**3. Ring‐piston groove‐cylinder liner interaction**

In engine power cylinder system development, utilizing CAE tool has become a standard approach to design and optimize the system. Traditional CAE tools are two‐dimensional (2D) which considers the ring motion along the cylinder axis and the twist. However, the variation along the ring circumference is assumed to be identical. The demand for better understanding of the power cylinder system requires three‐dimensional (3D) CAE tools to simulate the varia‐ tion along the ring circumference as well. Researchers have started working on 3D modeling. One variation along the ring circumference is the contact pressure between the ring face and the cylinder bore interface, and the ring side and piston groove side interface. The interactions are discussed in this section.

The green mesh shown in **Figure 13** represents the free‐shape ring while the red mesh rep‐ resents the deformed ring shape under the cylinder bore constraints without temperature compensation. It is obvious that the ring is pushed inward from its free state. The constraint forces that push the ring to its deformed position are shown in **Figure 14**. The blue and red bars represent the constraint forces at a certain circumference location at the upper and lower corners at ring face. And the green and purple dots show the separation gaps between the ring

From **Figure 14**, it is found that the two contact forces at the same cross section are identical since the ring has a symmetric cross section and there is no twisting moment on the ring. The

**Contact Force and Separation Gap**


**Circumference Location (DEG)**

Force (up) Force (low) Gap (up) Gap (low)

0

7

14

**Gap (um)**

21

28

35

Power Cylinder System for Internal Combustion Engines http://dx.doi.org/10.5772/intechopen.69762 173

face and the cylinder bore.

**Figure 14.** Constraint force and separation gap.

**Force (N)**

**Figure 13.** Free‐shape and deformed ring meshes.

## **3.1. Ring‐cylinder bore contact**

When the free‐state ring is installed into the cylinder liner, the ring is constrained at its front face by the cylinder wall. Every point on the ring front face needs to be tracked whether it is in contact with the cylinder wall or not. However, due to the computation time and resource, it is not possible with the existing computation tool. And the most important thing is how the contact force/pressure distributes along the ring circumference. Thus, in this section, the ring is specified constrained at 13 different cross‐section locations along the circumference [21–23]. The ring conformability is modeled using finite element method (FEM) [24, 25] for a keystone compression ring. The approach solving the problem is based on penalty method‐based opti‐ mization that minimizes the strain energy of the piston ring [26–30].

As shown in **Figure 13**, the middle constraint locates at the ring back (opposite to the ring gap) front face. Other constraints are symmetric about the ring back and distribute with an increment of about 30°. The free‐shape ring mesh and the deformed ring mesh without tem‐ perature compensation are shown in **Figure 13**.

**Figure 13.** Free‐shape and deformed ring meshes.

circumference with the consideration of cylinder liner ID deformation. In addition, the influ‐ ence from piston secondary motion can also be implemented to further understand the ring pack behavior. This will capture the gas flow in the circumference direction, which the current commercial two‐dimensional (2D) models are not capable of. As a result, the ring dynamics, oil consumption, friction, and wear for the ring pack can be better modeled and understood to guide design. The next section is an introduction to the 3D modeling work for the ring pack. The 2D ring pack dynamics model is still widely used in the automotive and heavy‐duty industries during product development, given the experience and fidelity built on this approach. Some improving activities include implementing wear model at the ring face and side based on different wear mechanism, oil consumption model due to oil evaporation, oil throw‐off, oil scraped back to the combustion, and so on. In addition, 3D ring pack dynamics models are being developed using different approaches, including full FEA with hexahedron element, discretizing the ring using space beam elements, and so on, with different orders of success. The 3D model approach will be discussed in the next section with more detail.

