Technical field of the invention

The present invention relates to a mounting element for resiliently supporting an internal combustion engine in accordance with the preamble of claim 1 . The invention also concerns a method for monitoring vibrations of an internal combustion engine as defined in the preamble of the other independent claim.

Background of the invention Despite the aim of balancing the inertia forces and torques of piston engines, operation of a piston engine always induces vibrations. The vibrations can often be a significant source of noise. The vibrations can also directly cause inconvenience to the persons affected by the vibrations. This is often the case for example in passenger ships. The transmission of vibrations from an engine to the engine foundation, such as to the hull of a ship, can be reduced by using resilient mounting elements. The resilient mounting elements comprise rubber elements or similar elastic members, which dampen vibrations. In order to address vibration problems, it is advantageous to monitor the vibrations. It is known to equip engines with acceleration sensors, which provide information on the vibrations. However, the use of acceleration sensors does not always provide sufficient data for analyzing the vibrations in terms of free forces, free couples and mechanical power transmission from the engine to the mounting platform.

Summary of the invention

An object of the present invention is to provide an improved mounting element for resiliently supporting an internal combustion engine. The characterizing features of the mounting element according to the invention are given in the characterizing part of claim 1 . Another object of the invention is to provide an im- proved method for monitoring vibrations of an internal combustion engine. The characterizing features of the method are given in the characterizing part of the other independent claim.

The mounting element according to the invention comprises a body having a first support surface that can be supported against a rigid mounting platform, and a second support surface that is configured to support a resilient member. The mounting element further comprises at least three force sensors that are arranged on the first support surface of the body and configured to support the body of the mounting element in a vertical direction when an engine is mounted on the mounting element. In the method according to the invention, forces transmitted from the engine to a mounting platform of the engine are measured using mounting elements defined above.

With the mounting element and method according to the invention, the forces transmitted to the engine foundation can be easily monitored. By providing the mounting element with at least three force sensors, the mounting element can be stably supported against the mounting platform.

According to an embodiment of the invention, at least four force sensors are arranged on the first support surface of the body of the mounting element. This makes the mounting element more stable. According to an embodiment of the invention, exactly four force sensors are arranged on the first support surface of the body of the mounting element. By using exactly four force sensors, analyzing of the measurement data is easier. The force sensors can be arranged in a square shape. By arranging the force sensors symmetrically, analyzing of the data is made less complicated. According to an embodiment of the invention, the force sensors are triaxial force sensors capable of measuring forces in three directions that are orthogonal to each other. This allows monitoring of all the forces that are transmitted from the engine to the mounting platform.

According to an embodiment of the invention, the mounting element comprises a base plate and the force sensors are sandwiched between the body of the mounting element and the base plate for preloading the force sensors. The preloading increases the linearity of the output of the force sensors. By provid- ing the mounting element with a base plate, the mounting element can be formed as a complete unit that is easy to assemble.

According to an embodiment of the invention, the mounting element comprises at least three accelerometers. With the accelerometers, the information provid- ed by the force sensors can be completed.

According to an embodiment of the invention, the accelerometers are attached to the base plate.

According to an embodiment of the invention, the accelerometers are triaxial accelerometers capable of measuring accelerations in three directions that are orthogonal to each other. Vibrations in all directions can thus be monitored.

According to an embodiment of the invention, the number of the accelerometers equals the number of the force sensors.

According to an embodiment of the invention, the second support surface has a shape of a truncated cone. The first support surface can form the base of the truncated cone.

A mounting arrangement according to the invention comprises an internal combustion engine, at least four mounting elements defined above and at least four resilient members, wherein the mounting elements are supported against a mounting platform and at least one resilient member is arranged between each mounting element and the engine. The mounting arrangement can comprise a base frame, which is supported by the mounting elements and on which the engine is arranged.

According to an embodiment of the invention, in the method for monitoring vibrations, power transmitted through the mounting elements from the engine to the mounting platform is determined on the basis of the data produced by the force sensors and the accelerometers. The power better describes the vibrations compared to simple force or acceleration measurements. Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

Fig. 1 shows a mounting element according to an embodiment of the invention, Fig. 2 shows a bottom view of the body of the mounting element of Fig. 1 ,

Fig. 3 shows an internal combustion engine that is arranged on a base frame and supported by mounting elements according to the invention,

Fig. 4 shows a cross-sectional view of the mounting element of Fig. 1 , and

Fig. 5 shows a cross-sectional view of a mounting element, which supports a support leg of a base frame of an engine.

