Method for starting an internal combustion engine with the aid of a belt-driven starter generator

Abstract

A method for starting an internal combustion engine using a starter generator to which the engine is connected via a belt drive, the belt drive including a belt pulley of the starter generator, a belt pulley of the internal combustion engine, and a belt connecting the belt pulleys in a torque-transmitting manner, includes operating the starter generator such that its drive torque output to the belt pulley of the starter generator is according to a drive torque curve by which an output torque generated temporarily on the belt pulley of the internal combustion engine exceeds the drive torque of the starter generator, taking a gear ratio of the belt drive into consideration.

Claims

1. A method for starting an internal combustion engine using a starter generator to which the internal combustion engine is connected via a belt drive, the belt drive including a belt pulley of the starter generator, a belt pulley of the internal combustion engine, and a belt connecting the belt pulleys in a torque-transmitting manner, the method comprising: operating the starter generator such that its drive torque output M.sub.0 to the belt pulley of the starter generator is according to a drive torque curve by which, taking a gear ratio i of the belt drive into consideration, an output torque M.sub.1 generated temporarily on the belt pulley of the internal combustion engine exceeds the drive torque output M.sub.0 of the starter generator, such that M.sub.1>M.sub.0*i; and after the temporary exceedance, the output torque M.sub.1 generated on the belt pulley of the internal combustion engine decaying over time from M.sub.1>M.sub.0*i to the drive torque output M.sub.0 of the starter generator taking the gear ratio i into consideration, such that M.sub.1 decays to M.sub.0*i, as the starter generator operates; wherein the drive torque curve according to which the starter generator operates is a linear drive torque curve having a torque gradient of at least M.sub.max/(0.5*T.sub.0), where M.sub.max is a peak torque value, and T.sub.0 is a period duration of a first natural frequency of the belt drive; wherein during the operating of the starter generator, a transmitted peak torque of the starter generator is less than a breakaway torque of a crankshaft of the internal combustion engine.

2. The method of claim 1, wherein the temporary exceedance is by more than 40%.

3. The method of claim 1, wherein the temporary exceedance is by more than 50%.

4. The method of claim 1, wherein the operation of the starter generator is such that the drive torque output M.sub.0 to the belt pulley of the starter generator increases from a torque of zero to a predefined setpoint drive torque value during a predefined acceleration duration.

5. The method of claim 4, wherein the acceleration duration is predefined as a function of the period duration T.sub.0 of the first natural frequency of the belt drive.

6. The method of claim 5, wherein the acceleration duration is set to at most double the period duration T.sub.0 of the first natural frequency of the belt drive.

7. The method of claim 5, wherein the acceleration duration is set to be at most equal to the period duration T.sub.0 of the first natural frequency of the belt drive.

8. The method of claim 5, wherein the acceleration duration is set to half the period duration T.sub.0 of the first natural frequency of the belt drive.

9. The method of claim 4, wherein the acceleration duration is at least 0.5 s.

10. The method of claim 1, wherein the drive torque curve is predefined as a function of at least one variable, which is selected from the group consisting of a length of the belt span between the belt pulley of the starter generator and the belt pulley of the internal combustion engine, an axial rigidity of the belt, a moment of inertia of rotating elements of the starter generator and the belt pulley of the starter generator, and a radius of the belt pulley of the starter generator.

11. The method of claim 1, wherein the decaying is a function of damping by the belt drive and the internal combustion engine.

12. The method as recited in claim 1, wherein the drive torque output M.sub.0 of the starter generator is a maximum peak torque output of the starter generator.

13. A device comprising: processing circuitry; and an interface to an engine-generator system that includes a starter generator to which an internal combustion engine is connected via a belt drive, the belt drive including (a) a belt pulley of the starter generator, (b) a belt pulley of the internal combustion engine, and (c) a belt connecting the belt pulleys in a torque-transmitting manner; wherein the processing circuitry is configured to generate, and output to the engine-generator system, control output that operates the starter generator such that its drive torque output M.sub.0 to the belt pulley of the starter generator is according to a drive torque curve by which, taking a gear ratio i of the belt drive into consideration, an output torque M.sub.1 generated temporarily on the belt pulley of the internal combustion engine exceeds the drive torque output M.sub.0 of the starter generator, such that M.sub.1>M.sub.0*i; wherein after the temporary exceedance, the output torque M.sub.1 generated on the belt pulley of the internal combustion engine decays over time from M.sub.1>M.sub.0*i to the drive torque output M.sub.0 of the starter generator taking the gear ratio i into consideration, such that M.sub.1 decays to M.sub.0*i, as the starter generator operates; wherein the drive torque curve according to which the starter generator operates is a linear drive torque curve having a torque gradient of at least M.sub.max/(0.5*T.sub.0), where M.sub.max is a peak torque value, and T.sub.0 is a period duration of a first natural frequency of the belt drive; wherein during the operating of the starter generator, a transmitted peak torque of the starter generator is less than a breakaway torque of a crankshaft of the internal combustion engine.

