Method for controlling a hybrid powertrain

Abstract

Method for controlling a hybrid powertrain with an internal combustion engine and an electric machine as well as a continuously variable transmission downstream of these with a variator controlled by a hydraulic system and a wrapping element clamped between conical disc sets of the variator at different radii depending on the transmission ratio, wherein a maximum input torque (M) applied to the variator is set higher than an input torque (M(V)) limited by a design of the variator in the underdrive (UD) of the variator in at least one transmission range (II, III) that differs from the underdrive (UD),wherein a first torque profile (102) of the maximum input torque (M) is set with the input torque (M(V)) limited by the design of the variator in a first transmission range (I) of the variator from underdrive (UD) up to a transmission ratio (i(a)) at a curve (105) of the Hertzian pressure that deviates from a power loss curve (109) of the variator, characterized in that in a second transmission range (II) of the variator with a mean transmission ratio between the transmission ratio (i(a)) at the curve (105) of the Hertzian pressure that deviates from the power loss curve (109) of the variator and a transmission ratio (i(b)) at a system pressure curve (108) of the maximum possible system pressure of the hydraulic system that deviates from a lower limit of a tolerance band (110) of the power loss curve (109), a second torque profile (103) of the maximum input torque (M) that is increased compared to the first torque profile (102) is set.

Description

[0001] The invention relates to a method for controlling a hybrid drive train with an internal combustion engine and an electric motor and a continuously variable belt transmission connected downstream thereof with a variator controlled by a hydraulic system and a belt means clamped between conical pulley sets of the variator at different radii depending on the transmission ratio.

[0002] EP 1 117 952 B1 discloses a method for reducing the thermal load of an automatic transmission for a motor vehicle in emergency operation.

[0003] DE 10 2015 100 764 A1 discloses a method for detecting anomalies in a continuously variable transmission.

[0004] DE 199 12 999 A1 discloses a dynamic variator protection module for belt variators.

[0005] Hybrid drivetrains comprising an internal combustion engine and an electric motor operable as a generator and electric motor, as well as a continuously variable transmission (CVT), are well known. For example, such a CVT is disclosed in WO 2015 / 110108 A1. The internal combustion engine and the electric motor are connected upstream of the CVT, so that the CVT's variator transmits the engine torque of the internal combustion engine and the drive torque of the electric motor. Due to the typical properties of the CVT, with a frictional connection between the belt drive, for example, the rocker elements of a plate-link chain, and the surfaces of the variator's conical pulley sets, the maximum input torque at the variator is limited, so that in conventional CVTs, correspondingly small electric motors must be combined with the internal combustion engine.The variator is designed for critical operating points, preferably in the extreme gear ratios with small running radii of the belt on one of the conical pulley sets.

[0006] A method for controlling the hybrid powertrain serves, among other things, to control the gear ratio of the belt transmission. For this purpose, a contact pressure is preferably generated by at least one oil pump in order to preload a respective loose pulley of the conical pulley sets against a fixed pulley while clamping the belt. The at least one oil pump applies different contact pressures to the loose pulleys of the conical pulley sets, so that, depending on the contact pressure, the belt on the corresponding conical pulley sets is displaced at different radii, thus setting a desired gear ratio.

[0007] The object of the invention is to further develop a method for controlling a hybrid powertrain. In particular, the object of the invention is to propose a method for increasing the maximum input torque of the CVT for a given CVT configuration.

[0008] The object is solved by the subject matter of claim 1. The claims dependent on claim 1 represent advantageous embodiments of the subject matter of claim 1.

