DE102013104433A1 - Method for operating powertrain in e.g. modular hybrid electric car, involves controlling motor to increase of engine speed in direction of predetermined engine idle rotation speed in response to reduction of engine speed - Google Patents

Abstract

The method involves engaging a release clutch (26) for drive-effective connection of a traction motor (22) with an internal combustion engine (20). The traction motor is operated to produce a loading torque being based on a charge of a battery (24). The engine is controlled to increase engine speed in a direction of a predetermined engine idle rotation speed in response to a reduction of the engine speed, which is resulted from a load associated with the loading rotational torque. The traction motor is operated for an adjustment of the loading torque for reducing load on the engine. An independent claim is also included for a method for operating a traction motor in a vehicle.

Description

This application claims the benefit of US Provisional Patent Application No. 61 / 643,508, filed on May 7, 2012, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL AREA

The present invention relates to a control strategy for a hybrid electric vehicle. More particularly, the disclosure relates to a strategy for charging the electric battery by using an internal combustion engine.

BACKGROUND

Vehicles traditionally use variable ratio transmissions to transfer power between an internal combustion engine and the vehicle wheels. In an automatic transmission, the controller selects the gear ratio in response to the vehicle speed and a driver request, which is generally communicated by depressing an accelerator pedal. In a Modular Hybrid Transmission (MHT) modular architecture, the vehicle also includes a traction motor connected to the input of a transmission. The traction motor is electrically connected to a battery. The traction motor may be used in either a motorization mode that uses energy from the battery to supplement engine performance, or a generation mode where the traction motor converts mechanical energy into electrical energy that is stored in the battery.

SHORT DESCRIPTION OF THE REVELATION

A method of operating a modular hybrid vehicle powertrain includes engaging an engine disconnect clutch, operating a traction motor to charge a battery by generating a boost torque based on a battery state of charge, and controlling an engine to respond to an increasing load by increasing engine torque. If the engine speed falls below a threshold, the method may include decreasing the boost torque to reduce the load on the engine. The method may further include engaging a launch clutch, controlling the engine to generate engine torque based on the engine speed and battery state of charge, and controlling the traction motor to generate a boost torque such that the engine and traction engine torque combined satisfy a driver requested torque. The method may further include controlling the traction motor to generate a minimum boost torque based on the engine speed.

One method of operating a traction motor includes applying a negative torque to an engine while generating electrical power such that the torque is independent of rotor speed, and then responding to a decrease in rotor speed below a threshold by increasing torque to reduce engine load , The negative torque may be based on a state of charge of a battery.

A vehicle powertrain includes an engine, a traction motor electrically connected to a battery, an engine disconnect clutch selectively coupling the engine to the traction motor, and a controller. The controller is programmed to engage the engine disconnect clutch, operate the traction motor to generate a first boost torque based on a battery state of charge, and respond to each resultant decrease in engine speed by increasing the torque generated by the engine. The controller may be further programmed to respond to a decrease in engine speed below a threshold by adjusting the boost torque to reduce engine load. The powertrain may also include a transmission gear and a starting clutch that selectively couples the electric motor to the input of the transmission gear. The controller may be further programmed to engage a launch clutch, control the engine to generate engine torque based on engine speed and battery state of charge, and control the traction motor to generate a boost torque such that the sum of the engine torque and the boost torque correspond to a driver requested torque ,

BRIEF DESCRIPTION OF THE DRAWINGS

1 FIG. 10 is a block diagram of an exemplary hybrid vehicle powertrain according to an embodiment of the present invention. FIG.

2 FIG. 10 is a flowchart illustrating one embodiment of the disclosed method. FIG.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It will be understood, however, that the disclosed embodiments are mere examples, and that other embodiments take various and alternative forms can. The figures are not necessarily to scale, some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be construed as limiting, but only as a representative basis for teaching a person skilled in the art various applications of the present invention. As one of ordinary skill in the art will appreciate, various features illustrated and described with respect to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not expressly illustrated or described are. The combinations of the illustrated features provide representative embodiments for typical applications. However, various combinations and changes in features consistent with the teachings of this disclosure may be desirable for particular applications or implementations.

