GB2087175A - Flasher apparatus for motor vehicles - Google Patents
Flasher apparatus for motor vehicles Download PDFInfo
- Publication number
- GB2087175A GB2087175A GB8131008A GB8131008A GB2087175A GB 2087175 A GB2087175 A GB 2087175A GB 8131008 A GB8131008 A GB 8131008A GB 8131008 A GB8131008 A GB 8131008A GB 2087175 A GB2087175 A GB 2087175A
- Authority
- GB
- United Kingdom
- Prior art keywords
- output
- current
- flasher
- voltage
- flasher apparatus
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 238000012544 monitoring process Methods 0.000 claims description 2
- 239000003990 capacitor Substances 0.000 description 6
- 238000010586 diagram Methods 0.000 description 2
- NDAUXUAQIAJITI-UHFFFAOYSA-N albuterol Chemical compound CC(C)(C)NCC(O)C1=CC=C(O)C(CO)=C1 NDAUXUAQIAJITI-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60Q—ARRANGEMENT OF SIGNALLING OR LIGHTING DEVICES, THE MOUNTING OR SUPPORTING THEREOF OR CIRCUITS THEREFOR, FOR VEHICLES IN GENERAL
- B60Q1/00—Arrangement of optical signalling or lighting devices, the mounting or supporting thereof or circuits therefor
- B60Q1/26—Arrangement of optical signalling or lighting devices, the mounting or supporting thereof or circuits therefor the devices being primarily intended to indicate the vehicle, or parts thereof, or to give signals, to other traffic
- B60Q1/34—Arrangement of optical signalling or lighting devices, the mounting or supporting thereof or circuits therefor the devices being primarily intended to indicate the vehicle, or parts thereof, or to give signals, to other traffic for indicating change of drive direction
- B60Q1/38—Arrangement of optical signalling or lighting devices, the mounting or supporting thereof or circuits therefor the devices being primarily intended to indicate the vehicle, or parts thereof, or to give signals, to other traffic for indicating change of drive direction using immovably-mounted light sources, e.g. fixed flashing lamps
- B60Q1/382—Electronic temporisation with semiconductor amplification
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Lighting Device Outwards From Vehicle And Optical Signal (AREA)
Abstract
In order to protect the output switch (T1) of the apparatus, means are provided to render the switch inoperative as a result of an excess current flow. T1 is normally on and is switched by the action of T2 and oscillator A1. When SW1 is closed a voltage builds on the selected lamp (L1 or L2). If this does not exceed the reference set by R6 and R7 at the negative input of A2 within a time set by R8 and C2 then the output of A2 is low, disabling T1. Thus a short circuit or a low load is detected. An overload is detected by means of sensing resistor R5. Should the current exceed the required value the output of A3 goes lower than the reference set by R16 and R17 causing monostable A5, A6 to go high for a period set by R21 and C3. This makes the output of A1 low, disabling T1. <IMAGE>
Description
SPECIFICATION
Flasher apparatus for motor vehicles
The invention relates to flasher apparatus for motor vehicles, that is to say direction indicator apparatus including electric lamps which can be caused to intermittently flash, selectively, according to whether a left turn or a right turn is to be made, and has for its object to provide an improvement thereon.
It is known to monitor the correct operation of such apparatus by means which measure the amount of electric current being used during the operation of the apparatus, a reduction in the amount of current flowing being used to indicate that one or more of the flasher lamps is inoperative.
Such means generally work quite well when the flasher lamps concerned are only four in number.
However, complications arise when the motor vehicle concerned is for example the tractor unit of an articulated road vehicle where the number of flasher lamps concerned is increased by at least two when a trailer is connected. This is because electric lamp bulbs of identical specification do not take exactly the same amount of electric current, and in fact it has been found that they vary in this respect within plus or minus 6% of a particular nominal current rating. It will be understood that as the number of electric lamps in the apparatus increases, it becomes increasingly difficult to say with certainty that a low current flow is due to one or more of the lamps being inoperative rather than to what might be called a "build up of tolerances", that is to say a collective reduction of current flow through the still operative lamps.The difficulty is made worse by the fact that a current flow through an electric lamp filament varies according to the temperature of the filament so that in the case of a flasher lamp which operates intermittently the current which it uses initially may be quite high but falls off rapidly due to increasing temperature as it continues to operate and if plotted graphically the current consumption is not a straight line graph but is curved.
