BACKGROUND

Driver assistance systems can be used in motor vehicles to take over certain tasks. Driver assistance systems can be limited to giving information to a vehicle driver. However, it is also possible for driver assistance systems to automatically control certain aspects of the driving of the motor vehicle. For example, a cruise control system makes it possible to automatically maintain a set speed. “GPS-controlled” cruise control systems, which acquire a road profile containing uphill and downhill slopes in advance, are also known. The cruise control system can then adapt a transmission ratio and speed for economical driving and suppress downshifts whenever appropriate, for example.

An operating method for driver assistance is disclosed in DE 10 2010 048 323 A1, for example. The operating method for a driver assistance system assists a vehicle driver of a motor vehicle in reducing fuel consumption by the motor vehicle. The operating method has the following steps: determining a driving recommendation to reduce the fuel consumption of the motor vehicle; determining at least one consumption-relevant road property of a road on the impending route of the motor vehicle, wherein the consumption-relevant road property affects the fuel consumption of the motor vehicle; and determining the driving recommendation which is suitable for increasing acceptance by the vehicle driver and making the manner of operation of the driver assistance system plausible by virtue of its depiction of future developments with respect to time.

SUMMARY

The present disclosure relates to an operating method for a driver assistance system and a motor vehicle. It is the underlying object of the present disclosure to provide an improved operating method for a driver assistance system. In particular, further potential for fuel saving and the operation of exhaust gas aftertreatment systems should be exploited.

The operating method is provided for in a driver assistance system, in particular a cruise control system, preferably a cruise control system controlled by a satellite location device, of a motor vehicle, preferably a commercial vehicle. The motor vehicle has an internal combustion engine that has a variable valve gear, in particular one that has a plurality of sliding cam systems, for adjusting the valve timing curves of the inlet and/or exhaust valves of the internal combustion engine. The method comprises determining at least one operationally relevant road property of a road on an impending route of the motor vehicle. The operationally relevant road property affects operation of the internal combustion engine of the motor vehicle. The method comprises determining a driving recommendation in accordance with the operationally relevant road property on the impending route of the motor vehicle and setting the variable valve gear in accordance with the driving recommendation determined.

By setting the variable valve gear in accordance with the driving recommendation determined, it is possible to exploit hitherto unexploited potential for fuel saving and for the operation of exhaust gas aftertreatment systems.

In particular, an operationally relevant road property can be operation of an exhaust gas aftertreatment device, e.g. an SCR or oxidation catalytic converter, a load of the internal combustion engine and/or the fuel consumption of the internal combustion engine.

In one embodiment, the variable valve gear allows adjustment of the inlet and/or exhaust valves within a predetermined adjustment range. The driving recommendation can then additionally be determined in accordance with the predetermined adjustment range.

In another embodiment, the operating method comprises informing a vehicle driver of the motor vehicle acoustically, visually and/or haptically of the driving recommendation. It is thereby possible to improve acceptance of the driver assistance system.

As an alternative or in addition, the operating method comprises automatically implementing the driving recommendation by means of the motor vehicle and/or the driver assistance system. Consequently, the burden on the vehicle driver of the motor vehicle can be relieved.

In a variant embodiment, the operationally relevant road property comprises a topology, in particular a downhill slope, an uphill slope and/or a bend of the road, of the impending route. Thus, the driving recommendation can be adapted to the topology.

In another variant embodiment, the operationally relevant road property comprises a traffic regulation, in particular a speed restriction and/or a priority regulation, applying to the road. Consequently, the driving recommendation can be adapted to the applicable traffic regulation.

In addition or as an alternative, the operationally relevant road property can comprise a current traffic situation. This has the advantage that the driving recommendation can be adapted to the current driving situation.

In one illustrative embodiment, the method comprises determining a current position of the motor vehicle by means of a location device, in particular by means of a satellite location device.

In another illustrative embodiment, the method comprises determining the impending route of the motor vehicle in accordance with a current position of the motor vehicle. In particular, the impending route of the motor vehicle can be read out of a route memory of a navigation system and/or received via a data link, for example.

In a development, the method comprises reading the operationally relevant road properties out of a navigation database and/or receiving the operationally relevant road properties via a data link, for example.

In another variant embodiment, the method comprises determining the driving recommendation in accordance with the operationally relevant road property on the impending route of the motor vehicle and with a current position of the motor vehicle.

In a further embodiment, the variable valve gear sets the timings of the inlet and/or exhaust valves in a cylinder-selective manner in accordance with the driving recommendation determined. Depending on the requirements, it is thus possible to adjust no valve, several valves or all the valves in accordance with the driving recommendation. It is thereby possible to exploit further potential, in particular in respect of fuel-efficient consumption.

For example, it is possible for the variable valve gear to adjust the timings only for some of the inlet and/or exhaust valves in accordance with the driving recommendation determined.

In one illustrative embodiment, the driving recommendation comprises a gear change, in particular an automatic gear change, to a higher gear. The variable valve gear is then switched to an upshift assistance mode to shorten a duration of the gear change.

