Hollow gear torque management in a hybrid electric vehicle to increase the available wheel torque

Abstract

Vehicle that includes the following: a power-split drive train comprising a power unit (18), a first motor / generator (16) and a second motor / generator (32); a planetary gear set (24) which is coupled to the power machine (18) and has a ring gear (26) for transmitting a ring gear torque to a differential (42); wherein the first motor / generator (16) is configured to selectively output torque to the differential (42); wherein the second motor / generator (32) can be connected to a sun gear (28) of the planetary gear set (24) to generate electrical energy; a chain, belt or mechanical loop that operatively couples the ring gear (26) and the first motor / generator (16) to the differential (42); and a control (12) configured to modify the output of the power machine (18) based on a minimum limit for the power machine torque output for the torque supplied through the ring gear (26) such that a desired torque is transmitted through the chain, belt or mechanical loop to the differential (42), wherein the torque output of the power machine is defined such that it is sufficient to meet the requested wheel torque.

Description

TECHNICAL AREA

[0001] The present disclosure relates to changing the engine torque in a hybrid vehicle for managing torque transmitted through a ring gear of a planetary gear set coupled to the engine. BACKGROUND

[0002] Hybrid vehicles are typically powered by two primary drive sources, such as an internal combustion engine and an electric motor (powered by a battery). One type of hybrid vehicle is a power-split hybrid. In a power-split hybrid, the internal combustion engine and the electric motor are allowed to deliver power to the wheels separately or in combination. A planetary gear set can be coupled to the internal combustion engine and a generator, allowing the internal combustion engine to charge the battery even when the electric motor is providing the torque needed to propel the vehicle. The generator can also act as an electric motor by supplying torque through the planetary gear set. One of the planetary gears (e.g., the ring gear) can also couple the internal combustion engine and generator to an output, such as a differential, that distributes torque to the wheels.

[0003] Particularly at low vehicle speeds, a situation can arise where the amount of wheel power is very low, even if the wheel torque demand is relatively high. An extreme example of this scenario is when the vehicle accelerates from a standstill with the accelerator pedal fully depressed, when the wheel speed is zero (and therefore wheel power is zero), but the wheel torque demand is at its maximum. Another similar situation can occur when the vehicle is traveling on sand or gravel at low speed or zero speed and the driver sharply depresses the accelerator pedal. In this and other similar scenarios, the resulting desired engine power, at a normal battery state of charge (SOC), corresponds to that required to overcome losses in the transmission and auxiliary systems.

[0004] The hybrid vehicle architecture should be designed to adequately accommodate such driving scenarios while delivering the expected amount of torque to the wheels to propel the vehicle. In one type of power-split hybrid, a series of reduction gears transfers torque from the planetary gear set to a differential, which then distributes the torque to the wheels. For example, in a motor vehicle, the engine may be connected to a carrier of a planetary gear set, while the sun gear is connected to a generator. The torque output from the engine causes the sun gear to rotate, which in turn turns the generator to either charge a battery or provide drive torque via a traction motor. Furthermore, a ring gear of the planetary gear set rotates a series of torque-reducing gears that ultimately lead to the traction motor and a powertrain output.There are control strategies that aim to supply the wheels with the optimal torque during low-speed, high-torque scenarios, as described above, based on the amount of torque transmitted through the ring gear. However, these control strategies take the series of reduction gears into account when deciding how much torque to generate from the engine and / or electric motor.

[0005] In another type of power-split hybrid, a chain, belt, or other continuous torque transmission element transfers the torque from the planetary gear set to a differential. No reduction gear is provided.

