Driver assistance system in a motor vehicle

Abstract

A driver assistance system in a motor vehicle, by which a predetermined speed or a predetermined distance to the vehicle ahead is to be maintained constant, comprising an electronic control unit by which, depending on a control deviation with respect to the predetermined speed or the predetermined distance, the drive system and / or the braking system is controlled with regard to the control deviation, characterized in that the control unit is designed such that, depending on a defined driving situation (driving situation 1, driving situation 2), the permissible control deviation in the direction of falling below the predetermined speed (v) or in the direction of exceeding the predetermined distance ("downward control deviation": dv downward 1 ;dv nach unten 2 ) is increased, but no increase in the rule deviation in the opposite direction is allowed.

Description

[0001] The invention relates to a driver assistance system in a motor vehicle according to the preamble of patent claim 1.

[0002] In motor vehicles with driver assistance systems, which in particular are designed to maintain a constant speed or a predetermined distance from the vehicle in front, methods are already known by which a drive system and / or a wheel brake system are controlled to achieve specific driver assistance objectives.

[0003] For example, DE 10 2004 017 115 A1 discloses a fuel-saving mode of operation for a cruise control system that generally allows a larger control deviation from the target vehicle speed. In this mode, the vehicle speed is adjusted in a sawtooth pattern around the target speed, alternating between an acceleration phase and a coasting phase.

[0004] Further cruise control systems are known from DE 103 45 319 A1 and the subsequently published DE 10 2005 045 891 B3.

[0005] The object of the invention is to further improve a driver assistance system of the type mentioned above with a view to reducing fuel consumption.

[0006] This object is achieved according to the invention by the subject matter of the independent patent claims. Advantageous further developments are the subject matter of the dependent patent claims.

[0007] In the driver assistance system according to the invention in a motor vehicle, a control deviation from a predetermined target vehicle speed or from a predetermined target distance from the vehicle in front is basically corrected in the usual way by means of an electronic control unit, whereby, however, the maximum permissible control deviation can be increased exclusively with regard to a reduction in vehicle speed, at least in defined driving situations. Such a driving situation is, in particular, the transition from a stationary state to a transient state, which is primarily caused by an increase or reduction in driving resistance, in particular by changes in the gradient of the road surface. This means that a tolerance band is increased in the direction of falling below the predetermined target speed or exceeding the predetermined target distance.This increase in the control deviation in the direction of falling below the specified speed or exceeding the specified distance is referred to below as "downward control deviation," as this measure allows a further reduction in the vehicle speed relative to the target vehicle speed. An increase in the control deviation in the opposite direction, in the sense of an "upward control deviation," i.e., a further increase in the vehicle speed relative to the target vehicle speed, is not permitted.

[0008] The detection of a reduction or increase in driving resistance or a parameter proportional to driving resistance can be made dependent on several criteria, such as falling below or exceeding a defined driving resistance or inclination threshold for a specified minimum period.

[0009] A drive system is defined as the interaction of at least one engine and a transmission, whereby both the engine and the transmission can be electronically controlled. However, the drive system can also consist of an electronically controlled engine (internal combustion engine, electric motor, etc.) and a manual transmission. The drive system can also include a hybrid drive.

[0010] Preferably, a defined driving situation is the detection of a reduction in driving resistance during traction operation. In this case, the system transitions from traction operation to overrun operation when the increased downward control deviation allows overrun operation to be achieved and can preferably be maintained initially, i.e., when safe overrun operation is possible and no control-related rapid oscillation between overrun and traction operation is to be expected.

[0011] Additionally or alternatively, a defined driving situation is the detection of an increase in driving resistance during traction operation. In this case, after detecting an increase in driving resistance, the system preferably switches to consumption-optimized traction operation with an increased downward control deviation. The increased downward control deviation is permitted until a specified time has elapsed and / or a further increase in driving resistance is detected. Consumption-optimized traction operation can be achieved, for example, by reduced target accelerations and / or by engaging a higher gear in automatic transmissions. In manual transmissions, a prompt to engage a higher gear can be issued to the driver.

[0012] In principle, an increased downward control deviation should only be permitted if no (prolonged) uphill drive or other (prolonged) increase in driving resistance is detected. For example, if a navigation system with topographical information were installed in the vehicle, it could be predicted whether an uphill drive is expected, and if so, how long and at what gradient.

[0013] The increase in the control deviation is preferably only permitted if the driver requests this mode of operation. Therefore, this mode of operation is only activated, for example, by manually operating a selector switch (only for this purpose or generally for economical operation) or by a driver-specific coding in the workshop requested by the driver.

