Multiple-meter driving apparatus

Abstract: A multiple-meter driving system intends to cut down on the amount of space needed and to reduce the manufacturing cost by providing a single controller (12) including a processing circuit (16), the controller (12) being adapted collectively to drive a plurality of meters mounted in a vehicle such as motorcar or the like. Pulse signals each having a frequency corresponding to an input signal from a vehicle speed sensor or the like in the vehicle are counted with respect to their period T by a plurality of counters (10a, 10b). The counts are then supplied to the controller (12). DC signals each corresponding to an input from a fuel sensor or the like are converted into digital signals by an A/D converter (14), which are also supplied to the controller (12). The processing circuit (16) in the controller (12) time-shares these input signals so as to perform operations of 1/T, sine and cosine. The results are again supplied back to the controller (12) which in turn directs them to pulse width modulating circuits (18a, 18b) corresponding to the respective meters to be indicated. Since the respective meters are driven on a time-sharing basis, the single controller (12) including the processing circuit (16) can drive the meters collectively.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a multiple-meter driving apparatus, particularly to an apparatus that collectively drives a speedometer, a tachometer, a fuel meter, a water temperature meter and other meters, all of which are used in vehicles such as motor cars and the like. Description of the Related Art: A sensor used in a speedometer or a tachometer is usually one that outputs pulse signals having frequencies which vary depending on the vehicle speed or engine revolution speed, respectively. The frequencies of these pulse signals are counted to provide a meter angle signal. On the other hand, the sensor generally used in a fuel meter or oil pressure meter outputs DC signals which are then converted into digital values which in turn provide meter angle signals. Each resulting meter angle signal is applied to two coils Ls and Lc which are disposed perpendicular to each other, as shown in Fig. 1. These coils create a magnetic field which in turn rotates a magnet M disposed therein. The magnet M is connected, for example, with a speedometer, as shown in Fig. 2. The rotation of the magnet M causes an angular displacement of the speedometer. A multiple-meter driving apparatus according to the preamble of claim 1 is known from the document EP-A-0 370 616. This apparatus uses a processing means comprising input counters for receiving pulse signals, and A/D converter means for receiving analog signals. All routines for input signal sampling are interrupt driven. Additionally, the meter angle signals are outputted to all meters individually with interrupt routines, where the interrupt timings are defined by a rather complex processing. SUMMARY OF THE INVENTION It is the object of the present invention to provide a multiple-meter driving apparatus of simple construction, which can collectively drive a plurality of meters. The multiple-meter driving apparatus of the present invention is defined by the features of claim 1. Its control means outputs a signal with a fixed cycle time of e. g. 20 ms. As soon as this signal is provided, the previously calculated and temporarily stored meter angle signals are outputted, and the input signals related to different parameters are processed one after the other. Due to this function the processing means can operate very effectively. Therefore, a single processing means can be used for operating a plurality of meters. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view schematically showing the coil arrangement of a cross-coil meter. Fig. 2 is a view showing a meter indicator in the cross-coil meter. Fig. 3 is a block diagram of one embodiment of a multiple-meter driving system constructed in accordance with the present invention. Fig. 4 is a block diagram of the details of a processing circuit usable in the controller of Fig. 3. Fig. 5 is a flowchart of the operation of the multiple-meter driving system shown in Figs. 3 and 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in connection with one preferred embodiment thereof illustrated in the drawings. Referring to Figs. 3 and 4, pulse signals are outputted respectively from speed and revolution sensors and have frequencies corresponding to the levels of vehicle speed and engine revolution speed which are sensed by the sensors. These pulse signals are inputted to counters 10a and 10b, respectively. Each of the counters 10a and 10b receives a reference clock from a reference clock generator (not shown). The period T of the inputted pulse signals is counted by this reference clock. The counts are supplied to a controller 12 which comprises a four-bit microcomputer. On the other hand, DC signals are outputted respectively from fuel and water-temperature sensors and have voltage values corresponding to the residual fuel quantity and water temperature. These DC signals are inputted to an A/D converter 14 wherein they are converted into digital signals. The digital signals are