In particular, the higher gear can comprise a higher ratio than a current gear.

In another illustrative embodiment, the driving recommendation comprises a sustained braking mode of the internal combustion engine. The variable valve gear can then be switched to an engine braking mode.

In a yet another development, in the upshift assistance mode and/or in the engine braking mode, at least one exhaust valve of the internal combustion engine is initially held closed in the compression stroke and/or in the exhaust stroke in order to compress air and is opened before a top dead centre position of a piston movement is reached in order to decompress the compressed air. It is thereby possible to achieve a considerable reduction in engine speed within a short time without actuating an exhaust throttle valve and an associated impairment of the operation of a turbocharger.

In one embodiment, a number of exhaust valves is determined in the upshift assistance mode in accordance with the operationally relevant road property on the impending route of the motor vehicle, with a required speed reduction for the gear change, with a required torque increase for the gear change, with a desired duration of the gear change, with a desired turbocharger speed and/or with a desired boost pressure.

As an alternative or in addition, a number of exhaust valves is determined in the engine braking mode in accordance with the operationally relevant road property on the impending route of the motor vehicle, in particular a downhill slope and/or a speed restriction. Thus, it is possible, for example, for one, several or all of the exhaust valves to be operated in the engine braking mode, depending on the downhill slope or the required speed reduction.

In the engine braking mode and/or an upshift assistance mode, it is possible, in particular, to omit fuel injection and/or to leave actuation of the at least one inlet valve unchanged.

In the engine braking mode and/or upshift assistance mode, the exhaust valve can, in particular, be opened between 100° crank angle and 60° crank angle before top dead centre. As an alternative or in addition, it is possible for the exhaust valve, after opening in the exhaust stroke, to close in the region between top dead centre and 30° crank angle after top dead centre. As an alternative or in addition, it is possible for the exhaust valve, after opening in the compression stroke, to close in the region between bottom dead centre and 30° crank angle after bottom dead centre. It is thereby possible to achieve an effective engine braking mode and upshift assistance mode.

In another embodiment, the driving recommendation comprises adapting an exhaust gas temperature, adapting an operating point of a turbocharger of the internal combustion engine, adapting an air flow rate and/or operating the internal combustion engine in a low-load range. The variable valve gear can then be switched to a Miller mode.

In particular, the low-load range can extend below a mean pressure of the internal combustion engine of 6 bar, 5 bar or 4 bar.

In the Miller mode, it is possible, in particular, for a closing point of an inlet valve to be advanced relative to a normal mode. In the normal mode, the inlet valve closes in the region of reaching a bottom dead centre position of a piston movement at the end of the inlet stroke. In the Miller mode, the closing point of the inlet valve is before the bottom dead centre position of the piston movement is reached. In the Miller mode, the closing point can be, in particular, equal to or more than 5° crank angle, 10° crank angle, 20° crank angle or 30° crank angle before the closing point in the normal mode.

In a development, a number of exhaust valves is determined in the Miller mode in accordance with the operationally relevant road property on the impending route of the motor vehicle, with a desired exhaust gas temperature, with a desired air flow rate, with a load of the internal combustion engine and/or with an operating point of a turbocharger of the internal combustion engine. Consequently, it is possible for just one, several or all of the inlet valves to be operated in the Miller mode, depending on the situation.

In one illustrative embodiment, each sliding cam system has a cam carrier, which is arranged on a camshaft of the internal combustion engine in a manner which prevents relative rotation and allows axial movement and has a first cam for a normal mode and a second cam, arranged offset in a longitudinal direction of the camshaft, for an engine braking mode, an upshift assistance mode and/or a Miller mode. The sliding cam system optionally puts the first cam and at least one exhaust valve and/or inlet valve into operative connection or puts the second cam and at least one exhaust valve and/or inlet valve into operative connection. The sliding cam systems offer a quick and reliable means of switching between different valve timing curves.

The disclosure also relates to a motor vehicle, in particular a commercial vehicle. The commercial vehicle can be a bus or a heavy goods vehicle, for example. The motor vehicle has a location device, in particular a satellite location device. The motor vehicle has a driver assistance system which is designed to carry out the operating method according to one of the preceding claims.

In a development, the motor vehicle has a navigation system and/or a variable valve gear for an internal combustion engine, having a plurality of cylinders, of the motor vehicle. The variable valve gear has at least one inlet valve and/or exhaust valve. The variable valve gear has at least one camshaft and a plurality of sliding cam systems for the plurality of cylinders. Each sliding cam system has a cam carrier, which is arranged on the camshaft in a manner which prevents relative rotation and allows axial movement and has a first cam and a second cam. The first cam and the second cam are arranged offset in a longitudinal direction of the camshaft.

In another embodiment, the variable valve gear has a phase adjuster. The phase adjuster is designed to adjust a rotation angle of the camshaft relative to a rotation angle of a crankshaft of the internal combustion engine. Thus, the phase adjuster can allow adjustment of the timings of the respective inlet and/or exhaust valves. The phase adjuster can be designed as a hydraulic phase adjuster, in particular as a rotary-actuator phase adjuster.

