Patent Publication Number: US-2005140208-A1

Title: Brake system for idle stop vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority of Korean Application No. 10-2003-0096595, filed on Dec. 24, 2003, the disclosure of which is incorporated herein by reference.  
     TECHNICAL FIELD OF THE INVENTION  
      The present invention relates to a brake system of a vehicle. More particularly, the invention relates to a brake system of an idle stop vehicle which prevents the vehicle from rolling down a slope by maintaining a negative pressure of a master cylinder booster for a predetermined time or by maintaining a pressure of a hydraulic unit by an engine or a brake control unit.  
     BACKGROUND OF THE INVENTION  
      Generally, a 14V power system is used for current vehicles. It is known that a maximum power that the 14V power system can supply is about 2.5 kW. However, recently, various types of electric or electronic equipment have been installed in vehicles making it difficult for the 14V power system to provide stable electric power to such equipment. Therefore, research on power systems of 35V or 42V is widely being undertaken.  
      An idle stop function is adopted to a 42V vehicle in order to decrease air pollution and to decrease fuel consumption. The idle stop is a function in which an engine is turned off instead of idling when the vehicle is stopped while an acceleration pedal is in an off-state and a brake pedal is in an on-state.  
      More concretely, in the idle stop vehicle, if the acceleration pedal switch is in an off-state, the brake pedal switch is in an on-state, and the vehicle speed is 0 in a state in which an ignition switch is not operated, the engine is automatically stopped. Then, if the brake pedal switch is turned to an off-state and the idle stop is released, the engine is restarted by an integrated starter generator (ISG). However, if the idle stop is released when the vehicle is stopped on an up-slope or a down-slope, the vehicle rolls on the slope due to a shortage of driving force while the engine is being restarted.  
      The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.  
     SUMMARY OF THE INVENTION  
      An embodiment of the present invention provides a brake system for maintaining a hydraulic pressure acting on wheels when an idle stop is released when a vehicle is on a slope. In one preferred embodiment of the present invention, a brake system of an idle stop vehicle is provided with an integrated starter generator. The brake system includes a starter motor for initial starting of the vehicle, an electric power supply device for supplying electric power to the starter motor, an air pump that is driven by the starter motor, a brake master cylinder booster that is connected to the air pump, a hydraulic unit for maintaining or releasing a hydraulic pressure of at least one wheel, and a controller for controlling at least one of the starter motor and the electric power supply device. The air pump is driven by the starter motor to form a negative pressure in the master cylinder booster such that a hydraulic pressure of the hydraulic unit is maintained if an idle stop is released while the vehicle is located on an up-slope whose slope angle value is higher than a first predetermined slope angle value or a down-slope whose slope angle value is lower than a second predetermined slope angle value.  
      In some embodiments, the brake system further includes a slope angle detection member that outputs a signal regarding a slope angle of a road on which the vehicle is located. The controller controls the electric power supply device and the starter motor based on the signal of the slope angle detection member.  
      In some embodiments, the controller is a microprocessor that is operated by a predetermined program. The predetermined program comprises instructions for determining whether the vehicle is in an idle stop state, determining whether an idle stop release condition exists if it is determined that the vehicle is in the idle stop state, determining a slope angle value of a road where the vehicle is located, and braking the vehicle if it is determined that the idle stop release conditions exists and if the slope angle value of the road where the vehicle is located is higher than a first predetermined slope angle value or lower than a second predetermined slope angle value. The braking may include driving the air pump by applying electric power to the starter motor, if it is determined that the idle stop condition exists and if the slope angle value of the road where the vehicle is located is higher than a first predetermined slope angle value or lower than a second predetermined slope angle value. The braking may also include maintaining a hydraulic pressure of the hydraulic unit for a predetermined time.  
      The program further may also include instructions for determining whether fuel injection has been started, and cutting off electric power supply to the starter motor, if it is determined that the fuel injection has been started.  
