DE102007030254A1 - Assistance for driving from stationary on a slope assesses the angle and direction of the slope, to set the brake force when the driver releases the brakes - Google Patents

Abstract

The system to assist the start of driving a motor vehicle from a stop on a slope establishes the pitch angle of the road and the direction to be driven. The results are used to set the braking force when the driver releases the brakes.

Description

Technical area

The The invention relates to a method for assisting a starting operation of a Vehicle on a slope starting from a driving state brought about by the driver of the vehicle by a brake application, in particular a vehicle standstill. The invention also relates to a to carry out the method suitable device. In particular, the invention comprises a complement a cruise control, such as an HDC control (HDC: Hill Descent Control).

Background of the invention

For example under the name HDC control functions are known, the one Vehicle lying on a downhill slope moved downhill through active braking interventions on one keep preset target speed. These control functions are especially for ATVs provided on a slope be moved, where the provided by the drive motor Engine drag torque is no longer sufficient even in the lowest gear, to delay the vehicle. To carry out The brake interventions usually become a known also from driving dynamics control systems ago hydraulic unit used, with the braking force regardless of a brake application of the Driver can be adjusted.

One HDC controller is designed to be comfortable in a wide gradient range Allow speed control. Due to the resulting controller structure and due The limited dynamics of the hydraulic unit can when rolling up the Vehicle on steep slopes in particular to overshoot over the Target speed and too high accelera tions come from what The driver is usually perceived as uncomfortable and reduced his confidence in the control function. Furthermore, it exists Problem that the HDC control the driver no support Starting in uphill direction offers. On steep slopes can it even vehicles with an automatic transmission during the Roll back up, what about the driver by a quick change from a brake to an operation of the accelerator pedal or by operating a parking brake can be prevented. However, this requires a considerable skill of the Driver and can be an unintentional especially on steep slopes roll back often not completely prevent the vehicle.

To increase the comfort when rolling in downhill is in the international patent application WO 01/14186 proposed to supplement a HDC controller by a system that builds a braking force by means of the brake system before or during the rolling until the braking force control is taken over by the HDC controller. However, when starting uphill, the system described does not provide any assistance to the driver. Furthermore, the known system does not differentiate between start-up operations in the forward and reverse direction, in which different starting strategies may be used in order to make the starting process more comfortable.

Presentation of the invention

It It is therefore an object of the present invention to provide assistance in Startup operations on a steep slope provide that in different starting situations a especially with regard to ride comfort as optimal as possible support for the driver offers.

According to the invention this Task by a method according to claim 1 and by a device according to claim 17 solved.

• – eine den Steigungswinkel des Gefälles charakterisierende Steigungsgröße und eine von einem Fahrer gewünschte Anfahrrichtung ermittelt werden,
• – die ermittelte Anfahrrichtung in Bezug auf die ermittelte Steigungsgröße bewertet wird, und
• – nach Maßgabe eines Ergebnisses der vorgenommenen Bewertung eine Bremskraft in einer Bremsanlage des Fahrzeugs eingestellt wird, nachdem ein fahrerseitiges Lösen der Bremse festgestellt worden ist.

Accordingly, a method of the type mentioned is carried out so that

• Determining a gradient variable characterizing the gradient angle of the gradient and a direction of approach desired by a driver,
• - the determined approach direction is evaluated in relation to the ascertained gradient size, and
• - According to a result of the assessment made a braking force in a brake system of the vehicle is set after a driver-side release of the brake has been determined.

• – wenigstens eine Ermittlungseinrichtung, mit der eine den Steigungswinkel des Gefälles charakterisierende Steigungsgröße und eine von einem Fahrer gewünschte Anfahrrichtung ermittelbar sind,
• – eine Bewertungseinrichtung, in der die ermittelte Anfahrrichtung in Bezug auf die ermittelte Steigungsgröße bewertbar ist, und
• – eine Steuerungseinrichtung, mit der nach Maßgabe eines Ergebnisses der vorgenommenen Bewertung eine Bremskraft in einer Bremsanlage des Fahrzeugs einstellbar ist, nachdem ein fahrerseitiges Lösen der Bremse festgestellt worden ist.

Furthermore, a device for assisting a starting process of a vehicle based on a driving state brought about by the driver of the vehicle by a brake application, in particular a vehicle standstill, is provided, comprising the following components:

• At least one determining device with which a gradient variable characterizing the gradient angle of the gradient and a starting direction desired by a driver can be determined,
• An evaluation device in which the ascertained approach direction can be evaluated in relation to the ascertained gradient variable, and
• - A control device, with the basis of a result of the evaluation made a braking force in a brake system of the vehicle is adjustable after a driver-side release of the brake has been determined.

The The invention includes the idea that a direction of approach desired by the driver determined and in relation to the determined value of the pitch angle the present gradient rated characterizing size is going to, while a starting operation, a braking force control in dependence from the result of the evaluation. This allows the brake force control be adapted to different starting situations, so that the ride comfort is increased when starting. The startup takes place In particular, from a standstill of the vehicle, but in principle also off other driving conditions, especially from a very slow ride. In addition, be pointed out that the term starting in the context of the invention in addition to a start in mountain climbing in particular also a start or rolling downhill includes.

