Method for automatically switching on and off an internal combustion engine

Abstract

Method for automatically switching off an internal combustion engine in a motor vehicle, in particular in a motor vehicle with an automatic transmission, by means of a start-stop device which automatically switches off the internal combustion engine when the vehicle has been braked to a standstill and held at a standstill for a predetermined time interval by actuating the brake pedal, wherein the motor vehicle driver can prevent the automatic switching off of the internal combustion engine within the predetermined time interval after the standstill has been reached, characterized in that an automatic switching off is prevented if the motor vehicle driver briefly at least partially releases the brake pedal and actuates it again within the predetermined time interval.

Description

[0001] The invention relates to a method for automatically switching off an internal combustion engine according to the preamble of patent claim 1 and to a method for automatically switching on an automatically switched off internal combustion engine according to the preamble of claim 6.

[0002] Currently, internal combustion engines are usually switched on and off manually by the driver using an ignition key. An exception is a process described in DE 100 23 331 A1. In this process, the brake pedal position or pressure is evaluated instead of the ignition key. The engine shutdown process is initiated when, after the vehicle has come to a standstill, the brake pedal is pressed more forcefully in its already depressed position. The disadvantage of such processes is that the driver alone is responsible for switching off the internal combustion engine. Analyses of current driving behavior show that, despite increased environmental awareness and rising fuel prices, manual shutdown of the internal combustion engine, e.g., at traffic lights, rarely occurs independently.

[0003] To reduce fuel consumption and pollutant emissions, processes and systems are currently being developed, and some are already in use, that automatically shut down a motor vehicle's internal combustion engine under certain conditions or when predefined shutdown conditions are met, and automatically restart it when predefined startup conditions are met. Such processes and systems, or start-stop systems, are particularly suitable for reducing fuel consumption in urban traffic, since in urban traffic the vehicle often comes to a stop at traffic lights or due to traffic, and the operation of the internal combustion engine is not required.

[0004] For example, EP 0 158 605 B1 discloses a device that shuts down or restarts the internal combustion engine depending on various conditions. One condition for initiating an automatic shutdown process is, for example, that the vehicle speed must remain below a threshold value for a certain period of time before the internal combustion engine is automatically shut down.

[0005] The disadvantage of such methods and devices is that the current traffic situation cannot be taken into account. The internal combustion engine is therefore switched off even in situations where the driver does not want it for reasons of comfort. For example, automatic switching off of the internal combustion engine in a turning lane or at a stop sign when driving can continue immediately is not desired. Particularly in vehicles with automatic transmission, the driver cannot prevent an automatic switch-off process if the internal combustion engine is automatically switched off when braking to a standstill. If a cost-effective pinion starter is used as the starting system, engaging - i.e. starting the running internal combustion engine - is not possible or is associated with a loss of comfort, since the pinion starter can in principle only engage again when the internal combustion engine is completely switched off.This may also result in longer start times.

[0006] To circumvent this problem, methods and systems are already known in which the driver can prevent automatic shutdown. For example, EP 1 469 195 B1 discloses a method for automatically shutting down an internal combustion engine in a vehicle, in which the driver can prevent the automatic shutdown process within a predetermined time interval after reaching a standstill. For example, the automatic shutdown process is not initiated if the driver presses the brake pedal with greater force within the predetermined time interval after reaching a standstill.

[0007] From the subsequently published DE 10 2008 060 350 A1, a method for automatically switching off an internal combustion engine in a vehicle is also known, wherein the automatic switching off is prevented if the driver presses the brake pedal harder within a predetermined time interval and then releases it again.

[0008] Furthermore, DE 102 11 461 C1 discloses a method for automatically switching off the internal combustion engine, whereby automatic switching off can be prevented within a predetermined time interval after reaching a standstill by releasing the brake.

[0009] For the sake of completeness, reference is made to JP 2000 002 129 A1 and US 2001 / 0013701 A1, which also disclose automatic start-stop systems.

