Intelligent measurements for cars

Intelligent measurements for cars DipI-Phys

A. Happe

Volkswagen AGI Research and Development, Division of Metrology, D-3180 Wolfsburg, Germany The requirements for the development of cars with regard to environmental protection, fuel economy, reliability, safety, handling, etc, are steadily growing. On the other hand, the introduction of CAD and CAM methods has decreased the time to develop a new car by a considerable amount. However, the number of test data is increasing and the time necessary to test the cars at different development stages is still too high. It has to be decreased by at least the same amount by means of computer-aided testing (CAT), so that the flood of data can be processed on board and the results can be presented to the test engineer immediately after or during the test in the form of an easily readable protocol. Keywords: CAT, top-dead-centre-measurement, catalyst-monitoring, wheel dynamometer, C M OS- processor Introduction Testing of cars on the road is often done under extreme weather conditions, for instance, in the polar region in winter or in Death Valley, Arizona, in summer. Therefore, all components of the test equipment have to work under severe environmental conditions, typically under temperatures from - 4 0 ° C to +85°C. Unfortunately, the instrumentation industry does not provide adequate equipment for the necessary road run tests under these conditions. Therefore, the automotive companies have to develop their own test equipment. Accordingly, we at Volkswagen have developed the double system FARES-MEDACS as the base of our mobile computer-aided measuring system. The MEDACS

system

MEDACS is a universal multiprocessor system for data acquisition on board vehicles under extreme environmental conditions. The following essentials give a survey

on the requirements on MEDACS, which have been fulfilled: • Operating temperature range: - 4 0 ° C to +75°C (ambient) • Operating at any supply voltage sufficient for spark ignition (5V to 16V) • Low power consumption: 3 30W • High reliability • Shock proof • Dust and splash water proof • Non-volatility of the stored data • Modularity • Flexibility in the adaptation of signal sources and procedures • Capsular housing, small size and light weight, to provide a wide choice of mounting positions without affecting the behaviour of the car. Fig 1 shows the system structure of MEDACS. We see here the modularity of MEDACS very well. To the sensor side (top left) we see the signal conditioning processors

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Happe (analogue-module, counter-module, frequency-module, analogue input for strain gauges with four channels per board, analogue input for active transducers with eight channels per board). Then, on the right-hand side, there is the measuring processor above and the communication processor below. Both work together with the dual-port memory in the middle of the picture. The CPU types are NSC 800, 80C 88 and 80C 86. Bottom left is the communication interface to the host computer FARES. All components are in CMOS technology. Fig 2 shows the tasks of the signal conditioning processors on the sensor level of MEDACS.

Processing of the digitized Data O Monitoring of the Power Supply 0 Memory Management 0 Distribution of the Commands O Generation of the Data Frame O Datareduction - Transient Recording - Classification - Calculation of Meanvalues - Logical and arithmetical Combination of Data

Fig 3 MEDACS: Tasks of the measuring processor Communication with the User or Hostcomputer

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O Guidance of the user O Command Handling and Conversion O Conversion of eledrical into physical Units O Data retrieval O Quicklook

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Fig 4 MEDA CS: Tasks of the communication processor

Linearisation Detecting of Extreme Values Level Monitoring Converting of Values

Fig 2 MEDACS: processors

Tasks of the signal conditioning

Fig 3 shows the tasks of the measuring processor and Fig 4 those of the communication processor. A main point of the MEDACS specification is the available data storage capacity of the dual-port memory. It has an addressable memory of 8 MByte, so that the storage capacity of MEDACS depends only on the number of the inserted memory boards. Each board has 64-kByte storage capacity to day. The trend goes rapidly to greater storage density; within a 19-in plug-in, for instance, a storage capacity of 1.6 MByte can be provided.

