Project 2

Objective:-

• To develop a forward energy-based fuel consumption model of a P1 hybrid vehicle. The main goal of this project is to understand the functionality of a P1 hybrid and be able to model it.
• The task of this project is to quantify the improvement in fuel economy numbers for the hybrid vehicle (kmpl), compared to the conventional vehicle, on the urban cycle (UDDS) and highway cycle (HWFET). Also, to analyze and understand the vehicle operating points in terms of engine and motor speed, torque, transmission speeds, pedal positions, gear, distance travelled, battery voltage, current, SoC, etc.

P1 Hybrid functionality:-

The P1 architecture, with the electric machine connected directly to the crankshaft, is the solution adopted by Honda on their first generation Integrated Motor Assist (IMA) technology. The electric motor functions as a generator during vehicle deceleration, as an engine starter, and as a motor (to assist the engine) during vehicle accelerations.

One of the biggest advantages of this solution is that the electric motor can provide higher torque than the Belt-Integrated Starter-Generator (BiSG), since there is no belt limitation (due to slip). However, since there is no speed / torque ratio between the electric machine and crankshaft, the torque requirements on the electric motor can be quite demanding.

Two examples of P1 MHEV architectures are:

• Honda Insight Hybrid 2009 (with Integrated Motor Assist technology)
• Mercedes Benz S400 Bluehybrid 2010

For example, the main characteristics of the crankshaft-mounted electric machine for mild hybrid Honda Insight 2009 are summarized in the table below.

Electric machine performance	Maximum torque (at crankshaft): up to 34 Nm Maximum power: 10 kW Efficiency: up to 94%
Hybrid modes (functions)	Idle Stop & Start Moving Stop & Start Engine load shift Torque assist (fill) Torque boost Sailing / Coasting Energy recuperation Brake regeneration
Advantages	Higher efficiency The 12V starter can be removed
Disadvantages	Output torque limited by the size of the electric machine Energy recuperation affected by engine friction losses High impact on existing vehicle architecture Higher overall cost of the electrical components Air cooling not possible for the electric machine
Overall characteristics	Torque Boosting Capability: High (if electric machine is capable) Electrical Energy Recuperation: Medium (due to engine losses) Driveability Improvements: Medium (depending on the torque capability of the electric machine) Electrical Creep / Drive: Possible (depending on the torque capability of the e-machine) Packaging: Difficult components integration (powertrain specially designed for this architecture) System Efficiency: High (no gear mesh or belt losses)

Simulink Model:-

Driver Model:-

It contains a PI controller to get the accelerator and brake pedal signals depending upon the drive cycle requirements.

Controller Model:-

• This is the brains of the vehicle.
• It generates desired engine and motor torque signals, gear signals, which are fed to the powertrain.

States:-

• The first state indicates that the vehicle has stopped.
• The second state indicates starting phase which is why only EM is used.
• The third state is the driving state where the engine is on and the EM is off
• The fourth state indicates regenerative braking where the engine throttle is o and the EM throttle is equivalent to the brake pedal signal.

Transitions:-

• State 1 – 2
• Acc>1 || SOC<SOC_min
• For the starting phase if the accelerator signal is more than 1 or if the SOC has fallen below the minimum value
• State 2 – 3
• Eng_Spd>Eng_idle_spd
• Between the starting and driving phase the transitions happens when the engine speed is greater than the engine speed at idle state.
• State 3 - 4
• Spd>6 && Brk>=2 && SOC0
• From driving to regenerative braking, if speed and brake signal are above certain values and SOC is less than its max value and the Clutch lock up is more than 0.
• State 4 – 3
• Spd<=5 || Brk<1 || SOC>=SOC_max ... || ClutchLockup==0
• If any of the previous conditions are not met then the vehicle will go from regen braking to the driving state.
• State 3-1
• after(1,sec) && Spd<0.5 && SOC
• Driving and stop condition, transition is indicated by checking the Speed values are below a certain threshold and the SOC value is less than its minimum and the acceleration is 0. This is checked after every second.

Engine Control Unit:-

• The idle speed controller keeps the speed above the idle speed and make sure that the engine is idling provided that the engine is on.
• The accelerator pedal from the driver unit provides the throttle signal as an input.
• It has two look up tables for maximum and minimum torque curves for various speed values.
• The input to the tables is the engine speed. This input along with the throttle and idle speed controller signals are multiplied together to get the required engine torque.

