GB2255411A

GB2255411A - Vehicle speedometer

Info

Publication number: GB2255411A
Application number: GB9208838A
Authority: GB
Inventors: Jerry Alan Gohl; Richard Lee Abel; Gail Marie Marchlewski; James Edward Nelson
Original assignee: Delco Electronics LLC
Current assignee: Delco Electronics LLC
Priority date: 1991-05-02
Filing date: 1992-04-23
Publication date: 1992-11-04
Anticipated expiration: 2012-04-23
Also published as: DE4214323C2; JPH05133961A; GB9208838D0; GB2255411B; DE4214323A1

Description

225)5411 VEHICLE SPEEDOMETER This invention relates to apparatus for

indicating the speed of a vehicle and more particularly to a nonlinear analogue speedometer.

The conventional automotive analogue speedometer includes a gauge with a needle pointer whose angular deflection indicates vehicle speed on a graphic display. In general, the angular deflection is determined by a signal with a frequency or amplitude that is indicative of vehicle speed in a substantially linear relationship.

Often a speedometer with a very high maximum indicated speed is desired on a vehicle. Achieving a speedometer with a high maximum indicated speed is difficult in certain instances because the is speedometer must be kept small, the maximum angle of deflection of the gauge is limited, and the required accuracy of the gauge may be difficult to achieve.

The required accuracy is typically a function of speed, e.g., the indicated speed must be within three percent of the actual speed. At low end speeds, the speedometer must be very accurate because the allowable percentage deviation allows only very few miles per hour deviation, and consequently a very low angular deviation for the pointer. Additionally, the low end speeds are where most drivers operate their vehicles a majority of the time, so it is important for the driver to be able to read these vehicle speeds accurately. The larger the speed range to be fitted into a scale of limited size and limited angular deflection, the smaller the angle between speed increments on the gauge and the more crowded and difficult the scale is to read.

The present invention seeks to provide improved apparatus for indicating the speed of a.

vehicle - According to an aspect of the present invention, there is provided apparatus for indicating the speed of a vehicle comprising an analogue speedometer; a driver circuit for driving the analogue speedometer and having a gain adjustable between an output connection and a feedback connection; and an amplification circuit coupled between the output connection and the feedback connection of the driver circuit and adapted to cause the driver circuit to drive the analogue speedometer in a non-linear manner.

The invention can provide an analogue speedometer that can indicate a high maximum speed without increasing the amount of space required and without sacrificing accuracy or readability at vehicle speeds that the driver most often uses. Such a speedometer can allow a high maximum indicated speed with an easily readable scale in the portion of the speedometer most used by the driver. Thus, it is possible to satisfy both maximum indicated speed requirements and accuracy requirements, while providing a speedometer easily readable by the driver.

A preferred embodiment includes a driver means. a gauge means, and a scale. The driver means receives an input signal of a frequency or magnitude substantially linearly related to vehicle speed and, in response to the input signal, develops a drive signal for the gauge means which, for at least a substantial part of the vehicle speed range, is non-linearly related to the input signal. The gauge means includes a pointer which is deflected in relation to the drive signal and indicates vehicle speed against a non-linear scale.

II An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a graphics plate of a prior art speedometer;

Figure 2 shows a first embodiment of graphics plate; Figure 3 shows a second embodiment of graphics plate; Figure 4 shows a schematic diagram of an embodiment of gauge driver; Figure 5 shows a circuit diagram of a first embodiment of gauge driver circuit; Figure 6 shows a circuit diagram of a is second embodiment of gauge driver circuit; and Figure 7 is a schematic diagram of an alternative embodiment of gauge driver.

Referring to Figure 1, a conventional speedometer has a graphics plate 10 with an evenly spaced continuous scale 12. For example the angle, a, between every increment of ten miles per hour (MPH), measured from centre point 14, is constant. Consequently, for a conventional speedometer with a pointer (not shown) to be accurate, it must be driven such that its angular displacement is linearly related to vehicle speed. As will be apparent, the higher the maximum speed within a given angular space, the smaller will be the angle a between consecutive speed indications. As a gets smaller, the speedometer becomes harder to read and harder to control accurately.