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The FARES system Let us now have a look at FARES, which we have developed as a more powerful computer system based on commercially available LSI 11-components of Digital Equipment Corporation. This additional computer system is not based on the CMOS technique and can only be used within the temperature range from 0°C to + 55°C. Fig 5 shows the system structure of FARES. Top left we see the different available CPUs which work on the well supported Q-Bus. All interfaces are standards, so that this system is very modular and very flexible. On the right-hand side we see the standard computer periphery of FARES, including MEDACS. The name FARES stands for the German word 'Fahrzeugrechnersystem' = car computer system. This

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M e a s u r e m e n t Vol 5 No 2, A p r - J u n 1987

Happe system can be programmed on board using high-level languages such as Fortran or Basic. Fig 6 shows schematically the structure of the flexible software system, FLEX 11, which we use with FARES/MEDACS.

The FLEX 11 software system The model of FLEX 11 consists of concentric shells. The features assigned to any shell are set over those of the next inner shell. The centre is the data base while the top shell represents the user interface. FLEX 11 manages the interaction. The database is included by a number of data handling modes. These are displayed to the user as a menu-system inside which he can activate the desired functions. The shell of the data-handling modes is surrounded by a service which guarantees a comfortable use of the system, even to the untrained user. He is guided by the computer by means of a dialogue which is easy to understand. This dialogue does not require any programming knowledge and a minimum of alertness. It is supported by a plausibility check which any user input is submitted to. Handling errors are caught by the system, so that they do not cause a program abort. Any valid inputs are reported by a logfile. This is useful for repeated test processing or a perturbation analysis. A block diagram of the complete FARES/MEDACS system is shown in Fig 7. The MEDACS part works at temperatures from - 4 0 ° C to +85°C, the other parts from 0°C to +55°C. E L F E is an older measuring

FARES

Fig 6 Structure of the software system FLEX 11 amplifier system of Volkswagen's which cannot be controlled by a computer. Because, at most, 15 % of the tests are done under very severe environmental conditions, the splitting of the computer aided measurement system into the MEDACS

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71

Happe part for the wider temperature range and the FARES part for the normal temperature range (from 0°C to 55°C) is very economic. All tests which are fulfilled under extreme temperature conditions can be done with MEDACS.

Configurations of MEDACS FARES with MEDACS

front-end

This configuration is a multi-purpose measuring system with large storage capacity (Winchester drive). Standard software FLEX 11 with menue technique affords great convenience with respect to data acquisition, data processing, graphics and documentation for test reports. Applicable at ambient temperatures from 0 ° to 55°C. Application examples: vehicle handling tests, brake tests, dynamic top-dead-centre measurements, time performance tests, etc.

Fig 10 View Jrom behind

MEDACS prepared via FARES for a special test MEDACS works (disconnected from FARES) as a selfreliant system for signal conditioning, data acquisition, preprocessing and storing. The stored data were postprocessed by FARES immediately after the test. Applicable at ambient temperatures from -40°C to +85°C. Application example: test of air conditioning systems. MEDACS-based special measuring equipment for longterm tests In this case MEDACS is PROM-programmed for a special measuring task. A very compact housing with integrated solid state memory is typical for this version. Postprocessing of data is done by FARES for instance. Applicable at ambient temperatures from -40°C to + 85°C. Application examples: controlling of catalysts in long term tests, fatigue load measurements in long-term test vehicles. Figs 9-12 show photographs of the FARES/MEDACS system mounted in test cars.

Fig 11 F A R E S / M E D A C S system mounted in the boot, with special power supply Jor long tests

Fig 9 F A R E S / M E D A C S in a rack in place of the passenger seat. The terminal with the keyboard has been fitted to the windscreen by means of a camera holder. This allows easy handling of the system by the driver. 72

M e a s u r e m e n t Vol 5 No 2, Apr-Jun 1987

Happe "-.,

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Fig 14 Dynamometer and vehicle co-ordinates