Transmission Control Unit:-

• It uses state flow to determine gear shifting.
• Velocity and throttle are taken as inputs and the gear used currently is given as an output.

Shift Logic

• The Gear_state state block decides which gear to shift to using the UP and DOWN decision arrows.
• The decision is done by the selection_state state block. Using the ComputeThreshold Simulink function it calculates the values of up_th and down_th which decide whether the gear state should be up or down.

Electric Motor Control Unit:-

• It has 2 input in which the 1st one is in from block which is EngSpd that was connected with maximum(EM_Max_trq) and minimum trq curve(EM_Map_spd) in which the maximum trq curve was connected directly with the switches and the minimum trq curve has -1 gain output because of regenerative braking and it was connected with the switches.
• Another input is from EM_thr and it has added some gain to get the output and it was connected with the switch.
• The output from the switch was limited hence the Rate limiter block was connected and the output was connected EM_trq_req.

Brake Control Unit:-

• The brake torque is calculated analytically and multiplying it with the brake signal, the magnitude of the brake torque which is required is generated.
• These three signals are connected to a bus, which is transferred to the powertrain block.

Powertrain Model:-

There are few main important components in Powertrain. Some of them are Engine, Motor, Crank, Transmission, Differential, Wheels and Vehicle dynamics. The Control signal was connected with the bus connector whereas the signal was transfers to the various part of the powertrain such as Engine, Electric Motor, Clutch lockup, Gear Command and Brakes.

Engine:-

The Engine act as a primary source of energy which used to generate the power of the vehicle to move. The max and min torque curves act as upper and lower bounds for the engine torque signal which is given to the 2D look up table of fuel consumption. The look up table gives the fuel flow rate and the integrator gives the total fuel consumed until that point.

Electric Motor:-

The electric motor was used to act as a second source of energy. This electric motor was functioned based upon the engine speed. The maximum and minimum torque curves are calculated under Eng_max_trq and Eng_map_spd respectively. Thus the elctric power and torque from electric motor was supplied.

Crank:-

The crank receives the input from Eng_trq and EM_trq whereas to crank and creates the energy/power for the vehicle to move.

Transmission:-

• The engine torque, transmission speed and the clutch lock up signal go into the torque converter.
• The gear output signals are sent to the transmission gear ratio look up table.
• The gear ratio is then multiplied with the transmission torque and transmission efficiency to get the transmission output torque.
• The gear ratio is also multiplied with the transmission speed to get the transmission output speed.

Differential:-

• The wheel speed is multiplied by the differential ratio to get the output speed
• Transmission torque is further multiplied or divided by the differential efficiency depending on whether the torque is positive or negative respectively.
• The output is the axle torque.

Wheels:-

• The brake torque is subtracted from the axle torque to get the net torque, which is then divided by the wheel radius to get the tractive force.
• The velocity is divided by the wheel radius to get wheel speed.

Vehicle Dynamics:-

The dynamic equation for calculating the road load is attached below. This equation is represented using the various mathematical blocks, which after integrating gives us the velocity.

Estimates Storage System(ESS) model:-

The input to the subsystem is the Electric Power. The outputs are the SOC and the power.

• The pack current is calculated by dividing the power by the voltage.
• The SOC estimation subsystem is used to calculate the SOC which is used as input to the terminal voltage subsystem.
• The battery voltage multiplied by the pack current gives the power.

SoC Estimation:-

• The pack current is integrated to get current in coulomb which is then divided by 3600 to get current in Ampere-hour.
• This is divided by the max ampere hour capacity to get the current soc.
• This after subtracting from the initial battery soc will give us the SOC value.

Terminal Voltage:-

• The pack current is divided by the no of parallel modules in the battery packs as the current in parallel is divided while the voltage remains the same. This gives us the current in one cell.
• This current is connected to the control port of the switch block. The other two blocks are connected to the charging and discharging resistance look up tables. The criteria being, if the current is greater than zero than cell is discharging otherwise the cell is charging.
• The input to the lookup tables is the SOC. The third lookup table gives us the open circuit voltage.
• The switch block decides the internal resistance of the cell (R). This is multiplied by the current to get (IR). This when subtracted from the open circuit voltage gives us the battery pack voltage.
• This battery pack voltage is divided but the no of modules in series to get the terminal voltage.

Conclusion:-

Hence the development of a forward energy-based fuel consumption model of a P1 hybrid vehicle was designed and it was attached with below.