Abstract:
A voltage regulating control system for vehicle systems which includes a power supply providing electrical power to the system and having a predefined maximum voltage. A controller controls an actuator performing a vehicle system function and the electrical load in the system wherein the controller has a first predefined minimum operating voltage. A voltage regulator communicates with the controller and the power supply and senses a system input voltage in the system. In response to a sensed voltage dip in excess of a predetermined value, the regulator changes an effective electrical impedance of the system to maintain the system voltage at a predefined minimum voltage greater than the first predefined minimum operating voltage required by the controller.

Description:
TECHNICAL FIELD  
         [0001]    The present invention generally relates to vehicle electrical systems and in particular to methods and circuitry for regulating vehicle control system voltages.  
         BACKGROUND OF THE INVENTION  
         [0002]    Mechanical linkage and hydraulic pressure operated controls for vehicles are well known in the art, and generally comprise control input devices operated by a user such as steering wheels, shift levers, and foot pedals which are directly interlinked with various vehicle controls individually or by combinations of mechanical push rods, gears, cables, or pressurized hydraulic systems. Such controls have been utilized in vehicles such as automobiles and trucks since the inception and initial manufacturer of such vehicles. As technology through the years has advanced, so also have these mechanical linkage and hydraulic pressure systems advanced with newer and more advanced innovations. Newer forms of technology wherein every vehicle now has one or more on-board computers in various forms assisting in vehicle operation and control. These computers through interconnection with various sensors and vehicle controls can rapidly acquire various objective input data, analyze this data, and then appropriately adjust the vehicle controls to more readily optimize the operation of the various vehicle systems and controls. As a result of the rapid computational power and speed of the computers, control commands can be issued at a much faster rate than older technology mechanical system configurations can respond. The requirement for increased control response time were initially felt in the aerospace industry where modern aircraft have evolved from the use of mechanically linked controls to electrically operated controls in a concept commonly known as “fly-by-wire”.  
           [0003]    As the quest for more and more improvements in vehicle efficiency, more accurate controls, and improved response times, the automotive and vehicle industries are turning with greater frequency to additional electronics and electrical systems to provide necessary vehicle controls. Initially, implementation of various electrical control systems was limited to vehicle systems such as power windows and power door locks, the industry is now moving to replace mechanically operated, systems with electrically operated systems. Braking systems, for example, is potentially one such system. Previously, to ensure the integrity of a vehicle system such as brakes one only had to ensure that the mechanical linkages were secure and properly adjusted and that the brake hydraulic system also maintained its integrity. With the implementation of electrical and electronic controls, maintenance of electric power to vehicle systems is now paramount.  
           [0004]    For example, by switching the vehicle braking system from one of mechanical linkages and hydraulic pressure systems to a purely electrical system, the only interconnection between the driver and the individual brakes at the four corners of the vehicle are electrical conductors. The input voltage to a load in such a system dips at the input terminals due to the current draw of the load through impedances from wiring, connectors, and the power source (battery or alternator). Large load current spikes cause severe voltage dips in the system, and some of these voltage dips may be severe enough to cause controller “brown outs” or resets. Consequently, in a purely electrical control of a vehicle system special attention must be paid to the fail-safe conditions of the electrical system.  
           [0005]    Therefore, maintaining operability during various system failure modes generally requires that some minimum amount of electric power be supplied to the various components to preclude the total loss of the system and potential loss of control of the vehicle as a result of the voltage “brown outs” or controller resets. Such instances of power dissipation, voltage dips, and voltage transients which individually or in some combination can have the combined effect of failing to meet the basic functionality of the system. One such effect could be causing a microprocessor system to reset thereby causing that system or that portion of the system to go off-line and thus its function become unavailable to the vehicle operator. Similar problems exist in the event of the failure of the on-board electric power generation system such that the vehicle must rely strictly on available stored battery power. In this case, system availability remains paramount even though the systems must operate in a degraded mode to maintain that availability. Thus, there is a need to provide a methodology by which the basic characteristics of the electric power are maintained to prevent, to the greatest extent possible, the failure or operational cessation of electrical systems on a vehicle.  
         SUMMARY OF THE INVENTION  
         [0006]    One aspect of the invention is a vehicle system incorporating a voltage regulating control. The system includes a power supply providing electrical power to the system and having a predefined maximum voltage. A controller controls an actuator performing a vehicle system function and the electrical load in the system wherein the controller has a first predefined minimum operating voltage. A voltage regulator communicates with the controller and the power supply and senses a control system input voltage in the control system. In response to a voltage dip in excess of a predetermined value, the regulator changes an effective electrical impedance of the control system to maintain the system voltage at a predefined minimum voltage greater than the first predefined minimum operating voltage required by the controller.  
