United States Patent [191
`Steiner
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,939,652
`Jul. 3, 1990
`
`[54] TRIP RECORDER
`[75] Inventor: Jack Steiner, Quebec, Canada
`[73] Assignee: Centrodyne Inc., Montreal, Canada
`[21] App1.No.: 167,871
`[22] Filed:
`Mar.14,1988
`[51] Int. Cl.5 ............................................ .. G06F 13/00
`[52] U.S. C1. ........................ .. 364/424.04; 364/424.03;
`340/438
`[58] Field of Search .................... .. 364/424.0l, 424.03,
`364/424.04, 431.01, 442; 73/489, 490, 491,
`117.3; 340/438, 439
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`4,188,618 2/1980 Weisbart ...................... .. 364/424.64
`4,258,421 3/1981 Juhasz ct a1. .
`..... .. 364/442
`4,395,624 7/ 1983 Wartski ........... ..
`364/424.04
`4,646,241 2/1987 Ratchford et a1.
`.... .. 364/424.06
`4,692,882 9/1987 Skovgaard et al.
`364/424.01
`4,757,454 7/1988 Hisatake et a1. ......... .. 364/424.01
`Primary Examiner-Gary Chin
`Attorney, Agent, or Firm-Chilton, Alix & Van Kirk
`
`ABSTRACT
`[57]
`A system for monitoring, recording and displaying
`vehicle operating parameters is described, which is
`capable of simultaneously providing operating data for
`the driver, an on board summary of critical trip parame
`ters, and storage of monitored vehicle operating data
`for subsequently generating reports off-line which de
`scribe in detail the selected trip information. The system
`consists of a Vehicle Mounted Unit [VMU] which ac
`cepts inputs from a variety of sensors. Using these in-:
`puts, the VMU continuously computes the various pa
`rameters in order to provide the operating data as well
`as the on board trip summary. Detailed data are simulta=
`neously stored in the VMU memory for subsequent
`processing by an off-line computer. The contents of the
`VMU memory may be transferred to the computer in a
`variety of ways. A direct connection can be made be»
`tween the VMU in the vehicle and the computer; the
`VMU can be removed from the vehicle and subse
`quently connected to the computer; or an intermediate
`device, such as the optional Data Transport Unit
`[DTU] described, may be used to transfer VMU data to
`the computer.
`
`8 Claims, 10 Drawing Sheets
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`TOYOTA Ex. 1110, page 1
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`

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`US. Patent Jul. 3, 1990
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`TOYOTA Ex. 1110, page 2
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`TOYOTA Ex. 1110, page 4
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`TOYOTA Ex. 1110, page 5
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`US. Patent Jul. 3, 1990
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`US. Patent Jul. 3, 1990
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`Sheet 7 of 10
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`TOYOTA Ex. 1110, page 8
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`US. Patent Jul. 3, 1990
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`Sheet 891" 10
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`‘ 4,939,652~
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`TOYOTA Ex. 1110, page 9
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`

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`US. Patent
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`Jul. 3, 1990
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`Sheet 9 of 10
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`TOYOTA Ex. 1110, page 10
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`TOYOTA Ex. 1110, page 10
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`US. Patent Jul. 3, 1990
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`Sheet 10 0f 10
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`4,939,652‘ _
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`FIGURE IO
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`DATA ENTRY
`MEANS
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`TOYOTA Ex. 1110, page 11
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`4,939,652
`2
`same time requiring signi?cantly less memory than
`would be needed to record individual samples in a con
`tinuous stream. This compression scheme retains the
`bene?ts of having all the data available for subsequent
`analysis while greatly reducing the memory require
`ments.
`It is a further object of this invention to develop a
`data collection scheme that lends itself to high resolu- ‘
`tion recording for relatively short periods of time while
`minimizing the amount of memory required. This
`scheme is particularly useful in case of accidents but
`may also be used for any short duration event record
`ing.
`It is a further object of this invention to design the
`vehicle unit in such a manner that data transfer to the
`computer can be carried out in either of several ways.
`(1) by removing the unit from the vehicle and directly
`connecting said unit to the computer without any inter
`mediate device.
`(2) by directly connecting the unit in the vehicle to
`the computer without any intermediate device other
`than the connecting cable.
`(3) by using a portable data transfer unit to read the
`VMU (Vehicle Mounted Unit) while in the vehicle.
