TECHNICAL FIELD

The present disclosure relates to a system with multiple electric drive axles and a coordinated electric axle control method.

BACKGROUND AND SUMMARY

Electric drive systems, such as electric drive axles, have been provided in vehicles owing in part to their modularity. However, certain electric drive axles have made performance tradeoffs between launch torque and cruising speed efficiency. Further, other drive axles have posed packaging constraints on surrounding components or vice versa. Packaging multi-motor drive axles between frame rails can prove difficult in some vehicle platforms, for instance. These packaging constraints and the inability to reach performance targets with regard to off the line acceleration, in certain scenarios, may hinder the drive axle's applicability and ultimately customer appeal.

WO 2019/195229 A1 to David et al. teaches a powertrain where in one embodiment multiple motors are coupled to a continuously variable traction drive transmission. In this powertrain embodiment, two motors are attached to a planetary gear reduction with a high ratio. Within the planetary assembly, the sun and ring gears function as the transmission's inputs and the carrier functions as the transmission's output.

The inventors have recognized several drawbacks with the powertrains taught by David. For instance, the above described powertrain embodiment may demand tradeoffs to be made with regard to vehicle launch and cruising performance, due to system architecture. As an example, the range of transmission ratios in David's powertrain may be selected to favor off the line acceleration at the expense of high speed cruising efficiency or vice versa. Further, David is silent with regard to the powertrain's specific end-use component layout. In practice, David's system and other prior powertrains may therefore impose space constraints on surrounding vehicle components (e.g., the frame, battery system, passenger cabin, auxiliary systems, etc.) in certain vehicle platforms. These space constraints may precipitate modification or redesign of certain vehicle systems to accommodate for the space inefficient transmission. Vehicle production times and costs may be resultantly driven up.

To address at least a portion of the abovementioned issues, the inventors have developed an electric drive system. The electric drive system includes a first multi-motor drive unit with a first planetary gear reduction that transfers power between a first set of motors and a first set of axle shafts. The electric drive system further includes a second multi-motor drive unit with a second planetary gear reduction that transfers power between a second set of motors and a second set of axle shafts. Further in the system, the first and second multi-motor drive units have asymmetric gear ratios. In this way, the drive units may be tailored to efficiently operate at different speeds. For instance, one motor may provide greater launch torque at low speeds and the other motor may more efficiently operate at higher cruising speeds.

Further, in one example, a first and second motor in the first multi-motor drive unit have a common rotational axis. In such an example, the first motor and the second motor are positioned on opposing axial sides of an output gear. Positioning the motors in this manner allows for tight package space installation between the tandem axles.

In yet another example, the first and second motors in the first multi-motor drive unit have rotational axes that are arranged parallel to one another. In such an example, the first and second motors may be arranged adjacent to one another on one side of an output gear. In this way, the motors may be longitudinally arranged in the vehicle. This longitudinal motor layout allows for tight package space installation between the frame rails, for example. As such, the electric drive system may be adopted in a far wider range of vehicle platforms than previous electric drive systems.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

