Abstract:
In a method for operating a motor vehicle, an actuation speed of a power input element, e.g., an accelerator pedal, is detected and evaluated, and a drag torque is influenced as a function of the detected actuation variable. At least one measure which influences the drag torque is carried out if the following conditions are all satisfied: (i) an actuation speed is less than a limiting value, (ii) a position of the input element is greater than zero, and (iii) the power input element is actuated in the direction of a power reduction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for operating a motor vehicle, as well as a computer program and a control device for operating a motor vehicle. 
     2. Description of Related Art 
     Driving machines of vehicles are usually operated with the aid of an accelerator pedal, i.e., the pedal is used to transmit a request for a desired driving torque to the driving machine. Methods for converting a position (angle) of the accelerator pedal into an electrical signal are known. This signal is detected by an engine control unit and used to control the driving machine. This principle is used, for example, in gasoline or diesel engines, hybrid drives and electric motors. Methods are furthermore known for using variables derived from the accelerator pedal position to, for example, evaluate a behavior of the driver or to additionally control the driving machine. 
     Publications in this field are, for example, published international patent application document WO 09144064, U.S. Pat. No. 4,805,751, U.S. Pat. No. 4,848,544, published German patent application document DE102005002265 and U.S. Pat. No. 4,830,155. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method, computer program and a control device for operating a motor vehicle, which method, program and device provide the advantage that a motor vehicle drive may be used particularly efficiently as a function of the position and the actuation speed of a power input element. This makes it possible to protect the environment and save fuel and driving energy. 
     During operation of the motor vehicle, a position of the power input element is continuously detected and evaluated. An actuation speed of the input element may be ascertained according to the absolute amount and the sign from the ascertained position with the aid of mathematical operations, for example. If the input element is actuated in the direction of a power reduction, a measure which influences the drag torque of the drive may be deduced therefrom. The drive is, for example, a diesel engine, a spark ignition engine, a hybrid drive or an electric drive. The measure influencing the drag torque may be selected in such a way, for example, that a driver&#39;s intention ascertained from the actuation speed with regard to the movement of the motor vehicle is supported particularly well. At the same time, manipulated variables of the drive or the motor vehicle may be altered in such a way that a particularly energy-efficient movement of the motor vehicle is subsequently achieved. 
     If the power input element, for example an accelerator pedal, is moved back by the driver with the intention of reducing the power, two different effects may be intended thereby. In a first case, a so-called sailing mode may be intended, in which the vehicle is not to be further accelerated but rather to coast over a comparatively long distance at a comparatively low negative acceleration or, optionally, the speed is to even be maintained. In a second case, the intention may be to place the motor vehicle in a so-called coasting mode, in which the vehicle speed is additionally reduced by a so-called engine drag torque. This is based on the consideration that the vehicle drive which is not supplied with energy performs an additional braking action due to friction effects, and the vehicle consequently is slowed down at a comparatively high negative acceleration. According to the present invention, the actuation speed of the accelerator pedal is also utilized to distinguish between the two cases. This is accomplished in that one or multiple limiting values are compared to an instantaneous actuation speed of the accelerator pedal. 
     The present invention is also helpful in connection with automatic distance control systems, which are being used more and more today and are usually based on a measurement of the distance to a vehicle traveling ahead, with the aid of radar. In this case, the power input element may also rather be “virtual,” for example, include a control variable of a control and regulating device which is ascertained by taking the distance measurement signals into account. 
     In particular, it is provided that the measure includes at least reducing a fuel quantity to be injected, preferably discontinuing the fuel injection and influencing the position of the throttle valve of an internal combustion engine which drives the motor vehicle. Discontinuing—or at least reducing—the fuel injection ensures that no or only a small amount of energy is used for the drive during the measure. The drive or the motor vehicle characteristics may be additionally influenced by intentionally controlling the throttling losses with the aid of the position of the throttle valve of the internal combustion engine. 
