WO2004098941A1

WO2004098941A1 - Accelerator pedal signal controller

Info

Publication number: WO2004098941A1
Application number: PCT/AU2004/000596
Authority: WO
Inventors: Paul Dawson
Original assignee: Dawson, Nicole
Priority date: 2003-05-07
Filing date: 2004-05-07
Publication date: 2004-11-18
Also published as: AU2003902172A0

Abstract

A speed or acceleration control module (10) which is connected between a power control pedal (12) and an engine/motor control module or (ECM) (14) wherein the power control pedal (12) outputs an analog pedal position signal (16) to the control module (10). The control module (10) process this signal (16) by comparing actual speed/acceleration values of the vehicle with corresponding control data and dependent on said comparison delivers a modified signal output (18) to the ECM (14) thereby controlling the vehicle’s speed/acceleration at the respective control values. Also a radio system detecting the vehicle’s proximity to a fixed position dependent on the strength of the radio signal between a transmitter at the fixed position and the vehicle mounted receiver is described.

Description

112438376

ACCELERATOR PEDAL SIGNAL CONTROLLER

FIELD OF THE INVENTION

The present invention relates broadly to a speed or acceleration control module for a vehicle and relates particularly, though not exclusively, to a control module for retrofitting to a vehicle to function in conjunction with the electronic accelerator pedal and the engine control unit (ECU) to operate as a variable speed controller. The invention further relates to a speed or acceleration control device and system for a vehicle. The invention also relates to a vehicle proximity sensing system.

BACKGROUND OF THE INVENTION

Automotive technology has led to the rapid inclusion of "by wire' systems for the control of many functions in a vehicle. The "by wire' term refers to a function which is actuated electronically, but was once actuated mechanically. One such function being the control of the power of the motor. Previously, the power of a combustion engine was controlled by a mechanical linkage or cable between the engine air intake throttle valve and a motor power control pedal. A motor power control "by wire' system replaces this linkage with an electronic system. The motor power control pedal, rather than cause effect via mechanical movement has an electronic position sensor fitted to it. This sensor is often, but not limited to , a potentiometer which provides an analog voltage level proportional to the position of the motor power control pedal. Hence, as the pedal is pushed, the signal output changes proportionally to the travel of the pedal. Typically, this signal is received by the vehicle motor control module, and used to control an electric actuator, which in turn varies the engine air intake throttle valve, hence effecting throttling of the engine and engine power. The position of the motor power control pedal is proportionally related to the position of the throttle valve which in turn is related to the power output of the motor.

With vehicles that are driven by electric motors, the "by wire' principal is the same. The motor power control pedal provides an output signal which is then received by the motor control module which in turn controls a power amplifier or similar device. The output of the power amplifier drives the electric motor which in turn provides driving force to the vehicle with a proportional amount of power. 112438376

2.

Speed limiting devices have been developed which allow the speed of a vehicle to be controlled. With vehicles driven by combustion engines, the method of causing this 'speed limit' was to limit the air intake of the engine as the speed of the vehicle approached the 'speed limit', regardless of the position of the power control pedal. In one such system, this was effected by including a secondary throttle valve in series with the primary throttle valve which alone was connected to the throttle pedal. The secondary throttle valve was actuated by a speed limiting control system. As the vehicle neared its limited speed, the secondary throttle would start closing, in effect overriding the primary valve. In an alternate speed limiting system, the cable from the motor power control pedal to the engine throttle valve is segmented by a speed limiting system. When the motor power control pedal is actuated, the cable attached to the pedal actuates a mechanical device in the speed limiting system. This mechanical device in turn actuates another cable which is connected to the engine throttle valve, the speed limiting system acting as a go between. Hence, if the vehicle nears the speed limit, the speed limiting system halts the travel of the cable to the throttle valve, even though the travel of the cable from the motor power control pedal might exceed this. Existing by- wire engine power control systems also include a static maximum speed parameter that can be factory preset. They are operated by reducing the throttle position (and hence engine power) if the speed of the vehicle exceeds the maximum speed parameter regardless of the position of the associated power control pedal.

