Method for ascertaining a wheel circumference of a driven wheel, control method for a drive motor, control unit, and vehicle

Abstract

A method for ascertaining a wheel circumference of a driven wheel of a vehicle includes measuring a rotational speed of the driven wheel during a predefined time span, measuring an acceleration of the vehicle in the direction of the longitudinal axis of the vehicle during a predefined time span, determining a distance traveled by the vehicle based on the measured acceleration, and determining the wheel circumference of the driven wheel based on the measured rotational speed and the ascertained distance traveled.

Claims

1. A method comprising: measuring, using a rotation speed sensor mounted on a bicycle, a rotational speed of a driven wheel of the bicycle during a predefined time span; measuring, using an acceleration sensor mounted on the bicycle, an acceleration of the bicycle in a direction of a longitudinal axis of the bicycle during the predefined time span; determining, using a control unit mounted on the bicycle, a distance traveled by the bicycle during the predefined time span using the measured acceleration obtained from the acceleration sensor; determining, using the control unit, a wheel circumference of the driven wheel of the bicycle using the measured rotational speed obtained from the rotation speed sensor and the determined distance; and controlling, using the control unit, a drive motor of the bicycle based on the determined wheel circumference; prior to the predefined time span and while the bicycle is at rest, calibrating the acceleration sensor wherein the calibrating includes, based on a measured acceleration by the acceleration sensor, determining an acceleration offset in the direction of the longitudinal axis of the bicycle, which is applied in the determining of the wheel circumference.

2. A control unit of a bicycle, comprising: a rotation speed sensor mounted on a first part of the bicycle; an acceleration sensor mounted on a second part of the bicycle; and an arithmetic unit mounted on a third part of the bicycle and communicatively coupled to the rotation speed sensor and the acceleration sensor; wherein: the rotation speed sensor is configured to measure a rotational speed of a driven wheel of the bicycle during a predefined time span; the acceleration sensor is configured to measure an acceleration of the bicycle in a direction of a longitudinal axis of the bicycle during the predefined time span; and the arithmetic unit is configured to: determine a distance traveled by the bicycle during the predefined time span based on the measured acceleration obtained by the arithmetic unit from the acceleration sensor; determine a wheel circumference of the driven wheel based on the determined distance and measured rotational speed obtained by the arithmetic unit from the rotation speed sensor; and control a drive motor of the bicycle based on the determined wheel circumference; and wherein: the arithmetic unit is configured to, prior to the predefined time span and while the bicycle is at rest, calibrate the acceleration sensor; and the calibration includes, based on a measured acceleration by the acceleration sensor, determining an acceleration offset in the direction of the longitudinal axis of the bicycle, which is applied in the determining of the wheel circumference.

3. The control unit as recited of claim 2, wherein the control unit is configured to generate, based on the determined wheel circumference, a control signal that is output by the control unit, to control the drive motor of the bicycle.

4. A bicycle, comprising: a rotation speed sensor mounted on a first part of the bicycle; an acceleration sensor mounted on a second part of the bicycle; and an arithmetic unit mounted on a third part of the bicycle and communicatively coupled to the rotation speed sensor and the acceleration sensor; wherein: the rotation speed sensor is configured to measure a rotational speed of a driven wheel of the bicycle during a predefined time span; the acceleration sensor is configured to measure an acceleration of the bicycle in a direction of a longitudinal axis of the bicycle during the predefined time span; and the arithmetic unit is configured to: determine a distance traveled by the bicycle during the predefined time span based on the measured acceleration obtained by the arithmetic unit from the acceleration sensor; determine a wheel circumference of the driven wheel based on the determined distance and measured rotational speed obtained by the arithmetic unit from the rotation speed sensor; and control a drive motor of the bicycle based on the determined wheel circumference; and wherein: the arithmetic unit is configured to, prior to the predefined time span and while the bicycle is at rest, calibrate the acceleration sensor; and the calibration includes, based on a measured acceleration by the acceleration sensor, determining an acceleration offset in the direction of the longitudinal axis of the bicycle, which is applied in the determining of the wheel circumference.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an electric bicycle according to an example embodiment of the present invention.

(2) FIG. 2a is a flowchart that illustrates a method for ascertaining a wheel circumference according to an example embodiment of the present invention.

(3) FIG. 2b is a flowchart that illustrates a control method for a drive motor according to an example embodiment of the present invention.

(4) FIG. 3 illustrates a control unit according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(5) An electric bicycle 100 in the form of a vehicle is depicted in FIG. 1. Electric bicycle 100 includes pedals 110 and a drive motor 120, in particular, an electric motor, for propelling electric bicycle 100. Electric bicycle 100 further includes a speed sensor 130. Speed sensor 130 is, for example, a Reed sensor, which measures a rotational speed or a number of revolutions of a magnet 131 situated on the spokes of a driven wheel 160 of electric bicycle 100. Electric bicycle 100 further includes an acceleration sensor 140. Acceleration sensor 140 is situated, for example, on the frame of electric bicycle 100 and/or in a control unit 150. Acceleration sensor 140 measures an acceleration of electric bicycle 100 in the direction of longitudinal axis 170 of electric bicycle 100, that is, for example, in the direction of forward travel of electric bicycle 100. Control unit 150 is situated on electric bicycle 100, as well. Drive motor 120 of electric bicycle 100 is preferably controlled by control unit 150 as a function of a magnitude of a pressure applied by a bicycle rider of electric bicycle 100 to a pedal 110. For example, a limiting speed prescribed by law, i.e., a maximum speed, of 25 km/h is provided in the context of the control of electric motor 120. In normal operation, for example, the speed of electric bicycle 100 is determined as a function of rotational speed n and wheel circumference U of drive wheel 160. Therefore, according to the related art, wheel circumference U is programmed into control unit 150 by the manufacturer of an electric bicycle 100 and is consequently stored in a storage device of control unit 150. Accordingly, in the case of a flat tire and/or replacement of the tire and/or the wheel rim of wheel 160, the related art does not provide for automatic adjustment of stored wheel circumference U. Consequently, in the related art, e.g., the tachometer functions and the limiting speed have a small degree of inaccuracy. In addition, the programming of wheel circumference U in accordance with the related art is susceptible to errors and is costly for the manufacturer of electric bicycle 100.

