82 Technical Notes/JSAE Reriew 15 (1994) 73-86

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Fig. 5. Actual vehicle test result (70 km/h random pylon slalom).

5. Conclusions

From the preceding examination on simulation, it is clarified that the time series pattern inputs of steering angles and using the approximate equation based on a 2-degree-of-freedom linear vehicle mathematical model are effective.

From the test performed for actual vehicles running on a dry asphalt road, it is also evident that the system can provide good estimation and noise reduction capa- bility under conditions with an unknown velocity and unknown random steering inputs.

The future task is mainly to examine whether or not the present system can be further applicable to various possible conditions, such as changes of actual road surface or running conditions induced by acceleration or deceleration of vehicles.

References

[1] Funabashi, K., On the Capabilities of Neural Networks, IEICE Technical Report on MBE88-52 (1988).

Development of light weight cylinder block

Hisashi Kajikawa ,,a, Shouji Nomura a, Hiroaki Yasuda b, Makoto Mihara b Powertrain Production Engineering Department, Mazda Motor Corp., 3-1, Shinchi Fuchu-cho, Akigun, Hiroshima, 730-91 Japan

9 Powertrain Engineering Department, Mazda Motor Corp., 3-1, Shinchi Fuchu-cho, Akigun, Hiroshima, 730-91 Japan

(Received 31 August 1993)

I. Introduction

Weight reduction of a cylinder block (C/B) im- proves the vehicle power to weight ratio and lowers the fuel consumption. Therefore, manufacture of C/B's with thinner walls has been widely adopted.

However, this method has led to other problems such as stiffness reduction due to thin walls. Therefore, we studied material changes of C /B with liner which would offset this loss in stiffness and permit significant weight reduction.

* Corresponding author.

2. Development goals

By adding magnesium, the graphite in cast iron is spheroidized, resulting in improved mechanical proper- ties including Young's modulus and tensile strength. Therefore, we decided to use nodular graphite cast iron (ductile cast iron, or DCI) instead of conventional gray cast iron (FC) to get higher stiffness and strength. Table 1 shows that DCI has superior mechanical prop- erties compared to FC.

3. Properties of ductile cast iron C / B (DCI C / B )

3.1. Functional properties of DCI C / B

DCI offers the advantages of high stiffness and strength, offset by a lower damping ratio than FC

SSDI 0389-4304(93 )E0012-4 JSAE9430121

Technical Notes/JSAE Review 15 (1994) 73-86 83

Table 1 Mechanical properties of FC and DCI

Young's modulus Tensile strength

FC 122 GPa 255-305 MPa DCI 171 GPa 440 MPa (ratio) (1.4) (1.6)

Table 2 Result of FEM analysis

Weight reduction Resonance frequency (Hz)

rate (%) 1st torsion 1st bending

FC C/B - 387 859 DCI C /B 12.3 434 922

(1/8). To determine the vibration properties resulting from using DCI for C/B, it was necessary to evaluate an identical C / B manufactured from FC. Figure 1 shows the comparison between DCI C / B and FC C/B; both the first-order torsional and bending reso- nance frequencies are about 1.2 times higher than those of the FC C/B. Thus the stiffness (El) of C / B is increased by (1.2) 2 times with DCI.

Prior to the test, higher vibration amplitudes were a cause for concern. However, due to the increase in stiffness and resonant frequency coupled with an im- provement in structural damping, it was found that the vibration levels were decreased for the critical regions of the frequency band.

Accordingly it was assumed that while maintaining the higher stiffness and resonance frequencies, light weight DCI C/B's with low vibration levels are feasi- ble.

3.2. Possibility of weight reduction by FEM analysis

Following the C /B testing, weight reduction poten- tial from the use of DCI was investigated. Table 2 shows the results. It was found that with DCI, despite a 12% C / B weight reduction achieved by thinning, the resonant frequencies were slightly higher than with FC.

Thus it can be assumed that a weight reduction of

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more than 12% is possible without an increase in vibration.

It was also found that a 25% reduction in wall thickness (from 4 mm to 3 mm) was required to achieve it.

4. Production problems

DCI was used for C / B with thinner walls. However production problems such as elephant skin (a type of misrun) and shrinkage defects occurred. These prob- lems and their solutions are described below.

4.1. Elephant skin

Elephant skin occurred in the upper portion of DCI C/B. The mechanism of the elephant skin formation was investigated by thermal analysis, as shown in Fig. 2. The following facts were established:

(a) Considerable temperature drop was observed during the filling of the the mold with molten cast iron.

(b) Elephant skin occurred in the regions where molten cast iron temperature drops to 1440 K (eutectic solidification temperature of equilibrium diagram (1); Fe-C-Si (2.5%).

From this result, we believe that elephant skin is attributed to

(1) Beginning of the eutectic solidification accompa- nied by falling temperature.

(2) Abrupt viscosity increase accompanied by begin- ning of the eutectic solidification.

It was therefore assumed that, if the temperature of molten cast iron is kept above 1440 K during the mold fill, elephant skin would not occur.

To achieve this, gating to the involved portion of the mold was enlarged to improve the flow of the melt. Subsequent tests proved the effectiveness of this action in maintaining the temperature of the upper portion of C /B above 1440 K. In this case elephant skin was eliminated.

4.2. Shrinkage cavities

Massy solidification (DCI's solidification type) tends to generate shrinkage cavities in DCI versus FC. How- ever, part geometry influences this problem. An ideally

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Technical Notes/JSAE Retiew 15 (1994) 7_7-86

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tions, however, adopting a suitable shape to prevent shrinkage cavities is often very difficult.

Therefore, improvement of solidification balance by setting chills was investigated by solidification analysis and the following found;

Solidification balance was improved (directional so- lidification was attained) by chill's cooling capacity and, in this case, areas where shrinkage cavities usually occurred were defect free.

4.3. Microstructure of DCI C / B

The microstructure of DCI C / B as investigated by a microscope, and it was confirmed that DCI C/B's exhibit sound spheroidized graphite (graphite nodular- ity is over 70%) in the ferritic/pearlitic matrix.

In summary, it was confirmed that production of DCI C / B without defects, such as elephant skin, shrinkage cavities, and anomalous structure is possible.

Fig. 2. (a) Temperature distribution of C/B; (b) Portion of elephant skin.

designed DCI C / B had no shrinkage cavities. Solidifi- cation analysis was made to investigate this geometrical factor and the following were observed:

(a) C / B which have shrinkage cavities had areas where shrinkage cavities coald be generated (tempera- ture gradient is under 0.5 K/cm) in the same area.

(b) C / B which have no shrinkage cavities also have no areas where shrinkage cavities could be generated.

To depress shrinkage cavities, the C / B should be designed with suitable geometry. Due to design limita-

5. Conclusion

DC1 is a suitable cast iron for weight reduction because of its high Young's modulus. And when it is used instead of FC for C/B, weight reduction of over 12% is possible.

Although there had been some problems to make light weight DCI C/B, satisfactory production methods were developed.

References

[1] Akechi, et al., Nodular Graphite Cast Iron Basic and Application (in Japanese), Agune P. 13 (1983).