DE10242122A1 - Motor vehicle hill holder system in which a minimum engine set of torque is determined when the vehicle is stationary and the engine torque is then monitored until it exceeds the minimum, at which point the brakes are released - Google Patents

Abstract

Method for preventing a motor vehicle from rolling back when it is driving up a hill, whereby the brake pressure is kept at a high level until the engine torque (MANTR) has reached a minimum level (Mmin). The method has the following steps: determination of the wheel longitudinal force and the vehicle inertia force when stopped; calculation of a minimum torque value based on the measured values; calculation of the engine torque when setting off; and releasing of the brakes when the engine torque exceeds the minimum torque. An Independent claim is made for a system for preventing a motor vehicle from rolling back on a hill.

Description

The invention relates to a method and a system for preventing a vehicle from rolling back when starting on an incline according to the preamble of the claim 1 or 5.

Procedures and systems of the beginning mentioned type, which the driver of a motor vehicle when starting support on the mountain, are also referred to in the literature as "hillholders" Hillholder essentially works on the following principle: Starting a car on a slope, the wheel brake pressure is automatic kept at a high level so that the vehicle is disengaged Condition does not roll back. One press the handbrake is no longer required. The driver can Now grind in the clutch and move off in the usual way. Reached the drive torque generated by the vehicle engine a predetermined Threshold, the brake pressure is automatically reduced.

A critical phase in this process is the moment the vehicle is started and released Brakes. If the wheel brake pressure is released too early, this leads to roll back of the vehicle. On the other hand, if the brake pressure is held too long, this leads to an unnecessary Delay of Starting process or a jerky and therefore uncomfortable starting process and especially to a higher one Load on engine and clutch.

Hillholder systems known to date control the brake pressure of the wheel brakes depending on the current drive torque. The brake pressure is reduced at the moment when the drive torque of the internal combustion engine exceeds the downhill torque of the vehicle. The downhill drive torque is in turn determined by an evaluation of the braking behavior of the vehicle during a Stopping process estimated. This is relatively inaccurate.

It is therefore the object of the present invention to optimize the control of the wheel brakes on a hill holder.

This object is achieved according to the invention by the features specified in claim 1 or 5. Further Embodiments of the invention are the subject of dependent claims.

The main idea of the invention consists of the minimum drive torque required to start the vehicle (corresponds approximately to the downhill force) from the wheel longitudinal forces and the inertia force to calculate the vehicle. For this, the on the wheels of the Longitudinal forces acting on the vehicle as well the inertia of the Vehicle using suitable sensors during a stopping process determined and from this the minimum drive torque calculated. The forces determined or the minimum drive torque will be while the vehicle is stationary preferably saved. Finally, when the vehicle starts up the current drive torque is determined and compared with the calculated minimum drive torque. Reaches or exceeds the current drive torque is the minimum drive torque, so the brake pressure is reduced and the vehicle can move without risk of rollback set in motion.

So far in this description and in the claims to certain powers is referred, the respective statement applies equally to the corresponding Moments and vice versa, as well as for them derived sizes. A restriction should not be done with it.

By determining the wheel longitudinal forces and the inertia the minimum drive torque required to start the vehicle is very high exactly determinable. The wheel brakes can thus at that exact moment solved in which the drive torque generated by the vehicle engine and the downhill torque is the same.

For example, to determine the longitudinal wheel forces Sensors are used that are incorporated into the tire wall or are applied to the tire wall. Optionally, too So-called tire contact sensors are used, which are on the tire tread are arranged.

When transferring a drive or braking torque on a wheel, the sensors generate as a result of Deformation of the tire a corresponding signal. When using Several sensors can also change the phase position between two Sensor measuring signals be evaluated. In this case the change in phase is on Measure of that from Wheel transferred to the road personnel or moments.

The inertia force can e.g. in a known manner by evaluating the wheel speed sensors and calculating the deceleration of the Vehicle can be determined.

The wheel longitudinal forces and the inertia force are preferably calculated at a vehicle speed, the bigger is as a given minimum speed. The minimum speed is at least 3, preferably at least 5 km / h. This has the advantage a steadier vehicle behavior and a measuring range that can be detected exactly by the sensors.

The current engine torque and the engine speed are required to calculate the current drive torque during a start-up process. The corresponding signals are preferably filmed tert to eliminate unwanted interference.

When calculating the current Drive torque during of a starting process, the motor moment of inertia is preferably also taken into account.

A Hillholder system according to the invention comprises at least one wheel brake, a wheel speed sensor, engine speed sensor and a sensor system for measuring longitudinal wheel forces and a control unit, the to carry out of the method described above set up accordingly is.

The invention is illustrated below the attached Exemplary drawings closer explained. Show it:

1 a vehicle starting on an incline with the forces acting on the vehicle;

2 a schematic representation of a Hillholder system integrated in the vehicle;

3 a flow chart to explain the essential method steps of the Hillholder method according to the invention; and

4 a flowchart to explain a specific embodiment of the Hillholder method according to the invention.

1 shows a snapshot of a vehicle 1 during a stopping process that is moving and decelerating on a slope (slope angle α) at a speed v. As a result of the application of the wheel brakes 4 work on the wheels 8th the forces F _LVL , F _LHL in the longitudinal direction of the wheel. On all four wheels 8th of the vehicle 1 the wheel longitudinal forces F _{L also} contribute FL = F LVL + F LVR + F LHL + F LHR (F _LVL : front left; F _LVR : front right; F _LHL : rear left; F _LHR rear right)

When the steering is not turned, the longitudinal wheel forces F _L correspond to the wheel forces acting in the longitudinal direction of the vehicle. If, on the other hand, the steering is turned, the resulting force acting in the longitudinal direction of the vehicle can be determined, for example, by evaluating the steering angle. The force acting in the longitudinal direction of the vehicle can also be determined, for example, by evaluating the longitudinal and transverse wheel forces, provided that a corresponding sensor system is provided. When calculating the minimum drive torque, however, the influence of the steering position can usually be neglected.

Sensors are used to determine the longitudinal wheel forces 9 provided (cf. 2 ), which are arranged for example in the tire wall. The change of from the sensors 9 The measurement signals supplied are a measure of the deformation of the tire and thus of that on a wheel 8th moments transmitted to the tire.

As in 1 An inertial force F _T and a downhill force F _H on the vehicle can also be seen during the stopping process 1 ,

The inertial force F _T = m · a can be determined by knowing the vehicle mass m by evaluating the wheel speeds n and calculating the vehicle acceleration (deceleration) a. For the minimum drive torque required for starting, the following therefore applies: M min = –F H R = (F L - m a) r where r is the wheel radius. The minimum drive torque thus corresponds to the product of the slope downforce F _H and the wheel radius, neglecting frictional forces.

The minimum drive torque M _min determined in this way is stored in the system during vehicle standstill. In a subsequent starting process, the current drive torque M _ANTR is finally _compared with the minimum drive torque M _min .

The current drive torque M _ANTR is determined from the current motor torque M _Mot and the motor moment of inertia M _dyn . Engine torque M _Mot and engine speed n _Mot are supplied by appropriate devices or sensors. The motor speed n _Mot is used in particular to calculate the motor moment of inertia M _dyn :

Here J _{Mot is} the moment of inertia of the motor.

The current drive torque M _ANTR is thus calculated as: M ANTR = (M Mot - M dyn ) * I ges

Where i _{tot is} the total transmission ratio of the drive train.

The brake is released during a starting process at the moment when the drive torque M _{ANTR is} sufficiently large to prevent the vehicle from rolling back, ie if M ANTR ≥ M min

2 shows a corresponding Hillholder system for performing the method described above. The system essentially comprises a control unit 2 who have signals from a wheel speed sensor 3 , a sensor system for measuring the longitudinal wheel forces 5 , a device for determining the current engine torque 6 , and an engine speed sensor 7 receives, and which is able to a wheel brake 4 to control in the manner described above.

As mentioned, the wheel force measures sensors 5 the wheel longitudinal forces F _L. The vehicle acceleration or deceleration a is based on that of the wheel speed sensor 3 delivered signals calculated. The minimum drive torque M _min can be calculated in a simple manner using these values.

To calculate the current drive torque M _ANTR during a start-up, the device 6 to determine the engine torque M _Mot and the engine speed sensor 7 received signals evaluated. Both signals can be filtered using suitable filters in order to reduce interference.

The current drive torque M _ANTR is finally calculated as described above.

3 and 4 show the essential process steps in the implementation of the method described above in the form of a flow chart. 3 shows the calculation of the minimum drive torque M _min during a stopping process and 4 releasing the brakes 4 during a start-up process.

In steps 10 and 11, the control unit 2 first the longitudinal wheel forces F _L and the vehicle acceleration a are determined and the minimum drive torque M _{min is} calculated therefrom in step 12. This value is, for example, in the control unit 2 saved until the next start.

When starting, then according to step 13 of 4 that of the facility 6 received engine torque M _Mot evaluated and in step 14 the engine moment of inertia M _dyn calculated taking into account the engine speed n _Mot . The current drive torque M _ANTR is the result of the evaluation of step 15.

The current drive torque M _ANTR is finally compared in step 16 with the minimum drive torque M _min . If the current drive torque M _{ANTR is} less than the required minimum drive torque M _min , the current drive torque M _{ANTR is recalculated} at regular times (branching back to step 13). If, on the other hand, the current drive torque M _{ANTR is} greater than or equal to the minimum drive torque M _min , the brake pressure is released in step 17 and the brake 4 Approved.

The invention thus has the advantage that the clutch state and the braking forces no longer have to be taken into account when calculating the minimum drive torque M _min , and thus a more accurate calculation of the minimum drive torque M _{min is} possible.

1

vehicle

2

control device

3

Speed sensor

4

wheel brake

5

sensors for measuring the longitudinal wheel forces

6

Facility to determine the engine torque

7

Engine tachometer

8th

wheel

9

Wheel sensors

10-17

steps

v

speed

F _L

Wheel longitudinal force

F _H

Downhill force

F _T

inertial force

n

wheel speed

M _{Mo t}

engine torque

n _Mot

Engine speed

α

lead angle

Claims (6)

Method for preventing a motor vehicle from rolling backwards ( 1 ) when starting on an incline, in which the wheel brake pressure is maintained at a high level until the drive torque (M _ANTR ) generated by a vehicle engine has _reached a predetermined minimum drive torque (M _min ), characterized by the following steps: - determining the Longitudinal wheel forces (F _L ) and the inertia force (F _T ) of the vehicle ( 1 ) during a stopping process, - calculating a minimum drive torque (M _min ) based on the determined values (F _L , F _T ), - calculating the current drive torque (M _Antr ) during a start-up process, and - releasing the brakes ( 4 ) if the current drive torque (M _Antr ) is greater than or equal to the minimum drive torque (M _min ). A method according to claim 1, characterized in that the calculated minimum drive torque (M _min ) or a value derived therefrom is stored. Method according to claim 1 or 2, characterized in that the longitudinal wheel forces (F _L ) and the inertial force (F _T ) are calculated at a vehicle speed (v) which is greater than a predetermined minimum speed, in particular greater than 3 km / h. Method according to one of the preceding claims, characterized in that the signal of a device ( 6 ) to record the engine torque (M _Mot ) and / or a device ( 7 ) is filtered to record the engine speed (n _mot ). System for preventing the rolling back of a motor vehicle ( 1 ) when starting on a slope, including a wheel brake ( 4 ), a wheel speed sensor ( 3 ), as well as means ( 6 ) for the detection of the engine torque (M _Mot ), characterized by a sensor system ( 5 ) for measuring the wheel longitudinal forces (F _L ) during a stopping process and a control unit ( 2 ), which calculates a minimum drive torque (M _min ) on the basis of the longitudinal wheel forces (F _L ) and an inertia force (F _T ) and which determines the current drive torque (M _Antr ) of the vehicle engine during a start-up process and the brakes ( 4 ) triggers when the current drive torque (M _Antr ) reaches a value that is equal to or almost the same as the minimum drive torque (M _min ). System according to claim 5, characterized in that filters are provided to filter the engine torque (M _Mot ) and / or the engine speed (n _Mot ).