DE102018204419A1 - Drive device for a motor vehicle - Google Patents

Abstract

The invention relates to a drive device for a motor vehicle with an automatic start / stop (15) with a control unit (25), the engine stop (S) triggers at a driver-side brake pedal operation, as soon as a stop operation (.DELTA.t) is present and by the brake pedal actuation actual brake pressure (p) exceeds a brake pressure threshold (BDS), and the control unit (25) by a driver-side brake pedal actuation a renewed engine start (S) triggers as soon as the actual brake pressure generated by the brake pedal operation ( p) the brake pressure threshold (BSD) falls below and lies in particular at 0, that is, the brake pedal is completely released, during the stopping process (.DELTA.t) to the vehicle standstill (t), the control unit (25), the brake pressure threshold (BDS) to a lower limit ( UG), so that even at a low brake pedal actuation of the thus correlating actual brake pressure (P) exceeds the brake pressure threshold (BDS) and the control unit (25) triggers the engine stop, wherein the control unit (25) keeps the brake pressure threshold (BDS) unchanged at the lower limit value (UG) from the time of entry (t) of the vehicle stoppage, over a usage safety time interval (Δt), wherein the control unit (25) sets the brake pressure threshold (BDS) to an upper limit (OG) after expiration of the safety period (.DELTA.t).

Description

The invention relates to a drive device for a motor vehicle with an automatic start / stop system according to the preamble of claim 1.

In a generic automatic start / stop system, a control unit triggers an engine stop as soon as the control unit detects a vehicle stopping process and an actual brake pressure generated by a driver-side brake pedal actuation exceeds a brake pressure threshold. In contrast, the control unit triggers a renewed engine start in the case of a driver-side brake pedal actuation as soon as the actual brake pressure generated by the brake pedal actuation drops below the brake pressure threshold and lies in particular at 0, that is, the brake pedal is completely released.

The automatic start / stop system sets the brake pressure threshold to a lower limit or minimum value during the stopping process until the occurrence of vehicle standstill. This already exceeds the brake pressure threshold at a low brake pedal actuation of the thus correlating actual brake pressure and triggers the engine stop the engine.

In the above stopping operation (i.e., engine stop already made), the driver intuitively relieves the brake pedal almost completely until the onset of vehicle arrest to achieve comfortable stopping without vehicle pitching. Against this background, the lower limit of the brake pressure threshold during the stopping process is dimensioned so small that even with the almost complete brake pedal discharge of the thus correlated actual brake pressure continues to exceed the brake pressure threshold. This ensures that only with an actually complete brake pedal discharge, it comes to a drop below the brake pressure threshold and thus to a restart of the engine during the stopping process, but otherwise even with a minimal brake pedal load correlating therewith the actual brake pressure exceeds the brake pressure threshold (to to stop the engine).

With regard to safety of use of the automatic start / stop system, it is known from the prior art that the control unit keeps the brake pressure threshold unchanged at the lower limit value (ie minimum value of, for example, 0.1 bar) from the onset of vehicle standstill. over a safety-of-use time interval, which may be 3 seconds by way of example. After expiration of the safety period, the control unit sets the brake pressure threshold to an upper limit (for example 3 bar). If the actual braking pressure which correlates therewith is lower than the brake pressure threshold now set to the upper limit value when the brake pedal actuation is too low, the control unit triggers the renewed engine start.

For a renewed engine start during the safety period, the following applies in the prior art: Thus, the actual brake pressure by appropriate brake pedal relief by a pressure difference to below the brake pressure threshold (set to the minimum value) to reduce. In a start / stop operation on a road gradient, this results in the following problem: The driver is in the stopping process (that is already stopped engine) with the onset of vehicle standstill, the brake pedal intuitively almost completely relieve to achieve a vehicle pitching motion , Subsequently, however, there is an increased driver-side brake pedal load with a correspondingly increased actual brake pedal pressure in order to avoid unintentional vehicle roll-back. During the use safety time interval, the engine is restarted by a driver-side brake pedal relief, in which the actual brake pressure is reduced by a pressure difference to below the brake pressure threshold (set to the minimum value). In this case, the driver-side brake-pedal release made in the use-safety time interval inevitably leads to a roll-back movement of the vehicle. This is perceived as disturbing by the driver and is possibly stopped only via a separate from the automatic start / stop system roll detection system.

From the DE 10 2015 220 807 A1 a method for controlling a motor vehicle drive train is known. From the DE 10 2015 203 453 A1 For example, there is known a method of assisting the launching of a vehicle on a slope with Hill Start Assist system. From the DE 10 2015 206 658 A1 is an adaptive automatic start-stop system for a motor vehicle with automatic transmission, taking into account obstacles known.