Under The approach direction is understood as the direction of travel, in which the driver wishes to drive the vehicle. in this connection can it be the forward or reverse direction act. That is, it is determined whether the driver is likely to drive the vehicle in the vehicle longitudinal direction forward or drive backwards in the vehicle longitudinal direction would like to. Based on the evaluation of the approach direction in relation to the pitch angle of the gradient characterizing slope size can In particular, be determined whether the driver is the vehicle to a gradient expected to start in uphill or downhill. at the gradient size can it is for example the means of a longitudinal acceleration sensor (G-sensor) determined longitudinal inclination angle of Vehicle or a derived therefrom size.

The Brake force control is advantageous after a driver-side Solve the Brake has been detected. This can be the case, for example. when it has been determined that the one commanded by the driver Has reduced braking force to a predetermined level, and / or that an actuating means the brake of the driver in a predetermined manner, for example with a given solubility gradient moved, in particular solved becomes. In one embodiment the method and the device is a driver-side release of the brake then detected when a characterizing the braking force a Threshold reached. When using a hydraulic brake system For example, it may be the size characterizing the braking force to act on a present in the brake system brake pressure. A Brake force control takes place in such brake systems in the rule by setting a brake pressure.

In an embodiment of the method and the device is provided that desired by the driver Approach direction based on an inserted in a transmission of the vehicle Gear or by means of a gearbox of the vehicle set Drive level is determined.

These embodiment has the advantage that due to the provided indirect provision of the desired by the driver Approach direction no additional the approach direction indicating signals are given by the driver have to, so that the determination of the desired Approach direction unnoticed by the driver and thus without any loss of comfort carried out can be. Under the term gear are doing in the context of Invention both manual transmission and automatic transmission or understood automated transmissions.

A further embodiment of the method and the device records characterized by the fact that in the assessment of the approach direction in relation determined on the slope size whether the driver is driving the vehicle uphill or in wishes to start a downhill.

As previously mentioned, exist with regard to whether the vehicle is uphill or downhill approached, different requirements for the approach strategy. Advantageously, the aforementioned embodiment allows these starting situations to differentiate and the brake force control to those in the respective Approach situation to adapt to existing requirements.

Further sees an embodiment of the method and the device, that in the case that the Driver wants to start in downhill direction, set a braking force which is sized so that the vehicle due to a downgrade force moved at a low speed.

Advantageous is in this embodiment during a startup in downhill a braking force is set, which is only a low speed of the vehicle, allowing high acceleration of the vehicle when starting in downhill can be avoided. This can be prevented in particular before entry in a HDC control vehicle speeds and / or accelerations occur, which feels the driver as unpleasant and comfort-reducing.

It was also found that a driver high reverse acceleration in the As a rule feels particularly uncomfortable that higher accelerations in the forward direction, however, are often perceived without discomfort.

A Development of the method and the device therefore includes that in the event that a reverse direction As the direction of approach is determined, set a greater braking force is considered as in the case that a forward direction as approach direction is detected.

hereby accelerates the vehicle when reversing Approach in downhill direction less strong than in forward direction Approaching downhill.

A Further development of the method and the device include in the event that the driver desires to start downhill, one Braking force is set, which is such that the vehicle is held at a standstill.

at This development has the advantage that the vehicle initially not in downhill riding when the driver releases the brake. Developed by this The driver usually has a particularly high level of confidence in the intended Support function because he has the support undoubtedly noticed in this case.

Furthermore is an embodiment of the method and the device thereby characterized in that the braking force with a predetermined Bremskraftgradienten is reduced.

hereby is taken into account the fact that the initially set braking force, for example at a terrain change not to a desired one Speed, especially on the HDC target speed, accelerated can be. Thus, for example, the present slope during the To change the startup procedure in such a way that the vehicle could return to a standstill when the braking force was not would be reduced.

A embodiment of the method and the device also provides that the braking force only after a predetermined first holding time has elapsed, with the determination the driver's side release The brake starts, is reduced.

One Advantage of this embodiment is that the vehicle acceleration at the beginning of the startup process is kept very low, which the driver especially at very big Gradients are usually perceived as comfortable, and by what the driver's confidence in the HDC function is further increased. If after the driver's release the brake first a braking force is set, which is such that the Vehicle is held at a standstill, then the vehicle rolls first then when the braking force is reduced, i. especially only after the first holding time has expired.

As already mentioned, the proposed method and the proposed one are suitable Device with its embodiments especially for support a HDC function that the vehicle on a downhill on a predetermined speed holds. The provided support allows it, the startup process for to make the driver more comfortable until the brake force control by the HDC controller, that is, until the HDC target speed is reached.

there is an embodiment the method and the device characterized in that the braking force is reduced until a braking force control by a speed controller, in particular a HDC controller adopted which is a speed of the vehicle to a predetermined Target speed controls.

