GB2394311A

GB2394311A - A method / device for improving vehicle traction.

Info

Publication number: GB2394311A
Application number: GB0319689A
Authority: GB
Inventors: Siegried Senedzuk; Ulrich Hessmert
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2002-08-27
Filing date: 2003-08-21
Publication date: 2004-04-21
Anticipated expiration: 2023-08-21
Also published as: GB0319689D0; GB2394311B; DE10239120A1

Abstract

The method of improving the vehicle traction, includes a step of reducing an engine moment (torque) after the determination (step 102) of slip g of at least one drive wheel has exceeded a first drive slip threshold g 1. Further, the engine torque is increased, steps 112 or 114, after the determination (step 104) of slip g of at least one drive wheel has not exceeded a second drive slip threshold g 2. The increasing of the engine torque is characterized by at least one magnitude into which the development over time of a magnitude which affects the driving dynamics enters. The increase in the engine torque may be implemented at different rates based on the determination of a time interval W t, step 108. The time interval is preferably determined from the time in which the first drive slip threshold is exceeded to the time in which the 2<nd> drive slip threshold is not exceeded. The determined time interval is compared to a predetermined limit, tmax, whereby if the time interval is grater than the predetermined limit than the engine torque is increased slowly, alternatively if the time interval is less than the predetermined limit than the engine torque is increased quickly.

Description

Improvement of vehicle traction Prior art

The invention is based on a drive slip regulation system according to the features of the pre-characterizing clauses of the independent claims.

15 Such a drive slip regulation system is known from DE 37 43 471 Al. In the case of unpermitted drive slip on at least one wheel, it reduces the engine moment and then raises it again in steps. The step height is kept constant, and the hold time between steps is varied depending on the slip, 20 the vehicle acceleration and/or the number of regulation cycles which have already occurred.

The features of the pre-characterizing clauses of the independent claims are taken from DE 37 43 471 Al.

Advantages of the invention The invention is based on a method and/or a device to 30 improve the vehicle traction. In this method, after a first drive slip threshold is overshot by the slip of at least one driven wheel, the engine moment is reduced. After a second drive slip threshold is subsequently undershot, the engine moment is raised again. The core of the invention is

characterized in that raising the engine moment is characterized by at least one magnitude into which the development over time of a magnitude which affects the driving dynamics enters. The advantage of the invention is 5 that because of the involvement of the development over time of a magnitude which affects the driving dynamics, it is made possible to allow facts which are relevant to the driving dynamics and before the engine intervention in time to affect the raising of the engine moment, and in 10 particular to detect and mask out short-term disturbances (e.g. short-term variations of the wheel rotational speed caused by unevennesses in the road).

The magnitude which affects the driving dynamics can be a 15 magnitude which describes the contact between a Lyre and the road surface. In particular, magnitudes such as the wheel slip (the longitudinal slip of the wheel), a friction index which describes the wheel adhesion or magnitudes related to the tyre deformation are conceivable.

An advantageous form of the invention is characterized in that the magnitude which affects the driving dynamics is the wheel slip of at least one wheel of the vehicle. Since in the case of ASP (drive slip regulation) the wheel slip 25 of the vehicle is captured in any case, implementation of the invention in the vehicle controller is possible without significant additional cost.

Another form of the invention is characterized in that the 30 development over time of the magnitude which affects the driving dynamics enters the magnitude which characterizes the raising of the engine moment in such a way that:

- the time interval between overshooting the first drive slip threshold and undershooting the second drive slip threshold is determined, and - the determined time interval enters the magnitude 5 which characterizes the raising of the engine moment.

In this way the duration during which the critical slip limit was overshot is captured. It is thus possible to distinguish whether a short- term overshooting of the slip 10 limit or a longer overshooting of the slip limit was involved. Different handling of these two cases is thus possible. Another advantageous form is characterized in that the 15 magnitude which characterizes the raising of the engine moment is the rate at which the engine moment is raised or changed. This makes it possible to raise the engine moment faster in situations which are not critical to the driving dynamics than after situations which are critical to the 20 driving dynamics.

An advantageous form consists of raising the engine moment in a jump in the case of short-term overshooting of the drive slip threshold. The term "short-term' is understood 25 to mean that the duration of overshooting the drive slip threshold is less than a specifiable limit. The overshooting duration is a time interval, the start of which is characterized by the time at which the first drive slip threshold is overshot, and the end of which is 30 characterized by the time at which the second drive slip threshold is undershot.

In an advantageous form, it is also possible that the magnitude which characterizes the raising of the engine moment is the amount by which the engine moment is raised.

Thus the engine moment can be raised by a greater amount in 5 situations which are not critical to the driving dynamics than after situations which are critical to the driving dynamics are present.