[0010] The object of the invention is to provide an alternative method for automatically switching off and on an internal combustion engine in a vehicle with and without automatic transmission, which method enables the driver to prevent the automatic switch-off process in a simple and intuitive manner when the vehicle is decelerated to a standstill.

[0011] This object is achieved according to the invention by a method according to claim 1 and a method according to claim 6. Advantageous further developments are the subject matter of the dependent claims.

[0012] The method according to the invention for automatically shutting down an internal combustion engine in a motor vehicle (preferably in a motor vehicle with an automatic transmission) by means of a start-stop device is fundamentally designed such that the internal combustion engine shuts down automatically when (in addition to the other predetermined and fulfilled shutdown conditions) the vehicle has been braked to a standstill and held stationary for a predetermined time interval by actuating the brake pedal. Within the predetermined time interval after reaching a standstill, the driver is given the opportunity to prevent the automatic shutdown. Automatic shutdown should be prevented if the driver recognizes that further travel is imminent.

[0013] In contrast to the aforementioned prior art, the invention is characterized in that the automatic shutdown process is not prevented when the driver releases the brake pedal, but only when the driver continues to depress it after releasing it, i.e., only briefly (= lifting the brake or the brake pedal). Accordingly, it is not the pressure or torque reduction or the brake pedal travel traveled when the brake pedal is released that is evaluated as a trigger to prevent the automatic shutdown process of the internal combustion engine, but rather the subsequent pressure or torque buildup (detected within a relatively short time interval) or the brake pedal travel traveled when the brake pedal is subsequently depressed again.This is intended to prevent the automatic shutdown process from being inhibited if the driver inadvertently releases the brake pedal while braking to a stop, and preventing the shutdown process is not actually intended. Only the subsequent re-pressing of the brake pedal from the briefly released state is interpreted as a request to inhibit the automatic shutdown process.

[0014] This method is particularly advantageous for vehicles with automatic transmissions, as the driver typically leaves the gearshift lever in the normal position when the vehicle is stationary, and there is no clutch pedal that could be evaluated for the driver's input. The term "automatic transmission" refers not only to conventional automatic transmissions but also to all at least partially automated transmissions, including dual-clutch transmissions (transmissions with and without converters, EGS, SMG). However, this method can also be used in vehicles with manual transmissions. The start-stop system can, for example, be a standalone control unit or integrated into the engine control unit.

[0015] Advantageously, the automatic shutdown of the internal combustion engine is only prevented when the brake pedal is re-actuated at least by a predetermined amount during the brief release process to prevent the automatic shutdown process after release. For example, the brake pedal position or the built-up braking torque or the generated braking force can be evaluated. Accordingly, the automatic shutdown of the internal combustion engine is only prevented when the brake pedal is re-actuated at least until the original brake pedal position prior to release is reached and / or at least until the original braking force and / or the original braking torque prior to release is reached during the brief release process to prevent the automatic shutdown process. This clearly ensures that the driver's intention to prevent the automatic shutdown process is recognized.

[0016] In an advantageous embodiment of the invention, the extent to which the brake pedal or brake is initially released during the brief release process can also be evaluated and taken into account within the shutdown prevention system. Accordingly, for example, an automatic shutdown of the internal combustion engine due to a brief release of the brake pedal can only be prevented if the brake pedal is released by more than a predetermined brake pedal travel during the brief release and / or if the brake pedal is released at least far enough during the brief release that the applied braking force is reduced by more than a predetermined braking force difference value and / or the applied braking torque is reduced by more than a predetermined braking torque difference value compared to the initial value.The respective differential value can also be specified variably depending on certain parameters. In particular, the differential value can be specified such that at the time when the brake pedal is minimally depressed, i.e., at the reversal point of the brief release process, it is only depressed to the extent that the vehicle would no longer be held stationary by the braking force or braking torque applied at that time. Furthermore, the braking position gradient and / or the braking force gradient and / or the braking torque gradient when the brake is released can also be evaluated and taken into account.