Farther includes an embodiment of the Procedure and the device that in the event that the driver wishes to start in mountain climbing a braking force is set, which is such that the Vehicle is kept at a standstill.

hereby prevents the vehicle from rolling back downhill, if the driver wishes to drive the vehicle uphill, which from a driver usually also felt very uncomfortable becomes.

moreover is a further development of the method and the device characterized in that the braking force after a predetermined second holding time reduces, and / or that the braking force is reduced, if a set by the driver on a drive motor of the vehicle Drive torque exceeds a threshold.

Of the Advantage of this development is that the driver possibility is given after actuation the brake system on the intended for controlling the drive motor To change the accelerator pedal to start the vehicle without it rolling back downhill. In particular, the HDC function can thereby be extended by a start-up assistance which allows a comfortable and safe start on a slope.

In an associated embodiment of the method and the device, it is provided that the braking force reduction is accelerated when the drive motor set by the driver ment exceeds the threshold.

hereby reduces the risk of the driver driving the engine Vehicle stalled due to excessive braking force during startup, and On the other hand, the braking force can be reduced sufficiently slowly, when the driver does not request drive torque. This can be, for example be the case when he hits the vehicle contrary to the detected Would like to start approaching.

Further sees an embodiment of the method and the apparatus that the threshold in dependence determined by the determined slope size becomes.

hereby In particular, the threshold may be determined such that the sufficient drive torque is reached when the threshold is reached is great to drive the vehicle in mountain climbing or at least in Standstill to stop, so no more brake assistance required is.

moreover includes an embodiment of the method and the device, that the braking force and / or the braking force gradient in dependence determined by the determined slope size becomes.

Advantageous can the braking force and / or the Bremskraftgradient in this embodiment considering the determined slope size to the present Approach situation to be adjusted. In particular, the braking force be determined so that it is on the one hand sufficiently large to the on the vehicle acting downhill force in the desired Way to compensate, i. the vehicle either at a standstill to keep or with a low acceleration in downhill riding on the other hand is not so great that a desired Rolling prevented or a startup is difficult.

moreover a computer program product is provided, the software code sections which involves a procedure with each or all of the previously described features executable when the software code sections are on a processor device accomplished become.

Around an addition for one HDC function provides an embodiment of the computer program product that the software code sections are part of a software are with which a speed control, in particular an HDC function, accomplished when running the software on a processor device.

Furthermore it is also provided in an embodiment of the device, that it is part of a cruise control system, in particular an HDC control system.

The aforementioned and other advantages, features and expedient embodiments of Invention will also be apparent from the embodiments which will be described below with reference to the figures.

Brief description of the figures

From the figures shows:

1 a schematic representation of selected components of a vehicle, which is suitable for carrying out the invention,

2 a schematic hydraulic circuit diagram of a hydraulic unit of the vehicle,

3 1 is a schematic block diagram of a device for carrying out a method according to the invention,

4 a flow diagram illustrating a pressure control in the case of start in downhill and

5 a flow diagram illustrating a pressure control in the event of startup in uphill.

Detailed description of exemplary embodiments

In 1 are exemplary selected components of a four-wheeled vehicle shown, which may be, for example, a four-wheel drive off-road vehicle. The vehicle has a drive motor 101 in which one of the driver by means of an accelerator pedal 102 requested engine torque can be generated, which via a drive train to the four wheels 103 of the vehicle is transferable. The drive motor 101 is replaced by an in 1 Not shown engine control device controlled, in particular receives and converts the accelerator pedal signals. The driveline includes a transmission 104 in which it may be a manual transmission or an automatic transmission, which by the driver by means of a selector lever 105 is served. The remaining elements of the powertrain are in 1 not shown for clarity. The gear 104 provides multiple forward gears in which the vehicle is propelled by the engine torque in the forward direction, and at least one reverse gear in which the vehicle is driven by the engine torque in the reverse direction. If it is the transmission 104 a hand then the selector lever 105 designed as a shift lever with which in the transmission 104 inlaid gear is selected. If it is the transmission 104 is an automatic transmission, then several levels are provided by the driver by means of the selector lever 105 selected who can and include one or more forward gears and at least one reverse gear. The gear shift is in the automatic transmission of a in 1 not shown transmission control made according to the set gear.

The vehicle also has a hydraulic brake system, which is controlled by the driver by means of a brake pedal 106 can be operated. By a movement of the brake pedal 106 in a pressure build-up direction is by means of a brake booster 107 a brake pressure in a master cylinder 108 constructed, which is also referred to below as a form. The master cylinder 108 is embodied in one embodiment as a so-called tandem master cylinder having two pressure chambers, each with a pressure medium reservoir 115 are connected and a two wheel brakes 109 supply comprehensive brake circuit. The pressure chambers are through hydraulic lines 111 with the wheel brakes 109 connected via the set in the pressure chambers form to the wheel brakes 109 can be transferred. The wheel brakes 109 For example, they are designed as disc brakes in which a brake piston is actuated at a pressure build-up and against a rotationally fixed with the corresponding wheel 103 the vehicle connected brake disc is pressed, whereby a braking force is generated. The brake system also contains a hydraulic unit (HCU) 110 that allows the brake pressure in the wheel brakes 109 regardless of a driver's brake application.