Description of embodiments of the invention

Figure 1 shows a mounting element 1 according to an embodiment of the invention. The mounting element 1 is used for resilient mounting of an internal combustion engine. Figure 3 shows schematically a mounting arrangement according to an embodiment of the invention. In the mounting arrangement, an engine 10 is mounted on a mounting platform 7 using mounting elements 1 according to the invention. The engine 10 of figure 3 is a large piston engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing electricity. The cylinder bore of the engine 10 is at least 150 mm and the engine 10 comprises a plurality of cylinders. The engine 10 is mounted on a rigid mounting platform 7. The mounting platform 7 can be, for instance, a hull of a ship or a floor structure, such as the floor of a power plant or an engine room. In figure 3, the engine 10 is not directly supported by the mounting elements 1 , but the engine 10 is arranged on a base frame 1 1 , which is supported by a plurality of mounting elements 1 . In figure 3, the base frame 1 1 is supported by four mounting elements 1 . One mounting element 1 is arranged in each corner of the base frame 1 1 . In practice, the minimum number of mounting elements 1 needed for supporting an engine 10 is four. However, also a larger number of mounting elements 1 can be used. In addition to the engine 10, also a generator could be arranged on the same base frame 1 1 . The purpose of the resilient mounting elements 1 is to reduce transmission of vibrations from the engine 10 to the ground, i.e. to the mounting platform 7. The number of the mounting elements 1 needed depends on several factors, such as the size of the engine 10 and the construction of the base frame 1 1 .

The mounting element 1 comprises a body 2. The body 2 of the mounting element 1 is a rigid part that can be made of steel or other suitable material with similar properties. In the embodiment of the figures, the mounting element 1 further comprises a base plate 9, against which the body 2 of the mounting el- ement 1 can be supported. The base plate 9 can be provided with holes for attaching the base plate 9 to the mounting platform 7, for example by means of bolts. Via the base plate 9, the mounting element 1 is rigidly connected to the mounting platform 7. The base plate 9 is made of the same or a similar material as the body 1 of the mounting element 1 . More details of the mounting element 1 can be seen in figures 2 and 4. Figure 2 shows a bottom view of the body 2 of the mounting element 1 of figure 1 . Figure 4 shows a cross-sectional view of the mounting element 1 of figure 1 . The body 2 of the mounting element 1 comprises at least a first support surface 3 and a second support surface 4. The first support surface 3 can be sup- ported against the mounting platform 7 shown in figure 3. The second support surface 4 is configured to support a resilient member (not show in figures 1 -3). Figure 5 shows an example of a resilient member 8 supported against the second support surface 4. The first support surface 3 does not need to be supported directly against the mounting platform 7, but other rigid elements, such as the base plate 9, can be arranged between the first support surface 3 and the mounting platform 7.

In the embodiment of the figures, the second support surface 4 has a shape of a truncated cone. The resilient member 8 shown in figure 5 is therefore a sleeve-like part having a similar shape. The resilient member 8 is made of rub- ber or some other material with similar elastic properties. The material of the resilient member 8 is selected so that the resilient member 8 is capable of carrying the load caused by the engine 10 and other structures, such as the base frame 1 1 , which it needs to support. Because of the shape of the second support surface 4 and the resilient member 8, the mounting element 1 can effec- tively carry both vertical and horizontal forces. In the embodiment of the fig- ures, the mounting element 1 comprises also a second resilient member 13 (shown in figure 5), which is arranged against a third support surface 12 of the body 2 of the mounting element 1 . The third support surface 12 is an inner cylindrical surface of the body 2 of the mounting element 1 . The second resilient member 13 is therefore a sleeve-like cylindrical part. The second resilient member 13 carries horizontal forces.

