Engine specs for large saloon (sedan vehicle)

[freestylecruz]

Need some help with this question. I have given it loads of thought, but my assumptions are not getting through. Here it is:

1. Objective

(a) To determine the power needed to give the chosen vehicle the required performance; to determine the bottom and intermediate gear ratios.

(b) To arrive at a suitable engine specification for the vehicle in order to give the required performance.

2. Data

(a) Use the data for the vehicle from the following table:

Mass CDA rtyre Vmax
___ ____ ____ _____
Kg m2 m km/h

Large saloon 1600 0.69 0.33 216


The mass values given above for an unladen vehicle. An appropriate payload allowance must therefore be made.

(b) For all the vehicles, the following rolling resistance coefficient values may be used, though alternative values may be substituted if though appropriate.h

Up to 140 km/h = 0.015 220 km/h = 0.0170
180 km/h = 0.0153 240 km/h = 0.0190

(c) Transmission efficiency: make the appropriate assumptions. One method of estimating transmission efficiency is to assume 97% per meshing pair.

For all the vehicles assume that the gearbox has 5 forward speeds; that the 4th gear is “correctly” matched so that the maximum power speed of the engine corresponds to the maximum possible vehicle speed, and that 5th gear is 25% “overdrive”.

For all the vehicles there is a requirement to be able to climb a 36% gradient at the maximum torque speed in the lowest gear.


3. Method

Note that the transmission matching required in this assignment may be determined by plotting either the tractive power or road load power against vehicle speed, or plotting tractive force and road load against vehicle speed.

(a) Select one of the four vehicles given above. The same calculations are required for all the vehicles: only the values of the parameters differ.

(b) Plot the level load curve and determine the engine power required to give the stated vehicle maximum speed.

(c) Choose appropriate values for the following parameters:

• engine type: spark ignition or Diesel;
• a suitable type of combustion chamber and appropriate mean effective pressure at torque peak for the chosen engine type;
• suitable maximum port velocity based in inner valve seat diameter (d);
• suitable valve sizes and hence determine the mean piston speed; check that this is appropriate for the engine duty;
• a suitable value of torque “back-up” in order to determine the mean effective pressure at the power peak.



(d) For the required maximum power determine the required total piston area using:

Power = ¼ Pe A Vp

where: Pe = mean effective pressure at maximum engine speed, as chosen above;
Vp = mean piston speed (at maximum engine speed);
A = total piston area;
& note that the ¼ is replaced by ½ for a 2-stroke engine.

For the required duty choose the number of cylinders and hence the bore size. Determine the stroke to give a suitable engine speed, and hence determine the swept volume.
Is the swept volume appropriate for the class of vehicle and engine type?

Note that an interactive process may be needed to obtain the best compromise between the number of cylinders; the stroke/bore ratio; an acceptable maximum engine speed. The bore and stroke values may also be rounded at this stage, or slightly adjusted to bring the swept volume below a target value (e.g. a tax threshold of 2.0 litres).

(e) Choose an appropriate engine speed at which peak torque will be developed; convert the chosen mean effective pressure values at peak power and peak torque into torque values at the flywheel. Use these values to sketch an appropriate torque curve (on graph paper). Read off torque values from the graph for speeds between peak torque and peak power.

(f) Determine the overall gear ratios for 4th and 5th gears (25% difference).

Convert the engine torque curve to a tractive effort curve, or a tractive power curve in 5th gear, plotting this on the road load curve. (Remember transmission efficiency, which may differ in 4th and 5th). Hence determine the maximum speed of the vehicle in 5th gear.

(g) Determine the first gear ratio by plotting either the road load power or torque to climb the required gradient. Determine 2nd and 3rd gear ratios assuming a geometric progression.


It would be absolutely great if I get some help for this.

 

[Danger]

I'm confused. A "saloon" is a room in which to drink beer. Why would it have a drivetrain?

Or do you happen to mean a "sedan"?

 

[freestylecruz]

saloon is another term for a sedan.

 

[Danger]

I know; that was a joke. We don't use the term "saloon" for cars in North America, but being a Canuck I understand Brit-speak.

 

[rezeew]

I can offer some guidance and suggestions for approaching this question. First, it is important to understand that engine specs for a large saloon vehicle will vary depending on the specific requirements and desired performance of the vehicle. Therefore, it is important to carefully consider the objective and data provided to make accurate calculations and assumptions.

To begin, you will need to determine the power needed to give the vehicle the required performance. This can be achieved by plotting the level load curve and calculating the engine power required to reach the stated maximum speed. From there, you can make assumptions about the type of engine (spark ignition or diesel) and choose a suitable combustion chamber and mean effective pressure for that engine type.

Next, you will need to select appropriate values for maximum port velocity, valve sizes, and torque "back-up" to determine the mean piston speed. This will help you determine the required total piston area using the equation provided. It is important to note that this equation may differ for 2-stroke engines.

Once you have determined the required power and piston area, you will need to choose the number of cylinders and determine the bore and stroke sizes. This will also require an interactive process to find the best compromise between these values and the desired engine speed. It is important to consider the swept volume and whether it is appropriate for the class of vehicle and engine type.

After determining the engine specifications, you will need to plot an appropriate torque curve and determine the overall gear ratios for 4th and 5th gears. Keep in mind that the 5th gear should be 25% "overdrive." You will also need to consider transmission efficiency, which may differ between gears.

Finally, you will need to determine the first gear ratio by plotting the road load power or torque needed to climb the required gradient. From there, you can calculate the 2nd and 3rd gear ratios assuming a geometric progression.

In summary, determining engine specs for a large saloon vehicle requires careful consideration of the objective, data, and various parameters such as engine type, combustion chamber, piston speed, and gear ratios. It may also require an interactive process to find the best compromise between these values and the desired performance of the vehicle. I hope this helps you in your calculations and assumptions. Good luck!