WO2000015485A1

WO2000015485A1 - Improvements in or relating to motor vehicles

Info

Publication number: WO2000015485A1
Application number: PCT/GB1999/003029
Authority: WO
Inventors: Brian Stapleton Stratford
Original assignee: Brian Stapleton Stratford
Priority date: 1998-09-12
Filing date: 1999-09-13
Publication date: 2000-03-23
Also published as: GB2341355A; GB9819838D0; GB2341355B; AU5874199A

Abstract

The present invention relates to a car comprising a roof (4), a rear and cabin side-walls (6) and containing a driver's seat, in which the cabin side-walls taper inwardly towards the rear and the roof of the car is taller at the rear than at the driver's seat. The present invention also relates to a car comprising a roof, a rear and containing a driver's seat and having a driver's entrance port (8) disposed at the rear or between the driver's seat and the rear, and the roof of the car is taller at the rear than at the driver's seat. The present invention also relates to a car comprising a retractable tail-cone (10) which preferably is extendible and retractable whilst the car is in motion.

Description

IMPROVEMENTS IN OR RELATING TO MOTOR VEHICLES

The invention relates to motor vehicles and more particularly to passenger cars.

It is known to construct motor vehicles in such a way as to diminish their air resistance. To attain this end various forms have been adopted for the external shape of a car. These forms are characterised by an effort to give the vehicle body a streamline shape whilst still allowing sufficient cabin space.

Streamlined vehicles with a cabin substantially wider at the driver's seat than at the front and rear are known (e.g. UK patent application no. 494,664 and US patent 4,772,060), where a cabin with a relatively pointed front and cabin side-walls tapering outward rearward of the front to a wide point about the driver's seat and then inwards towards the rear giving a general elliptical view in plan section were introduced to reduce drag. However, the general design features of modern vehicles, for example a wide seating arrangement for passengers, rear access for luggage space, combined with length limitations for parking and urban driving as well as the width of wheel spacing needed for stability lead to a car design which is generally rectangular in plan section. Current car design takes into account cost and weight factors, so even though a very long sleek car could have less aerodynamic drag than a short rectangular car, it would tend to be more expensive as well as heavier, with the increased weight leading to higher fuel consumption.

Increasingly there is a need for cars of low fuel consumption, be it of petrol, diesel, gas, battery power or the like. A reduction in fuel consumption would make the car more acceptable as its effect on the environment would be reduced - lower emissions and less use of resources. Diminished air resistance will decrease the fuel consumption of a vehicle. A reduction in fuel consumption also may be achieved by providing a car of lightweight material but here the reduction in fuel consumption must be weighed against the requirement for cars to be crashworthy, i.e. resistant to impact.

It is an aim of the present invention to provide a motor vehicle which overcomes at least one disadvantage described above associated with known motor vehicles. According to the first aspect of the invention there is provided a car comprising a roof, a rear and cabin side- walls and containing a driver's seat, in which the cabin side- walls taper inwardly towards the rear and the roof is taller at the rear than at the driver's seat.

The car according to the first aspect of the invention has its streamlining almost entirely on the cabin side-walls, preferably with the car substantially narrower, over its full height, at the rear of the car than at the driver's seat. It should be appreciated that the driver's seat may be moved between fore and aft positions and any reference to the position of the driver's seat is intended to include the seat in either the fore or aft positions or a position therebetween. Furthermore it should be appreciated that it is not intended that the driver's seat be limited to a seat in the conventional sense. A car driver may in future kneel or stand to drive a car. Therefore the "driver's seat" is intended to include the region in which the driver of a car is situated to drive the car.

The car according to the first aspect of the invention may have a conventional plan form (the view in plan section), that is, that the car in plan view is generally rectangular with a wheel at or about each corner in order to provide conventional stability and manoeuvrability. However, it may be that the planform of the car according to the first aspect of the invention is modified to take into account the cabin side-wall tapering as is discussed in the Examples.

"Boat-tailing" is a term sometimes used for the aerodynamic tapering, or the gradual decrease, of the cross-sectional area of a body towards the trailing edge. Conventionally on a car, or, more specifically, on a car which has a substantial amount of boat-tailing, the boat-tailing is carried out on the roof. Small amounts of boat-tailing are often carried out on cabin side-walls but ordinarily to a smaller degree than is achieved in various current conventional cars by shaping the roof and rear window.