     An embodiment of the method provides that the throttle valve is opened all the way when injection is deactivated. This supports the sailing mode of the motor vehicle particularly effectively. The wider the throttle valve is opened, the smaller are the throttling losses brought about thereby, and a drag torque generated by the non-driven internal combustion engine is minimized accordingly. This results in a longer sailing of the vehicle without consuming fuel. 
     It is furthermore provided that the position of the throttle valve is changed in such a way that a speed of the motor vehicle remains at least approximately the same. This allows the characteristics of the motor vehicle to be set in sailing mode in a more differentiated way. For example, an approximately constant speed of the vehicle may be maintained in this way when driving downhill. The position of the throttle valve may thus be used as an additional, sensitive brake to prevent an undesirably high speed, for example when driving downhill. 
     The sailing mode of the motor vehicle may take place particularly efficiently if the measure includes opening a clutch which connects the wheels of the motor vehicle to a driving machine driving the motor vehicle. This allows the remaining friction losses of the drive to be maintained at a particularly low level and the consumption of fuel or energy to be minimized. 
     In addition, it is provided that a driving machine designed as an internal combustion engine is operated in idle mode during an operation in which the clutch is open. This makes it possible to ensure that the essential parts of the drive are decoupled from the wheels and the driving machine is operated using a particularly small amount of energy in this state, without it being necessary to subsequently restart the internal combustion engine. 
     The method may be applied particularly effectively in sailing mode if the measure includes generating a driving torque with the aid of an electric motor. This allows the motor vehicle speed to be kept approximately constant or a particularly long coasting to be achieved—in particular for a hybrid or electric drive. The driving torque generated by the electric motor is used to compensate for remaining friction losses. 
     In one embodiment of the method, no fuel is injected and at least one measure which increases the drag torque is carried out if the actuation speed is greater than a limiting value and the position of the input element is reduced to zero. Exceeding the limiting value is used as a criterion for detecting a coasting mode requested by the driver. This means that the vehicle is neither supposed to continue to accelerate nor continue to move at a constant vehicle speed, but instead the vehicle is braked comparatively quickly compared to a sailing mode using a defined braking action. For this purpose, no or only a small amount of fuel is injected or the drive is no longer supplied with energy, on the one hand, and an additional measure which increases the drag torque is carried out, on the other hand. 
     To achieve this, it is proposed that a torque which increases the drag torque is generated by an electric motor or generator. This allows the kinetic energy of the vehicle to be additionally reduced in a controlled manner. This is advantageous, in particular in hybrid or electric drives in which the energy generated thereby may optionally flow into a battery which allows the overall energy consumption to drop. 
     Alternatively or additionally, it is provided that a throttle valve of an internal combustion engine which drives the motor vehicle is closed as the measure which increases the drag torque. An effective measure for additionally braking the vehicle is thus also described for a conventional internal combustion engine. 
     The method according to the present invention may be applied more flexibly if the selection of the measure or measures is a function of a course of the road and/or a traffic situation. 
     The roadway gradient, other roadway properties, the vehicle speed, the course of the road and/or the traffic situation may thus be taken into account. The traffic situation may be ascertained, for example, from operating variables of the driving machine or the vehicle or from the vehicle movement detected over a previous period of time. 
     In addition, the method according to the present invention provides that the course of the road is ascertained from the data of a GPS and/or a yaw-rate sensor. The course of the road may be ascertained particularly accurately with the aid of the GPS (global positioning system). In addition, the vehicle movement may be detected with the aid of an acceleration sensor and/or a yaw-rate sensor. In this way, the measure derived from the position and actuation speed of the accelerator pedal may be used in a more differentiated manner for controlling the internal combustion engine or the drive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a simplified schematic view of a motor vehicle having an internal combustion engine. 
         FIG. 2  shows a simplified schematic view of a motor vehicle having a hybrid drive. 
