DE102004043119B4 - Method for determining parameters - Google Patents

Abstract

The invention relates to a method for starting assistance on a slope with a brake activated at standstill. To improve start-up assistance and to make it cost-effective, the method provides the following steps: reducing the brake pressure in the wheel brakes, determining data at the time of vehicle movement, and determining an externally-caused, vehicle-driving or braking-stop size from the determined data.

Description

The invention relates to a method for determining parameters of a vehicle with a brake activated at standstill and to a method for setting a brake pressure in a brake cylinder on at least one wheel of a vehicle, with a brake which is maintained at standstill of the vehicle by a brake actuated by the driver.

From the DE 36 18 532 A1 is a traction help for a motor vehicle on a slope known. These so-called start-up aids on the mountain should simplify the complicated handling of brake, parking brake, clutch and engine. At the same time, however, it should be ensured that the vehicle does not roll backwards in order, for example, to avoid collisions with vehicles standing downhill. If a vehicle wants to start on the mountain, apply in first approximation in 1 schematically represented laws. The weight F _{G of} the vehicle can be decomposed into a normal component F _N and a tangential component F _T on the tire of a unicycle model. F _T leads together with the tire radius r _R to a downhill torque M _H according to the formula M _H = F _G × sin α × r _R

Here, α is the pitch angle. The downhill torque M _H would result in the vehicle rolling downhill without further intervention. It is counteracted by the holding braking torque M _B and the additional motor torque M _M introduced during the start. A traction aid on the mountain, for example, affect the braking torque M _B. However, the influence must be such that it is ensured at all times that the inequality M _H <M _B + M _M is satisfied. Only then is a backward rolling of the vehicle safely avoided. In order to meet the above equation, the knowledge of the slope output torque is required. According to the statements in the DE 36 18 532 A1 , The brake system has a arranged between the master cylinder and the wheel brake valve, which is closed at standstill to maintain a brake actuation pressure and is opened to cancel the brake actuation pressure. If the vehicle is to be brought from a standstill in a driving condition, it is checked whether the motor torque predetermined by the driver corresponds to a starting torque required for starting. In this case, the required starting torque is determined as a function of a sensor-detected current angle of inclination of the vehicle on a slope and the vehicle weight.

In addition, it is known to determine an externally caused, the vehicle driving or braking size in an observer. The observer receives internally induced quantities driving or braking the vehicle, determines from this how the longitudinal dynamics of the vehicle would have to develop, compares this result with actually measured values of the longitudinal dynamics, and excludes from any deviations externally caused, vehicle driving or braking variables. especially moments ( EP 1 023 547 B1 ).

Furthermore, from the EP 1 023 546 B1 a method of assisting the launching of a vehicle on a hill, in which the vehicle drive torque during startup and externally caused moments are determined, and the service brake, the parking brake and / or the engine torque are influenced in dependence on the determined moments.

M_B

= erforderliches Bremsmoment

M_H

= Hangabtriebsmoment

M_A

= Antriebsmoment des Motors

If the driver releases the brake in the method described above for starting up, the brake pressure is initially held and reduced when the clutch is engaged via the torque balance. This is: M _B = M _H - M _A

M _B

= required braking torque

M _H

= Downhill torque

M _A

= Drive torque of the motor

• a) zum Aktivieren der Funktion und
• b) zur Berechnung des Hangabtriebsmoments

erforderlich sind.The function is activated only when stopping on gradients. To obtain the functionality described above, sensors are used which

• a) to activate the function and
• b) for the calculation of the slope output torque

required are.

bestimmt werden kann.Inclination sensors or vehicle speed and acceleration sensors are used to calculate the slope output torque, by means of whose output signals a gradient can be determined. In this case, the acceleration signal contains not only the acceleration in the longitudinal direction of the vehicle but also the gravitational component g · sinα. On the other hand, the vehicle speed can be determined via the wheel speed sensors. Thus, the differentiated value of the vehicle speed exactly corresponds to the actual acceleration of the acceleration signal, so that the slope of the relationship

can be determined.

The DE 100 41 444 A1 discloses a method for controlling wheel brakes of a vehicle, wherein in at least one operating condition with the brake pedal applied, braking force is maintained on at least one wheel of the vehicle regardless of the amount of pedaling, the lane inclination being determined and the braking force being maintained when the roadway incline is in the direction of future direction of travel of the vehicle shows, and in the presence of at least one condition, in particular when a driver's approach has been detected, the braking force is reduced again.

In the DE 199 49 203 A1 is a motor vehicle with at least one drive means, such as an internal combustion engine, at least one output device, at least one arranged between the drive means and the drive means torque transmission device, such as a clutch, at least one transmission device which is substantially in the torque flow between the at least one drive means and the output device is arranged, and described at least one Hillholder device for at least temporarily preventing unwanted movements of the motor vehicle. The motor vehicle furthermore has at least one electronically controlled clutch device for controlling and / or regulating the clutch actuation or an automated manual transmission, wherein a braking effect can be exerted on at least one part of the motor vehicle at least indirectly from the hillholder device under predetermined conditions.

