# help me in design calculation for hybrid car



## PStechPaul (May 1, 2012)

The basic equations are:

T(lbft)=HP*5252/RPM

HP=T(lbft)*RPM/5252​So 13HP at 1500 RPM is 45.5 lbft

58 lbft at 1000 RPM is 11HP

These are probably the peak values. Usually an electric motor has a fairly flat torque curve up to maximum RPM and the HP is linear up to that point and then levels off or drops.


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## chipsmore29 (Aug 7, 2012)

thanks for the reply....but what i mean is how they calculate the value?for example,for motor,stated that power is 13hp at 1500rpm.how do they get the value 13hp at 1500rpm?is there any other value or parameter or other formula before to get it?the formula that i know is like P=IV or P=Tw or T=Fr....correct me if im wrong....


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## PStechPaul (May 1, 2012)

For an electric motor you can get the power from the equation:

P = E * PF * V * I​Where E is efficiency and P is power factor. V is voltage and I is current.

The E and PF are nameplate data determined by design and testing.

If you really need to determine the actual power or torque you need to do a dynamometer test. You can connect a generator to the output shaft and add a resistive load to get the approximate power (if you know the generator efficiency). And you can determine torque by mounting the motor on a set of bearings or rollers and then adding a torque arm and a scale, so a 2 foot arm reading 50 pounds will be 100 lbft torque.


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## chipsmore29 (Aug 7, 2012)

thanks PStechPaul....im looking for a formula that will give me the hp and torque numbers based on the input....can someone show me the calculation/formula/other factor needed for this?just use the example given above and justify it....can show me the flow of calculation and formula needed including efficiency etc....thanks in advance


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## TigerNut (Dec 18, 2009)

chipsmore29 said:


> thanks PStechPaul....im looking for a formula that will give me the hp and torque numbers based on the input....can someone show me the calculation/formula/other factor needed for this?just use the example given above and justify it....can show me the flow of calculation and formula needed including efficiency etc....thanks in advance


For an internal combustion engine, there is no simple formula that gives you power and torque based on number of cylinders, displacement, bore/stroke, etcetera. The power and torque curve (not just single values), as a function of RPM, depend on those parameters, but also the cylinder head design, valve size and number, port shape and volume, the camshaft profile, and a bunch of other things. When a manufacturer quotes a power and torque number, this is typically based on actual power and torque measurements that were made on a dynamometer.

Similarly, the power output of an electric motor depend on a great number of design parameters, not just the voltage and current. The torque and speed capabilities of a motor depend on the number of magnetic poles and the number of turns of wire in the poles and armature... and then the power handling depends on the resistance of those wires and the overall size of the motor. You couldn't expect a small motor to put out so much torque that it would twist its output shaft in half.

It sounds like you need to first obtain some grounding in algebra and physics; then do some research on basics of electric motors and internal combustion engines; and THEN you will have a better understanding of how to apply the information Paul tried to give you.


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## chipsmore29 (Aug 7, 2012)

TigerNut said:


> For an internal combustion engine, there is no simple formula that gives you power and torque based on number of cylinders, displacement, bore/stroke, etcetera. The power and torque curve (not just single values), as a function of RPM, depend on those parameters, but also the cylinder head design, valve size and number, port shape and volume, the camshaft profile, and a bunch of other things. When a manufacturer quotes a power and torque number, this is typically based on actual power and torque measurements that were made on a dynamometer.
> 
> Similarly, the power output of an electric motor depend on a great number of design parameters, not just the voltage and current. The torque and speed capabilities of a motor depend on the number of magnetic poles and the number of turns of wire in the poles and armature... and then the power handling depends on the resistance of those wires and the overall size of the motor. You couldn't expect a small motor to put out so much torque that it would twist its output shaft in half.
> 
> It sounds like you need to first obtain some grounding in algebra and physics; then do some research on basics of electric motors and internal combustion engines; and THEN you will have a better understanding of how to apply the information Paul tried to give you.


oic....it seems like i need to study a lot of things to do this project.i just know a little bit of formula which is the general formula of speed,torque,etc....mmmm....i cant find any source from book or internet the complete sample calculation for ice design as well as motor design.do you have any source or sample calculation for these design?can u tell me what is the exact parameter/value/any related things and the formula needed in order to design ice and motor(BLDC)?my mind is really mixed up with a lot of formula and i dont know which formula that i should use....really appreciate ur help...


