Method and engine stability control system for a hybrid electric vehicle

A method for controlling a hybrid electric vehicle having a control system, a traction motor, and an engine includes generating an activation signal during a predetermined vehicle maneuver. The predetermined vehicle maneuver is a threshold hard braking maneuver on a surface having a low coefficient of friction. The method also includes processing the activation signal using the control system, and using the traction motor to command an injection or a passing of a feed-forward torque to the driveline of the vehicle. The feed-forward torque is in the same direction as the engine torque, and prevents a drive shaft of the engine from spinning in reverse during the maneuver. The method may include generating the activation signal in response to detecting an active state of the ABS controller. A hybrid electric vehicle includes an engine, a traction motor, and a control system configured to execute the above method.

TECHNICAL FIELD

The present invention relates to a method and engine stability control system for a hybrid electric vehicle.

BACKGROUND

Vehicle drive wheels can lock up during certain vehicle maneuvers, for example when executing a hard braking maneuver on a low-friction surface. This in turn can trigger a state activation in an antilock braking system (ABS) controller. To unlock the drive wheels, the active ABS controller automatically commands high frequency brake pressure pulsations.

SUMMARY

A method is disclosed herein for use aboard a hybrid electric vehicle having a control system, a traction motor, and an engine. The drive shaft of the engine may rotate in reverse during certain vehicle maneuvers. The present method therefore includes automatically generating an activation signal during a predetermined vehicle maneuver, and in particular during a hard braking maneuver on a threshold low coefficient of friction surface. The method further includes injecting or passing a feed-forward torque from the traction motor, or from multiple traction motors if the vehicle is so configured, to the driveline. The feed-forward torque is passed in the same direction as engine torque to prevent the drive shaft from spinning in reverse during the maneuver.

A hybrid electric vehicle includes an internal combustion engine configured to output an engine torque via a driveshaft of the engine, a first and a second traction motor, and a control system. The control system is configured for detecting the predetermined vehicle maneuver noted above, and for selectively injecting the feed-forward torque to prevent the driveshaft from spinning in reverse during the maneuver.

A control system for a hybrid vehicle includes at least one vehicle control module in communication with the engine and the traction motors. The control module is used to detect the predetermined vehicle maneuver, to generate an activation signal in response to the detected predetermined vehicle maneuver, and to inject the feed-forward torque to the driveline as noted above.

DETAILED DESCRIPTION

A hybrid electric vehicle10is shown inFIG. 1. The vehicle10includes a distributed control system (C)50configured to selectively control the stability of an internal combustion engine (E)12during a predetermined vehicle maneuver. The control system50does this by executing a method100(seeFIG. 2) via a set of control signals (iC)(arrow40). The control system50executes the method100in response to an activation signal (iA)(arrow25) that is indicative of the predetermined vehicle maneuver, as explained in detail below. The control signals (arrow40) are automatically generated and/or processed by various portions of the control system50, and then used to prevent engine spin from occurring during the maneuver.

The predetermined vehicle maneuver may be embodied as any vehicle event triggering an activation of an antilock braking system (ABS) controller21, or triggering equivalent ABS capabilities resident in another vehicle control module. The predetermined vehicle maneuver may include a hard braking event executed on a road surface having a threshold low coefficient of friction (μ), i.e., a low-μ surface. Typical low-g surfaces include wet, icy, oily, or gravel-coated road surfaces. If a hard braking maneuver, e.g., a driver stepping forcefully on a brake pedal, is executed on a surface that is slippery enough to cause an activation of the ABS controller21, this is considered herein to be a threshold low-μ surface. The control system50responds to such a maneuver by selectively injecting or passing a feed-forward torque from a traction motor (M1)16and/or (M2)18to the vehicle's driveline in the direction of engine torque to prevent reverse engine spin from occurring, i.e., reverse rotation of a driveshaft15.