The disadvantage of these known systems is that they are singularly focused on the speed of the vehicle. They have little regard for, or capability of controlling, the dynamics of acceleration through the vehicles full range of capability. To illustrate the point consider a motor car which has a full throttle rate of acceleration of 10 km/hr per second between the range of 0 and 100 km/hr on level ground. Now consider that the intended speed limit for the vehicle is 5 km/hr, about walking pace. It is obvious that with the above systems if the driver is inclined to 'plant the foot' on level ground, the vehicle will exceed the speed limit regardless of the fact that a limiting system is in place. Knowing this, one might then adjust the above systems by limiting the maximum opening of the throttle valve so that the maximum possible rate of acceleration is 1 km/hr per second on level ground. However should the vehicle then reach a steep hill it is unlikely that it will progress any further as the ability for the engine to produce enough power to overcome the hill is proportional to the amount of air admitted to the throttle valve. Further, consider the same vehicle which in one 112438376

3. area is limited to 5 km/hr, and in another area is limited to 100 km/hr. One can see that the mentioned systems are not capable of delivering a solution applicable to the two.

With vehicles driven by electric motors, the general method of limiting the speed of the vehicle has been to limit the power output to the electric drive motor. Again, this produces the problem whereby the power output of the machine is statically limited in order to prevent over-accelerating. Consider an electric forklift, the dynamics of the vehicle will change when the vehicle is under load compared with it is not. Again, if the power requirements of the vehicle substantially change, or the differential between speed limits required in mutually exclusive areas is great, the known systems are not capable of delivering an acceptable solution.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a speed or acceleration control module for a vehicle, said control module comprising a processor being adapted to receive a position signal from a position sensor operatiyely coupled to a power control - mechanism of the vehicle, the processor being configured to compare actual speed and/ or actual acceleration values with respective control speed and/ or control acceleration values and, dependent on said comparison, deliver a modified signal output to an engine control module of the vehicle thereby controlling its speed and/or acceleration at the respective control values.

According to another aspect of the invention there is provided a speed or acceleration control device for a vehicle, said control device comprising:

a position sensor being adapted to detect the position of a power control mechanism of the vehicle and provide a position signal representative of said position; and

a processor being in communication with the position sensor so as to receive its position signal, the processor being configured to compare actual speed and /or actual acceleration values with respective control speed and/ or control acceleration values and, dependent on said comparison, deliver a modified signal output to an engine control module of the vehicle thereby controlling its speed and/or acceleration at the respective control values. 112438376

4.

According to a further aspect of the invention there is provided a speed or acceleration control system for a vehicle, said control system comprising:

a position sensor being adapted to detect the position of a power control mechanism of the vehicle and provide a position signal representative of said position;

a processor being in communication with the position sensor so as to receive its position signal, the processor being configured to compare actual speed and/ or actual acceleration values with respective control speed and/ or control acceleration values and, dependent on said comparison, deliver a modified signal output to an engine control module of the vehicle thereby controlling its speed and/ or acceleration at the respective control values; and

vehicle positioning means being operatively coupled to the processor whereby said positioning means is effective in varying the control speed and/ or control acceleration values dependent on the position of the vehicle.

Preferably the vehicle positioning means includes a radio receiver and transmitter system having a radio receiver mounted to the vehicle and operatively coupled to the processor, and a radio transmitter located at a preselected fixed position remote from the vehicle whereby depending on the detected position of the vehicle said radio system varies control speed and/of acceleration values. More preferably, the radio transmitter is configured to transmit said control values to the radio receiver.

Alternatively or additionally the vehicle positioning means includes a global positioning system (GPS) having a GPS receiver mounted to the vehicle and operatively coupled to the processor whereby, depending on the detected position of the vehicle, the GPS in conjunction with the processor varies the control speed and /or acceleration values. Typically the processor includes preset speed and acceleration values which set the control speed and/or acceleration values depending on latitude and longitude readings of the GPS.

Preferably the speed or acceleration control system also comprises means for determining the actual speed and/or acceleration values for the vehicle, said speed/ acceleration means communicating with the processor. More preferably said speed/ acceleration means includes a speed signal generator. 112438376

5.

According to another aspect of the invention there is provided a vehicle proximity sensing system comprising a radio receiver being adapted to mount to a vehicle and operatively communicate with a radio transmitter located at a fixed preselected position remote from the vehicle, the radio receiver being configured to detect its and the vehicle's proximity to the fixed position dependent on the strength of the radio signal between the transmitter and the receiver.

