ADELANTO, Calif. — This is the fourth article in a four-part series on regenerative braking characterization by Marco Victorero, Test Engineer, Braking Systems in Applus IDIADA.
Review part 1 | Review part 2 | Review part 3
The objective of this article is to present new advanced testing procedures for regenerative braking. The two first parts of the article introduced the work and presented the methodology –test procedure, instrumentation, post-processing formulae, etc.– for the vehicles whose regenerative system was characterized in terms of durability and performance testing. The 3rd part focused on the results for the brake durabilities: Vehicle 1 completed a short Los Angeles City Traffic (LACT) test, while Vehicle 2 data was gathered across a Mojácar durability. This 4th and last part, on the other hand, will present the main results for Vehicles 3 and 4, that were tested in IDIADA HQ’s proving ground.
- Performance Testing
- Vehicle 3
The regenerative behavior of the vehicle is highly tuneable due to the different selectable levels available through paddles behind the steering wheel – Level 0 (no regeneration), Level 1, Level 2, Level 3 and i-Pedal (Single Pedal).
Brake blending is available in all levels except for the neutral gear and Level 0 which have the same strategy – no regeneration at all.
Coastdown deceleration (no brake pedal application) levels vary from 0,8m/s2 of the Level 1 to 2,3m/s2 of the i-Pedal mode.
The vehicle is not capable of controlling the wheel slip with the electric motors, hence the regeneration is always disconnected when a panic brake application is performed. Nevertheless, this disconnection is performed with a certain slope and keeping a certain amount of small regeneration in the “background” throughout the stop.
The vehicle is able to brake up to ~0.35g without any hydraulic pressure applied – no blending (first 20mm of pedal stroke does not build up hydraulic pressure at higher regen modes.
On low μ surface, the vehicle decreases the amount of regenerative braking regardless of the regen level selected (highest or lowest) to what can be called a baseline level of regeneration on front and rear motors cycling around 5kW for both motors. Electric motors cycle while in this baseline regeneration but seems not to be related to wheel speed control since slip is not critical during these manoeuvres.
Still on low μ, when demanding brakes from the driver, i.e. brake pedal application, electric motors disconnect completely the regeneration on front and rear axles. Hydraulic braking, ABS/ESC pump takes control of the wheel slip. Stability of the vehicle is prevailing over regeneration capabilities.
1.1.2. Vehicle 4
The regenerative behaviour in the vehicle is highly tuneable due to the different selectable levels available – D gear: Low, Moderate, High and Adaptative modes, B gear.
Brake blending is available in all levels except for the neutral gear with no regeneration at all.
Coastdown deceleration levels vary from 0.5m/s2 of the D low to 1.8m/s2 of the D High mode.
The vehicle prevails the energy recuperation from the braking, hence the regeneration is always connected even with high decelerations. Even with panic brake application, regeneration is connected but with a decreased level in comparison with reduced deceleration.
The vehicle is able to brake up to ~0.2g without any hydraulic pressure applied – no blending (around first 18mm of pedal stroke does not build up hydraulic pressure at any regen modes).
In coastdown condition at low μ surface, without demanding brakes from the driver, the vehicle prevails the regeneration over the control of wheel slip. It can be noticed that while increasing the regen level selected, the wheel slip increases and there is no control of it through the regen system. Wheel lock appears in case of high regen with “B” gear. In that case, stability control system takes control of the wheel slip. Driver intervention is required through the steering wheel to keep vehicle stability.
When demanding brakes from the driver, i.e. brake pedal application, the vehicle decreases the amount of regenerative braking at low μ surface regardless of the regen level selected to what can be called a baseline level of regeneration on front and rear motors cycling around 10kW-5kW for both motors. Wheel slip is less in comparison with coastdown condition at low μ surface. Hydraulic braking, ABS/ESC pump takes control of the wheel slip throughout brake application. In addition, vehicle stability is better than in coastdown condition as less driver intervention through the steering wheel is needed.
Regeneration capabilities of the vehicle are prevailing over stability while increasing the regen level selected in coastdown condition. When demanding brakes from the driver, the vehicle decreases the amount of regenerative braking and wheel slip control is done by hydraulic braking in all regen levels.
2. Conclusion
This article has explained different regenerative braking analysis tools/methods, distinguishing durability from performance testing. In that sense, results from 4 vehicles have been presented – two of them completing a Los Angeles City Traffic (LACT), the other two tested on multiple braking surfaces in IDIADA HQ’s proving ground.
About Applus IDIADA
With more than 25 years’ experience and 2,450 engineers specializing in vehicle development, Applus IDIADA is a leading engineering company providing design, testing, engineering, and homologation services to the automotive industry worldwide.
Applus IDIADA is located in California and Michigan, with further presence in 25 other countries, mainly in Europe and Asia.