In engine power cylinder system development, utilizing CAE tool has become a standard approach to design and optimize the system. Traditional CAE tools are two‐dimensional (2D) which considers the ring motion along the cylinder axis and the twist. However, the variation along the ring circumference is assumed to be identical. The demand for better understanding of the power cylinder system requires three‐dimensional (3D) CAE tools to simulate the varia‐ tion along the ring circumference as well. Researchers have started working on 3D modeling. One variation along the ring circumference is the contact pressure between the ring face and the cylinder bore interface, and the ring side and piston groove side interface. The interactions

When the free‐state ring is installed into the cylinder liner, the ring is constrained at its front face by the cylinder wall. Every point on the ring front face needs to be tracked whether it is in contact with the cylinder wall or not. However, due to the computation time and resource, it is not possible with the existing computation tool. And the most important thing is how the contact force/pressure distributes along the ring circumference. Thus, in this section, the ring is specified constrained at 13 different cross‐section locations along the circumference [21–23]. The ring conformability is modeled using finite element method (FEM) [24, 25] for a keystone compression ring. The approach solving the problem is based on penalty method‐based opti‐

As shown in **Figure 13**, the middle constraint locates at the ring back (opposite to the ring gap) front face. Other constraints are symmetric about the ring back and distribute with an increment of about 30°. The free‐shape ring mesh and the deformed ring mesh without tem‐

mization that minimizes the strain energy of the piston ring [26–30].

perature compensation are shown in **Figure 13**.

**3. Ring‐piston groove‐cylinder liner interaction**

are discussed in this section.

**3.1. Ring‐cylinder bore contact**

172 Improvement Trends for Internal Combustion Engines

The green mesh shown in **Figure 13** represents the free‐shape ring while the red mesh rep‐ resents the deformed ring shape under the cylinder bore constraints without temperature compensation. It is obvious that the ring is pushed inward from its free state. The constraint forces that push the ring to its deformed position are shown in **Figure 14**. The blue and red bars represent the constraint forces at a certain circumference location at the upper and lower corners at ring face. And the green and purple dots show the separation gaps between the ring face and the cylinder bore.

From **Figure 14**, it is found that the two contact forces at the same cross section are identical since the ring has a symmetric cross section and there is no twisting moment on the ring. The

**Figure 14.** Constraint force and separation gap.

plot also shows that the constraint force at the ring back is the highest. At the cross sections approximately 30° away from the ring back, the lowest constraint forces are found for the sec‐ tions that are in contact against the cylinder wall. The constraint forces at the ring tips vanish such that the ring separates from the cylinder wall in its front face at its two tips. The separa‐ tion gap is defined as the radial distance between the cylinder wall ID and the ring tip OD. A 34‐μm separation gap is found for this specific ring from the FEA model.

## **3.2. Result of ring‐cylinder bore‐groove side contact**

Another example is given in this section for ring‐cylinder bore‐groove side contact using a scraper ring with a positive static twist. The scraper ring has a taper face and cuts off at the ring inner upper corner, which promotes positive twist when installing the ring into the pis‐ ton groove. The cross section of the scraper ring is shown in **Figure 15**.

> The deformed ring shape is shown in **Figure 16** after installing into the cylinder liner and piston groove. The displacement in the *z*‐direction (axial direction) is amplified by 100 times

K

K

Power Cylinder System for Internal Combustion Engines http://dx.doi.org/10.5772/intechopen.69762 175

In this case, the ring back and ring butt ends are in contact with the groove bottom side, while the ring touches the groove top side at about 60° from the end gap (120° from the ring back). The constraint forces between the ring and the piston groove sides are important since it dictates the contact pattern which will affect the ring‐groove side wear eventually. More details about the ring, cylinder liner, and piston groove interactions can be found

Ultimately, the interactions between the ring face‐liner bore interface and the ring side‐piston groove side interface are used to model the wear between them [17] as well as the ring pack dynamics that heavily influences engine oil consumption, to further optimize the ring pack

and power cylinder design and improve the durability of the subsystem.

**Figure 16.** Deformed ring shape after installing into the cylinder liner and piston groove.

in order to illustrate the ring deformation distinctly.

Ring/oil film‐convective coefficient 100 W/m2

**Ring material Steel** Modulus of elasticity 200.0 GPa Poisson's ratio 0.3 Cylinder bore diameter 108.0 mm Coefficient of thermal expansion 13.0E‐6/°C Thermal conductivity 45 W/m K Ring/gas‐convective coefficient 25 W/m2

Address all correspondence to: chengc22@msu.edu

Michigan State University, MI, USA

from Refs. [22, 23].

