GB2266397A - Vehicle manoeuvring aid - Google Patents

Abstract

A vehicle (12) bears an acoustic echo ranging system (26) and a capacitive system (13) both for sensing obstacles to the rear of the vehicle. An alarm signal generator is operated to give an alarm signal to the vehicle operator when either system senses an obstacle. This arrangement provides the advantage that the capacitive system can detect objects within the minimum range or blind areas of the acoustic system. <IMAGE>

Description

2266397 Vehicle Manoeuvring Aid This invention relates to a vehicle

manoeuvring aid and in particular to a road vehicle parking aid.

Many accidents involving road vehicles are collisions occurring during parking due to the relatively poor visibility to the rear of most vehicles and the fact that the vehicle operator generally has to divide his attention between looking backwards and forwards to guide the vehicle.

It has been proposed to overcome this problem by providing acoustic proximity sensors directed around the vehicle to provide a warning to the driver of the close proximity of objects around the vehicle. These acoustic sensors operate on the well known echo ranging principle where the time delay between transmitting a pulse of sound energy and receiving an echo is used to calculate the distance to an object. One system of this type is described in our co-pending UK patent application No. 9225820.1.

Sensors of this type have been found to be unsatisfactory in practice because they suffer from low short range detection accuracy and as a result do not P/8896/P48 2 necessarily give adequate warning of objects close to the vehicle. This is due to the fact that the transmitted acoustic signal must be transmitted as a narrow beam in order to prevent the system being triggered by objects to the side which the vehicle cannot possibly collide with. As a result close to the vehicle there are blind areas between the narrow acoustic beams where objects can be situated without being detected.

In theory this problem could be overcome by using large numbers of acoustic sensors, but this is too expensive for any practical system due to the cost of the acoustic sensors.

A second problem with conventional acoustic proximity warning systems is that they cannot detect objects below a minimum range from the transmitter and receiver. This is because the receiver cannot sense return signals which arrive while the transmitted sound energy is being transmitted because the transmitted sound energy drowns the return out. This minimum range obviously depends on the length of the transmitted sound pulses emitted by the system.

This invention was intended to provide a vehicle P/8896/P48 3 manoeuvring aid overcoming these problems, at least in part.

This invention provides a vehicle manoeuvring aid comprising a first acoustic, sensing system and a second capacitive sensing system, both arranged to sense obstacles in the same direction, and an alarm signal generator for generating an alarm signal to the vehicle operator when either system senses an obstacle.

This provides the advantage that the capacitive system can detect objects within the minimum range or blind are.as of the acoustic system.

A vehicle manoeuvring aid incorporating the invention will now be described by way of example only with reference to the accompanying diagrammatic Figures in which; Figure 1 shows a general plan view of car employing a prior art acoustic proximity warning sensor;

Figure 2 shows a general view of a car employing a manoeuvring aid according to the invention; Figure 3 shows a more detailed view of the manoeuvring aid of Figure 2; P/8896/P48 4 Figure 4 is an explanatory graph showing the working of the system of Figure 3; Figure 5 shows a detailed view of an alternative manoeuvring aid according to the invention; and Figure 6 shows a general view of a car employing a further manoeuvring aid according to the invention.

Referring to Figure 1 a car 1 bearing an acoustic proximity warning system is shown in plan view from above. The car 1 bears two acoustic transmitter and receiver units 2A and 2B at the rear of the car 1 on its rear bumper. These are linked to power supply and signal processing electronics (not shown). Each of the acoustic transmitter and receiver units 2 transmits a fan shaped beam 3 of sound energy and the presence of objects within the beams 3 is detected by sound energy reflected from the object being received at the acoustic transmitter and receiver unit 2. This is a conventional acoustic echo-ranging system.

The transmitted power, pulse repetition frequency and pulse length of the acoustic transmitter and receiver units 2 and the signal processing used on the received signal P/8896/P48 defines the maximum range of the acoustic units 2 and this maximum range is denoted by a dashed line 4. The acoustic proximity sensing system has a maximum range of about 1.2m and a minimum range of about 10Omm, the minimum range being determined, as explained above, by the pulse length of the acoustic signal transmitted and by the acoustic transmitter and receiver units 2.

