Turbocharging is a technology that uses the exhaust gases produced by an internal combustion engine to drive an air compressor. The primary function of turbocharging in cars is to increase the volume of air entering the engine, thereby boosting engine power and torque and making the vehicle more responsive. However, following turbocharging, both the pressure and temperature within the engine rise significantly; consequently, advancements in materials are also crucial when implementing turbocharging technology in engines.

High-temperature resistance

The gas in a turbocharger generates high temperatures due to compression and intense friction; even after cooling, the gas temperature generally exceeds 100 °C. Consequently, the materials used for hoses in turbocharger systems must be capable of withstanding high temperatures. Ordinary natural rubber, styrene-butadiene rubber (SBR) and polybutadiene rubber (BR) are unable to meet the requirements for use under high-temperature conditions; therefore, specialised high-temperature-resistant rubber materials must be employed. As turbocharger pressures continue to rise, the temperature of the gas passing through the hoses also increases. If the pressure reaches 3.5×10⁵ Pa, the temperature of the gas passing through the hoses can exceed 250 °C, and there are very few types of rubber capable of withstanding such high temperatures.

Oil Resistance

The gas passing through the hoses in a turbocharging system is generally contaminated with oil vapour; therefore, the hoses must possess a certain degree of oil resistance, particularly resistance to high-temperature oil vapour. Some rubbers with good high-temperature resistance (such as silicone rubber) have poor oil resistance, so an inner lining must be added to the inner wall of the silicone rubber hose to prevent corrosion from the oil vapour.

Strength

Turbocharging systems are not only subject to high temperatures but also to a certain degree of pressure; in particular, the pressure on the high-temperature sections of the piping is relatively high. Although reinforced hoses are generally used in turbocharging systems (with the reinforced layer constituting the primary pressure-bearing component), the rubber itself must also possess a certain degree of strength to enhance the overall strength of the hose. Furthermore, to meet the requirements of the manufacturing process and assembly, the rubber must also exhibit high tensile strength and tear strength.

Compression set

Generally, turbocharger hoses are connected to metal pipes using clamps to form a piping system. At high temperatures, the rubber must possess good resistance to deformation; otherwise, excessive compression set may cause the clamps to loosen and the hose to detach, leading to a safety incident.

Cold resistance

Although the hoses operate in a high-temperature environment once the engine has started, they are exposed to cold air once the engine is switched off. When the engine is started in cold conditions during winter in cold regions, the rubber hoses vibrate at low temperatures. If the rubber has poor low-temperature resistance, the hoses may become hard and brittle, leading to problems such as tearing, detachment and loss of vibration-damping capability.

Adhesion Strength

The rubber layer of a hose must maintain good adhesion to the reinforcement layer and the inner lining under harsh conditions such as cold, heat, and exposure to oil and gas, and must possess sufficient adhesion strength to ensure that delamination does not occur. Adhesion strength is dependent on the properties of the rubber itself and the rubber formulation, and is also closely related to the impregnation and pre-treatment of the reinforcement layer, the choice of adhesive, and the bonding process; therefore, all these factors must be thoroughly considered.

Hardness

The rubber should have a suitable hardness. If the hardness is too high, the hose will be too rigid to provide effective vibration damping, and will be difficult to fit and prone to coming loose; if the hardness is too low, sufficient strength cannot be guaranteed.