| Author |
Thread |
NEW THREAD | POST REPLY |
V Laxmanan
Location:
Posts:
|
Subject: Magnesium and Hybrid Vehciles
|
Consumer Reports 2005 also has actual overall fuel economy values (as opposed to EPA Ratings). Here I report the results of my analysis of the data for 18 small cars with automatic transmission. Once again, we find that:
1. As curb weight increases, engine HP increases.
2. As curb weight increases, the observed overall mpg decreases.
The graph of weight versus mpg HP shows a nice downward trend. The classical least squares fitting gives the following linear regression equation relating curb weight (x) and the mpg (y).
y = -0.0104x + 54.2 with r*r = 0.806
Here r*r is the linear regression coefficient. The high value (perfect correlation means r = + 1.0 or r = - 1.0) means a high degree of correlation between these variables.
The simpler method of fitting a straight line by considering extreme values from the data set yields the following equation,
y = -0.0106x + 55.53
Notice that the slope and the intercept are essentially the same as that obtained by least squares fitting procedure.
Again, the reciprocal of the slope has the units of pounds per mpg and is equal to 96 (least squares) or 94 (simple extreme points fit). In other words, if the vehicle weight decreases by about 100 pounds, the fuel economy will increase by 1 mpg.
It is of interest to note that the data for Toyota Prius falls off the graph and is an outlier. This was excluded from the linear regression analysis. The Toyota Prius is a hybrid vehicle with an observed fuel economy of 44 mpg. The curb weight was 2950 lbs. Extrapolating using the equations above, the vehicle weight must drop to about 1000 lbs to achieve the same fuel economy with a conventionally powered vehicle.
A similar trend is also observed when we consider the data for all vehicles in CR study. The data for Honda Insight and Toyota Prius fall on a line with a steeper slope. In other words, a smaller change in weight (72 pounds) is required to increase the fuel economy by 1 mpg. Hybrids could therefore benefit even more so from an increased use of lightweight magnesium components.
|
|
| 13-Jun-2005 18:28 |
Quote |
V Laxmanan
Location:
Posts:
|
Here I report the results of my analysis of the actual observed mpg values for 66 vehicles from Consumer Reports 2005.
The observed mpg and vehicle ratings are given on pages 10 to 17. The vehicles included in this study cover the entire range of curb weights (from 1875 to 5900 pounds) and all vehicle types. Consumer Reports divides vehicles into small cars (automatic transmission), small cars (manual), luxury sedans, family sedans, large sedans, upscale sedans, Roadsters, and so on. The highest and lowest mpg and the middle values of the mpg from each vehicle type were included in the analysis.
Once again, the graph of curb weight versus mpg shows a nice downward trend. The classical least squares fitting gives the following linear regression equation relating curb weight (x) and the mpg (y).
y = -0.00477x + 38.53 with r*r = 0.862
Notice that the r*r value is quite high (perfect correlation means r = + 1.0 or r = - 1.0). The slope is less than that obtained when we consider only the data for small cars with automatic transmission. To arrive at the above regression equation, I excluded 6 vehicles from my list, since the graph revealed that these six vehicles had significantly higher mpg, for the same curb weight. The vehicles excluded were Honda Insight, Honda Civic Toyota Prius (all three were hybrids), Toyota Echo and Mini Cooper. The Echo is a 5-speed manual, and the Mini, developed by BMW, is a small convertible.
Again, the reciprocal of the slope has the units of pounds per mpg and is now equal to 192.9 lbs/mpg. In other words, considering the actual observed mpg values (not the EPA ratings) for all vehicle types, we conclude that if the vehicle weight decreases by about 200 pounds, the fuel economy will increase by 1 mpg.
The data for Honda Insight and Honda Civic, Toyota Prius, and the three other vehicles noted earlier, are outliers on the graph. This data was excluded from the linear regression analysis.
Now, extrapolating using the above linear regression equation above, even if the vehicle weight drops to about 1000 lbs, we find that the mpg would only increase to 33.75 mpg. In other words, conventional engines and transmissions will not help achieve significant improvements in fuel economy even if the use of lightweight materials like aluminum and magnesium is increased very significantly.
Significant improvements in mpg can only come from new (or revolutionary) technologies such as the hybrid vehicles. For the two hybrids (Honda Insight and Honda Civic),
y = - 0.0195x + 87.53
The reciprocal of the slope equals 51.33 lbs/mpg. In other words, a reduction in vehicle weight of just 50 pounds will result in an improvement of 1 mpg for the hybrid vehicle. This agrees with the previous findings reported in the earlier post.
Hybrids could therefore benefit even more so from an increased use of lightweight magnesium components. The new and more stringent fuel economy standards introduced by China (noted in an earlier post) also demand light weight vehicles and, perhaps, new and/or revolutionary technology.
|
|
| 18-Jun-2005 06:10 |
Quote |
| |
NEW THREAD | POST REPLY |
|
