Abstract:
A vehicle braking system including an auxiliary circuit for activating the vehicles brake system independent of the position of the vehicle ignition switch. In a preferred embodiment, the auxiliary circuit is actuated through actuation of the vehicle service brake pedal, enabling the braking system to be operable whenever the brake pedal is activated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a motor vehicle brake control system and particularly to a system modification for activating the system when the vehicle is inoperative. 
     2. Description of the Prior Art 
     Safety, convenience and operating modules are typical components of a motor vehicle electrical system. The electrical system is powered by the vehicle storage battery, which is charged by the vehicle&#39;s engine driven alternator when the vehicle is operated. This battery has a finite energy capacity and therefore, current drain when the vehicle is inoperative must be limited, so as to provide cranking energy to start the vehicle&#39;s engine following prolonged periods of non-use. When the vehicle operator turns the key in the vehicle ignition switch, an electrical activation signal is sent through the electrical system to activate the vehicle electrical system enabling the safety, convenience and operating modules to be used by the operator. 
     To power up the vehicle electrical system using the ignition key, the operator must have the ignition key in a specific position. Occasionally, the operator may need to use vehicle functions quickly without having to have the ignition key in the switch or having it turned to a specific position to activate electrical system operating and monitoring features. Therefore, a need exists for a system enabling a vehicle electrical system to be operative without use of the ignition key. This type of feature would be especially beneficial for vehicles which feature an all electrical brake system or an electrical brake booster in which braking hydraulic pressure is boosted through an electromechanical booster unit, which does not require intake manifold vacuum as a pressure source. For such vehicles, it is desirable that the driver would not be required to have the key in a specific position or the engine running to be able to apply enough brake pressure to prevent vehicle motion. While this feature would be beneficial, cost is always a factor. Accordingly, it would be desirable to add an alternative method of activating portions of the vehicle electronics without making a significant impact on the cost of the electrical system. 
     Alternative methods of activating a vehicle&#39;s electronics other than with a key turned in the ignition switch have been proposed. U.S. Pat. No. 5,945,745, issued Aug. 31, 1999 describes an apparatus for controlling power to a vehicle electrical system when the ignition is off. While this apparatus would activate the electrical system with the ignition switch off, it requires several expensive components to be added to the vehicle electrical system, including a microprocessor. 
     U.S. Pat. No. 6,037,675, issued Mar. 14, 2000, also discusses a system for activating electrical systems in a vehicle using a method other than turning the key in the ignition switch. In this system, the operator can use a security card or can push a button on a remote unit to activate the vehicle electrical system. However, since this invention utilizes an entirely separate remote control unit, there is also significant additional cost. 
     From the above discussion, it is clear that the need exists for a system for activating a motor vehicle&#39;s electronics without the need to have an ignition key in a specific position or adding additional expensive components. It is therefore a primary object of this invention to fulfill that need by providing a system which allows operators to activate portions of the vehicle&#39;s electronics which does not require using the vehicle ignition key. 
     SUMMARY OF THE INVENTION 
     Briefly described, these and other objects are accomplished according to the present invention by providing an electrical circuit having a switch associated with actuation of the service brake pedal, so that when the operator applies force to the brake pedal, even when the ignition key is not in the proper position, power will be applied to the brake system to activate it, thus making its functions available. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of electrical circuit elements of a representative vehicle braking system in accordance with the prior art. 
     FIG. 2 is an electrical block diagram of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in detail to the drawings, shown in FIG. 1 is a representative electrical block diagram of a vehicle braking system  10  according to the prior art. When the ignition switch  12  is closed (the key is turned in the vehicle ignition), an activation electrical or “wake-up” signal  14  is sent to the voltage regulator  16  and microprocessor  26  which activates the external brake electronics  20  through the actuation circuitry  22  and the monitoring circuitry  24 . This is a typical means of activation in a prior art vehicle electrical system. Various alternative approaches could be used. For example, instead of a low current signal being applied to voltage regulator  16 , ignition switch  12  could be a high current capacity switch through which all power to vehicle braking system  10  flows. Microprocessor  26  may maintain operation of external brake electronics  20  for some set time period or when certain system steps are completed after activation signal  14  is no longer present through “keep-alive” signal  17 . 
     External brake electronics  20  is of a type which applies hydraulic pressure or an electrical signal for applying braking torque using electrical power. Brake torque is applied through actuation of service brake pedal  18 , which modulates hydraulic pressure or electrical actuation signals through electric brake booster  19 . 
     A vehicle braking system in accordance with the present invention is illustrated in FIG.  2 . Components of vehicle braking system  30  shown in FIG. 2 which are identical to those described with reference to FIG. 1 are identified by like reference numbers. As shown in FIG. 2, the vehicle braking system  30  differs from vehicle braking system  10  with the addition of circuit  32  which includes brake switch  34 . Brake switch  34  may be the presently available brake lamp-activating switch present on conventional motor vehicles. Alternatively, brake switch  34  may be a dedicated switching device provided solely to provide for the functions of the present invention. 
     Brake switch  34  may also be based on various operating principles. For example, in a manner similar to existing typical brake lamp activating switches, brake switch  34  may be a plunger type, contact switch which responds to movement of the brake pedal arm. Alternatively, switches based on pressure applied to the brake pedal, or other force detecting electrical switches could be implemented. Similarly, various switching techniques based on displacement of the brake pedal such as optical devices, variable reluctance proximity pick-ups, or active electrical sensors based on Hall effect devices or other elements could similarly be used. In any event, however, brake switch  34  provides an electrical signal when the brake pedal  18  is actuated manually by an occupant of the vehicle. 
     As shown in FIG. 2, the electrical activation signal applied by closing brake switch  34  is applied to one input of OR gate  36 . The other input of OR gate  36  is connected with vehicle ignition switch  12 . Accordingly, activation electrical signals originating from the vehicle operating voltage or battery voltage can be applied to OR gate  36  through inputs generated by vehicle ignition switch  12  or brake switch  34 . In either case, a logic signal is provided by the output of OR gate  36  providing actuation signal  14 , which activates external vehicle braking electronics  20  in the manner explained in connection units FIG.  1 . This activation signal enables the functions of the vehicle service brakes. As discussed previously, such functions may be used to stop a rolling vehicle where the vehicle engine is not operating or in other circumstances in which the ignition switch is switched to the open position. This approach would especially be useful in panic situations. For example, an operator would instinctively depress the brake pedal  18  to stop vehicle motion. When this occurs, the vehicle braking system  30  is active without any other active steps required by the operator such as turning an ignition switch or another device. 
     Since brake switch  34  provides an electrical activation signal only while it is physically actuated by the vehicle occupant, the vehicle braking system  30  becomes deactivated when the vehicle operator discontinues actuation of the brake pedal or the microprocessor  26  switches off the voltage regulator by deactivating the keep-alive signal  17  after some pre-set time has elapsed. Accordingly, continuous current drain from the vehicle&#39;s battery does not occur while the ignition switch is in the open position. This avoids draining the on-board electrical storage battery. 
     Since keep-alive signal  17  is operative to maintain brake system operation only for a limited duration after activation signal  14  is not present, system  30  is said to be normally deactivated when the activation signal is not present. 
     While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.