[0009] The proposed method is used to control a hybrid drivetrain. A hybrid drivetrain within the meaning of this invention contains at least the following drivetrain components: an internal combustion engine, an electric motor, and a continuously variable transmission downstream of these, with a variator controlled by a hydraulic system and a belt drive clamped between conical pulley sets of the variator at different radii depending on the gear ratio. The electric motor can be operated as a motor or generator and can be arranged in the pulley plane or at the transmission-side output of the internal combustion engine, for example, coaxially to the crankshaft.The belt drive can preferably be designed as a link chain with a plate-linked chain comprising two plates connected to each other by means of two rocker arms rolling on each other, or as a push-link belt, with the end faces of the rocker arms rolling between the surfaces of the conical pulley sets. The radius of the belt drive on the two conical pulley sets, and thus the transmission ratio of the belt drive, is adjusted hydraulically by applying a contact pressure and an additional control pressure to each idler pulley of the two conical pulley sets.

[0010] A starting element, such as a starting clutch or a hydrodynamic torque converter, can be arranged between the internal combustion engine and the electric motor and the belt transmission. An additional friction clutch can be provided between the internal combustion engine and the electric motor.

[0011] The electric motor can be used for purely electric driving, as a booster for the internal combustion engine, as a starter for the internal combustion engine, as a generator during recuperation when the internal combustion engine is switched off or separated from the rest of the drive train by a friction clutch and / or as a generator for charging an electric accumulator.

[0012] In order to make better use of the belt transmission's torque transmission capabilities, a maximum input torque applied to the variator's input side is set based on the variator's gear ratio. This means that the applied maximum input torque is adjusted relative to the maximum input torque originally specified according to the variator's design such that the maximum transmittable torque that is harmless to the variator is transmitted for every variator gear ratio, for example, preferably for gear ratios between 2.8 and 0.40. In this way, depending on the variator's gear ratio, the maximum input torque originally specified by the corresponding variator design can be set higher for a given gear ratio.This allows, for example, a torque greater than the originally specified input torque to be transmitted to the variator during boost operation of the internal combustion engine and electric motor. This means that higher input torques can be applied at specified gear ratios than the input torque originally specified by the variator design without having to increase the size and redesign the variator. It has been shown that if the belt transmission is designed for the original maximum input torque that can be applied without damaging the variator, this is limited at the largest and smallest gear ratios of the variator, and that at the medium gear ratio, an input torque greater than this input torque can be applied without damage.It is therefore proposed that in a gear ratio range of the underdrive and the overdrive of the variator, in which the belt transmission assumes a minimum radius on a conical pulley set, the input torque be transmitted according to the design of the belt transmission and that for gear ratios in between, an increased input torque be permitted or set, which may depend on further operating parameters.

[0013] In such a method, it is preferably proposed that several torque curves of the maximum input torque be assigned to corresponding gear ratio ranges. According to the invention, a first torque curve is set in a first gear ratio range of the variator between the underdrive and a gear ratio at an increasing Hertzian pressure compared to an average power loss.This first torque curve of the maximum input torque can be set depending on the originally limiting design parameters, for example the Hertzian pressure between the belt means, for example the end faces of rocker pieces of a plate chain, and the conical pulley set in frictional contact with this, the maximum possible system pressure of the hydraulic system and / or the maximum power loss of the friction contacts of the belt means compared to the contact surfaces of the conical pulleys of the conical pulley sets or the like, for example at the maximum input torque according to the design of the variator.The Hertzian pressure can be determined, for example, by taking into account the load acting on the contact surfaces between, for example, the end faces of the rocker elements of a plate-link chain and the contact surfaces of the conical pulleys, depending on the number of elements forming contact with the conical pulleys, such as rocker elements and / or similar elements. The system pressure can be determined, for example, depending on the shaft strength of the shafts supporting the conical pulley sets, a limit pressure for the seals used in the hydraulic system, and / or similar elements.It has also been shown that, depending on the current running time in the first gear ratio range, the torque curve can be extended beyond a torque curve designed for long-term load. Experience has shown that the running time of the belt transmission in the first gear ratio range is short, and thus no damage to the belt transmission - variator and / or belt - is to be expected. The maximum input torque can therefore be set to an average power loss. As the variator's power loss increases beyond the first gear ratio range and into a second gear ratio range, the torque curves are adjusted to the lower end of the tolerance band of the power loss curve across the gear ratio, since these gear ratios have a longer service life.

