Method and control unit for determining vehicle speed, assistance system and vehicle

Abstract

The invention relates to a method for determining the speed (V) of a vehicle (100) using a speed sensor (10), wherein the speed sensor (10) comprises a signal generator (11) with multiple increments (12) and a signal receiver (13), and wherein the speed sensor (10) can count increments (11) passing the signal receiver (13), comprising: - detecting increments (12) as they pass the signal receiver (13) in a time interval (dt), - marking sensor signals (S) when increments (12) are detected using timestamps (ti) within the time interval (dt), - determining a speed (V), in particular an average speed (V*), of the vehicle (100) in the time interval (dt) as a function of the detected increments (12) and of corresponding timestamps (ti) within the time interval (dt).

Description

The invention relates to a method for determining a speed of a vehicle with the aid of a rotational speed sensor, in particular at low vehicle speeds, preferably close to a vehicle standstill, for example after a brake actuation, for example below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h. Furthermore, the invention relates to a corresponding computer program product for carrying out a corresponding method. The invention furthermore relates to a corresponding control unit for carrying out a corresponding method. The invention furthermore relates to a corresponding assistance system, for example for a driving dynamics control, a speed control, a slip control, a braking force distribution, a standstill control, etc., and to a corresponding vehicle having a corresponding control unit.Rotational speed sensors are often used to detect a vehicle speed. Speed sensors in turn usually use incremental disks in order to detect angle changes of a vehicle wheel and to determine the vehicle speed from this. The speed determination is based here on the fact that increments are counted which pass through the rotational speed sensor within a unit of time. In very slow vehicle travel, an inaccurate speed signal is frequently generated. This is because, during a slow vehicle travel, only a few increments pass the rotational speed sensor, for example only 5 increments, so that the counter position is 5, but this can correspond to a further rotation in a range from 4.01 to 5.99 increments.One possible solution for increasing the accuracy in a speed measurement can provide for increasing a number of increments. However, this can result in additional costs during production of the rotational speed sensor.It is therefore an object of the invention to overcome at least partially one of the disadvantages described above. In particular, it is an object of the invention to provide an improved method for determining a speed of a vehicle with the aid of a rotational speed sensor, in particular at low vehicle speeds, preferably close to a standstill of the vehicle, for example after a brake actuation, for example below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h, which enables a determination of the vehicle speed with increased accuracy and which can be carried out with little computing effort and without additional additional complexity in the configuration of the rotational speed sensor. It is a further object of the invention to provide a corresponding control unit for carrying out a corresponding method. Furthermore, it is an object of the invention to provide a corresponding assistance system, for example for a driving dynamics control, a speed control, a slip control, a braking force distribution, a standstill control, etc.The object is achieved by a method for determining a speed of a vehicle with the aid of a rotational speed sensor, in particular at low vehicle speeds, preferably close to a vehicle standstill, for example after a brake actuation, for example below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h. Furthermore, the object is achieved by a corresponding computer program product for carrying out a corresponding method. The object is furthermore achieved by a corresponding control unit for carrying out a corresponding method. Furthermore, the object is achieved by a corresponding assistance system, for example for a driving dynamics control, a rotational speed control, a slip control, a braking force distribution, a standstill control, etc.The invention provides a method for determining a speed of a vehicle with the aid of a rotational speed sensor, in particular at low vehicle speeds, preferably close to a vehicle standstill, for example after a brake actuation, for example below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h.In this case, it can be provided that the rotational speed sensor has a signal transmitter with a plurality of increments and a signal receiver, wherein the rotational speed sensor can count the increments that pass the signal receiver in a time interval. The signal transmitter with several increments can be designed, for example, in the form of an incremental disk.The method has the following method steps:detecting (for example comprising detecting and counting) (at least two) increments when passing the signal receiver in a time interval,marking sensor signals when detecting increments using time stamps within the time interval,determining a speed, in particular an average speed, of the vehicle in the time interval as a function of the detected increments and of corresponding time stamps within the time interval.The method proposes using time stamps of an increment pass to improve the speed determination. In particular at low speeds, for example after a brake actuation, for example below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h, preferably close to a vehicle standstill, the time stamp of the pass can thus be detected as well during an incremental pass. In this way, an average speed (V*) in the time interval can be determined with an increased accuracy on the basis of two increments and the corresponding time stamps.If irregularities in the application of increments are present in the signal transmitter, these can be taken into account in the time acquisition, for example if a deviation value is used. If the irregularities in the application of increments are known, these can be compensated exactly in the speed determination.Furthermore, a longitudinal acceleration (a) of the vehicle can be used in an advantageous manner. If the longitudinal acceleration of the vehicle is known in a time interval and if it is approximately constant or is provided only with a small rate of change, then the vehicle speed at the beginning (t1) and at the end (t2) of the time interval (dt) and optionally at any further point in time can be determined therefrom with little computing effort.A vehicle speed at the end of the time interval dt can be calculated, for example, as follows: V(t2)=V*-0.5*dt*a.Furthermore, an at least short-term prediction can be carried out beyond the time interval. For this purpose, the vehicle speed can be simply extrapolated over the end of the time interval.With the aid of the method, advantageous uses can be provided for the vehicle speed which is now precisely determined.On the basis of the now exactly known speed at a specific time of the measurement, the time of the vehicle standstill can be exactly determined with constant brake actuation. If a slight release of the brake