DE1255955B - Device for examining the operation of an internal combustion engine - Google Patents

Description

GERMAN mTTGS® PATENT OFFICE

EDITORIAL

German class: 42 k -22/01

Number: 1 255 955

File number: E 23560IX b / 42 k

1233 955 Filing date: September 21, 1962

Opened on: December 7, 1967

The invention relates to a device for examining the operation of an internal combustion engine, in which a crankshaft is driven via pistons, whereby the machine periodically is subjected to normal and abnormal vibration pulses. The device is used for display and Determination of the function of an internal combustion engine and for the analysis of the operation by measurement these normal and abnormal vibration pulses that occur in the course of operation.

Devices for sensing machine vibrations that have facilities for graphic recording, are known. A known device of this type enables the transmission of the oscillating movement a spring-loaded sensor by inducing an electric current, which amplifies and is made visible on an oscilloscope. Another well-known vibration indicator is used the magnetostrictive properties of a rod. This device is screwed into the machine block and firmly connected to this and works in such a way that the vibrations of the engine are opposed can be measured at a stationary reference point. Other known devices work according to the piezoelectric principle and partly by means of a seismic mass fixed to a rigid metal container is connected, which itself is connected to the surface of the machine. These well-known Devices in which the sensor device is firmly attached to the machine or to a part of the machine connected, have the disadvantage that they reduce the vibrations of the machine to which they are firmly attached are to participate. There are also known devices that transmit the oscillating motion enable a spring-loaded sensor by inducing an electrical current and to make visible. But this device is also, if it is firmly connected to the machine in a known manner is included in the vibratory movements of the machine.

The invention is based on the object of providing a simple and easy-to-use device create, with which internal combustion engines can be checked quickly and easily and with which Sensor and recording device isolated from the machine vibrations on a relatively solid Point are arranged.

This object is achieved by means of the device according to the invention for examining the operation of an internal combustion engine, in which a crankshaft is driven via pistons, whereby the machine periodically normal and abnormal device for examining the operation
an internal combustion engine

Applicant:

Esso Research and Engineering Company,
Elizabeth, NJ (V. St. A.)

Representative:

Dr. K. Th. Hegel, patent attorney,
Hamburg 52, Giesestr. 8th

Named as inventor:

Victor F. Massa, Berkeley Heights, Ν. J .;

Hsue C Tsien, Livingston, Ν. J .;

John J. Heigl, Short Hills, Ν. J. (V. St. A.)

Claimed priority:
V. St. ν. America September 22, 1961
(139 979),

dated July 16, 1962 (210 141) - -

Vibration pulses is subjected, and which is characterized by being a spring-loaded Low-contact vibration pickup, which on the one hand with the internal combustion engine in radial distance to the axis of the crankshaft, preferably rigidly attachable via the engine air cleaner is and on the other hand cooperates with a registration device and that of one at relative fixed points fixedly arranged carrier device is held tangential to the crankshaft axis. Is beneficial the device according to the invention is designed so that the contact arm has a on the carrier device attached frame and held on this seated bearing brackets and on this frame is attached to the recorder and that contact arm and recorder via one with his one End part rotatably coupled to the contact arm and at its other end part via a pen in constant contact with a recording strip, the changes in movement of the contact arm Reinforced transmitting mechanical linkage interact.

The device according to the invention can be checked easily in any workshop

709 707/281

internal combustion engines are used. The machine is checked simply by having the Device according to the invention at a relatively fixed point that isolates from machine vibrations is temporarily fixed to the automobile body and with the spring-loaded arm that is tangential is aligned in a radially shifted position over the axis of rotation, the entire body movements of the machine can be measured, which accurately indicates the correct operation or a malfunction. The device is preferably designed so that it emits a continuous signal which depends on the extent of the movement of the engine fluctuates. The changes in the output signal are recorded with the recording device, and they can, if necessary, be reinforced and resized by means of suitable means and / or frequency can be varied.

There are devices for adjusting the position of the contact arm so that this during can be held in the desired position during the test period. You can swivel one Provide mounted lever, one end of which cooperates with a member on the spring-loaded Contact arm is attached and can move back and forth with this so that the Pivoting lever moved around its pivot point in accordance with the movement of the contact arm. Included the arms of this pivot lever can have any desired length ratio to one another, so that the outer tip controls the movements of the contact arm with any desired amplification or magnification can reflect.