(6) A flowchart of a method for ascertaining wheel circumference U of a driven wheel 160 of a vehicle 100 is represented in FIG. 2, the vehicle 100 being, for example, an electric bicycle as shown in FIG. 1. The method can include an optional calibration 205 of an acceleration sensor signal of acceleration sensor 140. Calibration 205 takes place with electric bicycle 100 at rest. For the calibration, an acceleration offset OS in the direction of longitudinal axis 170 of vehicle 100 is determined as a function of an acceleration a measured with the aid of acceleration sensor 140. Subsequently, rotational speed n of driven wheel 160 of electric bicycle 100 is measured 210 during a predefined time span t. As an alternative to measuring 210 rotational speed n, the number of revolutions k can be measured in step 210. At the same time, acceleration a of electric bicycle 100 in the longitudinal direction of electric bicycle 100 is measured during predefined time span t. During predefined time span t, acceleration a can vary, that is, have an acceleration characteristic. The predefined time span is, for example, a time period between 0.1 seconds and 5 minutes. Subsequently, a distance s traveled by electric bicycle 100 is ascertained as a function of the acceleration measured during predefined time span t. Distance s traveled is ascertained 240, for example, by integrating measured acceleration a or the acceleration characteristic twice, and/or by summing the acceleration values during predefined time span t in accordance with formula 1.
s=.sub.t.sub.0.sup.t.sup.1.sub.t.sub.0.sup.t.sup.1a(t).Math.tdt.sup.2.sub.t.sub.0.sup.t.sup.1.sub.t.sub.0.sup.t.sup.1a.sub.n.Math.t.sub.n(formula 1)

(7) Finally, wheel circumference U is determined 250 as a function of the revolutions k measured during predefined time span t and of distance s traveled, the number of revolutions k being measured or being ascertained from rotational speed n. Wheel circumference U is determined 250, for example, according to formula 2.

(8) $\begin{array}{cc}U=\frac{s}{k}& \left(\mathrm{formula}2\right)\end{array}$

(9) After determination 250, determined wheel circumference U can be stored, for example, in an electrical storage device of control unit 150.

(10) Subsequently, for example, a speed v of electric bicycle 100 is optionally ascertained as a function of rotational speed n of driven wheel 160 and of stored wheel circumference U. Since stored wheel circumference U corresponds to determined or actual wheel circumference U of electric bicycle 100, ascertained speed v of electric bicycle 100 is highly accurate. In a subsequent, optional step, ascertained speed v is indicated to the bicycle rider of the electric bicycle, for example, on a display of control unit 150 in the form of a tachometer function.

(11) A flowchart of a control method for drive motor 120 is represented in FIG. 2b. The control method for drive motor 120 starts with the acquisition 270 of a wheel circumference U. Wheel circumference U is acquired, in particular, from an electrical storage unit of control unit 150, wheel circumference U having been determined, in particular, according to the method, described in FIG. 2a, for ascertaining wheel circumference U of driven wheel 160 of the vehicle. Subsequently, drive motor 120 is controlled 280 as a function of determined wheel circumference U.

(12) A block diagram of control unit 150 for implementing one of the methods of the present invention is shown in FIG. 3. Control unit 150 includes at least an input signal interface 301, an arithmetic unit 302, an electrical storage unit 305, an output signal interface 303, and a display connecting socket 304. Control unit 150 measures rotational speed n of driven wheel 160 during a predefined time span t, that is, during a time period between starting time to and ending time ti, using speed sensor 130. Control unit 150 is connected to speed sensor 130, in particular, via input signal interface 301. In addition, during predefined time span t, control unit 150 simultaneously measures acceleration a of electric bicycle 100 in longitudinal direction 170 of electric bicycle 100, using acceleration sensor 140. Acceleration sensor 140 can be situated in control unit 150. Alternatively or optionally, control unit 150 can be connected to acceleration sensor 140, in particular, via input signal interface 301 or a second input signal interface 301. Arithmetic unit 302 ascertains, e.g., according to formula 1, the distance s traveled by the electric bicycle during predefined time span t. Afterwards, arithmetic unit 302 determines wheel circumference U of driven wheel 160 as a function of distance s traveled and rotational speed n measured during time span t. Determined wheel circumference U is saved, in particular, in electrical storage unit 305. Optionally, control unit 150 can be configured to generate an output signal, in particular, at output signal interface 303, to control 280 drive motor 120 as a function of wheel circumference U. In addition, on an indicating device 305, for example, on a display of control unit 150, control unit 150 is optionally configured to indicate a wheel circumference U or information, e.g., tachometer functions, which are ascertained as a function of wheel circumference U. The indicating device is connected to control unit 150 by, for example, display connecting socket 304.