         FIG. 3  shows a simplified schematic view of a motor vehicle having an electric drive. 
         FIG. 4  shows a flow chart for a computer program for execution on a control and/or regulating device of the motor vehicle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The same reference numerals are used for functionally equivalent elements and variables in all figures. 
       FIG. 1  shows a simplified schematic view of a motor vehicle  10 . In the drawing, the following elements are shown from left to right: an accelerator pedal  12 , a control and/or regulating device  14  having a memory in which a computer program  11  is stored, an internal combustion engine  16 , a clutch  18 , a transmission  20  and wheels  22  driven by transmission  20 . In the present case, internal combustion engine  16  includes four cylinders  24   a  through  24   d  and fuel injectors  26   a  through  26   d  assigned to cylinders  24   a  through  24   d . Fuel injectors  26   a  through  26   d  are controlled by control and/or regulating device  14  with the aid of control lines  28 . 
     A throttle valve  30 , which may be used to set the air supply of the four cylinders  24   a  through  24   d , is shown symbolically in the lower area of the drawing of internal combustion engine  16 . Control lines  32 , which start at control and/or regulating device  14 , are furthermore provided to set throttle valve  30 , to actuate clutch  18  or to disengage clutch  18 , at least as needed. 
     During operation of motor vehicle  10 , control and/or regulating device  14  continuously ascertains position  13  of accelerator pedal  12 , actuation speed  15  of accelerator pedal  12  and a direction of accelerator pedal actuation in the sense of power increase or power decrease. As a function of the ascertained variables, control and/or regulating device  14  may carry out at least one measure which influences the drag torque of internal combustion engine  16 . 
     If control and/or regulating device  14  determines that actuation speed  15  of accelerator pedal  12  is less than a limiting value  58  and simultaneously that a position  13  of accelerator pedal  12  is greater than zero and simultaneously that accelerator pedal  12  is also actuated in the direction of a power reduction, control and/or regulating device  14  at least temporarily discontinues or reduces a fuel injection through fuel injectors  26   a  through  26   d . At the same time, throttle valve  30  is opened all the way. Alternatively, clutch  18  is set in such a way that the transmission of force between internal combustion engine  16  and transmission  20  is interrupted. In this case, internal combustion engine  16  is also operated in an idle mode. In both cases, a so-called sailing mode is set, in which motor vehicle  10  is supposed to continue to travel, for as long as possible, without or with a reduced energy supply—albeit at decreasing speed. 
     In addition, data of a GPS  33  (global positioning system), which is shown in the left area of the drawing, and a yaw-rate sensor  35  are evaluated to ascertain the course of the road and current traffic situation. For example, if it is apparent from the ascertained data that motor vehicle  10  is traveling downhill, the position of throttle valve  30  is changed in such a way that a speed of motor vehicle  10  remains at least approximately the same. 
     If, in another case, control and/or regulating device  14  determines that actuation speed  15  of accelerator pedal  12  is greater than limiting value  58  and simultaneously that position  13  of accelerator pedal  12  is reduced to zero, the fuel injection into cylinders  24   a  through  24   d  with the aid of fuel injectors  26   a  to  26   d  is at least temporarily discontinued or reduced. At the same time, at least one measure which increases the drag torque of internal combustion engine  16  is carried out. In the present case, throttle valve  30  of internal combustion engine  16  is closed for this purpose. In this way, a particularly high drag torque is generated, after which the vehicle speed of motor vehicle  10  is reduced comparatively quickly. 
       FIG. 2  shows a motor vehicle  10  which is similar to the one in  FIG. 1 , motor vehicle  10  in  FIG. 2  having a hybrid drive. In addition, motor vehicle  10  therefore includes an electric motor  40 , a battery  42  and control lines  44  for controlling electric motor  40  with the aid of control and/or regulating device  14 . Electric motor  40 , which may also operate as a generator, is mechanically connected to transmission  20  and electrically connected to battery  42 . 
