Disturbance mitigation techniques for hybrid power-split transmissions

A system and method for controlling a hybrid power-split transmission of a vehicle involve obtaining measured rotational speeds of an engine and an electric motor of the transmission, wherein the transmission comprises at least two input shafts having a gear set therebetween and an output shaft, wherein one input shaft is coupled to the engine and another input shaft is connected to the electric motor, determining a main torque profile for the electric motor based on a set of operating conditions of the vehicle, calculating a speed difference between the measured rotational speeds of the engine and the electric motor, determining a disturbance torque profile for the electric motor based on the calculated speed difference, and performing closed-loop control of the electric motor based on a combination of the main and disturbance torque profiles to mitigate a disturbance at the output shaft of the transmission.

FIELD

The present application generally relates to hybrid transmissions and, more particularly, to techniques for mitigating disturbances in a hybrid power-split transmission of a hybrid vehicle during transient events.

BACKGROUND

A hybrid vehicle typically includes both an internal combustion engine and one or more electric motors. One specific type of hybrid vehicle includes a hybrid power-split transmission comprising an engine and at least one electric motor that are each coupled to a separate input shaft. Via a system of gears, the engine and the electric motor(s) are each capable of providing torque to an output shaft of the hybrid power-split transmission. These devices, however, do not always operate at the same frequency. The frequency of the engine, for example, depends on its firing rate. When rotational speed differences between the engine and the electric motor(s) occur, a disturbance (i.e., noise/vibration/harshness, or NVH) at the output shaft could occur. This disturbance could be continuous, often referred to as “rattle,” or instantaneous, often referred to as “clunk,” and could be felt by a driver of the vehicle, which is undesirable. Accordingly, while such hybrid transmission systems work well for their intended purpose, there remains a need for improvement in the relevant art.

SUMMARY

According to one example aspect of the invention, a control system for a hybrid power-split transmission of a vehicle is presented. The hybrid power-split transmission comprises at least two input shafts having a gear set therebetween and an output shaft, wherein one input shaft is coupled to an engine and another input shaft is connected to an electric motor. In one exemplary implementation, the control system comprises: an engine speed sensor configured to measure a rotational speed of the engine, a motor speed sensor configured to measure a rotational speed of the electric motor, and a controller configured to: determine a main torque profile for the electric motor based on a set of operating conditions of the vehicle, calculate a speed difference between the measured rotational speeds of the engine and the electric motor, determine a disturbance torque profile for the electric motor based on the calculated speed difference, and perform closed-loop control of the electric motor based on a combination of the main and disturbance torque profiles to mitigate a disturbance at the output shaft of the hybrid power-split transmission.

In some implementations, wherein the disturbance is at least one of rattle and clunk at the output shaft caused by a transient event. In some implementations, the transient event is a start of the engine using the electric motor. In some implementations, the controller is further configured to determine the main torque profile based on an average of the measured engine and electric motor speeds. In some implementations, the transient event is a stop of the engine. In some implementations, the transient event is a tip-in or tip-out of an accelerator device of the vehicle.

In some implementations, the disturbance torque profile modifies the main torque profile such that the speed of the electric motor matches the speed of the engine to mitigate the disturbance. In some implementations, the hybrid power-split transmission further comprises another electric motor coupled to another separate input shaft. In some implementations, the controller is further configured to control the other electric motor to pre-load at least some gears of the gear set to further mitigate the disturbance.

According to another example aspect of the invention, a method of controlling a hybrid power-split transmission of a vehicle is presented. The hybrid power-split transmission comprises at least two input shafts having a gear set therebetween and an output shaft, wherein one input shaft is coupled to an engine and another input shaft is connected to an electric motor. In one exemplary implementation, the method comprises: obtaining, by a controller of the vehicle, measured rotational speeds of the engine and the electric motor, determining, by the controller, a main torque profile for the electric motor based on a set of operating conditions of the vehicle, calculating, by the controller, a speed difference between the measured rotational speeds of the engine and the electric motor, determining, by the controller, a disturbance torque profile for the electric motor based on the calculated speed difference, and performing, by the controller, closed-loop control of the electric motor based on a combination of the main and disturbance torque profiles to mitigate a disturbance at the output shaft of the hybrid power-split transmission.

