Abstract:
A vehicle cruise control system includes an ECO-cruise mode such that a rate of acceleration of the vehicle during cruise control is less than or equal to a maximum that is a function of vehicle speed and road grade. Further, the rate is a function of the vehicle speed and a difference between the vehicle and target cruise control speeds.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to vehicle cruise control operation and the management of fuel consumption during cruise control operation. 
       BACKGROUND 
       [0002]    Conventional cruise control systems are designed to maintain vehicle speed by controlling the vehicle accelerator. This results in an acceleration request when the speed drops below a predetermined hysteresis level and a deceleration request when the speed increases above a predetermined hysteresis level. Along with the deceleration request, the vehicle&#39;s brakes may be applied to reduce the vehicle speed to the vehicle set speed. When traveling up a steep incline, the acceleration request may be such that it is equivalent to wide open throttle. 
       SUMMARY 
       [0003]    A vehicle cruise control system includes at least one controller programmed to, in response to a decrease in vehicle speed relative to a target cruise speed in an absence of driver acceleration demands, cause the vehicle to accelerate at a rate. The rate is less than or equal to a maximum that depends on road grade and the vehicle speed, and depends on the vehicle speed and a difference between the vehicle and target cruise speeds. 
         [0004]    A method of controlling vehicle speed includes receiving a target cruise control speed and a cruise control operating mode, selecting a speed control gain based on the cruise control operating mode and a difference between vehicle speed and the target cruise control speed, and generating a weighted speed error from the difference based on the speed control gain. The method further includes generating a road gradient compensation ratio based on the cruise control operating mode and a road gradient force representing a road grade, and accelerating the vehicle at a rate based on the road gradient compensation ratio, the weighted speed error, and the vehicle speed such that the rate increases as the vehicle speed increases when the road grade is generally constant in an absence of driver acceleration demands and the rate decreases as the road grade increases in the absence of driver acceleration demands. 
         [0005]    A method for controlling vehicle speed includes, in response to a decrease in vehicle speed relative to a target cruise control speed in an absence of driver acceleration demands, causing the vehicle to accelerate at a rate. The rate is less than or equal to a maximum that depends on vehicle speed and road grade, and depends on the vehicle speed and a difference between the vehicle and target cruise control speeds such that the rate increases as the vehicle speed increases when the road grade is generally constant and the rate decreases as the road grade increases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  illustrates an example hybrid electric vehicle with cruise control functionality; 
           [0007]      FIG. 2  illustrates a flow diagram of driver evaluator and driver assist blocks of a vehicle cruise control algorithm; 
           [0008]      FIG. 3  illustrates a flow diagram of an ECO-cruise control algorithm. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0010]    An engine or motor is a machine designed to convert energy into useful mechanical motion. The engine or motor can be an internal combustion engine, an electric motor or other electric machine. The efficiency at which this conversion is performed is based on criteria such as the beginning rotational speed, the desired rotational speed, and how quickly to accelerate from the current speed to the desired speed. 
         [0011]    Certain vehicles equipped with cruise control functionality use general algorithms and calibration schemes when cruise control is activated. One common algorithm is a simple PID control loop which is enabled when the vehicle speed crosses a threshold point. The result of this control method is that the throttle may reach a fully open position. This may result in sub-optimal fuel economy as the current control system tries to achieve a desired cruise control performance. 
         [0012]      FIG. 1  depicts an example of a plug-in hybrid-electric vehicle. A plug-in hybrid-electric vehicle  102  may comprise one or more electric motors  104  mechanically connected to a hybrid transmission  106 . In addition, hybrid transmission  106  is mechanically connected to an engine  108 . The hybrid transmission  106  may also be mechanically connected to a drive shaft  110  that is mechanically connected to wheels  112 . The electric motors  104  can provide propulsion when the engine  108  is turned on. The electric motors  104  can provide deceleration capability when the engine  108  is turned off The electric motors  104  may be configured as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric motors  104  may also reduce pollutant emissions since the hybrid electric vehicle  102  may be operated in electric mode under certain conditions. 