14. The device of claim 13, wherein the decay is a function of damping by the belt drive and the internal combustion engine.

15. The device as recited in claim 13, wherein the drive torque output M.sub.0 of the starter generator is a maximum peak torque output of the starter generator.

16. A non-transitory computer-readable medium on which are stored instructions that are executable by a processor, the instructions which, when executed by the processor, cause the processor to perform a method for starting an internal combustion engine using a starter generator to which the internal combustion engine is connected via a belt drive, the belt drive including a belt pulley of the starter generator, a belt pulley of the internal combustion engine, and a belt connecting the belt pulleys in a torque-transmitting manner, the method comprising: operating the starter generator such that its drive torque output M.sub.0 to the belt pulley of the starter generator is according to a drive torque curve by which, taking a gear ratio i of the belt drive into consideration, an output torque M.sub.1 generated temporarily on the belt pulley of the internal combustion engine exceeds the drive torque output M.sub.0 of the starter generator, such that M.sub.1>M.sub.0*i; and after the temporary exceedance, the output torque M.sub.1 generated on the belt pulley of the internal combustion engine decaying over time from M.sub.1>M.sub.0*i to the drive torque output M.sub.0 of the starter generator taking the gear ratio i into consideration, such that M.sub.1 decays to M.sub.0*i, as the starter generator operates; wherein the drive torque curve according to which the starter generator operates is a linear drive torque curve having a torque gradient of at least M.sub.max/(0.5*T.sub.0), where M.sub.max is a peak torque value, and T.sub.0 is a period duration of a first natural frequency of the belt drive; wherein during the operating of the starter generator, a transmitted peak torque of the starter generator is less than a breakaway torque of a crankshaft of the internal combustion engine.

17. The non-transitory computer-readable medium of claim 16, wherein the decaying is a function of damping by the belt drive and the internal combustion engine.

18. The non-transitory computer-readable medium of claim 16, wherein the drive torque output M.sub.0 of the starter generator is a maximum peak torque output of the starter generator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows a system including an internal combustion engine, a belt-driven starter generator, and a vehicle electrical system, used in an example embodiment of the present invention.

(2) FIG. 2 shows an example drive torque curve generated by the starter generator on the belt pulley of the starter generator, according to an example embodiment of the present invention.

(3) FIG. 3 shows an example drive torque curve on the crankshaft or belt pulley of the internal combustion engine, from the beginning of the starting process through the breakaway of the crankshaft, all the way to the subsequent acceleration process, according to an example embodiment of the present invention.

(4) FIG. 4 shows different output torque curves on the crankshaft or belt pulley of the internal combustion engine, which result in different drive torque curves, according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(5) FIG. 1 schematically shows a system 200 including an internal combustion engine 300, a belt-driven starter generator 100 as an electric machine, and a vehicle electrical system 30, based on which a preferred example embodiment of the present invention is described below.

(6) The starter generator includes a generator component 10 and a power converter component 20. The power converter component is usually operated as a rectifier during generator operation of the machine, and as an inverter during motor operation.

(7) Internal combustion engine 300 is equipped on its crankshaft 301 with a belt pulley 302 and connected via a belt 310 to a belt pulley 11 of starter generator 100, an (optional) belt tensioner designed as a reciprocating belt tensioning system 320 being provided here, which is able to tension belt 310 during operation independently of the direction of torque.

(8) The belt drive, including belt pulley 302, belt pulley 11 and belt 310 usually designed as a V-belt or V-ribbed belt, provides an appropriate gear ratio i as a function of the circumferences of the belt pulleys. Correspondingly, a drive torque M.sub.0 output from the starter generator 100 to belt pulley 11 is translated into an output torque M.sub.1=M.sub.0*i output from belt pulley 302 to crankshaft 301, and vice versa.

(9) To start internal combustion engine 300, starter generator 100 is operated as a motor. Electric drive torque M.sub.0 of the starter generator 100 (see FIG. 2) is divided into the acceleration torque for overcoming the inertia of the rotating elements (rotor of the generator and belt pulley 11 of the belt drive connected thereto) and the torque which is introduced via belt pulley 11 into belt 310. Until the breakaway of crankshaft 301, belt 310 is tensioned as a result of its elasticity, and crankshaft 301 remains at rest. If the rotor having belt pulley 11 no longer absorbs any acceleration work, an overshooting of output torque M.sub.1 occurs, as shown in FIG. 3, since the inertia of the rotating elements now in turn introduces a torque into the system.

