RESTART PROCEDURE AND RESTART ORDER FOR STARTING AN INTERNAL COMBUSTION ENGINE OF A MOTOR VEHICLE

Description

[0001] The invention relates to a restarting method and a restarting arrangement for starting an internal combustion engine of a motor vehicle.

[0002] Such procedures and arrangements are now widespread within the context of start-stop functionality. Start-stop functions allow the combustion engine to be temporarily switched off during stop phases without the driver having to manually operate the ignition switch. At the end of such a standstill phase, the switched-off combustion engine is automatically restarted (restart) as soon as the driver wishes to continue driving. This restart also occurs without manually operating the ignition switch.

[0003] Several methods and corresponding devices for restarting have already been implemented. In a method according to EP 1 063 424 B1, the restart process is initiated based on the position of the brake pedal, which is detected by suitable sensors. When the brake pedal is released from its actuated position (braking position), the motor vehicle's combustion engine is started when the brake pedal returns to its original position. The starting process is triggered by detecting a specific transition position of the brake pedal when it returns to its original position.

[0004] A pressure-controlled method is known from EP 1 541 864 B1. Here, the temporal progression of the brake pressure when the brake pedal is released is evaluated, and the restart process is then triggered based on a negative brake pressure gradient. The brake pressure gradient must exceed a threshold value for the control electronics in a control unit to trigger the restart process as part of a start-stop function. With this solution, it may happen that the threshold value cannot be reached if the brake is released very slowly, so additional measures are required to initiate the restart.

[0005] Further methods are known from WO2015 / 079296A1, EP2808520A1 and DE102013216622A1.

[0006] For example, an additional lower threshold value p SU of the brake pressure can be taken into account, at which the restart process is initiated. This relationship is derived from the Figure 5, which shows a braking force profile p Pr (braking force p over time t). The stop phase begins when a stop threshold value p SS is exceeded and ends when the lower threshold value p SU is undershot, at which point the restart is triggered. The value p SU is below the value p SS by a fixed pressure difference Δp Fix.

[0007] Especially in connection with the gradient procedure, in which the restart process is not triggered due to an insufficient brake drop gradient, but only when the lower pressure threshold p SU is undershot, a restart can be perceived as delayed.

[0008] The task is therefore to provide a restart procedure or a restart device that ensures sensitive start-stop functionality.

[0009] This object is achieved by the inventive method according to claim 1 and by the restart arrangement according to claim 10.

[0010] Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the present invention.

[0011] The restart method according to the invention for automatically starting an internal combustion engine of a motor vehicle by actuating the brake pedal is characterized by the following: First, the brake pressure is detected by a brake pressure sensor, and the corresponding brake pressure signal sequence is output to a control unit, e.g., an engine control unit (ECU). Based on this brake pressure signal sequence, a brake pressure profile is determined, from which a reference pressure value is in turn determined. This reference pressure value serves as a (variable) initial value for detecting a brake release state. This means that the stop phase within the scope of a start-stop function is not terminated based on fixed, preset brake pressure threshold values ​​(see above), but rather based on the determined reference pressure value.

[0012] The brake release condition is detected when, when a brake pedal is released, a brake pressure drop is detected that exceeds a pressure drop threshold, i.e., a specific (but possibly variable) deviation from the reference pressure value. The start signal to a starter motor for starting an internal combustion engine is sent when this brake release condition is detected.

[0013] With the method according to the invention described above, it is possible to derive a sensitive and, if necessary, driver-specific restart condition based on the individual braking behavior—by determining an individual reference pressure value from an actual brake pressure profile. This condition is determined based on a variable brake release state. This noticeably improves restart behavior for the driver by ensuring that it always feels "the same," possibly also depending on the driver. The restart behavior is thus optimized.

[0014] There are designs in which the reference pressure value can be determined depending on a profile section of the determined brake pressure profile. Typically, a brake pressure profile during a start-stop phase—which is actually a stop-start phase—is hat-shaped (see [Fig. Fig. 3 - 5). This means that initially there is a relatively steep increase in brake pressure, which remains largely constant on a plateau during the stop phase, and then drops again shortly before restarting until the brake pressure is completely released. To influence the restart behavior, different sections of this profile can now be evaluated to determine a reference pressure value.