In some implementations, the disturbance is at least one of rattle and clunk at the output shaft caused by a transient event. In some implementations, the transient event is a start of the engine using the electric motor. In some implementations, the controller is further configured to determine the main torque profile based on an average of the measured engine and electric motor speeds. In some implementations, the transient event is a stop of the engine. In some implementations, the transient event is a tip-in or tip-out of an accelerator device of the vehicle.

In some implementations, the disturbance torque profile modifies the main torque profile such that the speed of the electric motor matches the speed of the engine to mitigate the disturbance. In some implementations, the hybrid power-split transmission further comprises another electric motor coupled to another separate input shaft. In some implementations, the method further comprises controlling, by the controller, the other electric motor to pre-load at least some gears of the gear set to further mitigate the disturbance.

DETAILED DESCRIPTION

Referring now toFIG. 1, a functional block diagram of an example hybrid vehicle100is illustrated. The hybrid vehicle100(hereinafter, “vehicle100”) includes a hybrid powertrain104that provides torque to a driveline108(a differential, wheels, etc.). In the illustrated exemplary implementation, the hybrid powertrain104comprises an internal combustion engine112(hereinafter, “engine112”) that combusts an air/fuel mixture to generate drive torque at a crankshaft116and a hybrid power-split transmission120(hereinafter, “transmission,” and also known as an “electrically variable transmission,” or EVT). In one exemplary implementation, the engine112is an Atkinson cycle engine having a compression ratio of approximately 12.5:1. This type of engine112is able to utilize a maximum amount of power generated by combustion of the air/fuel mixture, thereby increasing performance of the hybrid vehicle100. One drawback of this type of engine112is poor power/performance at low speeds. The transmission120, however, is able to generate drive torque to compensate for the poor power/performance of the engine112, particularly at low speeds. It will be appreciated that other suitable engine configurations could be utilized.

The transmission120comprises first and second electric motors124A,124B (collectively, “electric motors124”) powered by a battery system128. The transmission120further comprises a one-way clutch132, a planetary gear set136, and a final drive gear140. The engine112is selectively connected to the planetary gear set136via the one-way clutch132. Electric motor124A is also connected to the planetary gear set136, which in turn is connected to the driveline108via the final drive gear140. Electric motor124B is connected to both the planetary gear set136and directly to the final drive gear140such that the electric motors124A,124B and the planetary gear set136are able to achieve a wide range of gear ratios. Details of this planetary gear set136are shown inFIG. 2and discussed in greater detail below. The electric motors124A,124B are also configured to recharge the battery system128(e.g., via regenerative braking techniques).

A controller144controls operation of the hybrid powertrain104. This includes, but is not limited to, controlling combinations of the engine112and the one-way clutch132and the electric motors124A,124B to achieve a desired torque output and a desired gear ratio of the transmission120. The controller144receives driver input from an accelerator device148(e.g., an accelerator pedal). The controller144also receives speed measurements from various speed sensors. These include, for example, an engine speed sensor152that measures a rotational speed of the engine112(i.e., the crankshaft116), a first motor speed sensor156A that measures a rotational speed of electric motor124A, and a second motor speed sensor that measures a rotational speed of electric motor124B. These measured speeds are utilized by the controller to perform disturbance (i.e., rattle and/or clunk) mitigation at an output shaft of the transmission120, which is illustrated inFIG. 2and discussed in more detail below.

Referring now toFIG. 2and with continued reference toFIG. 1, a schematic diagram of the transmission120is illustrated. The transmission120comprises three separate input shafts204A,204B, and204C. Input shaft204A is coupled to the crankshaft116of the engine112. A flywheel and damper208is connected to input shaft204A and the one-way clutch132. A torque limiting or breakaway clutch212is connected to the one-way clutch132and a carrier gear216of the planetary gear set136. The planetary gear set136further comprises a planetary pinion gear220, a sun gear224, and a main shaft gear228. The sun gear224is connected to input shaft204B, which in turn is coupled to an output shaft of electric motor124A. Motor speed sensor156A measures the rotational speed of the input shaft204B (or the output shaft of the electric motor124A, which is the same).

The planetary gear set136further comprises a ring gear232connected to the planetary pinion gear220and a separate transfer/idler gear236. A final drive pinion gear240is connected to the transfer/idler gear236and the final drive gear140. The final drive gear140is also connected to a differential244via an output shaft248of the transmission120. The differential244splits the final driveshaft torque to the wheels of the driveline108. The transfer/idler gear236is also connected to another pinion gear252. A park clutch256is connected to the pinion gear and input shaft204C, which in turn is coupled to an output shaft of electric motor1248. Similar to electric motor124A, motor speed sensor156B measures a rotational speed of input shaft204C (or the output shaft of the electric motor124B, which is the same).

