Patent Application
20210394481
The present disclosure relates to a tube for use in a motor vehicle. More particularly, the present disclosure relates to a multi-layer tube which can be employed for transporting fluids for temperature control in a motor vehicle.
Single and multi-layer tubes of synthetic materials such as plastics and elastomers have been proposed for coolant lines. Coolant lines for electrical vehicles are growing in demand. Cooling systems for electrical vehicles and vehicles with internal combustion engines are similar. Both circulate coolant through a series of heat exchange pipes to transfer heat away from the engine.
Batteries in electrical vehicles must be cooled along with other conventional parts of the motor vehicle. Cooling systems for batteries in electrical vehicle operate at temperatures of at most around 60° C. which are significantly lower than the temperatures at which cooling systems for internal combustion engines operate which is at most around 125° C. The lower temperatures at which electrical vehicles operate present an opportunity for employing different materials for coolant tubes.
It is important that a coolant tube be constructed of material that provides a barrier against coolant diffusion and leakage. Additionally, because the tube will carry coolant at low temperatures it must be able to withstand cold temperature gravel impact without breaking at low temperatures. Furthermore, the coolant may be transported at higher pressures in the cooling system, so the tube must have an adequate burst pressure and connection or hoop strength for connection to the system often with a barbed quick connector.
In general, the most successful multi-layer tubes have been co-extruded employing an outer layer composed of a material resistant to the exterior environment. The innermost layer is composed of a material which is chosen for its ability to block diffusion of coolant, low cost and long-term serviceability.
The use of high-density polyethylene (HDPE) for coolant tubes was not previously thought practical due to its anticipated exposure in coolant systems in internal combustion engines to temperatures close to its melting point. However, cooling systems in battery powered and hybrid electrical vehicles present new and broad opportunities for a material with excellent coolant resistance at lower cost than other materials on the market.
It is an objective to provide a low-cost multi-layer tube that will transport fluids exceptionally in a motor vehicle, particularly in an electrical motor vehicle.
The present disclosure comprises a multi-layer tube including an inner layer comprising a thermoplastic material, an intermediate layer comprising high density polyethylene (HDPE) and an outer layer comprising a thermoplastic material. HDPE is a low-cost material with great cold impact resistance. The HDPE intermediate layer is sandwiched between the outer layer and the inner layer of a thermoplastic material. The thermoplastic material is selected to facilitate the balanced tube properties such as sealability, burst strength, connector hoop strength and ease of extrusion for a low-cost, robust multi-layer tube.
One or more exemplary embodiments of the present invention will be described below in conjunction with the following drawing figure, in which:
The present disclosure is a multi-layer tube 10 shown in
The tube 10 may be used for coolant transport for batteries in an electrical vehicle and lower temperature coolant transport for motors in both electrical and internal combustion vehicles. Typically, the coolant will be some type of glycol-based coolant, such as ethylene glycol. The tube 10 may typically encounter about 60° C. to about 70° C. continuous temperature for battery or motor cooling applications and about 80 to about 95° C. peak temperature and about 1 to 4 bar maximum gage pressure.
The tube 10 comprises the intermediate layer 16 of polyethylene. Preferably, the intermediate layer is a HDPE. HDPE is known for its high strength-to-density ratio. HDPE has an excellent low temperature impact resistance. The density of the HDPE can range from 930 to 970 kg/m3 and is preferably 940 to 950 kg/m3. HDPE has little branching resulting in its higher density and stronger intermolecular forces and tensile strength than for low density polyethylene. Ethylene monomer may be polymerized with Ziegler-Natta catalyst under appropriate polymerization conditions to yield HDPE. The HDPE should have a cold tensile impact strength of about 95 to about 105 KJ/m2 at −30° C. using the ISO 8256 test. The HDPE has a relatively lower hoop strength. Hence, the HDPE in the intermediate layer is sandwiched between an inner layer 14 and an outer layer 18 to provide the necessary qualities. The intermediate layer 16 may have a wall thickness of about 0.1 to about 1 mm and preferably about 0.1 to about 0.7 mm. In any of the embodiments disclosed herein, the tube 10 may include the inner layer 14 which surrounds the intermediate layer 16 by coating an inner surface of the intermediate layer. The tube 10 may also include the outer layer 18 which surrounds the intermediate layer 16 by coating an outer surface of the intermediate layer. The intermediate layer 16 may be completely encased between the inner layer 14 and the outer layer 18.
