Catalytic converter testing

Details Catalytic converter testing Catalytic converter testing

1999-07-13

2001-10-09

Kwok, Helen (Department: 2856)

Measuring and testing

Vibration

Vibrator

Reexamination Certificate

active

06298729

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a testing method and apparatus for evaluating the mechanical durability of a catalytic converter assembly designed for mounting within the exhaust system of a motor vehicle.
Catalytic converter assemblies must provide a very high level of mechanical and thermal durability because of the harsh conditions of vibration and high temperature encountered in the automotive exhaust system environment. The assembly for a typical catalytic converter includes a catalyst support honeycomb mounted within a protective exterior enclosure, the honeycomb most often being composed of a refractory, high surface area ceramic material for effective support of an active catalyst. To protect the honeycomb from mechanical shock or vibration damage, it is typically supported within the enclosure by a layer of a refractory, resilient mounting material, this layer being pre-compressed in the course of converter assembly to apply a predetermined holding force to the exterior of the honeycomb. In general, it is the deterioration of this resilient layer through exhaust system vibration at high temperature that is the usual cause of honeycomb breakage and ultimate converter failure.
Many different vibration testing systems have been developed to test the resistance of mechanical and electrical components to physical damage under laboratory conditions. Typically, these systems employ vibration tables, activated by electrical or electromechanical means, on which the devices to be tested are mounted for exposure to controlled vibration. U.S. Pat. Nos. 5,083,463 and 5,641,910 are representative of the different table designs which have been developed for such systems.
The use of sensors to collect information about test conditions during vibration testing is also known. U.S. Pat. No. 4,539,845 to Molimar, for example, describes a device for fatigue-testing a mechanical component mounted between armatures activated by an electromagnetic vibrator wherein a displacement sensor is placed between the armatures to generate a sinusoidal feedback signal for controlling vibration conditions.
The design of vibration testing apparatus is of course dictated largely by the conditions to be encountered by the tested part in use. U.S. Pat. No. 4,445,381 to Russenberger, for example, describes a vibration testing apparatus for fatigue testing a part at low frequencies, mainly to avoid part heating that would affect fatigue performance. An important feature of the vibrator design of this apparatus is an arrangement of vibrator isolation springs, and elastomer rods within the vibrator electromagnetic oscillator, that make the resonance frequency of the vibrator independent of the elastic properties of the part under test. The development of higher frequency vibration modes in the system is also suppressed.
A test technique often used to assess the mechanical durability of catalytic converters is the hot vibration test. The hot vibration test is performed using a variety of methods. Most automobile companies have developed their own hot vibration test to simulate accelerated exposure. The test results are judged using a simple pass/fail criterion. Lacking quantitative data there is no possible method for establishing incremental design improvements or defining marginal system durability. That is, if a part fails there is no means of understanding how close it came to failing, or if it fails how close it came to passing.
The hot vibration test most often utilizes an engine as a source for hot gas, and an electrodynamic shaker table for simulating the vehicle vibration. The engines provide a highly variable source of input temperature. The lack of temperature control complicates assessment of the thermal gradient within the converter and consequently the system durability.
The hot vibration test is additionally commonly conducted using a single (e.g. 100 Hz) frequency sine wave vibration exposure. This is unrealistic because most automobiles produce a range of frequencies ranging from a few tens of hertz up to approximately 1000 Hz. In the case of motorcycle engines, vibration frequencies may range from 100 Hz to as high as 2000 Hz, and the need for converter mounting systems capable of withstanding even higher operating temperatures has been recognized. Despite these issues, however, the hot vibration test remains an industry standard for assessing converter durability regardless of its limitations.
SUMMARY OF THE INVENTION
In accordance with the invention, a new testing apparatus and method have been developed to quantitatively evaluate the mechanical durability of catalytic converters under conditions closely approximating those of ordinary or severe anticipated use. The new method and apparatus provide significantly more information about converter mounting systems and mount durability than can be derived from the highly variable, expensive, and qualitative hot vibration tests of the prior art. This is because the mechanical durability of the converter is measured under controlled thermal and vibrational conditions simulating those found in actual engine exhaust systems.
Thermal conditions like those found in typical engine exhaust systems are simulated using heating means that generate heat directly within the interior of the catalyst support honeycomb of the converter, in the same way that heat is generated by catalytic reactions occurring in use. By this means the extent of heating may be controlled to match that specific to a particular vehicle exhaust system being designed. The mechanical forces encountered by the converter assembly in actual use are simulated through the use of an electrodynamic shaker table or other controllable vibration device. Such devices can be programmed to subject the converter to any selected frequency or frequency spectrum that, again, may be appropriate for the design of an exhaust system for a particular vehicle or vehicle type. The vibration table may also be programmed to apply increased levels of input energy to further accelerate the component aging.
In a first aspect, then, the invention includes improved apparatus for the vibration testing of a catalytic converter for a motor vehicle (e.g., a car, truck, bus, motorbike, etc.). Central to the apparatus is a support structure for rigidly supporting the catalytic converter to be tested, and a vibrator connected to the support structure for vibrating the structure and attached converter in a controlled fashion. In most cases, the converter will contain both a ceramic honeycomb catalyst support and a refractory resilient mounting layer supporting the honeycomb within the protective exterior converter enclosure. A preferred support structure for the testing apparatus consists of a load frame, designed for minimal flexure under vibration and incorporating means for attaching to and rigidly supporting the converter enclosure. The vibrator may consist of an electrodynamic vibration table to which the load frame is rigidly attached.
The apparatus further includes a heater for preferentially heating the honeycomb catalyst support mounted within the protective converter enclosure, and a sensor for measuring the force and/or the acceleration experienced by the honeycomb in the course of the vibration test. A suitable heater is an electrical heating element disposed within or adjacent to the honeycomb, while a convenient system for measuring the force being applied to the vibrating honeycomb includes a load cell in direct or indirect contact with the honeycomb during the test.
Certain specialized exhaust system designs, particularly including designs for motorbike exhaust systems, require a converter placement that is either within or directly adjacent to a heated section of the exhaust system, e.g., within an exhaust resonance chamber built into the exhaust line. Successfully simulating the converter environment in such cases requires additionally heating the exterior of the protective converter enclosure during the test. For this purpose the testing apparatus of the invention may include

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