, causing transfer of pressure among an outlet portion and an inlet portion, resulting in variation in the effective piston area applying the braking pressure. 
     Load sensing proportioning valve—this valve is used to control the hydraulic pressure to the rear wheels, with the opening position of the valve simultaneously varying in relation to the car weight. 
     Metering valve—this valve is used to decrease the abrupt hydraulic pressure of the front disk brake in low hydraulic pressure situations by decreasing the hydraulic pressure transmitted to the front wheels until the hydraulic pressure transmitted to the rear wheels becomes higher than the tension of return spring of the rear brake shoe. With this feature, brake pad life is prolonged. 
     In addition, an anti-lock brake device is used to prevent wheel lock from occurring when, for example, a car is braked on a road with low friction. The anti-lock brake device decreases the stopping distance and helps with control of the car by maintaining the vehicle&#39;s direction and enabling steering control by keeping the wheels at the ideal slip rate. 
     However, in the prior art, the method for controlling hydraulic pressure to obtain the proper braking force, except with regard to the anti-lock device, depends on the driver recognizing the need to provide the correct brake pedal effort and to know to apply the brakes in sufficient time. In an emergency, if a driver applies the brakes strongly (to increase the brake force), wheel lock can occur based on the abrupt pedal stroke and resultant increase in hydraulic brake pressure. The prior art addresses this problem with the use of valves that provide measured decrease of braking pressure and thereby enhance braking safety. However, even with these systems, if the hydraulic pressure increases abruptly in the tandem brake master cylinder, which is the starting point for building hydraulic pressure, wheel lock—the so-called “skid state”—can occur. In this event, stopping distance increases and braking safety decreases abruptly. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an apparatus for regulating pressure in the hydraulic brake system that causes the brake lining and brake shoe to approach each other in such a manner that when a driver applies the brakes, the initial response time is shortened, braking efficiency is improved, the slip rate between the tire and the road is kept in the ideal state, stopping distance is shortened, and fluid in the tandem brake master cylinder flows into the inventive apparatus so as to prevent the pressure of the tandem brake master cylinder from rising too rapidly, even in the event of a driver urgently applying the brake pedal. 
     An embodiment of the present invention includes an apparatus characterized as follows: a head of a piston is inserted into an upper cylinder of a housing so as to slide within the cylinder and forming a pressure chamber between the upper surface of the housing and the head of the piston; a sealing member is placed in a groove formed on the circumference of the piston near the head, the sealing member preventing leakage of hydraulic fluid past the head of the piston; a fixing member is threadably secured about the lower part of the housing; the lower end of a rod for coupling to the piston is inserted in a projecting extension having a concave opening that is formed on the fixing member; a spring is placed between a shoulder on the piston and the fixing member in order to support the piston such that the spring is compressibly loaded to provide a constant opposing pressure between the piston and the fixing member; a pressure controller pad located between the spring and the upper surface of the fixing member; an inlet hole in the upper cylinder through which brake fluid is able to flow into the pressure chamber; and an air discharge valve in the upper chamber for bleeding air from the pressure chamber. 
     In an embodiment of the present invention, the lower end of the rod coupled to the piston is located at a distance from the bottom of the projecting concave extension of the fixing member such that the piston is capable of moving a fixed distance, the fixed distance being the distance between the bottom of the projecting concave and the lower end of the rod, the movement being opposite the spring pressure, and the movement occurring when the pressure in the pressure chamber is higher than the pressure loading of the spring. 
     In an embodiment of the present invention, movement of the piston is limited by a shoulder within the housing. 
     An embodiment of the present invention includes a pressure controller pad that controls any unbalance of the spring at its contact point with the fixing member and at the same time reduces the elastic resistance of the spring with respect to the housing and the fixing member. 
     In an embodiment of the present invention, as the rod moves relative to the projecting extension concave section, openings form and are closed in the wall of the projecting extension, through which air is able to pass. 
     In one embodiment, in which the apparatus of the present invention is directly connected to the brake master cylinder, an inlet hole is formed in the horizontal surface of the upper cylinder and an air discharge valve is secured on the side surface of the upper cylinder. 
     In one embodiment, in which the apparatus of the present invention is directly connected to the brake master cylinder, the inlet hole is directly attached to the tandem master cylinder. In another embodiment, in which the apparatus of the present invention is indirectly connected to the brake master cylinder, the pressure regulating device is connected to the master cylinder by a connecter and pipes. 
     In another embodiment, in which the apparatus of the present invention is indirectly connected to the brake master cylinder, two housing portions are formed into a single connected body. 
     In one embodiment, the apparatus of the present invention is located downstream of hydraulic fluid flow of top dead center of the tandem brake master cylinder in the advancing direction of the primary and the secondary ring figured cups. 