then fed to the controller 12. The controller 12 comprises a processing circuit 16 which time-shares the inputted signals to produce meter angle signals. The meter angle signals are sequentially outputted to a drive circuit for driving the respective meters. Referring particularly to Figs. 4 and 5, the controller 12 and processing circuit 16 will be described in more detail with respect to their operations. In Fig. 4, the controller (4-bit microcomputer) 12 receives period values T1 and T2 of pulse signals from the counter 10a and 10b and also digital signals from the A/D converter 14, the digital signals being variable dependent on the residual fuel quantity and water temperature. The controller 12 takes and supplies these signals to the processing circuit 16 every 20 msec. More particularly, the controller 12 first takes the period T1 from the counter 10a and then feeds it to a filter 16a in the processing circuit 16. The filter 16a is a low-pass filter for removing only high-frequency components from the period T1 signal which has been provided from the controller 12 (S101 - S103). The filtered signal is then supplied from the filter 16a to a 1/T operator 16b. The 1/T operator calculates the inverse number 1/T of the supplied period T1 so as to calculate the frequency f1 of the original pulse signal (S104). The re sulting frequency f1 is then fed to an amplifier 16c wherein the frequency f1 is adjusted by a gain a from a ROM contained within the controller 12 or the processing circuit (S105). This causes a meter indication to be provided in response to the magnitude of input for every type of vehicle in which the meter is mounted. In the illustrated embodiment, the adjustment of the gain will be performed in accordance with the following equation: x = 720xf1/frxa/2048+o where x is an angle of deflection; f1 is a calculated frequency; fr is a selected range of frequency (including 250 Hz, 500 Hz, 1000 Hz and 2000 Hz); a is the aforementioned gain using 11-bit data which represents 1 ≦ a ≦ 2047; and o is an adjusted offset angle. After adjusted with respect to the gain, the frequency f1 is further offset adjusted (S106) and supplied to a sine operator 16d and a cosine operator 16e. Each of the operators 16d and 16e calculates sine and cosine signals to be supplied to the cross-coil meter so that it will indicate an angle corresponding to the frequency f1 (S107 - S108). The calculated sine and cosine signals are again supplied back to the controller 12. The controller 12 transfers these sine and cosine signals to the respective one of a number of pulse width modulating (PWM) circuits 18a, 18b, ... which are provided for each of the meters to be driven (S109). After the signal from the counter 10a has been processed and supplied to the corresponding PWM circuit, the controller 12 then takes the period signal T2 from the counter 10b. The period signal T2 is supplied to the processing circuit 16 wherein it is similarly processed to output a meter angle signal to the corresponding PWM circuit (S110). In such a manner, the period signals can be sequentially taken from the counters 10a and 10b and timeshared by the controller 12 to provide meter indications. A digital signal is taken from the A/D converter 14 and supplied to a filter 16f by the controller 12. The filter 16f is also a low-pass filter for removing high-frequency components from the digital signal, as in the filter 16a. After the high-frequency components have been removed from the digital signal, the latter is then supplied directly to the amplifier 16c without passing through the 1/T operator 16b, unlike the aforementioned period signal. At the amplifier 16c, the digital signal is adjusted with respect to the gain thereof. Thereafter, sine and cosine signals are similarly calculated and supplied to the controller 12 which in turn provides the sine and cosine signals to the corresponding PWM circuit. Subsequently, the controller 12 instructs the A/D converter 14 so that another DC signal is selected. The same process as described above is performed to output a meter drive signal to the corresponding PWM circuit. When 20 msec. elapses after all the inputted pulse and DC signals have been processed, the outputs of all the PWM circuits are simultaneously provided to the respective drivers 20a, 20b, ... to cause the cross-coil meters to perform their meter indications. During the next cycle through 20 msec., the same process is again made to update the PWM signals to be supplied for providing new meter indications in the meters (S110). In such a manner, detection signals from various sensors are supplied to the controller which in turn timeshares them to form meter angle signals. The meter angle signals are sequentially provided to the meters. Thus, a single controller can collectively control a plurality of meters. This saves on the space needed to contain the multiple-meter driving system and also reduces the manufacturing cost. Although the embodiment has been described as to the multiple-meter driving system handling two different pulse signals and two different DC signals, the number of pulse or DC signals may be selected suitably depending on the number of meters to be used in the vehicle.