Preferably the radio transmitter is one of a series of transmitters located at respective fixed - positions and together defining a zone. More preferably the radio receiver thus operates to detect the presence or otherwise of the vehicle within or adjacent the zone.

Preferably the radio receiver is designed to receive data transmitted from the radio transmitter. More preferably said data is received when the radio receiver and the associated vehicle is located within the zone. Even more preferably the transmitted data includes control speed and/or control acceleration data which controls the vehicle.

BRIEF DESCRIPTION OF THE FIGURES

In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a speed or acceleration control module for a vehicle, together with a corresponding speed or acceleration control device and system, will now be described, by way of example only, with reference to the accompanying drawings which:

Figure 1 is a schematic representation of a speed or acceleration control module of an embodiment of the invention fitted to an existing 'by-wire' motor power control system;

Figure 2 is a schematic illustration of a speed or acceleration control system including the control module of Figure 1 together with vehicle positioning means;

Figure 3 is an embodiment of the speed or acceleration control system of Figure 2 for a combustion engine having a electronic throttle body; and

Figure 4 is a variant of the system of Figure 3 with the vehicle having an electric motor drive. 112438376

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As best shown in Figure 1 there is a speed or acceleration control module 10 according to an embodiment of one aspect of the invention which is connected between a power control pedal 12 and an existing motor control module or ECM 14. This and other embodiments of the invention can be adapted to any vehicle with an acceleration ^•by-wire' system, an electronic motor power control pedal or electronic accelerator control such as a rotary handle, lever or knob. The vehicles to which this and other aspect of the invention may be installed include but are not limited to cars, trucks, motor bikes, forklifts, pallet trolleys, trains, trams, tractors, headers, earth movers, front end loaders and excavators. The vehicles to which the system is fitted may be powered by any means including combustion motors or electric motors.

The electronic motor power control pedal 12 outputs an analog signal 16 to the control module 10 of this embodiment of the invention. The analog signal 16 is directly related to the mechanical position of the control pedal 12. The control module 10 reads the pedal position signal 16 and processes this signal by comparing actual speed and/ or actual acceleration values or data for the vehicle with corresponding control data. For example, the corresponding control data may include target speed and target acceleration for the vehicle. The control module 10, on processing of the analog signal 16, and dependent on the comparison between the actual and control data, delivers a modified signal output, or in this instance an analog output signal 18, to the ECM 14. In a combustion engine and as shown in the lower part of Figure 1 the analog output signal 18 is used by the ECM 14 as a reference for positioning of an engine throttle control valve 19. That is, the output signal 18 from the control module 10 of this embodiment of the invention is directly related to the position of the throttle control valve 37. I vehicles with an electric motor drive, the output signal 18 is directly related to the level of power amplification supplying the drive motor.

This embodiment of the invention effectively alters the function of the power control pedal 12 from a variable power control device to a variable speed/acceleration control device. In this example the control pedal 12 position is considered in percentage terms where fully depressed is 100%, half depressed is 50% and not depressed at all is 0%. 112438376

7.

In this example the control module 10 includes two control values or variables in the form of target speed and target acceleration where these control values are derived from corresponding constants of maximum speed and maximum acceleration. These control variables represent that target speed /acceleration which the control module 10 wishes the vehicle to operate at.

Target speed is in this example proportionally equal to the position of the control pedal 12 as a percentage of the maximum speed. Therefore, if the maximum speed is 80 km/hr then for i pedal positions of 25%, 50%, and 75% the target speed is respectively 20 km/hr, 40 km/hr, and 60 km/hr. The target acceleration is in this embodiment calculated in two parts where the first part is such that the initial acceleration is equal to the percentage pedal figure multiplied by the maximum acceleration. Therefore ,if the maximum acceleration is 16 km/hr per second, and the pedal position is 25%, then the initial target acceleration is 4km/hr per second. The second part of the acceleration calculation applied to the initial acceleration figure is in this example dependent on actual parameters, such as actual speed and actual acceleration, for the vehicle. The second part of the acceleration calculation is in this embodiment only applied where the actual speed of the vehicle nears the target speed and in this instance where the difference of the target and actual speeds is less than the target acceleration. If this is the case then the final target acceleration is equal to the initial target acceleration multiplied by a ratio of the difference of the actual and target speeds (considered over a nominal period) divided by the initial target acceleration. Therefore, if the initial target acceleration is 4 km/hr per second and the actual speed is 18 km/hr (the target speed being 20 km/hr) then the difference of target and actual speeds is 2 km/hr and the second part of the acceleration calculation is applied as the difference in target and actual speeds of 2 km/hr is less than the target acceleration of 4 km/hr per second. The second part of the acceleration calculation alters the initial target acceleration of 4 km/ hr per second by multiplying it by the ratio of 2 km/hr per second by 4 km/hr per second (or 1/2). Thus, the target acceleration equals 2 km/hr per second under these conditions.