`(4) by connecting said VMU via commerical modem
`and telephone link to the computer.
`In accordance with the invention, a system may in
`clude one or more of the above data transfer methods.
`Thus, a system may include only transfer data method
`No. l or transfer data method No. 4. In addition, it is
`possible to have a single embodiment which includes all
`of the above data transfer methods.
`A further object of the invention is to provide a data
`entry scheme whereby the driver can enter data into the
`unit using only the available switches and displays
`which are an integral part of the VMU, and not requir
`ing a separate input device. This objective is realized in
`a manner which requires that the driver needs only a
`limited number of codes, and the resulting data are
`available in the computer report in man-readable form.
`A circuit is also described which provides an orderly
`shut-down of the on-board unit in the event of either
`power interruption or complete removal of the unit
`from the vehicle.
`These objects will be more clearly understood with
`reference to the accompanying detailed description, the
`appended claims and the drawings, in which:
`
`1
`
`TRIP RECORDER
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to the ?eld of vehicle monitor
`ing systems. In particular it deals with the method of
`compressing data for on board storage and subsequent
`transfer of these data to a computer for analysis.
`2. Description of the Prior Art
`Prior art vehicle monitoring systems have either pro
`vided display means only, with no provision for storage
`means, or they have used on-board paper or magnetic
`tape as the storage media, as disclosed in U.S. Pat. Nos.
`3,099,817; 3,964,302; 4,050,295; 3,864,731; 3,938,092;
`3,702,989 and 3,792,445. Such electromechanical stor~
`age means suffer the disadvantages of being unreliable
`and bulky. Purely electronic solid-state memory has
`been used, but one of the difficulties of using solid-state
`memory to provide storage for continuous real-time
`data, such as has been disclosed in U.S. Pat. No.
`4,188,618, is that this approach requires large amounts
`of memory to achieve the required resolution over a
`recording period of several weeks. Some systems that
`have used solid-state memeory have not recorded con
`tinuous real-time data. Instead, they compared the raw
`data to pre-set limits, and recorded only those data
`which fell outside the limits. A system representative of
`this approach is the subject of U.S. Pat. No. 4,258,421.
`The limitations to this approach are that the raw data
`are not available for subsequent analysis. One is thus
`unable to scrutinize the data for events that were within
`the previously defined limits, since these were not re
`corded.
`Another problem has been the question of how to
`transfer the on-board data to the off-line computer.
`There have been several approaches to this problem.
`Either an intermediate unit was used to transfer the data
`to the computer, as disclosed in U.S. Pat. No. 4,258,421,
`or the memory portion of the on-board unit was made
`40
`removable, in which case some additional unit was still
`required to read the data and interface to the computer.
`This latter example has been disclosed in U.S. Pat. No.
`4,188,618, which also describes other methods of trans
`ferring the data to the computer, each of which requires
`a separate embodiment.
`It is a desirable feature of vehicle recording systems
`to allow the driver or operator to enter data which are
`subsequently available as part of the computer report. It
`is also desirable that these data be presented in a man~
`readable form (such as English language). The solution
`to this problem has generally been to provide a separate
`input device, as disclosed in U.S. Pat. No. 4,258,421.
`This device may be an alphanumeric keyboard or some
`other device which presents codes to the recording
`system.
`In the latter case the codes can then be included in the
`report directly, or they can be translated into man-read
`able form by the computer. The problem with this ap
`proach is that, due to the large amount of information
`that generally needs to be entered, the driver would
`need a very lengthy list of all the codes and their mean
`ings.
`
`45
`
`' BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an overall block diagram of the vehicle
`monitoring and recording system;
`FIG. 2 shows a front view sketch of an embodiment
`of the vehicle mounted unit;
`FIG. 3 shows a memory map of the compression
`scheme in the preferred embodiment of the invention;
`FIG. 4 shows in schematic form the circular memory
`buffer used in the high resolution data collection
`scheme;
`FIG. 5 is a block diagram of the power fail detection
`scheme in the preferred embodiment;
`FIG. 6 is a block diagram of the vehicle mounted unit
`embodying the principles of the invention;
`FIG. 7 is a pictorial representation of a mounting
`bracket which permits removal of the vehicle mounted
`unit in accordance with the invention;
`FIG. 8 shows a ?owchart of the mechanism of data
`transfer in an embodiment of the invention;
`
`SUMMARY OF THE INVENTION
`It is an object of this invention to develop a data
`compression scheme that can provide “real-time" data
`as opposed to data outside pre-set limits, while at the
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`FIG. 9 is a detailed schematic diagram of the power
`crossing he would enter one code corresponding to the
`fail detection circuit of FIG. 6; and
`category, border crossings, and a subsequent code indi
`FIG. 10 is a pictorial representation of the optional
`cating the actual State line. As a further example, if the
`Data Transport Unit.