[0015] It is possible, for example, to evaluate the rising section and to determine the reference pressure value in the transition phase from the rising phase to the plateau phase.

[0016] Another possibility is to evaluate the profile of the plateau section in which the maximum brake pressures are maintained by calculating an average value from these signals.

[0017] Another possibility is, for example, to record the transition from the plateau section to the decline section and to define a reference pressure value here.

[0018] A further variation may also be to calculate the average value of the transition values ​​from the rising section to the plateau section and from the plateau section to the falling section and thus determine the reference pressure value.

[0019] In one group of embodiments of the method, the reference pressure value is determined as a function of several start-stop cycles within an operating cycle (e.g., the driving of a specific driver). This makes it possible to determine a driver-specific, preferred reference pressure value and define it as the initial value for determining the brake release state.

[0020] A particularly simple method for determining the reference pressure value is to determine the brake pressure maximum of a determined brake pressure profile and, based on this, to record the brake release state.

[0021] There are also designs in which the pressure drop limit is variable and can be determined individually.

[0022] For example, there are methods in which the pressure drop limit can be determined based on the determined reference pressure value. It can be determined, for example, as a percentage deviation from the reference pressure value. This allows, for example, the pressure drop limit to be increased or decreased in the same way at very high maximum brake pressures in order to detect the brake release state.

[0023] In other methods, the pressure drop limit can also be increased or decreased linearly, degressively or progressively with the reference pressure value.

[0024] In other methods, the pressure drop limit can also be determined depending on the adjustable shift characteristics of an automatic transmission. For example, with emissions-optimized shift and driving characteristics, it should be increased to allow for a later restart and an extended stop phase, while with sporty shift and driving characteristics, it should be shortened to keep the stop phases as short as possible.

[0025] There are also methods in which the pressure drop limit can be determined depending on a driver type classification. Such driver type classifications are implemented in motor vehicles, for example, in adaptive automatic transmissions.

[0026] In order to further individualize the brake release behavior or to improve the restart behavior, additional restart conditions can be introduced to initiate the restart.

[0027] For example, the condition that a lower threshold is exceeded can be added to trigger the restart function. This is useful, for example, if determining the reference pressure value or the pressure drop limit is not possible or fails for some reason.

[0028] It is also possible to activate a master brake switch when the brake is released, which can be combined with a manual transmission or the selector lever of an automatic transmission, for example. The stop state is terminated, or the restart is triggered, when the gearshift lever is moved from the park position to the drive position, thereby initiating the starting process.

[0029] There are also versions in which the output of the brake pressure signal sequence can be switched on or off and the restart process is only triggered, for example, due to a brake pedal position or when a lower pressure threshold is undershot.

[0030] There are further situations in which the restart procedure should be prevented for safety or other functional reasons. This includes, for example, a situation in which a vehicle door, trunk lid, and / or hood is open.

[0031] Another situation can occur, for example, if a sensor or detector detects an accident. This could include significantly increased acceleration, the deployment of an airbag, or an unusual change in the vehicle's position from its normal position (skidding, rolling over, etc.).

[0032] To protect a power source (deep discharge of a battery), a lower voltage limit can also be set in the vehicle electrical system; if the voltage is below this limit, a restart process is not carried out.

[0033] A similar situation applies, for example, if a parking brake is applied at the same time and therefore a brake pressure-dependent restart request should not be made.

[0034] A further aspect of the invention relates to a restart arrangement for a motor vehicle with a hydraulic brake system, a brake pressure sensor, a starter, and a control unit. The control unit is in communication with the starter and the brake pressure sensor, and the control unit contains a restart algorithm as an executable program with which the restart method according to the invention can be executed. Such a configuration makes it particularly easy to implement the method according to the invention in a vehicle purely by programming, if necessary even subsequently by means of a software update.

[0035] It is sensible to design the entire restart process so that it can be switched on or off as required. In a special embodiment, the switch can be activated via a gear selector lever, for example, or is located as a separate switch on the gear selector lever, making it easily accessible.