The hydraulic unit 110 is designed in a manner known to those skilled in the art and includes an arrangement of electronically switchable valves and a pump. A hydraulic circuit diagram of an embodiment of the hydraulic unit 110 is fragmentary in 2 shown in a schematic representation. 2 illustrates the section of the hydraulic unit 110 , which is assigned to one of the two brake circuits. For the other brake circuit, the hydraulic unit points 110 an identical valve arrangement. The wheel brakes 109 a brake circuit are within the hydraulic unit 110 via a separating valve 201 and one inlet valve each 202 with the corresponding pressure chamber of the master cylinder 108 connected. The valves 201 . 202 have a spring-actuated passage position and an electromagnetically switchable blocking position. In an exclusively controlled by the driver braking is in the master cylinder 108 established form directly to the wheel brakes 109 transfer. To perform an automatic brake pressure build-up, the isolation valve 201 operated (ie closed) and a switching valve 203 , which has a spring-actuated blocking position and an electromagnetically switchable passage position, opened. In this way arises between the master cylinder 108 and the suction side of an electric motor 205 driven pump 204 a hydraulic connection, while the master cylinder 108 from the pressure side of the pump 204 is decoupled. The pump 204 is at this valve position capable of pressure medium from the master cylinder 108 in the wheel brakes 109 to promote and brake pressure in the wheel brakes 109 to increase. Furthermore, the brake pressure in the wheel brakes 109 against one in the master cylinder 108 existing form be reduced. This is every wheel brake 109 an outlet valve 206 assigned, which has a spring-actuated blocking position and an electromagnetically switchable passage position. For pressure reduction in a wheel brake 109 will be the corresponding inlet valve 202 closed and the associated outlet valve 206 open so that the pressure fluid from the wheel brake 109 in a low-pressure accumulator 207 can escape. By means of the pump 204 the pressure medium is then when the switching valve is closed 203 and open isolation valve 201 from the low-pressure accumulator 207 in the master cylinder 108 conveyed back. In addition, the hydraulic unit includes 110 a pressure sensor 208 , with the one in the master cylinder 108 existing form can be recorded.

The hydraulic unit 110 is controlled by a control device 112 controlled, which contains an HDC control system, by the driver, for example by means of a switch 113 can be activated. Typically, activation occurs when the driver is assisted by the HDC controller during off-road driving 114 wishes. The HDC control system includes in particular the actual HDC controller 114 , which determines the vehicle speed when driving downhill by a suitable control of the hydraulic unit 110 stops at a predetermined target speed. The HDC controller 114 is designed in a manner known to those skilled in the art and therefore will not be explained further here. For an exemplary embodiment of the HDC controller 114 is based on the international patent application WO 96/11862 directed. In one embodiment is the HDC controller 114 realized as a software stored in a memory of the controller 112 is stored and on a processor of the controller 112 is performed. The inside of the control device 112 Processes that are carried out are cyclically traversed in so-called loops with a specific loop time.

In addition, the HDC control system includes in addition to the HDC controller 114 the control module 115 to perform an additional function that provides assistance during a downhill approach. This support is carried out especially on slopes with a slope greater than 15% or a pitch angle greater than 9 degrees. The control module 115 For example, it is designed as a software module that controls the HDC controller 114 containing software added and simultaneously with the HDC controller 114 is activated.

By means of the additional function, the vehicle acceleration is influenced in a targeted manner after a standstill of the vehicle caused by the driver in order to make the starting process more comfortable. The additional function is based on the assumption that the driver after the establishment of the vehicle standstill a form in the master cylinder 108 which is sufficiently large to keep the vehicle at a standstill.

A stoppage of the vehicle is determined based on a speed signal, which is determined from the signals of wheel speed sensors. The speed signal is in the controller 112 determined or in egg ner further control device, from which it to the control device 112 is transmitted. In one embodiment, the speed signal corresponds to the wheel speed of the slowest wheel 103 of the vehicle. A stoppage of the vehicle is detected when the speed signal is less than a predetermined threshold, for example, 1 km / h, or when it has assumed the value zero.

If it is determined that the vehicle is at a standstill, then the intended additional function in the control module 115 executed. The structure of the control module 115 is in 3 schematically illustrated by a block diagram. It includes a slope calculator 301 in which an estimate Road_Grad for the present slope is determined, which is defined here as the sine of the present pitch angle. The estimated value Road_Grad is determined from the longitudinal inclination angle of the vehicle, which is detected in a manner known to the person skilled in the art with the aid of a longitudinal acceleration sensor (G sensor), whose signals are sent to the control device 112 and in particular the slope calculating device 301 be transmitted.

For the longitudinal inclination angle α of the vehicle applies sin (α) = (α sensor ∓ dv / dt) / g (1) where g is the gravitational acceleration and a _{sensor is} the longitudinal acceleration measured by the longitudinal acceleration _sensor and v is the vehicle longitudinal speed. The quantity dv / dt denotes the wheel acceleration, that is, the rate of change of the vehicle speed. The upper (negative) sign in Equation 1 applies to forward travel and the lower (positive) sign applies to reverse travel. The signs have been chosen in Equation 1 so that the pitch angle is positive when the vehicle is inclined in the uphill direction, ie when the front axle of the vehicle is higher than the rear axle. Thus, the pitch angle is negative when the vehicle is inclined in downhill, ie, when the front axle of the driving tool is lower than the rear axle. At standstill, the wheel acceleration is equal to zero or negligible, so that the estimated value Road_Grad can be determined directly from the longitudinal acceleration signal. In order to determine the estimated value Road_Grad for the slope, the calculated value for sin (α) is preferably filtered in order to reduce the effects of possible decay of the longitudinal acceleration sensor. In particular, a PT1 filtering can be carried out, for example, so that Road_Grad = PT1 (a _sensor ) applies.