As previously discussed, when the rotational speeds of the engine112and electric motor124A are different, a disturbance could occur at the planetary gear set136, which is then transmitted to the output shaft248of the transmission120. This is particularly true for transient events where electric motor and engine speed widely vary. Non-limiting examples of these transient events include engine start (i.e., using the electric motor), engine stop, and tip-in/tip-out of the accelerator device148. One solution to mitigate this disturbance is to “pre-load” the planetary gear set136using electric motor124B. This involves the electric motor124B driving the various gears such that there is no gap present between the gear teeth. By eliminating the gap between the gear teeth, gear lash is mitigated, thereby mitigating the disturbance. This technique, however, only partially mitigates the disturbance and also does not solve the core problem. The techniques of the present disclosure operate to synchronize the speeds of the engine112and electric motor124A, thereby mitigating or eliminating the source of the disturbance.

Referring now toFIG. 3A, a first example control architecture300is illustrated. This control architecture300represents a generic control architecture that could be applicable to any transient events and could be implemented by controller144. A main torque profile generator304generates a main torque profile for electric motor124A based on a set of operating parameters of the vehicle100. This main torque profile depends on the type of operation being performed (engine start, engine stop, acceleration, deceleration, etc.) and the set of operating parameters include any suitable parameters for determining the amount of torque needed from the electric motor124A. In some implementations, various main torque profiles for various operating procedures may be predetermined and stored at a memory of the controller144. A disturbance mitigator308calculates a speed difference between the measured engine and motor speeds received from sensors152and156A. The disturbance mitigator308also determines a disturbance torque profile based on this calculated speed difference. The main torque profile and the disturbance torque profile are both fed to a combination block312(e.g., a summation) that generates a motor torque command for electric motor124A based on a combination of the profiles.

Referring now toFIG. 3B, a second example control architecture350is illustrated. This control architecture350represents a specific control architecture applicable for engine start transient events and could be implemented by controller144. A main torque profile generator354generates a main torque profile according to an engine start profile (e.g., a desired engine speed for firing the engine112). The main torque profile generator354, however, also takes into account an average, as calculated by average block358, of the measured engine and motor speeds received from sensors152and156A. Using the average of these speeds could result in the main torque profile being adjusted to provide a smoother engine start. In some implementations, the main torque profile is also fed to a gear pre-loading calculator362that determines a motor torque command for electric motor124B to pre-load gears of the transmission120to further mitigate the disturbance at the transmission output shaft. Similar to the configuration300ofFIG. 3A, a disturbance mitigator366calculates the speed difference and determines a disturbance torque profile. Also similar to the configuration300ofFIG. 3A, a combination block370(e.g., a summation) determines the motor torque command for electric motor124A based on a combination of the profiles.

Referring now toFIG. 4, a flow diagram of an example method400of clunk and rattle mitigation for the hybrid power-split transmission is illustrated120. At404, the controller144obtains the measured engine speed (e.g., from the engine speed sensor152) and the measured motor speed (e.g., from motor speed sensor156A). At408, the controller144determines a main torque profile for the first electric motor124A based on the set of vehicle operating parameters. At412, the controller144calculates a speed difference between the measured engine and electric motor speeds. At416, the controller144determines a disturbance torque profile based on the calculated speed difference. At420, the controller144performs closed-loop control of the electric motor124A based on a combination of the main and disturbance torque profiles. The disturbance torque profile, for example, could be an oscillating signal to cancel the disturbance caused by the main torque profile. This closed-loop control involves continuing to monitor and calculate the speed difference until the disturbance at the transmission output shaft has been eliminated or mitigated as much as desired.

It will be appreciated that the term “controller” as used herein refers to any suitable control device or set of multiple control devices that is/are configured to perform at least a portion of the techniques of the present disclosure (an engine control unit, a transmission control unit, a hybrid control unit, etc.). Non-limiting examples of the controller include an application-specific integrated circuit (ASIC), one or more processors and a non-transitory memory having instructions stored thereon that, when executed by the one or more processors, cause the controller to perform a set of operations corresponding to at least a portion of the techniques of the present disclosure. The one or more processors could be either a single processor or two or more processors operating in a parallel or distributed architecture.