Method for operating a belt-driven starter generator

Abstract

A method for operating a belt-driven starter generator of an internal combustion engine, in which a time interval between an onset of a rotary motion of the belt-driven starter generator and an onset of a rotary motion of the internal combustion engine is determined, the determined time interval is compared to a reference value, and the structural change of a belt of the belt-driven starter generator is inferred therefrom, and a torque of the belt-driven starter generator and/or a torque of a component connected to the belt is restricted as a function of the structural change of the belt.

Claims

1. A method for operating a belt-driven starter generator of an internal combustion engine, comprising: determining a time interval between an onset of a rotary motion of the belt-driven starter generator and an onset of a rotary motion of the internal combustion engine; comparing the determined time interval to a reference value and inferring a structural change of a belt of the belt-driven starter generator from the comparison; and restricting, as a function of the structural change of the belt, at least one of: (i) a torque of the belt-driven starter generator, and (ii) a torque of a component connected to the belt.

2. The method as recited in claim 1, wherein the component connected to the belt is deactivated as a function of the structural change of the belt.

3. The method as recited in claim 1, wherein at least one of: (i) the torque of the belt-driven starter generator, and (ii) the torque of the component connected to the belt, is restricted if the structural change of the belt reaches a threshold value.

4. The method as recited in claim 1, wherein at least one of: (i) the torque of the belt-driven starter generator, and (ii) the torque of the component connected to the belt, is restricted when a difference between the determined time interval and the reference value reaches a threshold value.

5. The method as recited in claim 1, wherein at least one of: (i) the torque of the belt-driven starter generator, and (ii) the torque of the component connected to the belt, is restricted as a function of an extent of the structural change of the belt.

6. The method as recited in claim 1, wherein the time interval is determined when the internal combustion engine is started with the aid of the belt-driven starter generator.

7. The method as recited in claim 1, wherein a multitude of time intervals is determined, and the multitude of time intervals is statistically evaluated and compared to the reference value.

8. The method as recited in claim 7, wherein at least one of: (i) a statistical mean value is determined from the multitude of time intervals in the course of the statistical evaluation, and (ii) a time sequence analysis is carried out.

9. The method as recited in claim 1, wherein at the onset of the rotary motion of the belt-driven starter generator, a first time stamp is determined or received, and at the onset of the rotary motion of the internal combustion engine, a second time stamp is determined or received, and the time interval is determined from the first time stamp and the second time stamp.

10. The method as recited in claim 1, wherein when the structural change of the belt is detected, at least one of: (i) an error entry is made in an error memory, and (ii) a visual and/or an acoustic notification is output.

11. An arithmetic unit, designed to operate a belt-driven starter generator of an internal combustion engine, the arithmetic unit designed to: determine a time interval between an onset of a rotary motion of the belt-driven starter generator and an onset of a rotary motion of the internal combustion engine; compare the determined time interval to a reference value and inferring a structural change of a belt of the belt-driven starter generator from the comparison; and restrict, as a function of the structural change of the belt, at least one of: (i) a torque of the belt-driven starter generator, and (ii) a torque of a component connected to the belt.

12. A non-transitory machine-readable storage medium on which is stored a computer program having program code for operating a belt-driven starter generator of an internal combustion engine, the computer program, when executed by a processor, causing the processor to perform: determining a time interval between an onset of a rotary motion of the belt-driven starter generator and an onset of a rotary motion of the internal combustion engine; comparing the determined time interval to a reference value and inferring a structural change of a belt of the belt-driven starter generator from the comparison; and restricting, as a function of the structural change of the belt, at least one of: (i) a torque of the belt-driven starter generator, and (ii) a torque of a component connected to the belt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrates a belt drive of a motor vehicle having an internal combustion engine and a belt-driven starter generator, which is set up to execute a preferred specific embodiment of a method according to the present invention.

(2) FIGS. 2a and 2b schematically show a belt drive of a motor vehicle having an internal combustion engine and a belt-driven starter generator, which is operated in a motor mode and in a generator mode.

(3) FIG. 3 schematically shows a preferred specific embodiment of a method according to the present invention in the form of a block diagram.

(4) FIG. 4 schematically shows a diagram of time intervals plotted against starting operations of an internal combustion engine, the diagram being able to be determined in the course of a preferred specific embodiment of a method according to the present invention.

(5) FIG. 5a-5c schematically show a belt drive of a motor vehicle having an internal combustion engine and a belt-driven starter generator while the internal combustion engine is started with the aid of the belt-driven starter generator.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(6) FIG. 1 schematically shows a belt drive of a motor vehicle, which is denoted by 100.

(7) An internal combustion engine 110 of the motor vehicle has a crankshaft, which is connected to a crankshaft drive wheel 150 in a torsionally fixed manner. Crankshaft drive wheel 150 is developed as a belt pulley, for example.