      In other embodiments of the present invention, a brake system of an idle stop vehicle having an integrated starter generator includes a slope angle detection member for detecting a slope angle value of a road where the vehicle is located, a hydraulic unit maintaining or releasing hydraulic pressure of at least one wheel, and a control unit for controlling the hydraulic unit. The control unit may be a microprocessor operated by a predetermined program which includes instructions for determining whether the vehicle is in an idle stop state, determining whether an idle stop release condition exists if it is determined that the vehicle is in the idle stop state, detecting a slope angle value of a road where the vehicle is located, and maintaining a hydraulic pressure of the hydraulic unit for a predetermined time, if it is determined that the idle stop conditions exists and if the slope angle value of the road where the vehicle is located is higher than the first predetermined slope angle value or lower than the second predetermined slope angle value.  
      The control unit may be an anti-lock brake system (ABS) control unit, which maintains a braking force by delaying operations of normally closed valves (NC valves) that are disposed at wheels for a predetermined time.  
      According to other embodiments of the invention, there is provided methods for performing the above-mentioned instructions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention, where:  
       FIG. 1  is a schematic block diagram of a brake system of an idle stop vehicle according to an embodiment of the present invention;  
       FIG. 2  is a flowchart showing operations of the brake system of the idle stop vehicle according to an embodiment of the present invention; and  
       FIG. 3  is a flowchart showing operations of the brake system of the idle stop vehicle according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.  
       FIG. 1  is a schematic diagram of a brake system of an idle stop vehicle according to an embodiment of the present invention. As shown in  FIG. 1 , the brake system of the idle stop vehicle comprises a starter motor  10  for initial starting of the vehicle, an electric power supply device  20  supplying electric power to the starter motor  10 , an air pump  30  that is coaxially connected to an output shaft of the starter motor  10  to be driven, a brake master cylinder booster  40  connected to the air pump  30 , and a controller  50  controlling the starter motor  10  and the electric power supply device  20 .  
      An integrated starter generator (ISG)  92  is disposed between an engine  91  and a transmission  93  such that the engine  91  and the transmission  93  are connected to each other therethrough in series. However, a belt-type integrated starter generator can also be used. The ISG  92  is connected to an output shaft of the engine  91  and to an input shaft of the transmission  93  so as to transmit a driving force from the engine  91  to the transmission  93 , or the ISG  92  starts the engine  91  or generates an electric current when an idle stop is released.  
      In an idle stop vehicle, the starter motor  10  is connected to the engine  91  and performs initial starting of the vehicle. In some embodiments, the engine  91  is connected to the ISG  92 , and power of the ISG  92  is transmitted to the transmission  93 . The starter motor  10  is controlled by the controller (e.g., an ECU)  50 , may be connected to a flywheel to start the engine  91 . The starter motor  10  and the ISG  92  are connected to the electric power supply device  20  including at least one battery, so that an electric current is supplied to the ISG  92  and the starter motor  10 .  
      The air pump  30  is disposed to one side of the starter motor  10 , and the air pump  30  is driven by the starter motor  10 . The air pump  30  and the engine  91  are each connected to a brake master cylinder booster  40 , and they form a negative pressure in the master cylinder booster  40  to generate a braking force when a brake pedal is depressed by a driver.  
      The master cylinder booster  40  is connected to a hydraulic unit  95 , and the hydraulic unit  95  distributes a hydraulic pressure to each wheel  94  so that the vehicle is braked. Therefore, a negative pressure is formed in the master cylinder booster  40  by the engine  91  when the engine  91  operates, and a negative pressure can still be formed in the master cylinder booster  40  by the air pump  30  driven by the starter motor  10  when the engine  91  does not operate.  
      In some embodiments, the controller  50  may be a microprocessor that is operated by a predetermined program. The idle stop state can be determined based on a signal of an engine control unit (ECU) or an engine control module (ECM), and if the controller  50  is formed integrally with the engine control unit or the engine control module, the controller  50  can determine the idle stop state by itself.  
      A slope angle detection member  60  outputs a signal regarding a slope angle of a road where the vehicle is located to the controller  50 . The controller  50  calculates a slope angle value of the road based on the slope angle signal.  
      The predetermined program stored in the controller  50  can be a program for performing operations that will be stated hereinbelow. That is, the controller  50  is programmed to carry out instructions for performing a brake control method for an idle stop vehicle that will be explained hereinbelow.  
      In  FIG. 2 , a flowchart for showing operations of the brake system of the idle stop vehicle according to an embodiment of the present invention is shown. As shown in  FIG. 2 , at step S 210 , it is determined whether a vehicle is currently in an idle stop state. If it is determined that the vehicle is in the idle stop state in step S 210 , it is determined whether an idle stop release condition exists at step S 220 .  
