Down Hill Brake(DHB)

There is no engine in EV or FCV system. We propose Down Hill Brake which will assist mechanical friction brake instead of engine brake on long and steep downhill road.

Down Hill Brake System Contribution to Safety of EVs, FCVs         (New technology which is under development)

SNT proposes Down Hill Brake (DHB) for EV and FCV.
DHB prevents fade of friction brake on long and steep downhill road when the state of battery charge becomes full.
Necessity of the DHB and its outline are shown below.
For vehicle with internal combustion engine, engine brake assists friction brake for wheel brake.
Drivers make shift change into low gear range on long and steep road in order to use engine brake effectively.

We often see caution signs recommending usage of low gear range beside long and steep downhill road.
In JAPAN, there is a typical long and steep downhill road in HAKONE mountain area near TOKYO.
That is steep downhill road with 7% average gradient and 60 km/h typical driving speed.

On such steep downhill road, effective and strong enough brake is required.
However, heating of the brake is an important concerned issue.
Without engine brake, enormous amount of heat will be generated.
If the amount of heat becomes too large, fade of friction brake for wheel brake will be occurred.

The result of estimation about heat is surprising.
If the assumptive conditions are 7% downhill gradient and 60km/h driving speed, the amount of heat is equal to 17×1000W electric heaters in the case of a vehicle with 1.5 ton weight. In the case of a vehicle with 15 ton weight, the heat amount is equal to 170×1000W electric heaters !
For conventional vehicles with an engine, the engine exhausts such large heat to outside of the vehicle.
For trucks, exhaust brakes are often utilized, which realize larger engine brake by narrowing exhaust gas passage.
For heavy duty trucks with heavy weight, so-called “Retarder” is often utilized, which is dedicated device for providing auxiliary brake torque in powertrain.

For EV and FCV, electric motor acts two role, driving motor or generator. When it works as a generator, the generator provides regenerative braking function.
On short distance downhill road, the regenerative brake actuation is surely effective.
If capacity of generator is large enough, vehicle can be driven down without friction brake and in such case, heat is not generated at friction brake.

As described on previous page , the regenerative brake acts as lifeline, pulling rope from top of the mountain.

However, on long and steep downhill road, generator works for very long time.
Charging of battery lasts for long time, then the state of battery charge will become full condition.
Just after when the state of battery charge becomes full, generator can not send electric power to battery.
So, generator has to stop working and regenerative brake will be stopped.
Because the regenerative brake cease its working, large heat will be generated at the friction brake.
Enormous amount of heat will be generated and by that, fade of friction brake will be occurred.

As described above, there is a vital issue to be solved for EV and FCV.
Time-out issue exists for inevitable lifeline on long and steep downhill road.
By the time-out, state of battery charge becomes full, and the vital lifeline will be broken off.

FCV is more critical than EV for this point of view.
Because the battery capacity of FCV is much smaller than that of EV, so, “Time-out” situation will more often happen.
DHB proposed by us solves the critical safety issue.
DHB is so to say “Sustainable Lifeline” , which can last its working endlessly such as engine brake.
So, DHB can prevent fade of friction brake on long and steep downhill road.

As candidate systems for DHB, various kind of our new technologies have already been patented.
The promising candidate solution is compression-expansion cycle system.
The system heats up cool air to hot air by compression and the heated hot air will be exhausted to outside of the vehicle.

This figure shows the actual structure of DHB.
It looks as if internal combustion engine, however it is completely different from conventional internal combustion engine.
It has no ignition plug but has valve for brake performance control.
By the similar way to engine brake working, this DHB heats up cool air to hot air by compression simultaneously at compression phase, and exhausts the heated hot air to outside of the vehicle rapidly at the top dead center just before expansion phase.
Sustainable brake torque is generated by resistance against the compression.
By the adjusting valve, maximum chamber pressure is controlled and brake torque is also controlled.
4 times stronger brake torque can be obtained by this.
From 4 stroke cycle compression to 2 cycle, 2 times.
By using 2 times larger compression ratio, 2 times.
Over all, 4 times stronger brake torque can be obtained.
The compression ratio can be increased because there is no combustion, so, free from knocking issue.

Thus, to make DHB size smaller is possible and by that, DHB can be installed inside transmission as the left figure.
Some dedicated clutch for DHB can be added.
By that, DHB can be separated in normal driving condition.
Some silencer also can be added as shown in the figure.
However, to remain DHB activation sound is one good strategy for noticing ” DHB is working “ to the driver.

The other ideas for candidate systems for obtaining sustainable brake assist for friction brake can be listed up.
However, in the case of those systems, good solution for cooling can not been found.
Because all those other systems require heat transfer by air wind, and such cooling by air wind works slowly.
Those can not provide simultaneous heating up cool air to hot air and rapid exhaust the hot air to outside of the vehicle, by same way as the proposed compression-expansion system.
Consequently, DHB by compression-expansion system is much promising candidate solution for providing sustainable brake assist with good performance and small size.

Because DHB can be made by small size and high capacity, and DHB can exhaust hot air rapidly to outside of the vehicle, the budget of DHB can be derived from the budget of retarder and its cooling system.
SNT has been developing such DHB with smaller size and high capacity.
Several nice ideas to realize that has been already found and those ideas are now applied for patent.

Compression-expansion type DHB has been already registered as a patent.
By that, novelty of the compression-expansion type DHB has been proven.
We think it is very important to spread useful technology world wide, therefore, we are willing to provide license broadly and fairly to every company who have needs of utilizing this technology.

Our company aims to contribute to safe and comfortable car life.
Therefore, to contribute to establishing safe EV, FCV era is our earnest wish.

Now, we are welcoming our partner for DHB evolving.
We believe that DHB will be surely good business in EV and FCV era, so we wish recommending you to get this business with us.
We are heartily waiting alliance offer from the readers of this our proposal.

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