(8) Via a belt 120, e.g., via a ribbed V-belt, internal combustion engine 110 is connected to a belt-driven starter generator 130 in a torque-transmitting manner. Belt 120 in particular engages in a non-positive and/or positive manner with crankshaft drive wheel 150 and with a drive wheel 131 of starter generator 130. Drive wheel 131 is connected to a rotor of starter generator 130 in a torsionally fixed manner. Internal combustion engine 110 may be connected to further components 160 such as ventilators or coolant pumps via belt 120.

(9) A first control unit 115 is specifically set up for controlling internal combustion engine 110, and a second control unit 135 is specifically set up for controlling starter generator 130. Control units 115 and 135 are connected to each other in a data-transmitting connection via a field bus 170, such as a CAN bus, in particular. Second control unit 135 is specifically set up for executing a preferred specific embodiment of the method according to the present invention. It is pointed out that, as an alternative or in addition, first control unit 115 may also be set up for executing a preferred specific embodiment of the method according to the present invention.

(10) A starter generator is able to be operated as a motor and also as a generator. The belt must therefore be able to transmit torque in both directions. For this reason, the belt is developed as a ribbed V-belt, for example. Depending on whether starter generator 130 is operated in a motor mode or a generator mode, the taut strand and slack strand of belt 120 change. In addition, a corresponding belt tensioner 140 is provided for preloading belt 120. Belt tensioner 140 may be developed as a pendulum-type belt tensioner, which includes two pendulum arms 141a and 141b, for instance, which are connected to each other especially via a spring mechanism 143. For example, axes of rotation of these two pendulum arms 141a and 141b are co-linear with respect to an axis of rotation 132 of drive wheel 131 of starter generator 130. Other specific embodiments of pendulum-type belt tensioners or two-arm tensioners that have axes that are not co-linear with respect to the axis of rotation of the starter generator are also possible. This axis of rotation 132 of drive wheel 131 thus also simultaneously represents an axis of rotation of the pendulum-type belt tensioner 120. Each pendulum arm 141a and 141b is connected to a separate tension roller 142a and 142b, respectively.

(11) FIGS. 2a and 2b show belt drive 100 analogous to FIG. 1. Starter generator 130 is shown in a motor mode in FIG. 2a, and in a generator mode in FIG. 2b.

(12) For example, in the motor mode according to FIG. 2a, drive wheel 131 of starter generator 130 is rotating at a rotational speed about axis of rotation 132. In this case torque is transmitted via belt 120 from starter generator 130 to internal combustion engine 110. Starter generator 130 generates a drive torque M.sub.m. In this case, a belt section of belt 120 between drive wheel 131 and crankshaft drive wheel 150 forms taut strand 122, and a belt section between drive wheel 131 and further component 160 forms slack strand 121.

(13) In the generator mode according to FIG. 2b, drive wheel 131 rotates at a rotational speed co, for example. In this case, torque is transmitted via belt 120 from internal combustion engine 110 to starter generator 130. Starter generator 130 now generates a braking torque M.sub.g instead of a drive torque M.sub.m. The positions of taut strand 122 and slack strand 121 are reversed in comparison with the motor mode.

(14) Depending on which type of torque is generated by starter generator 130, the position of pendulum-type belt tensioner 140 and belt 120 changes. The arms of pendulum-type belt tensioner 140 rotate about axis of rotation 132 in the direction of taut strand 122.

(15) Special properties of belt 120, in particular its length, are precisely adapted to the system made up of internal combustion engine 110, starter generator 130, and further components 160. Wear and elongation of the belt may lead to restricted functioning of belt drive 100, e.g., to diminishing preloading and thus to a diminishing transmittable torque.

(16) For the timely detection of a structural change of belt 120 that exceeds a permissible measure, for extending the service life of belt 120, for avoiding excessive stressing of a belt 120 that exhibits wear, and for avoiding tearing of a worn belt 120, control unit 135, for example, is designed to execute a preferred specific embodiment of a method according to the present invention, which is schematically shown in the form of a block diagram in FIG. 3.

(17) In step 201, belt drive 100 is at rest and neither internal combustion engine 110 nor starter generator 130 is being operated. In this case, pendulum-type belt tensioner 140 is not deflected and is in its position of rest or its center position. Belt 120 is likewise in its position of rest and is not deflected.

(18) Internal combustion engine 110 is to be started up with the aid of starter generator 130. For this purpose, starter generator 130 is operated in the motor mode. In step 202, starter generator 130 is set into a rotary motion.

(19) As soon as second control unit 135 detects this onset of the rotary motion of starter generator 130, second control unit 135 determines a first time stamp according to step 203.

(20) Because of the generated torque in starter generator 130, pendulum-type belt tensioner 140 and belt 120 are deflected from their respective positions of rest. The taut strand is shortened, and the slack strand is lengthened. As soon as the taut strand has been sufficiently tensioned, internal combustion engine 110 is also set into rotary motion in step 204. This onset of the rotary motion is usually detected by first control unit 115, e.g., by monitoring a crankshaft pulse-generating wheel. According to step 205, first control unit 115 generates a second time stamp and notifies second control unit 135 accordingly via the CAN bus. Using the first and the second time stamps, the time interval between the onset of the rotary motion of starter generator 130 and internal combustion engine 110 is determined in second control unit 135 according to step 206.