takes place only for a few 10 milliseconds to achieve the standstill, the vehicle can very comfortably come to a standstill without significantly lengthening the stopping distance.The exact vehicle speed can likewise be used to improve a corresponding assistance system which requires the rotational speed of the wheel, for example for a driving dynamics control, a rotational speed control, a slip control, a braking force distribution, a standstill control, etc., and the control quality thereof. In this way, it is possible to dispense with the use of filters which are intended to compensate for a variation in the ascertained wheel speeds by the inaccurate speed determination. If the speed is determined here by additional use of time stamps, the filtering can be reduced and the accuracy can be increased at the same time.Overall, it can be established that an increase in the accuracy in the determination of the vehicle speed can be made possible with the aid of the method. Accurate travel speed can be used in an advantageous manner for standstill prediction. A release of the brake shortly before the vehicle standstill is reached can thus also be predicted and carried out precisely or can be proposed to the driver in order to minimize a stopping jerk or to enable a uniform deceleration to the standstill, preferably without a noticeable and / or appreciable extension of the braking path. An exact driving speed can also be used in an advantageous manner to improve a plurality of assistance systems and / or functions in the vehicle.The method can furthermore provide:determining a longitudinal acceleration of the vehicle in the time interval,determining a speed of a vehicle at the beginning and / or at the end of the time interval as a function of the determined longitudinal acceleration.For the sake of simplicity, a longitudinal acceleration of the vehicle can be ascertained as a function of the detected increments and of corresponding time stamps within the time interval. In addition, it is conceivable that the longitudinal acceleration of the vehicle can be estimated. It is also conceivable that the longitudinal acceleration of the vehicle can be detected by another sensor in the vehicle. Knowing the longitudinal acceleration of the vehicle, the vehicle speed can be determined easily and with little computing effort at the beginning and at the end of the time interval and, if applicable, at any further point in time, whether it be within the time interval or even beyond the end of the time interval.The method can furthermore provide:predicting a speed of a vehicle outside the time interval as a function of the ascertained longitudinal acceleration.In this way, advantageous predictive functions can be provided, such as for example for determining a time of the vehicle standstill and / or a braking path until a vehicle standstill, etc.In order to further increase the accuracy in determining the speed, it can be provided that irregularities in the arrangement of increments (is meant at the signal transmitter) are taken into account in determining an average speed of the vehicle in the time interval as a function of detected increments and of corresponding time stamps.Thus, at least one deviation term, for example in the form of an offset value, can be taken into account. In addition, it is conceivable that, given an exact knowledge of increment sizes, the accuracy can be maximized when determining the speed.According to a particular advantage, the method for determining a speed of a vehicle can be carried out at low vehicle speeds, in particular close to a standstill of the vehicle, preferably after a brake actuation, preferably below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h. In this way, the cases can be taken into account in which only a few increments pass the rotational speed sensor and yet a reliable and accurate determination of the speed can be made possible.Further advantages in connection with the method can result if the following method steps are carried out:using the determined speed of a vehicle for determining a time of a vehicle standstill and / or a stopping distance after a brake actuation, and / orusing the determined speed of a vehicle to propose a time for releasing a brake control before a vehicle standstill.In this way, the comfort during the stopping of the vehicle can be increased considerably, the stopping force can be nearly prevented without significantly lengthening the stopping distance.Further advantages in connection with the method can result if the following method steps are carried out:using the determined speed of a vehicle for an assistance system of the vehicle, for example for a driving dynamics control, a rotational speed control, a slip control, a braking force distribution and / or a standstill control, and / orusing the determined speed of a vehicle to ascertain and / or adapt vehicle wheel rotational speeds.In this way, the control quality can be significantly increased in the corresponding assistance systems which require the rotational speed of the wheel. At the same time, the design of electrical and / or electronic units in the corresponding assistance systems can thereby be simplified.Furthermore, the invention provides a computer program product comprising instructions which, when the computer program product is executed by a computer, cause the computer program product to carry out a method which can be carried out as above. With the aid of the computer program product, the same advantages can be achieved as described above in connection with the method according to the invention. These advantages are referred to in the present case in their entirety.Furthermore, the invention provides a control unit, having a computing unit and a memory unit in which a code is stored which, when at least partially executed by the computing unit, carries out a method which can proceed as above. With the aid of the control unit, the same advantages can be achieved as described above in connection with the method according to the invention. These advantages are referred to in the present case in their entirety.Furthermore, the invention provides an assistance system, for example for a vehicle dynamics control, a rotational speed control, a slip control, a braking force distribution, a standstill control, etc., for a vehicle, having a control unit which can be designed as described above. With the aid of the assistance system, the same advantages can be achieved as described above in connection with the method according to the invention. These advantages are referred to in the present case in their entirety.Further advantages, features and details of the invention will become apparent from the following description, in which a plurality of exemplary embodiments of the invention are described in detail with reference to the drawing. The figure shows: FIG. 1 shows a schematic illustration of a vehicle in which a method in the sense of the present disclosure can be carried out.FIG. 1 serves to explain a method within the meaning of the invention, which was developed for determining a speed V of a vehicle 100 with the aid of a rotational speed sensor. The method can be carried out in particular at low vehicle speeds, preferably close to a vehicle standstill, for example after a brake actuation, for example below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h, in order to