Figure 2 shows a graphics plate 16 of a first embodiment of analogue speedometer. The graphics plate 16 includes a plurality of graphic symbols providing a continuous scale divided into two portions, 18 and 22 on either side of switching point 20. In portion 18 the ten mile per hour speed indications are evenly spaced at an angle P. In the portion 22, the angular spacing (r N) between each successive 10 MPH speed indication is gradually reduced. For example, r, between the 70 and 80 MPH indications is greater than r 2, between the 80 and 90 MPH indications, which is greater than r 3, etc.

The benefit of this construction of scale can be seen when Figure 2 is viewed in comparison to Figure 1. Both scales have the same maximum indicated speed, approximately 145 MPH, and both scales have substantially the same maximum deflection angle. However, the speed indications of portion 18 of the scale in Figure 2, representing the vehicle speeds which are most commonly used by a majority of vehicle drivers, are spaced by greater angles P than the same indications in Figure 1. This larger angle p allows the vehicle driver to determine more accurately the vehicle speed and allows a greater angular tolerance for the speedometer pointer.

The speed indications of portion 22, which are spaced progressively closer together, represent speeds rarely used by many drivers. In general, it is less important whether a driver is travelling at 186 or 191 kilometres per hour (115 or 118 MPH) than it is whether the driver is travelling at 58 or 62 kilometres per hour (35 or 38 MPH). Additionally, the decreasing angle between indicated speeds in portion 22 has little effect on speedometer tolerance requirements because at higher speeds there can generally be greater indicated speed deviation. For example, 3 percent of 57 kilometres per hour (35 MPH) is about 1.5 kilometres per hour (1 MPH) allowable deviation, but 3 percent of 162 kilometres per hour 3r (100 MPH) is about 4.9 kilometres per hour (3 MPH) of allowable deviation. Therefore, the closer spacing between the higher speed indications is not detrimental.

Figure 2 is just one embodiment of how the speedometer scale may be arranged. Alternative embodiments include having a fixed angle r for the portion 22 of the scale, e.g., rl=r 2=..=r n <P, or having a scale in which the angles between the successive speed indications are progressively smaller throughout the entire scale range, for example as shown in Figure 3 where A 1 >A 2 >... > A N The general structure of a first embodiment of gauge can be better understood with reference to Figure 4. A signal indicative of vehicle velocity on line 30 is fed into the driver circuit 32. In general, the velocity signal is a series of pulses, e.g. 6500 pulses per kilometre (4000 pulses per mile). The driver circuit 32 provides a drive signal on drive lines 34 to a pointer rotator 36 for moving the pointer 38, attached to shaft 37. Preferably, the pointer rotator 36 is an air core gauge.

The pointer 38 moves to and fro on the non-linear speed scale of graphics plate 16 in non-linear relation to the velocity speed signal on line 30, in a manner such that an accurate indication of vehicle speed is indicated by the pointer 38.

Referring to Figure 5, which shows a first embodiment of driver circuit 32, the driver circuit includes a gauge driver IC 120 which is a standard air core meter driver integrated circuit, for example the driver LM 1819 readily available to the public from National Semiconductor TM, on which the following description is based. The gauge driver IC

120 has a gain control output at pin 8 and inputs at pins 5 and 6. Altering the characteristics of the circuitry between the gain control output and inputs adjusts the gain of a Norton amplifier 140 of the driver IC 120.

Power is supplied to the driver IC 120 from line 65, connected to the vehicle power supply. Power travels through diode 82 and resistor 84 to pin 13 of driver IC 120 to provide power to the internal regulated power supply 122. The circuit comprising zener diodes 112 and 118, capacitor 114, and resistor 116 protect the driver IC 120 against voltage spikes and provide a reference voltage on line 115 for function generator 134 of driver IC 120 (through pin 1) and for the air core gauge 149. The driver IC 120 is connected to ground 60 at pins 7 and 14. Within the driver IC 120, the internal regulated power supply 122 provides a temperature stable regulated voltage, V.,,., at line 66 (pin 11).