[0014] According to the invention, in a second gear ratio range of the variator with a medium gear ratio, for example, with a gear ratio of the variator between 1.8 and 1, a second torque curve of the maximum input torque is set that is higher than the first torque curve of the maximum input torque. The lower gear ratio corresponds to the upper gear ratio of the first gear ratio range. The upper gear ratio of the second gear ratio range is provided at a gear ratio at which the maximum possible system pressure of the hydraulic system increases compared to the lower limit of the tolerance band of the power loss curve.This torque curve is higher than the originally designed maximum input torque according to the variator design and, with the unchanged design of the belt transmission, enables boost operation of the hybrid drive train at torques that exceed the maximum torque of the internal combustion engine, the electric motor, or a combination thereof. The electric motor can be designed with high power outputs of, for example, 20 kW to 200 kW, preferably 50 kW to 120 kW, in order to make a correspondingly high contribution to boost operation. As an alternative to boost operation of the internal combustion engine using the electric motor, the electric motor can form the main drive and the internal combustion engine can form a boost function. The torque curve is preferably adjusted in the second gear ratio range depending on the maximum possible or permissible system pressure of the hydraulic system.

[0015] A third gear ratio range follows the upper gear ratio of the second gear ratio range up to the overdrive. In this gear ratio range, a torque curve can be set that initially increases, remains constant, or decreases compared to the second torque curve of the maximum input torque, with the torque curve preferably following the power loss curve at the lower limit of its tolerance band. Due to the power loss decreasing with increasing gear ratio, the torque curve can drop after a torque maximum towards the overdrive. The power loss can be determined, for example, as a function of the thermal load on the contact surfaces between the belt drive, such as the end faces of the rocker elements of a plate-link chain and the conical pulley sets, the cooling capacity of the belt drive, and / or the like.

[0016] The torque curves of the maximum input torque, which can be adjusted depending on the gear ratio, or an overall limit torque curve of the maximum input torque across the spread of the belt transmission can be adjusted within a tolerance band arranged around the power loss, whereby, depending on the running time for the corresponding gear ratios, the corresponding adjustable maximum input torque can be adjusted in a medium tolerance band up to a lower limit of the tolerance band.Furthermore, the torque curves or an overall torque curve of the maximum adjustable input torque can be corrected depending on the time components in the respective gear ratios or gear ratio ranges, so that certain running times for these gear ratios are achieved without causing damage due to input torques that are excessive compared to the belt transmission's design. If necessary, the originally permitted input torque is reduced according to the variator's design if a specified running time is exceeded. The running time can be adapted to existing influencing factors such as operating temperature, operating pressure, and / or similar.

[0017] The torque curves or a total torque curve of the maximum input torque can be adjusted depending on the link strength of links of a belt designed as a link chain.

[0018] The invention is explained in more detail with reference to the exemplary embodiment illustrated in the single figure. This shows a diagram with the maximum adjustable input torque of a belt-drive transmission plotted against the gear ratio of a variator of a belt-drive transmission.

[0019] Diagram 100 shows the behavior of a belt transmission over the ratio i of its variator. The variator is formed from a drive shaft driven by an internal combustion engine and / or an electric motor with the maximum input torque M adjustable on the variator, with a first conical pulley set comprising a fixed pulley and a loose pulley that is hydraulically displaceable axially relative to the fixed pulley. Arranged parallel to the drive shaft is an output shaft connected to an output, for example, a differential, with a second conical pulley set comprising a fixed pulley and a loose pulley that is hydraulically displaceable axially relative to the fixed pulley.Between the conical running surfaces of the conical pulley sets, a belt in the form of a plate chain with rocker pieces connecting them and rolling on one another is arranged, the end faces of which are each pre-tensioned between a loose wheel and a fixed wheel of a conical pulley set by means of a contact pressure of a hydraulic system and are displaced radially on the conical pulley sets depending on a control pressure applied differently to the conical pulley sets.Depending on the control pressure, a predetermined ratio i is set between the maximum slow ratio, the underdrive UD, for example i=2.7 via a ratio i(a), a ratio i(b), a ratio i=1 and a maximum fast ratio, the overdrive OD with a ratio of, for example, i=0.4 and depending on the ratio i, the maximum adjustable input torque M on the drive shaft is a predetermined input torque up to the maximum setting torque.