[0006] Hybrid vehicles without a power-split drivetrain are known from DE 696 16 738 T2 and US 2013 / 0 035 845 A1. BRIEF OVERVIEW

[0007] According to one embodiment, a vehicle with a power-split drivetrain comprising a power unit, a first motor / generator and a second motor / generator, a planetary gear set coupled to the power unit and having a ring gear for transmitting ring gear torque to the differential, wherein the first motor / generator is configured to selectively output torque to the differential; wherein the second motor / generator can be driven by a sun gear of the planetary gear set to generate electrical energy; a chain, a belt or a mechanical loop and at least one control unit that operatively couples the ring gear of the first motor / generator to the differential;and a control configured to modify the output of the power machine based on a ring gear torque threshold for the torque supplied by the ring gear, such that a desired torque is transmitted through the chain, belt, or mechanical loop to the differential, and with a drive element coupled to the chain, belt, or mechanical loop to provide torque to the chain, belt, or mechanical loop, the drive element having a central shaft operatively coupled at its ends to the ring gear and to the first motor / generator. The chain, belt, or mechanical loop can be considered a continuous torque transfer member (CTTM) that operatively couples the ring gear and the electric machine to the differential.

[0008] The at least one control unit can be configured to increase the output of the power unit in order to maintain the ring gear torque above a ring gear torque threshold in order to transmit the desired torque through the CTTM to the differential.

[0009] A drive element, such as a gear or sprocket, can be coupled to the CTTM to provide it with torque. The drive element can have a central shaft that is operatively coupled at one end to the ring gear and at the other end to the electric machine. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a power-split hybrid electric vehicle according to an embodiment of the present disclosure. Fig. 2A and Fig. 2B are graphical representations of a planned engine speed and a planned engine torque as a function of the desired engine power. Fig. Figure 3 is a flowchart of a control strategy according to an embodiment which is implemented by at least one control for controlling the output of the power machine in such a way as to supply sufficient ring gear torque. Fig. Figure 4 is a further flowchart of an implemented control strategy by at least one control for controlling the output of the power machine in such a way as to supply sufficient ring gear torque, according to one embodiment. DETAILED DESCRIPTION

[0010] Embodiments of the present disclosure are described here. It is understood, however, that the disclosed embodiments are purely exemplary and that other embodiments can be designed in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching a person skilled in the art how the embodiments can be used in different ways.It is obvious to a person skilled in the art that various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to create embodiments not explicitly illustrated or described. The combinations of illustrated features provide exemplary embodiments for typical applications. However, various combinations and modifications of the features, consistent with the teachings of this disclosure, may be desirable for specific applications or implementations.

[0011] With reference to Fig. 1 A hybrid electric vehicle (HEV) comprises a power-split powertrain. The following describes power-split components that provide either a mechanical or an electrical power flow path to the wheels, or both. A vehicle system controller (VSC) and / or a powertrain control module (PCM) 12 comprise one or more controllers in a network of processors and controllers configured to control various components in the powertrain. These controllers can be generally referred to as one or more "controllers." Among other components, the controller 12 controls an electric traction battery 14. The battery 14 has a two-way electrical connection through which it receives and stores electrical energy (e.g.,during regenerative braking) and furthermore supplies the energy to an electric traction motor 16 (or motor / generator, M / G1) for propulsion. The control unit 12 also controls the operation of an internal combustion engine (ICE) 18. Both the traction motor 16 and the engine 18 are capable of driving a transmission 20, which ultimately supplies torque to the vehicle's wheels.

[0012] It is understood that references to a “motor” 16 and a “generator” 32 are made for the sake of simplicity and distinction. However, one or both of these can generally be referred to as an “electric machine” or motor / generator (M / G). Both the motor 16 and the generator 32 can function as a motor by providing torque to the drive train and as a generator by converting mechanical power into electrical energy.

[0013] The power unit 18 supplies power to a torque input shaft 22, which is connected to a planetary gear set 24. A freewheel clutch (not shown) can be provided along the input shaft 22 and selectively connects the power unit 18 to the planetary gear set 24. The input shaft 22 drives the planetary gear set 24, which comprises a ring gear 26, a sun gear 28, and a planet carrier assembly 30. In particular, the input shaft 22 is drive-connected to the carrier assembly 30 to drive the remaining parts of the planetary gear set 24.

[0014] A generator 32 (M / G2) is driven by the sun gear 28 of the planetary gear set 24. The generator 32 can be engaged with the sun gear 28, so that the generator 32 either rotates with the sun gear 28 or does not rotate with it. When the freewheel clutch couples the motor 18 to the planetary gear set 24, the generator 32 can generate energy as a reaction element to the operation of the planetary gear set 24. The electrical energy generated by the generator 32 is transmitted via electrical connections 36 to the battery 14, where it is stored for later use, such as for powering the vehicle or auxiliary components. The battery 14 can also receive and store electrical energy through regenerative braking in a known manner.

