Reliabilty of Toyota Hybrids

To see why the Toyota Hybrid is so reliable mechanically we must look at the various approach they have taken in design.


Ok. We have electric motors coupled to an internal combustion engine. Suffice to say that on the EV side the electric motors are 100% reliable. In the last 6 years reconditioning and repairing the battery I have not come across 1 instance of EV drive motor failure. Putting this aside we will look at how the internal combustion engine and transmission contributes to this reliability.

Engine

Maximum efficiency of a conventional engine occurs at around half of the engine's peak power output. So if the engine has it's peak power at 12,000 RPM maximum efficiency would be around 8000 RPM. This means that at the low RPM end ( low speeds and idling) and the high RPM end it is not optimum.

Toyota uses the Atkinson cycle engine. Maximum RPM 4500 in the Generation II Prius (2000 - 2003) and 5000 r.p.m in the Generation III Prius (2003 - 2009 ). The lower end of the spin rate 0 - 2500 is taken up by the EV drive, leaving the ICE to work in it's most efficient range of 2500- 4500 RPM. 

Reducing the spin rate also allows lightweight parts to be used, therefore reducing inertia and friction losses. 

The crankshaft is offset from the cylinder axes so that during the combustion stroke the force from the piston is transmitted to the crankshaft through a straight rather than tilted connecting rod.

The valves have narrow stems and low force springs to reduce energy lost in operating the valves. 

Starter Motor
There is no starter motor. This function is taken up by the electric motor MG1


Alternator
There is no alternator. This is taken up by a DC/DC converter. As there is no moving parts in a converter it is more reliable.


Generator
There are no belt driven generators. The same EV motor that drives the vehicle also acts as a generator.


Transmission
The planetary gear system used does not employ a clutch and reduction gears. A chain drive transfers power efficiently avoiding losses through axial thrust. 

No clutch means we are rid of another gadget that requires frequent replacement and poorer efficiency as they wear out.
Simplicity of the design in the transmission devoid of reduction gears makes for a transmission system that I have yet to see fail.

Less is More

The sum of it is that in the Toyota Hybrid design, the system is simpler and less complicated. Coupling an electric motor to the system sounds complicated but in reality they have put in a more reliable drive train to take care of the low end spin and employed an ideal ICE design for the top end spin. This marrying of the best of both world contributes to the efficiency and reliability of the Toyota Hybrid engine.

Honda Hybrid Vs Toyota Hybrid

The Powertrain

Honda's design - Integrated Motor Assist system uses an electric motor between the engine and continuously variable automatic transmission (CVT) to aid propulsion and turn the 1.3-liter i-VTEC 4-cylinder engine off at stoplights. Integrated Motor Assist is a "mild," or "power assist," hybrid system because the electric motor can't propel the car on its own from a stop, though it can do so for a short time in some steady cruising situations.
Honda's EcoAssist, has guidance and scoring functions, as well as an "ECO" mode that dulls throttle response to improve mileage. The guidance function includes a digital speedometer that turns green when you are driving efficiently and blue when you are hard on the gas.
The gasoline engine delivers maximum power of 69Kw at 6000 rpm. It uses 2 spark plugs per cylinder. The two spark plugs in each cylinder can fire either sequentially or simultaneously, enabling more efficient burning during lean-burn mode and more often lean-burn operation. The VTEC cylinder idling system of the engine closes the valves in three of the four cylinders when the car is decelerating, reduces the power lost to the engine by 50 percent and allows the IMA to extract more electrical energy during braking. The rocker arms operating the intake and exhaust valves have two modes: valve-lift mode or idle mode. They are engaged via a synchronizing piston. During deceleration, the synchro piston disengages the lift-mode rocker arm so that the valves remain at rest, effectively sealing off the cylinder.

