Method for investigation of structure borne noise paths

Abstract: The invention relates to a method for investigation of structure borne noise paths in a complex structure consisting of at least two parts connected by connecting elements for example dampers or engine mounts or suspension isolators, whereby one of these parts generates vibrations which cause noises. The method comprises the following steps: attaching at least one actuating device (6) comprising an additional inertial mass and an actuator to a point in the vicinity of a connecting element (4) between two parts of the structure said actuator (6) being connected with a controller (20); attaching at least one sensor (7, 8) for detecting the amount of vibration near the point in which the actuating device (6) is attached or in the actuating device, said sensor(s) being connected with the controller; obtaining (a) reference signal(s) from the part which generates vibrations; driving the controller (20) according a predetermined control strategy in consideration of said reference signal; measuring the change of vibration or noise at predetermined locations of the structure; calculating the influence of the vibrational force transmitted by the connecting element (4) on the measured values.

Description: The invention relates to a method for investigation of structure borne noise paths in a complex structure according the preamble of claim 1. Furthermore the invention is directed to a system for investigation of structure borne noise paths in a complex structure according to the preamble of claim 8. One example of such complex structure is a vehicle body on which a combustion engine is mounted. In this case the combustion engine forms the first part of the structure whereas the vehicle body forms the other part. Engine mounts forming connecting elements between these parts are provided to minimize transfer of vibrations from the combustion engine to the vehicle body. Another example of such complex structure is the suspension of a wheel of a vehicle. Vibrations are induced by the axle of a road wheel of the vehicle into the vehicle body. Such complex structures have a lot of degrees of freedom and it is not easy to determine forces acting between parts of the structure and causing vibrations and noise. In order to be able to minimize vibrations and noise by structural changes it is necessary to learn a lot about the dynamic behaviour of the system. One method of prior art is to attach one or more sensors like accelerometers on critical parts of the structure to be able to determine the amount and the velocity of deviations of these parts. However it is not always easy to determine forces acting on certain parts of the structure like an engine mount. In many cases it is not possible to determine even the direction of such force. It is therefore not uncommon to obtain misleading results during such inventions of complex structures. One approach to be able to determine the force acting upon an engine mount is to insert an element which is adapted to measure the force or alternatively to disconnect parts which are suspected vibration paths. However, in such a case a lot of adaptions have to be made on the structure. On the one hand this leads to a change of the structure itself so that the results obtained by this method are not fully reliable and on the other hand this method is very time consuming and cumbersome. Further knowledge of the system and its behaviour can be gained by changing engine mounts to such ones of another type. However, this is also time consuming and allows only a trial and error approach for optimisation of the system. US-A 5,133,527 and US-A 5,418,858 disclose active mount systems in which vibrations and noise are minimized by an electronic circuit in which data from sensors are inputted and which calculates a certain control force to be generated by some actuators. Such systems can be very effective and allow a substantial reduction of noise and vibration. However, such systems make it necessary that all components have to be built in into each vehicle produced and to work over the whole lifetime of such vehicle. Therefore the costs of such systems are high. US 5,332,061 A describes an active vibration control (AVC) system for attenuating vibrational frequency components generated by an engine and transferred through an engine mounting unit to vibrate a motor vehicle body. With such system it is possible to improve the dynamic behaviour and the noise of a vehicle however, it is not possible to get enough information for making appropriate changes or to design an engine mounting unit so as to improve vibration and noise. Similar arguments are true for the method disclosed in US 5,418,858 A. Starting from the closest prior art known from US-A- 5 332 061, it is an object of the invention to avoid these problems and to provide a method which is easily applicable and a method and a system which allow to obtain reliable results for subsequent optimisation of the structure and connecting elements. According to the present invention this method consists of the steps of the characterizing part of claim 1. Further the invention relates to a system of claim 8. It is essential that the behaviour of the structure is changed by the application of the active control so that information of the system is obtainable. Important is that the change of behaviour may be conducted without mounting or dismounting parts of the structure. In this way it is possible to calculate forces acting in the structure in different operating conditions even if it is not possible to measure them directly. Further it is possible to simulate different parts and their influence on the behaviour of the structure. So it is possible to simulate another engine mount instead of the mount actually used in the structure. Since these operations are possible by changing the control strategy of the controller such experiments are very effective and easy to conduct. The frequency range of operation, for vehicle applications, will typically be 30 HZ to 800 HZ. The system can be used in one of two modes of operation 1) Harmonic vibration cancellation whereby a reference signal is taken from a prime source of vibration and the controller is set up to cancel one or multiple harmonics (integer and/or non integer) of the reference frequency. The reference frequency need not to be stationary but could, for example, be generated by an engine crankshaft speed sensor in vehicle applications. The actuator is applied to the point of interest in order to cancel the vibration at that point and chosen direction. Assessment of the influence of reducing the vibration at the test point upon the overall structure can then be assessed by conventional measurement and subjective assessment. 2) Broad band cancellation similar in application to the narrow band harmonic system but here the controller is set up to cancel all frequencies within the pass band of interest. The control system may use feed forward or feedback control methods as appropriate e.g. making use of established LMS filtered X and filtered error or other suitable algorithms. In preferred embodiments of the present invention different control strategies are applicable. In the following the invention is further described by some preferred embodiments. Fig. 1 shows schematically a structure with a system according to the present invention. A vehicle 1 is equipped with an internal combustion engine 2. The combustion engine 2 comprises an engine mount 3 with a resilient element 4 which is attached at the part 5 of the vehicle body which is not shown for sake of convenience. In the vicinity of the resilient body 4 there is attached an electromagnetic type actuator 6 which is designed to apply predetermined forces to the part 5 of the vehicle body. A sensor 7 which is an accelerometer senses the dislocation of part 5 in the vicinity of engine mount 3. A further sensor 8 senses the dislocation of the engine mount 3 on the side of the combustion engine 2. A force measuring element 9 measures the force acting on the part 5 of the vehicle body induced by actuator 6. A reference signal sensor 10 detects the speed of the engine of the vehicle. Further a microphone 11 or number of microphones is (are) disposed in the interior of the vehicle preferably in a position corresponding to the occupants head(s). An additional sensor 12 detects vibrations at another part of the vehicle body. A controller 20 consists internally of an adaptive cancellation controller 21 and a setting and evaluation unit 22. The controller 20 is connected to sensors 7, 8, 9, 10, 12 and to the microphone 11. Based upon signals inputted by these sensors the adaptive cancellation controller calculates a control signal. This control signal is fed to an amplifier 23 which drives the actuator 6. The control signal of the cancellation controller 21 is calculated according to a control strategy determined by the setting and evaluation unit 22. Such control strategy which may be also extended to a multi-channel vibration control is disclosed in Elliott, Stothers and Nelson "a multiple error LMS algorithm and its application to the active control of sound and vibration" IEEE transactions on acoustics, speech and signal processing Oct. 1978. Further details of such control strategies are disclosed in US-A 5,133,527 and US-A 5,418,858. The method is not limited to these control strategies. One example of operation of the system of the present invention is that a control strategy is chosen so that dislocation of sensor 7 is minimized. This simulates a situation in which part 5 of the vehicle body is very stiff at the frequency or frequencies of control. The force measured by sensor 9 which may be a strain gauge corresponds to the force acting in part 5 and in the engine mount 3 if it would be very stiff. By changing the control strategy it is possible to simulate different degrees of stiffness of part 5. In such cases it is not possible to determine the force acting on part 5 based upon the signal of force sensor 9. However, comparing dislocations measured by sensors 7 and 8 and considering the characteristic of the resilient element 4 it is possible to calculate the force transferred by this engine mount 3. It will be noticed that by this arrangement displacements and forces may be measured and calculated with respect to a predetermined direction. If it is necessary to investigate forces acting in other directions additional sensors and actuators have to be applied. In the same way it is possible to simulate resilient elements with different characteristics. Comparing phases and amplitudes of the signals from sensors 7 and 8 such simulations may be conducted. In addition to their use by the controller microphone 11 and the additional sensor 12 allow to evaluate the results of different simulations in terms of riding comfort.