`driver needed to indicate the weight of the load he was
`carrying, he would enter one code for load weight and
`then enter the actual weight. At the time of report gen=
`eration, the computer would use the category entry as a
`key to retrieve the text for both the category and the
`data. The entered data are time-stamped for detailed
`reporting.
`Although a numeric code has been discussed above, it
`will be apparent to one skilled in the art that it would be
`equally appropriate to use an alphanumeric code con=
`sisting of alphanumeric characters.
`FIG. 3 is a memory map of the compression scheme
`referred to in the SUMMARY OF THE INVEN
`TION. This compression scheme allows the recording
`of “real-time” data while signi?cantly reducing the
`amount of memory required for data storage, and as a
`result is. more readily adaptable for use with solid state
`memories. A single parameter is chosen, and at ?xed
`time intervals, data representative of the total activity
`during that time interval are recorded in contiguous
`memory locations 301. The compression is achieved
`primarily by the fact that each record is a summary of
`the activity of the function during the time interval, as
`opposed to being an instantaneous sample. In the case of
`vehicle speed for example, one could record average
`speed during the time interval. Or, in the case of dis
`tance travelled, one could record the total distance
`travelled in each time interval.
`At each time interval therefore, a summary of the
`particular activity chosen is recorded in contiguous
`memory locations 301. Thus, if the time interval is
`chosen to be one second, there would be 3600 records in
`each hour of use. Whereas, if the time interval is chosen
`to be one minute, there would only be 60 records in
`each hour of use. It is evident that the latter choice of
`interval use 60 times less memory than the former.
`However, the former choice of time interval being
`much shorter than the latter choice of time interval,
`results in a more accurate representation of the instanta
`neous value of the activity, and therefore has better
`resolution. The value of the time interval is thus a trade
`off between available memory and resolution. The
`“real-time” data 303, are shown in FIG. 3 as the adja
`cent memory locations of the contiguous memory sec
`tions. To achieve further compression, data are not
`recorded during the interval that the function has zero
`value. Instead, a summary block, item 302, is inserted in
`memory, which indicates the length of time the function
`was zero. A summary block may also contain data cor
`responding to the total activity, since the last summary
`block, for functions with less stringent resolution re
`quirements.
`Although the illustrated embodiment contemplates a
`summary block between two memory locations con
`taining data, it will be apparent to one skilled in the art
`that the periods of inactivity can be summarized in
`other predetermined memory locations which are not
`contiguous with the remainder of the memory loca
`tions.
`FIG. 4 is a summary of a data collection scheme
`which lends itself to high resolution data monitoring for
`short periods of time. This provides a ‘magni?ed’ view
`of the activity of one of the functions prior to and fol
`lowing a speci?ed event.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`FIG. 1 is an overall block diagram of the system. It
`consists of a vehicle mounted unit 104 which receives
`inputs from various input means 101. The input means
`are transducers 102 which provide the VMU with elec
`trical signals corresponding to the measured parame
`ters. The VMU may also accept inputs from discrete
`devices item 103 which monitor the state of various
`vehicle components. The VMU processes the input data
`for immediate or subsequent display and records data in
`its internal memory for computer 111 report generation.
`At the end of a trip, or whenever the customer so de
`sires, data are transferred from the VMU to the com
`puter 111 using transfer means 105. Several alternatives
`20
`of transferring the data as described in SUMMARY OF
`THE INVENTION are shown in FIG. 1 as items 109,
`106, 107 and 108. These are all_available in a single
`embodiment.
`Although FIG. 1 illustrates the availability of all four
`data transfer methods in a single embodiment, as above
`described, it is within the scope of the invention to
`include only a single data transfer method in a system,
`or to include two or three of the data transfer methods
`in any inventive system.
`FIG. 2 is a front view sketch of the preferred embodi
`ment of the VMU. The Status Indicators 201 and Dis
`play Banks items 202 and 203, are used to provide con
`tinuous driver information as well as statistical data'for
`owners or managers.