It is also possible that the link attached to the contact arm consists of two collars on the contact arm or on to provide an extension of the same, which cooperate with a fork piece on the pivotable arm is attached. The member attached to the contact arm can also be designed as a rack be that cooperates with a pinion which is rigidly arranged on the arm of the pivot lever.

The recorder at the other end of the lever can be a pen or pencil point which slides on a moving recording strip and records the movements of the lever. However, a differential transformer can also be provided which is provided with an armature which is coaxial in the longitudinal direction of its current-carrying wire coil and preferably slides within the same and forms the mentioned spring-loaded contact arm or in constant contact is held with it and moves with it. In this preferred embodiment of the Subject of the invention, the contact arm is rigidly attached to the armature and forms a coaxial extension same. If the contact arm is against the motor or a motor accessory is held, moved according to the motor movement, then the armature comes in the longitudinal direction within the transformer winding into one in terms of both frequency and amplitude corresponding movement. This movement of the armature within the winding or coil causes fluctuations the electric field and the current passed through the winding, the z. B. recorded graphically and the records can then be compared to a standard chart so that you can quickly find an impeccable

Can determine the work of the engine and its causes.

The invention is explained in more detail below with reference to the drawings. It shows
F i g. 1 is a schematic view in elevation showing an apparatus including a mechanical recorder on an automobile engine of a conventional type;
F i g. 2, on an enlarged scale, the front view ίο of the contact arm and recording device of the device shown in FIG. 1,

F i g. 3 shows a section according to 3-3 of FIG. 2, with various parts omitted,
F i g. 4 is an elevational view of a modified embodiment of the contact arm and recorder on a device;
F i g. 5 shows a section according to 5-5 of FIG. 4,
F i g. 6 shows the front view of a further embodiment of the support arm and recording device, in which parts have been broken away or left out,

F i g. 7 shows a section according to 7-7 of FIG. 6,
F i g. 8 a schematic view of a modified embodiment of the device;

F i g. 9 to 21 recorded with a device according to the invention, illustrating the engine power graphic records and

F i g. 22 a curve recorded with a device according to the invention, which shows the relative roughness shows the running of an engine with fuels with different aromatic content.

The in F i g. The device illustrated in FIG. 1 has a support rod 11, for example a light metal tube, to which support supports 13 and 15 are attached. Each support is attached with a suction cup 17, which is preferably made of rubber, to a part of the vehicle to be tested which is suitable as a solid base 64. The supports 13 and 15 are adjustable in the longitudinal direction of the support rod 11 and can be fixed by adjusting screws 19. If necessary, a vertical adjustment of the support rod 11 with respect to the supports 13 and 15 can also be provided.

A registration device 24 is also provided so that it can slide in the longitudinal direction of the support rod 11 and has a clamping device 21 which can be designed as a C -shaped screw clamp or in a similar manner, as shown, for example, in FIG. 3 is shown, or it is as shown in FIG. 1, fastened to the support rod 11 with a wing nut 22. Vertical adjustability can also be provided in this case.

The vibration sensor is formed by a contact arm 25 which can slide in its longitudinal direction and which, as shown in FIG. 1 and 2, is elastically loaded to the right by a spring 26. The spring 26 is arranged between a holder 27, which can be arranged relatively fixed or adjustable in order to change the tension of the spring with respect to the recording device, and a collar 28 which is fastened to the contact arm 25 by an adjusting screw 29. As one can see from FIG. 2, the registration device has a housing or a frame 30 in which the registration devices are arranged. The contact arm is slidably mounted in the lower part of the housing 30 and slides freely and smoothly through bearing mounts 31 and 32 which are attached to the housing or frame 30 or are made in one piece with this. A collar 33 serves to limit the

Movement of the contact arm 25 to the right under the action of the spring 26 and is attached to the contact arm, preferably adjustable, with the aid of an adjusting screw 34.

Another collar 35, which is also adjustably fastened by means of an adjusting screw 36 on the contact arm 25 , has such an arrangement that it rests closely on the rounded lower end part 37 of a pivotably mounted registration lever 38. The registration lever 38 is pivotable on a pivot pin 39 which is arranged on the housing or frame 30. When the contact arm 25 moves to the left or right, the registration lever 38 is pivoted about the pivot pin 39. The upper end of the registration lever 38 carries a pen 40 which records the movements of the lever 38 via a registration strip 41. The upper end of the registration lever 38 is preferably slightly loaded by a flexible leaf spring 43 towards the registration strip 41 , so that a suitable writing pressure is exerted on the pen. Ink or pencil can be used as the pen 40; The recording is preferably carried out by friction, and for this purpose the surface of the recording strip 41 is designed accordingly in a known manner.