[0036] A vehicle with such a restart arrangement can be adapted to its start-stop behavior either individually for the driver or also with regard to other boundary conditions (environmental protection / emissions / consumption, wear, etc.).

[0037] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows a schematic overview of a vehicle configuration with which the restarting method according to the invention can be carried out or which comprises a restarting arrangement according to the invention. Fig. 2 shows a functional diagram showing the essential components of an exemplary embodiment of a method according to the invention. Fig. 3 shows a brake pressure time diagram illustrating aspects of a method according to the invention; and Fig. 4 shows a brake pressure time diagram explaining the difference from a method according to the prior art; and Fig. 5 shows a brake pressure time diagram illustrating a known restarting method / start-stop method.

[0038] The basic function of the restart method according to the invention and the components required for it are first explained using the Fig. 1 explained.

[0039] The overview in Fig. 1schematically shows a motor vehicle 1 with an internal combustion engine 2 that drives the wheels 3. The wheels 4 are not shown as driven here, but can also be driven in other embodiments. All wheels 3, 4 have hydraulically actuated brakes 5, which are part of a hydraulic braking system in which the brakes 5 are actuated via the brake pedal 6, a brake pressure booster 7, a master brake cylinder 8, a hydraulic unit 9 with a hydraulic pump 10, and brake lines 11.

[0040] The actuation of the brake pedal 6 is detected, for example, by a switch 12, which is connected to a control unit 13 via a signal line 17. The brake pressure built up in the brake lines 11 and / or in the brake pressure booster 7 is detected by a brake pressure sensor 14, which also supplies corresponding brake pressure data to the control unit 13 via a signal line 17.

[0041] The internal combustion engine 2 is started as needed by an electric starter 15, which is also connected to the control unit 13 via a signal line 17 and receives a start signal from there if necessary. The electric starter can be designed, for example, as a starter-generator integrated into the crankshaft (ISG) or coupled to the engine via a belt drive (RSG). It can also be an electric drive motor in a hybrid drive concept.

[0042] Furthermore, a bus system 16 (e.g., a CAN bus system) can be provided, via which communication and signal transmission between various electrical and electronic units in the motor vehicle 1 is realized. These include, for example, the combustion engine itself, the switch 12, the brake pressure sensor 14, the electric starter 15, and the hydraulic pump 10. Additional sensors 18 and function switches 19 are also connected to the control unit 13 via the signal lines 17 and can control the restart functions described below.

[0043] Signal lines 17 are in Fig. 1 shown as solid lines and hydraulic or pressure lines 11 as dashed lines.

[0044] A start-stop functionality is implemented in the system described above as follows. A brake pressure p is detected by means of the brake pressure sensor 14, which transmits corresponding brake pressure signals to the control unit 13. In an alternative not forming part of the invention, or in addition, a

[0045] Actuation of the brake pedal can also be signaled to the control unit 13 via switch 12.

[0046] After a certain brake pressure has been built up, the control unit 13 sends a stop signal to the engine.

[0047] When a restart condition occurs, the control unit 13 sends a restart signal S WS to the electric starter 15, which then restarts the combustion engine 2.

[0048] Based on Fig. 2The sequence of the method according to the invention will now be explained. A restart algorithm with several function blocks can be called up in the control unit 13. This algorithm is available in the control unit (13) as an executable program with which the restart process can be carried out.

[0049] The brake pressure signals from the brake pressure sensor 14, which represent the brake pressure p, run into a first function block 101, in which they are further processed into a brake force profile p Pr (see also Fig. 3 - Fig. 5 ).

[0050] In a second function block 102, a reference pressure value p R is determined from this brake force profile p Pr. In a third function block 103, a pressure drop limit value Δp G is determined. And in a fourth function block 104, a brake release state is detected when, when the brake pedal is released, a brake pressure drop Δp is detected starting from the determined reference pressure value p R that falls below the pressure drop limit value Δp G. ​​This case occurs when the (absolute) brake pressure p detected by the brake pressure sensor 14 falls below the difference between the reference pressure value p R and the pressure drop limit value Δp G. ​​Then, in a fifth function block 105, the restart signal S WS is sent to the starter 15 and the combustion engine 2 is started again.