**Table 3.** Main parameters for the ring.

**Author details**

Chao Cheng

From **Figure 15**, four nodes of the cross section at a given circumference location are consid‐ ered for the ring‐piston groove side interaction and are numbered as node 1, node 2, node 3, and node 4 as shown. These four nodes are constrained by the groove in the axial direction. This means nodes 1 and 2 should stay in contact or above the groove bottom side, while nodes 3 and 4 should stay in contact or below the groove top side. Two nodes on the ring front face are constrained by the cylinder bore in the radial direction, at the front face top and bottom edges, respectively. The groove has zero angles at its top and bottom sides. The nominal clear‐ ance between the groove and the ring axial thicknesses is 0.1 mm.

The main parameters describing the ring are listed in **Table 3**.

The constraint locations along the ring circumference are equally spaced with about 30° from one butt end to the other. The number of constraint locations is found to be able to repre‐ sent the ring/cylinder liner/groove side contact force/pressure distribution pattern and also save calculation time. Increasing constraint locations will increase computation time expo‐ nentially, while decreasing the constraint locations may result in the contact force/pressure pattern not being able to be well represented.

**Figure 15.** Constraints on ring cross section.


**Table 3.** Main parameters for the ring.

plot also shows that the constraint force at the ring back is the highest. At the cross sections approximately 30° away from the ring back, the lowest constraint forces are found for the sec‐ tions that are in contact against the cylinder wall. The constraint forces at the ring tips vanish such that the ring separates from the cylinder wall in its front face at its two tips. The separa‐ tion gap is defined as the radial distance between the cylinder wall ID and the ring tip OD. A

Another example is given in this section for ring‐cylinder bore‐groove side contact using a scraper ring with a positive static twist. The scraper ring has a taper face and cuts off at the ring inner upper corner, which promotes positive twist when installing the ring into the pis‐

From **Figure 15**, four nodes of the cross section at a given circumference location are consid‐ ered for the ring‐piston groove side interaction and are numbered as node 1, node 2, node 3, and node 4 as shown. These four nodes are constrained by the groove in the axial direction. This means nodes 1 and 2 should stay in contact or above the groove bottom side, while nodes 3 and 4 should stay in contact or below the groove top side. Two nodes on the ring front face are constrained by the cylinder bore in the radial direction, at the front face top and bottom edges, respectively. The groove has zero angles at its top and bottom sides. The nominal clear‐

The constraint locations along the ring circumference are equally spaced with about 30° from one butt end to the other. The number of constraint locations is found to be able to repre‐ sent the ring/cylinder liner/groove side contact force/pressure distribution pattern and also save calculation time. Increasing constraint locations will increase computation time expo‐ nentially, while decreasing the constraint locations may result in the contact force/pressure

34‐μm separation gap is found for this specific ring from the FEA model.

ton groove. The cross section of the scraper ring is shown in **Figure 15**.

ance between the groove and the ring axial thicknesses is 0.1 mm.

The main parameters describing the ring are listed in **Table 3**.

pattern not being able to be well represented.

**Figure 15.** Constraints on ring cross section.

**3.2. Result of ring‐cylinder bore‐groove side contact**

174 Improvement Trends for Internal Combustion Engines

The deformed ring shape is shown in **Figure 16** after installing into the cylinder liner and piston groove. The displacement in the *z*‐direction (axial direction) is amplified by 100 times in order to illustrate the ring deformation distinctly.

In this case, the ring back and ring butt ends are in contact with the groove bottom side, while the ring touches the groove top side at about 60° from the end gap (120° from the ring back). The constraint forces between the ring and the piston groove sides are important since it dictates the contact pattern which will affect the ring‐groove side wear eventually. More details about the ring, cylinder liner, and piston groove interactions can be found from Refs. [22, 23].

Ultimately, the interactions between the ring face‐liner bore interface and the ring side‐piston groove side interface are used to model the wear between them [17] as well as the ring pack dynamics that heavily influences engine oil consumption, to further optimize the ring pack and power cylinder design and improve the durability of the subsystem.

**Figure 16.** Deformed ring shape after installing into the cylinder liner and piston groove.