determine the speed V of the vehicle 100.The method addresses a rotational speed sensor 10, which can have a signal transmitter 11 with a plurality of increments 12 and a signal receiver 13, wherein the rotational speed sensor 10 can count increments 11 which pass the signal receiver 13 in a time interval dt. The signal transmitter 11 with several increments 12 can be designed, for example, in the form of an incremental disk.The method has the following method steps:detecting (for example comprising detecting and counting) (at least two) increments 12 when passing the signal receiver 13 in a time interval dt,marking sensor signals S when detecting increments 12 with the aid of time stamps ti within the time interval dt,determining a speed V, in particular an average speed V*, of the vehicle 100 in the time interval dt as a function of the detected increments 12 and of corresponding time stamps ti within the time interval dt.An incremental run with corresponding time stamps can be provided as the sensor signal. An increment sweep may include at least two increments and two corresponding time stamps on the sweep of corresponding increments.In particular at low speeds V of the vehicle 100, for example after a brake actuation, for example below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h, preferably close to a vehicle standstill, an incremental run can thus be detected with at least two increments and the two corresponding time stamps.On the basis of (by means of) at least two increments and the corresponding time stamps, an average speed V* of the vehicle 100 can be determined in the corresponding time interval.Even if this average speed V* of the vehicle 100 is determined as the speed V of the vehicle 100, this can increase the accuracy in determining the speed V of the vehicle 100.In order to further refine the determination of the speed V of the vehicle 100, a longitudinal acceleration a of the vehicle 100 may be taken into account.If the longitudinal acceleration a of the vehicle 100 is known in a time interval and if it is approximately constant or is provided only with a small rate of change, then the speed V of the vehicle 100 at the start t 1 and at the end t 2 of the time interval dt and optionally at any further point in time (within and / or even outside the time interval dt or predictive) can be determined therefrom with little computing effort.A vehicle speed V at the end t 2 of the time interval dt can be calculated, for example, as follows:Furthermore, an at least short-term prediction beyond the time interval dt (t>t2) can be carried out. For this purpose, the vehicle speed V can be extrapolated simply via the end t2 of the time interval dt.The method may provide several advantageous uses for the determined vehicle speed V.An example of advantageous uses for the determined vehicle speed V can be stopping the vehicle. On the basis of the determined speed V at a specific point in time t of the measurement, the point in time t of the vehicle standstill can be determined with constant brake actuation. It is advantageously possible, shortly before the vehicle standstill is reached, for example only for a few 10 milliseconds, for the brake to be released (if appropriate slightly) automatically and / or proposed to the driver. In this way, the vehicle 100 can comfortably come to a standstill without significantly lengthening the stopping distance.Advantageous uses for the specific vehicle speed V can be provided by assistance systems 120 in the vehicle 100, for example, a driving dynamics control, a speed control, a slip control, a braking force distribution, a standstill control, etc.In this way, it is even possible to simplify corresponding electrical circuits in the assistance systems 120 which require the rotational speed of the wheel, for example by omitting the use of filters which are intended to compensate for a variation in the ascertained wheel speeds by the inaccurate speed determination.If irregularities are present in the signal transmitter 11 when the increments 12 are applied to the signal transmitter 11, these can be taken into account in the time acquisition, for example as a deviation value or an offset value. If the irregularities in the application of the increments 12 to the signal transmitter 11 are known exactly, these can be compensated accordingly in the speed determination.The method can furthermore provide:determining a longitudinal acceleration a of the vehicle 100 in the time interval dt,determining a speed V of a vehicle 100 at the beginning t1 and / or at the end t2 of the time interval dt as a function of the determined longitudinal acceleration a.For the sake of simplicity, the longitudinal acceleration a of the vehicle 100 can be ascertained, for example estimated, as a function of the detected increments 12 and of corresponding time stamps ti within the time interval dt.It is also conceivable that the longitudinal acceleration a of the vehicle 100 can be determined by a special sensor of the vehicle 100.Knowing the longitudinal acceleration a of the vehicle 100, the vehicle speed V can be determined easily and with little computing effort at the beginning t1and at the end t2of the time interval dt and optionally at any further time t, be it within the time interval dt or beyond the time interval dt.The method can furthermore provide:predicting a speed V of a vehicle 100 outside the time interval dt as a function of the ascertained longitudinal acceleration a.In this way, improved predictive functions may be provided in the vehicle 100, such as for determining a time of vehicle standstill and / or a braking path until vehicle standstill, etc.As already mentioned above, the method can also provide:using the determined speed V of a vehicle 100 for determining a time of a vehicle standstill and / or a stopping distance after a brake actuation, and / orusing the determined speed V of a vehicle 100 to propose a time for releasing a brake control before a vehicle standstill.As already mentioned above, the method can also provide:using the determined speed V of a vehicle 100 for an assistance system 120 of the vehicle, for example for a driving dynamics control, a rotational speed control, a slip control, a braking force distribution and / or a standstill control, and / orusing the determined speed V of a vehicle 100 for ascertaining and / or adapting vehicle wheel rotational speeds.A corresponding computer program product and a corresponding control unit 110 for carrying out a corresponding method likewise each represent an aspect of the invention. The control unit 110 is only schematically illustrated in FIG. 1.A corresponding assistance system 120 and a vehicle 100 with a corresponding control unit 110 likewise each represent an aspect of the invention and are likewise only schematically represented in FIG. 1.The foregoing explanation of the embodiments describes the present invention solely by way of examples. Of course, individual features of the embodiments can be freely combined with one another, insofar as technically expedient, without departing from the scope of the present invention.List of reference characters100 Vehicle 110 Control unit 120 Assistance system 10 Rotational speed sensor 11 Signal transmitter 12 Increments 13 Signal taker a Longitudinal acceleration dt Time interval t 1 Start t 2 End ti Time stamps S Sensor signal V Speed V* Average speed