Furthermore, starting aids for motor vehicles are known on a slope without a sensor. It sees the DE 199 50 162 A1 to trigger the traction help, the brake pressure must be increased by the driver, so that a time-delayed deactivation of the service brake control pressure takes place.

The DE 195 25 552 A1 discloses a method and an arrangement for holding a vehicle on an inclined road and when starting on the mountain, in which, taking into account the vehicle speed and the brake pedal operation or corresponding criteria, braking force is applied to one or more vehicle wheels, in particular to the wheels of an axle, ie maintained, increased and dismantled. In addition to sensing the vehicle speed and brake pedal operation, the starting torque is determined, the operating condition of the vehicle engine or the ignition is determined, and the actuation of a vehicle parking brake and the activation or activation of the holding system are determined, wherein these data are logically linked and evaluated.

• – Aus Komfortgründen muss auf die automatische Aktivierung verzichtet werden, um ein unerwünschtes Anfahren gegen einen Bremsdruck in der Ebene zu vermeiden. Das System muss bei Bedarf manuell aktiviert werden.
• – Das Hangabtriebsmoment kann nicht bestimmt werden, wodurch je nach Steigung entweder ein Zurückrallen des Fahrzeugs oder ein Anfahren gegen Bremsdruck unausweichlich ist.

Systems without gradient sensor have the following disadvantages:

• - For reasons of comfort, the automatic activation must be avoided in order to avoid an undesired approach to a brake pressure in the plane. The system must be activated manually if necessary.
• - The downhill torque can not be determined, which is inevitable depending on the slope either a ricochet of the vehicle or a start against brake pressure.

The invention has for its object to provide a further method for supporting the active startup of a motor vehicle on a slope with an activated at standstill brake that improves transitions from a standstill in a driving cost.

According to the invention, this object is achieved by the following steps:
Reducing the brake pressure in the wheel brakes,
Determining vehicle data at the time of vehicle movement or at a brake pressure below a threshold and
Determining an externally caused, the vehicle driving or braking size from the determined vehicle data.

mit

p_b

= Bremsdruck

μ_b

= Bremsbelagreibwert

r_b

= effektiver Reibradius

A_RBZ

= druckbeaufschlagte Fläche im Radbremszylinder

m_Fzg

= Fahrzeugmasse

r_R

= Reifenradius

By controlled pressure reduction and simultaneous observation of the vehicle movement, a slope estimation can be made during the starting process of a vehicle (change of the driver from brake to accelerator pedal) on a slope. This can be determined from the brake pressure present during the vehicle movement according to the following relationship

With

p _b

= Brake pressure

μ _b

= Brake pad friction coefficient

_b

= effective friction radius

A _RBZ

= pressurized area in the wheel brake cylinder

m _veh

= Vehicle mass

r _R

= Tire radius

This model-based slope estimation replaces the function of an additional tilt sensor generated by the method according to the invention can be saved. With the slope estimation, the downhill torque M _H can be calculated in a model as described in the prior art.

It is advantageous that at the time of movement of the vehicle or when the brake pressure is below a limit value, data is determined which reflects the pressure in the wheel brakes and the rotational behavior of at least one wheel, and the driving variable is determined based on the model based on the model. In this case, the model-based variable M _{H is} calculated from the sensor signals of a brake control, in particular driving stability control, which are already present in a brake system according to the prior art. Because the model-based quantity is calculated from the sensor signals of wheel speed sensors and at least one brake pressure sensor. In order to determine whether the vehicle rolls downhill forwards or backwards, a direction of travel detection is provided in which preferably at least one wheel speed sensor is designed such that it determines the direction of rotation. With the use of direction-detecting wheel sensors, a direction of travel detection can be realized, which detects a direction of the slope (forward or reverse rolling vehicle) of the vehicle moving from standstill.

M_H

= Hangabtriebsmoment

M_BV

= Bremsmoment zum Zeitpunkt der Fahrzeugbewegung

M_A

= Antriebsmoment

ermittelt werden.In addition to the calculation of the slope output torque according to the known models, z. For example, after mFzg · sinα + r _R , the model-based size can also be simplified by the relationship M _H = M _BV - M _A With

M _H

= Downhill torque

M _BV

= Braking torque at the time of vehicle movement

M _A

= Drive torque

be determined.

If the brake pressure falls below a limit value and no movement of the vehicle is determined, a standstill in the plane can be concluded. The traction help can then be deactivated.

In addition to the inventive determination of parameters for a traction help, the above object is also achieved by a method for setting a brake pressure in a brake cylinder on at least one wheel of a vehicle, with a standstill of the vehicle, a braked by the driver brake pressure aufrechthaltenden brake comprising the steps :
Recognition of a driver's approach,
Reduction of the brake pressure in the brake in response to the detected start-up request
Monitoring a vehicle movement and maintaining the brake pressure and / or increasing the brake pressure by a predetermined value after detected vehicle movement.