[0015] The battery 14, the motor 16, and the generator 32 are each interconnected via electrical connections 36 in a two-way electrical flow path, so that each component is electrically connected for use in propulsion and energy recovery. In one propulsion mode, the battery 14 supplies stored electrical energy to the motor 16, causing the motor 16 to rotate downstream components of the drivetrain (described below). The power unit 18 can also propel the vehicle by supplying some of its power to the generator 32, which can transfer electrical energy to the battery or directly to the motor 16. In another propulsion mode, the drive of the planetary gear set 24 by the power unit 18 causes the ring gear 26 to transmit torque to the downstream components of the drivetrain (described below).During this mode, the generator 32 can be decoupled from the planetary gear set 24, so that it does not generate any electrical power (for example, when the battery 14 has a high state of charge). If no selective decoupling of the generator 32 is provided, the generator 32 can provide a reaction or negative torque when the state of charge of the battery 14 is high.

[0016] An endless torque transmission element 40 transmits a torque output from the power machine 18 or the motor 16, or from both. The endless torque transmission element 40 can be a chain, a belt, or another mechanical loop with an input area (drive area) and an output area (driven area). The endless torque transmission element 40 mechanically couples the output of the power machine 18 and / or the motor 16 to a differential 42. In particular, both the ring gear 26 and the motor 16 provide a mechanical output to a shaft 44 that extends through a drive element 46, such as a sprocket or the like. The drive element 46 can be arranged between the ring gear 26 and the motor 16 so that it receives torque from both sides. Alternatively, the motor 16 can be located on the same side of the drive element 46 as the ring gear 26.The drive element 46 drives a driven element 48 (e.g., another sprocket) via the mechanical coupling with the continuous torque transmission element 40. At one end opposite the shaft 44, the differential 42, which receives torque and distributes it to and divides it between the vehicle's drive wheels 52, is coupled to the continuous torque transmission element 40.

[0017] Based on the above description of a power-split hybrid, it is evident that there are two power sources for the drivetrain. The first power source is the motor 18, which supplies torque to the planetary gear set 24. The other power source comprises only the electric drive system, which includes the motor 16, the generator 32, and the battery 14, with the battery 14 acting as an energy storage medium for the generator 32 and the motor 16. The generator 32 can be driven by the planetary gear set 44 and can alternatively act as a motor, supplying power to the planetary gear set 24.

[0018] It goes without saying that the power-split vehicle is from Fig. Figure 1 is merely exemplary, and the present disclosure is not to be construed as limiting it to such an arrangement. Other power-split vehicle architectures are intended to fall within the scope of protection of the control strategy of the present disclosure. It is understood, however, that in all embodiments an endless torque transmission element (instead of a torque reduction gear set) is provided for supplying torque from the torque-generating elements to the wheels.

[0019] When one or both power sources are operated to supply torque to the wheels, torque is transmitted through the endless torque transmission element 40. The combined torque ultimately delivered to the wheels is the sum of the torque provided by the motor 16 (motor torque) and the torque provided by the ring gear 26 (ring gear torque), as shown in the following equation (1): TRad=THohlr.+TMotor

[0020] The amount of ring gear torque depends on the reaction torque supplied by generator 32, which in turn depends on the engine torque and the extent to which the driven engine speed changes. It follows that the maximum available wheel torque occurs when motor 16 and engine 18 each supply full torque.

[0021] The desired power output of the power engine is planned based on the following equation (2): PKraftm._gew=PRad_gew.+PVerliese+PNebenverbr−PBatterie where P Rad_gew . represents the desired wheel power, P Verluste represents the expected electrical losses, P Nebenverbr . the electrical auxiliary consumers (e.g. HVAC - Heating / Ventilation / Air-Conditioning, heating, ventilation and air conditioning; radio, etc.) and P Batterierepresents the desired battery charge level or discharge level for SOC management (SOC - State Of Charge).