Toyota's design - Hybrid Synergy Drive system uses a 73-Kw 1.8-liter (ZVW30) 4-cylinder engine aided by two electric motors, one of which assists the engine when more power is needed. Toyota quotes total output at 100 KW and acceleration of  zero to 100 kph in 9.8 seconds.
Hybrid Synergy Drive is a full hybrid system because the motor can propel the vehicle up to 42 kph without the aid of the engine. The Prius also has an "EV" button that allows the car to be driven on electric power alone. The upshot is that drivers can aim to keep the engine off as often as possible.
The Atkinson cycle engine delivers maximum 73Kw power at 5000 rpm and only starts once the vehicle has passed a certain speed and after starting operates in a narrow speed band.

Conclusion :  The electric motor will still be operating at peak capacity long after the engine has given up so maintaining efficiency will depend on the durability of the petrol engine.
Without a doubt the engine in the Honda works much harder. In the Prius the engine only operates from 2500 rpm - 5000 rpm, wheres in the Honda it is working from 0 rpm to 6000 rpm. This means that a Honda engine that has done 100,000 Kms would have significantly more wear and tear than the Prius which would probably only show the wear and tear of a vehicle that has done about 50,000 Kms.
The Honda engine is more complicated and uses 8 spark plugs. This just means more things to go wrong and higher maintenance cost.

We must bear in mind that all comparisons are done with vehicle in peak condition and this is only true when the vehicle is new. My opinion is that overall Toyota's design is far superior. It will still be running perfectly (like new) even after the vehicle has done 500,000 Kms, and it will cost a lot less to maintain.

A Very Good Car

I remember many years ago while stopping at traffic lights I often wondered to myself how good it would be if the engine can turn itself off. I personally know of people who actually turn their engine off to save fuel! This is false economy as it takes more fuel than you would save when starting the vehicle again.

Well today the hybrid vehicle does it as a matter of course and not only that - it saves energy from braking to release when required and turns the engine off when cruising as well.

Just how good is the Hybrid car when compared to a standard vehicle?

1) Fuel Economy
A well maintained Generation one Prius ( 1997 - 2000 ) still return 20 - 22 Kms to the litre (4.5L/100Kms) This is after clocking up more than 200,000 Kms on the odometer! A standard vehicle would have loss so much compression that it's fuel economy would have deteriorated at least 25% from new.

You can still purchase a good used Generation one Prius for $6000.  If you are currently spending $100 on fuel a week, you could save $2500 a year. This means recouping the cost of your purchase within 3 years at the most. This savings alone should sway thinking people towards purchasing a used hybrid, especially if you have to drive good distances going to and from work.

Generation two Prius (NHW11)  are even more economical and Generation three (NHW20) even better still.

2) Internal Combustion Engine

This engine shuts off when not required. This means that the odometer reading does not represent the actual wear and tear as an engine in a conventional car. My guess is that if we half the odometer reading it would represent the actual wear and tear when compared to a conventional car.

The engine oil in a vehicle that has done 150,000 kms, is still golden a month after an oil change. This means that the piston rings are still intact.

3) Starts every time

One thing I noticed was that the hybrid car will start every time as long as the HEV battery and 12 volt battery are in good working order.
In 12 year old conventional vehicles starting is always questionable as it depends on the state of the 12 volt battery, the starter motor, the alternator, the idling, the timing chain and the distributor. Most of these components are not used in the hybrid car - Less parts to go wrong therefore starts every time.

4) Smooth Quiet and vibration free ride

Although it can best be described as medium saloon, It drives like a large saloon. The combination of the electric engine and the petrol engine contributes to this smooth ride. Being quiet and vibration free adds to the comfort of driving a hybrid.

5) Brakes pads

Regenerative braking recovers the energy from braking which are then stored in the batteries for reuse. This means that the brake pads are not used in normal braking. Most hybrids even at 150,000 Kms still have their original set of brake pads.

6) Spark Plugs

I have personally taken a set of spark plugs out of a car that has done 150,000 Kms. The gap was so large that it stopped firing in one cylinder.

All this goes to show that cost of mechanical maintenance is much lower than a conventional vehicle.