The vehicle10may include the engine12, a transmission (T)14, and the traction motors16and18, with the fraction motors operating as fast actuators. Other vehicle embodiments may use a single fraction motor. The transmission14can be selectively powered by the engine12, the traction motor16, the traction motor18, or any combination thereof depending on the transmission operating mode or state, as determined by a shift control algorithm or logic (not shown). The vehicle10includes an energy storage system (ESS)20, e.g., a rechargeable battery pack, which is electrically connected to the traction motors16and18via a traction power inverter module (TPIM)22. The transmission14has multiple operating modes or states, each with an associated driveline inertia level.

The ESS20may be recharged during operation of the vehicle10via regenerative braking, and may be optionally recharged via an offboard power supply (not shown) when the vehicle is idle when configured as a plug-in hybrid electric vehicle. As understood in the art, a power inverter inverts electrical power from alternating current (AC) to direct current (DC), and vice versa, to enable use of a multi-phase AC permanent magnet or induction devices, i.e., the traction motors16and18, with a DC battery, e.g., the ESS20.

The control system50is used aboard the vehicle10to maintain control over the engine12, the transmission14, and each of the traction motors16and18. The control signals (arrow40) are communicated to the affected vehicle systems when needed, e.g., via a controller area network (CAN), serial bus, data routers, and/or other suitable means. The control system50may include as many different vehicle control modules as are required to maintain optimal control, including the ABS controller21, a braking control module (BCM)24, motor control processors (MCP)26and28, a hybrid control module (HCM)30, an engine control module (ECM)32, and a battery or ESS control module (ESSCM)34. For simplicity and clarity, the control system50is represented inFIG. 1as a single device, although separate controllers, either in functionality or in structure, may be used within the scope of the present invention.

The hardware components of the distributed control system50ofFIG. 1can include one or more digital computers or host machines each having a microprocessor or central processing unit, read only memory (ROM), random access memory (RAM), electrically-programmable read only memory (EPROM), a high-speed clock, analog-to-digital (A/D) and digital-to-analog (D/A) circuitry, and input/output circuitry and devices (I/O), as well as appropriate signal conditioning and buffer circuitry. Each set of algorithms or code resident in the control system50or readily accessible thereby, including any algorithms or computer code needed for executing the present method100as explained below with reference toFIG. 2, can be stored in tangible/non-transitory computer-readable memory (M)36, and executed by a host machine or other suitable hardware portions of the control system50as needed to provide the disclosed functionality.

The engine12is capable of selectively generating a sufficient amount or level of engine torque for rotating the drive shaft15. An input assembly11can be used to connect the engine12to an input member13of the transmission14. The specific configuration of input assembly11can vary with the vehicle design. For example, the input assembly11may be a clutch and damper assembly that selectively connects and disconnects the engine12from the vehicle driveline as needed, or it can be a grounding clutch or brake that selectively brakes the drive shaft15when the engine is not running.

Each of the traction motors16and18has a respective motor output shaft17and19. Thus, input torque to the transmission14may be generated and delivered by the engine12as engine torque and/or the traction motors16,18as motor torque. Output torque from the transmission14can be delivered to a set of drive wheels39via an output member23. The actual configuration of the transmission14can vary depending on the design of the vehicle10, and may include one or more planetary gear sets, an electrically variable transmission, rotating clutches, braking clutches, hydraulic or electromechanical activation components, etc.

As noted above, the distributed control system50shown inFIG. 1is configured to execute the present method100(seeFIG. 2) to optimize engine stability at low vehicle speeds during a threshold vehicle maneuver, e.g., a maneuver in which the ABS controller21enters an active state. Such a maneuver may be embodied as the hard braking maneuver on a threshold low-pt surface as noted above, wheel lock up upon hitting an obstacle such as a pothole, or any other event in which the ABS controller21becomes active. This in turn results in generation of the activation signal (arrow25), whether from the ABS controller21or from another control module.