The resilient members 8, 13 carry a mounting cap 14. The mounting cap 14 comprises an outer skirt 15, which is configured to be engaged with the resilient member 8, and an inner skirt 16, which is configured to be engaged with the second resilient member 13. A supporting leg or other supporting area 17 of an engine 10 or a base frame 1 1 is arranged on an upper surface of the mounting cap 14 and attached to the mounting cap 14, for example by means of bolts 18. The supporting area 17 is rigidly connected to the engine 10 or to the base frame 1 1 . It can be an integral part of the engine 10 or the base frame 1 1 . In case the engine 10 is arranged on a base frame 1 1 , the engine 10 is rigidly connected to the base frame 1 1 . There is thus a rigid connection between the mounting cap 14 and the engine 10. As the engine 10 moves due to unbalanced inertial forces and torques, the forces are transmitted to the mounting cap 14. The mounting cap 14 is connected to the body 2 of the mounting element 1 only via the resilient members 8, 13. The connection between the engine 10 and the body of the mounting element 1 is thus flexible. The resilient elements 8, 13 dampen vibrations and reduce transmission of vibrations from the engine 10 to the mounting platform 7.

The mounting element 1 according to the invention comprises force sensors 5, which can be seen in figures 2, 4 and 5. The force sensors 5 are arranged on the first support surface 3 of the body 2 of the mounting element 1 . In the embodiment of the figures, the mounting element 1 comprises four force sensors 5. The force sensors 5 are arranged in a square shape. The minimum number of force sensors 5 needed for the mounting element 1 is three. The mounting element 1 could also comprise more than four force sensors 5, for instance five or six force sensors 5. The force sensors 5 are arranged between the body 2 of the mounting element 1 and the base plate 9. The body 2 of the mounting element 1 is supported against the base plate 9 only via the force sensors 5. The force sensors 5 thus carry the vertical load of the engine 10 and the base frame 1 1 . The force sensors 5 are preferably triaxial force sensors, i.e. sensors that are capable of measuring forces in three directions that are orthogonal to each other. The force sensors 5 are sandwiched between the body 2 of the mounting element 1 and the base plate 9 by attaching the base plate 9 to the body 2. The base plate 9 is attached to the body 2 by means of stud bolts 19. One bolt 19 goes through each force sensor 5. The bolts 19 are used for pre- loading the force sensors 5. The preloading improves the linearity of the output of the force sensors 5.

According to an embodiment of the invention, the mounting element 1 is further provided with accelerometers 20, which can be seen in figures 4 and 5. The accelerometers 20 are preferably triaxial accelerometers, which are capable of measuring accelerations in three orthogonal directions. The mounting element 1 is provided with at least three accelerometers 20. In the embodiment of the figures, the mounting element 1 comprises four accelerometers 20. The accelerometers 20 are arranged in a square shape. The mounting element 1 could also comprise more than four accelerometers 20. Preferably the number of the force sensors 5 and the accelerometers 20 is the same, but this is not necessary. Each accelerometer 20 is arranged in the proximity of a force sensor 20. The accelerometers 20 are arranged in the space between the body 2 and the base plate 9 of the mounting element 1 .

When the engine 10 is operated, vibrations of the engine 10 are transmitted via the mounting elements 1 to the mounting platform 7. Because of the force sensors 5 and the accelerometers 20 of the mounting elements 1 , the vibrations transmitted through each mounting element 1 can be monitored. The mounting elements 1 provide data on both the forces and accelerations experienced at each mounting point of the engine 10, i.e. at the locations where the engine 10 is supported against the mounting platform 7 by the mounting elements 1 . The mounting elements 1 can be standard mounting elements that are equipped with the sensors 5, 20 for measuring the forces and accelerations, and therefore no other modifications of the engine 10 or the mounting platform 7 are necessary. The outputs of the force sensors 5 of each mounting element 1 are processed to produce a single force value for each force component in an xyz-coordinate system. The outputs of the four force sensors 5 are summed together and divided by the number of the force sensors 5 in the mounting element 1 . For each mounting element 1 , force values F _x , F _Y and F _z are thus calculated. The outputs of the accelerometers 20 are processed in a similar way. The outputs of the accelerometers 20 are integrated to get vibration velocities. Vibration velocity values v _x , v _Y and v _z can then be calculated for each mounting element 1 . The forces and vibration velocities can be used for determining the power transmitted from the engine 10 to the mounting platform 7 through each mount- ing element 1 .

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims. For instance, the invention can be applied to many different kinds of mounting elements.