Greater Efficiency from Tool-Based Drivability Calibration
Manufacturers are required to calibrate a large number of vehicles under huge time constraints. Consumers expect perfectly tuned drivability and a vehicle character that goes with the make, so-called branding. But test vehicles are not available until a very late stage in the development process, and are few and far between. Until now, the majority of drivability assessments have been based on gut instinct – the “seat-of-the-pants feel”. In cooperation with ETAS, IAV has developed a measurement and assessment system based on INCAFLOW that makes it possible to calibrate even a large number of vehicles very efficiently.
It was a challenging exercise: car manufacturers have often expressed the wish for a system that facilitates vehicle tuning in the calibration process while at the same time efficiently defining the specific vehicle’s character. Calibration criteria previously ascertained on a subjective basis were also to be described objectively. IAV has developed a measurement and evaluation system of this type in cooperation with ETAS. The new assessment algorithms for engine and transmission drivability are offered as toolboxes in addition to the INCA-FLOW tool which was successfully launched many years ago: the Engine Drivability Toolbox (EDT) and the Transmission Drivability Toolbox (TDT).
Carmakers’ vehicle ranges are becoming increasingly differentiated and diverse. The many derivatives with their different powertrain configurations, from small to large engine, from manual transmission, automated manual transmissions, torque-converter transmissions, dual-clutch to CVT transmissions, the various hybrid systems with different electric motor variants and the P1, P2, P3, P4 system configurations as well as the combined systems, such as P1/P4, and, ultimately the DHT systems, take the work involved in calibrating drivability beyond all proportion. Combustion engines are also required to meet increasingly stringent emission limits under real driving conditions (RDE, real driving emissions). And CO2 emissions are having to be reduced in the stringent WLTP (Worldwide Harmonized Light- Duty Vehicles Test Procedure) cycle.
Many consumers also expect their dream vehicle to provide the kind of drivability that meets their personal demands – one which, ideally, they can tailor to their own particular taste. For example, a top-class sedan will tend to accelerate smoothly and jerk-free whereas a sports car needs to respond more spontaneously. There are also noticeable differences in gear-shifting and start-off behavior. Every car maker has its own branding which must be stamped on its various fleet models.
Calibration engineers have the job of tuning each individual vehicle type so that it meets the general technical specifications while at the same time giving it the appropriate drivability stamp. In particular, this character is defined by longitudinal dynamic drivability which is determined by balancing many parameters in the various control units of the powertrain’s components. In addition to using development tools, the engineers’ subjective perception carries tremendous weight.
The INCA-FLOW Engine Drivability Toolbox and the Transmission Drivability Toolbox significantly simplify this calibration work. They are easy to use and fully integrated into the existing calibration tool chain. The system can be put into operation in the vehicle within a few minutes. It manages without any sensors of its own and reads out the vehicle’s signals via the existing bus systems, such as CAN (Controller Area Network), FlexRay or XCP (Universal Measurement and Calibration Protocol). Optionally, an external acceleration sensor can be used which, for example, quickly attaches to a seat rail. Measurement systems already available from ETAS, such as the ES5xx series, can also be used.
The subsequent procedure is straightforward: during the driving maneuver, the measurement and evaluation system records the powertrain’s physical variables in real time. Generally speaking, acceleration and speed signals are suitable for creating reliable evaluation variables, such as load change, pedal dosage, gear-shifting and driving off. The system evaluates this measurement data and graphically displays relevant physics-based drivability parameters on an objective basis in the form of numerical values – also in relation to reference vehicles. Offline evaluation is also possible, such as in the office and together with colleagues.
Fast calibration chain
From information fed back directly, the INCA FLOW toolboxes provide the capability of identifying exact powertrain parameters that can be used to calibrate longitudinal dynamic drivability in line with specific requirements. If these parameters are changed during the ongoing calibration drive, data on new reproducible, objective and physical variables can be fed back at high speed.
The measurement and evaluation system demonstrates its full benefits if binding calibration targets are already defined as acceptance criteria in the form of target variables at the start of a project. During the calibration test drive, these can be measured and optimized in a targeted manner to produce the required result. This permits target-oriented project tracking at every milestone.
The INCA-FLOW Engine Drivability Toolbox and the Transmission Drivability Toolbox are very powerful tools for efficient vehicle calibration. As such, they meet the current need to process a large number of vehicles in a short period of time. One major advantage lies in the objectification of drivability assessment which, to date, has mainly been based on subjective criteria. Physical values replace gut instinct, produce faster results and simplify management decisions.
The article was published in automotion 02/2019, the automotive engineering magazine of IAV. Here you can order the autmotion free of charge.