Abstract:
Methods for improving operation of a stop-start system of a vehicle include controlling an electrical load delivered to an electrically heated windshield (HWS) subsystem of the vehicle prior to a stop cycle or a start cycle of the stop-start system. The methods include steps of discontinuing the electrical load delivered to the HWS subsystem for a predetermined time period prior to a determined predicted stop cycle of the stop-start system. The methods further include differently apportioning the electrical load delivered to a passenger&#39;s side and a driver&#39;s side of the HWS subsystem. The differently apportioning may be according to a determined ambient temperature value, and further may include steps of differently apportioning the electrical load for predetermined time periods determined according to the ambient temperature value. Vehicle stop-start systems and vehicles implementing the methods are described.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to stop-start systems for a vehicle. In particular, the disclosure relates to systems for controlling an electrical load supplied to a heated windshield to maximize availability of vehicle stop-start systems. 
       BACKGROUND 
       [0002]    Vehicle stop-start systems (also referred to as idle stop systems) are used to improve fuel efficiency/economy by stopping/starting the vehicle engine during the drive cycle depending on engine status. For example, in a vehicle equipped with a stop-start system when the engine is idling or approaching idle, i.e. the vehicle speed approaches or is equal to zero or when the vehicle is coasting, the stop-start system automatically shuts down the engine. When the operator depresses the accelerator pedal (or the clutch in a vehicle equipped with a manual transmission) or releases the brake pedal, the stop-start system automatically and seamlessly restarts the engine. This reduces the amount of time spent at idle, likewise reducing fuel consumption and engine emissions. While most common in electric hybrid vehicles, stop-start systems are also found in vehicles lacking a hybrid electric powertrain, for example in so-called “mild” or “micro” hybrids including an internal combustion engine but no electric motor. 
         [0003]    The three primary components of most stop-start systems are the vehicle engine, an electric starter/generator, and a battery. Particularly robust starters and batteries are required because of the frequent engine stop-start cycles incurred by stop-start systems. Stop-start systems are particularly reliant on the vehicle battery during the start phase of the cycle. Therefore, because of the number of vehicle components placing an electrical load on the battery and starter, control of power consumption is important in allowing a stop-start system to perform efficiently. This can be a particular issue for components that typically rely on the internal combustion engine for power but must continue to operate during a “stop” cycle of the stop-start system. This can include compressors, coolant pumps, windshield wipers, exterior/interior lights, entertainment/information systems, interior climate control systems, window defogger/demister systems, and others. The load imposed on the vehicle battery and/or the starter by such components can reduce efficiency of the system in restarting the engine, or in a worst case scenario may delay or impede restarting of the engine. 
         [0004]    Vehicle components such as defog/defrost/demisting HVAC blower systems place a significant load on the vehicle electrical subsystems, which can be particularly disadvantageous during a stop cycle of a stop-start system. Further exacerbating the problem, it is known to provide a heated windshield (HWS) subsystem to aid the HVAC blower system in defrosting/defogging/demisting the vehicle windshield. Conventional electrical load management strategies call for activation of the HWS subsystem to aid in defrosting/defogging/demisting any time heated air is flowing to the windshield and ambient conditions are at a predetermined temperature value, for example less than 15° C. However, these systems create a significant current draw which can impair stop-start capability or even render it unavailable. 
         [0005]    Thus, a need is identified in the art for improvements to vehicle stop-start systems. In particular, improvements to vehicle electrical load management during a start phase of a stop-start cycle are desirable. 
       SUMMARY 
       [0006]    In accordance with the purposes and benefits described herein and to solve the above-summarized and other problems, in one aspect methods are described for improving operation of a stop-start system of a vehicle by differently managing an electrical load supplied to a heated windshield subsystem of the vehicle. In particular, an electrical load supplied to a heated windshield subsystem of the vehicle is differently apportioned to a driver&#39;s side and a passenger&#39;s side of the windshield. 
         [0007]    In embodiments, an electrical load supplied to the passenger&#39;s side of the heated windshield subsystem is reduced. In other embodiments, the electrical load is differently apportioned to the driver&#39;s side and passenger&#39;s side of the heated windshield subsystem according to determined ambient temperature. The electrical load may be differently apportioned for predetermined time periods. In still other embodiments, the predetermined time periods are determined according to the predetermined ambient temperature. Ambient temperature-dependent timers may be provided to time the predetermined time periods. 
         [0008]    In other aspects of the disclosure vehicle stop-start systems and vehicles incorporating same for implementing the described methods are provided. 
         [0009]    In the following description, there are shown and described embodiments of the disclosed stop-start electrical load management systems and methods. As it should be realized, the described systems and methods are capable of other, different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the devices and methods as set forth and described in the following claims. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawing figures incorporated herein and forming a part of the specification, illustrate several aspects of the disclosed stop-start electrical load management systems and methods, and together with the description serve to explain certain principles thereof. In the drawings: 
           [0011]      FIG. 1  is a block diagram representation of a vehicle including a stop-start system; 
           [0012]      FIG. 2  is a flow chart representation of a method according to the present disclosure for improving operation of a vehicle stop-start system during a stop cycle; and 
           [0013]      FIG. 3  is a flow chart representation of a method according to the present disclosure for improving operation of a vehicle stop-start system during a start cycle. 
       
