A little tour on the hills

Time for a little tourism near home: Langhe


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The trip was about 150 km with a consumption of 3.9 l/100km, with AC on.
By comparison, a similar trip with my Ford C-Max 1.6TD scored 4.8 l/100km.
Comfort is second to none: the CVT allows for a relaxed driving and the overall silence allows enjoying the view.

Practice makes perfect

Lately, I've been able to practice this slope.
Time after time, I learned to maximize recharge and I've come to this:

At the end of the slope, battery is 8 bars full, with a gain of 16% versus 14% of my first attempts:

There's a noticable difference in the charging current: in this run we have a steady flow to the end of the slope.

On the previous attempt, charging was interrupted by the intervention of the braking system that was triggered by a hole on the road: whenever the system senses the wheels losing grip during regenerative braking, "classic" braking kicks in, disabling regeneration.

This is even more evident in the following graphs, where wheel cylinder pressure is sensibly lower than the previous run.

Previously, pressure ramped up and current levelled down.

The pratical effect of having a fully charged battery can be felt in the next 3 km, where the car runs in EV mode up to nearly 70 km/h.

Winter vs Summer

Last winter, when the car was brand new, I've got my best mileage on an one hour 50km trip hillside, with 3.9 l/100km. Even if it was winter, I didn't use any heating.

Today I had the chance to drive the same trip again.

This time I've scored 3.7 l/100km, with A/C on.

GPS temporal displacement

Everybody uses GPS.

We already know that the positioning provided has an error, usually in the range of 4 to 10 meters.

That's about space, but what about time?

By using Torque we can estimate it.

Torque log files contains GPS coordinates and the speed calculated from GPS readings: we can try to relate it to the speed reading from OBD, that is instantaneous, while the GPS speed is subjected to the delay induced by the GPS itself.

From the chart, we can say that the OBD speed is accurate, but the GPS value is delayed by an interval between 1 and 2 seconds.

Speed and Charge

How much current can you get from speed?
In the following graph:

• speed is in blue, left vertical axis
• RPMs in red, right axis, useful to check when the engine stops beeing dragged.
• change current in yellow, left axis, negative values are indicative of recharge.

I drove a straigh, plain road up to 76 km/h and then I left the accelerator pedal alone, to let the car loose speed until 46 km/h (see the blue line decreasing over time)


The engine continued to spin without burning any fuel, then at 66 km/h it stopped (see the sudden break in the red line).

Charging current is not steady, it follows the speed, but not linearly (check the yellow line, lower values mean higher charge).

A graph of current values by speed shows a pattern:

Higher current values are in the lower part of the graph.

The higher recharge effect is at 66 km/h with 24A.

That is precisely the speed where the engine stopped, but neighbouring values vary widely.

The slope returns to a linear behavior at 62 km/h with 22A.

So, if you're going to drive down a hill and you want to maximize your recharge, it's better to drive at 60 km/h rather than 70.

Android Activity Recognition Battery Usage

I'm using an amazing android app called AutomateIt.
It's kind of a scheduler on steroids: it can execute actions based on triggers like time, position, connection status.
The latest release added support for "activity recognition": the phone should be able to tell if you're walking, driving, or standing still.
I defined a rule that turns on Bluetooth while I'm driving, so I can use my car hands free system.
It actually works, but at what price?
Here are the effect on a Samsung Galaxy S2 Plus.
This a night with an activity recognition rule defined: check the last hours in the graph: battery depletes at a rate of 1% every 4 hours.

Here is a night without any activity recognition: a 1% of battery juice lasts for 5 hours.

It seems that using activity recognition shorten you battery running time by 20%.

Even more improvements

My daily commute has reached 3.9 l/100km.

With A/C on.

Different routes, different mileage

Sometimes I read posts of people disappointed by the mileage results of their Yaris Hybrid.
Results are heavily influenced by the kind of your average trip.
By comparison, in this season, my daily commute home-work-home, a 9+9km trip on urban and plain suburban roads, scores 4.2 l/100km.
A different trip, home-countryside-home, a slightly longer 12+12km trip on urban and hill roads, scores 3.8 l/100km (with A/C on).

Braking, HSD style.

Here is a long brake on a straight road, right before a traffic light.
Speed in blue
Hydraulic brake in black
Charging current in red

At 5:02:22, at a speed of 57 km/h, I began applying pressure on the brake pedal.
I applied the same pressure throughout the whole maneuver.
As soon as began braking, some current started flowing to the battery as the charging effect of the speed loss.
Current topped at 75A at 41 km/h.
At 5:02:37, as soon as speed lowered to 10 km/h, hydraulic braking kicked in.

Downhill reloaded

I tested again the same slope.
This time driving in D.

It seems there's still an exponential charging at the beginning (15:13:00 - 15:13:45), and then a linear progression.
Here's the speed graph:

One hypothesis for the change from exponential to linear of the charging progression was battery temperature.

Here's the current flow, charging the battery.
At 15:14:25 there's a sudden break.

At that time, the system began to use hydraulic brakes.
Note that at 15:14:45 brakes were not in use, but Amperes stayed low, even if speed was well in excess of 45km/h.