     An embodiment of the present invention includes bleeding air from the system, which is accomplished by raising the pressure of the tandem brake master cylinder, discharging pressure via the check valve, and compensating for pressure difference, such that a narrow gap is maintained between the brake lining and the drum. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the figures: 
     FIG. 1 is a schematic view of a brake system of the prior art; 
     FIG. 2 is a section view showing the schematic structure of a master cylinder of prior art; 
     FIG. 3 is a section view showing the inventive apparatus in accordance with an embodiment of the present invention; 
     FIG. 4 shows schematically an embodiment of the present invention, in which the inventive apparatus is directly connected to the tandem master cylinder; and 
     FIG. 5 shows schematically another embodiment of the present invention, in which the inventive apparatus is indirectly connected to the tandem master cylinder. 
    
    
     DETAILED DESCRIPTION 
     The invention is now described in detail, as follows. FIG. 3 is a section view of the apparatus in accordance with one embodiment of the present invention, showing the pressure regulating device  200 . FIG. 4 shows a pressure regulating device  200  that is directly connected to the hole  150  of the master cylinder  100  by threadable connection. FIG. 5 shows a pressure regulating device  200 ′ that is connected to holes  150  of the master cylinder  100  via connecters  300  and a pipes  310 . 
     In FIG.  3  and FIG. 4, the pressure regulating device  200  comprises a piston  220  with a head  222  inserted in the upper cylinder  211  of the housing  210 , such that the piston  220  and head  22  are capable of moving up and down within the upper cylinder  211 , as viewed in FIG. 3. A pressure chamber  228  is formed between the upper surface  212  of the housing  210  and the head  222  of the piston  220 . A sealing member  224  is placed in a groove  223  formed in the intermediate of head  222  of the piston  220  in order to prevent hydraulic fluid leakage. 
     A fixing member  250  is threadably attached to the lower part of the housing  210  such that the lower end of the rod  226  of the piston  220  is inserted in the concave portion of the projecting extension  252  formed in the fixing member  250 . One or more openings  253  in the wall of the projecting extension  252  allow air flow into and out of the concave portion of the projecting extension  252 . 
     A spring  230  is compressibly placed between an expansion portion  225  of the piston  220  and the fixing member  250  so as to support the piston  220 , with the lower end of the rod  226  of the piston  220  located at set distance from the bottom of the concave portion of the projecting extension  252 . 
     If the pressure of pressure chamber  228  is higher than the pre-pressure of the spring  230 , the piston  220  drops to the bottom of concave portion of the projecting extension  252 . 
     The expansion portion  225  of the piston  220  is stopped by the shoulder  213  of the housing  210 , which limits the rising motion of the piston  220 , as viewed in FIG.  3 . 
     The pre-pressure and the spring constant vary, depending on the vehicle model and a pressure controller pad  240  having an “O” like shape, which is arranged between the spring  230  and the upper surface of the fixing member  250 . The pressure controller pad  240  controls any unbalance of the spring  230  where the spring  230  abuts the fixing member  250 , which is threadably connected to the housing  210 . In addition, the pressure controller pad  240  reduces the elastic resistance of spring  230 . 
     The pressure chamber  228  in the housing  210  has an inlet hole  270  for allowing hydraulic fluid to flow to the tandem master cylinder, and an air discharge valve  275  for discharging air from the pressure chamber  228 . As shown in FIG. 4, in the embodiment in which the apparatus is directly connected to the brake master cylinder, an opening  270  is formed in the horizontal surface  212  of the cylinder  211 , as shown in FIG. 3, and the air discharge valve  275  is located on a side wall of the upper cylinder  211 . The embodiment of the pressure regulating device  200 ′ indirectly connected to the master cylinder  100 , as shown in FIG. 5, is connected to the master cylinder  100  by a connecter  300  and hydraulic lines  310 . The pressure regulating device  200 ′ includes two housing portions  210 ′ and  210 ″ and a connecting body  315 , which are formed into a single unit. The device  200 ′ of this embodiment is similar to the pressure regulating device  200 , as described in FIGS. 3 and 4, except that the two housing portions  210 ′ and  210 ″ are part of a single unit, and the positions of the inlet hole  270  and the air discharge valve  275  are reversed 
     Preferably, in this embodiment, the pressure regulating device  200 ′ is connected to the tandem brake master cylinder  100  by connecting portions that are connected at similar points in the hydraulic flow relative to the primary and the secondary ring figured cups as the embodiment in which the device  200  is directly connected to the brake master cylinder. 
     The operation of the pressure regulating device  200 ′ in application for a tandem brake master cylinder on a motor vehicle will now be described. 
