Patent Application
20220379872
This disclosure relates to control of an electrified vehicle that efficiently allocates and distributes powertrain torque between primary and secondary axles.
Electrified vehicles including hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs) may include multiple powertrain actuators that can be used to provide electric all-wheel drive (eAWD) functionality. Based on inputs from the driver, such as accelerator pedal position, a vehicle controller determines a total driver-demanded torque and controls the actuators to deliver the torque to the wheels for each axle. One or more primary powertrain actuators may provide propulsive powertrain torque to wheels of an associated primary axle and one or more secondary powertrain actuators may provide propulsive powertrain torque to wheels of an associated secondary axle. An eAWD system has the capability and flexibility to allocate and distribute torque between the primary and secondary axles to satisfy the driver-demanded torque. Because the losses generated by operating an electric motor vary as a function of speed and generated torque, control of the speeds and torques of the electric motors impacts engine fuel consumption and electric range of the vehicle. However, allocating torque based only on minimizing losses may result in applied torque having different directions for the front and rear axles under some operating conditions.
Embodiments of the disclosure include a vehicle having an engine configured to selectively apply propulsive torque to wheels of a first axle of the vehicle, a first electric machine configured to selectively apply propulsive torque to the wheels of the first axle of the vehicle, a second electric machine configured to selectively apply propulsive torque to wheels of a second axle of the vehicle, a traction battery electrically coupled to the first and second electric machines, and a controller configured to control engine torque, first electric machine torque, and second electric machine torque to provide a driver demand torque at the wheels of the first and second axles, wherein the controller allocates torque between the first and second electric machines based on associated combined losses of the first and second electric machines and maintaining the torque of the first and second electric machines in the same direction. The controller may be further configured to control the second electric machine torque based on a difference between the driver demand torque and the engine torque, and to control the first electric machine torque based on the second electric machine torque. The controller may be further configured to retrieve a target value for the second electric machine torque from a lookup table stored in memory accessible by the controller and indexed based on a total electric machine torque, the total electric machine torque corresponding to a difference between the driver demand torque and the engine torque. The controller may be further configured to control the first electric machine torque based on a difference between the total electric machine torque and the target value for the second electric machine torque. The lookup table may include only target values greater than zero.
In various embodiments, the vehicle includes a transmission having a plurality of gears connecting both the engine and the first electric machine to the first axle. The vehicle may also include a planetary gear set connecting the engine to the transmission, wherein the engine torque is adjusted based on a torque ratio of the planetary gear set. The vehicle may include a third electric machine connected to the first axle by the planetary gear set and electrically connected to the traction battery.
Embodiments may include a system having a first electric machine configured to provide torque to at least one wheel of a primary axle, a second electric machine configured to provide torque to at least one wheel of a secondary axle, and a controller programmed to control torque of the first and second electric machines to deliver a driver demand torque to at least one of the primary and secondary axle wheels based on combined power loss associated with torque delivered by the first and second electric machines, wherein the torque delivered by the first and second electric machines is in the same direction. The controller may be further programmed to control the second electric machine to deliver torque greater than or equal to zero. The controller may be further programmed to control the second electric machine torque in response to a target value retrieved from a lookup table stored in memory accessibly by the controller, the lookup table indexed by the driver demand torque.
In various embodiments, the system includes an engine configured to deliver engine torque to the at least one wheel of the primary axle, wherein the controller controls the torque delivered by the first and second electric machines in response to a difference between the driver demand torque and the engine torque. The system may include a third electric machine, wherein the engine and the third electric machine are coupled to the at least one wheel of the primary axle through a planetary gear set. The controller may determine the driver demand torque in response to an accelerator pedal position, determine the second electric machine torque from a lookup table based on a difference between the driver demand torque and the engine torque, and determine the first electric machine torque based on the second electric machine torque and the difference between the driver demand torque and the engine torque.