In addition to the determination of the slope Road_Grad also takes place a recognition and evaluation of the driver direction desired in the block 302 , In this block, it is first determined in which direction of travel the driver wishes to start the vehicle, that is, it is determined whether the driver wishes to move the vehicle in a forward or backward direction. This is done by determining the during standstill in the transmission 104 engaged gear or selected during standstill gear, including the block 302 an information G1 is supplied via the engaged gear or the selected gear. If it is me in the transmission 104 is a manual transmission, the gear engaged is detected by a sensor which transmits the information Gl to the control device 112 transmitted. The sensors may include, for example, switches located in the gearbox or in the shift gate of the selector lever 105 are arranged and are each actuated upon insertion of a particular gear, or magnetic and / or electrical distance sensors, which are arranged in the shift gate and the position of the selector lever 105 each characteristic of a particular gait. When it comes to the transmission 104 is an automatic transmission, then the set gear is detected by the transmission control and to the controller 112 reported. For this purpose, for example, an information indicating the engaged gear level Gl via a data bus, in particular via the CAN bus commonly used in vehicles (CAN: Controller Area Network), to the controller 112 be transmitted.

• – der Fahrer wünscht ein Anfahren in Bergaufrichtung; dies ist der Fall, wenn die Steigung Road_Grad positiv ist und an dem Getriebe 104 ein Vorwärtsgang bzw. eine Vorwärtsfahrstufe eingestellt ist, oder wenn die Steigung Road_Grad negativ ist und an dem Getriebe ein Rückwärtsgang bzw. eine Rückwärtsfahrstufe eingestellt ist;
• – der Fahrer wünscht ein Anfahren in Vorwärtsrichtung bergab; dies ist der Fall, wenn die Steigung Road_Grad negativ ist, und an dem Getriebe 104 ein Vorwärtsgang bzw. eine Vorwärtsfahrstufe eingestellt ist;
• – der Fahrer wünscht ein Anfahren in Rückwärtsrichtung bergab; dies ist der Fall, wenn die Steigung Road_Grad positiv ist und an dem Getriebe 104 ein Rückwärtsgang bzw. eine Rückwärtsfahrstufe eingestellt ist.

Further, in the block 302 the directional intention of the driver is evaluated in relation to the present slope Road_Grad. In particular, the following cases are distinguished:

• The driver wishes to start in the uphill direction; this is the case when the slope Road_Grad is positive and at the transmission 104 a forward gear is set, or when the slope Road_Grad is negative and the transmission is set to a reverse gear or a reverse gear;
• The driver wishes to start downhill in the forward direction; this is the case when the slope Road_Grad is negative, and at the transmission 104 a forward gear or a forward gear is set;
• The driver wishes to start downhill in a backward direction; this is the case when the slope Road_Grad is positive and at the transmission 104 a reverse gear or a reverse gear is set.

Depending on the result E of the evaluation, ie, depending on which of the aforementioned three cases has been determined, a brake pressure level is then determined by the additional function. For this the result E of the evaluation becomes the block 303 in which, on the basis of the result of the evaluation, a pressure threshold P_Thr is calculated, which is used for the brake pressure control in the case of a start-up following a standstill. The brake pressure control is thereby by the block 304 performed. This checks if the driver depresses the brake pedal 106 solves and takes over the brake pressure control when the pre-pressure during the brake pedal release operation reaches the calculated pressure threshold P_Thr. In one embodiment, first of all, a brake pressure corresponding to the pressure threshold P_Thr in the wheel brakes 106 maintained, which is then degraded after a predetermined pressure holding time. To carry out the pressure control is the block 304 preferably also the determined slope Road_Grad supplied.

In a starting operation in downhill direction, the pressure threshold P_Thr is determined in one embodiment so that the vehicle starts at a low acceleration when a pressure threshold P_Thr corresponding brake pressure in the brake system, in particular in the wheel brakes 109 is set. In a further embodiment, it may be provided that the pressure threshold P_Thr is determined so that the vehicle is kept at a standstill during the pressure-holding time and only starts to roll during the subsequent brake pressure reduction.