Any object within the beams 3A and 3B, outside the minimum range of the system and closer to the car 1 than the maximum range denoted by the dashed line 4 will generate a response from the acoustic proximity sensing system. To ensure that the system is usable the maximum combined width of the two beams 3A and 3B within the maximum range 4 must be kept small enough to avoid large numbers of false alarms triggered by objects to the side of the car 1 which the car is in no danger of colliding with. This limits the angular width of the beams 3A and 3B and as a result there is a gap 34 (shown shaded in Figure 1) between the beams 3A and 3B close to the car 1.

Clearly no warning will be produced by an obstacle in this gap 34 or inside the minimum range of the system.

Referring to Figure 2 a vehicle manoeuvring aid P/8896/P48 6 generally shown at 1 is shown mounted on a car 12. This manoeuvre aid is intended for use as a parking aid. In this example the parking aid is intended to operate when reversing, so it is mounted on the rear of the car 12.

The parking aid comprises an acoustic system and a capacitive system.

The capacitive part of the parking aid is formed by a metal conductive strip 13 mounted across the rear of a car and insulated from the body of the car 12 by an insulating strip 14 between the conductive strip 13 and the car body.

Referring to Figure 3 the capacitive part of the parking aid is shown in more detail. The conductive strip 13 is linked to a digital timing circuit 15. The digital timing circuit 15 alternately connects the conductive strip 13 to its positive voltage rail supply at 5 volts and earth through a resistor 16 of known value and measures the voltage of the conductive strip 13 using a voltage sensor 17. A switch 18 is arranged to connect the conductive strip 13 to either the plus 5 volts rail supply or earth and the switch is controlled by a switch control unit 19 which operates the switch 18 in response to the voltage value produced by the voltage measuring unit 17. When the P/8896/P48 7 conductive strip 13 is at a voltage of 3 volts the switch control unit 19 throws the switch 18 to connect the conductive strip 13 to earth, similarly when the voltage of the conductive strip 13 is 1 volt the switch control unit 19 throws the switch 18 to connect the strip 13 to the plus 5 volts supply. As a result the voltage of the strip 13 varies cyclically between 1 and 3 volts, as shown in Figure 4. The period t taken to complete one charging and discharging cycle is dependent on t-he switching voltages used, the resistance of the resistor 16 and the capacitance of the conductive strip 30. Since the resistance of resistor 16 is constant any changes in the period t must be due to changes in the capacitance of the conductive strip 13. In order to allow the changes in the period t to be measured the switch control unit 19 is also connected to a timing unit 20 which is supplied with a pulse by the switch control unit 19 each time the switch control unit 19 throws the switch 18. Thus the timing unit 20 receives a pulse each time the voltage of the conductive strip 13 reaches a value of 1 volt or 3 volts i.e. at each peak or trough on the graph of Figure 4.

The timing unit 20 is also supplied with a high frequency clock signal from clock 21. The timing unit 20 is essentially a counter which counts the clock pulses from the P/8896/P48 8 clock 21 and is reset to zero by every second pulse from the switch control unit 19, when the timing unit 20 is reset it sends its current count to a processor 22.

The processor 22 stores the numerical information from the timing unit 20 in a memory 23 and compares the latest count with a rolling average of the counts received over the previous 8 seconds and measures the difference between the counts and the rolling average.

The capacitance of the conductive strip 13 is dependent on the proximity of nearby objects, as the car 12 moves closer to the objects the capacitance of the conductive strip 13 will increase and as a result the period t of each charging and discharging cycle will become longer and so the count received by the processor 22 will increase. The processor 22 compares the difference between the last received count and the rolling average of the counts received over the preceding 8 seconds with a threshold also stored in memory 23, if the difference is negative or is positive and below the threshold the processor 22 takes no action. However if the difference is positive and above the threshold the processor 22 signal an alarm unit 24. The threshold is set so that the time change will exceed the threshold when an obstacle moves within 10Omm of conductive P/8896/P48 9 strip 13.

A conventional acoustic echo ranging system 25 is also connected to the alarm generator 24. The acoustic echo ranging system 25 employs a pair of acoustic transmitting and receiving units 26 situated within the rear bumper of the car 12 and facing backwards. The two acoustic transmitting and receiving units 26 are placed to provide coverage to the rear of the car 12 as shown in Figure 1. Acoustic echo ranging units of this type are well known and are disclosed for example in our co-pending application no. 9225820.1, the content of which is included herein by way bf reference and it is not necessary to describe such systems in detail herein.