[0014] The invention is based on the following finding: In certain driving situations, particularly when driving downhill, fuel consumption can be significantly reduced by appropriately controlling the drive system, in principle in a known manner. However, such consumption-optimized control of the drive system can contradict the requirement to precisely maintain a specified vehicle speed. The driver assistance system according to the invention therefore gives higher priority to consumption-optimized control within a limited range than to the main task underlying the driver assistance system. However, a larger control deviation is not permitted in the direction of higher vehicle speed and thus also not in the direction of closer distance, since braking from an excessively high vehicle speed is always considered uneconomical and there would also be a risk of exceeding the permissible driving speed or falling below the minimum distance.

[0015] The invention is distinguished from the prior art, for example, DE 10 2004 017 115 A1, in particular by the fact that, firstly, an upward control deviation is specifically undesirable, and secondly, a downward control deviation is permitted depending on at least one possible fuel-reducing measure. Various increased control deviations can also be permitted depending on the respective possible measure or the respective defined driving situation.

[0016] The drawing illustrates an embodiment of the invention. It shows a possible curve of the vehicle speed v over time t in economical operation during cruise control to the specified target vehicle speed v soll .

[0017] With respect to a given target vehicle speed v sollFirst, according to known procedures, a relatively narrow tolerance band is generally used to define a maximum permissible control deviation upwards, dv nach oben , and a maximum permissible control deviation downwards, dv nach unten 0 However, if defined driving situations exist, e.g., driving situation 1 = "increased driving resistance" or driving situation 2 = "reduced driving resistance", the maximum permissible control deviation is increased downwards according to the respective driving situation: dv nach unten 1 or dv nach unten 2 .

[0018] For example, the maximum permissible control deviation dv nach unten 2In driving situation 2, the system can be applied in such a way that unfired overrun operation can be ensured by the drive system. The statements regarding an increase in the control deviation with respect to a target speed apply analogously to an increase in the control deviation with respect to a target distance. The "downward control deviation" always refers to a reduction in speed. Therefore, in connection with the control deviation of the target distance, the "downward control deviation" here is to be understood as an exceeding of a target distance. According to the invention, this produces a more sluggish follow-up control behavior.

Claims

[1] Driver assistance system in a motor vehicle, by means of which a predetermined speed or a predetermined distance from the vehicle in front is to be kept constant, with an electronic control unit by means of which the drive system and / or the braking system is controlled with a view to compensating for the control deviation, depending on a control deviation related to the predetermined speed or the predetermined distance, characterized by that the control unit is designed in such a way that, depending on a defined driving situation (driving situation 1, driving situation 2), the permitted control deviation in the direction of falling below the specified speed (v) or in the direction of exceeding the specified distance (“control deviation downwards”: dv downwards 1 ;dv nach unten 2 ) is increased, but no increase in the control deviation in the opposite direction is permitted. [2] Driver assistance system according to claim 1, characterized by that a defined driving situation (driving situation 1) is the detection of a reduction in the driving resistance or a parameter proportional to the driving resistance in traction operation and that after detection of the reduction in the driving resistance, the system switches from traction operation to overrun operation if the increased control deviation downwards (dv nach unten 2 ) the overrun operation can be achieved. [3] Driver assistance system according to one of the preceding claims, characterized by that a defined driving situation (driving situation 2) is the detection of an increase in the driving resistance or a parameter proportional to the driving resistance in train operation. [4] Driver assistance system according to the preceding claim, characterized bythat after detecting an increase in driving resistance, the train switches to consumption-optimised train operation with an increased downward control deviation, whereby the increased downward control deviation (dv nach unten 1 ) is permitted until a specified time has elapsed and / or a further increase in driving resistance is detected. [5] Driver assistance system according to one of the preceding claims, characterized by that the increase in the control deviation downwards (dv nach unten 1 ; dv nach below 2) is only permitted if the driver actively selects this mode of operation. [6] A method in a motor vehicle by means of which a predetermined speed or a predetermined distance from the vehicle in front is to be kept constant by means of an electronic control unit, in which the drive system and / or the braking system is controlled with a view to compensating for the control deviation depending on a control deviation related to the predetermined speed or the predetermined distance, characterized by that, depending on a defined driving situation, the permitted control deviation is increased by means of the control unit in the direction of falling below the specified speed or in the direction of exceeding the specified distance (“control deviation downwards”), but no increase in the control deviation in the opposite direction (“control deviation upwards”) is permitted.

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