Abstract:
A system providing protection to a power steering assist circuit in the event of a reversal of polarity of the power supply is disclosed. The circuit has a solenoid, a recirculating diode in an electrically parallel connection with the solenoid, and a protection device connected in electrical series with the recirculating diode. The protection device may be an n-channel field effect transistor. A power supply having a positive terminal connected to the circuit and negative terminal connected to the ground provides power to the circuit. In the event that the negative terminal of the power supply is connected the circuit and the positive terminal of the power supply is connected to the ground, the protection device will prevent the flow of current through the recirculating diode.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Modern motor vehicles are often equipped with “active braking” systems in which individual wheel brakes are actuated and/or released under microprocessor control to prevent wheel lockup and undesirable wheel slip values. These active braking systems typically include wheel speed sensors and electrically controlled regulating valves which modulate the supply of pressurized hydraulic fluid to each wheel&#39;s brake cylinder.  
         [0002]     Modern motor vehicles and particularly vehicles desired for off-road use, such as sport utility vehicles (“SUVs”) are also often equipped with “hill decent control” (“HDC”) systems in which individual wheel brakes are actuated and/or released and the lowest possible drive transmission gear is engaged and/or disengaged under microprocessor control. Engaging the lowest possible transmission gear allows the engine of the vehicle to slow the vehicle&#39;s wheels, which is referred to as “engine braking”. HDC systems automatically actuate the wheel brakes to supplement engine braking on steep descending slopes in order to maintain a specified low speed for maintaining control of the vehicle.  
         [0003]     HDC systems are typically manually activated by the driver. This is because the methods used to control the actuation of the brakes and the engagement of the transmission gears when descending a steep slope are different from the methods used to actuate the brakes when the vehicle is traveling along a normal road surface. There exists a need to automatically engage the HDC system when the vehicle is descending a hill or slope and to automatically disengage the HDC system when vehicle is traveling along a flatter surface.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     In satisfying the above need, a method for determining if a vehicle is in a downhill situation is provided. The primary components required in order for the method to execute are an electronic control unit (“ECU”), wheel speed sensors in electrical communication with the ECU and capable of measuring the speed of each wheel of the vehicle, and a longitudinal accelerometer in electrical communication with the ECU and capable of determining the longitudinal acceleration of the vehicle. Longitudinal accelerometers are typically present in motor vehicles having modern electronic braking systems providing one or more of the following capabilities: anti-lock braking (“ABS”), traction control system (“TCS”), electronic stability program (“ESP”) and active-rollover protection (“ARP”).  
         [0005]     In accordance with this invention, to determine if a vehicle is a downhill situation, the ECU will determine a wheel speed vehicle acceleration value by evaluating the wheel speed sensors over a period of time. Next, a threshold value based on a reading provided by a longitudinal accelerometer and the wheel speed vehicle acceleration value is determined by the ECU. This threshold value will be compared to a first downhill value which is indicative of the vehicle positioned on a slope. If the threshold value is greater than the first downhill value, a downhill counter will be increased. Subsequently, the threshold value will be compared to a first flat value which is indicative of the vehicle positioned on a flat relatively surface. If the threshold value is less than the first flat value, a downhill counter will be decreased. Finally, the downhill counter will be compared to a downhill situation value which is indicative of when the vehicle is positioned on a slope. If the downhill counter is greater than the downhill situation value, the vehicle is determined to be in a downhill situation.  
         [0006]     In another embodiment of the invention, the threshold value will be calculated by the ECU by subtracting the longitudinal accelerometer reading from the vehicle acceleration value.  
         [0007]     In another embodiment of the invention, the method further includes increasing the downhill counter if the threshold value is greater than a second downhill value. The second downhill value is indicative of a slope steeper than the slope represented by the first downhill value.  
         [0008]     In still yet another embodiment of the invention, the method further includes decreasing the downhill counter if the threshold value is less than a second flat value. The second flat value represents a surface that is flatter than the surface represented by the first flat value. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a block diagram of an automobile system for determining if the vehicle is in a downhill situation; and  
         [0010]      FIGS. 2A and 2B  are a flow chart illustrating the method executed by the system to determine if the vehicle is in a downhill situation. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     Referring now to  FIG. 1 , a vehicle  10  is diagrammatically shown. The vehicle  10  includes an electronic control unit (“ECU”)  12 , a longitudinal accelerometer  14 , a front driver-side wheel speed sensor  16 , a front passenger-side wheel speed sensor  18 , a rear driver-side wheel speed sensor  20 , and a rear passenger-side wheel speed sensor  22 . The longitudinal accelerometer  14  is in electrical communication with the ECU  12 . The longitudinal accelerometer  14  will communicate to the ECU  12  the longitudinal acceleration of the vehicle  10  along a longitudinal centerline  11  (i.e. the fore-and-aft acceleration of the motor vehicle).  
         [0012]     The wheel speed sensors  16 ,  18 ,  20  and  22  are in independent electrical communication with the ECU  12 . The wheel speed sensors  16 ,  18 ,  20  and  22  will communicate the wheel speed of wheels  24 ,  26 ,  28  and  30 , respectively.  
         [0013]     Referring now to  FIGS. 2A and 2B , a method for determining if a vehicle is in a downhill situation is provided at reference numeral  50 . Block  52  denotes the start of the method. In block  54 , a wheel speed vehicle acceleration value is determined by the ECU. The wheel speed vehicle acceleration value is representative of the vehicle&#39;s acceleration based on input from the wheel speed sensors by evaluating the wheel speed sensors over a period of time.  