`’
`The switches, items 204, 205, 206 and 207, are used to
`control the operation of the VMU and to select the data
`to be displayed. The above displayed outputs may be
`inhibited under program control and, in any event, do I
`not form an essential feature of this invention.
`A method is described which allows these same
`switches, in combination with the display means, to
`provide a driver data entry scheme that avoids the ne
`cessity of an external input device. Since there are only
`four switches, it is necessary to provide codes to repre
`sent the input data. The four switches, items 204, 205,
`206 and 207, in combination with the Display Banks
`items 202 and 203, can represent numeric codes 0000
`through 9999, which gives a total of 10,000 individual
`numeric codes. Each of these numeric codes can then be
`assigned an input data item. For example, the numeric
`code 0101 might be chosen to represent “Border cross
`ing Quebec to New York”.
`The large number of codes in such a simple scheme
`would be very inconvenient to the user, since he would
`be forced to memorize numerous different codes for all
`of the input data that he needs. The data entry scheme
`in this invention reduces the number of input codes that
`would otherwise be required in the simple scheme de~
`scribed above, and still provides the entered data in
`man-readable form in the computer report.
`This is accomplished by separating the data into two
`parts: a data category; and the data itself. A single nu
`meric code is entered ‘corresponding to the data cate
`gory. Switch 206 is used to slew the displays to the
`required number. This is followed by entering the ac
`tual data in a similar fashion using switches 204 and 205.
`As an example, if a driver wishes to indicate a State line
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`TOYOTA Ex. 1110, page 13
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`4,939,652
`5
`6
`The data compression scheme described above is
`FIG. 6 is a block diagram of the hardware in the
`preferred embodiment of the VMU. The main compo
`used to continuously record data in a circular buffer.
`The time interval however, is chosen to be far shorter
`nents of the VMU hardware are a microprocessor 504
`and associated Input/Output (I/O) and integral timer
`than that used in the compression scheme described
`above, to provide greater resolution. This is acceptable
`unit 615, program memory 606, data memory 506, mem
`ory for program control parameters (program data
`since the event of interest is of short duration, resulting
`memory) 622, display interface 613, user data entry
`in a relatively short record. The circular buffer 400 is
`interface 623, sensor interface 602, serial communica
`used such that data are recorded in the buffer until it is
`tions interface 610, 611 and real-time clock circuitry
`full, as de?ned by memory address pointer 402, at
`which time recording continues at the beginning of the
`505, 609. Also shown are the reset and powerfail detect
`circuitry 616, the power supply 604 and the internal
`buffer, as de?ned by memory address pointer 403, over
`miniature backup battery 509.
`writing previous data. This provides a record of the
`The microprocessor 504 and I/O and timer 615 units
`latest activity of the vehicle. As in the main compres
`may comprise any of a number of currently available
`sion scheme, data are not recorded during a period of
`units, for example the National Semiconductor NSC800
`“no activity”. Instead, an indication of the duration of
`this period is inserted into storage to improve compres
`and NSCSIO, respectively. The program memory 606,
`comprises an erasable programable read only memory
`sion.
`Again, the summary blocks of the inactivity periods
`(EPROM) such as National Semiconductor 27C256.
`need not be in line with the remainder of the summary
`The data memory 506, comprises random access mem
`blocks but can be disposed at other predetermined
`ory (RAM) devices, such as NEC 4464. Program data
`memory 622, comprises an electrically erasable pro
`memory locations.
`A method is provided whereby the data collected for
`gramable read only memory (EEPROM) such as NCR
`59308. The display interface 613, comprises a digit se
`some time prior to an external event 404 and for some
`time following that event, are retained. This is achieved
`lector, such as NSC 74HC4017, an output driver, such
`by inhibiting further writing to the circular buffer 400.
`as Motorolla ULN2003, and a binary~coded-decimal
`Any of various types of discrete input devices, such as
`(BCD) to seven-segment display driver, such as NSC
`74I-IC48. The user data entry interface 623, comprises
`a manual or impact switch, may be used to initiate data
`retention via the read/write control 401.
`an input buffer such as NSC 74HC244. The sensor inter
`Data retention may be accomplished by copying the
`face 602, comprises an input buffer, such as NSC
`74HC244, and a prescaler. The serial communications
`contents of the circular buffer 400, to some other loca
`interface 610, 611, comprises a universal asynchronous
`tion in memory, or by allocating a different memory
`receiver transmitter (UART), such as National Semi
`area for subsequent use as a circular buffer. Memory
`address pointers 402 and 403 are provided to determine
`conductor 858, and an RS232 driver such as Motorola
`MC1488. The real-time clock circuitry 505 comprises a
`the record start and stop locations within the buffer.