The initial aerodynamic advantage of providing cabin side-walls tapering inwardly towards the rear of the car is that the full flow relevant to the analysis for a car includes the reflection in the ground, as shown in Figure 1. For this total flow, of car plus reflection, the plane of the ground becomes just a plane of symmetry. Consequently the relevant, fundamental, thickness aspect ratio for the flow may be related to twice the height of the car, divided by the width, rather than just the height to width ratio. That tends to make the width of the car become the "thickness" of the three-dimensional body being analysed and twice the height become the "span". Then, rather than tapering downwards on the height, the width could be the more fundamental dimension aerodynamically for the application of boat-tailing.

On a car according to the first aspect of the invention with tapering cabin side- walls towards the rear of the vehicle it should be appreciated that as the cabin thins towards the rear the wheels and possibly suspension may protrude from a plan view of the car. Accordingly, to reduce the drag associated with such protruding elements wings may be provided to cover any elements that would otherwise become uncovered to the airflow, with the wings and under-surface being designed aerodynamically for reasonably streamlined flow in conjunction with the remainder of the car.

The wings provide a channel for airflow between the wheels and cabin side-walls. It is preferably that these airflow channels are large in such a way that adequate airflow can occur through the channels. One way of keeping the airflow channels relatively large whilst maintaining a generally rectangular planform to the wheels is to reduce the wheel thickness, possibly by say up to a half. This allows the original volume taken up by the wheel to be utilised as the airflow channel. Such reduction in wheel size is made especially possible by providing a lightweight car.

In the first aspect of the invention the roof structure is arranged to take the cabin side- wall tapering into account. With cabin side-wall tapering the width of the roof decreases in its approach to the rear of the car. Such a situation could tend to produce various undesirable three-dimensional flows and a core or cores of high loss flow opposing the diffusion. It is therefore essential that the central meridian line of the roof rises rearwards. Simultaneously there may be a change in roof section shape, such that the roof leads to a tail fin. The result is that each semi-span of the boundary layer which had approached on the roof is rotated to some extent with the local roof, in a controlled process, as the air moves rearwards, so that it crosses the trailing edge distributed, although in an imperfect manner, respectively on each side of the upper part of the tail fin. Such an arrangement could be more efficient than maintaining either a horizontal roof, or a downward sloping boat-tailing roof, when the side-walls of the cabin are specified as the main walls for the cabin boat-tailing.

It should be noted that the roof of the vehicle need not reach its highest point at exactly the rear of the vehicle. It may be that the roof height reaches a peak behind of the driver's seat but then lessens towards the rear of the car. However, it is preferred that the peak of the car^'s height is substantially about the rear of the car.

The provision of the raised roof at the rear of the vehicle allows roll bars to be easily added to the roof structure for safety. Furthermore the raised roof provides for a larger window area at the rear of a car for increased rear visibility. A further advantage is that the extra roof height at the rear of the car allows for ease of access to the vehicle through doors rearward of the driver's seat, a point which is particularly important with reference to a preferred embodiment of the first aspect of the invention as discussed below.

The preceding discussion describes the general direction in which the aerodynamic design is taken.

A further preferred feature which aids reducing the fuel consumption of a car according to the first aspect of the invention whilst maintaining the structural stability of the car is the provision of a driver's entrance port disposed at the rear or between the driver's seat and the rear.

In many small aeroplanes the pilot enters the cockpit by climbing over the side-wall of the fuselage. Most of the height of the side-wall alongside the cockpit is therefore permanently fixed. As such it forms an integral and very important part of the structure of the cockpit and of the whole aeroplane.

In contrast the modern car is designed to suit our convenience. Each of the structural side-walls which are on an aeroplane are replaced, in conventional cars, by one or more holes - the doorways through which we enter and leave the car. As a result the stress loads have to be transmitted or redirected around the holes (other than the load parts which can go through the doors) so that the local loads are magnified. To overcome the local stresses metal structures are included in conventional cars to add strength. These metal structures add to the weight of the car and are thus undesirable.

Provision of the driver's entrance port towards the rear of the car allows a substantial area of fixed structural cabin side-wall to be provided on each side of the car around and forward of the driver's seat. Consequently, according to a preferred embodiment of the first aspect of the invention access to the vehicle is provided through the driver's port only.

One of the more important considerations in determining the strength needed in a car is the load line during front impact. Thus providing a fixed structural cabin side-wall near the front of the vehicle, possibly integral with the front of the car, provides additional strength during front impact. The increased area of structural cabin side- wall could lead towards reduced maximum stresses and a reduction in the weight of the car, possibly with the construction employing substantially greater use of lightweight materials of reasonably low manufactured cost. Additionally, a lightweight car could thus have improved crashworthiness, which could be built into the arrangement as compared to a conventional car as a result of lower stressing and lower weight.

