**2. Technical methods for implementation of variable compression ratio technology in piston engines**

Theoretically, there are several possible methods of using the variable compression ratio VCR technology in piston engines. Some of them were used in prototype engines and they undergo operational tests.

**Table 1** schematically presents selected VCR layouts together with a brief analysis of their technical and operational features, including advantages or disadvantages in relation to the conventional construction of the engines. Noteworthy is the solution (f) of a complex lever-gear crank system, developed and applied by the French research group MCE-5 Development [2], as well as the SAAB SVC engine [3, 4], according the principle (a) and solution (c) implemented in the FEV Motorentechnik research engine [5].

There are many specific and unique constructions of VCR engines or even engine ideas and patents. **Table 1** collects the best-known approaches for VCR engine:


Each of above are presented and widely discussed by Shaik et al. [6]. The SAAB's SVC engine according to the solution (a) has been developed earlier by Larsen [3]. The compression ratio is variable from 8:1 to 14:1. Similarly to the shifted cylinder head method (g), it reveals good compression ratio control ability, but with slight change in piston kinematics. As a common drawback of both systems, a worse reliability and durability characteristic can be pointed. The solution (b) based on piston deck height variation uses a complicated special piston construction [6]. It also does not provide easy and precise control of compression ratio. Eccentric on main bearings (c) seems to be devoid of substantial disadvantages, but it makes the crankshaft block more complex. This solution is developed by FEV and used in their concept VCR car [5]. Nissan Motors developed a multilink rod-crank mechanism [6] according to the layout (d). It provides moderate compression ratio control ability at significant change in piston kinematics. Changing compression ratio using a small chamber with moving piston/valve (e) is relatively simple method to be applied in standard engines conversion into the VCR engines. As the drawback of this manner for changing compression ratio, the poor combustion chamber

**Design layouts**

**117**

**Technical and operational**

 **features**

**(a)**

**(b)**

**(c)**

**(d)**

**(e)**

**(f)**

**(g)**

**[3, 4]** Neutral

6¼ Neutral

↘

Neutral

↓↓↓

 ↑↑

 ↑

↑

↑↑

↑↑↑

 Neutral

↘↘

Neutral

 Neutral

↘↘↘

↘

Neutral

↘↘

Neutral

↘↘

↗↗

Neutral

Neutral

6¼

6¼6¼6¼

Neutral

6¼6¼6¼

 Neutral

 Neutral

↘↘↘

Neutral

Neutral

Neutral

*Application of Variable Compression Ratio VCR Technology in Heavy-Duty Diesel Engine*

Neutral

 ↘ Neutral

Combustion

Cranckshaft

Mechanical

Engine design integrity and dimensions

Impact of variability of

Accuracy of control and range of changes in

↗*—improvement,*

**Table 1.** *Technical methods of application*

 *VCR technology in piston engines and their technical and operational*

 *features.*

↘*—deterioration,*

 *↑—high mark, ↓—low mark, and* 6¼

compression

 ratio on cyl. capacity

compression

 ratio ↑↑ *—distinctive*

 *mark.*

 Neutral

 and friction losses

 mechanism

 kinematic

 chamber consistency

**[6]**

**[5]**

**[7]**

**[6]**

**[1, 2]**

**[8, 9]**

*DOI: http://dx.doi.org/10.5772/intechopen.93572*


### **Table 1.** *Technical methods of application VCR technology in piston engines and their technical and operational features.*