Embodiments may also include a method performed by a vehicle controller that includes controlling torque delivered by an engine and first and second electric machines to wheels of a first and second axle to meet a driver demand torque such that torque delivered by the first and second electric machines is allocated based on torque-related losses of the first and second electric machines, and such that the torque delivered by the second electric machine is greater than or equal to zero. The method may further include delivering the torque from the engine and the first electric machine to wheels of only the first axle and delivering the torque from the second electric machine to wheels of only the second axle. The method may also include delivering the torque from the engine through a planetary gear set to the first axle. In one embodiment, the method includes coupling a third electric machine to the first axle through the planetary gear set. The method may include controlling the torque delivered by the engine and the first and second electric machines by controlling the second machine torque based on retrieving a target torque from a lookup table stored in memory accessible by the vehicle controller indexed by a difference between the driver demand torque and the engine torque. The method may further include controlling the torque delivered by the first electric machine to wheels of the first axle based on the torque delivered by the second electric machine to the second axle.
Embodiments of the disclosure may provide one or more associated advantages. For example, one or more embodiments of a vehicle or method according to the disclosure optimize powertrain efficiency without complex runtime calculations to determine the torque allocation among the engine and electric machines. The allocation of electric machine torque does not sacrifice all-wheel drive features with full AWD capability available on demand. Constraining torque for the secondary axle electric machine(s) to zero or greater ensures that the primary and secondary axle electric machines deliver torque in the same direction to maintain vehicle stability. Those of ordinary skill in the art may recognize one or more additional advantages based on the representative embodiments described with reference to the corresponding figures.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, 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 produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
The processes, methods, or algorithms disclosed herein can be deliverable to/implemented by one or more processing devices, controllers, or computers, which can include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information stored on volatile or persistent non-transitory storage media such as ROM devices and information alterably stored on writeable storage media such as FLASH devices, MRAM devices and other solid-state, magnetic, and/or optical media. The processes, methods, or algorithms can also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers, or any other hardware components or devices, or a combination of hardware, software and firmware components.
The present inventors have recognized that, an electric all-wheel drive (eAWD) system has the freedom to allocate and distribute torque between the primary and secondary axles in various ways where the total of the primary axle and secondary axle torques equals the total driver-demanded torque. In addition, it is desirable to distribute this torque between both axles in the most efficient way possible to minimize fuel consumption and maximize electric range during operating conditions where full AWD operation is not needed. Furthermore, the losses generated by operating an electric motor vary as a function of speed and generated torque such that for a given vehicle speed it is desirable to select motor torques that minimize total electric losses. As such, various embodiments according to the disclosure provide a control system that determines the distribution of torque between the primary and secondary actuators that uses the least amount of electric power and is applied during times when the AWD system is not needed. In addition, the present inventors have recognized that under certain vehicle conditions of various prior art implementations, it is possible that torque allocations for engine torque may result in a negative torque for one or more electric machines in a hybrid eAWD application, which may lead to vehicle instability. As such, embodiments according to this disclosure ensure that the torque applied to each axle is in the same direction.
In the schematic block diagrams of
In the representative embodiment of
Transmission 122 is mechanically connected to internal combustion engine 140 via planetary gearset 130. The transmission 122 is also mechanically connected to a drive shaft 132 that is mechanically connected to the wheels 120. The electric machines 110, 112, 114 can provide propulsion and regenerative braking capability when the engine 140 is turned on or off. During regenerative braking, one or more of the electric machines 110, 112, 114 operate as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric machines 110, 112, 114 may also reduce vehicle emissions by allowing the engine 140 to operate at more efficient rotational speeds and allowing the hybrid-electric vehicle 100 to be operated in electric mode with the engine 140 off under certain conditions.
A high-voltage traction battery or battery pack 150 includes a plurality of low voltage cells connected in groups or strings to provide a desired energy storage capacity and output voltage/current that can be used by the electric machines 110, 112, 114 when operating as motors, and transferred/stored when operating as generators. A battery pack 150 typically provides a high-voltage DC output that may be converted to a three-phase AC current using associated electronic circuitry to interface with the electric machines 110, 112, 114. Traction battery pack 150 may include an associated battery energy control module (BECM) in communication with one or more vehicle controllers, such as a vehicle system controller (VSC) 160 and AWD controller 170 over a wired or wireless vehicle network.