(21) This determination of the time interval is repeated especially upon each start of internal combustion engine 110 with the aid of starter generator 130, which is sketched by reference numeral 207. As a result, a multitude of time intervals is determined, which may be stored in second control unit 135, for instance.

(22) With each newly determined time interval, the time intervals are evaluated and compared to a reference value. A statistical evaluation of the stored multitude of time intervals is carried out for this purpose in step 208. In particular, a time sequence analysis is performed, the time sequence analysis making it possible to determine a trend of the time interval.

(23) If the evaluation indicates that a respective difference between the determined time interval and the reference value reaches a threshold value over a certain number of starting operations of internal combustion engine 110 (for instance over at least five starting operations), then a structural change of belt 120 that exceeds a permissible measure will be detected.

(24) If a structural change in belt 120 is detected, the torque of starter generator 130 as well as that of further components 160 is reduced in step 209 as a function of the structural change of belt 120.

(25) Depending on the extent to which the determined time interval exceeds the threshold value in each case, a permissible maximum value of the torque is restricted to different degrees. The greater the difference between the respectively determined time interval and the reference value, the more the torque of starter generator 130 and of further components 160 will be restricted, or the lower the permissible maximum value of the torque will be selected.

(26) The torque of the BSG may be restricted in stages of 5 Nm, for instance. As an alternative or in addition, active components of the belt drive are also able to be switched off under different operating conditions (e.g., an engine start). Although this may result in a restriction of the function of the corresponding components in the belt drive (such as a slightly extended motor startup time), no unexpected function failure (such as a belt breakaway) will be encountered.

(27) In addition, according to step 209, a warning lamp may be activated in an area of an instrument panel of the vehicle, for example, and/or an error entry in an error memory may be made.

(28) FIG. 4 schematically shows a diagram that is able to be determined in the course of the statistical evaluation of the time intervals. The individual time intervals t have been plotted against the associated startup operation X during which they had been determined in each case. With the aid of the time sequence analysis, a trend or a trend curve 301 of the determined time intervals is established in the form of a linear function.

(29) If the difference between the respectively determined time interval t and reference value t.sub.Ref exceeds the threshold value, this especially corresponds to an exceeding of a permissible maximum value t.sub.max of determined trend curve 301. As soon as trend curve 301 exceeds maximum value t.sub.max over a certain number of starting operations (e.g., between starting operations X.sub.1 and X.sub.2), a structural change of the belt that exceeds a permissible degree is detected.

(30) In the following text, a mathematical correlation between the time interval and geometrical variables of the belt drive will be explained with the aid of FIGS. 5a-5c, in which a portion of the belt drive is schematically illustrated analogous to FIGS. 1, 2a and 2b during the startup of internal combustion engine 110 with the aid of starter generator 130.

(31) In FIG. 5a, the belt drive is schematically shown in the position of rest and denoted by 100a. Pendulum-type belt tensioner 140a and belt 120a are in their respective positions of rest. FIG. 5b shows the belt drive, denoted by 100b, after time interval t following the onset of the rotary motion of starter generator 130. Pendulum-type belt tensioner 140b is deflected in this case, and the taut strand is sufficiently shortened in order to set internal combustion engine 110 into a rotary motion.

(32) FIG. 5c shows the pendulum-type belt tensioner in its position of rest (140a) and in its correspondingly deflected position (140b). Deflected pendulum-type belt tensioner 140b is deflected by an angle of deflection in comparison with its position of rest 140a.

(33) The deflection of pendulum-type belt tensioner 140 counteracts inertia of mass J of starter generator 130, in particular. The following correlation exists between torque M of starter generator 130, its inertia of mass J, and the change in rotational speed of starter generator 130 or its drive wheel 131:

(34) $M=J\frac{d}{\mathrm{dt}}=J\frac{d^2}{{\mathrm{dt}}^2}$

(35) The covered angle of rotation of starter generator 130 or its drive wheel 131 results from this correlation as follows:

(36) $=\frac{M}{J}\mathrm{dtdt}$

(37) Time interval t between the onset of the rotary motion of starter generator 130 and internal combustion engine 110 results from this equation as follows:

(38) $t=\sqrt{\frac{2J{}_{\mathrm{erf}}}{M}}$
.sub.erf denotes the required angle of rotation for starting internal combustion engine 110. The breakaway torque required for starting internal combustion engine 110 in particular defines a required angle of deflection .sub.erf of belt tensioner 140, which in turn is proportional to angle of rotation of starter generator 130, in particular.

(39) A reference value for time interval t for a new, wear-free belt lies in the low ms range, for instance, and may amount to 16 ms, for example. A structural change of the belt that exceeds a permissible measure leads to reduced preloading and to a change in the position of rest of the pendulum-type belt tensioner in particular. This increases the required angle of deflection .sub.erf, and time interval t becomes greater.