Major components of a typical ABS system include a wheel speed sensor (S)54positioned in close proximity to each drive wheel39, and any required hydraulic, electric, and/or electromechanical brake components48. In one possible embodiment, the brake components48can include brake discs, calipers, drums, pads, rotors, etc., as understood in the art, as well as any fluid or electromechanical activation devices. The wheel speed sensors54collectively provide wheels speed signals (ω39)(arrow52) to the BCM24. When any of the drive wheels39are approaching a locked state, the brake components (BC)48are automatically controlled to individually modulate the braking pressure applied at each wheel, thus preventing the wheels from locking up or, barring that, subsequently unlocking any locked wheels.

The distributed control system50shown inFIG. 1can also receive and process various other input signals, including but not limited to output torque and rotational speed of the engine12, motor torque, torque direction, and rotational speed of the traction motors16and18, throttle or accelerator position, etc. The control system50, and in particular the HCM30, then achieves a targeted gear ratio or transmission operating mode or state in the most efficient manner by coordinating engine speed and motor speeds in a manner that is dependent upon the current transmission operating strategy.

Referring toFIG. 2, method100may be executed by the control system50ofFIG. 1to address the condition in which the predetermined vehicle maneuver causes the drive wheels39to lock up, which may in turn activate the ABS controller21. Heavy motor inertia complicates the ability of any ABS-related portions of the distributed control system50to unlock the drive wheels39. Additionally, under certain transmission operating modes at low speeds there is a chance that, when executing a predetermined vehicle maneuver, the engine12shown inFIG. 1will rotate or spin backward, at least momentarily. The present method100is therefore executed by the control system50to prevent such engine spin and thus protect the engine12during this maneuver.

Beginning with step102, and referring to the structure of the vehicle10shown inFIG. 1and explained above, the distributed control system50collects a preliminary set of vehicle information. Step102may include processing braking signals, vehicle speed, and/or wheel speeds via the BCM24or another suitable module, calculating wheel slip via the wheel speed signals52, determining the activation state of the ABS controller21, transmission output speed, etc. The method100then proceeds to step104.

At step104, the control system50determines whether or not the information collected at step102corresponds to a predetermined vehicle maneuver, such as a threshold hard braking maneuver executed on a low-μ surface. Step104may take place in the BCM24or other suitable control module, and may include comparing information from step102to calibrated thresholds. Other factors that could be evaluated at step104include a rapid deceleration of the input member13of the transmission14in conjunction with a vehicle speed and/or wheel speeds that remain relatively constant, within a calibrated range, or that do not otherwise decrease at a rate that would be indicated by such rapid braking.

If the predetermined vehicle maneuver is not detected at step104, the method100repeats step102. Otherwise, the method100includes passing the results of step104to the HCM30from the BCM24or other control module, if used, over a serial data link or other suitable high-speed communications channel. The method100then proceeds with step106.

At step106, the control system50calculates and injects a suitable amount of feed-forward torque (TFF) to the vehicle driveline, in the direction of engine torque, using the traction motors16and/or18. As the engine12is a slow actuator relative to the actuation speed of the traction motors16and18, it can take considerable time to produce sufficient engine torque. A rapid event such as driveline load following a threshold hard braking event on a low-μ surface could cause the engine12to spin backward before the engine can protect itself. This may be particularly problematic when the engine12is turned off. Torque is thus injected to the driveline at step106in the direction of engine torque via the fast-actuating traction motors16and/or18in order to prevent the engine12from spinning backward, and thus to control engine stability.

The amount of feed-forward torque may be calculated, for example, in a manner that depends on the vehicle speed, engine speed, transmission operating mode or state, etc. The feed-forward torque may be calculated using calibrated gains or via any other suitable approach. The method100then proceeds to step108.

At step108, the HCM30verifies whether a calibrated duration has elapsed. If so, the feed-forward torque is terminated, and the method100is finished. If not, steps106and108may be repeated in a closed loop until the calibrated duration has elapsed.