[0022] With the given desired power output, the power engine speed and the power engine torque are planned by a characteristic map that is designed to supply the planned power engine speed and the planned power engine torque at an efficient power engine speed setting point. Fig. 2A represents a characteristic map of the planned engine speed and Fig. 2B represents a characteristic map of a planned power machine torque, which is selected during operation based on the above criteria. Fig. 2B further includes lines for the minimum limit for engine torque and minimum engine power, as described below.)

[0023] Particularly at low vehicle speeds, a situation can arise where the amount of wheel power is relatively low, while the wheel torque demand is relatively high. Such a scenario occurs, for example, when the vehicle operator requests rapid full acceleration (fully depressed accelerator pedal) after the vehicle has come to a stop. At the moment of the initial acceleration request, the wheel speed is zero, and therefore the wheel power is also zero, but the wheel torque demand is at its maximum. Another similar situation can occur when the vehicle is traveling on sand or gravel at low speed or at zero speed, and the operator sharply depresses the accelerator pedal.According to various embodiments of the present disclosure, the control unit 12 is programmed to maximize the wheel torque supplied in situations such as those described above.

[0024] The control strategy provided here ensures maximization of wheel torque when the accelerator pedal is fully depressed, provided that the requested wheel torque at full depressurization is at least as high as the sum of the maximum available engine torque and the maximum available auxiliary torque. It also ensures that the requested wheel power can be achieved when operating with the pedal not fully depressed. An example of an algorithm used and implemented by the controller 12 is given with reference to Fig. 3 and Fig. 4 shown and described.

[0025] Fig. 3 and Fig. Figure 4 are diagrams illustrating the operation of a system or a method for controlling a vehicle according to the embodiments of the present disclosure. It is obvious to a person skilled in the art that the diagrams shown in Figure 4 represent the operation of a system or a method for controlling a vehicle according to the embodiments of the present disclosure. Fig. 3 and Fig. The operations or functions shown can be performed by software and / or hardware depending on the specific application or implementation. The various operations or functions may be performed in a different order or sequence than explicitly shown and described, depending on the specific processing strategy, such as event-driven, interrupt-driven, etc. Likewise, one or more operations, tasks, or functions may be performed repeatedly, in parallel, and / or omitted under certain operating conditions or for specific applications, even if this is not explicitly shown.In one embodiment, the operations shown are primarily implemented by software, instructions, or code stored in a non-volatile, computer-readable storage device and are executed by one or more microprocessor-based computers or controllers to control the operation of the associated vehicle components.

[0026] With reference to Fig. In step 3, an exemplary algorithm 100 begins at step 102 in response to, for example, a high torque demand at low vehicle speeds and low wheel power, as explained above. First, a minimum limit for the engine torque output (T) is set at step 104. Kraftm._min ) determined. The minimum limit for the motor torque output ensures that the torque output from the motor is sufficient to meet the requested wheel torque. Using a maximum limit for the motor torque (T Motor_max) and assuming that the engine speed is constant, the engine torque for a given wheel torque requirement should exceed the product of the gear ratio and the difference between the wheel torque and the engine torque limit as represented by the following relationship: TForce_min≥transmission ratio*(TRad−TMotor_max) The transmission ratio depends on the difference between the drive element 46 and the driven element 48 if gears are used. Other mechanisms can, of course, be employed that provide a change in rotational speed between the shaft 44 and the differential input, which should be taken into account in equation (3). If there is no transmission ratio difference between the drive element 46 and the driven element 48, and the endless torque transmission element translates the torque at a 1:1 ratio, this term can be omitted. In such a scenario, the minimum limit for the engine torque output is directly equal to the difference between the torque at the wheels and the maximum limit for the engine torque.

[0027] After determining the minimum torque of the power engine, a minimum power engine output (P) can be determined at 106. min ) using the characteristic map in Fig. 2B. The minimum power output of the power unit represents the minimum amount of power required to meet the wheel torque requirements during the desired acceleration event.

