Robert,
That makes sense but, depending on what you do, seems like a possible
point of failure, and in a dangerous way.
First, I wonder what Tesla does. If they do it, it's probably well
thought out.
Second, I think what you really want to detect is when the traction
shifts from static friction to dynamic friction. With the latter
friction, the wheel has essentially lost traction. During regen, that
means it will stop rotating or rotate very, very little.
Am I making an assumption, here? Let's consider that you have very light
regen. In that case, it may not provide enough resistance to break the
static friction. As you increase the regen, eventually the static
friction will break free. Since the dynamic friction is much less, the
regen should lock up the wheel, more or less instantly. I think it will
stay locked up until the regen is lowered.
So, I think it would be sufficient to detect that there is no wheel
rotation rather than detect the speed. You certainly could use a speed
sensor but treating this in a binary fashion may open the possibility of
other devices.
Peri
------ Original Message ------
From: "ROBERT via EV" <[email protected]>
To: "Corbin Dunn" <[email protected]>; "[email protected]"
<[email protected]>; "[email protected]"
<[email protected]>
Cc:
Sent: 23-Feb-17 1:37:39 PM
Subject: Re: [EVDL] Wheel Speed Sensor
No sensor mounted in the transmission will work for regenerative
braking. The motor/engine is directly connected to the transmission.
The transmission is connected to the differential. The differential
allows one wheel to rotate faster than the other wheel. Think about
going around a curve. The inside wheel must rotate faster than the
outside wheel or the vehicle will slide. This is the purpose of the
differential. Any speed sensor mounted in the transmission measures
the speed of the motor as ratio of the gearing. It is a fixed ratio.
However, because the differential can allow one wheel to rotate faster
than other wheel i.e no direct ratio. regenerative braking can cause an
instability via loss of traction on one wheel. To prevent this
instability, the inverter must know the speed of each wheel and reduce
regenerative braking. Now you know why I want to install wheel speed
sensors on my Porsche 914.
________________________________
From: Corbin Dunn <[email protected]>
Sent: Thursday, February 23, 2017 8:10 AM
To: ROBERT
Subject: Re: [EVDL] Wheel Speed Sensor
Ah! Okay..I haven’t heard of those. It sounds just like my Bug’s
speedometer though. I think using speed would work just fine…but there
are so many variables, like the type of car, motor, and controller.
corbin
Il giorno 22 feb 2017, alle ore 8:46 PM, ROBERT
<[email protected]<mailto:[email protected]>> ha scritto:
Wheel speed sensors are installed at the wheel. The wheel has a tone
ring with gear teeth and the sensor reads the teeth as the wheel
rotates. It is sometimes called an ABS wheel speed sensor because the
ABS brakes use the signal to determine if one wheel is "locking up"
during braking. The sensor is also used by the regen braking system to
prevent causing an instability. I would like to install sensors on the
rear wheel of an EV conversation.
________________________________
From: Corbin Dunn
<[email protected]<mailto:[email protected]>>
Sent: Wednesday, February 22, 2017 3:34 PM
To: ROBERT; Electric Vehicle Discussion List
Subject: Re: [EVDL] Wheel Speed Sensor
A wheel speed sensor? You found a car without a speedometer? I mean, it
is proportional. I removed my tach gauge once I knew what speed
produced what RPM.
corbin
Il giorno 17 feb 2017, alle ore 9:09 AM, ROBERT via EV
<[email protected]<mailto:[email protected]>> ha scritto:
Has anyone installed a wheels speed sensor on an EV conversion? I am
referring to a vehicle that was not originally supplied with a wheel
speed sensor. Has anyone connected a wheel speed sensor to an
inverter (AC motor controller)?
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