The object of the invention is to provide a drive device for a motor vehicle with an automatic start / stop system, which enables a more comfortable operation in comparison with the prior art.

The object is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the subclaims.

According to the characterizing part of claim 1, the control unit of the automatic start / stop system has an evaluation unit. This determines whether in the use safety time interval one compared to the stopping process or for The occurrence of vehicle standstill increased brake pedal load with correspondingly increased actual brake pressure is present or not. In the absence of an increased actual brake pressure, the evaluation unit allows the brake pressure threshold to be set unchanged to the lower limit value in the safety-of-use time interval. In the presence of an increased actual brake pressure, by contrast, the evaluation unit sets the brake pressure threshold during the use-safety time interval from the lower limit value (that is to say the minimum value) to a safety limit value.

By increasing the brake pressure threshold from the lower limit value to the safety value, the pressure difference is reduced by which the actual brake value is to be reduced so that it falls below the brake pressure threshold for a restart of the engine.

The safety value to which the brake pressure threshold is raised from the lower limit (ie minimum value) is such that the brake pressure reduction correlated with the brake pedal unloading does not result in unintentional vehicle roll over the pressure differential. This means that sufficient braking power is still provided during the abovementioned brake pressure reduction in order to avoid vehicle roll movement. In one embodiment, the safety value may correspond approximately to the upper limit of the brake pressure threshold. The safety value is also always smaller than the current actual brake pressure designed during the use safety time interval.

The invention is based on the fact that the driver in the stopping process (that is, when already stopped) with the onset of vehicle arrest the brake pedal intuitively almost completely relieved to achieve a comfortable stop without a vehicle pitching motion. The lower limit value during the stopping operation and during the use safety time interval is preferably dimensioned so small that even with the almost complete brake pedal discharge, the actual brake pressure correlating therewith still exceeds the brake pressure threshold, whereby an unintentional engine start (for example due to a further minimization of the brake pedal load) is avoided. In this constellation, it is thus achieved that only when the brake pedal is actually fully depressed does the brake pressure threshold be undershot, and thus a renewed engine start during the use-safety time interval.

Hereinafter, an embodiment of the invention with reference to the accompanying figures will be described.

• 1 in einem Blockschaltdiagramm einen Antriebsstrang für ein zweispuriges Fahrzeug;
• 2 ein grob vereinfachtes Blockschaltdiagramm, das Programmbausteine der Start-/Stopp-Automatik gemäß einem nicht von der Erfindung umfassten Vergleichsbeispiel betrifft;
• 3 und 4 jeweils Bremsdruck-Zeit-Diagramme, anhand denen ein Start-/Stopp-Betrieb gemäß dem Stand der Technik veranschaulicht wird;
• 5 in einer Ansicht entsprechend der 2 eine Start-/Stopp-Automatik der Erfindung; und
• 6 ein Diagramm entsprechend der 4, anhand dem der erfindungsgemäße Start-/Stopp-Betrieb des Fahrzeugs erläutert wird.

Show it:

• 1 in a block diagram of a powertrain for a two-lane vehicle;
• 2 a rough simplified block diagram, the program modules of the automatic start / stop according to a not included in the invention Comparative example concerns;
• 3 and 4 each brake pressure-time diagrams illustrating a start / stop operation according to the prior art;
• 5 in a view corresponding to 2 a start / stop system of the invention; and
• 6 a diagram corresponding to the 4 on the basis of which the start / stop operation of the vehicle according to the invention will be explained.

In the 1 is a drive train of a two-lane vehicle indicated. This has an internal combustion engine 1 , a starting element 3 as well as a transmission 5 on that via an axle differential 7 abrades on vehicle wheels of a vehicle axle. An engine control unit 9 the internal combustion engine 1 , a control unit 11 of the starting element 3 and a transmission control unit 13 of the transmission 5 are in signal connection with an automatic start / stop system 15 , This generates based on a variety of driving parameters an engine stop signal S _stop or an engine start signal Sstart, with which the drive train is controlled accordingly. In the 1 is the automatic start / stop system 15 in signal communication with a brake pedal sensor 17 , which detects an actual hydraulic brake pressure p _is in the hydraulic brake lines and this to the automatic start / stop 15 transmitted and with a vehicle speed sensor 19 shown transmitting an actual vehicle speed.

