GB2342173A

GB2342173A - Evaluating a substantially periodic signal

Info

Publication number: GB2342173A
Application number: GB9922060A
Authority: GB
Inventors: Ewald Stuible; Frank Sager; Thomas Kahnert
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-09-30
Filing date: 1999-09-17
Publication date: 2000-04-05
Anticipated expiration: 2019-09-17
Also published as: FR2783922A1; JP2000111567A; GB9922060D0; GB2342173B; DE19844780A1

Abstract

A method of rotational speed detection for a substantially periodic signal comprises randomly selecting signal edges for evaluation in the computation of rotational speed, wherein the random selection of evaluation parts of the signal results in their unequal spacing from each other.

Description

2342173 METHOD OF AND EVALUATING MEANS FOR EVALUATING A SUBSTANTIALLY

PERIODIC SIGNAL The present invention relates to a method of and evaluating means for evaluating a substantially periodic signal, especially a rotational speed signal obtained with use of a pulse wheel.

For detection of the rotational speed or translation speed of a shaft of a wheel it is common to use a pulse wheel which is connected with the shaft and the rotational speed of which is ascertained. Such a pulse wheel has a given number of angle marks or teeth together with gaps between the angle marks or teeth and is scanned by a stationary sensor, for example an inductive sensor or a wheel sensor. When the pulse wheel rotates, the sensor supplies an output signal which corresponds with the marks of the pulse wheel. For ascertaining the rotational speed, time spacings between signal flanks are usually evaluated. The shorter the time spacings, the higher the rotational speed. A speeddetermining method in which the rotational speed of a shaft is carried out in the described manner is disclosed in DE-OS 34 23 664.

According to a first aspect of the invention there is provided a method for the evaluation of a substantially periodic signal, in particular a rotational speed signal, in which time intervals between signal edges are evaluated for ascertaining a rotational or translational speed, characterised in that the selection of the signal edges used for ascertaining a rotational or translational speed takes place according to a predeterminable scheme in which the spacings between the signal edges used for rotational speed computation are unequal.

Preferably, the signal edges used for ascertairTing the speed are evaluated according to an irregular time sequence in which the signal edge respectively following an evaluation time point is taken into consideration. For preference, a mean value is formed from several computed rotational or translational speed values or edge spacings. The method ran be used in conjunction with a travel dynamics regulation system or an anti-blocking regulating system, wherein the ascertained rotational speed is the rotational speed of a wheel of a motor vehicle and the translational speed of the wheel is ascertained from the rotational speed of the wheel subject to consideration of the geometric relationships and this is processed by the appropriate regulating system.

2 According to a second aspect of the invention there is provided a device for performance of the method according to the first aspect of the invention, characterised in that a pulse wheel standing in connection with the rotating shaft is scanned by means of a stationary sensor for the production of the signal to be evaluated, the output signal of the sensor being fed to evaluating equipment.

A method exemplifying the invention may have the advantage that inaccuracies, which can arise due to production tolerances in the manufacture of the pulse wheel, have a reduced effect on accuracy in rotational speed detection. Thus, it is possible to use a pulse wheel in which the spacings between angle marks or the lengths of the angle marks or the wheel need not be absolutely identical. This has the advantage that such a pulse wheel can be produced by a more economic method. For example, punched grid pulse wheels can be used in which positive and negative tolerances of the angle marks alternate periodically, whereby corresponding signal edges of a rectangular signal obtained by scanning have shifts in spacing which, in principle, are undesired. These advantages result from a random selection being made for the evaluation of the signal edges. Thus, the inaccuracies caused by production tolerances cancel out in advantageous manner in the ascertaining of rotational speed and in a mean value formation. The method can be used in particularly advantageous manner in travel dynamic regulating systems or motor vehicles, in which not only rotational speeds are computed from the spacing of the signal edges, but also different speeds, for example wheel speeds and the vehicle speed, wherein prevailing conditions such as wheel diameter, number of the angle marks on the pulse wheel, etc. are also taken into consideration.

An example of the method and embodiment of the evaluating means of the present invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic block diagram of rotational speed detecting equipment; Fig. 2 is a diagram of a speed-dependent periodic signal provided by the equipment of Fig. 1; and 3 Fig. 3 is a diagram illustrating a known method of evaluating the signal of Fig. 2 and a method, which exemplifies the invention, of evaluating the same signal.

Referring now to the drawings there is shown in Fig. 1 rotational speed detecting equipment comprising a pulse wheel 10 which has angle marks or teeth 11 and gaps 12 and which is connected with a shaft 13. The marks are scanned by a stationary sensor 14, the output signals of which are formed into rectangular signals and evaluated in computing equipment 15 for ascertaining rotational speed and ascertaining an associated translational speed. The shaft 13 is, for example, a wheel axle of a motor vehicle so that the rotational speed of the wheel can be ascertained by the equipment. Such an equipment is used in conjunction with, in particular, anti-blocking regulating systems (ABS) or travel dynamics regulating systems (TDR), in which different magnitudes relevant for the system are obtained from rotational speeds of wheels. The shaft 13 can also be another shaft of an internal combustion engine, for example a crankshaft or camshaft, in which case the rotational speed of the shaft or a presettable rotational speed mean value can be ascertained.