[0020] The maximum adjustable input torque over the entire spread of the variator, depending on the gear ratio i, is shown as the total torque curve 101.

[0021] The overall torque curve 101 is divided into the individual torque curves 102, 103, 104 of the transmission ranges I, II, III via the transmission ratio.

[0022] In the gear ratio range I, which can extend, for example, from the underdrive UD with maximum gear ratio down to a gear ratio i(a), for example 1.9>i>1.6, preferably 1.7>i>1.8, the torque curve 102 is essentially set to variables dependent on the Hertzian pressure, the maximum system pressure, and the power loss, and is essentially the input torque M(V) for which the variator was originally designed. The input torque M(V) and thus the torque curve 102 in the first gear ratio range I is essentially limited, since the plate-link chain rolls off the drive-side conical pulley set with only a few rocker elements on a tight radius.In gear ratio range I, the Hertzian pressure shown in curve 105 for the set torque curve 102, the maximum possible system pressure shown in system pressure curve 108, and the power loss shown in power loss curve 109 are therefore limiting. In this case, the input torque M(V) can be increased compared to the dashed areas 106, 107 of the Hertzian pressure and the resulting input torque for setting the torque curve 102 up to an average power loss of the tolerance band 110 of the power loss curve, since no damaging effect occurs due to the short current running time in these gear ratios, and the input torque reduced in area 107 can be adjusted to the input torque M(V) with the torque curve 102 shown.

[0023] The gear ratio range I is limited at the gear ratio i(a), since at this gear ratio i(a) the curve 105 of the Hertzian pressure rises compared to the power loss curve.

[0024] In the gear ratio range II, which follows the gear ratio range I and increases, for example, up to the gear ratio i(b), the torque curve 103 of the maximum adjustable input torque M is made possible. In the gear ratio range II, the system pressure curve 108 is relevant for the maximum possible system pressure of the hydraulic system with the shaft strength of the input and output shafts, the limit pressure for the seals used in the hydraulic system and other components and / or the like, so that the maximum adjustable input torque is adjusted to the system pressure curve 108 according to the torque curve 103 of the gear ratio range II and, after a transition phase, from the average power loss to the lower limit of the tolerance band 110 of the power loss curve 109.

[0025] In gear ratio range II, the belt transmission can be operated beyond its original design with the input torque of torque curve 103 that is higher than the input torque M(V). For example, as shown in the exemplary embodiment shown, the set torque transmittable via the variator can be increased by approximately 20% to 50%. This enables a boost function of the drive train, whereby the internal combustion engine or the electric motor can serve as the main drive and the electric motor or the internal combustion engine can serve as the boost element, and whereby the electric motor can be designed to be correspondingly powerful. The upper limit of gear ratio range II for gear ratio i(b) results in the exemplary embodiment shown from the maximum possible system pressure of the system pressure curve 108, which increases compared to the lower limit of the tolerance band 110 of the power loss curve 109.

[0026] In the gear ratio range III, which adjoins gear ratio II and has a ratio between gear ratio i(b) and overdrive OD, the power loss curve 109 is relevant for the power loss of the rocker contact surfaces relative to the surfaces of the conical pulley pairs, including their cooling and thermal loads. The torque curve 104 therefore follows the lower limit of the tolerance band 110 of the power loss curve 109. This torque curve 104 initially rises slightly compared to the torque curve 103 and falls as it approaches overdrive OD because, in overdrive, the radius of the belt on the conical pulley set of the output shaft decreases. A boost function with a maximum adjustable input torque that exceeds the input torque M(V) according to the original design of the variator can still be used up to gear ratios of, for example, 0.7>i>0.6.