A small electric motor 59, preferably a synchronous motor, is used to drive the conveyor device which supplies the recording strips 41. Via a mechanical linkage 51 , not shown in detail, the motor 50 drives a transport roller 52 , which in turn drives a transport roller 54 via an intermediate gear 53 . The rollers 52 and 54 are arranged on frame 30 mounted in the housing or axes, one of which is provided for the transport roller 52 axis in F i g. 2 is denoted by 55.

60 denotes a supply of recording strip paper, which is arranged in the form of a roll on a shaft 61 which is mounted in notches 62 of holders 63. The brackets 63 form the side frames of the recording device 24. The driven means fed by supply lines 65 promotes current motor 50 when the switch is turned on 66, the strip chart 41 g in the F i. 2 and 3 in the direction from bottom to top.

When the device according to the invention has been brought into the registration position, the motor vehicle engine is cranked, and the displacement movements of a suitable part of the motor are transmitted via the contact arm 25 and amplified by its end part 37 and the registration lever 38 , and then the pen 40 rotates an amount that exceeds the amplitude of the motor movement many times. So that the device according to the invention senses and registers the movements of the engine caused by the function of the internal combustion engine and not just minor vibrations of its components and, in a motor vehicle of conventional design, generally the air cleaner has the greatest displacement amplitude or relative movement around the crankshaft or the center of gravity of the engine As a rule, it is expedient to arrange the device according to the invention in such a way that the contact arm 25 touches the engine air cleaner, which is identified by 23. In the zero position, the pen 40 is approximately in the middle of the registration strip 41. Motor movements as a result of irregular running are then transmitted to the pen 49 in such a way that it moves to the right and left of the center line (cf.Fig. 1 and 2) oscillates, whereby the type of displacement, its periodicity, amplitude and the like are graphically recorded. The tab 41 is gradually fed upward during recording. If necessary, a gear shift or a motor speed changing device can be provided with which the recording strip 41 can be conveyed at changed speeds for a precise strip analysis.

In some cases, especially when a very precise adjustment of the collars 28 and 35 is difficult, it may be useful to use a mechanical amplifier with a rack and pinion, as shown, for example, in FIGS. 4 and 5 is illustrated. In the case of the FIGS. 4 and 5, the spring 26 .4 between the laterally adjustable bracket 27 ^ 4 and the adjustable collar 28 , 4 is held under pressure. The contact arm 25 A is designed essentially in the same way as that in FIGS. 1 and 2 illustrated contact arm 25. Between the bearing holders 31 and 32 , a toothed rack, preferably formed from two toothed rack parts 31A and 315 that can move relative to one another and can be adjusted with the aid of screws 32 , 4, is provided. One of the rack parts has slots that allow a slight longitudinal adjustment of one half of the rack with respect to the other half. In this way, every play in the movement can be recorded, and the full movement of the motor or motor part, even if it has only a small amplitude, can be transferred to the recording device 24 . It is useful that the actuating linkage of the pen 40 is designed so that the motor movements or displacements are multiplied by a factor of 20 to 50 or higher. If desired, a double multiplication mechanism for high multiplication factors can be built in.

In Fig. 6, an arrangement is shown in which a contact arm 255 is used, which is formed essentially the same as the contact arms 25 and 25 , 4 in FIGS. 1, 3, 4 and 5. The contact arm 255 is loaded against the engine air cleaner 23 by a coil spring 265 , and the coil spring 265 is arranged between a fixed bracket 245 and a collar 285 . The collar 285 can be adjustably attached to the contact arm 255 by an adjusting screw 280 so that the compressive stress on the spring 265 can be changed. A U- shaped bracket 281 is fastened to the contact arm 255 with screws 282. From Fig. 7 it can be seen that the upwardly bent parts of the holder 281 receive the lower end of a pivot arm 283 which is pivotable about a fixed axis 284. The axle 284 is mounted in the housing or frame 39. The lower end of the arm 283 carries a fixed pin 285 which engages without substantial horizontal play in a slot 286 which is elongated in the vertical direction and which is provided in each side of the U- shaped bracket 281 . When the air cleaner 23 is displaced, the holder 281 moves to the right and to the left, so that the arm 283 swings about its axis 284. The upper end of the arm 283 is connected by a pin 287 to a link 28S , which in turn is connected to a further arm 289

is in communication by a pin 290. The arm 289 is pivotably mounted about a fixed pin 291 in a vertical plane. At its upper end it carries a pen 292, and the upper part 293 of the arm 289 consists of a flexible leaf spring which is pretensioned so that the contact between the pen 292 and the registration strip is maintained. The recording strip is secured against the pen by a support plate 295, as shown in FIG. 7 to be seen, supported. The pen 292 records the lateral movement of the arm 25 B , which is caused by the displacement of the air cleaner 23 and the return movement of the spring 26 B , in a greatly enlarged form.