Also, in modern heavy goods vehicles provided with trailers, large numbers of banks or parallel indicating lamps have to be provided to comply with legal requirements, so that with existing apparatus the task of detecting an open-circuited lamp is extremely difficult.
Furthermore, in existing flasher apparatus, no provision is made to protect the components against a short-circuit occurring in the wiring to the lamp units. Since the main output switch of the flasher unit which is controlled by an oscillator, is normally a power transistor, this device will be vulnerable to excessive overload currents arising in the event of a short-circuit occurring in the wiring to the lamp units. In other words, no control can be exercised by the manufacturer of the switch as to what load will be added in terms of the number of lamps which it will be required to supply. Consequently, in existing flasher apparatus the adding of further lamps in the circuit can cause catastrophic failure of the switch output device.
It is therefore an object of the present invention to overcome partially or wholly the above mentioned disadvantages occurring in known flasher apparatus for motor vehicles.
According to the present invention there is provided a flasher apparatus for motor vehicles wherein the output switch is rendered inoperative firstly in the case where excess current flows through the lamp units thus indicating that one or more lamps are short circuited, and secondly where overload current flows due to a short-circuit occurring in the wiring to the lamp units.
Preferably, the means for detecting an excessive flow of current operates on the principle of detecting the rise in voltage at the instant that current flows in the lamp units, and comparing whether the rise in voltage exceeds a predetermined voltage within a given period of time. In this case, the output switch is switched to a non-conductive state if the voltage rise is insufficient within the given period of time.
Preferably, the means for detecting an overload of short-circuit current operates on the principle of monitoring the current flow through the output switch. In the event that the current exceeds a given value a monostable device is actuated to produce a pulse which inhibits the output switch for the duration that the monostable device remains in its unstable state.
The present invention will now be described in greater detail by way of example, with reference to the accompanying drawings, of which:
Figure 1 is a circuit diagram of a preferred form of circuit for protecting the output switch of flasher apparatus in the event of overload and short circuit currents and also for indicating the failure of one or more lamp units, and
Figure 2 is a further protection arrangement which will be referred to.
Referring now to Figure 1 of the drawings, L1 and
L2 represent respective banks of left and right indicator lamps on a vehicle or tractor/trailer combination. The main battery supply for the respective banks of lamp units is obtained from the positive terminal of the battery through a load resistor Rs, an output switch in the form of a PNP power transistor T1 and the switch SW1.
The circuit also comprises differential amplifiers
Al -A6, resistors R1 - R21, capacitors C1 - C5, diodes
D1- D6, and a zener diode Z1.
The transistor T2 is effectively in parallel with the transistor T1. The base electrode of the transistor T1 is connected firstly directly to the collector electrode of the transistor T2 and secondly to the negative terminal of the battery through the resistor R11 and diode D6. The capacitor C4 is connected across the base and emitter electrode of the transistor T1.
The base electrode of the transistor T2 is supplied from the output from the differential amplifier Al through the resistor R5. The positive input to the differential amplifier is obtained across a potentiometer chain comprising resistors R1 and R2. The negative input to the differential amplifier Al is connected to the output of the differential amplifier
A6 through the diode D4 and to the negative terminal of the battery through the capacitor C1.
Feedback resistors R3 and R4 are respectively associated with the negative and positive inputs of the differential amplifier Al.
The negative input of the differential amplifier A2 is connected to a potentiometer chain comprising the resistors R6 and R7 across the battery voltage.
The positive input to the differential amplifierA2 is connected to the collector electrode of the transistor T1 through the diode D2. A parallel circuit comprising the resistor R8 and diode D1 is also connected between the positive input of the differential amplifier A2 and the negative terminal of the battery. The capacitor C2 is connected between the positive input to the differential amplifier A2 and the output of the differential amplifier Al.
The output of the differential amplifier A2 is connected to the base electrode of the transistor T2 through the resistor R10. The resistor R9 is connected between the base and the emitter electrodes of the transistor T2.