Fig 12 FARES/MEDACS monitor arrangement for long-term tests

Examples

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applications

The multicomponent wheel dynamometer The first example is a multicomponent wheel dynamometer with FARES/MEDACS instrumentation. Fig 13 shows a photograph of the multicomponent wheel dynamometer. It can easily be mounted on each standard Volkswagen drive shaft. The output signals of the four 3component transducers of the wheel dynamometer and the vehicle co-ordinate system are shown in Fig 14. The multicomponent rotating wheel dynamometer

measures directly the three components of all forces and moments acting on a wheel. Four 3-component quartz transducers are used for this task. They deliver together 12 outputs. The force components are Fxdl..4, Fydl..4 and Fzd~..4: They can be reduced to eight components by summing all components working in the same direction. From these eight outputs, six resultant values can be derived: • the three components of the resultant force • the three components of the resultant moment vector, both relative to the ISO-coordinate system of the vehicle. For this, the eight force components measured in the rotating wheel co-ordinate system have to be transformed into the ISO-coordinate system for cars with regard to the momentary angle of wheel rotation. This transformation should be possible with a high resolution of 1° of the angle of rotation at a speed of 200 km/h. For the 16 multiplying and the six summing operations in this worst case we have 90#s of time. Fig 15 shows the task definition for the computer for the transformation of the co-ordinates from the transducer or wheel-based rotating co-ordinate system into the vehiclebased co-ordinate system.

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Fig 15 Task of the computer for transformation of co-ordinates 73

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Fig 16 shows as an example the transformation equation for the vertical force Fzl. The single terms of the equation are products of the force components and of the values of the trigonometrical functions. A system of six equations of this form for each wheel has to be solved. To fulfill this high demand with respect to the computing power, we have developed a special co-ordinate transformation computer with multiplying digital/analogue converters. Fig 17 shows its block diagram. Fig 18 shows the block diagram of the complete measuring equipment for wheel dynamometers. In this form the system has been tested on a test stand with a built-in non-rotating wheel dynamometer. The data of both dynamometers agree very well. Figure 19 shows the complete measuring equipment in a car. The upper two plug-ins are the charge amplifiers of the piezo transducers. Fig 20 shows the rotating wheel dynamometer on a test stand, where its measuring values can be compared with those of the static three-component dynamometer of the test stand. The results of the test are shown in Figs 21-24.

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Determination of top-dead-centre The next example concerns us with the problem of the determination of top-dead-centre (TDC) of the piston of a running internal combustion engine. For this purpose we use microwaves, which we transmit via the glow plug bore

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Vol 5 No 2, Apr Jun 1 987

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Fig 24 Longitudinal force F x measured with a static normal load o f F~ = 3 k N at a speed o f V = 60 km/h

into the prechamber of the diesel engine (or via the insulator of the spark plug into the combustion chamber of a petrol engine). To illustrate the spatial relations, Fig 25 shows the cylinder barrel and cylinder head of a diesel engine with cut-away front half. At the left-hand side we see the

microwave oscillator, which is coupled to the prechamber by means of a quartz-filled waveguide. This is shown diagrammatically in Fig 26. The measuring method is based upon the Doppler shift of the microwaves, which are reflected by the piston moving up and down, and the varying cavity resonance

Measurement

Vol 5 No 2, A p r - J u n 1 9 8 7

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Happe properties of the combustion chamber. The system works with a frequency of 61.4 GHz and can be used for sparkignition as well-as for compression-ignition engines, particularly for direct-injection engines with a very small glow plug bore. A coupling device superimposes a part of the microwave oscillator signal on the microwave signal which is reflected from the cavity combustion chamber. The resulting signal recorded over the crank angle is symmetrical with the top-dead-centre (TDC). For data acquisition and data processing - i e , the calculation of the point of symmetry - FARES is used in a special assembly. To coordinate the microwave signal to the crank angle, different methods are possible:

Fig 25 Cylinder barrel and head o / a diesel engine with microwave oscillator

(1) Simultanous registration of the flywheel pins - 1 2 before and 20 ° after TDC. (2) Simultanous registration of the flywheel teeth. (3) Registration of the crank angle by means of a precision crank-angle marker.