[0051] The determination of the reference pressure value p R and the pressure drop limit Δp G is now carried out using the Fig. 3explained. Different approaches are possible, but they all follow the same basic principle.

[0052] In a first exemplary embodiment, the maximum brake pressure p Max is determined based on the brake pressure profile p Pr and set as the reference pressure value p R. The restart condition is then specified such that the pressure drop from the maximum brake pressure p Max must be a certain Δp so that the restart signal S WS is emitted and the stop phase t St is terminated between t 0 and t 1 (shaded area in the diagram). This ensures that, regardless of the maximum brake pressure p Max actually reached, the restart signal is always generated at the same brake pressure drop Δp. This makes it possible to implement a sensitive, rapid, and perceived consistent restart condition.

[0053] In alternative embodiments, the reference pressure value p R can also be determined in another way, for example by analyzing different phases / sections of the brake pressure profile. Fig. 3 shows a profile section I in which the transition from an increasing phase to a plateau phase is detected. This value p RI can then be set as the reference pressure value p R.

[0054] In another embodiment, a descent phase (Section III in Fig. 3 ) in which the transition from the plateau phase to the descent phase is determined as p RIII and this value is set as the reference pressure value p R.

[0055] It is also possible to evaluate only the plateau phase (Section II) and, for example, to calculate an average maximum value as p RII, which should then serve as the reference pressure value p R.

[0056] Similarly, there are embodiments in which the pressure drop limit value Δp G is also determined variably depending on the brake pressure profile p Pr or in another way.

[0057] It is also possible to determine the reference pressure value p R and the pressure drop limit value Δp G from several determined braking force profiles p Pr, which were determined, for example, during a trip of a specific driver.

[0058] For example, it can be related in percentage terms to the reference pressure value p R. However, it can also be provided that the pressure drop limit Δp G varies progressively, degressively or linearly with the reference pressure value p R and, in particular, with a corresponding maximum brake pressure p Max. Fig. 3 This is indicated by the designations Δp GI to Δp GIII.

[0059] Further conditions may apply beyond those set out in the Fig. 2The sixth and seventh functional blocks 106, 107 shown can be implemented. For example, functional block 106 can determine the pressure drop limit Δp G based on a so-called driver type classification, or alternatively, based on the shift characteristics of an automatic transmission. This takes into account, for example, the tendency to drive more or less "sportily." It can be assumed that, for example, with a sporty shift characteristic or a sporty driver type classification, the pressure drop limit Δp G will be reduced, resulting in an earlier restart of the combustion engine 2.

[0060] The seventh function block 107 can also be used to observe additional conditions for the output of the restart signal S WS . These can be considered as AND and / or OR conditions. For example, this could be the additional consideration of a brake pressure falling below a lower threshold value p SU at which a restart signal should be output.

[0061] Or the restart signal S WS is triggered or blocked via one or more switches 18 or sensors 19. This can be achieved by detecting certain positions of vehicle components such as vehicle doors, trunk lids, and the hood, by detecting accident situations, by undershooting a lower voltage limit in the vehicle electrical system, or by signaling that, for example, a parking brake is applied, and in such cases, the output of a restart signal S WS is prevented by actuating the brake pedal 6.

[0062] The difference to a conventional restart request, as shown by the Fig. 5 described in the introduction, shows the Fig. 4 Based on the maximum braking value p Max detected via the braking profile p Pr , which is defined as the reference pressure value p R , and a defined or otherwise determined pressure drop limit value Δρ G , the stop phase according to the present invention is ended after a period of time Δt 1 . Δt is the period of time between the times t 0 and t 1 .