`A method is provided for suspending the normal
`real-time clock chip, such as NSC 58167A, and a crystal
`oscillator 609.
`operation of the device in the event of a power failure,
`and for recording the time and duration of said failure.
`There are provided address and data lines 619 and
`I/O lines 618 to interconnect the various components of
`The feature of recording the time and duration of the
`the VMU. Also shown are the sensor inputs 630, dis
`failure is particularly useful to detect unauthorized re
`crete device inputs 631, user data entry switch inputs
`moval of the unit, particularly since the unit is designed
`633 and event switch inputs 632. The discrete device
`to be portable for data transfer to the computer. The
`method comprises:
`inputs 631 may be used to sense the occurrences of
`brake applications, headlight on/off and the like, while
`(1) electronic circuitry to detect and respond to
`the data entry switch inputs 633 are provided for enter
`power failure.
`45
`ing driver operational codes, such as border crossings,
`(2) means of recording the time, data and duration of
`amount of load being carried and the like. Event switch
`the power failure.
`inputs 632 are used to trigger the high resolution
`FIG. 5 is a block diagram of the power fail circuitry.
`scheme described below, automatically or manually
`A drop in the supply voltage along line 501 is detected
`by the power fail detect circuitry item 502 and causes an
`when an accident occurs.
`Power is supplied to the unit from the vehicle’s bat
`interrupt to be issued to the microprocessor 504 along
`tery 605, through the power supply 604 when the unit is
`line 510. The microprocessor 504 then initiates execu
`mounted in the vehicle, and when it is removed from
`tion of a power fail routine which saves, in non-volatile
`the vehicle the backup battery 509 provides sufficient
`memory 506, data currently being processed, as well as
`power to maintain the data stored in random access
`the current time and date. The signal on line 510 is also
`memory 506 and the real-time clock chip 505, for a
`fed to the reset circuitry item 503, which after allowing
`period of approximately six months.
`sufficient time for the microprocessor 504 to complete
`The display interface 613 provides a link between the
`it’s shut down routine, halts the microprocessor 504.
`microprocessor 504, and the front panel display 612.
`When power is restored, the time and date are recorded
`in memory 506, thereby enabling the duration of the
`The user data entry interface 623 provides an interface
`to the push-button switches 633 used by the operator for
`power failure to be determined.
`entering data and selecting operating modes of the dis
`play 612.
`The microprocessor 504 serves to execute a control
`program stored in program memory 606, which con
`trols the operation of the VMU. The microprocessor
`504, operating in accordance with said control program
`executes the following functions:
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`The following description is given only as an example
`of a possible embodiment of the invention and is in no
`way intended to define or limit the scope of the inven
`tion.
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`TOYOTA Ex. 1110, page 14
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`

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`4,939,652
`7
`8
`(1) Causes receiving, processing and storing, in data
`The high resolution data collection scheme, in the
`preferred embodiment, is implemented by using a 60
`memory 506, of data received from the sensor inputs
`630, and various switch inputs 631, 632, 633.
`byte area in data memory 506, as a circular buffer, to
`(2) Emits signals to drive the display 612.
`record, at one second intervals, the average speed at
`(3) Controls the receiving and transmitting of serial
`which the vehicle was moving during the one second
`interval. The average speed at each interval is stored at
`, data between the serial communications interface 610,
`consecutive byte locations in the 60 byte buffer. Refer
`611 and communications port 120.
`ence to FIG. 4, will promote a better understanding of
`(4) Responds to an interrupt from the power fail
`the scheme._
`detect circuit 616, and provides an orderly shut-down
`Whenever the average speed is zero for a period of
`of the microprocessor 504, in the event of a power
`failure.
`three seconds or more, a summary block is stored in the
`memory buffer, instead of recording zero distance, for
`Means are provided to allow customizing of the oper
`the duration of time for which zero data is received
`ation of the VMU control program. This is accom
`from the distance sensor. The summary block contains
`plished by storing parameters, used by the program, in
`values which indicate the length of time for which the
`program data memory 622. These parameters can be set
`average speed was zero.