(10) FIG. 2 shows a diagram of an example linear curve of drive torque M.sub.0 of starter generator 100. Beginning at a point in time t.sub.0, drive torque M.sub.0 is linearly increased to the desired maximum drive torque value M.sub.max up until a point in time t.sub.1. The desired drive torque value M.sub.max is the peak torque here, but can also be the maximum permanent torque. The slope, i.e., the torque gradient, determines the level of overshooting of output torque M.sub.1, as shown in FIG. 3.

(11) FIG. 3 shows a diagram of an example curve of output torque M.sub.1 on crankshaft 301 of internal combustion engine 300 standardized to transmitted maximum drive torque i*M.sub.max. Starting at point in time 0 (corresponds to t.sub.0 in FIG. 2), output torque M.sub.1 increases. Maximum drive torque M.sub.max is reached approximately at t=0.01 here. However, due to the dynamics of the belt drive, the output torque continues to increase and overshoots by up to approximately 1.6 times the transmitted drive torque (i*M.sub.max). This is sufficient for the crankshaft to break away and accelerate. The output torque correspondingly decreases again and decays as a function of the damping of the system (belt drive together with internal combustion engine).

(12) FIG. 4 shows three curves 401, 402 and 403 of output torque M.sub.1, standardized to the transmitted maximum drive torque i*M.sub.max, plotted against time t, standardized to the first natural period duration T.sub.0 of the belt drive. Curve 401 corresponds to a torque gradient of M.sub.max/(0.2 T.sub.0), curve 402 corresponds to a torque gradient of M.sub.max/(0.5 T.sub.0), and curve 403 corresponds to a torque gradient of M.sub.max/(1.5 T.sub.0). It becomes apparent that the level of the overshooting decreases with the torque gradient, i.e., the stronger the acceleration, the higher is the achievable peak output torque. In particular, the torque gradient should thus be at least M.sub.max/(0.5 T.sub.0) for a linear drive torque curve. A preferred maximum torque gradient can be indicated, e.g., as M.sub.max/(0.5 s), since no significant increase in the peak output torque is to be expected with even greater acceleration, and engines that may be accelerated even more must be relatively robust, which in turn results in increased space requirement and costs. Moreover, such a sudden acceleration can prevent re-tensioning of a preferably used belt tensioner, and thus result in slipping of the V-ribbed belt, and thus in premature wear of the V-ribbed belt.

(13) The excessive increase is dependent on different variables of the belt drive, which are meaningfully taken into consideration when predefining the drive torque curve, i.e., during control of the starter generator.

(14) The main influencing variables on the excessive increase are: length L.sub.R of the belt span between starter generator 100 and crankshaft 301 the axial rigidity E*A of the belt used, E corresponding to the modulus of elasticity of the belt, and A corresponding to its cross-sectional surface moment of inertia J.sub.RSG of the rotor of the starter generator having belt pulley 11, and gradient M.sub.max/(t.sub.1t.sub.0) of the drive torque.

(15) In an example embodiment of the present invention, the acceleration duration (t.sub.1t.sub.0) is twice the period duration T.sub.0 of the first natural frequency of the belt drive. A lower limit for the acceleration duration (t.sub.1t.sub.0) can be 5 m, for example, as was already mentioned above.

(16) The first natural frequency of the belt drive depends on the above-mentioned parameters of the belt drive.

(17) The moments of inertia of the crankshaft or of the internal combustion engine do not have to be taken into consideration since only the time until the breakaway of the crankshaft is considered.

(18) To ascertain the natural frequency, the following differential equation of the belt drive is formed, neglecting damping effects:

(19) $J_{\mathrm{RSG}}.Math.{\stackrel{\mathrm{.Math.}}{}}_{\mathrm{RSG}}+\frac{E.Math.A}{2L_R}.Math.r_{\mathrm{RSG}}^2.Math.{}_{\mathrm{RSG}}=0,$
where r.sub.RSG is radius of belt pulley 11 and .sub.RSG is angular acceleration.

(20) Based on this, the natural frequency

(21) $f_0=\frac{{}_0}{2}=\frac{1}{T_0},\mathrm{where}{}_0=\sqrt{\frac{\frac{E.Math.A}{2L_R}.Math.r_{\mathrm{RSG}}^2}{J_{\mathrm{RSG}}}}.$

(22) If according to alternative specific embodiments additional components, such as a water pump or air-conditioning compressor, are situated in the belt drive, this may be taken into consideration by adjusting the term 2L.sub.R. It may be adjusted, for example, to the sum of the span lengths of the slack and tight spans. In many applications, this corresponds approximately to the total length of the belt.