         [0013]    Battery pack  114  stores energy that can be used by the electric motors  104 . The vehicle battery pack  114  typically provides a high voltage DC output. The battery pack  114  is electrically connected to a power electronics module  116 . The power electronics module  116  is also electrically connected to the electric motors  104  and provides the ability to bi-directionally transfer energy between the battery pack  114  and the electric motors  104 . For example, a typical battery pack  14  may provide a DC voltage while the electric motors  4  may require three-phase AC current to function. The power electronics module  16  may convert the DC voltage to three-phase AC current as required by the electric motors  104 . In a regenerative mode, the power electronics module  116  will convert the three-phase AC current from the electric motors  104  acting as generators to the DC voltage required by the battery pack  114 . The methods described herein are equally applicable to a pure electric vehicle or any other device using a battery pack. 
         [0014]    In addition to providing energy for propulsion, the battery pack  114  may provide energy for other vehicle electrical systems. A typical system may include a DC/DC converter module  118  that converts the high voltage DC output of the battery pack  114  to a low voltage DC supply that is compatible with other vehicle loads. Other high voltage loads, such as compressors and electric heaters, may be connected directly to the high-voltage bus from the battery pack  114 . In a typical vehicle, the low voltage systems are electrically connected to a 12V battery  120 . An all-electric vehicle may have a similar architecture but without the engine  108 . 
         [0015]    The battery pack  114  may be recharged by an external power source  126 . The external power source  126  may provide AC or DC power to the vehicle  102  by electrically connecting through a charge port  124 . The charge port  124  may be any type of port configured to transfer power from the external power source  126  to the vehicle  102 . The charge port  124  may be electrically connected to a power conversion module  122 . The power conversion module may condition the power from the external power source  126  to provide the proper voltage and current levels to the battery pack  114 . In some applications, the external power source  126  may be configured to provide the proper voltage and current levels to the battery pack  114  and the power conversion module  122  may not be necessary. The functions of the power conversion module  122  may reside in the external power source  126  in some applications. 
         [0016]    The vehicle engine, transmission, electric motors and power electronics may be controlled by a powertrain control module (PCM)  128 . The vehicle cruise control function can reside in almost any electronic module including the PCM  128 . The vehicle cruise control function may also reside in a module separate from the PCM  128 , including but not limited to a body control module (BCM), an instrument panel cluster (IPC), a steering column control module (SCCM), an infotainment module, a navigation module, etc. 
         [0017]    In addition to illustrating a plug-in hybrid vehicle,  FIG. 1  can illustrate a battery electric vehicle (BEV) if components  108 ,  122 ,  124  and  126  are removed. Likewise,  FIG. 1  can illustrate a traditional hybrid electric vehicle (HEV) or a power-split hybrid electric vehicle if components  122 ,  124  and  126  are removed. 
         [0018]      FIG. 2  illustrates an example of an ECO-cruise control flow diagram  200 . This ECO-cruise control function  200  can be implemented in the Powertrain Control Module  128  or other module which controls or modifies the speed control. This ECO-cruise control example flow diagram  200  includes a Driver Evaluator (DE)  202  and a Driver Assist (DA) function block. 
         [0019]    The Driver Evaluator (DE)  202  is a function block that generates requests such as driver force request  206 . Driver Assist (DA)  204  is a functional block that generates requests such as traction torque request  208 . The DA  204  arbitrates a driver acceleration request  210  with other vehicle acceleration requests  212 , such as speed control and speed limiting, and generates traction torque request  214 . 
         [0020]    In the DE  202 , the system determines a driver torque request  216  based on input such as pedal position  218 , output shaft speed  220 , vehicle speed, engine speed or an equivalent, etc. The driver torque request  216  is converted to the driver force request  206 . In the DA  204 , the system converts the driver force request  206  to a driver acceleration request  214 . The system  200  also determines other vehicle acceleration requests  212  from various inputs including vehicle speed control, a speed cruise control function, a vehicle speed limiting function, adaptive speed control function, etc. The ECO-cruise functionality may be implemented in the vehicle speed control function which determines the vehicle acceleration request  212  for the speed control using ECO-cruise Mode  222 . An arbitrated acceleration request  224  is determined by arbitrating the driver acceleration request  214  with these other vehicle acceleration requests  212 . The system converts the arbitrated acceleration request  224  to a traction force request  226  and then determines the final traction torque request  208 . 