The acoustic system 25 also supplies a signal to the alarm unit 24 when a return acoustic signal above a threshold amplitude is detected by one of the acoustic transmitting and receiving units 26. The signals from the acoustic system 25 to the alarm generator 24 indicate the distance of the acoustically sensed object from the car 12 and the alarm generator 24 generates an acoustic alarm through a speaker 27 within the driving compartment of the car 12 and a visual alarm using a light 28 situated on the dashboard of the car 12.

P/8896/P48 The alarm generator 24 causes the speaker 27 to produce a warning signal as a series of sound pulses which increase in rate as the acoustically sensed obstacle gets closer to the car and simultaneously causes the light 28 to flash faster as the acoustically sensed obstacle gets closer to the car 12. When the acoustically sensed obstacle is within a preset distance of the car 12 or if it is alerted to a capacitively sensed object by the processor 22 the alarm generator 24 causes the light 28 to light continuously and the loudspeaker 27 to generate a continuous high pitched sound. The alarm generator 24 is also supplied with data indicating which gear the car 12 is in along a line 29 and will not generate a warning signal unless the car is in neutral or reverse gear, thus avoiding unnecessary alarms when the car is being driven forward.

A manual override button 30 is also placed on the car dash board and when the override button 30 is pressed the alarm generator 24 is inhibited from producing an alarm for a short period of time, this allows the driver to reverse close to an obstacle he has already been warned of without being further distracted by the alarms 27 and 28.

A similar arrangement of acoustic and capacitive P/8896/P48 systems could also be placed on the front of the car 12. In this case the alarm generator 24 will be enabled by data along the line 29 indicating that first, neutral or reverse gears have been selected. Alternatively the enabling or disabling of the alarm generator 24 could be controlled by the actual speed of the vehicle rather than the gear selected, this would be particularly useful in vehicles fitted with an automatic gear box or cars not having gears at all such as electric vehicles.

Although the vehicle manoevring aid shown has an acoustic system mounted within the vehicle's bumper (or fender) and a capacitive system mounted elsewhere as an alternative, if the vehicle had non-conductive plastic bumpers, the capacitive system could also be placed on the bumpers.

Where a car has both capacitive and acoustic proximity warning systems facing to the front and the rear of the car 12 the alarm generator 24 will receive inputs from four separate systems, two acoustic systems 25 and two capacitive systems 15 and is arranged to sound its alarms in response to proximity warnings from the forward facing sensors when the car is in first or neutral gear or from the rearward facing sensors when the car is in neutral or reverse gear.

P/8896/P48 Alternatively the alarm generator 24 could produce an alarm in response to a proximity warning from any of the sensors regardless of whether the car 12 was in first, neutral or reverse gears or two separate warning lights could be arranged, one to be lit when the warning came from the forward facing sensors and one to be lit when the warning came from the rearward facing sensors.

The capacitance of the conductive strip 13 could of course be measured in other ways to achieve the same result, for example referring to Figure 5 an alternative capacitive sensing system is shown in which the conductive strip 13 is connected to an inductance 30 so that the conductive strip 13 acting as a capacitor and the inductance 30 form a resonant tuned circuit. This tuned circuit is incorporated into an oscillator 31 so as to generate an output at the resonant frequency of the tuned circuit.

The output from the oscillator 31 is supplied to a frequency sensor 32. The frequency sensor 32 measures the output frequency of the oscillator and compares it to a frequency value stored in a memory 33, if the frequency from the oscillator drops more than a preset amount below the frequency value stored in the memory 33 the frequency sensor 32 signals an alarm generator 24 as before. As each P/8896/P48 - 13 frequency value is received it is stored in the memory 33 and each new frequency value is compared with the rolling average of the frequency values received over the previous 8 seconds.

The environmental conditions around the car 12 will affect the capacitance of the conductive strip 13, in particular rain or mist can significantly change the capacitance of the conductive strip 13 and it is in order to allow for this that the time values supplied to the processor 22 are compared by it with the rolling average of the values stored in the memory 23 whichwere received.over the previous 8 seconds rather than with a fixed value stored in the memory 23. Because the values are compared with the rolling average of those received over the previous 8 seconds any gradual change in capacitance produced by external environmental changes, as well as any gradual changes caused by corrosion or similar weathering effects on the conductive strip 13, will be below the threshold and will not trigger an alarm. Thus these gradual changes are automatically corrected for by the system calibrating itself at each reading.