Claims: Method for investigation of structure borne noise paths in a complex structure consisting of at least two parts (2, 5) connected by connecting elements for example dampers or engine mounts (3) or suspension isolators, wherein one of these parts (2, 5) generates vibrations which cause noises, said method comprising the following steps: attaching at least one actuating device comprising an additional inertial mass and an actuator (6) to a point in the vicinity of a connecting element (4) between two parts (2, 5) of the structure, said actuator (6) being connected with a controller (21); attaching at least one sensor (7) for detecting the amount of vibration near the point in which the actuating device is attached or in the actuating device, said at least one sensor (7) being connected with the controller (20); obtaining a reference signal or signals from the part (3) which generates vibrations; drivingly connecting the controller (20) to the actuating device (6) in order to activate the actuating device (6); said method being characterized by the following steps: providing more than one control strategy for driving the controller (20); driving the controller (20) according to different predetermined control strategies in consideration of said reference signal or signals; measuring the change of vibration or noise at predetermined locations of the structure for said different control strategies; calculating the influence of the vibrational force transmitted by the connecting element (4) on the measured values. Method according to claim 1, wherein the controller (20) performs a narrow band cancellation of vibration harmonics of the reference signals. Method according to claim 1, wherein the controller (20) performs a broad band cancellation of vibration. Method according to claim 1 or 2, wherein the controller (20) utilizes a feed forward control strategy. Method according to claim 1 or 2, wherein the controller (20) utilizes a feed back control strategy. Method according to one of claims 1 to 5, wherein the controller (20) is set up to allow for emulation of dynamic absorbers. Method according to one of claims 1 to 6, wherein one control strategy consists in minimization of dislocation at the point at which the actuator (6) is attached. System for investigation of structure borne noise paths in a complex structure consisting of at least two parts connected by connecting elements like dampers or engine mounts (3), wherein one of these parts (2, 5) generates vibrations which cause noises, said system comprising: an actuating device (6) attached at a point in the vicinity of the connecting element; a sensor (7) for detecting vibrations attached at a point of the structure in the vicinity of the actuating device; a reference signal sensor (10) for obtaining a reference signal from the part which generates vibrations; (a) at least one further sensing device (8, 9, 11, 12) for evaluation of the amount of vibration or noise transmitted by the structure; a controller (20) connected with the actuator (6), the sensor (7), the refence signal sensor (10) and the at least one further sensing device (8,9,11,12), which controller (20) is designed to drive the actuator (6) according to the signals from the sensor (7), the refence signal sensor (10) and the at least one further sensing device (8, 9, 11, 12), characterized in that said controller (20) comprises a cancellation and a setting and evaluation unit (22) for setting different control strategies and for obtaining information about the dynamic behaviour of the structure. System according to claim 8, wherein the at least one further sensing device is a microphone (11), an accelerometer (12) or a force measuring device (9) or multiples of such sensor devices.

Inventors: QUINN DAVID CHARLES, QUINN, DAVID CHARLES
Applicants: AVL LIST GMBH
Application year: 1996
Main classification: F16F15
IPC codes: F16F7, G01H1, F16F15, B60K5, G01M17