The inner layer 14 may be co-extruded with the other layers during the extrusion process or other layers may be extruded around the inner layer in a subsequent process such as by crosshead extrusion. The outer layer 18 may be co-extruded with the other layers during the extrusion process or may be extruded around other layers in a subsequent process such as by crosshead extrusion. The inner layer 14 may comprise a material chosen for its coolant permeation resistance, flexibility, connection seal-ability, hoop strength and insulating characteristics and may have a wall thickness of about 0.1 to about 1 mm and preferably about 0.1 to about 0.7 mm. The outer layer 18 may comprise a material chosen for its structural qualities, such as abrasion resistance, hoop strength, impact resistance, chemical resistance or insulating characteristics, its extrudability and finish and may have a wall thickness of about 0.1 to about 1 mm and preferably about 0.1 to about 0.8 mm.
In an embodiment, the inner layer 14 and the outer layer 18 may be made of a melt processable, thermoplastic material. The inner layer 14 and the outer layer may be made of the same or different thermoplastic materials. The thermoplastic material may be a thermoplastic material selected from the group consisting of homopolymers or co-polymers of substituted or unsubstituted alkenes having no more than four carbon atoms, vinyl alcohol or vinyl acetate, and mixtures thereof. The thermoplastic material may be selected from the group consisting of zinc-chloride resistant Nylon 6, Nylon 11, Nylon 12, polyether block amides.
A preferred thermoplastic for the inner layer and/or the outer layer 18 comprises polypropylene. The polypropylene may be a polypropylene homopolymer, a polypropylene copolymer or a polypropylene based thermoplastic elastomer (TPE). A polypropylene copolymer comprises a propylene polymerized with at least another alkene monomer. In a copolymer, the polypropylene is covalently bonded with the other alkene monomer in the polymer chain. Polypropylene homopolymers or copolymers can be manufactured by any known process. For example, propylene polymers can be prepared from propene monomer in the presence of Ziegler-Natta catalyst systems or metallocene catalyst systems. Block copolymers can be manufactured similarly except propylene is generally first polymerized by itself or with another alkene monomer in the first reactor phase to form the semi-crystalline matrix and low crystallinity or amorphous segments of propylene and the other alkene monomer are then copolymerized, in a second stage or subsequent stages, in the presence of the polymer produced in the first reactor. The other alkene monomer should have no more than four carbons and is preferably ethylene. Commercial polypropylene random and block copolymers are widely available from multiple polypropylene producers and encompass a wide range of grades. Random polypropylene copolymers are preferred.
Random copolymers of propylene can contain the comonomers inserted in a random manner so that the main chain crystallinity is disrupted, leading to drops in the melting point of the copolymer from about roughly 165° C. for the homopolypropylene to as low as about 130° C. in the random copolypropylene depending on the amount and type of comonomer employed.
The copolymers of polypropylene can be copolymerized in a multi-step process to obtain block copolypropylenes where chain segments consist of relatively crystalline homopolypropylene or random copolypropylene and chain segments of relatively amorphous or low crystallinity propylene ethylene copolymers. The melting points of the block copolymers will be dominated by the more crystalline segments of the copolymer to give a melting point of about 165° C. for a homopolypropylene block copolymer or lower for a random copolypropylene block copolymer.
Ethylene is the preferred comonomer for a polypropylene copolymer, but other olefin monomers may be suitable. Additionally, random copolypropylene is preferred over block copolypropylene. The mass fraction of comonomer, particularly ethylene, in the propylene copolymer should be between about 0.1 and about 15 wt %, preferably between about 0.2 and about 6 wt %.