It may be considered that the near side region of a car would be less vulnerable in front impact than would be the offside, the offside being closer to oncoming vehicles. Also the passenger seat is less frequently occupied than the driver's seat. Also, access to and from the car is of less of a hazard when carried out from the near side rather than the offside.

For these reasons it is preferred that access to the car is from the near side of the car only. This allows the offside of the vehicle to be provided as a single cabin side-wall, with the improved structural stability that this provides allowing the offside cabin side-wall to be provided in a lightweight material or in a lightweight design.

According to a preferred embodiment of the first aspect of the invention access to the car is provided through a driver's port in the near-side of the car only. In such an arrangement it would be advantageous to improve access to the driver's seat. Improved access arrangements could include tipping seats or folding seats, including a folding arrangement against a fixed cabin side-wall, with the near side front seat more easy to slide between fore and aft positions than conventional cars and being controllable both from all the seats and from outside the vehicle. The arrangement should also provide improved areas for gripping and stepping, for access to the car, while the floor of the car in the path to the driver's seat should be kept relatively clear of controls and fixings. Furthermore it is preferable that the driver and any passengers of the car be able to stand upright during much of the entry or exit from the car. To that end, as will be seen in the Examples, the floor and a lower part of the cabin could be built slightly wider than the cabin side-walls to provide a sill, allowing provision of a footrest. The increased roof height at the rear may ease the driver's entry by increasing the headroom, while even additional headroom (for example by provision of a dome) may be provided without undue compromise of the aerodynamics.

Emergency exits could be provided to compensate for a reduction in doors, possibly being provided in the roof or in offside windows.

From the above discussion it is shown that it is preferable to provide the cabin of a car as a shell of fixed structure, preferably only containing one entrance port, the driver's entrance port. By providing the cabin as a shell the structural integrity of the car is increased as compared to a car made up of several pieces. This allows the shell to be provided in a more lightweight material or design than a car made up of several pieces, as the resistance to stress in the shell will be greater. For this reason it is preferred that any windows in the cabin are provided as fixed areas of transparency integral with the shell. An alternative is that window holes are included in the shell but are filled with fixed windows that are not intended to be opened.

According to a further embodiment the car of the first aspect of the invention also has a retractable tail-cone. Preferably the tail-cone is extended when the vehicle is travelling at moderate to high speeds. Correspondingly the tail-cone is preferably retracted and stowed in the rear of the car for low speed driving such as urban driving and for parking and garaging. The rear tail-cone provides a reduction in medium and high-speed drag resulting in a reduction in fuel consumption at moderate to high speed as compared to a car without a tail-cone.

Although called a "cone", the geometry is thought of as any suitable tapering shape, for example a frusto-cone or series of concentric square or rectangular cylinders.

In a preferred embodiment dashboard indication would keep the driver informed as to whether the tail-cone were extended or retracted. Extension and retraction could both in principle be automatic and be dependent on for example time at speed. However, until experience were gained on the use of tail-cones in real situations, it would probably be preferable to require the driver to make a positive movement within his controls in order to authorise the system to take action either way.

In order to keep the length of the cone to a minimum it would be preferable to design the car for the best known aerodynamics consistent with the purposes of the car. On cars of suitable shape, tail-cones entirely of purely circular and co-axial cross- sections, i.e. axi-symmetric tail-cones could be used. These might be expected to have advantages of simplicity and cheapness, stiffness, possible freedom from vortex shedding, and suitable clearances for other traffic when turning. Cars according to the first aspect of the invention are especially designed for axi-symmetrical tail-cones.

A qualification on the above rather general discussion is that the change of section for the roof, especially given the blend, where necessary, with an axi-symmetrical tail- cone, makes it more difficult to distinguish between roof and cabin side-wall boat- tailing, although the objective remains as described.

According to a second aspect of the invention there is provided a car comprising a roof, a rear and containing a drivers seat and having a driver's entrance port disposed at the rear or between the driver's seat and the rear, and the roof of the car is taller at the rear than at the driver's seat.

The features of the driver's entrance port and car roof are as described in accordance with the first aspect of the invention and preferred embodiments thereof. In the second aspect of the invention the roof structure is arranged to provide additional headroom at the rear of the vehicle, at or around the driver's entrance port.