[0028] At 108, the maximum limit of the engine power (P) is reached. Kraftm._max ) to prevent battery overcharging. This value represents the maximum amount of engine power that the engine is permitted to transmit, taking into account the battery's maximum charge level. The maximum engine power to prevent battery overcharging can be calculated and limited using the following equation (4): PKraft._max=Prad_gew.−PBatterie_Lade_Grenze+PVerliers+PNebenverbraucher where P Batterie_Ladung_GrenzeThis represents a maximum charging power limit, which is the maximum charging strength of the battery, which may be limited by the design of the battery connector and the chemical properties of the battery.

[0029] The control system sets a maximum power limit, as generally illustrated by blocks 110-114. If the minimum power required to meet the wheel torque demand is greater than the maximum available power (taking into account the prevention of SOC overload), the minimum power transmitted by and from the ring gear and into the endless torque transmission element is increased to at least the maximum available power. Specifically, at 110, a comparison between P min and P Kraftm._max carried out. If the minimum power output of the power machines (P) min ) below the maximum limit for engine power (P Kraftm._max) is, the control unit sets a minimum threshold value for the ring gear power (P) at 112. min_Hohlr. ) as the specific minimum power output of a power machine (P min However, if the minimum power output of the power engine (P) min ) the maximum limit for engine power (P Kraftm._max If this value is exceeded, the control system sets the threshold value P at 114. min_Hohlr . equal to the maximum limit for engine power (P Kraftm._max ).

[0030] At 116, the desired power output (P) is achieved. Kraftm._gew. ) determined using the above equation (2).

[0031] Based on the above description, it is clear that if the desired motor power determined from the wheel power request is below the minimum motor power required to deliver the wheel torque, the control system can increase the motor power request to this lower value. This ultimately increases the power transmitted by the ring gear. However, if the desired motor power determined from the wheel power request already exceeds the minimum motor power required to deliver the wheel torque, such a measure is unnecessary, and the motor power request can remain unchanged.

[0032] The engine power command can then be determined using the parameters above, so that the engine can deliver power to meet the torque requirement at the wheels, especially in the low-speed, high-torque situations described above. At 118, a comparison is made between the desired engine power (P) Kraftm._gew. ) and the minimum threshold for the ring gear power (P min_Hohlr. ) (as determined in 110-114). If the desired engine power exceeds the minimum ring gear power, the control unit sets the engine power command at 120 to the desired engine power (P). min_Hohlr. However, if the minimum ring gear power exceeds the desired motor power, the controller sets the motor power command to the minimum ring gear power at 122. The algorithm ends and can return at 124.

[0033] In steps 118-122, the management of the power output set and controlled by the control system is carried out in such a way that the power output through the ring gear exceeds a threshold value in order to provide the wheels with the desired torque.

[0034] Fig.Figure 4 represents a simplified, more detailed control strategy or algorithm 200 that provides the desired wheel torque according to the embodiments of the disclosure. At 202, a minimum power output from the motor is determined to meet the torque requirement. At 204, the current maximum available output from the motor is determined similarly to that shown in step 108. At 206, a minimum threshold for the ring gear torque is determined in a similar manner to that described with reference to blocks 110-114. In particular, the minimum threshold for the ring gear torque corresponds to the lower of the minimum power output required to meet the wheel torque requirements or the maximum available power output.At 208, the control system modifies the output of the power machine in such a way that the ring gear torque exceeds the minimum threshold value for the ring gear torque.

[0035] Various embodiments of the present disclosure, described above, provide a strategy for modifying the engine output (engine power) to supply ring gear torque to the wheels to meet the requested torque. In short, the control strategy determines and modifies the engine power requirement such that the resulting ring gear torque exceeds an associated threshold. The ring gear threshold can be determined, as detailed above, using an engine torque limit and a requested wheel torque. In some embodiments, the minimum engine power requirement is determined and provided, resulting in an engine torque output high enough to supply the minimum ring gear torque.This minimum level of motor power, taking into account the motor efficiency, provides the desired wheel torque. In some embodiments, the maximum motor power output can be determined based on the wheel power requirements and battery charge limits.

[0036] When the output of the power machine is changed to ensure that the torque supplied through the ring gear is above a ring gear torque threshold, torque to meet the desired requested wheel torque is transferred through the endless torque transmission element and to the wheels.