           [0007]    Another aspect of the invention is a method for regulating the voltage of a vehicle system of the type having a power supply, a controller, and an actuator. The method comprises the steps of defining a minimum system voltage; sensing a current demand for the system during operation of the actuator; increasing an effective impedance of the actuator when the sensed current demand approaches a predefined maximum; and limiting the system voltage to a predefined minimum.  
           [0008]    These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a block diagram of a system configuration incorporating an analog embodiment of a bus voltage regulating function.  
         [0010]    [0010]FIG. 2 is an analog low voltage control circuit diagram of the bus voltage regulating embodiment of the system in FIG. 1.  
         [0011]    [0011]FIG. 3 is a block diagram of a system configuration incorporating a software controlled embodiment of a bus voltage regulating function.  
         [0012]    [0012]FIG. 4 is a software process flow diagram of the bus voltage regulating embodiment of the system in FIG. 3. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    Referring to FIGS. 1 and 2, wherein like numerals indicate like or corresponding parts throughout the several views, a vehicle system generally represented at  10 . System  10  includes a power supply  12 , such as a standard 12-volt power bus, that provides electrical power to the system  10 . A low voltage control circuit  16  according to one embodiment of the invention is interposed between power supply  12  and a control loop  13  at summer  24 . Control loop  13  includes a controller  14  into which is directed a plurality of data signals (not shown) and operator initiated control commands. Controller  14  in turn issues commands to control loop  13  to initiate desired actions by actuator or motor  20  for performing a desired system function such as, for example, actuating a brake, turning a wheel, or some other critical vehicle operation function. Control loop  13  further includes feedback loops  18  and  22  for evaluating and maintaining desired control of system functioning in a manner well known in the art, and therefore an explanation of which is not deemed necessary to an understanding of the preferred embodiments.  
         [0014]    [0014]FIG. 2 represents an analog circuit that represents one possible embodiment of a low Voltage Control Circuit  16  for regulating the voltage of the electrical signal in loop  13  above a predefined minimum. The predefined minimum voltage is some voltage greater than the minimum operation voltage requirement for controller  14 . By maintaining loop  13  voltage above the minimum operating voltage for controller  14 , controller  14  can be prevented from entering a reset mode as a result of a voltage dip occurring during a high current demand request by motor  20 . The bus voltage to be regulated comes into circuit  16  as the SWBAT input  30 . The +5V signal  32  provides a control reference for circuit  16 . The VREG* signal  34  is an output from circuit  16  as a signal to indicate to system  10  that the power bus  12  voltage has dipped and the voltage regulation function of circuit  16  is modifying the original current request. When VREG*  34  is a logic “1”, the voltage control circuitry is off and the system  10  is in normal operation. When VREG*  34  is a logic “0”, the voltage control circuitry is active and the system is in a reduced output capability condition.  
         [0015]    Jumper  36  provides flexibility to connect resistor  38  in parallel with resistor  40  such that the voltage regulation function may be changed to a second voltage such as switching from a 12 volt system to a 42 volt system. For example, jumper  36  is installed to operate in a 12-volt system with a regulation voltage of 7.2 volts and jumper  36  is uninstalled to operate in a 42-volt system with a regulation voltage of 25 volts. With this constraint, further description will refer to SWBAT  30  as a 42-volt system and attempt to regulate the voltage at 25 volts.  
         [0016]    Amplifier  42  in conjunction with resistors  44 ,  46 ,  48 ,  50 ,  52 , and  54  and with capacitors  56 ,  58 , and  60  form a closed loop control compensation. Resistor and capacitor values labeled “Unused” are available to modify the compensation as required in various systems. The illustrated configuration provides simple proportional control of the SWBAT voltage  30 . The +5V signal  32  provides a control reference to the non-inverting input  41  of amplifier  42 .  
         [0017]    Resistors  40  and  62  form a voltage divider to generate Vfb  64  such that Vfb=SWBAT*0.1992. Capacitor  66  in conjunction with resistors  40  and  62  creates a low pass filter to eliminate noise effects from SWBAT  30 . The cutoff frequency of this filter is sufficiently high in frequency to not influence the operation of the voltage control function of this invention.  
         [0018]    Under normal system conditions, the SWBAT  30  voltage is near  42  volts. Even with moderately high current spikes, the SWBAT  30  voltage remains significantly above the 25-volt regulation threshold. In this condition, the voltage of inverting input  43  of amplifier  42  is much higher than the voltage of the non-inverting input  41 . This causes the output of amplifier  42  to saturate at 0 volts. When the output of amplifier  42  is below the activating threshold voltage of transistor  70  (typically 2-4 volts), transistor  70  is off and has no effect on the C LIMIT value at summer  24 . Also the input to inverter  72  is a logic “0”. This cause the VREG* signal  34  to be a logic “1” therefore indicating that the voltage control circuitry is off and the system is in normal operation.  