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Fig 27 Microwave TDC measuring system on the basis o["F A R E S 76

M e a s u r e m e n t Vol 5 No 2, Apr-Jun 1 987

Happe According to the sequence of this listing, the accuracy of the measurement can be increased. The really interesting quantity is the distance of a special event from the dynamically measured TDC in crank angle degrees. For petrol engines, this event is the ignition spark; for diesel engines, it is normally the start of fuel injection. Fig 27 shows the TDC measurement system set up in the engine compartment of a car. In the middle background can be seen the microwave oscillator, which has nearly the volume of a human fist. On the display we can see the engine's speed of rotation in revolutions per minute, the injection angle and the deviation of the dynamically measured TDC from the statically measured TDC bY means of the flywheel pins. Fig 28 shows typical measured microwave signals over the crank angle - above for the cranked engine and below for the fired engine. Fig 29 illustrates the search process for the symmetry position of the signal curve. We shift a window of _ 20 ° crank angle (CA) in that manner over the signal curve that its centre is being moved from - 4 ° C A to +4°CA relative to the static TDC, which is given by the flywheel

pins. Each two measuring values symmetrical about the centre of the window are subtracted one from the other and the difference values are added. The sum of these difference values is co-ordinated to the crank angle value of the window centre. Then the window centre is shifted to the right and the difference process is repeated. If the window centre reaches the position + 4°CA, each centre angle value has its co-ordinated sum of differences. The dynamically measured TDC is there, where this sum of differences is minimum. Because of these necessary calculations, a dynamic measurement of TDC on line is not possible. The result is ready after a measuring time of 1 s. Let us now have a look at an example for the master-master version of MEDACS. Figure 30 shows the diagram of the structure of MEDACS as a temperature recorder for 101 measuring channels. In this mode MEDACS works disconnected from FARES, as a selfreliant system for signal conditioning, data acquisition, preprocessing and storing. The data transfer between MEDACS and FARES can be protected by means of the data transfer protocol KERMIT. For the postprocessing of the data all features of FARES are available.

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M E D A C S as a special s y s t e m The task is: Monitoring of catalysts in long-term tests under real conditions. (see fig 31) In general, there are two methods implemented. First, a time at level classification of 16 temperature channels and secondly, four transient memories for 16 channels with different kinds of trigger conditions. Additionally, there is the registration of time. Fig 32 shows the block diagram of the MEDACS Monitoring Recorder. On the left you see the signals coming from the sensors. The digital signals are captured by counters and the analogue signals by ADCs. After

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that, all the 16 digitised signals have to pass two procedures: the classification routine above and the continuous storage in the four transient memories below. At the end of the test the results of the classification are stored in the 16 classification memories with 32 elements each. On the other hand, there are data records available of up to four important periods from all signals, if the chosen trigger events have happened. Fig 33 shows the actual MEDACS-Monitoring Recorder. The outer dimensions are comparable to those of a children's shoe box. A special plug box is necessary for convenient connection of the different sensors. It is illustrated in Figure 34. The complete system is so small and lightweight that it was no problem to mount it into a car for the Monte Carlo Rally. For the postprocessing of the recorded data we have comfortable software for FARES. Fig 36 shows a test engineer in front of a monitor. On the screen we see 'mini'

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T5 = Temperatureof Lambda-Probe T9-10= Temperatureof Oil, Intake P13 = Pressureof Oil, Manifold, Charger v = DrivingSpeed

Fig 31 Monitoring of catalysts in long-term tests ~ Digital ~ Signals

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Fig 32 Block diagram of the MEDACS monitoring recorder 78

Fig 33 The MEDA CS monitoring recorder Measurement Vol 5 No 2, Apr-Jun 1987

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diagrams of the recorded data of all channels. You can select the diagram which is of interest. Fig 37 shows a plotted diagram of recorded data over the time axis. The ordinate axis is divided in relative units. The upper curve represents the manifold pressure p~. At the right-hand side appears the physical quantity, the range and the unit. Fig 38 shows as an example for classified data the frequency curve of the engine speed. rel, Einheiten

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Fig36Testengineerusingmonitor Measurement Vol 5 No 2, Apr-Jun 1987

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