Hybrid System Power Flow

Hybrid System Power Diagram

Multiplying voltage by amperage results in total amount of wattage. Examples:

1) 200V x 30A = 6000W

2) 300V x 20A = 6000W

The same total wattage is achieved in both formulas. This allows the opportunity to start with a lower voltage, more compact battery pack, and by providing higher voltage down the line the same total wattage output is achieved. (As shown in formula example 1).  

In traditional vehicles the chassis must serve the purpose of grounding the battery. But in hybrid vehicles the design is such that the battery is grounded through the dc, dc converter (internal to the ac/dc inverter in Toyota Prius models) freeing up chassis space.

SMR (System Main Relays) are put in place on the negative and positive wires from the HV battery as a safeguard. When the vehicle is not in ready mode the relays are opened dropping the voltage to zero.

Power Up (Toyota Hybrids with Smart Key Entry)

 

1. Off (LED not lit)
2. Accessory (LED Green) - powertrain not functioning, shift selector not functioning, accessories have power
3. Key ON, Engine OFF (LED Amber) - only neutral and park can be selected, accessories have power, Techstream can communicate with vehicle's ECU's and  pull  DTC's (Diagnostic Trouble Codes)
4. Ready (LED not lit) Engine running, Powertrain functioning. Charge to 12v battery.

T.I.S. (Toyota Information System)

  

• Search must be performed for index to appear
• Some helpful, and often hidden indexes for engine diagnostic, are located in the SFI Section: Parts Location, System Diagram, Terminals of ECM, Data List/Active Test

 T.I.S Part II 

A) Home

    1) Library

         a) Summary

• SB/TT - Service Bulletin/Tech Tips
• RM - Repair Manual
• EWD - Electric Wiring Diagram
• NCF - New Car Features
• SC - Service Campaign
• Accy - Dealership Add-ons eg: remote start           

A) Home

    1)Library

       a) Tech Training

• T256 - Basic Maintenance
• T072 - Diagnostics, HV Battery

TIS Navigation



 

Pulling Diagnostic Trouble Codes, 2008 Toyota Prius

In Key On, Engine Off mode the Techstream is hooked up and notes code P0A0D-350. TIS shows this code to be for the high voltage interlock circuit. Further inspection confirms the 'service plug', which is connected to the high voltage battery is missing the fuse. Keshau and I replace the 'service plug' with one that contains the proper fuse. We clear the codes and no further codes are present on vehicle.

 

HV Battery Diagram

 

Keshau and I remove the HV battery pack from vehicle. (Note: TIS suggests unnecessary steps for this procedure). Due to Keshau's experience and common sense we are able to streamline the process saving time. After the HV battery is removed we inspect the wiring routing and begin to draw a diagram representing the flow of power within the battery.

 Above: Shows the HV battery assembly out of vehicle and the metal top casing removed to expose the HV battery ECU, System Main Relays, Resistor, Heat Sensing Wiring, Modules, and Positive/Negative Cables.



And we finish our diagram:





Grrrrrrrrrrrrrr.....

Back in the battery goes.....and I'm wrenching so fast the camera can barely capture.

To Further understand the start up and shut down procedure of the hybrid system Jack discusses the concept of VB (Battery Voltage), VL (Voltage Low), and VH (Voltage High). VB is the current voltage output of the battery before entering the inverter. VL is the battery voltage after entering the inverter. And VH is the battery voltage after entering the inverter and having been 'boosted' by the boost inverter. The boost inverter is a component located internal to the inverter on the 2008 Prius. We also review the SMRs (System Main Relays) including their functionality and circumstances under which they open and/or close.

In order to chart this activity we hook up the Data Stream and map a customized chart for the above PIDs (VB, VL, VH) and the three SMRs. By watching the activity from the Data Stream we are able to understand when the relays close, why, and how that affects the VB, VL, and VH. Simply fascinating.

In conclusion, now when I 'ready on' a Generation Two Prius I have an clearer picture of what the vehicle is achieving and how the voltage cycle works.

 

  Prius Plug-In ECU's

1. PICC - Plug-In Control ECU
2. Power Management Control ECU (formerly known as HV ECU in Generation 2 Prius)
3. DCM - Telematics Transceiver

High Voltage Battery Data

"We are running hot!"

 

     A. SOC - State of Charge

         1) Voltage, Amperage, and temperature readings are needed

     B. Power Resource VB

     C. Power Resource IB (current)

     D. Charge Control Value

     E. Discharge Control Value

     F. Block Voltages

         1) Maximum

              a) Maximum rate of charge at any given time (not current reading)

              b) Can be affected by ambient temperature     

         2) Minimum 

              a)Minimum rate of charge at any given time (not current reading)

              b) Can be affected by ambient temperature    

    G. Cooling Fan

    H. Temperatures, One, Two and Three

         1) Reading from heat sensing wires running along underside of HV battery

     I. Delta State of Charge

         1) Generation One Prius

              a) Code will show above 20%

         2) Generation Two Prius

              a) Code will show above 0%

         3) Generation Three Plug-In

              a) No default

Note: Master warning light is not only for the hybrid system. When master warning light and MIL (malfunction indicator light) are on this almost always indicates a problem with the hybrid system.

With standard 12v batteries, as the SOC steadily declines, the voltage also steadily declines at the same rate. In the case of High Voltage batteries eg. nickel metal hydride and lithium ion as the SOC steadily declines the voltage starts to decline, levels off, and then rapidly falls.