         [0019]    As the SWBAT voltage  30  approaches 25 volts, the voltage at Vfb  64  approaches 5 volts. Under this condition, the voltage of the inverting input  43  and the non-inverting input  41  of amplifier  42  become equal, and amplifier  42  enters the active state. The output of amplifier  42  begins to rise in voltage until it reaches the activating threshold of transistor  70 . At this instant, transistor  70  begins conducting current from the C LIMIT summing node  24 . This current conduction reduces the current request to the closed loop current control  18 , which reduces the load current draw from the power supply  12 . This is the beginning of input voltage regulation to maintain a minimum voltage at the input terminals of the system. If the load current continues to increase, SWBAT voltage  30  continues to fall lower (only by millivolts because the circuit is in closed loop control of the SWBAT voltage), and the output voltage of amplifier  42  increases. This increase causes transistor  70  to conduct more current, which reduces the current request, C LIMIT  24 , further. The increase in the output voltage of amplifier  42  (also increased conduction of transistor  70 ) does not permit the continued increase in the load current. This modulation continues to keep the value of the SWBAT voltage  30  near the desired threshold value of 25 volts. While the output of amplifier  42  is above the input threshold of inverter  72 , the VREG* signal  34  is at a logic “0” indicating that the voltage control circuitry is active and the system is in a reduced output capability condition. When the load request is reduced and the SWBAT voltage begins to rise above the minimum threshold (25V), the output of amplifier  42  returns to 0 volts, and the system returns to normal operation.  
         [0020]    In the event that the SWBAT voltage  30  continues to fall below the 25 volt threshold, the output of amplifier  42  rises to the maximum value causing transistor  70  to enter a maximum conduction condition. Under this situation, the current draw from C LIMIT summing node  24  is forced to the maximum load current reduction value which is defined by resistor  74 . Resistor  74  creates a voltage divider with the output impedance of current request circuit  15 . The maximum reduction percentage is defined as the value of resistor  74  divided by the sum of resistor  24  and circuit  15  resistance. As the value of resistor  74  decreases, the maximum reduction percentage increases.  
         [0021]    The above schematic represents but one embodiment of an analog circuit to perform a voltage limiting function, and those skilled in the art will recognize that other variations of circuit  16  will perform a like function.  
         [0022]    Turning now to FIGS. 3 and 4, another embodiment is illustrated wherein the voltage regulation function is performed in a microprocessor. Like ending numerals indicate like or corresponding parts to the system described in FIG. 1 above. A vehicle system is generally represented at  110 . System  110  includes a power supply  112 , such as a standard 12-volt power bus, that provides electrical power to the system  110 . A voltage sensing function  102  and voltage control calculation function  104  are performed in microprocessor  114  and function to replace control circuit  16  as described in the above embodiment. Control loop  113  includes a microprocessor controller  114  into which is directed a plurality of data signals (not shown) and operator initiated control commands. Controller  114  in turn issues commands to control loop  113  to initiate desired actions by actuator or motor  120  for performing a desired system function such as, for example, actuating a brake, turning a wheel, or some other critical vehicle operation function. Control loop  113  further includes feedback loops  118  and  122  for evaluating and maintaining desired control of system functioning in a manner well known in the art, and therefore an explanation of which is not deemed necessary to an understanding of the preferred embodiments.  
         [0023]    Voltage Sensing  102  and Voltage Control Calculation  104  functions which replace analog circuit  16  in the embodiment illustrated in FIGS. 1 and 2 as previously noted are performed by software in microprocessor  114  in the instant embodiment. A flow diagram of these functions is illustrated in FIG. 4 and their operation is discussed below.  
         [0024]    Referring now to FIG. 4, the Voltage Sensing  102  and Voltage Control Calculation  104  functions are illustrated according to their respective steps. Sampling of the power bus voltage is performed at  102 . Microprocessor  114  then compares the sampled voltage to predefined values which as in the previous example are illustrated as 42 volts for the power bus voltage, and a threshold voltage of 25 volts. At step  202 , Voltage Control Calculation  104  function determines whether the sampled bus voltage is below the threshold limit of 25 volts. If not the Load Current Reduction is set at zero as shown in block  204  and the power signal is transmitted unchanged to summer  124 . If decision  202  determines that the voltage is below the 25 volt threshold, microprocessor calculates the desired load current reduction percentage at  206 . The monitoring of reduction percentage is illustrated at  208 . If the reduction percentage is less than or equal to the maximum, the load current reduction is performed to the calculated level at  210  and transmitted to summer  124 . If, on the other hand, the calculated load current reduction is greater than the maximum, the load current reduction is set to the maximum permitted at  212  and transmitted to summer  124 . The maximum load current reduction must be defined as a system condition to maintain proper system operation.  
         [0025]    The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principals of patent law, including the doctrine of equivalents.