[0037] It is understood that the above references to "torque" and "power," such as the minimum threshold for ring gear power, can be replaced by simple mathematical properties of the relationship between torque and power (power = torque * speed). Thus, the minimum threshold for ring gear power can also be a minimum threshold for ring gear torque by simply dividing by the speed. The present disclosure should not be limited to strict "power" thresholds or strict "torque" thresholds. Such an example of a conversion is carried out between steps 104 and 106. According to the embodiments of the present disclosure, the engine power is modified to provide the desired torque to the wheels.

[0038] The processes, procedures, or algorithms disclosed herein may be delivered to or implemented by a processing unit, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Likewise, the processes, procedures, or algorithms may be stored as data and instructions executable by a controller or computer in many forms, including, but not limited to, information permanently stored on non-writable storage media such as ROM devices, and information modifiably stored on writable storage media such as floppy disks, magnetic data storage tapes, CDs, RAM devices, and other magnetic and optical media. The processes, procedures, or algorithms may also be implemented in an executable software object.Alternatively, the processes, procedures or algorithms can be implemented wholly or partially using suitable hardware components, such as ASICs (Application Specific Integrated Circuits), FPGAs (Field-Programmable Gate Arrays), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components.

[0039] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The terms used in the description serve to describe, not to limit, the invention, and it is understood that various modifications can be made without departing from the intent and scope of protection of the disclosure. As previously described, the features of different embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated.While various embodiments may have been described as offering advantages or being preferable to other embodiments or implementations of the prior art with respect to one or more desired properties, it is, as is obvious to the person skilled in the art, that compromises may be made between one or more features or properties in order to achieve the desired overall system characteristics, depending on the specific application and implementation. These features may include, but are not limited to, cost, strength, durability, life-cycle costs, marketability, appearance, packaging, size, ease of maintenance, weight, manufacturability, ease of assembly, etc.Embodiments that are described as less desirable than other embodiments or implementations of the prior art with respect to one or more properties are therefore not outside the scope of protection of the disclosure and may be desirable for certain applications.

Claims

[1] Vehicle comprising the following: a power-split drive train comprising a power unit (18), a first motor / generator (16) and a second motor / generator (32); a planetary gear set (24) which is coupled to the power machine (18) and has a ring gear (26) for transmitting a ring gear torque to a differential (42); wherein the first motor / generator (16) is configured to selectively output torque to the differential (42); wherein the second motor / generator (32) can be connected to a sun gear (28) of the planetary gear set (24) to generate electrical energy; a chain, belt or mechanical loop that operatively couples the ring gear (26) and the first motor / generator (16) to the differential (42); and a control (12) configured to modify the output of the power machine (18) based on a minimum limit for the power machine torque output for the torque supplied through the ring gear (26) such that a desired torque is transmitted through the chain, belt or mechanical loop to the differential (42), wherein the torque output of the power machine is defined such that it is sufficient to meet the requested wheel torque. [2] Vehicle according to claim 1, further comprising a drive element (46) which is mechanically coupled to the chain, belt or mechanical loop to provide torque to it, wherein the drive element (46) has a central shaft (44) which is operatively coupled at its ends to the ring gear (26) and to the first motor / generator (16). [3] Vehicle according to claim 1 or 2, wherein the control (12) is configured to change the output of the power machine (18) based on the fact that the first motor / generator (16) outputs torque at or after a maximum altitude. [4] Vehicle according to one of claims 1 to 3, wherein the control (12) is configured to further modify the output of the power unit (18) based on the fact that a requested wheel torque exceeds a sum of a maximum available engine torque and a maximum available power unit torque. [5] Vehicle according to any one of claims 1 to 4, wherein the control (12) is further configured to increase the output of the power unit (18) based on the fact that a wheel torque is below a wheel torque threshold. [6] Vehicle according to any one of claims 1 to 5, wherein the control (12) is further configured to increase the ring gear torque beyond the ring gear torque threshold in response to the fact that the vehicle speed is below a vehicle speed threshold and the wheel torque is below a wheel torque threshold.

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