Lexus has been hard at work developing advanced drivetrain technologies focused on establishing a new standard in dynamic performance for the brand’s BEV products. By weaving technologies such as Steer-by-Wire (SBW) and Interactive Manual Drive (IMD) into the BEV experience, Lexus hopes to create a more satisfying and connected driving experience.
The Lexus RZ series, as equipped in some global markets, offers more BEV power and even an F Sport model that involves two of these foundational technologies, along with DIRECT4 traction, that are focused on enhancing driver directional and BEV system control in all conditions.
With over 12 years of development, the Lexus true Steer-By-Wire system holds the promise of variable ratio steering speed to suit a range of conditions in addition to offering responsiveness that will be necessary to match high torque BEV systems. This adaptive capability allows SBW to enhance a driver’s feeling of control with enhanced steering precision.
The Lexus Steer-By-Wire system replaces the mechanical connection to the steering wheel with electronic signals between the steering wheel and steering rack. Computer control interprets the amount of steering angle based on vehicle speed and driver input on a specialized yoke. A strong electric motor applies torque to the steering rack to communicate direction to the front wheels.
The system can be very sensitive to inputs and multiply steering effort and steering angle in low-speed situations (parking, tight turning) and greatly reduces steering sensitivity in high-speed situations (highway lane change). The control surface itself is no longer round as the system no longer needs as many revolutions of a traditional steering wheel given the SBW system’s ability to generate more aggressive steering angles with less drive input on the yoke.
With the range of inputs at all speed regulated and tuned by computer control, drivers will have the flexibility in the future of tuning their steering input to desired tastes. The result is a feeling of greater control with a steering control surface that is more responsive, requiring less effort, while enabling high driver confidence. With layers of system redundancy, a high level of safety has also been achieved for the SBW system.
The Lexus Interactive Manual Drive (IMD) is a driver-focused technology that electronically mimics the shifting feel and action of manual transmission vehicles using steering column-mounted paddle shifters. This is not the technology needed for the BEV application that can inherently deliver consistent power without torque multiplication provided by a traditional internal combustion engine (ICE) transmission
However, for Lexus engineers the engagement and control of engine power in the internal combustion vehicle felt like a missing driver engaging component within the BEV idea. Initially, this idea could have been viewed as unnecessary until over 400 subjects drove the initial prototypes. This feeling of controlling engine revs and application of power added an element of engagement many testers didn’t even know they missed.
As equipped in certain Rz models, the system introduces synthetic shift points with associated shift shock that mimics the feel of a mechanical manual transmission moving through gears. The stepped-shift feeling and accompanying synthetic driveline shock of the RZ BEV system are all tuned by Lexus engineers with the goal of making the BEV experience more enjoyable and engaging.
Rz models so equipped offer 8 speeds worth of engaging shifting through the BEV powerband to help better involve drivers along with more unique engine sounds. Utilizing steering column mounted paddle shifters, drivers become more involved in the power delivery with a system that rewards proper upshifts and deceleration with downshifts.
Lexus sees a bright and dynamically engaging future for BEVs with technologies focused on DRIVERS. As systems like SBW and IMD evolve along with DIRECT4, future sporty Lexus models will add capabilities in terms of control, responsiveness and excitement. Given the power levels of future BEV systems, SBW, IMD and DIRECT4 can work together and achieve levels of dynamic performance simply not possible with today’s technology.