The pressure threshold P_Thr is in the block 302 also determined depending on the present slope Road_Grad. It can be provided that the present slope Road_Grad is multiplied by a predetermined factor in order to determine the pressure threshold P_Thr. In this embodiment, the pressure threshold P_Thr is thus proportional to the slope Road_Grad. Likewise, it may be provided that a characteristic curve of a in the control device 112 stored polygon train is determined, and the pressure threshold P_Thr is determined on the basis of this characteristic from the slope Road_Grad. The characteristic can be designed so that at higher grades Road_Grad a change in the slope Road_Grad leads to a greater change in the pressure threshold P_Thr than at lower slopes Road_Grad. In another embodiment, an arbitrary function can also be specified, which is used to determine the pressure threshold P_Thr from the present slope Road_Grad, and this function can also have the aforementioned property of the polygon train. The factor, the traverse or the function can be determined in the context of driving tests so that the vehicle rolls in the desired manner. In particular, it can be determined by suitable specification of the pressure threshold P_Thr, whether the vehicle sluggish, that is rolling at a low acceleration, or whether the acceleration when rolling should be higher, and whether the vehicle already rolls on during or after the pressure holding phase.

If the downhill direction has been determined as the driver's desired direction, then, when determining the pressure threshold P_Thr, it is preferably also taken into account whether the driver desires to start in the forward or in the reverse direction. Accordingly, these cases become as described above in the block 302 distinguished in the evaluation of the direction of the driver. In this case, when starting in the reverse direction, a higher pressure threshold P_Thr is determined than when starting in the forward direction, so that the vehicle acceleration is lower in a roll-up in the reverse direction than in a forward feed. As a result, the fact is taken into account that a driver feels a rollback in the reverse direction in the rule as particularly unpleasant and therefore he has a higher confidence in the additional function at a slow rolling in the reverse direction. In this case, it may be provided that a separate factor or traverse or a separate function is specified for the determination of the pressure threshold P_Thr for the backward rolling. Likewise, it can be provided that the pressure threshold P_Thr determined by means of the factor, the traverse or by means of the function is increased by a predetermined value, if determined has been desired that a roll in the reverse direction of the driver is desired. This value can also be determined as a function of the present slope Road_Grad and, for example, be greater for larger gradients than for smaller gradients.

In addition, it can be provided that the pressure threshold P_Thr can additionally be determined as a function of the load state of the vehicle, that is to say, in particular, of the vehicle mass and / or of one or more further variables. Such further variables can be, for example, the pitch angle of the vehicle, the state of wear of the wheel brakes 109 and the coefficient of friction of the roadway. A non-zero pitch angle can falsify the determination of the slope Road_Grad, so that at a known pitch angle, a corresponding correction can be made. At a high brake wear and a low friction coefficient of the road, the effectiveness of the brake system of the vehicle is limited, so that if necessary, a higher pressure threshold P_Thr can be determined if an increased brake wear or a low coefficient of friction is detected.

The pressure control by the block 304 is carried out when starting in downhill in a different way than when starting in uphill. In the event that it has been determined that the driver desires to start downhill, the pressure control will be schematically illustrated in the flowchart in FIG 4 illustrated. In the block 304 It is first checked during the standstill of the vehicle, whether the driver releases the brake. A release of the brake is detected, for example, at a drop in the form P_Drv, by means of the pressure sensor 208 is detected, the signals to the control device 112 transmitted and in particular the block 304 be supplied. Additionally or alternatively, a release of the brake can also be determined when the position of the brake pedal 106 is changed with a threshold exceeding the rate of change in Druckabbaurichtung. The pedal gradient, ie the rate of change with which the position of the brake pedal 106 is changed, can be determined, for example, by evaluating the signals of a pedal travel sensor on the brake pedal 106 is arranged.

During the dissolution process will step through the block 401 checked if the form P_Drv the in the block 303 detected pressure threshold P_Thr below. For this purpose, the pre-pressure P_Thr is preferably based on the signals of the pressure sensor 208 supervised. If it has been determined that the pre-pressure P_Drv has reached or fallen below the pressure threshold value P_Thr, then the in the wheel brakes 109 present brake pressure in step 402 maintained or imprisoned. This is done, for example, by closing the isolation valves 201 the two brake circuits and / or by closing the intake valves 202 the wheel brakes 109 , Further, in one embodiment, a pressure hold phase of a predetermined duration is started. This is done, for example, by initializing a counter whose value is incremented n loop by loop (step 403 ) until it reaches a predetermined threshold N_Thr1 (see step 404 ), which is set so that the N_Thr1-fold loop time just corresponds to the intended duration of the pressure hold phase. The duration of the pressure maintenance phase, ie the threshold value N_Thr1, is determined in driving tests in such a way that a comfortable start-up is ensured. It can be provided that for a roll in the reverse direction, a longer holding time, ie, a larger threshold value N_Thr1, is specified, as for a roll in the forward direction.

After the end of the pressure maintenance phase, ie when the counter has assumed the value n = N_Thr1, the brake pressure in the wheel brakes 109 by an appropriate control of the hydraulic unit 110 with a given pressure gradient in step 405 reduced. Here, the brake pressure can be reduced, for example, per loop by a predetermined amount. Further, when rolling in the reverse direction, a lower pressure gradient can be set than when rolling forward in order to avoid the occurrence of high vehicle accelerations when rolling back in the reverse direction. The brake pressure reduction can be necessary for various reasons. For example, the detected pressure threshold P_Thr may be too high such that the vehicle does not already roll up during the pressure hold phase as in one embodiment, or the pressure threshold P_Thr would be too great to move the vehicle at a low speed due to a change in terrain. For example, the pitch could decrease so that the vehicle stops again after coasting due to excessive brake pressure. When the pressure threshold P_Thr has been determined so as to hold the vehicle at standstill when there is a brake pressure corresponding to the pressure threshold P_Thr, the brake pressure release is required for the vehicle to start up.