Each vehicle controller may include a processor in communication with one or more non-transitory computer readable storage media or memories that store data and instructions executable by the processor to control one or more associated components or systems. Data may be organized in an array or lookup table accessible by one or more index variables or parameters. In one embodiment, at least one vehicle controller accesses a memory including a lookup table having values for secondary electric machine torque indexed based on a total electric machine torque, which corresponds to a sum of primary and secondary electric machine torque. The lookup table may include only target torque values that are greater than zero. In one embodiment, the target torque values are determined based on the design characteristics of the primary axle 116 and secondary axle 118 and calculated for the most efficient value for torque of secondary electric machine 112 for any given total electric demand torque and vehicle speed. The target values may be calculated by iterating over a range of total electric torque and vehicle speed operating points and then calculating total losses for a range of possible combinations of target torques for primary electric machine 110 and secondary electric machine 112. One strategy for determining target values is described in commonly owned US The resulting values stored in the lookup table in memory are constrained such that primary axle torque applied to primary axle 116 is in the same direction as secondary axle torque applied to secondary axle 118. During operation vehicle operation, the VSC 160 can access the previously stored lookup table to determine the optimal primary and secondary axle torques provided by primary electric machine 110 and secondary electric machine 112 to meet the current driver demand at the current vehicle speed as described in greater detail with reference to
In addition to providing energy for propulsion, the traction battery 150 may provide energy for other vehicle electrical systems including an HV compressor or heater, for example. A typical system may include a DC/DC converter module that converts the HV DC output of the traction battery 150 to a low voltage DC supply that is compatible with other low-voltage vehicle accessories. The low-voltage systems may be electrically connected to an auxiliary battery (e.g., 12V, 24V, or 48V battery).
The electrified vehicle 100 may be a plug-in hybrid vehicle (PHEV) in which the traction battery 150 may be recharged by an external power source, such as a power utility grid, or may be a standard hybrid that charges traction battery 150 from operating one or more electric machines 110, 112, 114 as a generator, but does not receive power from an external power source. The external power source may be connected by an electrical cord or via wireless charging, which may be referred to as hands-free or contactless charging, that uses inductive or similar wireless power transfer.
The various components described as well as additional components that are not explicitly illustrated or described may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a vehicle network that may be implemented as a serial bus (e.g., Controller Area Network (CAN)) or via discrete conductors. In addition, VSC 160 may coordinate the operation of the various components and may communicate directly or indirectly with one or more other vehicle controllers, such as AWD controller 170, secondary axle motor controller 180, a BECM, a body controller, and a battery charger controller or control module, for example.
As generally illustrated by the simplified block diagram of
The vehicles 100, 200 of
Total delivered wheel torque is made up of three components: primary axle electric machine torque (τmot_p), secondary axle electric machine torque (τmot_s), and output torque from the planetary gearbox due to engine power (τeng). For embodiments that do not include an internal combustion engine, the engine power can be omitted or considered as zero. The total demanded driver torque may be determined using known strategies based on inputs such as vehicle speed, accelerator pedal position, cruise control status, etc. The total driver-demanded torque (τtot) may be represented as:
τtot=τeng+τmot_p+τmot_s
A total demanded electric machine torque (τtot_elec) can then be calculated according to:
τtot_elec=τtot−τeng=τmot
To ensure vehicle stability, the torque applied to each axle should be in the same direction. In certain vehicle conditions, it is possible that τeng is greater than τtot which could cause a negative τtot_elec while τtot is positive. According to various embodiments of the present disclosure, in this case τmot_s is constrained to zero and the vehicle controller(s) will allocate all of the electric machine torque to the primary axle (i.e. τmot_p=τtot_elec).
Based on the design characteristics of the primary axle and secondary axle, a lookup table stored in memory accessible by the vehicle controller(s) is populated with values corresponding to a desired efficiency value for τmot_s for any given τtot_elec and vehicle speed as represented at 300 in
During vehicle operation, the vehicle controller(s) determine a total driver demanded torque as represented at 310. A corresponding total demanded electric torque is then determined based on engine torque according to equation (1) for current engine operating conditions as represented at 320. The controller(s) retrieves a corresponding target value from the previously stored lookup table for the secondary axle torque to control the secondary electric machine as represented at 330. The primary axle target torque to control the primary electric machine is then calculated at 340 according to:
τmot_p=τtot_elec−τmot_s.
The controller(s) then control the engine and the primary and secondary electric machines to deliver the associated target torques to allocate the total electric machine torque between the primary and secondary axles as represented at 350.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which 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, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
