Does the braking performance of PHEVs degrade over time due to battery drain

The braking performance of Plug-in Hybrid Electric Vehicles (PHEVs) can be influenced by several factors related to their hybrid system, but it does not inherently degrade over time simply due to battery drain. However, specific issues related to regenerative braking and vehicle design can affect the feel and effectiveness of braking as the vehicle ages or as battery state changes.

How Braking Works in PHEVs

PHEVs use a combination of conventional friction brakes and regenerative braking, which recovers energy during deceleration by using the electric motor to slow the vehicle and recharge the battery. The interaction between these systems can influence braking feel and performance.

Effect of Battery State on Braking

• Regenerative braking effectiveness depends on the battery’s state of charge. For example, when the battery is near full charge, regenerative braking is limited because there is less capacity to absorb recovered energy. This can cause the system to rely more on friction brakes, potentially altering braking response and feel on the driver.
• Some users have reported delayed or reduced regenerative braking effectiveness over time or at certain battery charge levels. For instance, a 2018 PHEV owner noted that regenerative braking seemed to engage later, increasing stopping distance as the vehicle aged.
• Specific models may also have software or design quirks. For example, the 2022 Mitsubishi Outlander PHEV reportedly starts the petrol engine to provide braking force instead of regenerative braking when the battery is above 55% charge, which is seen as a significant design flaw by some users.

Overall Braking Performance Over Time

• The additional weight of a PHEV from the battery pack can affect overall braking performance compared to a non-hybrid internal combustion engine (ICE) vehicle, potentially resulting in longer stopping distances.
• Some hybrids and PHEVs have been found to have longer braking distances compared to their non-hybrid counterparts, partially due to the use of low rolling resistance tires aimed at improving fuel economy, which can compromise braking grip.
• Reports from PHEV owners include instances where the brakes feel less responsive or even momentarily release during braking, suggesting possible issues with brake system calibration or regenerative braking integration.

Does Battery Drain Cause Braking Degradation?

• Battery drain itself (meaning a decrease in battery capacity or charge over time) does not directly degrade the friction brakes or braking system physically.
• However, as battery capacity diminishes with age, the regenerative braking capability may be reduced, forcing greater reliance on friction brakes. This can change the braking feel but does not necessarily mean decreased stopping performance if the friction brakes are well-maintained.
• Delayed or reduced regenerative braking engagement as battery charge and condition change can make braking feel different or less smooth, which might be perceived as degraded braking.

Summary

• PHEV braking combines friction and regenerative braking, with regenerative braking performance influenced by battery state and charge level.
• Battery drain or lower battery charge can reduce regenerative braking effectiveness, altering braking feel and potentially increasing stopping distance temporarily.
• Overall braking distance and performance may also be affected by vehicle weight, tire choice, and system calibration but are not typically degraded permanently over time solely due to battery drain.
• Some PHEV models have reported issues with regenerative braking logic or system design that affect braking performance independent of battery drain.

In conclusion, while battery state and aging can influence regenerative braking contribution, they do not inherently cause permanent degradation of PHEV braking performance. Proper maintenance of the friction brakes and system calibration remains important to ensure consistent and safe braking performance over the vehicle’s life.