Usually motor movements have a fairly small amplitude, often only around 0.8 mm or is less. Even a very irregularly running engine is not exposed to very large movements. It is therefore important for a good engine test that both the minor movements as well as those of greater amplitude can be recorded.

It is therefore advisable to provide springs 26, 26 ^ 4 or 26 B made of such a material and form them in such a way that they do not move over the frequency band of the engine displacements and amplitudes, i.e. with regard to speeds and accelerations that are to be investigated Resonance. In addition, the springs must not rebound under any of the normal accelerations or primary motion impulses transferred to them. Since automobile engines have operating speeds that are usually within the range of 200 to 5000 rpm, the springs must be both out of resonance and rebound free within a frequency range of about 3 to 300 Hz and a maximum normal amplitude when considering the engine displacements above this want to graph the entire area. A relatively short spring of moderate mass or stiffness is useful for this purpose. Such a spring usually has a length of less than 75 mm in its coiled form and exerts a pressure of at least several kilograms against the contact arms 25, 25 A or 255 when the pen 40 or 292 is in its central, ie Zero position.

When the spring 26 or 293 is selected and tensioned in a corresponding manner, the device is adjusted and applied to the registration position on the support rod 11 so that it is slid to the motor air cleaner 23 until the pen 40 or 292 is on the graphic scale is in the middle position.

The in F i g. 8 has a support rod 10 provided with a longitudinal slot, which is held in a position above the motor vehicle engine to be examined and transversely to its axis, for example by resting with its ends on the fenders 42 and optionally being clamped to them. There is a support arm 12 provided with a slot and directed downwards, which is arranged slidably in the slot of the support rod 10 and can be clamped and held on the support rod 10 with a wing screw 18. The vibration sensor, which is formed by a differential transformer 14 , is located in the slot of the support arm 12

Slidably arranged and can be adjusted and tensioned vertically in this. The differential transformer 14 has a live wire coil and a magnetic armature which is arranged so that it is slidable in the axial direction and longitudinal direction within the coil. At the outer end of the armature, a spring-loaded contact arm 20 is attached coaxially to the armature. The position of the support arm 12 in the slot of the support rod 10 and the position of the vibration sensor in the slot of the support arm 12 are set so that the spring-loaded contact arm 20 is loaded against the side of the motor vehicle engine or against an accessory part rigidly attached to it and moving with it. The contact arm 20 moves in its longitudinal direction and in its axial direction in accordance with the lateral movements of the motor vehicle engine, so that the armature is moved back and forth within the coil, whereby the electric field of the differential transformer 14 is changed. The electrical field of the transformer is connected to a pickup and amplification device 16 and the output is passed to a recorder 24, for example an electrographic brush recorder. The changes in the electric field caused by the movement of the motor are recorded on this in the form of a coherent diagram. The recording device 24 should preferably be able to operate at different speeds.

Instead of the in FIGS. 1 to 7 and the mechanical design shown in FIG. 8 illustrated Differential transformer can also have acoustic vibration transducers, which are a corresponding provide a continuously changing signal to the movement of the motor vehicle engine, or electrical devices such as potentiometers or variable resistors can be arranged, as well as photosensitive or optical devices, all of which would be familiar to those skilled in the art for these purposes are known.

With the device according to the invention, all types of irregularities in the engine performance an internal combustion engine are checked, for example by changes in the Fuel quality or delivery or other factors and the running of the Affect the motor. One can see the effect of different fuels on the running of the engine Check idle speeds and at high engine speeds, and it can be stationary or in Vehicles in motion are examined. You can also use the device according to the invention to determine differences in the initial value and in the total value of fuel volatility Use different speeds from idling to high speeds and during acceleration, and one can determine the tendency to stall the engine as a function of the fuel liquid investigate. A device according to the invention can also be used for the detection and determination of fuel properties, for example vapor lock, cold start, warm-up time and starting torque output, as well as for the investigation of various anti-knock agents. It can be the engine irregularities examined at low pressure, idling, operating pressure, high speed and during acceleration and, for example, that

Exposed spark plugs, abnormal cylinder internal pressure or low pressure caused by leaking Valves and / or piston rings caused during operation and initial gasification difficulties with rich and lean fuel-air mixtures as well as after-run due to compression ignition or hot compression chamber deposits to be examined.