Claims: A multiple-meter driving apparatus comprising: a plurality of counter means (10a, 10b), each for receiving a pulse signal corresponding to a first type of input, and for outputting a count value as a period signal representing the period of said pulse signal; A/D converter means (14) for receiving at least one DC signal corresponding to a second type of input, and for converting said at least one DC signal into a corresponding digital signal; a processing means (16) for processing said period signals and said at least one digital signal as input signals for providing output meter angle signals; and a plurality of drive means (18, 18b, ...; 20a, 20b; ...), each for driving an allocated meter of a plurality of meters of said multiple-meter based on said output meter angle signals as received from said processing means; characterized in that a control means (12) is provided for outputting a sequence of signals with a predetermined fixed interval to said processing means; and said control means (12) and said processing means (16) are arranged to perform the following steps: a) processing of a first one of said input signals when receiving a signal of the said sequence of signals with a predetermined fixed interval; b) generating a signal at the end of the processing of the said first input signal to provide the result of the said first processing to a first one of the said drive means; c) generating a signal, after step b) is finished, to start the processing of a next one of the said input signals and generating again a signal to provide the result of the said next processing to a next one of the said drive means; d) repeating step c) for all input signals one after the other to provide the respective results to one of the said drive means after the other; e) transferring, when having finished step d), the contents of each drive means to the allocated one of the said meter circuits; and f) restarting the above sequence of steps when receiving, after this transfer operation, the next signal of the said sequence of signals with a predetermined fixed interval. A multiple-meter driving apparatus as defined in claim 1 wherein said first type of input represents the speed of a vehicle or the revolution speed of an engine and wherein said second type of input represents the residual fuel quantity or cooling water temperature in the vehicle. A multiple-meter driving apparatus as defined in claim 1 wherein said processing means (16) comprises: a first low-pass filter (16a) for removing high-frequency components in the period signal outputted from each of said counter means; a second low-pass filter (16f) for removing high-frequency components in the digital signal outputted from said A/D converter means (14); a 1/T operator (16b) for calculating the inverse number 1/T of the period signal T outputted from said first lowpass filter (16a); an amplifier (16c) for amplifying the output of said 1/T operator (16b) or second low-pass filter (16f) with a given gain; a sine operator (16d) for sine calculating the signal from said amplifier (16c) to form a sine signal which in turn is outputted therefrom to said control means (12); and a cosine operator (16e) for cosine calculating the signal from said amplifier (16c) to form a cosine signal which in turn is outputted therefrom to said control means (12). A multiple-meter driving apparatus as defined in claim 3 wherein said drive means comprises a plurality of modulating circuits (18a, 18b) each for modulating the pulse width of each of the meter angle signals consisting of the sine and cosine signals from said control means (12), and a plurality of drivers (20a, 20b) for said meters, each of which is adapted to drive the corresponding one of said meters based on the corresponding one of the modulated signals from said modulating circuit (18a, 18b).

Inventors: FUKUDA KAZUYUKI, MURASE HIROSHI, FUKUDA, KAZUYUKI, MURASE, HIROSHI, FUKUDA, KAZUYUKI, ROHM CO., LTD., MURASE, HIROSHI, ROHM CO., LTD.
Applicants: ROHM CO LTD, ROHM CO., LTD.
Application year: 1992
Main classification: G01D21
IPC codes: G01D21, G01R19, G01R5, G01D7