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## major (Apr 4, 2008)

chipsmore29 said:


> i cant find any source from book or internet the complete sample calculation for ice design as well as motor design.do you have any source or sample calculation for these design?can u tell me what is the exact parameter/value/any related things and the formula needed in order to design ice and motor(BLDC)?


This normally requires an engineering degree and about 10 years of experience in the field to comprehend for each the ICE and EM.


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## TigerNut (Dec 18, 2009)

chipsmore29 said:


> oic....it seems like i need to study a lot of things to do this project.i just know a little bit of formula which is the general formula of speed,torque,etc....mmmm....i cant find any source from book or internet the complete sample calculation for ice design as well as motor design.do you have any source or sample calculation for these design?can u tell me what is the exact parameter/value/any related things and the formula needed in order to design ice and motor(BLDC)?my mind is really mixed up with a lot of formula and i dont know which formula that i should use....really appreciate ur help...


A core principle for an electric motor's operation is the Lorentz Force equation: http://en.wikipedia.org/wiki/Lorentz_force. Page down to where they talk about force on a current-carrying wire. Pretty much everything else about electric motor design is geometry and mechanics of materials.

For an internal combustion engine, the principal objective is to burn gasoline in the cylinders at or near the stoichiometric air/fuel ratio, so that the expanding gas can force the pistons to do work via the connecting rods acting on the crankshaft. The more fuel/air mixture you can burn in a given amount of time (i.e. the higher the cylinder pressure, RPM, and/or displacement), the more power you can make. Everything else is fluid dynamics and mechanics of materials.

That's a pretty glib overview, and intentionally so, but as we've been saying: There is no single, simple formula for motor or internal combustion engine design. First of all, you will need really good applied math background including algebra, geometry and calculus. Secondly, you need to understand the chemistry and physics principles involved; third, as Major says, at least a decade working full-time on engines and/or motors, before you can confidently take a motor or engine design and predict its performance purely based on the internal parameters.


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## PStechPaul (May 1, 2012)

IMHO the OP is too much concerned about details that are not really directly relevant to a DIY hybrid or EV. A hobbyist with a basic knowledge of physics and electrical principles can design and build an EV with guidance from people with experience on this forum, and from the many books and websites about DIY projects and commercial EV and hybrid design. The DIY resources pretty much provide a step-by-step process to accomplish the goal of using electric power for vehicular propulsion, or for simply augmenting it as a hybrid. 

If the goal is designing a hybrid vehicle from the ground up, then it requires an advanced college level understanding of many disciplines, as well as practical experience in design engineering. I would dare say that *all* commercial hybrids and EVs were developed over several years of intense effort by a team of engineers, technicians, mechanics, and businessmen.


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## jk1981 (Nov 12, 2010)

chipsmore29 said:


> Engine Type: In-Line 4-Cylinder...
> ...how do they get the *horsepower and torque*?what is the formula used?
> 
> for electric motor (BLDC motor):...
> ...how do they get the *horsepower and torque*?what is the formula used?


They measure it.

If you want to design your own ICE or BLDC from scratch then I'd suggest you seek out an engineering degree course.

I'm a little confused exactly what you want to achieve? If it's understanding how an ICE can be modeled... why bother, unless you're making your own from scratch you just look up the data. If you want an overview of modeling BLDC performance it's a little simpler and arguably more worthwhile. http://web.mit.edu/scolton/www/SCThG.pdf is a reasonably digestible paper on the subject.

If you want to build a DiY hybrid then I'd start with determining your basic requirements and resources. Look to see if your requirements are realistically achievable or whether you'll have to compromise then consider whether that compromise leaves you with something worthwhile.


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