TECHNICAL FIELD

Embodiments of the invention relate to a device for calming traffic.

BACKGROUND Traffic calming devices such as speed bumps operate on the principle that an obstruction placed in the way of a vehicle will encourage drivers to slow down to avoid the unpleasant sensation of passing over the obstacle at speed, and the corresponding damage that this may cause to their vehicles.

However, speed bumps suffer from the disadvantage that the potential damage done to a vehicle will depend on the configuration of that vehicle. For example, sports cars which have a low clearance height might suffer damage not only to the suspension, but also to the body of the vehicle if the clearance height is not sufficient. In contradistinction, sport utility vehicles have high clearance heights and suspension designed to accommodate obstacles. Therefore, drivers of such vehicles have little or no incentive to slow down in the knowledge that the potential damage to their vehicles will be minimal.

Dynamic speed bumps which are raised and lowered on demand are known. However, these dynamic speed bumps operate by being attached to a speed sensor which determines the speed of the approaching vehicle and lowers the speed bump if the speed is less than the speed limit.

Such dynamic speed bumps suffer from the disadvantage that they are costly to produce and maintain, and require significant energy requirements to operate. SUMMARY

According to a first aspect, the invention provides a traffic calming device comprising a moveable obstacle and a retraction mechanism for moving the obstacle when a vehicle is brought into contact with the obstacle, wherein the retraction mechanism comprises a release system for moving the obstacle at a predetermined speed.

The obstacle is a cradle for engaging with one or more wheels of a vehicle. The obstacle may be retractable.

The obstacle may be deflateable and said movement of said obstacle at the predetermined speed may comprise deflating the obstacle.

The retraction mechanism may comprise a fluid release and my be an hydraulic piston.

The fluid release may further comprise a release valve.

A flow rate of the release valve may be adjustable.

The predetermined speed may be variable so that a user may set the predetermined speed in dependence on a speed limit. The predetermined speed may be set by adjusting a flow rate of the release valve.

The predetermined speed may be related to a fluid flow rate of said release valve.

The obstacle may comprise a cradle for engaging with one or more wheels of the car, wherein the cradle may be engaged with the retraction mechanism, the retraction mechanism may comprise an hydraulic cylinder, the cradle may be adapted for pivotal movement relative to a surface upon which the wheel proceeds, wherein the cradle may be engaged with the hydraulic cylinder so that the pivoting movement of the cradle commensurate with a forward direction of the vehicle compresses the hydraulic cylinder, the retraction mechanism may further comprise a release valve engaged with the hydraulic cylinder so that the hydraulic cylinder has a maximum rate of operation, and so that the pivoting movement of the cradle is limited by the maximum rate of operation of the hydraulic cylinder.

The cradle may comprise first and second arms.

The retraction mechanism may comprise a first and a second hydraulic cylinder, each hydraulic cylinder being connected to corresponding arms of the cradle so that pivoting of the cradle in a first direction engages the first hydraulic cylinder and pivoting of the cradle in a second direction engages the second hydraulic cylinder.

A further embodiment of the invention relates to a method for calming traffic comprising providing a moveable obstacle and moving the obstacle at a predetermined speed when a vehicle is brought into contact with the obstacle.

The obstacle may be a cradle for engaging with one or more wheels of a vehicle.

The obstacle may be retractable.

The obstacle may be deflateable and said step of moving of said obstacle at the predetermined speed may comprise deflating the obstacle.

The obstacle may be moved by a fluid release.

The obstacle may be moved by an hydraulic piston.

The method may further comprise providing a release valve.

A flow rate of the release valve may be adjustable. The predetermined speed may be variable so that a user may set the predetermined speed in dependence on a speed limit.

The predetermined speed may be related to a fluid flow rate of said release valve.

The method may comprise the further step of reversing a movement of the obstacle once the vehicle is out of contact with the obstacle.

The obstacle may be moved back to an initial position.