Another preferred thermoplastic for the inner layer and/or the outer layer 18 is a TPE. A TPE is a thermoplastic comprising a primary phase with a secondary phase of elastomer or rubber. Thermoplastic elastomers have the properties of thermoplastics but with hardness more like rubber. A suitable TPE that adheres to the polyethylene intermediate layer 16 is most suitable. Suitable thermoplastic elastomers include thermoplastic rubbers with a composition composed of a styrene-ethylene/butylene-styrene block copolymers and polyvinyl chloride compounds with plasticizers.
A preferred TPE is a thermoplastic vulcanizate (TPV). A TPV is a vulcanized alloy of mostly fully cured ethylene-propylene diene monomer (EPDM) particles encapsulated in a polypropylene matrix. The polypropylene matrix comprises the primary phase and the ethylene-propylene diene monomer comprises the secondary phase. TPV is commercially available from various suppliers including under the SANTOPRENE product line, a thermoplastic rubber composition, from ExxonMobil Chemical in Irving, Tex. and the SARLINK product line, an oil resistant thermoplastic composition commercially available from Teknor Apex of Pawtucket, R.I. TPV is also available from Elastron Group which is manufactured in Kocaeli, Turkey. A preferred TPV should have a Shore A Hardness between about 55 to about 95, and preferably about 80 to about 90 based on ISO 868. The thermoplastic, such as polypropylene, that does not have a phase of EPDM will have a greater Shore A Hardness. If desired, these materials may be modified to include flame retardants, plasticizers and the like.
In order to get strong adhesion between a layer comprising polypropylene and a layer comprising polyethylene an adhesive layer may be employed. As shown in
As shown in
An ethylene copolymer-based adhesive may be employed as the adhesive layer 22, 32, 42 or 44, such as ethylene vinyl acetate and ethylene methyl acrylate adhesives when the tube 10, 20, 30 or 40 will not be subjected to elevated temperatures for extended periods. Lower density ethylene-α-olefin copolymer or higher comonomer propylene-α-olefin copolymer-based adhesives may also be used as the adhesive layer 22, 32, 42 or 44.
A suitable adhesive for the adhesive layer 22, 32, 42 or 44 can be either a polypropylene based adhesive or a TPE based adhesive. A preferred polypropylene-based adhesive is an anhydride-modified polypropylene resin. Each adhesive layer 22, 32, 42 or 44 may have a wall thickness of about 0.05 to about 0.5 mm and preferably about 0.05 to about 0.2 mm.
While it is within the scope of this disclosure to prepare a tubing material having a plurality of overlying layers of various thermoplastic materials, the tube 10, 20, 30, 40, 50, 60 of the present disclosure generally has a maximum of nine layers, inclusive of the adhesive layers. In the preferred embodiment, the tube 10, 20, 30, 40, 50, 60 has three or four layers.
The tube 10, 20, 30, 40, 50, 60 of the present invention is suitable for use in motor vehicles, and may comprise an outer layer 18 or outside layer 56 which is non-reactive with the external environment and can withstand various shocks, vibrational fatigues and changes in temperature, as well as exposure to various corrosive or degradative compounds to which it would be exposed through the normal course of operation of the motor vehicle. Suitable materials for use in the present invention may be composed of any melt-processible extrudable thermoplastic materials which are resistant to ultraviolet degradation, extreme changes in heat. The material of choice may also exhibit resistance to environmental hazards such as exposure to road salt, zinc chloride and CaCl2, and resistance to degradation upon contact with materials such as engine oil and brake fluid.
Referring now to
The multi-layer tube 10, 20, 30, 40, 50, 60 has strong properties necessary for automotive coolant transport. The tube 10, 20, 30, 40, 50, 60 is expected to withstand impact of 1.5 J (2 ft-lbs) of force at −40° C. and exhibits a coolant permeation resistance better than traditional EPDM tubes. The tube 10, 20, 30, 40, 50, 60 is capable of being made into a corrugated tube without delamination and has adequate resistance to burst pressures that it will encounter during typical operation and also withstand vacuum pressure that it will encounter during manufacturing and testing. The tube also has sufficient seal-ability and hoop strength to enable it to couple with a barbed connection without leakage.
While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.
Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.
In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