The device according to the invention can not only be used on four-stroke and two-stroke internal combustion engines use, but with all types of fuel operated with liquid and gaseous fuels Internal combustion engines for automobiles, watercraft, aircraft and power plants, including Engines with compression ignition, such as diesel engines, aircraft jet turbines, pilot injection engines, such as gas-diesel oil engines working according to the two-fuel process, provided that the Motors are not mounted so rigidly that any detectable lateral motor movement is excluded. The device according to the invention can also be used advantageously for electrically operated machines, generators and other prime movers subject to external motion may be used changes with the operating efficiency.

In the F i g. Figures 9 through 21 illustrate various recordings made with the invention Device have been added. FIGS. 9 to 16 show the movement of an Otto engine again under different conditions.

The line 198 in FIG. 9 was recorded with the engine running quietly; the irregularities are relatively minor. The sharp and strong displacements that occur at irregular time intervals and have a strongly changing amplitude, which can be seen from the difference between the lines 199 and 200 in FIG. 10, occur when the ignition timing is set too early. The in the F i g. The diagrams shown in FIGS. 11 and 12 were taken for engines which are operating at a reasonably quiet idle speed, but which have spark plugs firing intermittently (FIG. 11) or periodically (FIG. 12). The vibrations are considerable, but have a fairly uniform amplitude, as can be seen from the somewhat uniform lines 201 in FIG. 11 and 202 in FIG.

A faulty carburetor setting is determined with the device according to the invention in diagrams as shown in FIG. 13 and 14 are shown. Characteristic for this is the irregularly jagged course of the lines 203 (for moderately incorrect carburetor setting) and 204 (for severely incorrect carburetor setting).

The diagrams in FIGS. 15 and 16 show poor compression, indicating poorly fitting valves, broken or damaged piston rings or cylinder walls, or a combination of defects in the valves and piston rings. F i g. Fig. 15 shows a trace obtained at starting when the engine is cranked by the starter. Initially, the load causes a large displacement (A) at cranking, followed by smaller displacements (B) when one or two of the engine cylinders begin to fire, followed by larger displacements (C) when the engine stops firing and cranking away-

is set. This is followed by a rapidly progressive decrease in displacement (Z) as the various cylinders begin to fire until normal engine idling is reached at (E). The diagram shown in Fig. 16 differs therefrom, which was obtained by means of the device according to the invention on an engine with a low internal pressure in a cylinder. The traces 206 have a substantially reduced ίο amplitude and maintain a precisely periodic distance from each other.

FIG. 17 shows a graphic recording made with a device according to the invention the engine movement reproduced, which is the after-run effects after switching off the ignition an Oldsmobile engine at a compression ratio of 10: 1.

18 and 19 show recording lines obtained from a Chevrolet V8 engine. In the case of the in FIG. 18 reproduced test the engine was operated at first in the normal idling, then air-fuel mixture candle with a rich by throttling the air flow to the carburetor and thereafter exposing a Zünds5, the artificially induced by bridging a spark plug with a short-circuit ^connection: was driven. F i g. 19 shows the trace obtained during acceleration and subsequent deceleration from 32.2 km / h to 96.6 km / h with and without spark plug failure. Included ; the first part of the illustrated line was obtained with working spark plugs under deceleration, the following part of the line was determined with intermittent spark plugs initially under acceleration, then under deceleration, and the subsequent part of the line shows the diagram when the plugs are working and accelerated A comparison shows that the acceleration to 96.6 km / h without the spark plug dropping out took place in a shorter time than with the spark plug dropping out. In this way, the failure of spark plugs during acceleration or high internal cylinder pressure can easily be detected by means of the device according to the invention.
Even more precise results can be achieved by means of the device according to the invention if the transport speed of the registration strip 41 in the registration device 24 is increased so that the individual changes in displacement can be identified in greater detail. A comparison of FIGS. 20 A and 20 B, which are a graph of the changes in engine motion with induced spark plug firing at various strip line speeds. F i g. 20A shows the line image with the induced exposure of a spark plug at a normal transport speed of the recording strip of 5 mm / s and FIG. 20B the image with the same exposure at a higher transport speed of 25 mm / s. In this way, once a malfunction has been detected, the device according to the invention can be used to precisely determine the faulty cylinder or the faulty spark plug.
FIGS. 21A, 21 and 21C show diagrams as they arise when the engine movement changes as a result of two different fuels and incorrectly working spark plugs

