Wonder how the AC and brakes work while not moving????

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saywatt

Well-known member
Joined
Jul 14, 2011
Messages
234
Location
Elk, WA
I wondered this after having my LEAF for less than a week. AC and Power Steering typically have pumps—AC has a compressor, and power brakes have a pump. When I turn the car on, I hear a motor so I assumed it was the drive motor at some slow idling speed to run the two pumps OR each had it own electric motor. So I asked Nissan and the answer I received was that each has its own motor but still uses the Li-Ion to run them. Just FYI
 
You sure lived up to your username with your first post!

The power steering and brakes are both electric and I think run off the 12V. There are no pumps.

The AC has a compressor which runs off the pack voltage. You can clearly hear it if it's on, it sounds like a refigerator. If the AC is off, the faint whirr sound you hear when not moving is the motor/inverter/charger coolant pump. You also hear it when you charge.
 
Correction—I meant the power steering, not brakes. And an AC compressor is a pump, in a way. As I said, but perhaps not clear as to who said it, it was a Certified Nissan LEAF technician (you know, the guys who are going to be working on our cars) who said the AC and power steering have their own motors and use the drive battery for their power. Who am I to disagree with "Scotty"? :)
 
Trust me when I say the $20 service manual knows more than the Certified Nissan Techs. It's not the first time they have told people wrong info...and it won't be the last.

Page STC-14 of the service manual clearly shows the electric PS motor (it's not a pump, it's a servo applying force directly to the steering shaft, there is no fluid involved) powered by 12V.

As I agreed, the A/C compressor does run off the high voltage. So they were only partially wrong.

Read my other posts, I'm not someone that would say something I'm not 100% sure of.

Now Beam me up!
 
turbo2ltr said:
Trust me when I say the $20 service manual knows more than the Certified Nissan Techs. It's not the first time they have told people wrong info...and it won't be the last.

Page STC-14 of the service manual clearly shows the electric PS motor (it's not a pump, it's a servo applying force directly to the steering shaft, there is no fluid involved) powered by 12V.

As I agreed, the A/C compressor does run off the high voltage. So they were only partially wrong.

Read my other posts, I'm not someone that would say something I'm not 100% sure of.

Now Beam me up!


Same as so many other cars. Nissan techs can be anywhere form clueless to very well informed but few are EV or electrical expects. They may be able to rebuild a part (not done much now) but they sure have no idea how to repair an inverter. It's scary having to coach the Nissan techs and service people on whats wrong with the car and how things work. I'm sure in time this will change a bit.
 
Luckily other Nissan cars use the same power steering systems, so they will know how to fix it.. motors, inverters and batteries will just be a swap with factory rebuilt parts and hopefully no one gets electrocuted in the process.
 
"The power steering and brakes are both electric and I think run off the 12V. There are no pumps".

Yes they have a electronic component due to the regeneration process. However they are standard hydraulic brakes. The brake system uses brake fluid and essentially is a mechanical system. What makes it unique is that electronically the system determines what is happening (how fast you are applying the brakes, how much pressure you are applying, etcetera) it then decides how much regeneration will take place and how much actual braking (using the disk brake pads) will occur. It is a really cool system. Lots of failsafe’s built in.
Manny
 
The brakes are assisted by a hydraulic pump:


From the Nissan Service Manual, page BR-11:
Contains a motor and generates boost force according to the amount that the brake pedal is depressed and the amount of cooperative regenerative brake control.
Uses the boost force to generate fluid pressure in the master cylinder.

The pump generates hydraulic pressure which then acts directly on the master cylinder's piston.

This differs from ICE cars where intake manifold vacuum is used to "power" the "brake booster" which in turn supplies mechanical force on the input shaft of the brake master cylinder's piston.
 
OK, so if we strip off all the semantics:

The brakes, which I mistakenly included in the original post, use a hydraulic pump with a kind of motor component.

The power steering uses a servo, a kind of a motor,

The AC uses a compressor, which includes a kind of a motor.

So, I'll give the LEAF tech better than 50% right/wrong. He was probably just stating the answer to my question in layman's terms.......kind of how I did above.
 