    
    
       [0014]    Reference will now be made in detail to embodiments of the disclosed systems and methods, examples of which are illustrated in the accompanying drawing figures. 
       DETAILED DESCRIPTION 
       [0015]    At a high level, the disclosed stop-start electrical load management systems and methods solve the above-described problems and improve efficiency of a vehicle stop-start system by differently managing an electrical load supplied to a heated windshield heated windshield subsystem of the vehicle. In particular, an electrical load supplied to a heated windshield subsystem of the vehicle is differently apportioned to a driver&#39;s side and a passenger&#39;s side of the windshield. 
         [0016]    With reference to  FIG. 1 , a vehicle  100  including a start-stop system is schematically depicted in block diagram form. While stop-start systems are most commonly encountered in hybrid or micro hybrid vehicles, as noted above use of stop-start systems in non-hybrid vehicles is known and the use of the presently described methods and systems in non-hybrid vehicles is contemplated herein. The vehicle may include an engine  110 , a battery  112 , and a plurality of electrical subsystems  114  such as windshield wipers, exterior/interior lights, entertainment/information subsystem, interior climate control subsystem, window defogger/demister subsystem, heated windshield subsystem, and others. A starter/electric motor  116  may be included for restarting the engine  110  during a start cycle of the stop-start system. 
         [0017]    One or more controllers  118  are provided which communicate (see broken lines) with one or more of the engine  110 , starter  116 , electrical subsystems  114 , and battery  112 . As is known, the controllers  118  may be configured to initiate an auto stop or auto start cycle of the stop-start system on receipt of a suitable signal, such as the vehicle speed decreasing to a predetermined value. Thus, as the vehicle  100  approaches a stop, at a predetermined speed (for example, 1-2 kph) the one or more controllers  118  may issue a command to begin a process of stopping engine  110 . In that situation, fuel transfer to the engine  110  is discontinued, and starter  116  and electrical subsystems  114  rely on battery  112  for power. On receipt of a second signal, for example an operator releasing a brake pedal or depressing a clutch or accelerator pedal as discussed above, the one or more controllers  118  may issue a signal to reengage the engine  110   
         [0018]    The stages of a vehicle stop-start system stop cycle and start cycle are known in the art, and do not require extensive discussion herein. However, a discussion of a representative stop cycle and start cycle of a stop-start system is provided in the present Assignee&#39;s U.S. Published Patent Appl. No. 2013/0041556, the entirety of which is incorporated by reference herein. Briefly, a stop cycle may include a phase of preparing for an impending engine  110  stop, including preparing various other vehicle systems and subsystems for operating on battery power only. Fuel flow to the engine  110  is discontinued, and the engine is stopped when the engine speed reaches 0 or near 0. 
         [0019]    A vehicle start cycle may include a starter engage phase when the starter  116  attempts to restart the engine  110  in response to a start cycle indicator such as an operator releasing a brake pedal or depressing a clutch or accelerator pedal. When the engine  110  is able to crank under its own power, the starter  116  is disengaged. The engine increases speed to a target idle speed during an “engine speed increasing” phase. Once the engine reaches a speed at or above a target idle speed, the start cycle is finished. 
         [0020]    During the stop cycle, certain of the electrical subsystems  114  may be disabled or at least have their functionality restricted to reduce drain on battery  112 . For example, fully disabling the vehicle HVAC blower subsystem and/or the heated windshield subsystem would be disadvantageous under ambient conditions requiring continued windshield clearing. However, instantly restoring the full functionality of all disabled/functionality restricted subsystems  114  during the “engine speed increasing” phase may cause large drops in system voltage, potentially delaying or even preventing engine restart. Further, the electrical load required by particular subsystems such as window defrost/defog/demist subsystem, including heated windshield subsystem, may vary according to ambient temperature, i.e. the air temperature surrounding the vehicle  100 . 
         [0021]    To address this problem, in one aspect there is provided a method for differently managing an electrical load supplied to a heated windshield subsystem of the vehicle. With reference to  FIG. 2 , the method includes a step  200  of determining whether a stop cycle of the stop-start system is imminent. If so, at step  202  it is determined whether the HWS subsystem is in “AUTO” or automatic mode. If so, at step  204  it is determined whether ambient temperature is at or above a predetermined value. If not, the system resets. If so, at step  206  the HWS subsystem is temporarily disengaged. 
         [0022]    In an embodiment, controller area network (CAN bus) messaging indicates that a stop cycle is imminent, such as on determining that an engine speed is at or near 0 as described above, and the HWS subsystem is temporarily disengaged for a predetermined time period, for example 5-10 seconds, to allow the stop cycle to initiate without delay. An ambient temperature may be concurrently determined such as by a temperature sensor of known design. If the ambient temperature is determined to be at or above a predetermined value, such as 30° F. or higher, on completion of the stop cycle the HWS subsystem is disengaged and remains so until a start cycle is initiated (step  206   a ). In an alternative embodiment, if the ambient temperature is less than the predetermined threshold such that continued windshield clearing is required, it is further contemplated to adjust a maximum time of engine stoppage during which the HWS subsystem is disengaged to reduce risk of fogging, icing, etc., for example from 90 seconds to 2 minutes (step  206   b ). 
         [0023]    Certain predetermined system overrides may be provided to further mitigate risk of fogging, icing, etc. by preventing shutdown of the HWS subsystem during a stop cycle. In embodiments, the overrides preventing shutdown of the HWS subsystem during a stop cycle may include one or more of a determined probability of fogging of 40% or more (FogProb&lt;MaxAccFog), a vehicle operator manually actuating the vehicle defrost subsystem (defrost/max defrost actuated), a vehicle operator manually actuating the windshield wiper subsystem, a vehicle operator manually actuating the HWS subsystem, and others. 
         [0024]    In turn, with reference to  FIG. 3 , at step  300  a determination is made of whether a start cycle of the stop-start system is imminent. At step  302  an ambient temperature is determined, again by a temperature sensor of known design. In accordance with the determined ambient temperature, at step  304  a determination is made of whether a full timer cycle determining a full time period of activation of the HWS subsystem is required. If so, at step  306   a  an electrical load is differently apportioned to different portions of the HWS subsystem for the full timer cycle. If not, at step  306   b  the electrical load is differently apportioned to different portions of the HWS subsystem for less than the full timer cycle. 
         [0025]    By “differently apportioned” it is meant that an electrical load supplied to the HWS subsystem is differently provided to different portions of the windshield, i.e. the driver&#39;s side and the passenger&#39;s side of the windshield are treated differently. In an embodiment, the load provided to the passenger&#39;s side of the windshield is reduced. As will be appreciated, this allows the driver&#39;s side to receive more of the electrical load supplied to the HWS subsystem, and so the area of the windshield through which the driver must look is favored without having to increase the overall electrical load supplied to the heated windshield. 
         [0026]    An embodiment of the above-described method is shown in Table 1 below, depicting proposed electrical loads at predetermined ambient temperature ranges. As will be appreciated, the percentages shown therein are a percentage of the maximum electrical load which could be provided to particular portions of the HWS subsystem. As shown therein, at temperatures between −18° C. and 15° C. a consistently greater portion of the 75% (of maximum) electrical load provided is supplied to the driver&#39;s side of the heated windshield. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Proposed loads at ambient temperature during Auto-Stop 
               
