Regenerative Braking Question

[wstr75]

I've noticed on a number of occassions judging by the left dash guage (blue zone during regenerative braking) that the needle does not go into the blue zone when braking from, say 45 to 70 mph, but if I release braking pressure and re-apply braking the needle immediately goes into the blue. These stops were slow down for stop light stops rather than accident avoidance stops. The battery state was blue bars (not green). Anyone else see this on their car? Why would the car elect to use conventional braking rather than regenerative on the initial application of brakes and then to use regenerative on the second application just a moment later with essentially the same speed conditions?

[wwest]

I've noticed on a number of occassions judging by the left dash guage (blue zone during regenerative braking) that the needle does not go into the blue zone when braking from, say 45 to 70 mph, but if I release braking pressure and re-apply braking the needle immediately goes into the blue. These stops were slow down for stop light stops rather than accident avoidance stops. The battery state was blue bars (not green). Anyone else see this on their car? Why would the car elect to use conventional braking rather than regenerative on the initial application of brakes and then to use regenerative on the second application just a moment later with essentially the same speed conditions?

It might have to do with the initial level of charge in the hybrid battery when you first begin braking. If the level is close to the "top" then a low priority is given to regenerative braking in the firmware decision "tree". The system ECU is "watching" your braking and acclerator pedal activity, continuously, in order to be able, a majority of the time (hopefully), just what your "intent" is. It's tryingto predict the future, literally.

For instance if you have been cruising along at a relatively constant speed and then suddenly lift the accelerator pedal the system would likely conclude that you intend to begin coasting down to a lower speed. Now if you suddenly, immediately after releasing the accelerator, apply the brakes the system will probably assume you want to slow down quickly and the brakes are the proper resource for that.

On the other hand suppose you were just previously accelerating and now only slightly release the gas pedal. The system would properly assume you want to enter cruise "mode".

In your case when you first, initially, applied the brakes the system could have been indecisive about your intent. But then you released the brakes and then re-applied them (non-severe assumption here) and that would clearly imply a non-urgent coastdown and then it would be appropriate to engage the regeneration cycle.

If the hybrid battery were nearly discharged I have no doubt that regeneration would have begun the instant you released the accelerator, even before you applied braking the first time.

[wstr75]

I've noticed on a number of occassions judging by the left dash guage (blue zone during regenerative braking) that the needle does not go into the blue zone when braking from, say 45 to 70 mph, but if I release braking pressure and re-apply braking the needle immediately goes into the blue. These stops were slow down for stop light stops rather than accident avoidance stops. The battery state was blue bars (not green). Anyone else see this on their car? Why would the car elect to use conventional braking rather than regenerative on the initial application of brakes and then to use regenerative on the second application just a moment later with essentially the same speed conditions?

It might have to do with the initial level of charge in the hybrid battery when you first begin braking. If the level is close to the "top" then a low priority is given to regenerative braking in the firmware decision "tree". The system ECU is "watching" your braking and acclerator pedal activity, continuously, in order to be able, a majority of the time (hopefully), just what your "intent" is. It's tryingto predict the future, literally.

For instance if you have been cruising along at a relatively constant speed and then suddenly lift the accelerator pedal the system would likely conclude that you intend to begin coasting down to a lower speed. Now if you suddenly, immediately after releasing the accelerator, apply the brakes the system will probably assume you want to slow down quickly and the brakes are the proper resource for that.

On the other hand suppose you were just previously accelerating and now only slightly release the gas pedal. The system would properly assume you want to enter cruise "mode".

In your case when you first, initially, applied the brakes the system could have been indecisive about your intent. But then you released the brakes and then re-applied them (non-severe assumption here) and that would clearly imply a non-urgent coastdown and then it would be appropriate to engage the regeneration cycle.

If the hybrid battery were nearly discharged I have no doubt that regeneration would have begun the instant you released the accelerator, even before you applied braking the first time.

Like the Sargeant said on Forest Gump: WWEST, you are a $@%# genius!! Thanks for the excellent explanation of how the 400h computer makes its decisions!! The upshot is that I should take my foot off the gas first, wait a second and then apply the brakes.

[wwest]

I've noticed on a number of occassions judging by the left dash guage (blue zone during regenerative braking) that the needle does not go into the blue zone when braking from, say 45 to 70 mph, but if I release braking pressure and re-apply braking the needle immediately goes into the blue. These stops were slow down for stop light stops rather than accident avoidance stops. The battery state was blue bars (not green). Anyone else see this on their car? Why would the car elect to use conventional braking rather than regenerative on the initial application of brakes and then to use regenerative on the second application just a moment later with essentially the same speed conditions?

It might have to do with the initial level of charge in the hybrid battery when you first begin braking. If the level is close to the "top" then a low priority is given to regenerative braking in the firmware decision "tree". The system ECU is "watching" your braking and acclerator pedal activity, continuously, in order to be able, a majority of the time (hopefully), just what your "intent" is. It's tryingto predict the future, literally.

For instance if you have been cruising along at a relatively constant speed and then suddenly lift the accelerator pedal the system would likely conclude that you intend to begin coasting down to a lower speed. Now if you suddenly, immediately after releasing the accelerator, apply the brakes the system will probably assume you want to slow down quickly and the brakes are the proper resource for that.

On the other hand suppose you were just previously accelerating and now only slightly release the gas pedal. The system would properly assume you want to enter cruise "mode".

In your case when you first, initially, applied the brakes the system could have been indecisive about your intent. But then you released the brakes and then re-applied them (non-severe assumption here) and that would clearly imply a non-urgent coastdown and then it would be appropriate to engage the regeneration cycle.

If the hybrid battery were nearly discharged I have no doubt that regeneration would have begun the instant you released the accelerator, even before you applied braking the first time.

Like the Sargeant said on Forest Gump: WWEST, you are a $@%# genius!! Thanks for the excellent explanation of how the 400h computer makes its decisions!! The upshot is that I should take my foot off the gas first, wait a second and then apply the brakes.

Was I, or was I not, just compared to Forrest Gump..??

[markatty]

I've been seeing this behaviour more and more from my 400. When braking the charge indicator will only about 40% down in to the blue regardless of how hard I brake. I never had this happen before and I watch the needle a lot because I try to do as much braking with the generators as possible. I drive the same commuter route 3 days a week and exit ramps where the needle used to go to the bottom and stay there now won't move the needle to more than 40% charging. What I had seen previously was that if you stepped on the brake pedal hard at anytime the regular brakes kicked in.

I'm going to give this system a try, but if that is really the way it works I think it is a dumb design. "Double clutching" to generate electricity is overkill.