The auxiliary function is terminated when the brake pressure has been completely reduced, ie, when the brake pressure reaches zero, or when a control intervention from the HDC controller due to exceeding the target HDC speed 114 is made (steps 406 . 407 ). Preferably, it is provided that when reaching the target HDC speed in the wheel slow down 109 present brake pressure with the first brake pressure request of the HDC controller 114 is charged. After completion of the additional function, the pressure control in a manner known in the art of the HDC controller 114 made the hydraulic unit 110 so controls that the vehicle speed does not exceed the target speed.

If the driver requests an _engine torque M _engine during the pressure reduction in order to accelerate the vehicle more strongly, then it is at one in the 4 not illustrated embodiment also provided that the pressure reduction gradient is increased. By this measure, in particular prevents the drive motor 101 of the vehicle is strangled due to excessive braking force. The engine torque request can be detected by an increase of the _engine torque M _motor , its value from the engine controller, for example via the data bus of the vehicle to the control device 112 can be reported. Likewise, it may be provided to recognize the engine torque request when the accelerator pedal 102 has been entered by a predetermined pedal travel, which is based on signals on the accelerator pedal 102 arranged pedal travel sensor can be determined.

If in the block 302 it has been determined that the driver wishes to drive the vehicle in the uphill direction, then a pressure threshold P_Thr is determined which is so high that the vehicle does not roll downhill when a brake pressure corresponding to the pressure threshold P_Thr in the wheel brakes 109 is set. Preferably, this brake pressure is also determined as a function of the slope Road_Grad using a predetermined factor with which the slope Road_Grad is converted into a brake pressure. The factor can be determined, for example, so that the vehicle would not roll even at maximum load. Furthermore, it can be provided that the pressure threshold P_Thr is determined as a function of the vehicle mass and / or one or more further of the variables already mentioned above.

The through the block 304 in the event that it has been determined that the driver wishes to start uphill, is shown schematically in the flowchart in FIG 5 illustrated. Also in this case, it is checked in the manner described above, whether the driver releases the brake. During the dissolution process, the pre-pressure P_Drv is also based on the signals of the pressure sensor 208 is checked to determine whether the pre-pressure P_Dry reaches or falls below the calculated pressure threshold P_Thr (step 501 ). If this has been determined, then in step 502 the brake pressure in the wheel brakes 109 by a corresponding control of the hydraulic unit 110 maintained, in particular by closing the isolation valves 201 the two brake circuits and / or intake valves 202 the wheel brakes 109 , During a predetermined pressure maintenance phase, the brake pressure is then kept constant. The pressure holding phase is dimensioned so that the driver comfortably from the brake pedal 106 can switch to the accelerator pedal to set by means of the accelerator pedal sufficient for starting motor torque M _motor . In particular, the pressure maintenance phase can be selected to be longer than in the case of a start in downhill. To gauge the pressure holding phase, in step 502 For example, a counter is initialized whose value n is incremented in each loop (step 503 ). Furthermore, a counter threshold N_Thr2 is specified, wherein a multiplication of the loop time with N_Thr2 just results in the intended duration of the pressure maintenance phase.

During the pressure hold phase, ie, before the counter has accepted the predetermined value n = N_Thr2, the block will 304 in step 504 checked if that from the drive motor 102 provided _engine torque M _motor has exceeded a threshold M_Thr. The value of the _engine torque M _engine is thereby, as already described above, from the engine control to the control device 112 reported. In this case, the engine torque threshold M_Thr is predetermined in such a way that the vehicle can be approached without brake assistance when there is an engine torque corresponding to the threshold value M_Thr, or it can be stopped at the downward gradient. Preferably, the engine torque threshold M_Thr is determined as a function of the determined slope Road_Grad. Here again a factor can be determined in driving tests and in the control device 112 with which the determined slope Road_Grad is multiplied to calculate the engine torque threshold M_Thr. Likewise, the engine torque threshold M_Thr can also be determined on the basis of a characteristic curve specified by means of a polygon or on the basis of a functional relationship from the ascertained gradients Road_Grad. This makes it possible to specify non-linear relationships between the slope Road_Grad and the engine torque threshold M_Thr, so that the engine torque threshold M_Thr can be increased, for example, disproportionately with increasing slope Road_Grad. If in the step 504 is determined that the _engine torque M _motor has exceeded the threshold value M_Thr, then the brake pressure included in the service brake system in step 505 reduced to zero with a high brake pressure gradient. If this is done, then the additional radio will tion in step 506 completed.