         [0021]      FIG. 3 . illustrates a flow diagram for determining the vehicle acceleration request  212 . The ECO-Cruise Mode  222  may be selected by the driver or the selection may be performed automatically by another module, or a preference setting. The ECO-Cruise Mode  222  is an input that may be implemented many ways including a physical button, a soft button in a human machine interface (HMI), a graphical user interface (GUI), or automatically in an electronic module such as powertrain control module (PCM)  128 , a navigation module, an electronic stability control module or the like. With the ECO-Cruise Mode  222 , the control system  200 , when determining the vehicle acceleration request  212  in the vehicle speed control function, can use specific fuel economy tailored algorithms and calibrations to improve vehicle real world fuel economy. 
         [0022]    The ECO-Cruise Mode  222  input selects mode based road gradient filter constants  302 . The filter constants or filter coefficients  302  along with other inputs including wheel torque, output shaft speed, vehicle speed, acceleration, inclination (from a sensor such as a G-sensor), and other data are received by road gradient and road resistance determination block  304 . The road gradient and road resistance determination block  304  generates a road gradient force  306 , which may be calculated real-time or prior to operation and stored as a look-up table. The road gradient force  306  along with the ECO-Cruise Mode  222  is used to determine a road gradient compensation ratio  308  by selectively using a road grade based acceleration compensation matrix  310 . The road grade based acceleration compensation matrix  310  is a function of the road gradient force  306 , vehicle speed, and the ECO-Cruise Mode  222 . This vector calculation allows the road grade based acceleration compensation ratio  308  to adapt to operating parameters input via the road gradient force  306 . For example, if the vehicle speed increases, the road grade based acceleration compensation ratio  308  may also increase to compensate for the increase in force needed to accelerate the vehicle due to the increased air resistance. If the road grade increases, the Road Gradient Force will increase and the algorithm may decrease the road grade based acceleration compensation ratio  308 . Alternatively, if the road grade increases, the road grade based acceleration compensation ratio  308  may increase to overcome the additional force due to the elevation change. This can be implemented to include a normal road grade based acceleration compensation vector matrix  312  and an ECO-cruise road grade based acceleration compensation vector matrix  314 , but also may have other matrices for alternative modes including a sport mode, a highway mode, and a city mode. 
         [0023]    The ECO-Cruise Mode  222  is also an input to a speed control gain matrix  316 . This can be implemented to include a normal speed control gain  318  and an ECO-cruise speed control gain  320  but also may have other matrices for alternative modes including a sport mode, a highway mode, and a city mode. The speed control gain matrix  316  is shown with the input to the matrices being cruise vehicle speed error  322  and ECO-Cruise Mode  222 . The cruise vehicle speed error  322  is calculated by comparing the cruise vehicle speed set point  324  and a filtered vehicle speed  326 . The cruise vehicle speed error  322  is adjusted by the speed control gain constant derived from the speed control gain block  316  to determine a weighted cruise vehicle speed error  328 . 
         [0024]    The weighted cruise vehicle speed error  328  is a desired acceleration used to adjust the vehicle acceleration to achieve the cruise vehicle speed set point  324 . This weighted cruise vehicle speed error  328  is limited by a minimum acceleration  330  and a maximum acceleration  332 . The maximum acceleration  332  is compensated by the road gradient compensation ratio  308  to provide a weighted maximum acceleration  334 . The result of the weighted cruise vehicle speed error  328  limited by the minimum vehicle acceleration  330  and the weighted maximum vehicle acceleration  334  is the vehicle acceleration request  212 . 
         [0025]    The processes, methods, or algorithms disclosed herein can be deliverable to/implemented by a processing device, controller, or computer, which can include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic data tape storage, optical data tape storage, CDs, RAM devices, FLASH devices, MRAM devices and other magnetic and optical media. The processes, methods, or algorithms can also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers, or any other hardware components or devices, or a combination of hardware, software and firmware components. 
         [0026]    Exemplary embodiments are described above. It, however, is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. 
         [0027]    While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.