     During operation of motor vehicle  10  according to  FIG. 2 , other measures in addition to the measures described in  FIG. 1  may be carried out which are performed together with electric motor  40 . In a sailing mode of internal combustion engine  16 , electric motor  40  may support the sailing mode with the aid of comparatively little driving power and keep the vehicle speed of motor vehicle  10  constant or allow motor vehicle  10  to coast for a particularly long time. 
     In a coasting mode of motor vehicle  10 , electric motor  40  may operate as a generator and draw mechanical power from transmission  20  and transmit it as electrical power to battery  42 . In doing so, clutch  18  is preferably opened. 
       FIG. 3  shows another embodiment of motor vehicle  10 , which has an electric drive. Variables  13  and  15  of accelerator pedal  12  are continuously ascertained by control and/or regulating device  14  and used to control the drive, which in the present case is an electric motor  40 . Electric motor  40  acts upon wheels  22 . In motor mode, electric motor  40  receives electrical energy from battery  42 ; in generator mode, electric motor  40  supplies electrical energy to battery  42 . 
     If a sailing mode is set on the basis of the variables of accelerator pedal  12  ascertained by control and/or regulating device  14 , the supply of electrical energy from battery  42  to electric motor  40  may be interrupted in a first alternative, and motor vehicle  10  may thus coast at an ever slower speed. Alternatively, electric motor  40  and battery  42  may be used to maintain an approximately constant vehicle speed of motor vehicle  10  in sailing mode. In an essentially flat or inclined course of the roadway, electric motor  40  withdraws electrical energy from battery  42  to maintain the speed of motor vehicle  10 . 
     During downhill travel, electric motor  40  may be used to generate a drag torque to maintain a constant vehicle speed of motor vehicle  10 . Electric motor  40  operates as a generator and may feed electrical energy into battery  42 . 
     If a coasting mode is set in control and/or regulating device  14 , electric motor  40  operates as a generator and is able to advantageously store the energy taken from wheels  22  as electrical energy in battery  42 . The amount of drag torque may be changed with the aid of electrical variables. 
       FIG. 4  shows a highly simplified flow chart to be processed by computer program  11  for carrying out the method. In the drawing, the processing essentially takes place from top to bottom. In the present case, the flow chart is designed for operating a motor vehicle  10  according to  FIG. 1 . The procedure begins in a starting block  46 . 
     Position  13  and actuation speed  15  of accelerator pedal  12  are ascertained and evaluated in a query block  48 . If actuation speed  15  is positive for the purpose of a desired acceleration of motor vehicle  10 , or if actuation speed  15  is zero and position  13  of acceleration pedal  12  is simultaneously greater than zero, the program branches to an end block  54  and transfers to additional procedures (not shown in  FIG. 4 ), with the aid of which the driving power of internal combustion engine  16  is to be kept constant or intensified. In the other cases, the program branches to a query block  62 . 
     In query block  62 , the program checks whether actuation speed  15  is less than or greater than a limiting value  58  and whether position  13  of accelerator pedal  12  is greater than zero. If actuation speed  15  is greater than limiting value  58 , the program branches to a block  64 . If actuation speed  15  is less than limiting value  58 , the program branches to a block  68 . 
     In block  64 , the fuel injection into the combustion chambers of internal combustion engine  16  is greatly reduced and an idle mode of internal combustion engine  16  is set. Moreover, the position of throttle valve  30  is changed and/or clutch  18  is opened so that the vehicle speed decreases only slowly or remains approximately the same during downhill travel. This corresponds to a sailing mode of motor vehicle  10 . The processing of the flow chart is then resumed after starting block  46 . 
     In block  68 , the fuel injection is also greatly reduced or even discontinued, and a measure which increases the drag torque is carried out. In the present case, throttle valve  30  is closed for this purpose. This corresponds to a coasting mode of motor vehicle  10 . The processing of the flow chart is then also resumed after starting block  46 .