If the engine torque has not exceeded the threshold value M_Thr until the end of the pressure hold phase, ie until the counter reaches the value n = N_Thr2 (see step 507 ), then in step 508 begun to reduce the brake pressure with a predetermined brake pressure gradient, wherein the brake pressure is reduced, for example, in each loop by a predetermined value. The thus set brake pressure gradient is lower than that in step 505 set brake pressure gradient with which the brake pressure is reduced when the _engine torque M _motor has exceeded the threshold value M_Thr. As during the pressure maintenance phase, it is also checked during the reduction of the brake pressure whether the _engine torque M _Motor exceeds the _engine torque threshold M_Thr (step 509 ). If this is determined, then the pressure control with the step 505 continued, in which the remaining brake pressure is reduced with a high brake pressure gradient. After reducing the brake pressure to the value zero, the additional function then becomes in step 506 completed.

If the _engine torque M _motor does not exceed the threshold value M_Thr, then the brake pressure is further reduced until the vehicle has been accelerated downhill to a speed above the target HDC speed and a control action of the HDC controller 114 carried out or until the brake pressure in the brake system has been completely reduced (step 510 ). Then the additional function in step 506 completed. In the case of a control intervention of the HDC controller 114 the first brake pressure request is offset with the brake pressure still present in the brake system.

Characterized in that the brake pressure is reduced even if previously using the by the driver in the transmission 104 engaged gear or the selected gear has been determined that the driver would like to start the vehicle in the uphill direction, it is ensured that the driver can then roll the vehicle in downhill direction, if it corresponds to the uphill gear or one of the uphill corresponding Has set the drive level. This allows the vehicle to roll in downhill even when the forward gear is engaged (and the clutch is open) or when the forward gear is set, and it can be rolled forwards in the downhill direction with the reverse gear engaged (and the clutch open) or with the reverse gear engaged. The HDC controller 114 ensures that the HDC target speed is not exceeded after startup.

Claims (18)

Method for supporting a startup process of a Vehicle on a slope starting from a driving state brought about by the driver of the vehicle by a brake application, in particular a vehicle standstill in which - one the pitch angle of the gradient characterizing pitch size (Road_Grad) and one desired by a driver Approach direction to be determined - The determined approach direction is assessed in relation to the determined gradient size (Road_Grad), and - in accordance with a Result of the assessment made a braking force in one Brake system of the vehicle is set after a driver's side Solve the Brake has been detected. A method according to claim 1, characterized in that the desired by the driver approach direction based on a in a transmission ( 104 ) of the vehicle inlaid gear or one on a transmission ( 104 ) of the vehicle set driving level is determined. Method according to claim 1 or 2, characterized that the evaluation determines whether the driver is the vehicle wishes to start in a mountain uphill or downhill. Method according to one of the preceding claims, characterized characterized in that in the case that the driver in downhill wishes to start a braking force is set, which is such that the vehicle due to a downhill power with a low Speed moves. Method according to one of the preceding claims, characterized characterized in that in the case that a backward direction is detected as the approach direction will, a greater braking force is set as in the case that a forward direction as approach direction is detected. Method according to one of the preceding claims, characterized characterized in that in the case that the driver in downhill wishes to start a braking force is set, which is such that the Vehicle is kept at a standstill. Method according to one of claims 4 to 6, characterized that the braking force with a predetermined Bremskraftgradienten is reduced. Method according to one of claims 4 to 7, characterized that the braking force only after a predetermined first holding time, which begins with the determination of the driver-side release of the brake reduced becomes. Method according to one of the preceding claims, characterized in that the braking force is reduced until a braking force control by a speed controller ( 114 ), in particular an HDC controller, which adjusts a speed of the vehicle to a predetermined setpoint speed. Method according to one of the preceding claims, characterized characterized in that in the event that the driver is in mountain climbing wishes to start a braking force is set, which is such that the Vehicle is kept at a standstill. Method according to one of the preceding claims, characterized in that the braking force decreases after a predetermined second holding time, and / or that the braking force is reduced when one of the driver on a drive motor ( 101 ) of the vehicle set drive torque (M _motor ) exceeds a threshold (M_Thr). A method according to claim 11, characterized in that the braking force reduction is accelerated when the drive torque set by the driver (M _motor ) exceeds the threshold value (M_Thr). Method according to claim 11 or 12, characterized that the threshold (M_Thr) depends on the determined Gradient size (Road_Grad) is determined. Method according to one of the preceding claims, characterized in that the braking force and / or the braking force gradient dependent on from the determined gradient size (Road_Grad) is determined. Computer program product comprising software code sections, with which a method according to any one of the preceding claims is executable, when the software code sections are executed on a processor device. Computer program product according to claim 15, characterized in that the software code sections are part of a Software are, with a speed control, in particular an HDC function, executed when running the software on a processor device. Device for assisting a starting process of a vehicle on the basis of a driving state brought about by the driver of the vehicle by a brake actuation, in particular a vehicle standstill, comprising: at least one determining device 301 ; 302 ), with which a slope variable (Road_Grad) characterizing the gradient angle of the gradient and a direction of approach desired by a driver can be determined, - an evaluation device ( 302 ), in which the ascertained approach direction can be evaluated in relation to the ascertained gradient size (Road_Grad), and - a control device ( 304 ), with which a braking force in a brake system of the vehicle is adjustable according to a result of the evaluation made after a driver-side release of the brake has been determined. Device according to claim 17, characterized in that it is part of a speed control system ( 112 ), in particular an HDC control system.