Claims

Method for determining a speed (V) of a vehicle (100) with the aid of a rotational speed sensor (10), wherein the rotational speed sensor (10) has a signal transmitter (11) with a plurality of increments (12) and a signal receiver (13), and wherein the rotational speed sensor (10) can count increments (11) which pass through the signal receiver (13), having: - detecting increments (12) when passing through the signal receiver (13) in a time interval (dt), - marking sensor signals (S) when detecting increments (12) with the aid of time stamps (ti) within the time interval (dt), - determining a speed (V), in particular an average speed (V*), of the vehicle (100) in the time interval (dt) as a function of the detected increments (12) and of corresponding time stamps (ti) within the time interval (dt).Method according to Claim 1, further comprising: - determining a longitudinal acceleration (a) of the vehicle (100) in the time interval (dt), - determining a speed (V) of a vehicle (100) at the start (t1) and / or at the end (t2) of the time interval (dt) as a function of the determined longitudinal acceleration (a).Method according to Claim 2, further comprising: - predicting a speed (V) of a vehicle (100) outside the time interval (dt) as a function of the determined longitudinal acceleration (a).Method according to one of the preceding claims, wherein irregularities in the arrangement of increments (12) are taken into account in determining an average speed (V*) of the vehicle (100) in the time interval (dt) as a function of detected increments (12) and of corresponding time stamps (ti).Method according to one of the preceding claims, wherein the method for determining a speed (V) of a vehicle (100) is carried out at low vehicle speeds, in particular close to a vehicle standstill, preferably after a brake actuation, preferably below a threshold of 30 km / h, in particular 20 km / h, preferably 10 km / h or preferably 5 km / h.Method according to one of the preceding claims, further comprising: - using the determined speed (V) of a vehicle (100) for determining a time of a vehicle standstill and / or a stopping distance after a brake actuation, and / or - using the determined speed (V) of a vehicle (100) for proposing a time for releasing a brake actuation before a vehicle standstill.Method according to one of the preceding claims, further comprising: - using the determined speed (V) of a vehicle (100) for an assistance system of the vehicle (100), comprising in particular a driving dynamics control, a rotational speed control, a slip control, a braking force distribution and / or a standstill control, and / or - using the determined speed (V) of a vehicle (100) for determining and / or adapting vehicle wheel rotational speeds.A computer program product comprising instructions which, when the computer program product is executed by a computer, cause the computer program product to perform a method according to any preceding claim.Control unit (110), having a computing unit and a memory unit in which a code is stored which, when at least partially executed by the computing unit, carries out a method according to one of the preceding claims.Assistance system (120) for a vehicle (100), comprising a control unit (110) according to the preceding claim.

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