Cars according to the second aspect of the invention may also comprise a retractable tail-cone as described in accordance with the first aspect of the invention. As with the first aspect of the invention cars according to the second aspect of the invention are preferably especially designed for axi-symmetrical tail-cones.

According to a third aspect of the invention there is provided a car comprising a retractable tail-cone at its rear.

The retractable tail-cone is as described in accordance with the first and second aspects of the invention.

Additionally retractable tail-cones according to the third aspect of the invention are envisaged as being added to cars of conventional design. One might for example design a conventional saloon car, or a "hatch", to have reasonably good streamline flow right down over its rear window, so that the retractable tail-cone would need to cover only the rear area below the window and would be short accordingly. An "estate", however, may be considered by the car designer to require almost the whole height of the vehicle to be available for loads, as well as for loading at the rear, so that use of the simplest "square" shape for the upper and side surfaces of the rear of the car could cause the tail-cone to be long. Compromises would probably then be appropriate, in that some careful curving of the surfaces of the estate car close to the rear could much improve the total geometry without significant loss of space or height. Additionally, some truncation of the tail-cone at its rear end may considerably reduce its length while still leaving it with an overall advantageous performance.

Of the two examples just mentioned the estate, with its essentially full height at the rear of the car proper, would require a transparency in the tail-cone if internal rear vision were required. On the other hand, the particular saloon, or hatch, with its excellent aerodynamic design arranged to give at least reasonably good streamline flow over the rear window, that would not require the transparency in the retractable cone. Consequently the tail-cone would be much easier to design, both for its not requiring a transparency and for its shorter length.

From the above discussion one may conclude that, while "any" tail-cone which gives a fairly slow taper rate could probably improve the flow at the rear of a vehicle, and reduce the drag accordingly, it would probably be more satisfactory to design the tail- cone to suit the geometry and aerodynamics for any particular type of vehicle, rather as discussed for various types of circumstances. It would probably be even more satisfactory, as suggested above, to design the car and the tail-cone in conjunction with each other, in order that the steady aerodynamics, the mechanics, and the structural stability were all satisfactory.

The rear wheels of the car may be best moved rearward slightly, in order the better to hold the loads caused by the tail-cone. However, for cars already well capable for accepting the loading from large trailers, it may be that the loads from a moderate tail- cone could be found to be easily within the existing capabilities.

When using the tail-cone one should consider the tendency, when the car turned, for the rear of the cone to move sideways, geometrically, relative to a line of traffic, even if all the design were mechanically rigid. This effect would be as a result of the overhang from the rear wheels. An arrangement having a sideways converging taper would help the situation, the rear lights positioned accordingly. A rearward movement of the position of the rear wheels would also help in that respect, by reducing the overhang. A more complicated alternative, perhaps worth consideration, for a very large cone on a vehicle with a very large area of rear, would be to mount the cone on a trailer, with a flexible streamlined joint between the vehicle and the cone, and to make perhaps only the rear part of the cone retractable.

In principle a tail-cone could reduce the aerodynamic drag at high speed to a small fraction of conventional values for cars.

At least three car designs are envisaged as being adapted according to the first, second or third aspects of the invention. The first design is for the maximum cabin width to equal either the full width of the car, exclusive of mirrors, or almost the full width. That, in the particular version discussed here, allows a four-seat cabin. The second design is for a two-seat cabin in the style of a small aeroplane, i.e. with the seats in line fore and aft, with a maximum cabin width equal to about half the full width of the car. The third design is intermediate between the first two, with the maximum cabin width equal to about three-quarters of the full width of the car. In this third design of the three-quarters width, the seating is arranged primarily for one to two people in total, but is able to accommodate up to four on occasions. Each of the near side seats would perhaps be set back slightly behind the offside seats in order to allow plenty of "elbow space". In addition, say, the backs of the near side seats may fold down for conversion of the area to "office space^" or supplementary luggage space.

The four-seat car could be adapted to include an axi-symmetric tail-cone, extendible and retractable while the car is moving, as discussed in accordance with the third aspect of the invention.

The two-seat design provides a car which with cabin side-wall tapering has diminished drag and therefore may not require a tail-cone, dependent, for example, on the overall planform of the car, or on the spaces required in the cabin.

The car of intermediate width, to take four people on occasions, can be adapted to include a small axi-symmetrical tail-cone. Alternatively it could be adapted to cones of other shape, given that only a small size would be required. An alternative to a small tail-cone would be to provide an aerodynamic rear area for a bumper, registration plate and lights for example - in conjunction with a reasonably good aerodynamic performance.