The obstacle may be moved back to position which varies from an initial position. DESCRIPTION OF ACCOMPANYING FIGURES

Embodiments of the invention are described with reference to the accompanying schematic diagrams where:

Figures la to If are schematic diagrams of a traffic calming device according to a first embodiment under different configurations when a vehicle approaches at or below the speed limit;

Figure 2 is a schematic diagram of the traffic calming device of Figure 1 when a vehicle approaches at a speed in excess of the speed limit; and

Figure 3 is a schematic diagram of a traffic calming device according to a further embodiment of the invention. DESCRIPTION OF EMBODIMENTS

Embodiments of the invention are described hereafter with reference to the accompanying diagrams. Figure 1 illustrates a traffic calming device 10 according to an embodiment of the invention. The traffic calming device 10 comprises a cradle 12 mounted so that it can pivot about axel 14. The cradle 10 is mounted in a depression 60 formed in a road surface 70. In an alternate embodiment, the cradle is provided on top of the road surface.

The cradle 12 comprises two arms 52 and 54 which are formed with corresponding inner surfaces 20 and 18. Inner surfaces 20 and 18 are joined by middle surface 16.

A retraction mechanism 30 is attached to arm 54. The retraction mechanism 30 comprises an hydraulic cylinder 32 having an extendible shaft 34. The extendible shaft 34 is attached to the arm 54 at a pivot joint 36.

The retraction mechanism 30 of the traffic calming device 10 further comprises a pump 42 and a reservoir of hydraulic fluid 40. The reservoir 40 is connected to the hydraulic cylinder 32 by means of a supply line 46 and a return line 44. The retraction mechanism 30 further comprises a release valve 48 which, in this embodiment, is incorporated into the hydraulic cylinder and which allows fluid to flow from the hydraulic cylinder back through the return line 44 to the fluid reservoir 40. Therefore, the retraction mechanism is arranged so that the downward (in the orientation shown in the Figures) movement of the shaft 34 is limited by the rate at which fluid is released by the release valve 48.

It is to be realised that the location and configuration of the hydraulic cylinder and pump may be varied in further embodiments and the particular arrangement illustrated is provided by way of illustration only. In the embodiment illustrated, the cradle 12 is moveable in that it can pivot about the axel 14. This pivoting movement causes the extension and retraction of the shaft 34 of the retraction mechanism 30. It is to be realised that some lateral movement of the pivot joint 36 between the shaft 34 and the arm 54 of the cradle 12 will occur. Although not illustrated in this schematic diagram, such lateral movement is accommodated by the pivot joint 36.

In use, the pump 42 controls the flow of hydraulic fluid between the reservoir and the hydraulic cylinder 32 through the supply line 46 and the return line 44. In the embodiment illustrated, the pump 42 is therefore able to pivot the cradle. However, in normal operation, the pump 42 acts to pivot the cradle 12 so that arm 54 is lowered, and arm 52 is raised. Pivoting of the cradle 12 in the opposite direction will occur under the influence of a vehicle, as described below.

Also illustrated in Figure la is the wheel 50 of a vehicle. In Figures la to If the vehicle is travelling from right to left, and the operation of the traffic calming device 10 will be described with reference to these Figures.

Figure la shows the traffic calming device 10 in an operationally ready state. In this state, the cradle 12 has been pivoted so that the arm facing the oncoming wheel 50 is lowered, thereby raising the opposite arm. As illustrated in Figure lb, the wheel 10 then engages the traffic calming device by engaging with the surface 18 of arm 54 of cradle 12. As the wheel 50 progresses, it then comes into contact with the middle surface 16 and the surface 20 of arm 52. In the embodiment illustrated, the size of the cradle 12 and of the wheel 50 are such that the wheel engages with these three surfaces (18, 16 and 20) simultaneously. However, it is to be realised that wheel sizes will vary substantially from vehicle to vehicle and for other wheel sizes, fewer of the surfaces of the cradle will be engaged. Furthermore, the cradle need not have the profile illustrated.

In further embodiments, the cradle is provided with a profile adapted to the required design criteria. For example, the height of the profile may be designed relative to the speed limit of the location where the cradle is to be installed.

Advantageously, the profile presented to a vehicle travelling in the wrong direction will be greater than that presented to a vehicle travelling against the intended direction. This will discourage drivers from trying to circumvent the traffic calming device by veering onto the oncoming traffic lane.

As the wheel 50 progresses it pushes against the surface 20, this causes the cradle to pivot about axel 14, bringing arm 52 downwards and arm 54 upwards so that the cradle 12 moves to the orientation shown in Figure Id, and then continues moving until the cradle has pivoted to the furthest extent permitted, shown in Figure le, at which point, the wheel 50 will continue to move and will exit the traffic calming device 10, as shown in Figure If.