The sensor 14, for example an inductive sensor, Hall sensor and so forth, supplies an output signal which, after preparation, is present as rectangular signal. The resulting signal course is illustrated in the Figures 2 and 3.

In the case of pulse wheels which are manufactured by certain methods, for example in punched grid pulse wheels, positive and negative tolerances alternate periodically. The individual pitch error changes the sign from angle mark to angle mark. This relationship is due to manufacture and is difficult to reduce. The tolerance relationship illustrated is in Fig. 2, the tolerance being positive, negative and so forth in alternation. In the case of usual signal evaluation methods, in which spacings between presettable signal edges are evaluated, in particular spacings which correspond with associated edges of angle marks, these tolerances can add up in unfavourable manner so that the ascertained rotational speed as well as subsequently formed mean values for the translational speeds to be ascertained are inaccurate.

For higher rotational speeds, the ABS or ESP (electronic stability project) or TDR or other control device or computing equipment can evaluate only a limited number of angle marks, 4 since signal spacings become less as the rotational speed rises. In the case of usual methods of signal evaluation, the last information (signal edge) arriving within a certain regular time interval, for example a 2 millisecond time interval, is evaluated for the computation of rotational speed or translational speed. For certain rotational speeds, exactly every second signal edge or correspondingly every second angle mark edge of the pulse wheel is then evaluated. This leads, in the case of the alternate positive or negative tolerances illustrated in Fig. 2, to only positive or only negative tolerances entedng into the computation, which then accumulate unfavourably in the computation. Since the filtering of the translational speed signals is based substantially on a mean value formation, this filtering is ineffective at a corresponding resonance speed. The large error occurring during the rotational speed computation and the following translational speed computation then have the result, for example, that the travel dynamics regulating system, which processes the ascertained rotational speeds or translational speeds, provides regulation in an implausible manner.

In the case of an evaluating method exemplifying the invention, the evaluation of the incoming tooth flanks no longer takes place periodically, but at random. At random in this case means that scanning is carried out according to a presettable time raster with unequal time intervals. The difference between the known method and a method exemplifying the invention is illustrated in Fig. 3. In the case of the known method, the evaluation instants have spacings of 2 milliseconds from each other. In the case of the method exemplifying the invention, evaluation instants are after 0, 2, 3, 6, 8, 9, 13, 14, 17 and 19 milliseconds (ms). The next signal edge arriving after each indicated time interval is selected as a scanning instant and used for the ascertaining of rotational speed or for the computation of an associated translational speed. The fact that the irregular time intervals between predeterminable signal edges are of different length independently of the rotational speed, is taken into consideration in the computation of the rotational speed or translational speed. The output of the evaluation instants is performed by the computing equipment 15 or corresponding control device by means of a timer or an interrupt.

Since the signal scanning does not take place periodically, constantly different signal edges are evaluated for the detection of rotational speed. The alternate positive and negative tolerance thus can no longer superimpose in undesired manner. The filtering corresponding to a mean value formation is fully effective and the ascertained rotational or translational speed signal also does not have any great jumps in the region of the resonance speed. It is therefore made certain that the systems, which operate with the use of the ascertained rotational speeds, function reliably. Travel dynamics regulating systems do not regulate in unintended manner when rotational speed detection based on a method exemplifying the invention is employed.

The method can also be used for the detection of linear speeds or the like, insofar as successive mechanical spacings are evaluated which have positive and negative tolerances in alternation.

6

Claims

1 A method of evaluating a substantially periodic signal dependent on a speed, comprising the steps of selecting signal edges in the signal in accordance with a predetermined selection process in which the spacings between the selected signal edges are unequal and evaluating the time intervals between the selected signal edges to ascertain the speed.

2. A method as claimed in claim 2, wherein the step of evaluating is carried out in accordance with an irregular time sequence in which each evaluated signal edge follows a respective evaluation time point in the sequence.

3. A method as claimed in claim 1 or claim 2, comprising the step of forming a mean value from a plurality of ascertained speed values or evaluated signal edges.

4. A method as claimed in any one of the preceding claims, wherein the speed is the rotational speed of a motor vehicle and the method comprises the further steps of determining the translation speed of the wheel in dependence on the ascertained rotational speed and geometric relationships and processing the determined translation speed to obtain a parameter for use in a travel dynamics or brake anti-locking system of the vehicle.

5. A method as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

6. Evaluating means for evaluating a substantially periodic signal dependent on a speed, comprising means for selecting signal edges in the signal in accordance with a predetermined selection process in which the spacings between the selected signal edges are unequal and for evaluating the time intervals between the selected signal edges to ascertain the speed.

7. Speed sensing and evaluating equipment comprising a pulse wheel to be carried by a rotating shaft, a stationary sensor for scanning the pulse wheel so as to produce said signal, and evaluating means for evaluating the signal by a method as claimed in any one of claims 1 to 5.