In a further embodiment shown in Figure 6 a car 40 has first pair of acoustic transmitting and receiving units 41a P/8896/P48 and 41b mounted on its front end pointing forward anda second pair of acoustic transmitting and receiving units 42a and 42b mounted facing rearwards. The car 40 also has a first conductive strip 43 mounted on its front bumper and a second conductive strip 44 mounted on its rear bumper, both the conductive strips 43 and 44 are separated from the main body of the car by the bumper which is insulating so they act as capacitors. The bumpers and the conductive strips 43 and 44 are both wrapped around the wings of the car so that they pass along not only the front and rear of the car but part way along its sides. As a result the capacitive proximity warning sensors including the conductive strips 43 and 44 give a warning of objects close to the sides of the car 40 as well as close to its front and rear, allowing collisions due to the car 40 turning into objects close to its sides to be avoided. It would not be practical to have an acoustic proximity warning system facing to the sides of the car 40 because it is normal when parking to be quite close to objects to the side so such an acoustic system would continuously produce warnings unnecessarily, the relatively short range of the capacitive sensors ensures that only objects coming very close to the sides of the car will generate warnings.

The conductive strip 3 can be designed into a car as a P/8896/P48 decorative trim strip or existing trim strips could be used to allow addition of a parking aid.

Instead of or as well as providing a simple warning of close proximity the capacitive sensor could generate an actual distance value from the time or capacitance value and provide this to the driver.

Although the systems described are intended for use as parking aids they could be used as proximity warning or measuring systems for other types of close manouevring by vehicles.

Manoeuvring aids of the type described could of course be used on vehicles other than cars.

The switching voltages and rolling average time values used are only exemplary and can be varied as required to achieve best system performance.

The use of a rolling average in processing is not essential, some other forms of average could be used.

The precise alarms generated and their forms can be varied if'necessary.

P/8896/P48 16 -

Claims (12)

1. A vehicle manoeuvring aid comprising a first acoustic, sensing system and a second capacitive, sensing system, both arranged to sense obstacles in the same direction, and an alarm signal generator for generating an alarm signal to the vehicle operator when either system senses an obstacle.

2. A vehicle manoeuvring aid as claimed in claim 1 in which the first sensing system is an acoustic echo ranging system.

3. A vehicle manoeuvring aid as claimed in claim 1 or claim 2 in which the second, capacitive, sensing system comprises a conductor mounted on the exterior of the vehicle, capacitance sensing means for sensing the capacitance of the conductor and means for indicating to the signal generating means when the capacitance of the conductor increases.

4. A vehicle manoeuvring aid as claimed in claim 3 in which the capacitance sensing means alternately charges and discharges the conductor between two pre-set voltages P/8896/P48 17 and measures the time taken for a charging and discharging cycle in order to sense changes in its capacitance.

5. A vehicle manoeuvring aid as claimed in claim 4 and additionally comprising a memory associated with the capacitance sensing means, each charging and discharging cycle time in turn being stored in the memory.

6. A vehicle manoeuvring aid as claimed in claim 5 and additionally comprising comparator means which compares each charging and discharging cycle time with a rolling average of times taken by the charging and discharging cycle over a preceding pre-set period.

7. A vehicle manoeuvring aid as claimed in claim 1 in which the alarm signal generator generates a modulated signal in response to detection of obstacles above a pre-set range by the acoustic system with the modulation depending on the range and generates a continuous signal in response to detection of obstacles by the capacitive system or detection of obstacles below the pre-set range by the acoustic system.

8. A vehicle manoeuvring aid as claimed in any preceding P/8896/P48 - 18 claim where the alarm signal is acoustic.

9. A vehicle manoeuvring aid as claimed in any preceding claim where the alarm signal is visual.

10. A vehicle manoeuvring aid substantially as shown in or as described with reference to Figures 1 to 4 of the accompanying drawings.

11. A vehicle manoeuvring aid substantially as shown in or as described with reference to Figure 5 of the accompanying drawings.

12. A vehicle manoeuvring aid substantially as shown in or as described with reference to Figure 6 of the accompanying drawings.