[0027] The torque curves 104 and, in part, 103 are set to the lower limit of the tolerance band 110. Partially in the gear ratio range II and in the gear ratio range I, i.e., at higher gear ratios downshifting, for example, at gear ratios i>1.6, the damage due to short operating times is minimal at these gear ratios, so that the torque curve shown in range 107 can be adapted to the torque curve 102. Furthermore, the maximum input torque that can be set at the beginning of the gear ratio range II can also be within the tolerance band 110 for this reason. List of reference symbols 100 diagram 101 Total torque curve 102 Momentum curve 103 Momentum curve 104 Momentum curve 105 Curve 106 Area 107 Area 108 System pressure curve 109 Power loss curve 110 Tolerance band I Translation area 11 Translation area III Translation area i Translation i(a) Translation i(b) Translation OD Overdrive M Input torque M(V) maximum adjustable input torque UD Underdrive

Claims

[1] Method for controlling a hybrid drive train with an internal combustion engine and an electric motor and a continuously variable belt transmission connected downstream thereof with a variator controlled by a hydraulic system and a belt means clamped between conical pulley sets of the variator at different radii depending on the gear ratio, wherein a maximum input torque (M) applied to the variator in at least one gear ratio range (II, III) deviating from the underdrive (UD) is set higher than an input torque (M(V)) limited by a design of the variator in the underdrive (UD) of the variator,wherein a first torque curve (102) of the maximum input torque (M) is set with the input torque (M(V)) limited by the design of the variator in a first gear ratio range (I) of the variator from underdrive (UD) to a gear ratio (i(a)) at a Hertzian pressure curve (105) deviating from a power loss curve (109) of the variator, characterized by that in a second gear ratio range (II) of the variator with medium gear ratio between the gear ratio (i(a)) at the curve (105) of the Hertzian pressure deviating from the power loss curve (109) of the variator and a gear ratio (i(b)) at a system pressure curve (108) of the maximum possible system pressure of the hydraulic system deviating from a lower limit of a tolerance band (110) of the power loss curve (109), a second torque curve (103) of the maximum input torque (M) is set which is increased compared to the first torque curve (102). [2] Method according to claim 1, characterized by that different torque curves (102, 103, 104) are set via the transmission ratio (i) of the variator within a tolerance band (110) arranged around a power loss curve (109) of the variator. [3] Method according to claim 1 or 2, characterized by that the first torque curve (102) is also set as a function of the Hertzian pressure between the belt means and the conical pulley set in frictional contact with the latter, a maximum adjustable system pressure of the hydraulic system and / or a power loss of friction between the belt means and the conical pulley sets. [4] Method according to claim 3, characterized by that the first torque curve (102) is set as a function of a current running time interval of the belt means in the first transmission range (I). [5] Method according to one of claims 1 to 4, characterized bythat the second torque curve (103) within the second transmission range (II) is increasingly adjusted with the transmission depending on a maximum possible system pressure of the hydraulic system. [6] Method according to one of claims 1 to 5, characterized by that in a third transmission range (III) between a transmission (i(b)) at a system pressure curve (108) of the maximum possible system pressure of the hydraulic system deviating from a lower limit of a tolerance band (110) of the power loss curve (109) and the overdrive (OD) of the variator a lower limit of the tolerance band (110) of the power loss curve (109) following a torque curve (104) of the maximum input torque (M). [7] Method according to one of claims 1 to 6, characterized by that the power loss is determined as friction between the belt and the conical pulley sets. [8] Method according to one of claims 1 to 7, characterized by that the moment curves (102, 103, 104) are set depending on a link strength of links of a belt designed as a link chain.

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