Comparison of GPS performance across different Android devices

I had the chance to test GPS on a Galaxy Mini 2 and a Galaxy S2 Plus.
The test was done in the same place, one phone after the other.
Both phones didn't have any data connection, cellular of Wi-Fi, so positioning was done using only plain GPS.
Here is the Galaxy Mini 2.
Locking took 60 seconds with 5 satellites.

The Galaxy S2 Plus got its lock in 3 seconds with 16 satellites.

Note that on both phones, compass was way off.

Start-Stop vs HSD

"My car also turns itself off at a traffic light!"
This is a classic when someone is on the passenger seat, while driving.

Modern, non-hybrid cars have a start-stop system that shuts the engine down while standing still.

This is fundamentally different from an hybrid car:
A conventional car shuts the engine off after the car has stopped, and re-ignite it before moving again.
The HSD system works the opposite way: the engine shuts down before stopping and it starts again after the car is already moving.

Here is the detail of a stop at a traffic light.
Engine rpms in red; speed in blue.
The car comes to a full stop a 15:09:35 and starts again at 15:09:40:

The engine stops 30 seconds before the real stop, and starts again after the car is already in motion.

Driving downhill in B

I tried the same slope using the B gear instead of D.


Here is the original graph, while driving in D:

Now the same road again, in B:

The battery started at a different level then before but, driving in B, gained a 13% charge, a minimal difference against the 14% gained while driving in D.

Here are the speed graphs.
D:

B:

Driving in B will force you to press the gas pedal to gain some speed where the slope is not steep enough.
Look at 19:06:30, where the slope begins: the car builds up speed slower than when driving in D.

Some more graphs:

Can you actually drive with your engine off?

This is one of the recurring questions about hybrid cars.
Using Torque, I collected some data about my daily commute from home to work and back.
Here is one trip, from work to home.
Engine rpm are drawn in red: when the value is 0, the engine is off.
Veicle speed is blue: where speed is greater than 0 and the engine is off, we're moving with the electric motor.

With a little data processing, we can draw a graph to show when the car is moving regardless of which engine is using (gasoline or electric), and when is moving with 0 RPM:

 

Engine is off 55% of the time.
By comparison, in the trip from home to work, the engine is off 46% of the time.
On the average, in my daily trips, the engine is off 50% of the time.

There's a thread about this on the Hybrid Synergy Forum.

Battery gain on slopes

Some more experiments with Torque:
How much charge can you gain driving down a slope?
Here is the data from a downhill road: the road is 1.4km long, I drove it entirely with the engine off, with the D gear, with only a slight braking, trying to keep the speed under 45 km/h
The blue line is the GPS altitude.
The red line is the battery % charge level.
Battery starts at 54.9 % at 238.5 meters.
At the end of the road, altitude is 159 m and battery is at 69.01%.
So a 79m height difference caused a 14% gain on battery level.

There's another interesting fact: SOC level seems to increase exponentially until it reaches 60%: from there on, even if the road became steeper (and thus leading to higher charging rate) the charging increases linearly.

There's a thread about this on the Hybrid Synergy Forum.

Mileage improvements

My Yaris Hybrid has reached 5000km and it's beginning to show mileage improvements: last October, when it was brand new, my daily commute was ranked 4.4 l/100km.
Now, with the temperature range comparable to that of October, I see a 4.2 l/100km.

A trip by the sea, Reloaded

Some months ago, I've tested the Yaris on a highway trip.
I had the chance to drive the same trip again.
The car now has 5000 km under its wheels, and consumption was 4.9 l/100km, a little better than last time.

The hybrid foot

Does an hybrid car change your driving stile?
I think so.
Here is the trip from work to home, a couple of days after I bought the car:

and here it is the same, after 5 months:

Average speed is the same, but the throttle usage is way smoother.

A trip by the sea

Having survived Christmas and its endless lunches and dinners, a change of pace was necessary: so we decided for a walk near the sea.
From home, it's a 75+75km trip.

Here is the elevation profile of the road: it starts at 97m, goes up to 590m and down to 10m

On the downward slope, I was caught in a traffic jam: 15 minutes of stop-and-go slow moving.
Here is a snapshot, 9 minutes in the jam: not only I didn't use the engine at all, but I even charged the battery.

That's a fully charged battery, a rare sighting in normal traffic:

Back home, the total mileage was 5.0 l/100Km
I'll compare this result with a later summer trip, where temperatures will be more favorable to better mileage and the car will have more running (it only has 2500Km right now).

B

According to the manual, the B gear should be used on slopes to slow down the car without stressing the brakes.
Some people say that B gives a better grip on snowy roads, even on flat ones.
Since we had snow a couple of days ago, I've done some tests.
No hills here, so just flat, icy roads.
The B allows you to slow down approaching crossroads without touching the brakes: it may somewhat confuse the drivers that follow.
Anyway, while driving with the B on, and cruising at constant speed, I noticed an higher noise level than usual: the engine was running at high RPM rate.
At 68 km/h instant mileage was 6.2 l/100km
Shifting back to the D gear lowered consumption back to 5.0 - 5.2 l/100km.
I asked some Prius and Auris drivers, and it seems in those cars, driving in B, on a plain road, is just the same as driving in D, with no different RPM rates.
Is this a different behavior of the Yaris Hybrid?