      The idle stop release condition can be determined based on vehicle state information indicating a driver&#39;s intention to drive the vehicle, such as releasing the brake pedal and depressing the acceleration pedal. This is obvious for an ordinarily person skilled in the art, so further explanation will be omitted.  
      If an idle stop state is released in the idle stop vehicle, electric power is supplied to the ISG so that the engine is restarted. At this time, a specific time period from an instant when the idle stop release condition starts to an initial combustion explosion of the engine must lapse. If the idle stop is released while the vehicle is located on an up-slope or a down-slope, the vehicle can roll during the specific time period. Therefore, in an embodiment of the present invention, in order to prevent the vehicle from rolling down slopes, a negative pressure in the master cylinder booster of a brake system is formed for a predetermined time period even when the brake pedal is released.  
      Concretely, if the idle stop release condition exists, and if the value of the slope angle of the vehicle is higher than a first predetermined slope angle value or lower than a second predetermined slope angle value at step S 230 , the pressure differential within the master cylinder booster will be developed. For example, the first predetermined slope angle value may be 6% and the second predetermined slope angle value may be −6%.  
      If the slope angle value of the vehicle is higher than the first predetermined slope angle value or lower than the second predetermined slope angle value, electric power of the electric power supply device  20  is applied to the starter motor  10 , at step S 240 . The starter motor  10  is then driven by the electric power supplied from the electric power supply device  20 , and the air pump  30  that is coaxially connected to the starter motor  10  is consequently driven at step S 250 .  
      If the air pump  30  is driven, a negative pressure is formed in the master cylinder booster  40  even when the brake pedal is released. Thus, a braking force can be maintained for a predetermined time period by delaying operations of NC valves (normally closed valves)  101  that are connected to the hydraulic unit  95  and are respectively provided at each wheel. Here, the hydraulic unit  95  may include an ABS (anti-lock brake system) control unit  96 .  
      Then, at step S 260  if it is determined that fuel injection has started, the electric power supply to the starter motor  10  is cut off so that operation of the air pump  30  stops.  
      In  FIG. 3 , a flowchart for showing operations of the brake system of the idle stop vehicle according to another embodiment of the present invention is shown. The brake system of an idle stop vehicle according to another embodiment of the present invention comprises a slope angle detection member  60 , a hydraulic unit  95  for maintaining or releasing hydraulic pressure acting on wheels  94 , and a control unit  96  for controlling the hydraulic unit  95 . As shown in  FIG. 1 , the control unit  96  can preferably be an ABS control unit.  
      At step S 310 , it is determined whether a vehicle is currently in an idle stop state. If it is determined that the vehicle is in the idle stop state at step S 310 , it is determined whether an idle stop release condition exists at step S 320 . The idle stop release condition can be determined as stated above.  
      In this embodiment, by maintaining a braking force by delaying operations of the NC valves  101  that are disposed in each wheel  94  for a predetermined time, the vehicle is prevented from rolling on an up-slope or down-slope when the idle stop is released. Concretely, if the idle stop release condition exists, and if a slope angle value of the vehicle (i.e., a value representing the slope of a road where the vehicle is located) is higher than a first predetermined slope angle value or is lower than a second predetermined slope angle value, at step S 330 , the vehicle may roll. For example, the first predetermined slope angle value may be 6% and the second predetermined slope angle value may be −6%.  
      If the slope angle value of the vehicle is higher than the first predetermined slope angle value or lower than the second predetermined slope angle value, it is determined whether the hydraulic unit  95  is operating at step S 340 . If it is determined that the hydraulic unit  95  is operating, at step S 340 , an operation of the hydraulic unit  95  is maintained for a predetermined time period at step S 350 . At this time, the hydraulic unit  95  is preferably controlled by the ABS control unit  96 . For example, in order to maintain the braking force, the ABS control unit  96  delays operations of the NC valves  101  that are provided in the wheels  94  for a predetermined time period. In some embodiments, the predetermined time period is 0.7 seconds. Therefore, according to the brake system according to the embodiments of the present invention, even when the idle stop is released while a vehicle is located on a steep up-slope or on a steep down-slope, the vehicle can be prevented from rolling down the slope.  
      Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.