It will be appreciated therefore that as the actual speed nears the target speed, the target acceleration is reduced accordingly in order to prevent overrunning of the target speed. Further, the calculations can be applied where target speed is less than actual speed. Under 112438376

8. these circumstances target acceleration is considered to be negative or target deceleration. As the actual speed nears the target speed, the required deceleration approaches zero.

Importantly, the control module 10 determines whether modification of the output signal 18 is necessary according to a comparison of actual speed and control/target speed. If within limits the actual speed is sufficiently different to the target speed, the control module 10 then makes a comparison between actual and target rates of acceleration. If the actual rate of acceleration is within limits sufficiently equal to the target rate of acceleration, the control module 10 will make no changes to the output signal 18. If, however, the actual rate of acceleration is sufficiently different to the target acceleration the control module 10 then rectifies this by altering the output signal 18 to cause the power of the vehicle to increase or decrease as the need shall be. Hence, if actual acceleration is greater than target acceleration the control module 10 will reduce the actual acceleration by reducing the output signal 18. Further it may take into consideration the magnitude of the difference between actual and target acceleration when arriving at the magnitude of the change in the output signal 18.

Although the preceding example has been applied to speed/ acceleration values with the control pedal 12 being held 25% depressed, it will be appreciated that the control pedal may in practice be moved to various positions. The control module will continuously vary its target speed and target acceleration to suit the revised control pedal 12 position. In this manner, the control pedal 12 becomes a variable speed/ acceleration control pedal.

As best shown in Figure 2, and in a preferred embodiment of the invention, the control module 10 is coupled to and communicates with means for determining the actual speed and /or acceleration values for the vehicle. In this example this speed /acceleration means is in the form of a speed signal generator 19 which produces a pulse at equally distant intervals during the travel of the vehicles. Hence, the speed signal generator 19 indicates how far the vehicle has travelled by. timing the intervals between pulses. From a sample of these pulses, vehicle speed can be calculated by taking the known distance per pulse or group of pulses sampled and dividing it by the time elapsed during the sampling of these pulses. Acceleration is then calculated by differencing consecutive speeds of the vehicle and dividing the difference by the time elapsed between each sample of vehicle speed used to arrive at these speeds. These actual speed and/ or acceleration values are then used by the control module 10 according to the preceding example and algorithm so as to deliver the 112438376

modified signal output 18 to control the speed and/ acceleration of the vehicle. Generally, the speed and/ or acceleration are controlled to not exceed the control speed and/or acceleration which are set at maximum values.

As shown in the schematic diagrams of Figures 2 to 4 and according to an embodiment of another aspect of the invention, there is a speed or acceleration control syste designated generally as 20. The speed or acceleration control system 20 comprises a power control mechanism such as a pedal 22 including a position sensor (not depicted) being arranged to detect the position of the pedal 22 and provide the analog position signal 16 to the control module 10, this position signal 16 being representative of the position of the pedal 22. The control system 20 also comprises a processor 24 which is in communication with the position sensor of the pedal 22 and is configured to receive and process this signal in accordance with the preceding aspect of the invention. The control module 10 includes an analog to digital converter 25 which converts the analog position signal 16 to a corresponding digital signal for processing by the processor or microcontroller assembly 24.

The control system 20 further comprises vehicle positioning means which is operatively coupled to the processor 24 and designed to inform the processor 24 of the position of the vehicle whereupon the processor 24 controls the modified signal output 18 and thus the speed and/ or acceleration of the vehicle. In this embodiment the vehicle positioning means may include:

1. a radio receiver and transmitter system including a radio antenna 30 mounted to the vehicle and arranged to communicate with a radio transceiver 43 of the control module 10; and/ or

2. a GPS having a GPS antenna 34 mounted to the vehicle and communicating with a GPS receiver 36 of the control module 10.