1 shows a vehicle with a modular hybrid transmission. The solid lines showing the components in 1 Connect, show drivable connections that transmit power from one output of a component to an input of another component via a mechanism that limits the speed of the output in proportion to the speed of the input. It can be made for example via shafts or gears a drivable connection. The internal combustion engine 20 provides traction torque during stationary operation. The traction engine 22 adds additional torque during transient events and can act as a generator during braking and at other times. The traction engine 22 is electric with the battery 24 connected. The internal combustion engine 20 and traction engine 22 are selectively via the clutch release 26 coupled. In other words, engine 20 and traction engine 22 are connected driveably when the clutch 26 is engaged, and are disconnected when the clutch 26 disengaged. The torque of engine 20 and traction engine 22 is through the transmission gear 28 and the differential 32 to a set of drive wheels 30 transfer. The transmission gearbox 28 It selectively sets a gear ratio so that the engine operates at a high speed over a wide vehicle speed range. The transmission may be either a step ratio transmission with a finite number of discrete ratios or a continuously variable transmission. The differential 32 allows the outer wheel to rotate a little faster than the inner wheel when the vehicle turns around. The starting clutch 34 gives the engine 20 and the traction engine 22 from the transmission 28 and the wheels 30 while the vehicle is stationary, allowing the engine to idle. To start the vehicle is the starting clutch 34 gradually engaged. Finally, the gear pump 36 a hydraulic pressure for engaging the clutches ready, such as the clutch release 26 , the starting clutch 34 or the clutches in the transmission gear 28 ,

An MHT hybrid is operated in several different modes. When the vehicle stops, the starting clutch becomes 34 disengaged and the engine may be idling or off. When the engine is off, the disengagement clutch can turn off 26 also be disengaged. The traction motor may power the transmission pump by utilizing power from the battery so that the transmission is ready when the driver indicates a desire for movement. When the engine is idling, the disengagement clutch may fail 26 be engaged. An engine controller adjusts the engine torque to maintain the target idle speed. The engine controller may change the throttle opening, fuel injection parameter, ignition timing, etc. to adjust the engine torque. While the engine is idling, the traction motor can charge the battery by applying a charging torque.

As the vehicle moves, the wheels are powered by a combination of engine power and battery power. A controller determines how much combined torque is to be delivered based on the position of the accelerator pedal and the engine speed. The controller also selects from the various gear ratios and how the requested combined torque is split between engine torque and traction engine torque. The torque capacity and efficiency of internal combustion engines and traction motors differ significantly. The torque capacity of an internal combustion engine increases with engine speed over most of the operating range, while traction motors are capable of producing high torque at low speed and less torque at high speed. Internal combustion engines are most efficient when operated at relatively low speed and near their maximum torque capacity. Traction motors are more efficient at low torque but inefficient at very low speed and high torque.

In some driving conditions, the traction motor may power the vehicle by using energy stored in the battery. During these conditions, the engine is off and the disengagement clutch is disengaged. Since no fuel is consumed under these driving conditions, improves the overall fuel economy. Under other driving conditions, the traction motor is used to make the engine run more efficiently. Internal combustion engines tend to be more efficient at low speeds. Nevertheless, internal combustion engines may have limited ability to generate power when operated at low speed. Accordingly, in a non-hybrid vehicle, it is sometimes necessary to operate the engine at a faster speed to deliver the required amount of power to the wheels. In the modular hybrid, supplementing engine torque with traction motor torque sometimes allows the transmission controller to select a gear ratio so that the engine runs more slowly and efficiently.

Providing positive traction motor torque requires the use of stored energy from the battery. The stored electrical energy is obtained by operating the electric motor during braking events as a generator to absorb energy that would otherwise be converted to heat by the friction brakes. In some circumstances, the energy obtained from braking is insufficient to meet the requirements. Under such circumstances, the energy may be obtained by increasing engine torque beyond the level required to propel the vehicle and operating the traction motor at negative torque to produce electrical energy. This increases fuel consumption during charging, but results in an opportunistic implementation in net fuel savings.