The invention is specifically concerned with a start-stop driving operation in which a renewed engine start Sstart takes place during a safety-of-use time interval Δt _G described later. For easier understanding of the invention is first based on the 2 . 3 and 4 a conventional start-stop driving described: So are in the 2 in a rough simplified, incomplete block diagram a number of program blocks indicated in the automatic start / stop 15 for the signal processing during the use safety time interval Δt _G required are. Accordingly, in the 2 a building block 19 in which it is determined whether a stopping process Δt _AH (That is, vehicle speed is in a range of 0 to 25 km / h) is present or not. In addition, in the investigation module 19 determines whether the use safety time interval .DELTA.t _G is present or not.

The building block 19 is in signal connection with a converter module 21 in which a brake pressure threshold BDS described later is set to either an upper limit value OG or a lower limit value UG. The converter module 21 is again in signal connection with a comparator module 23 in which it is determined whether an actual brake pressure p _is is greater than the brake pressure threshold BDS. Both the building block 19 as well as the comparison block 23 are with an input side of a control unit 25 signal-connected, in which either a motor stop signal S _stop or an engine start signal Sstart is generated. The converter module 21 sets the brake pressure threshold BDS during a stop operation Δt _AH until the entrance t _stood a vehicle standstill and during the subsequent use safety time interval Δt _G to the lower limit UG. After expiration of the safety period Δt _G sets the converter block 21 the brake pressure threshold BDS to an upper limit (for example 3bar).

In the 3 is at the time t _stop from the building block 19 a startup process Δt _AH been determined until the entrance t _stood a vehicle standstill persists. In addition, at the time t _stop the actual brake pressure p _is above the brake pressure threshold BSD, which is set to the lower limit value UG.

The setting of the brake pressure threshold BDS on the lower limit value UG and on the upper limit value OG is performed for the following reasons: Thus, the driver relieves in the stopping process Δt _AH (that is already done engine stop) with the entrance t _stood of vehicle standstill, the brake pedal is almost completely intuitive to achieve a comfortable stopping without a vehicle pitching motion. The lower limit UG during the stopping process Δt _AH and during the use-safety time interval Δt _G is dimensioned so small (for example, 0.1 bar), that even with the almost complete intuitive brake pedal discharge of the correlated therewith actual brake pressure p _is still exceeds the brake pressure threshold BDS (set to minimum value). It is thereby achieved that only with an actually complete brake pedal discharge it comes to a drop below the brake pressure threshold BDS and thus to a new engine start during the use safety time interval .DELTA.t _G , but an unintended re-engine start is prevented by excessive brake pedal discharge.

In the 3 is at a time tstart within the use safety time interval Δt _G the brake pedal completely released by the driver. As a result, the brake pressure threshold BDS set to the lower limit value UG becomes the actual brake pressure p _is undershot, whereby a renewed engine start is triggered.

In the 4 another start-stop driving operation is shown in which the driver during the use-safety time interval Δt _G intends to restart the engine at the time t _start , In contrast to 3 done in the 4 after the entrance t _stood the vehicle standstill an increased driver-side brake pedal load with correspondingly increased actual brake pressure p _is , With the reinforced brake pedal load after entry t _stood the vehicle standstill prevents the driver during the use safety time interval Δt _G an unintentional rolling movement, such as a rollback at a roadway gradient.

In this constellation, the driver re-starts the engine during the use-safety time interval Δt _G Intended, so must the increased actual brake pressure p _is be reduced by a corresponding driver-side brake pedal relief by a pressure difference Ap up to below the brake pressure threshold BDS to trigger the engine start. Such a reduction of the actual brake pressure p _is However, the pressure difference Δp inevitably leads to a rolling-back movement of the vehicle, which is perceived as disturbing by the driver.

The following is based on the 5 and 6 a start-stop system 15 described by means of which such a perceived as uncomfortable rolling movement of the vehicle can be prevented: Accordingly, in the 5 shown start-stop automatic 15 in addition to those already using the 2 explained program blocks an evaluation 27 on. The evaluation unit 27 determines whether in the usage safety time interval Δt _G one in comparison to the stopping process Δt _AH or to entry t _stood the vehicle standstill increased driver-side brake pedal load with correspondingly increased actual brake pressure p _is present or not. In the absence of an increased actual brake pressure p _is leaves the evaluation unit 27 the brake pressure threshold BDS in the use safety time interval Δt _G unchanged at the lower limit UG (minimum value at, for example, 0, 1 bar) set. In the presence of an increased actual brake pressure p _is on the other hand, the evaluation unit sets 27 the brake pressure threshold BDS during the use safety time interval Δt _G from the lower limit UG to a safety value SW high.