709 707/281

Claims (3)

11 12 affect the roughness. The relative roughness values for the in F i g. The curve shown in Fig. 22 has been plotted under is on an empirical scale. Use of fuels with increasing F i g. 21A gives the lines for isooctane, FIG. 21B Aromatic content obtained by mixing to * for benzene, each with working spark plugs, and additional amounts of a hydroformat with a F i g. 21C shows the lines that occur under extreme conditions with two 5 aviator alkylate as well as by mixing the hydraulic missing spark plugs. formats were prepared with benzene and their addition can be seen that the course when using the composition in detail in the isooctane below is relatively calm, roughly according to a table. From the curve of FIG. 22 roughness degree of 12, when using benzene one recognizes that by means of the rough according to the invention, approximately corresponding to a roughness io according device indicated change degree of 38, and under the extreme conditions with in the motor movement easily and quickly between two missing Spark plugs are very rough, corresponding to a fuel with a high (over 80%) UQd a roughness degree of 100. 22 shows a diagram in which the degree of roughness of a 6-cylinder Chevrolet engine as a function of the percentage of the engine according to the invention lies in the fact that aromatics in the Fuel mixture is applied. that you can quickly, easily and inexpensively determine the aromatic content in percent of abnormal operation of an engine on the abscissa and the degree of engine roughness in a large number of disturbances in their relative change numbers on the ordinate. 10 means that 20 the relationship and feedback can be recognized and the most localized idle possible, 100 the roughest possible. Idle with two non-igniting spark plugs. Influence of the engine idling behavior through the aromatic content of the fuel in a 6-cylinder Chevrolet engine Tested fuels Isooctane aviator alkylate 76.5% alkylate, 23.5% light hydroformat% alkylate, 47% light hydroformat Premium commercial gasoline 30% Alkylate, 70% light hydroformate 7% alkylate, 93% light hydroformate 80% light hydroformate, 20% benzene 50% light hydroformate, 50% benzene Benzene (a) Based on the air-fuel ratio during the test. Patent claims: 1. Device for investigating the operation of an internal combustion engine, in which a crankshaft is driven via pistons, whereby the machine is periodically subjected to normal and abnormal vibration pulses, characterized by a vibration sensor designed as a spring-loaded contact arm (25 or 20) , which on the one hand connects to the internal combustion engine can be rigidly fixed at a radial distance from the axis of the crankshaft, preferably via the engine air cleaner (23) and, on the other hand, interacts with a recording device (24) and tangential to the carrier device (11, 13, 15 or 10, 12) fixedly attached to relative fixed points is held to the crankshaft axis. 2. Apparatus according to claim 1, characterized in that the contact arm (25) is held via a frame (30) fastened to the carrier device (11, 13, 15 ) and bearing holders (31, 32) attached to this and on this frame (30 ) also the recording device (24) Aromatics
% Air fuel
Percentage (a)
stoichiometric Engine roughness
degree (b) 0 85.5 12th 0 85.5 12th 15th 84.2 12th 30th 85.0 15th 36 85.3 12th 45 86.0 12th 60 87.0 19th 71.5 87.0 15th 82.0 87.6 19th 100 88.5 38 (b) 10 = quietest possible idle; 100 = roughest possible idling, corresponding to two misfiring spark plugs. is fixed and that the contact arm (25) and recording device (24) are rotatably coupled to the contact arm (25) at one end part (37) and at its other end part via a pen (40) in constant contact with a recording strip (41) standing mechanical linkage (37, 39, 38, 43) which intensively transmits the changes in movement of the contact arm (25) . 3. Apparatus according to claim 1, characterized in that the contact arm (20) is held via a support arm (12) provided with a slot on a support rod (10) which is fixedly mounted with its ends on fenders or sides of a carriage structure driven by the internal combustion engine and that Recording device (24) is arranged separately therefrom, preferably coupled to an amplifier (16) , and that the contact arm (20) and recording device (24) have a differential transformer (14) which has a current-carrying wire coil and an armature, which is preferably arranged to be slidable in the longitudinal direction within the coil. , at the outer end of the armature the contact arm (20) is attached and which is in conductive connection with the regi- 45