The model-based slope estimation for the functionality of a traction help with the inventive setting of a brake pressure according to claim 7 is not necessarily required because the brake pressure is already set according to the slope output torque M _H.

The invention thus provides a method for determining parameters for a starting assistance of a motor vehicle and a method for adjusting a brake pressure whose brake is activated at standstill and is to be deactivated controllable without actuation of the driver. In the method according to the invention, either data representing the slope is determined, this information going into the consideration of an operating state of the vehicle in which the vehicle is to be moved from standstill or the operating state in which the vehicle is moving from standstill should be set. The determination or setting of the operating state from which the vehicle is to be moved out of a standstill requires the detection of a start-up request, which is specified by the driver or a vehicle control system. In order to implement the approach, data or parameters or operating states of the vehicle are required that actually permit a transition from standstill to a driving operation. In particular, a torque balance of drive and braking torque is set as a function of vehicle data into which the externally generated driving variable of the downhill torque M _H is received.

Compared to a system with inclination sensor, there is the advantage of cost savings since the sensor can be dispensed with in the method according to the invention. At the same time the disadvantages of a system without inclination sensor are largely avoided. The manual activation of the system is no longer required because the system avoids starting against brake pressure in the plane by releasing the pressure. In addition to this comfort improvement, there is a cost savings, since the control element for activating the system can be dispensed with.

Another advantage is that the downgrade torque can be easily determined and thus, with the exception of a short roll, a rolling back of the vehicle or a start against brake pressure is avoided.

An embodiment of the invention will be described below with reference to the drawing and advantageously further features.

In the drawing, the brake pressure curve over time in at least one wheel cylinder of a vehicle brake at a traction help is shown. With 10 is called the brake pressure curve in the known starting aids, with 11 the brake pressure curve according to the inventive method on a slope and with 12 the brake pressure curve in the plane. At the time 13 the driver releases the brake and at the time 14 the driver closes the clutch. The brake pressure included when stopping by the driver 15 will at the time 13 when releasing the brake pedal no longer held, but drained controlled in a short period, so that the brake pressure curve 17 established. By means of the existing wheel sensors (wheel speed sensors) can the rolling of the vehicle at the time 16 detected on the basis of an output from the wheel speed sensors angular momentum or speed variable and the brake pressure at this time be included. From the torque balance listed above, the downhill torque can now be determined as follows: Downhill torque = braking torque at the time of unrolling - drive torque of the motor (usually 0 because it has not been engaged yet)

ermittelten Steigungswinkel berücksichtigt.Subsequently, the vehicle can by a low active pressure build-up at the time 18 brought to a standstill and waiting the engagement of the driver. The pressure build-up can take place via the activation of the pump present in the brake system or via an active booster. The value of the brake pressure to be controlled can be predetermined or model-based, with the estimate being based on the relationship

calculated slope angle taken into account.

If the vehicle is in the plane, it will not move, resulting in a complete reduction in pressure or a pressure drop below a limit. The limit value can be dimensioned depending on the vehicle mass so that the vehicle in each case, d. H. would have to roll even on small gradients. If no vehicle movement is detected when this limit value is undershot, the brake pressure can be reduced more quickly. If this reduction in pressure is completed before the driver is engaged, the uncomfortable approach against a brake pressure is avoided.

Claims (9)

Method for determining parameters of a vehicle with a brake activated at standstill, characterized by the steps Reducing the brake pressure in the wheel brakes, Determining vehicle data at the time of vehicle movement or at a brake pressure below a threshold and Determining an externally caused, the vehicle driving or braking size from the determined vehicle data. A method according to claim 1, characterized in that at the time of movement of the vehicle, data are determined which reflect the pressure in the wheel brakes and the rotational behavior of at least one wheel, and from the data, the driving variable is determined model-based. A method according to claim 1 or 2, characterized in that the model-based variable from the sensor signals of a brake control, in particular driving stability control, is calculated. Method according to one of claims 1 to 3, characterized in that the model-based variable from the sensor signals of wheel speed sensors and at least one brake pressure sensor is calculated. A method according to claim 3 or 4, characterized in that a direction of travel detection is provided, preferably at least one wheel speed sensor is designed so that it determines the direction of rotation. Method according to claim 1 or 2, characterized in that the model-based quantity is determined by the relationship Downhill torque = braking torque at the time of vehicle movement - drive torque is determined. A method for setting a brake pressure in a brake cylinder on at least one wheel of a vehicle, with a brake at a standstill of the vehicle brake pressure aufrechthaltenden brake characterized by the steps detecting a driver's Anfahrwunsches, reducing the brake pressure in the brake in response to the detected Anfahrwunsch Monitoring a vehicle movement and maintaining the brake pressure and / or increasing the brake pressure by a predetermined amount after detected vehicle movement. A method according to claim 7, characterized in that the vehicle movement is determined based on the wheel speed sensors of the vehicle. A method according to claim 7 or 8, characterized in that the direction of the vehicle movement is determined by means of rotational direction detecting wheel speed sensors.

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