A velocity signal in the form of pulses on line 30 (the velocity signal is of conventional form) flows through diode 50 to the circuit comprising resistors 52 and 58 and capacitor 56, which filters out high frequency noise from the velocity signal. The filtered signal on line 54 flows through resistor 25 62 to line 64, connected to pin 10 of driver IC 120, which in turn is connected to the base of internal transistor 124 of driver IC 120. The emitter of transistor 124 is grounded, as shown, and the collector (pin 9) is connected to resistor 86, which couples the transistor 124 to the output of operational amplifier 77. The signal on line 64 controls the current through transistor 124 which affects the voltage level at pin 9. The collector of transistor 124 (pin 9) is connected to capacitor 88 and resistor 90, 11 I 1 11 which is connected to the non-inverting input 144 of Norton amplifier 140 (pin 6). The output of the Norton amplifier 140 is coupled to the function generator 134 through line 138 and to pin 8 of the driver IC 120. Trimming resistor 126 and capacitor 128 are connected in parallel between pin 8 and the inverting input 142 of the Norton amplifier 140, at pin 5. Trimming resistor 126 is trimmed during circuit manufacture to calibrate the gain of the Norton amplifier 140, which, as explained below, affects the angular deflection of pointer 38 on portion 18 of the speed scale.

The output of the Norton amplifier 140 is also connected to resistor 98, which is connected to the non-inverting input of operational amplifier 94 and to ground 60 through resistor 104. The circuit comprising operational amplifier 94 and resistors 96, 98, 104, 106, 108, and 110 control the switch point 20 (Figure 2) and the roll-off rate (that is, the rate at which r N progressively changes) of the speedometer. The switch point 20 is set by resistors 108 and 110, which form a voltage divider between the regulated voltage on line 66 (pin 11) and ground 60, providing a reference voltage Vsw at junction 109. Resistors 96, 98, 104 and 106 control the roll-off rate. Resistor 96 is preferably of equal value to resistor 98 and resistor 104 is preferably of equal value to resistor 106.

The output of the operational amplifier 94 is fed, via resistor 80, to the non-inverting input of operational amplifier 77. operational amplifier 77 is connected in a circuit using four equal resistors 68, 70, 76 and 80, as shown, and has an output voltage V 2 on line 78, which is coupled to the collector of transistor 124 (pin 9 of driver IC 120) through resistor 86. The voltage V 2 is controlled by operational amplifier 77 when operational amplifier 94 is active, such that:

V2 = VREG - V I When the output of the Norton amplifier 140 (Vp,) is less than the voltage at the junction 109 of resistors 108 and 110, the operational amplifier 94 is inactive (V1 at line 92 equals zero volts and V2 equals the regulated voltage on line 66, V REG) and the function generator 134 is driven by line 138, linearly. When the output of the Norton amplifier 140 (Vp8) equals the voltage at junction 109, the switch point 20 (Figure 2) is reached. When the output of the Norton amplifier 140 (Vp,) is greater than the voltage, Vsw, at junction 109, the operational amplifier 94 becomes active, with an output voltage, V1:

V, -= (R /R V.

106 96) (Vp8 - Sw), if V P8 > V Sw.

Altering the voltage on pin 9 directly affects, via capacitor 88, resistor 90 and the non-inverting input 144 of the Norton amplifier 140, the output (line 138) of the Norton amplifier 140. The output of the Norton amplifier 140 on line 138 controls the function generator 134, which drives the air core gauge 149.