No, the brakes use an electromagnet actuator as a booster. There is no pump of any kind. There is a super capacitor in the back next to the charger to provide backup power for the brakes in case of a total electrical failure of the vehicle.

saywatt said:
OK, so if we strip off all the semantics:
The brakes, which I mistakenly included in the original post, use a hydraulic pump with a kind of motor component.
 
Its all semantics.. the impression I get is that brake motor helps you push down on the pedal, or does the foot pedal regulate (plus the brake computer) the amount of hydraulic pressure supplied to the calipers?. The pressure is generated by a rotating motor.. I believe the capacitor bank will supply emergency power to this motor if the main supply is not available but you can see where the brake pedal directly will provide a totally human powered failsafe.

It would be interesting to see if this system will be used in other cars, diesels and some fancy gasoline engines dont have lots of vacuum to power a vacuum brake booster.
 
It's no different than any other power brake system where you have a hydraulic master cylinder that has some form of power assist. I doubt the vehicle codes would allow for any other form of brake system at this time...


Herm said:
Its all semantics.. the impression I get is that brake motor helps you push down on the pedal, or does the foot pedal regulate (plus the brake computer) the amount of hydraulic pressure supplied to the calipers?. The pressure is generated by a rotating motor.. I believe the capacitor bank will supply emergency power to this motor if the main supply is not available but you can see where the brake pedal directly will provide a totally human powered failsafe.
 
mogur said:
No, the brakes use an electromagnet actuator as a booster. There is no pump of any kind.
You will need to provide a reference for that assertion, because there is no mention of an "electromagnet actuator" in the LEAF service manual. Unless of course, by "electromagnet actuator" you were referring to the brake assist electric motor.

From the LEAF service manual, page BR-12:
• Based on the commands from the control module of the electrically-driven intelligent brake unit, the motor
inside the electrically-driven intelligent brake unit is operated and presses the master cylinder piston.
• Pressing the master cylinder piston, and brake fluid is sent to the ABS actuator and electric unit (control
unit).


saywatt said:
OK, so if we strip off all the semantics:
The brakes, which I mistakenly included in the original post, use a hydraulic pump with a kind of motor component.
Herm said:
Its all semantics..
Each of those components has a motor: brakes, steering and A/C.

mogur said:
There is a super capacitor in the back next to the charger to provide backup power for the brakes in case of a total electrical failure of the vehicle.
Herm said:
I believe the capacitor bank will supply emergency power to this motor [...]
Ingineerix apparently thinks that there is a single supercapacitor.
 
Look at the cutaway drawing in the service manual. It appears to look much more like a typical electromagnetic actuator (solenoid if you will) than an electric motor to me. I think the English translation lost a little of the context along the way...

The ABS system uses a hydraulic pump, of course, as do virtually all such systems on any kind of hydraulically braked vehicle.

aqn said:
You will need to provide a reference for that assertion, because there is no mention of an "electromagnet actuator" in the LEAF service manual. Unless of course, by "electromagnet actuator" you were referring to the brake assist electric motor.
 
aqn said:
Ingineerix apparently thinks that there is a single supercapacitor.
There is one capacitor assembly, but inside the box it's made up of numerous small supercapacitors soldered to a PCB.

Similar to this unit which is used on the Prius:
pic

(picture courtesy of Hobbit)

FYI: All 12v accessories on the LEAF are ultimately powered by the traction pack, so the nissan tech is right when he says the power steering is powered by the main pack. Also: there is a hydraulic pump on the ABS system.

-Phil
 
I thought it was a rat on a wheel. Now I need to find out the source of that noise.
 
The important thing here, that we all must understand, is that the LEAF stops just fine with whatever technology it uses! :)
 
The quick-and-simple answer is that if the average temperature is lower, it will take more energy. If the car gained no heat (insulated by a fictional perfect insulator) running the fan after the car was cool would actually use more power. Now, because of how we judge temperature, a 75 degree car with a fan blowing directly on you is going to feel a lot colder, so therefore you can make use of the fan and not cool the car as much to save electrons.

In the real world, if you cool the car down, (preferably on grid power from the EVSE) then it will not take as much to maintain it, but there definitely will still be heat load. This is made substantially worse if you have a darker colored car (paint and interior). This is one of the reasons I love white!

-Phil
 
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