In the 6 the safety value SW is just below the increased actual brake pressure p _is , In this way, the pressure difference Δp is reduced by the actual brake pressure p _is is to be reduced to below the brake pressure threshold BDS to initiate a restart of the engine. The safety value SW is dimensioned so large that while, with the brake pedal reduction correlated brake pressure reduction on the pressure difference .DELTA.p there is no unintentional rolling vehicle movement.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102015220807 A1 [0007]
• DE 102015203453 A1 [0007]
• DE 102015206658 A1 [0007]

Claims (6)

Drive device for a motor vehicle with an automatic start / stop (15) with a control unit (25), the motor stop (S _stop ) triggers at a driver-side brake pedal operation when a _stop operation (.DELTA.t _AH ) is present and by the brake pedal Actuation of actual brake pressure (p _ist ) exceeds a brake pressure threshold (BDS), wherein the control unit (25) by a driver-side brake pedal actuation triggers a restart of the engine (S _start ), as soon as the actual brake pressure generated by the brake pedal operation ( p _is ), the brake pressure threshold (BSD) is below and in particular at 0, that is, the brake pedal is completely released, wherein during the stopping process (.DELTA.t _AH ) to the vehicle standstill (t _stood ), the control unit (25), the brake pressure threshold (BDS) to a lower limit value (UG) sets, so that even at a low brake pedal actuation of the thus correlating actual brake pressure (p _is ), the brake pressure threshold (BD S) exceeds and the control unit (25) triggers the engine stop, wherein the control unit (25) from entry (t _stood ) of the vehicle standstill, the brake pressure threshold (BDS) holds unchanged at the lower limit (UG), over a safety period ( Δt _G ), wherein the control unit (25) sets the brake pressure threshold (BDS) to an upper limit (OG) at the end of the useful safety time interval (.DELTA.t _G ), wherein for a renewed engine start in the use safety time interval (.DELTA.t _G ) of the Ist -Bremsdruck (p _is ) by corresponding driver side brake pedal discharge to a pressure difference (Δp) to be reduced to below the brake pressure threshold (BDS), characterized in that the control unit (25) has an evaluation unit (27) which determines whether in the use safety-Zeintintervall (.DELTA.t _G ) in comparison to the stopping process (.DELTA.t _AH ) and the entry (t _stand ) of the vehicle standstill reinforced brake pedal Bela Stung with correspondingly increased actual brake pressure (p _is ) is present or not, and that in the absence of an increased actual brake pressure (p _is ), the evaluation unit (27), the brake pressure threshold (BDS) in the use safety time interval (.DELTA.t _G ) unchanged to the lower Limit value (UG) can be set, and that in the presence of an increased actual brake pressure (p _is ), the evaluation unit (27), the brake pressure threshold (BDS) during the use safety time interval (.DELTA.t _G ) from the lower limit (UG) to a safety value (SW ). Drive device after Claim 1 , characterized in that the driver after entering (t _stood ) of the vehicle standstill with the increased brake pedal load prevents unintentional rolling movement of the vehicle, in particular a rollback at a roadway gradient. Drive device after Claim 1 or 2 , characterized in that with the increase of the brake pressure threshold (BDS) from the lower limit (UG) to the safety value (SW), the pressure difference (Δp) is reduced by which the actual brake pressure (p _ist ) is to be reduced, so that the brake pressure threshold (BDS) is fallen below for a restart of the engine. Drive device after Claim 1 . 2 or 3 , characterized in that the safety value (SW) to which the brake pressure threshold (BDS) is raised, is so dimensioned that during the correlation with the brake pedal relief brake pressure reduction on the pressure difference (Δp) there is no unintentional rolling vehicle movement that is, the vehicle is safely stopped until the engine is restarted. Drive device according to one of the preceding claims, characterized in that the safety value (SW) of the upper limit (OG), and / or that the safety value (SW) is less than the current actual brake pressure _(p) (during use safety time interval Δt _G ). Drive device according to one of the preceding claims, characterized in that the driver in the stopping process (Δt _AH ) with the entrance (t _stood ) of the vehicle standstill intuitively almost completely relieved the brake pedal to achieve a comfortable stop without a vehicle pitching motion, and that in particular the lower limit value (UG) during the stopping operation (Δt _AH ) and during the use safety time interval (Δt _G ) is dimensioned so small that even with almost complete brake pedal relief the actual brake pressure (p _ist ) correlating therewith _is the brake pressure threshold (FIG. BDS), whereby it is achieved that only when the actual brake pedal is de-pressurized does the brake pressure threshold (BDS) fall below the threshold and thus restart the engine during the use-safety interval (Δt _G ).

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