As shown in Figures Id, le and If, as the cradle 12 pivots, the shaft 34 extends as the cradle 12 pivots under the influence of wheel 50. The shaft 34 is not freely moveable, but the rate of the upward movement is controlled by rate at which the release valve 48 allows fluid to pass there through. So too, the rate at which the cradle 12 pivots is controlled by the release valve 48.

The rate at which the release valve 48 releases the fluid is set, taking into account the dimensions and other properties of the cradle 12 so that the maximum rate at which the cradle can pivot between the configurations shown in Figure la and that shown in Figure If corresponds to the vehicle travelling at the speed limit. If the wheel 50 of the vehicle engages with the cradle 12 when the vehicle is travelling at a speed which is greater than the speed limit, the result is shown in Figure 2. Since the cradle 12 has not completed its pivoting movement at the time the wheel 50 exits the traffic calming device (as shown in Figure 2), the arm 52 is still raised relative to the surface of the road by the relative height 'h', thereby presenting the wheel with a significant obstacle to overcome, hence passing a bump (shock) to the vehicle and its driver proportional to the speed of the vehicle. Depending on the relative sizes of the cradle and the wheel and a number of other factors including application (contact) area which may be taken into account when constructing the cradle, and configuring the traffic calming device 10, the arm 52 may cause significant damage to the wheel 50 including a flat tire, wheel damage and/or damage to the suspension of the vehicle.

Therefore, embodiments of the invention provide a cheap and easy to configure device which presents the drivers of vehicles with significant incentive to stick to the speed limit. Furthermore, since the cradle can be installed with little or no raised profile relative to the road surface, any vehicle with low road clearance will not be adversely affected in negotiating this traffic calming device, provided of course that the speed limit is adhered to.

Once the wheel 50 has passed over the cradle, the pump 42 is operated to pump fluid from the hydraulic reservoir 40 to hydraulic cylinder 32, thereby raising the shaft 34, causing the cradle 12 to pivot back to the orientation shown in Figure la. Alternatively, the cradle may not be returned all the way back to this position, but instead to an intermediate position such as the position illustrated in Figure Id, depending on factors such as the location, traffic flow, road authority pre-settings etc. to achieve the desired end result

The embodiment illustrated in Figures 1 and 2 comprises a single hydraulic cylinder. However, in further embodiments two hydraulic cylinders attached to respective arms of the cradle are provided.

Figure 3 illustrates a traffic calming device 80 according to a further embodiment. The traffic calming device 80 comprises a base 82 onto which a cushion 84 is mounted. In the embodiment illustrated, the cushion comprises a single bladder, but multiple bladders could also be used. Multiple bladders have the advantage of increasing the amplitude of the shock delivered to the vehicle.

The device 80 comprises a retraction mechanism which has a hydraulic cylinder 86 connected by a supply line 90 and a release line 92 to a hydraulic fluid reservoir 94. The hydraulic cylinder 86 is connected by a line 98 to the cushion 84. The hydraulic cylinder 86 comprises a release valve 88 which limits the rate at which fluid may pass through the cylinder 86.

During operation, the pump 96 pumps fluid from the hydraulic reservoir 94 through the supply line 92 to the hydraulic cylinder 86 thereby inflating the cushion 84. When the wheel of a vehicle engages with the cushion, the cushion will deflate by allowing fluid through the release valve 88 of hydraulic cylinder 86. Therefore, the obstacle presented to the vehicle can be reduced for those vehicles travelling at or below the speed limit.

The cushion 84 illustrated in Figure 3 has a symmetrical profile. In further embodiments, the cushion is provided with an asymmetrical profile so that, as the cushion deflates under the weight of the vehicle, the obstacle presented to the wheel of the vehicle has a constant height, provided that the vehicle is travelling close to the speed limit.

In a further embodiment, the cradle is pivoted by a spring and motor acting against the spring.

The retraction mechanism may be triggered by a sensor which could be piezoelectric. An electrically actuated flow valve may be used to time the retraction mechanism.

Advantageously, embodiments of the invention do not require vehicles which are travelling at or below the predetermined speed to slow down and speed up, as in the case with existing speed bumps. This reduces the environmental impact of these traffic calming devices. It is to be realised too that the embodiments of the invention can adapted to high speed roads such as highways and apply to all vehicle types.