[0017] Advantageously, the driver can be notified via a display element as soon as they can prevent the engine from automatically shutting down. If the specified operating conditions are met, an LED, for example, lights up, signaling the driver that the engine will soon be shut down by the start-stop system. Loudspeakers for an acoustic signal or other elements for visual or haptic signals can also be used as a display element. From this point on, the driver can prevent the engine from shutting down.

[0018] Analogous to the shutdown inhibitor described above, a corresponding method can also be used as a start-up requester for an automatically shut-off internal combustion engine. According to the prior art, a method is assumed for automatically switching on an automatically shut-off internal combustion engine in a motor vehicle, in particular in a motor vehicle with an automatic transmission, using a start-stop device. The start-stop device automatically switches off the internal combustion engine when predetermined shutdown conditions are met, and automatically switches the internal combustion engine back on as soon as a start-up requester is present. Analogous to the above, a start-up requester is present when the brake pedal actuated when the internal combustion engine is automatically shut off is briefly released, i.e., released and then actuated again (= lifting the brake or brake pedal).Accordingly, it is not the pressure or torque reduction or the brake pedal travel traveled when the brake pedal is released that is evaluated as the trigger for initiating the engine's activation process, but rather the subsequent pressure or torque buildup (detected within a relatively short time interval), or the brake pedal travel traveled when the brake pedal is subsequently depressed again. By evaluating the falling edge when the brake is released, it can be ensured, particularly in vehicles with automatic transmissions, that the vehicle remains stationary even after the engine has been successfully activated and there is no immediate start-up request.

[0019] Advantageously, the activation request is only present when the brake pedal is re-activated at least by a predetermined amount during the brief release process to restart the internal combustion engine. For example, the brake pedal position or the built-up braking torque or the generated braking force can be evaluated. Accordingly, the internal combustion engine is only restarted when the brake pedal, with the internal combustion engine switched off, is re-activated after release, at least until the original brake pedal position before release is reached and / or at least until the original braking force and / or the original braking torque before release are reached.

[0020] Advantageously, the difference in brake application between the initial brake application and the minimum brake application during the brief release process can also be evaluated and taken into account as part of the activation request. Thus, the activation request can only be present if the brake pedal is released by more than a specified brake pedal travel during the brief release with the internal combustion engine switched off and / or if the brake pedal is released at least far enough during the brief release that the applied braking force is reduced by more than a specified braking force difference value and / or the applied braking torque is reduced by more than a specified braking torque difference value. Furthermore, the braking position gradient and / or the braking force gradient and / or the braking torque gradient during brake release can also be evaluated and taken into account.

[0021] By combining the shutdown preventer according to the invention and the startup requester according to the invention, the overall system or the operating logic for automatically switching off and restarting the internal combustion engine becomes more comprehensible for the driver, since he always has the same procedure.

[0022] The drawing illustrates an exemplary embodiment of the invention. The figure shows a simplified flowchart for the method according to the invention for automatically switching off and on an internal combustion engine, using the example of a motor vehicle with an automatic transmission.

[0023] The method for automatically switching an internal combustion engine off and on is integrated into a start-stop device (not shown here) or into a control unit. In a first step 100, with the internal combustion engine running, all conditions (operating conditions and additional conditions) necessary for automatically switching off the internal combustion engine are queried. These include, for example, the vehicle speed, which must be approximately zero (vehicle stationary), the engine speed, which must be below a predetermined limit, and the brake pedal, which must be depressed. If all conditions are met, the method continues. Otherwise, it is aborted and the process starts again.

[0024] If all conditions are met, an LED is switched on as an indicator in a second step 110. This informs the driver that the internal combustion engine will be switched off after a specified time unless prevented. At the same time, a timer is started in step 110 to monitor the time t.