A disclosed method for determining the load torque in an MHT vehicle is in US Patent Nos. 4,194,954 2 shown. The charging torque is negative when the traction motor picks up energy from the engine to charge the battery. A negative value indicates that more energy is being supplied to the battery. In decision step 40 the controller determines if the engine is on. If not, charging by using engine power is not possible, so the charging torque at step 42 set to zero. If the engine is on, control determines at decision step 44 whether the vehicle is idling. At idle, the starting clutch is disengaged and the engine is controlled to maintain a certain engine speed. At idle, the boost torque is the main engine load. During idling, the charging torque becomes dependent on the state of charge at step 46 calculated. When the state of charge of the battery is low, the charging torque is set to a very negative value to charge the battery more quickly. When the state of charge is high, the charging torque is set to zero or to a slightly negative value to maintain the charge. If the vehicle is not idling, it must be in a driving condition. The controller calculates at step 48 a minimum traction motor torque based on engine speed. The minimum engine speed is adjusted to avoid requesting a combination of traction engine torque and traction engine speed at which the traction motor is inefficient. At step 50 A boost torque is calculated by subtracting a function of engine speed and state of charge from the driver requested input torque. The function is calibrated to bring the engine into an efficient operating condition. If the torque requested by the driver is low, the resulting charging torque is very negative and implies an aggressive charging of the battery. However, if the driver demand is high, the boost torque is set to a less negative value to ensure that sufficient engine power is available to meet the drive requirements. If the calculated boost torque is less than (more negative than) the minimum traction motor torque, the boost torque becomes 51 set to the minimum traction motor torque. When the calculated boost torque is positive, the boost torque becomes 51 set to zero. At step 52 The charging torque is filtered and the rate of change is limited to avoid sudden changes. Finally, the controller checks at step 54 whether the engine speed has fallen below a minimum. When the engine becomes excessively slower, the boost torque is adjusted to assist the engine 56 to relieve (the loading torque is made less negative). The minimum is calibrated to ensure, among other things, that the transmission pump generates sufficient hydraulic pressure to engage the clutches. Although the engine is commanded to generate enough torque to maintain engine speed, delays in engine response to changes in requested torque may occur. Since a traction motor reacts faster to changes in requested torque, it is sometimes more effective to control engine speed by controlling the load.

The processes, methods, or algorithms disclosed herein may be provided and / or implemented by a processing device, controller, or computer that may comprise any existing programmable electronic control unit or dedicated electronic control unit. In the same way, the processes, methods, or algorithms may be stored as data and instructions executable by a controller or computer in a variety of ways, including, but not limited to, information stored permanently in read-only media such as ROM devices and information that is stored variably on non-write-protected storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. These processes, methods or algorithms can also be implemented in a software-executable object. Alternatively, the processes, methods, or algorithms may be implemented in whole or in part using appropriate hardware components, such as application specific integrated circuits (ASIC), field programmable gate arrays (FPGAs), state machines, or other hardware components or devices, or as a combination of Hardware, software and firmware components.

Although embodiments have been described above, these embodiments are not intended to describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it will be understood that various changes may be made without departing from the spirit and scope of the disclosure. As described above, the features of various embodiments may be combined to form further embodiments of the invention, which are not expressly described or illustrated. While various embodiments with respect to a desired feature or features may be shown to be advantageous or preferred over other embodiments or prior art implementations, one of ordinary skill in the art will recognize that one or more features or features may be compromised. to achieve the desired overall system attributes that depend on the specific application and implementation. These attributes may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, operability, weight, manufacturability, ease of construction, and so forth. Therefore, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more features do not depart from the scope of the disclosure and may be desirable for particular applications.

Claims (9)

A method of operating a powertrain, comprising: Engaging a first clutch for drivingly connecting a traction motor to a motor; Operating the traction motor to generate a first charging torque based on a state of charge of a battery for charging the battery; and Controlling the engine to increase the engine speed toward a predetermined engine idle speed in response to a decrease in engine speed resulting from a load associated with the first charge torque. The method of claim 1, further comprising: further operating the traction motor to adjust the first boost torque to reduce the load on the engine in response to the decrease in engine speed below a threshold. The method of claim 1, wherein controlling the engine includes adjusting a throttle adjustment amount. The method of claim 1, wherein controlling the engine includes adjusting an ignition timing set value. The method of claim 1, wherein controlling the engine includes adjusting a fuel flow rate adjustment amount. The method of claim 1, further comprising: Engaging a second clutch for drivingly connecting the traction motor to a transmission gear; Controlling the engine to generate engine torque based on engine speed and state of charge; and further operating the traction motor to generate a second boost torque such that a sum of the second boost torque and the engine torque satisfies a net torque requested by the driver, the driver requested net torque based on the engine speed and an accelerator pedal position. The method of claim 6, further comprising: further operating the traction motor to produce a minimum boost torque, wherein the minimum boost torque is based on an engine speed. A method of operating a traction motor in a vehicle, the traction motor having a rotor connected for rotation to an engine at a positive rotor speed, the method comprising: Applying a negative torque to the engine when generating electrical energy, wherein the torque for rotor speeds above a threshold is substantially independent of the rotor speed; and increasing torque to reduce engine load in response to the decrease in rotor speed below a threshold. The method of claim 8, wherein the torque varies in response to changes in the state of charge of a battery.

Images