The air core gauge 149 has first and second coils 148 and 150 mounted at 90 degrees to each other. The function generator 134 generates drive signals in lines 136 and 130 for the first and second coils 148 and 150 of the air core gauge 149. The signal on line 130 is proportional to the cosine of the desired angular deflection of the pointer 38 (Figure 4). The signal on line 136 is proportional to the sine of the desired angular deflection of the pointer 38. When the coils 148 and 150 are driven 1 with the cosine and sine signals, the shaft 37 (Figure 4) of the gauge is rotated to the desired deflection angle.

The angular deflection, 6, of the air core gauge 149 can be described as follows:

E) = Kf SS V 2 R 126 IF where K is the gain factor of the function generator 134, typically 54 degrees per volt, fss is the frequency of the velocity signal on line 30, V 2 is the voltage on line 78 and R is the resistance of 126 resistor 126. When operational amplifiers 94 and 77 are active, V2 decreases, accounting for the roll-off in angular deflection per velocity increase above the switch point and for the non-linearity of the system.

The above circuit drives the speedometer gauge 149 non-linearly in relation to the vehicle velocity signal on line 30 and can be adjusted to drive the speedometer in a manner to indicate vehicle speed with the graphics plate 16 shown in Figure 2.

Adjustment of resistors 108 and 110 sets the switch point 20 and adjustment of resistors 96, 98, 104, and 106 sets the rate at which successive values of r decrease.

With slight alterations to the above-described circuit, the circuit can be used to drive a speedometer in a manner to indicate vehicle speed with the graphics plate 16 shown in Figure 3.

Figure 6 shows these alterations. Operational amplifier 77 with associated resistors 68, 70, 76, and 80 are omitted. Also, resistors 108 and 110 are omitted and the inverting input 102 of operational amplifier 94 is coupled, through resistor 106, to pin 8 of driver IC 120. Resistor 98 is connected to V REG on line 66, providing a voltage to the non-inverting input of operational amplifier 94. This embodiment is the equivalent of setting zero kilometres per hour (0 MPH) as the switch point.

With any of the above embodiments, the vehicle speedometer is easily readable at common driving speeds while achieving a high maximum indicated vehicle speed. Referring to Figure 7, there is shown an alternative embodiment of gauge driver, in which the velocity signal on line 30 is fed into a signal conversion unit 160 which converts the velocity signal into a non-linear velocity signal on line 162. Examples of circuits for the signal conversion unit 160 may include an A/D converter interfacing with a microprocessor or arithmetic unit that performs a simple non-linear conversion, and outputs a signal through a D/A converter interfacing with a standard gauge driver 164. The standard gauge driver 164 then drives a gauge through lines 34 non-linearly with respect to vehicle speed.

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Claims

Claims:

1. Apparatus for indicating the speed of a vehicle comprising an analogue speedometer; a driver circuit for driving the analogue speedometer and having a gain adjustable between an output connection and a feedback connection; and an amplification circuit coupled between the output connection and the feedback connection of the driver circuit and adapted to cause the driver circuit to drive the analogue speedometer in a nonlinear manner.

2. Apparatus according to claim 1, wherein the driver circuit is adapted to produce an output signal having sine and cosine components in response to a vehicle speed signal, the analogue speedometer being drivable by the sine and cosine components.

3. Apparatus according to claim 1 or 2, wherein the amplification circuit comprises a first operational amplifier which includes an inverting input coupled to a reference voltage and a non-inverting input coupled to the output connection of the driver circuit and is adapted to produce no output when the voltage at the output connection of the drive circuit is below the reference voltage and to produce an output voltage when the voltage at the output connection of the drive circuit is above the reference voltage; and a second operational amplifier which includes an inverting input coupled to the output of the first operational amplifier, a non-inverting input coupled to a regulated voltage supply, and an output coupled to the feedback connection of the driver circuit; whereby in use the voltage at the feedback connection of the drive circuit substantially equals the regulated voltage minus the output voltage of the first operational amplifier so as to drive the analogue speedometer in is a non-linear manner.

4. Apparatus for indicating the speed of a vehicle substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 7 of the accompanying drawings.

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