In this aspect of the invention the vehicle positioning means detects the position of the vehicle, either by its communicable proximity to an external radio transmitter or its GPS derived location, and the control parameters of speed and/or acceleration can be varied accordingly. In the case of the radio receiver and transmitter system, the control module 10 can for example receive maximum allowable speed and acceleration values and these operating parameters of the vehicle can be set externally of and remote from the vehicle. The 112438376

10. GPS may alternately or additionally be utilised to vary these control parameters where it is not for example practical to include a radio transceiver to give specific instructions to change such parameters. The GPS provides positioning data including latitude and longitude which determines the control speed and/ or acceleration ( or maximum speed/ acceleration limits) as dictated by reference control data held by the processor 24 for specific zones or regions defined by latitude and longitude data.

In a preferred embodiment, the radio transceiver 32 receives instructions via radio communication which allow the parameters of control of the system to be changed according to location, current time, weather conditions, traffic conditions and other external parameters. Generally, the control parameters include maximum speed of the vehicle and maximum allowable rate of acceleration. Radio receiver/ transmitter systems are well suited to this application as they can be reliably operated both indoors and outdoors in reliably exchanging quantities of data.

Importantly, the radio receiver/ transmitter system of this aspect of the invention can be used to create vehicle speed limiting zones. For example, if the radio antenna/ receiver 30/32 enters radio proximity to zone radio transmitters, these transmitters can instruct the control module 10 to change control parameters according to instructions/ data sent Furthermore, the control module 10 or processor 24 determines whether or not to accept the data and change the control parameters based on the signal strength of the radio data packet. Since radio signal strength diminishes according to the square root of the radius from the source of the signal, the distance between the vehicle and a zone transmitter can be gauged by the received signal strength. For example, a threshold signal strength, and as such distance of the radio transceiver/ antenna from a zone transmitter, may determine whether or not control parameters are varied for the vehicle. In this capacity, the described embodiment has the capacity to externally control zone speed and acceleration dependent on proximity of the vehicle to zone transmitters.

Figures 2 to 4 illustrate various embodiments of the speed or acceleration control system of the invention. The schematic of Figure 2 is a generic version of the control system whereas Figures 3 and 4 relate to vehicles powered by an internal combustion engine and an electric motor drive, respectively. For ease of reference, and in order to avoid repetition, similar components of the control system have been designated with the same reference numerals. 112438376

11. In a preferred embodiment of the invention the mechanical travel of the power control mechanism or pedal 22 is directly related to the speed of the vehicle. This can be contrasted with the prior art where the position of the power pedal is directly related to the power output of the vehicles engine. In the preferred example of the invention the power control pedal 22 is in effect a continuous speed control pedal which for instance can be used to create a variable speed limiting effect. For example, if a vehicle is faced with a 5 km/hr limit, the motor power control pedal will operate in a range from 0 to 5 km/hr. Considering linearly, from rest then holding the control pedal down through 50% of its mechanical travel the system will seek to accelerate the vehicle at a mild rate to 2.5 km/ hr and maintain that speed. The control module such as 10 ensures that this speed is maintained both on level ground and when the vehicle reaches an incline wherein the control module 10 alters the power of vehicle to overcome the incline and maintain the constant speed. Conversely, when the vehicle reaches a decline the control module 10 reduces the power of vehicle so as to maintain the constant speed.

In another example the speed limit parameter of the vehicle is increased to 100 km/hr and the maximum rate of acceleration is to be set at 10 km per hour per second over this range. If the motor power control pedal 22 is held at full travel and the vehicle driven on level ground, the control module 10 will ensure that the vehicle accelerates at 10 km/hr per second or less, up to the speed limit of 100 km/hr. If the power control pedal 22 position is then reduced to 70% the control module 10 will allow the vehicle to decelerate to 70 km/hr. The position of the pedal 22 directly causes the speed limit to proportionally vary which in turn causes the acceleration limit to proportionally vary, see the previous example and algorithm.

Now that a preferred embodiment of the present invention has been described in some detail it will be apparent to those skilled in the art that the speed or acceleration control module or system has the following advantages:

1. the control module can effectively change the function of an existing power control pedal from operating as a variable motor power control to ojperating as a variable vehicle speed control; 112438376

12.