`up and changed, at any time, by an off-line computer,
`Locations in the buffer are accessed in a circular
`example item 111 of FIG. 1, or the optional Data Trans
`manner, as described in the DETAILED DESCRIP
`port Unit [DTU], item 107 of FIG. 1.
`TION OF THE INVENTION, so that, at any one
`Compression of “real-time” data in the preferred
`instant, the buffer contains the average speed at each
`embodiment is accomplished in the following manner.
`second during the preceding'60 seconds. Two switches
`Refer to FIG. 3 also.
`'
`632, are provided to initiate transferring of the contents
`Sensor inputs 630, are polled by microprocessor 504,
`of the buffer to an area of data memory where it will be
`at a rate high enought to detect any data from the sen
`retained for subsequent analysis. One switch is an im
`sors. The data received from the sensors in this manner
`pact triggered switch that‘ will activate if the vehicle is
`25
`are in the form of electronic pulses. The count of pulses
`involved in an accident, and the other switch is a push
`received from each sensor is retained in registers lo
`button switch that may be manually activated by the
`cated in an area of data memory 506, reserved for this
`driver of the vehicle. A separate area in data memory
`purpose. Distance is chosen as the primary function in
`506, is allocated for retaining the contents of the circu
`this embodiment. At successive ?xed time intervals, the
`lar buffer, for each switch.
`count of pulses received from the distance sensor 640,
`The impact triggered switch may comprise a self
`during each ?xed time interval, is stored in memory
`triggering device such as an accelerometer switch, or a
`buffer within data memory 506, at contiguous locations,
`level detector switch. Either the self-triggering device
`and the register used to accumulate the count is reset to
`or the manual switch can be activated for any of a set of
`predetermined conditions, for example, emergency con
`ditions or simply the desire of the driver to retain the
`information.
`Activation of either switch causes the data from the
`circular buffer to be stored in the appropriate area of
`memory, after a delay of 15 seconds. The retained data
`therefore represents vehicle activity for a time period
`starting 45 seconds prior to activation of either switch,
`and ending 15 seconds after such activation. Along with
`the buffer contents, the time of switch activation and
`the memory address pointers are also stored, to permit
`association of the data with a speci?c time during analy
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`zero.
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`’
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`Whenever there is zero data received from the dis
`tance sensor for arspeci?ed time period, a summary
`block is stored in the memory buffer, instead of record
`ing zero distance, for the duration of time for which
`zero data is received from the distance sensor. When
`pulses are again received from the distance sensor, the
`process of storing distance data resumes at the memory
`location following the summary block entry.
`In the preferred embodiment, a summary block con
`tains the following data: a count of the number of ?xed
`time intervals during which the received data was zero;
`values representative of the total number of engine
`revolutions since the previous summary block entry;
`maximum RPM since the previous summary block en
`try; total fuel consumed since the previous summary
`block entry; and a date and time entry indicating the
`time at which recording of distance data resumed.
`The fuel data and engine RPM data which have been
`stored in the respective registers of data memory 506, as
`explained in the previous paragraphs, are transferred to
`the summary block 302. The respective registers of data
`memory 506 are then reset to zero, permitting data to be
`accumulated once again, for inclusion in the next sum
`mary block 302 entry.
`In the preferred embodiment, the memory available
`for the storage of the compressed “real-time” data is
`approximately 13,000 bytes. The distance data values
`are stored in successive bytes of this available memory,
`for each ?xed time interval. The ?xed time interval is
`user selectable to be either 15 or 60 seconds, depending
`on the desired data resolution. The data capacity of the
`VMU depends on the speci?c use of the vehicle, but is
`typically in the range of two weeks to twenty days.
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`sis.
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`Data transfer from the VMU is accomplished by
`means of the serial communications interface 610, 611
`and communications port 120. A communications pro
`tocol is implemented as part of the VMU control pro
`gram for data integrity during transmission. The physi
`cal size of the VMU is such that it is easily transportable
`and a mounting bracket is provided to permit easy re
`moval of the VMU from the vehicle so that it may be
`transported to the vicinity of the off-line computer for
`data transfer. FIG. 7 is a pictorial representation of the
`VMU and mounting bracket. The mounting bracket 701
`is meant to be installed permanently in the vehicle and
`allows the VMU to be easily connected or disconnected
`by means of the connector 702. When so installed in the
`mounting bracket 701, the VMU can be secured using
`the retaining screw