         [0014]     In block  56 , the longitudinal accelerometer provides the ECU with a longitudinal accelerometer reading. The longitudinal accelerometer reading directly measures the vehicle&#39;s longitudinal acceleration (i.e. the fore-and-aft acceleration of the motor vehicle).  
         [0015]     Next, as shown in block  58 , a threshold value is determined by having the ECU by calculating the difference between the longitudinal accelerometer reading and the wheel speed vehicle acceleration value. The threshold value is representative of the acceleration of the vehicle caused by having the vehicle positioned on a slope. For example, if the vehicle is positioned on a slope and not moving, the wheel speed vehicle acceleration value will be zero but the longitudinal accelerometer reading will represent a component of gravity from the slope; thus, the threshold value will be greater than zero. Conversely, if the vehicle is traveling on a flat surface and under a period of acceleration caused by slowing the vehicle, the wheel speed vehicle acceleration value and the longitudinal acceleration reading will be roughly equal; thus, the threshold value will be near zero.  
         [0016]     In block  60 , the threshold value is compared to a first downhill value. The first downhill value is a value representative of the vehicle descending a slope of approximately 20% grade, which is indicative of a vehicle in a downhill situation. However, the first downhill value can be adjusted to represent other grades. If the threshold value is greater than the first downhill value, the method follows line  62  to block  64 . Otherwise, the method will follow line  63 .  
         [0017]     In block  64 , a downhill counter will be compared to a counter maximum. If the downhill counter is less than the counter maximum, the method continues to block  65 , where the downhill counter will be increased. Otherwise, the method continues to line  63 . Preventing the downhill counter from exceeding the counter maximum will prevent the method from increasing the downhill counter to a very large value in the event that the vehicle is in a downhill situation for an extended period of time.  
         [0018]     After block  65 , the method goes to block  66  where the threshold value is compared to a second downhill value. The second downhill value is representative of a larger slope and thus is greater than the first downhill value. The second downhill value is a value representative of the vehicle descending a slope of approximately 37% grade, which is indicative of a vehicle in a downhill situation on a very steep slope. However, the second downhill value can be adjusted to represent other grades. If the threshold value is greater than the second downhill value, the method follows line  68  to block  70 . Otherwise, the method will follow line  63 . By taking into account the possibility that the vehicle is on a steeper slope, the method can more quickly determine if the vehicle is in a downhill situation.  
         [0019]     In block  70 , the downhill counter will be compared to the counter maximum. If the downhill counter is less than the counter maximum, the method continues to block  71 , where the downhill counter will be increased. Otherwise, the method continues to line  63 . Preventing the downhill counter from exceeding the counter maximum will prevent the method from increasing the downhill counter to a very large value in the event that the vehicle is in a downhill situation for an extended period of time.  
         [0020]     After block  71  or if the method followed line  63 , block  72  is performed. In block  72 , the threshold value is compared to a first flat value. The first flat value is representative of the vehicle on a flatter slope. The first flat value is a value representative of the vehicle descending a slope of approximately 18% grade, which is indicative of a vehicle not on a flat surface. However, the first flat value can be adjusted to represent other grades. If the threshold value is less than the first flat value, the method follows line  74  to block  76 . Otherwise, the method follows line  75 .  
         [0021]     Block  76  compares the downhill counter to a counter minimum. If the downhill counter is greater than the counter minimum, then the downhill counter will be decreased as shown in block  80 . Otherwise, the method will follow line  75 . Preventing the downhill counter from going below the counter minimum will prevent the method from decreasing the downhill counter to a very small or even negative value in the event that the vehicle is not in a downhill situation for an extended period of time.  
         [0022]     After block  80 , block  82  is performed. In block  82 , the threshold value is compared to a second flat value. The second flat value is representative of the vehicle traveling on a slope flatter than the slope representative of the first flat value. The second flat value is a value representative of the vehicle descending a slope of approximately 3% grade, which is indicative of a vehicle on a very flat surface. However, the second flat value can be adjusted to represent other grades. If the threshold value less than the second flat value constant, the method continues along line  84  to block  86 . Otherwise, the method follows line  75 . By taking into account the possibility that the vehicle is on a flatter surface, the method can more quickly determine if the vehicle is not in a downhill situation.  
         [0023]     In block  86 , the downhill counter is compared to the counter minimum. If the downhill counter is greater than the counter minimum, the method will follow line  88  to block  90  where the downhill counter will be decreased. Otherwise, the method will follow line  75 . Preventing the downhill counter from going below the counter minimum will prevent the method from decreasing the downhill counter to a very small or even negative value in the event that the vehicle is not in a downhill situation for an extended period of time.  
         [0024]     After block  90  is performed or if the method is following line  75 , block  92  will be performed. In block  92 , the downhill counter is compared to a downhill situation value. The downhill situation value is representative of the minimum downhill counter value required to determine if the vehicle is in a downhill situation. As shown by block  94 , if the downhill counter is greater than the downhill situation value, the ECU will determine that the vehicle is in a downhill situation. A downhill situation is when the vehicle is on a slope of approximately 20% or greater grade, but this can vary based on customer demands. As shown by block  96 , if the downhill counter is less than the downhill situation value, the ECU will determine that the vehicle is not in a downhill situation. A vehicle not in a downhill situation is when the vehicle is on a slope of approximately 18% or less grade, but this can vary based on customer demands. Either way, as represented by block  98 , once a determination of the vehicle&#39;s downhill situation has been made, the method will return to block  52  and start again. By executing the method  50  continuously, a determination of if the vehicle is in a downhill situation can be made in real-time.  
         [0025]     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.