     As shown in FIGS. 3,  4  and  5 , after the pressure regulating device  200  or  200 ′ is connected to the tandem brake master cylinder  100 , the brake pedal  1  is depressed and released repeatedly to bleed air from the system. Through this process, when the brake pedal  1  is depressed, brake fluid in the tandem brake master cylinder  100  flows from one opening to the wheel cylinder  7 ′ and from another opening to the pressure chamber  228 . As this occurs, air in the pressure chamber  228  is discharged through the air discharge valve  275 . As the pedal  1  is depressed, when the lining  9 ′ of the brake shoe contacts the brake drum  13 ′, the pressure in the tandem brake master cylinder  100  increases. At this point, if the pressure in the tandem brake master cylinder  100  is higher than the desired pressure as governed by the device  200  or  200 ′, the pressure in the pressure chamber  228  increases until this pressure exceeds the resistive pressure provided by the spring  230 , which includes a loaded pre-pressure. Upon this pressure in the chamber  228  exceeding the resistive pressure of the spring  230 , the spring  230  compresses, and the piston  220  moves to the bottom of the concave portion of the projecting extension  252 . 
     Upon the pedal  1  being released, by function of the return spring in the tandem brake master cylinder  100 , the primary ring figured cup  101  and the secondary ring figured cup  102  move toward the brake pedal  1 , and the inner pressure within tandem brake master cylinder  100  falls abruptly. At this moment, the restoring force of the spring  230  within the pressure regulating device  200  or  200 ′ exceeds the pressure of pressure chamber  228 , and the brake fluid stored in the pressure chamber  228  flows into the tandem brake master cylinder  100  up to the limit provided by volume of the space  257 . 
     As a result of this operation, brake fluid from the pressure regulating device  200  or  200 ′ returns to the tandem brake master cylinder  100  before fluid from the wheel cylinder  7 ′ returns to tandem brake master cylinder  100  because the pressure in pressure chamber  228  resulting from the pressure of the spring  230  is higher than the pressure typically present within the tandem brake master cylinder  100 . This is further the case because the pressure within the brake master cylinder  100  will have increased, such that this pressure exceeds a desired pressure, as regulated by a check valve  330 , resulting in the check valve  330  closing. Because the check valve  330  so closes, with some amount of brake fluid remaining within the wheel cylinder  7 ′, the gap between the brake drum  13 ′ and the brake lining  9 ′ is maintained at a minimum. 
     As indicated above, the bleeding of air from the brakes also helps to maintain a minimum distance between the drum  13 ′ and the lining  9 ′, while keeping the brake fluid in the pressure chamber  228  of the pressure regulating device  200  or  200 ′ full. 
     After air is bled from the brakes, if the pedal  1  is slowly depressed, the gap between the drum  13 ′ and lining  9 ′ remains narrow without the pressure regulating device  200  or  200 ′ operating, because the pressure in the tandem brake master cylinder  100  under this condition does not exceed the pressure of the spring  230 , which is set with a loaded pre-pressure that is greater than the pressure of the pressure regulating device  200  or  200 ′. 
     In an emergency, when the brake pedal  1  is urgently depressed, pressure in the tandem brake master cylinder  100  exceeds that of the spring  230 , including the loaded pre-pressure, and brake fluid in the tandem brake master cylinder  100  flows into the pressure chamber  228  of the pressure regulating device  200  or  200 ′. 
     Because, in conditions such as the emergency conditions described above, brake fluid flows into the pressure chamber  228  after the lining  9 ′ contacts the brake drum  13 ′, the pressure in the tandem brake master cylinder  100  prevents abrupt pedal stroke motion A of the brake pedal  1 , as shown in FIG.  4 . In addition, because the piston  220  is able to move as much as the space  257  of the pressure regulating device  200  or  200 ′ allows, the brake lining  9 ′ comes into contact more slowly with the brake drum  13 ′ than would occur absent the present invention, and, as a result, the revolution of wheels are stopped but skid is reduced. The extent to which this effect occurs varies as a function of the power applied to the pedal  1  in an emergency, the speed of the vehicle, the cross-sectional area of the tandem brake master cylinder  100 , the cross-sectional area of the piston  220  in the pressure regulating device  200  or  200 ′ relative to the brake pedal&#39;s stroke A, the size of the space  257  in the concave portion of the projecting extension  252 , and the pre-pressure applied by and the spring constant of the spring  230 . 
     As discussed above, if a vehicle is stopped without wheel lock, steering is improved relative to locked wheel conditions, braking safety is enhanced, the rate of vehicle stopping is increased, and stopping distance is reduced. 
     Industrial Applicability 
     As described above, the present invention provides an apparatus for regulating pressure in the hydraulic brake system such that stopping distance is decreased by maintaining a narrowed gap between the brake drum and the brake lining, while braking safety for a vehicle is further enhanced by preventing wheel lock when the brake pedal is abruptly applied. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. Therefore it is understood that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modification within the spirit and scope of the present invention as defined by the appended claims.