             
          
           
               
                 Ambient temperature (° C.) 
                 Driver side load 
                 Passenger side load 
               
               
                   
               
               
                   − 18-0  
                 Up to 50% 
                 Up to 25% 
               
               
                  0-15 
                 Up to 25% 
                 Up to 15% 
               
               
                 15-31 
                 0% 
                 0% 
               
               
                   
               
             
          
         
       
     
         [0027]    In turn, it is contemplated to provide the above electrical loads for time periods determined by ambient temperature-dependent timers, in order to account for differing ambient conditions which may create a requirement for greater or lesser time periods of HWS subsystem activation. In an embodiment, as shown in Table 2 below various predetermined time periods are selected for user-selected actuation of defrost/max defrost functions, user-selected HWS subsystem actuation, and for automatic HWS subsystem actuation during a start cycle of a stop-start system. It will be appreciated that the values and ranges for temperature settings, timer settings, etc. are representative only and non-limiting, and may be adjusted as necessary by the manufacturer according to ambient conditions, geographic locations, and other factors. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Proposed timer settings at ambient temperature during Auto-Stop 
               
             
          
           
               
                   
                   
                   
                 Timer for 
               
               
                 Ambient 
                 Timer for user 
                 Timer for Max 
                 Auto HWS 
               
               
                 temperature (° C.) 
                 selection (minutes) 
                 defrost (minutes) 
                 (minutes) 
               
               
                   
               
             
          
           
               
                   − 18-0  
                 15 
                 15 
                 ≦15 
               
               
                   − 1-5 
                 15 
                 15 
                 ≦6 
               
               
                  5-15 
                 10 
                 10 
                 ≦4 
               
               
                 &gt;15 
                 8 
                 8 
                 ≦2 
               
               
                   
               
             
          
         
       
     
         [0028]    As will be appreciated, by use of an ambient temperature-dependent timer to determine a time of actuation of the HWS subsystem in auto mode, a lesser time of actuation and so reduced power usage is possible. 
         [0029]    The foregoing has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Obvious modifications and variations are possible in light of the above teachings. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.