Overloads are detected by means of differential amplifier A3 which effectively monitors the current taken by the load resistors Rs. The negative and positive inputs to the differential amplifier A3 are connected to either ends of the load resistor Rs through respective resistor R12 and R1 4. The differential amplifier A3 is provided with a parallel feedback circuit to the negative input thereof consisting of the resistor R13 and capacitor C5.
The output from the differential amplifier A3 is applied to the negative input to the differential amplifier A4. The positive input to this differential amplifier receives the stabilized voltage provided by the potentiometer chain across the battery comprising the zener diode Z1, resistor R16 and resistor R1 7.
The output of the differential amplifier A4 is connected to the negative input of the differential amplifier A5 through the resistor R1 8. The positive input to the differential amplifier A5 is connected to the junction between a potentiometer chain across the battery comprising the resistors R19 and R20.
The output from the differential amplifier A5 is applied to the negative input of the differential amplifier A6 through the capacitor C3. The negative input to this amplifier is also connected to the positive terminal of the battery through a parallel network comprising the resistor R21 and the diode
D5. The positive input to the differential amplifier A6 is connected to the junction between the resistors
R19 and R20 comprising the potentiometer chain across the battery.
The output from the differential amplifier A6 is applied firstly to the negative input to the differential amplifier Al through the diode D4, and secondly to the negative input of the differential amplifier A5 through the diode D3.
The diode D6 is provided to prevent the circuit components and in particular the transistors from being damaged by reverse battery connection.
The circuitry surrounding TR1 is to:a) enable TR1 to switch on and off causing the external lamp load to flash, b) prevent damage to TR1 should there be a short-circuit as the external load, c) to switch off TR1 should there be more than a prescribed number of lamps or excessive load applied to TR1.
In order to readily understand the operation of the circuit a description will be given by way of example only.
TR1 is normally on, due to the connection of R11 from TR1 base to -ve and is caused to switch on and off by the action of TR2 and Icl (Icl forming an oscillator). It will be seen that lc2 is also connected to
TR1 via R10. As the -ve input will normally exceed the +ve input voltage its output will be low. This will cause T2 to conduct causing T1 to be disabled. In order to enable T1 a pulse is applied to C2 via Ic1 causing the +ve input of lc2 to go +ve with respect to the -ve input, so causing the output to go high and remove the clamp from T1 base by switching of
T2.
Should Sw 1 be closed in either position then a voltage will begin to build up across the lamp selected by Sw 1. Should this voltage rise not exceed the reference voltage set on the -ve input of lc2 within the period of time determined by R8 and C2 then the output of lc2 will revert to its low state and again disable T1.
Should however, the voltage have risen beyond this reference level set by R6 and R7 on the -ve input of lc2 then the output of lc2 would remain high for the period T1 was conducting which in turn is governed by the oscillator Ic1.
It can be seen therefore that should a short-circuit or load less than the required value be present at Sw 1 the transistor T1 will only switch on for a brief period and so protect the device from failure.
In order that further protection may be afforded to
T1 in the way of ensuring that even if a load greater than the prescribed maximum were placed on T1 a current monitor has been included and pulser circuit to indicate to the user that the maximum demand has been exceeded.
An explanation by way of example only will be provided.
Should T1 be conducting then the amplifier lc3 will monitor the current flowing to the external load via
Resistor Rs. Should the current flowing in Rs be within the design limits then the output of Ic will remain at a higher voltage than that set on +ve input of lc4, therefore lc4 output will remain low and Ic5 and 6 will remain in their steady state.
Should the current through Rs exceed a predeter mined level then the output of lc3 will go lowerthan than the voltage reference on the +ve input of lc4 and cause its output to go low. This causes the output of it5 to go low causing a -ve going pulse at the -ve input of lc6. This causes the output of lc6 to go high where it will remain for a period determined by R21 and C3 as Ic5 and 6 form a monostable. This will cause D4 to conduct and cause the -ve input of Ic1 to become greater than the +ve input so causing Ic1 output to go low and disable T1 as T2 is now on.
When the monostable period has ended the circuit will revert to normal operation previously described and the whole series of events repeat should the necessary conditions prevail.
Referring now to Figure 2, the modified circuit there illustrated is basically similar two that of Figure 1, the differences being such as will be readily apparent to those skilled in the art.