An advantageous form is characterized in that the amount by 10 which the engine moment is raised is chosen so that the engine moment which is present after the raising corresponds to what the driver specified. This makes it possible, in situations which are recognized as uncritical, to deactivate the ASR regulation and go over to controlling 15 the engine as the driver wishes.

An advantageous form consists of raising the engine moment in a jump if the determined time interval is less than a limit. An advantageous form is characterized in that: - the engine moment is raised faster and/or more strongly if the determined time interval is less than 25 a limit, and the engine moment is raised more slowly and/or more weakly if the determined time interval is greater than a limit.

30 Another advantageous form is characterized in that the development over time of the magnitude which affects the driving dynamics enters the magnitude which characterizes the raising of the engine moment in such a way that:

- the course of the slip over time between the overshooting of a first drive slip threshold and the undershooting of a second drive slip threshold is 5 determined, and - the course of the slip over time is integrated over time, and enters the magnitude which characterizes the raising of the engine moment.

10 Whereas in the previous form only the time interval between two points was determined, the course of the slip Over time now also has a role. In this way it is possible to distinguish whether the critical drive slip threshold was only overshot by a small amount or whether a large 15 overshooting of the drive slip threshold has taken place.

It is advantageous that the engine moment is raised in a jump if the value which results from integrating the slip over time is less than a limit. In this way, it is possible 20 to raise the engine moment quickly again after small or short-term overshootings of the slip.

It is also advantageous that: 25 - the engine moment is raised faster and/or more strongly if the value which results from integrating the slip over time is less than a limit, and - the engine moment is raised more slowly and/or more weakly if the value which results from integrating the 30 slip over time is greater than a limit.

This form also makes it possible to raise the engine moment quickly again after small or short-term overshootings of the slip.

5 The invention also includes a device to carry out the stated method.

Drawings 10 The drawings consist of Figs. 1 and 2.

Fig. 1 shows the sequence of the method according to the invention. 15 Fig. 2 shows the structure of the device according to the invention. Embodiments 20 In many known drive slip regulation systems, after the permitted slip threshold is undershot, the ASR setpoint moment (i.e. the engine moment which the ASR requires) is raised depending on the current operating parameters (residual slip, current acceleration). The duration of the 25 preceding slip phase is not taken into account. The result is that because of the only gradual increase of torque, the traction is temporarily limited. This is noticeable to the driver, and results in a noticeable loss of comfort while driving. However, if only a short-term overshooting of the permitted slip is present, it is possible to deduce an uncritical road disturbance, and therefore the setpoint torque can be

raised abruptly. A short-term road disturbance is present, for instance, if a wheel rotational speed changes for a short time because of an uneven road composition. Cases in which a wheel loses contact with the road surface for a 5 short time because of a spatially short lowering of the road can be imagined.

The temporary restriction of the vehicle traction can thus be significantly reduced. Therefore, after a merely short 10 term overshooting of the permitted slip range, the setpoint moment M_ ASR which ASR specifies is set to the maximum possible value.

In engine controllers, the engine is often controlled so 15 that the output engine moment is Mmot = min (M_driverreq, M_ ASR) where "min" means the smaller of the two values in the 20 following parentheses. Also M_driverreq.: the engine moment which the driver requests via the accelerator pedal position, and - M_ASR: the driver moment which the ASR regulation 25specifies. If M_ ASR is set to the maximum possible value for the engine as mentioned, M_driverreq. is always less than M_ ASR, and the result is Mmot = M_driverreq.

Therefore, there is now no further limitation of the engine power. Alternatively, an accelerated raising rate of the engine setpoint moment (idea the rate at which the engine moment increases over time) depending on the preceding slip 5 phase can be implemented.

The slip phase can be evaluated as a function of the duration and/or the amount of the slip (slip integral). In a first form, only the time span t2 - tl is considered. In 10 a second form, the integral t2 I2(t)dt tl is calculated. tl is the time at which a first specified 15 slip threshold is overshot. t2 is the time at which a second specified slip threshold is undershot. \(t) identifies the course of the slip over time. t is the time variable. 20 The sequence of one form of the method according to the invention is shown in Fig. 1. After the start of the method in block 100, in block 102 there is a test for whether the existing wheel slip overshoots a first threshold value X1. If this is not the case (marked with "n"), there 25 is a return to block 100 (because an uncritical situation is present). But if it is the case (marked with "y"), in block 104 a further interrogation is carried out: < X2.

I.e., whether the wheel slip now undershoots a second threshold value X2 is now investigated. If this is not the 30 case, there is a branch to block 106. There the time is incremented by At, and then the interrogation 104 takes

place again. However, if the interrogation 104 is fulfilled, i.e. in block 102 the wheel slip limit 11 was overshot and at a later time in block 104 the wheel slip limit X2 was undershot, in block 108 the time interval 5 At = t2 - tl is determined. t2 is the time at which the wheel slip limit X2 was undershot again, i.e. the wheel is now no longer in the critical slip range. tl is the time at which the wheel slip limit X1 was overshot, i.e. the wheel came into a critical slip range at this time. Following 10 block 108, in block 110 an interrogation At > tmax takes place. As mentioned, At is the time interval between overshooting and undershooting the slip thresholds, and tmax is a specifiable limit. If At > tmax (this means that there is a sufficiently large time interval between 15 overshooting and undershooting the slip thresholds), in block 112 the engine moment is slowly raised again, as specified by the ASR regulation. In the case of drive slip regulation, after an ASR intervention the engine moment is raised again with a specified rate of change.

On the other hand, if in block 110 it is established that At < tmax, i.e. the condition in block 110 is not fulfilled, there is a branch onward to block 114. In block 114, the engine moment is raised again very quickly 25 or even in a jump, because it was recognised that only an uncritical short-term disturbance was present.

The structure of the device according to the invention is shown in Fig. 2. Block 200 contains sensor means. By these 30 sensor means, for instance, the wheel slip is determined and passed on to the controller 201. This controller contains engine moment raising means 202, engine moment

reduction means 204 and other functions 203. The output signals of the controller drive actuators 205, for instance they can control a butterfly valve.

Claims

1. Method of improving the vehicle traction of a vehicle, wherein - after a first drive slip threshold (71) is overshot by the slip of at least one driven wheel, the engine moment (Mmot) is reduced, - after a second drive slip threshold (12) is undershot, 10 the engine moment (Mmot) is raised again, characterized in that raising the engine moment is characterized by at least one magnitude into which the development over time of a magnitude which affects the driving dynamics enters.

2. Method according to Claim 1, characterized in that the magnitude which affects the driving dynamics is the wheel slip of at least one wheel of the vehicle.

3. Method according to Claim 1, characterized in that the development over time of the magnitude which affects the driving dynamics enters the magnitude which characterizes the raising of the engine moment in such a way that - the time interval between overshooting the first drive slip threshold (71) and undershooting the second drive slip threshold (12) is determined, and - the determined time interval enters the magnitude 30 which characterizes the raising of the engine moment.

4. Method according to Claim 1, characterized in that the magnitude which characterizes the raising of the engine moment is the rate of change of the engine moment.

5 5. Method according to Claim 1, characterized in that the magnitude which characterizes the raising of the engine moment (Mmot) is the amount by which the engine moment is raised. 10

6. Method according to Claim 5, characterized in that - the amount by which the engine moment is raised is chosen so that the engine moment (Mmot) which is present after the raising corresponds to what the 15 driver specified (M_driverreq.).

7. Method according to Claim 3, characterized in that the engine moment (Mmot) is raised in a jump if the determined time interval is less than a limit.

8. Method according to Claim 3, characterized in that - the engine moment (Mmot) is raised faster and/or more strongly if the determined time interval is less than 25 a limit, and - the engine moment (Mmot) is raised more slowly and/or more weakly if the determined time interval is greater than a limit.

30

9. Method according to Claim 2, characterized in that the development over time of the magnitude which affects the driving dynamics enters the magnitude which characterizes the raising of the engine moment in such a way that

the course of the slip (aft)) over time between the overshooting of a first drive slip threshold (71) and the undershooting of a second drive slip threshold 5 (12) is determined, and the course of the slip over time is integrated over time, and enters the magnitude which characterizes the raising of the engine moment.

10 10. Method according to Claim 9, characterized in that the engine moment (Mmot) is raised in a jump if the value which results from integrating the slip over time is less than a limit. 15

11. Method according to Claim 9, characterized in that - the engine moment (Mmot) is raised faster and/or more strongly if the value which results from integrating the slip over time is less than a limit, and 20 - the engine moment (Mmot) is raised more slowly and/or more weakly if the value which results from integrating the slip over time is greater than a limit. 25

12. Device for improving the vehicle traction, including - engine moment reduction means, in which after a first drive slip threshold (71) is overshot by the slip of at least one driven wheel, the engine moment (Mmot) is 30 reduced,

engine moment raising means, after a second drive slip threshold (72) is undershot, the engine moment (Mmot) is raised again, 5 characterized in that the engine moment raising means are in such a form that raising the engine moment is characterized by at least one magnitude into which the development over time of a magnitude which affects the driving dynamics enters.

13. Method substantially as hereinbefore described with reference to the accompanying drawings.

14. Device substantially as hereinbefore described with 15 reference to the accompanying drawings.