[0063] According to the conventional method, the stop phase only ends after a significantly longer period Δt 2 , which lies between times t 0 and t 2 . This allows for a faster and therefore more sensitive restart or even an earlier restart. With the method according to the invention, the driver perceives a more immediate reaction (better response behavior) to the release of the brake. This response behavior can be further optimized or customized by determining the reference pressure value p R and the pressure drop limit value Δp G . List of reference symbols

[0064] 1Motor vehicle 2Combustion engine 3Wheels 4Wheels 5Brakes 6Brake pedal 7Brake pressure booster 8Master brake cylinder 9Hydraulic unit 10Hydraulic pump 11Brake line 12Switch 13Control unit 14Brake pressure sensor 15Electric starter 16Bus system 17Signal line 18Switch 19Sensor pBrake pressure tTime pSU Lower threshold pSS Stop threshold ΔpFix Fixed pressure difference pPr Brake force profile pR Reference pressure value pMax Maximum braking force ΔpBrake pressure drop ΔpG Pressure drop limit tSt Engine stop time t0, t1, t2 Times SWS Restart signal I - IIIBrake force profile sections 101First function block 102Second function block 103Third function block 104Fourth function block 105fifth function block 106sixth function block 107seventh function block

Claims

1. Restart method for automatically starting an internal combustion engine (2) of a motor vehicle (3) by means of a brake pedal actuation, comprising the following steps: detecting a brake pressure (p) by means of a brake pressure sensor (14), outputting a corresponding brake pressure signal sequence to a control unit (13), determining a brake pressure profile (pPr) from the brake pressure signal sequence, characterized in that the method additionally comprises the following steps: ascertaining a reference pressure value (pR) from the brake pressure profile, the reference pressure value (pR) being a brake pressure maximum (pMax) of an ascertained brake pressure profile (pPr), detecting a brake release state when, on releasing a brake pedal, based on the ascertained reference pressure value (pR) a brake pressure drop (Δp) is detected which exceeds a pressure drop limit value (ΔpG), and emitting a start signal (Sws) to a starter (15) for starting the combustion engine (2) when the brake release state has been detected.

2. Restart method according to claim 1, wherein the reference pressure value (pR) can be determined depending on a profile portion (I; II; III) of the ascertained brake pressure profile (pPr).

3. Restart method according to either claim 1 or claim 2, wherein the reference pressure value (pR) can be determined depending on a plurality of stopping cycles within one operating cycle by evaluating a plurality of brake pressure profiles (pPr).

4. Restart method according to any of claims 1 to 3, wherein the pressure drop limit value (ΔpG) can be determined depending on the ascertained reference pressure value (pR) and / or the ascertained brake pressure profile (pPr).

5. Restart method according to any of claims 1 to 4, wherein the pressure drop limit value (ΔpG) can be determined depending on an adjustable shift characteristic of an automatic transmission.

6. Restart method according to any of claims 1 to 5, wherein the pressure drop limit value (ΔpG) can be determined depending on the driver type classification of the particular driver.

7. Restart method according to any of the preceding claims, wherein the start signal (Sws) is emitted if at least one of the following conditions is met: the brake release state has been detected, the brake pressure falls below a lower threshold value (psu), when the brake is released, a main brake switch (8) is actuated.

8. Restart method according to any of the preceding claims, wherein the output of the brake pressure signal sequence can be selectively switched on or off.

9. Restart method according to any of the preceding claims, wherein the emission of the start signal (Sws) is prevented if at least one of the following conditions is detected by means of a switch (18) and / or a sensor (19): a vehicle door, a trunk lid and / or a hood is open, an accident situation exists, a lower voltage limit in the vehicle electrical system is not met, a parking brake is applied.

10. Restart arrangement for a motor vehicle (1) having a hydraulic brake system, a brake pressure sensor (14), a starter (15) and a control unit (13), wherein the control unit (13) is in communication connection (16; 17) with the starter (15) and the brake pressure sensor (14) and the control unit (13) contains a restart algorithm as an executable program with which the restart method according to any of the preceding claims can be carried out.

11. Restart arrangement according to claim 10 having a switch (18) with which the restart method can be selectively switched on or off.

12. Restart arrangement according to claim 11, wherein the switch (18) is actuatable via a gear selector lever or is arranged on said gear selector lever.

13. Vehicle having a restart arrangement according to any of claims 10 to 12.