The operation of the modified circuit is as follows:
Assume T1 to be off, the ref Vol will be equal to the supply voltage (E) and the ref Vr will be equal to (E x a) where a is equal to the ratio of R1 and R2; this will hold the +ve input of Al below that of the -ve input and Al output will be low. [When the output of Al goes high it shuts down the output holding the oscillator high (see circuit diagram)].
Should T1 conduct then the output of lamp current amplifier will fall and attempt to reduce Vol ref below that of Vr should this occur the output ofA1 will go high and shut down the output transistor, as would be the case should a short circuit or pure resistive load of a low value be present at the output. This action would not however be instantaneous as a step change would occur across C1 and a current would flow through the base of T2 and depending on its magnitude would cause a drop in Vr, should the drop in Vr fall below that appearing from Vol then the output of A1 would remain low for a given period before Vr returned to Vr max. Vr would then exceed
Vol and cause the output of Al to go high and shut down T1 thus turning the output off.The output would remain off for approximately 3 seconds.
When T1 again switches on (a normal lamp load assumed) then again the outputs of Vr and Vol will fall but Vr will be held lower than Vol providing a minimum critical dv/dt is maintained for the time it takes the IL amplifier to reduce its output (because of the reduction of IL with time) to a level less than the specified lamp load. Should this reduction have occurred, then should dv/dt cease the circuit will maintain Al output low due to the fact that Vr max. is designated to be lower than Vol max.
Should however the lamp loading be such that the critical minimum dv/dt is not maintained then Vr will begin to rise and will exceed the level Vol causing the output of Al to go high and again shut down T1.
It can be seen therefore that there are many combinations of effects that will cause the output transistor T1 to shut down.
The ultimate conclusion is that, should the output detect a load that provides a certain minimum dv/dt the circuit will function correctly. Should however the minimum dv/dt not be maintained under heavy current conditions the circuit will protect T1 by turning it off.
Thus there is provided flasher apparatus for motor vehicles by means of which the correct operation of the flasher lamps can be monitored and by means of which the main output switch is protected against excessive overload currents resulting from shortcircuits in the wiring to the lamp units.
Claims (6)
1. Flasher apparatus for motor vehicles wherein the output switch is rendered inoperative firstly in the case where excess current flows through the lamp units thus indicating that one or more lamps are short circuited, and secondly where overload current flows due to a short-circuit occurring in the wiring to the lamp units.
2. Flasher apparatus according to claim 1, in which flow of current operates on the principle of detecting the rise in voltage at the instant that current flows in the lamp units, and comparing whether the rise in voltage exceeds a predetermined voltage within a given period of time.
3. Flasher apparatus according to claim 2, in which the output switch is switched to a nonconductive state if the voltage rise is insufficient within the given period of time.
4. Flasher apparatus according to either one of claims 2 and 3, in which the means for detecting an overload or short-circuit current operates on the principle of monitoring the current flow through the output switch.
5. Flasher apparatus according to claim 4, in which in the event that the current exceeds a given value, a monostable device is actuated to produce a pulse which inhibits the output switch for the duration that the monostable device remains in its unstable state.
6. Flasher apparatus for motor vehicles, constructed, arranged and adapted to operate substantially as herein before described with reference to and as illustrated by Figure 1 or Figure 2 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8131008A GB2087175A (en) | 1980-10-14 | 1981-10-14 | Flasher apparatus for motor vehicles |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8033090 | 1980-10-14 | ||
| GB8131008A GB2087175A (en) | 1980-10-14 | 1981-10-14 | Flasher apparatus for motor vehicles |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2087175A true GB2087175A (en) | 1982-05-19 |
Family
ID=26277207
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8131008A Withdrawn GB2087175A (en) | 1980-10-14 | 1981-10-14 | Flasher apparatus for motor vehicles |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2087175A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1987003548A1 (en) * | 1985-12-11 | 1987-06-18 | Jasmond Pty. Ltd. | Adaptive switching circuit |
-
1981
- 1981-10-14 GB GB8131008A patent/GB2087175A/en not_active Withdrawn
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1987003548A1 (en) * | 1985-12-11 | 1987-06-18 | Jasmond Pty. Ltd. | Adaptive switching circuit |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |