ADELANTO, Calif. — This is the first article in a four-part series on regenerative braking characterization by Marco Victorero, Test Engineer, Braking Systems in Applus IDIADA.
- Introduction
The novel characteristics of regenerative brake systems require new methodologies and testing protocols. This means that characterization/validation of regenerative braking is a topic that is required for a significant number of clients.
The objective of this article is to present new advanced testing procedures for regenerative braking. Some low-cost strategies need to be identified to provide high added value measurements to the customers. In particular:
– New analysis protocols for regenerative brake (how to characterize brake regenerative in brake performance and brake durability tests).
– New tools for regenerative brake characterization.
Different performance/strategies and tools to characterize regenerative braking have been studied, highlighting the negative influence that a poor regenerative braking calibration has on vehicle stability/safety and the dependence of global efficiency on user, vehicle and driving path.
The work distinguishes durability from performance testing.
2. Methodology
2.1Durability Testing
2.1.1 Procedures
Vehicle 1 performs a reduced Los Angeles City Traffic (LACT) test, accumulating a total of three route runs (around 1000km):
The following data is monitored:
- Amount of energy recovered from the regenerative system was measured and quantified for each run through interpolation of battery current and tyre size.
- Number of stops along the route with accompanying data such as speeds, brake system temperatures, and regenerative contribution.
Vehicle 2 performs a complete Mojácar test (around 9600km). The test, originally intended to evaluate the brake system in terms of NVH and wear and brakes performance, includes instrumentation to characterize the regenerative actuation.
- Amount of energy recovered from the regenerative system was measured and quantified for each run through interpolation of battery current and tyre size.
- Number of stops along the route with accompanying data such as speeds, brake system temperatures, and regenerative contribution.
2.1.2. Counters
- Brake applications: based on BLS – hydraulic and fully/partial regen.
Note: BLS (Brake Light Switch) is the signal which turns on brake lights, it can be activated if the deceleration caused by the regenerative brake is higher than the limit values in the regulations to be applied.
- Regen applications: actual regen torque value.
- Hydraulic applications: hydraulic only, no regen torque.
2.1.3 Outputs
- Brake regen split
- Average regen rate [%] – total brake force and regen force ratio
- BPS
- BPS & Tbr≠0
- BLS – BPS
Note: BPS (Brake Pedal Switch) is a switch installed in the brake pedal with the purpose of activating brake lights.
- Work (Energy)
- Average /maximum regen deceleration
2.1.4. Calculations
For each brake application, the following outputs are calculated:
- Regen force (avg)
- Regen force (max)
- Regen rate [%]
- Average regen deceleration
- Maximum regen deceleration
- Regen work (energy)
- Regen power
These other variables are also monitored per brake application:
- Avg slope [ º ]
- Braking distance [m]
- SOC [%] avg
The following paragraphs summarize the main formulae:
- Slope:
- Regenerative braking force:
- Regenerative braking deceleration:
- Total braking force:
- Regenerative rate:
- Regenerative work (Energy, J):
- Regenerative power (W):
2.1.5. Braking classification
The following scenarios are distinguished:
- Total of Brake Applications: based on BLS: hydraulic & fully/partial regen
- Total of Brake Applications with Regeneration: count if Regen torque>0
- Total of Brake Pedal Application based on BPS: some vehicles regenerate without applying brake pedal, only releasing the acceleration pedal.
Consequently, the classification of brake applications is:
- Case 1: Brake application (only hydraulic) = condition BPS (on) & Regen torque = 0 Nm
- Case 2: Partial regenerative brake application = Brake press > X bar (eg. 0.5 bar) & Regen torque > 0 Nm
- Case 3: Brake application (only regenerative) = Brake press < X bar (eg. 0.5 bar) & Regen torque > 0 Nm
- Case 4: Regeneration without braking = BPS (off) & Regen torque > 0 Nm
Case 4 is sometimes referred to as ‘single pedal’ or ‘i-Pedal’ driving.
2.1.6. Statistics
For each route, the following statistics can be calculated:
- Split
- % of regen braking (fully & partial) (case 2 + case 3)
- % of fully regen braking (case 3)
- % of i-Pedal (case 4)
- Contribution
- Average of regenerative force/torque (case 2 + case 3), (case 3), (case 4)
- Average of regenerative rate (case 2 + case 3)
- Average of regenerative deceleration (case 2 + case 3), (case 3), (case 4)
- Average of maximum regenerative deceleration (case 2 + case 3), (case 3), (case 4)
- Energy
- Average regenerative work (case 2 + case 3), (case 3), (case 4)
- Total regenerative work on a route (case 2 + case 3), (case 3), (case 4)
- Average regenerative power (case 2 + case 3), (case 3), (case 4)
- Total regenerative power (case 2 + case 3), (case 3), (case 4)
- Histograms
- Num of stops vs. speed (stacked)
- Num of stops vs. regen torque (stacked)
- Num of stops vs. deceleration(stacked)
- Regen rate vs. slope
- Recovered energy vs. slope
- Num of stops vs. SOC
- Recovered energy vs. SOC
- Efficiency
- Global efficiency
- Total energy recovered
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.