[0025] Subsequently, in a next step 120, the elapsed time t is queried. As long as the elapsed time t is within the specified time interval tmax, a next step 140 monitors whether the brake pedal is lifted, i.e. released and then (immediately) actuated back to its original position before release. For this purpose, the brake pedal travel and / or the brake pressure and / or the braking torque can be evaluated, for example. If no brief release of the brake is detected, the program returns to step 120 and time monitoring continues. If the elapsed time t is greater than the specified time interval tmax, i.e., no shutdown preventer has been activated, the internal combustion engine is automatically shut down in step 130.

[0026] However, if a release and subsequent application of the brake to its original starting position is detected in step 140, this signals that the automatic shutdown of the internal combustion engine is prevented in a next step 150, and the internal combustion engine remains running. Only when the accelerator is applied in a final step 160 and the vehicle speed is again greater than approximately zero does the process begin again.

[0027] If, as already mentioned above, the internal combustion engine is shut down in step 130 because no brake release was detected within the time window, a check is made in step 200 after the internal combustion engine is shut down to determine when a switch-on request follows. For a better understanding of the invention, this example assumes that a switch-on request only occurs when the brake is released, i.e., briefly released, while the internal combustion engine is automatically shut down (briefly, since a new application must follow after release).

[0028] As soon as a brake release is detected in step 200, the internal combustion engine is switched on again in the next step 210 and the process proceeds to step 220. Only when the accelerator is applied in a final step 220 and the vehicle speed is again greater than approximately zero does the process begin again.

Claims

[1] Method for automatically switching off an internal combustion engine in a motor vehicle, in particular in a motor vehicle with an automatic transmission, by means of a start-stop device which automatically switches off the internal combustion engine when the vehicle has been braked to a standstill and held at a standstill for a predetermined time interval by actuating the brake pedal, whereby the motor vehicle driver can prevent the automatic switching off of the internal combustion engine within the predetermined time interval after reaching a standstill, characterized by that automatic switching off is prevented if the driver of the vehicle briefly releases the brake pedal at least partially and then presses it again within the specified time interval. [2] Method according to claim 1, characterized bythat the automatic shutdown of the internal combustion engine is prevented if, during the brief release process to prevent the automatic shutdown process, the brake pedal is actuated again after release at least until the original actuated brake pedal position before release is reached. [3] Method according to claim 1 or 2, characterized by that the automatic switching off of the internal combustion engine is prevented if the brake pedal is actuated during the brief release process to prevent the automatic switching off process after release at least until the original braking force or the original braking torque before release is reached. [4] Method according to one of the preceding claims, characterized bythat an automatic shutdown of the internal combustion engine due to a brief release of the brake pedal is prevented if the brake pedal is released by more than a predetermined brake pedal travel during the brief release and / or if the brake pedal is released during the brief release at least to such an extent that the applied braking force is reduced by more than a predetermined braking force difference value and / or the applied braking torque is reduced by more than a predetermined braking torque difference value. [5] Method according to one of the preceding claims, characterized by that the driver is informed by means of a display element as soon as he can prevent the automatic shutdown of the internal combustion engine. [6] Method for automatically switching on an automatically switched-off internal combustion engine in a motor vehicle, in particular in a motor vehicle with an automatic transmission, by means of a start-stop device which automatically switches off the internal combustion engine when predetermined switch-off conditions are met and automatically switches the internal combustion engine on again as soon as a switch-on request is present, characterized by that a switch-on request is present when the brake pedal, which is operated when the internal combustion engine is automatically switched off, is briefly released and then actuated again. [7] Method according to claim 6, characterized by that the activation request is present when the brake pedal is actuated again during the brief release process after release at least until the original brake pedal position is reached before release. [8] Method according to claim 6 or 7, characterized bythat the activation request is present when the brake pedal is actuated during the short-term release process after release at least until the original braking force or the original braking torque before release is reached. [9] Method according to one of claims 6-8, characterized by that the activation request is present when the brake pedal is released by more than a predetermined brake pedal travel during the brief release and / or when the brake pedal is released during the brief release at least to such an extent that the applied braking force is reduced by more than a predetermined braking force difference value and / or the applied braking torque is reduced by more than a predetermined braking torque difference value.

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