1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Newbie owner question

Discussion in 'Newbie Forum' started by Codemonkey757, Jun 17, 2019.

  1. Codemonkey757

    Codemonkey757 Junior Member

    Jun 17, 2019
    Virginia Beach, VA
    2011 Prius
    Hello, guys! I'm a new Prius owner, I love it so far, but I do have a question.

    Can anyone please explain to me exactly what a hybrid does? It was my understanding that the gas engine starts the car and while driving it charges the electric engine's battery. Once it's charged enough, the gas engine shuts down or is reduced and most of the power comes from the electric aspect. Yet I've only been driving for a few days in the city and have already used half a tank of gas. I'm using gas at the same rate as my old Mazda.

    I've glanced at the energy monitor, and very rarely does energy go from the battery to the generator to the wheels. Most of the time it's from the engine to the generator to the battery and wheels.

    Is there something wrong with my hybrid, or is this normal?
    Burna J likes this.
  2. bisco

    bisco cookie crumbler

    May 11, 2005
    2012 Prius Plug-in
    Plug-in Base
    congrats and welcome!

    1) half a tanker 'a few days' is meaningless. mpg = miles per gallon. reset trip a or b, fill the tank, drive until your down to 2 bars on the gauge and refill. divide gallons filled by miles driven to get mpg's.
    then you'll know if something is wrong or not.

    2) prius hybrid is a concert. there is no independent engine, battery or generator.
    depending on conditions, the computers decide when the battery should be used for power or recharged, and when the engine is used for power and/or heat, or when it is off.

    3) there's probably nothing wrong with your car, but it is 8 years old, and we don't know the history.
    how many miles on it?

    you have a lot to learn, and you've come to the right place. all the best!(y)
    #2 bisco, Jun 17, 2019
    Last edited: Jun 17, 2019
  3. Ronald Doles

    Ronald Doles Active Member

    Apr 21, 2019
    Columbus, OH
    2015 Prius v wagon
    Most of what I have said here has been covered in the threads by others on this website. If any member see's any errors, feel free to correct them.

    The 12 volt battery, located in the trunk, is lower capacity than in most cars because it is not used to start the car. It just provides power to all the electronics. The hybrid battery, located under the back seat, is a 200 volt battery that provides the motive power.

    There is no transmission as such in a hybrid. The internal combustion gasoline engine, ICE, is connected to a motor/generator, MG1. Electronics and road conditions determine whether it acts as a motor or a generator. The wheels are connected to a second motor/generator, MG2. There is no mechanical connection between the ICE/MG1 and the wheels/MG2.

    The inverter is located under the hood. It charges the 12 volt battery. The throttle position, brake pedal position, SOC, engine temperature, vehicle speed and other conditions determines where the inverter directs the high voltage power.

    To start the ICE, the inverter sends power from the hybrid battery to MG1 which acts as the starter motor. Once the ICE is running it spins MG1, acting as a generator, which provides power that can either charge the hybrid battery or provide power to MG2, acting as a motor, to move the vehicle.

    The electronics/inverter tries to maintain the hybrid battery at about 60% charged so that if power is required from the battery, it is available but if braking is required, there is capacity in the battery to accept this electrical energy.

    If the state of charge, SOC, of the hybrid battery is high enough and the temperature of the ICE is warm enough, a gentle accelleration at low speeds can be battery only for up to 2 miles. This is great for stop and go traffic. If a quicker accelleration is required or the hybrid battery SOC is low, the ICE will also start and assist in the accelleration. At freeway speeds, the ICE provides most of the motive power.

    Braking: Depending on brake pedal pressure, the inverter determines how much MG2, acting as a generator, is used to charge the hybrid battery. Heavy brake pedal pressure causes the inverter to put a greater generator load on MG2 which slows the car more rapidly and it charges the hybrid battery at a higher rate. This regenerative braking saves the energy that is normally wasted as heat in mechanical brakes and instead that kinetic energy is converted to chemical energy in the hybrid battery. Generator loading is actually what slows the vehicle. The mechanical brakes only kick in below about 8 mph. Since regenerative braking is the primary braking means, the mechanical brakes should last 100,000 miles.

    When coasting, MG2, acting as a generator, outputs a low charge. The inverter sends this current to the hybrid battery which gradually slows the vehicle down.

    The Prius ICE is an Atkinson cycle engine. Most automotive engines are Otto cycle for maximum power. Two traits of Atkinson engines are that they provide less power for a given engine size but they have higher thermal efficiency (convert more energy from the gasoline to motive power) than an Otto engine. This makes sense for a hybrid vehicle where the Atkinson gives better mileage and the lower power of the ICE can be assisted by the hybrid battery when more power is required.

    On most standard vehicles, the air conditioning, power steering and water pump are driven by a belt from the ICE. In order for the hybrid vehicle to travel at times without the ICE on, the air conditioning, power steering, water pump and power brakes were converted to run from individual electric motors. One advantage of this is the ICE can be off and the air conditioning will still function.

    There is a second cooling system for the inverter and it has a reservoir under the hood, uses part of the radiator and also has an electric pump.

    There are several temperature thresholds with the Prius. One is about 100 deg F. On a cold start in the morning, the ICE will run until that coolant temperature is exceeded and will not shut off when the vehicle is stopped. There is a second threshold at about 150 def F. Above that temperature the ICE will shut down when the vehicle stops. The third threshold is around 190 deg F. Above that, threshold, if the throttle is released at lower speeds, the ICE will shut off and it will remain shut down while coasting or if only light throttle pressure is re-applied.

    It is a pretty amazing system.
  4. TastyZombieSnack

    TastyZombieSnack Junior Member

    Jun 26, 2019
    New Hampshire
    2009 Prius
    Incredibly helpful post, thank you!
  5. jerrymildred

    jerrymildred Senior Member

    Oct 28, 2016
    Tampa, FL
    2017 Prius