2. the control system may be employed to wirelessly control speed and acceleration of vehicles to which it is fitted; and

3. the control system may be utilised to for example control a vehicles maximum speed and rate of acceleration and these control parameters may be changed according to external conditions such as location of the vehicle.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. For example, a forklift contains many functions that may cause the vehicle itself to become unstable above certain speed/ accelerations. These include laden mass, steering position, and height of lifting mechanism. When calculating target speeds and accelerations it may be useful to include feedback from these functions in order to adjust calculations and render the vehicle more safe in operation. All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.

Claims

902868713.CLAIMS

1. A speed or acceleration control module for a vehicle, said control module comprising a processor being adapted to receive a position signal from a position sensor operatively coupled to a power control mechanism of the vehicle, the processor being configured to compare actual speed and/ or actual acceleration values with respective control speed and/or control acceleration values and, dependent on said comparison, deliver a modified signal output to an engine control module of the vehicle thereby controlling its speed and/or acceleration at the respective control values.

2. A speed or acceleration control device for a vehicle, said control device comprising:

a positio sensor being adapted to detect the position of a power control mechanism of the vehicle and provide a position signal representative of said position; and

a processor being in communication with the position sensor so as to receive its position signal, the processor being configured to compare actual speed and /or actual acceleration values with respective control speed and/ or control acceleration values and, dependent on said comparison, deliver a modified signal output to an engine control module of the vehicle thereby controlling its speed and /or acceleration at the respective control values.

3. A speed or acceleration control system for a vehicle, said control system comprising:

a processor being in communication with the position sensor so as to receive its position signal, the processor being configured to compare actual speed and/ or actual acceleration values with respective control speed and / or control acceleration values and, dependent on said comparison, deliver a modified signal output to an 112438376

14. engine control module of the vehicle thereby controlling its speed and /or acceleration at the respective control values;

4. A speed or acceleration control system as defined in claim 3 wherein the vehicle positioning means includes a radio receiver and transmitter system having a radio receiver mounted to the vehicle and operatively coupled to the processor, and a radio transmitter located at a fixed position remote from the vehicle whereby, depending on the detected position of the vehicle, said radio system varies the control speed and/or acceleration values.

5. A speed or acceleration control system as defined in claim 4 wherein the radio transmitter is configured to transmit said control values to the radio receiver.

6. A speed or acceleration control system as defined in claim 3 wherein the vehicle positioning means includes a global positioning system (GPS) having a GPS receiver mounted to the vehicle and operatively coupled to the processor whereby, depending on the detected position of the vehicle, the GPS in conjunction with the processor varies the control speed and / or acceleration values.

7. A speed or acceleration control system as defined in claim 6 wherein the processor includes preset speed and acceleration values which set the control speed and/or acceleration values depending on latitude and longitude readings of the GPS.

8. A speed or acceleration control system as defined in any one of claims 3 to 7 also comprising means for determining the actual speed and/or acceleration values for the vehicle, said speed /acceleration means communicating with the processor.

9. A speed or acceleration control system as defined in claim 8 wherein said speed/ acceleration means includes a speed signal generator.

10. A vehicle proximity sensing system comprising a radio receiver being adapted to mount to a vehicle and operatively communicate with a radio transmitter located at a 112438376

15. fixed preselected position remote from the vehicle, the radio receiver being, configured to detect its and the vehide's proximity to the fixed position dependent on the strength of the radio signal between the transmitter and the receiver.

11. A vehide proximity sensing system as defined in daim 10 wherein the radio transmitter is one of a series of transmitters located at respective fixed positions and together defining a zone.

12. A vehicle proximity sensing system as defined in daim 11 wherein the radio receiver thus operates to detect the presence or otherwise of the vehide within or adjacent the zone.

13. A vehide proximity sensing system as defined in daims 10 to 12 wherein the radio receiver is designed to receive data transmitted from the radio transmitter.

14. A vehide proximity sensing system as defined in daim 13 (when it depends on either of daims 11 or 12) wherein said data is received when the radio receiver and the associated vehide is located within the zone.

15. A vehicle proximity sensing system as defined in claims 13 or 14 wherein the transmitted data indudes control speed and/ or control acceleration data which controls the vehicle.