The 2-seat car, by itself, if carefully designed, could have eliminated some component of drag. Consequently its total aerodynamic drag could be very much less than for conventional cars. The same conclusion on drag holds for the other two cars, provided they are used in conjunction with their extendible and retractable tail-cones. The car of intermediate width cabin would have a significantly reduced drag compared with conventional, even without tail-cones. Now small fuel consumption, overall, requires preferably that the weight of the car should be low, as well as its aerodynamic drag. Consequently all the configurations discussed above are suggested for use in conjunction with the lightweight designs.

For the narrower two cabin widths, fore and aft wings running between the front and rear wheels can slope downwards towards the rear, rather slowly, behind the front wheel fairings, in order to achieve streamline flow. The flow in the region is complex. It is proposed that air can be brought down by the well-rounded edge curve of the windscreen in favourable wing body interference. Then, with the air meeting from each forward direction, the airflow would be designed to leave the rearward facing surface of the wing as nearly as possible as a rearward, steady and low loss flow, as determined by a three-dimensional nodal shape built into the surface of the wing. The rearward running wing could then give the additional areas of permanently fixed cabin side-walls in the positions that are most important for achieving low stress. It would also allow a convenient means of access to the cabin, when used in conjunction with firm step positions and handholds for example.

Consequently the narrower two cabin widths seem to be suitable both for low drag and low weight.

Additional features which may be incorporated into cars according to the first, second or third aspects of the invention are described below:

If the car structure were largely in existing lightweight material, it might be considered appropriate to put a small number of ski-type runners, of tough galvanised steel, well inset into the floor, in a way that would allow them to reach and project externally without breaking the integrity of the floor, in order to give some protection should there ever be contact with the ground.

The strains in the shell structure, at least for crash situations, would tend to be large when constructed of existing lightweight materials of reasonably low manufactured cost. Consequently, if the single routine entry were, say, of a "stable door" type arrangement, then multiple bolts in say one half could act as part of the structure, during crash situations, even though the clearance at the bolts would be made large enough to allow them to be used freely in everyday routine. The bolts could ordinarily be operated manually, or by a local or driver's control, with indicators accordingly, and could have a manual over-ride on a suitably long handle. Such an arrangement could ease the stressing. Other doors might also have the dual purpose bolting.

Potentially the cars according to the first, second or third aspects of the invention could be both very fast and very light. The high speed could make additional control desirable relative to that of conventional cars, while both the lightness and the high speed could increase the effectiveness of aerodynamic controls compared with conventional controls acting through wheel friction. Consequently cars according to the present aspects of the invention may be fitted with variable aerodynamic control surfaces appropriately linked to the existing brakes and steering. They may also have aerodynamic surfaces to augment stability in side-winds. Some of the control or stabilising surfaces may themselves need to be stabilised against side-winds, perhaps by mounting them to obtain weathercock stability, with ailerons or flaps for the control function and possibly heavy damping for the stability.

A car according to any one of the first, second or third aspects may be adapted to be kept cool when parked in warm climates by incorporating solar panels into upward facing external surfaces of the car and using the energy provided by the solar panels to drive an air conditioning system. Additionally the car may comprise curtains or blinds for windows so as to keep direct heat from the interior of the car.

The discussion so far has implicitly been for cars with conventional types of power and conventional types of engine. The principles may be read across, however, with adaptation where required, to other types of power, such as man power, wind power, or some combination of say man, wind, battery, fuel cell, solar and conventional engine. The term "man power" is used to include any combination of one or more people providing the power.

Specific embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a conventional car and its reflection;

Figure 2a is a side view of a car according to a first aspect of the invention;

Figure 2b is a plan view of the car shown in Figure 2a;

Figure 3a is a side view of a car according to a second aspect of the invention;

Figure 3b is a plan view of the car shown in Figure 3a;

Figure 4 is a side view of a car according to a third aspect of the invention;

Figure 5 is a rear view of a conventional car adapted to comprise a rear tail-cone according to the third aspect of the invention;

Figure 6 is a side view of a car according to preferred embodiments of the first, second and third aspects of the invention;

Figure 7 is a plan view of the car shown in Figure 6.

Figure 8 shows an alternative arrangement to that shown in Figure 3b.

EXAMPLES

Figure 1 shows a conventional car 1 showing the aerodynamic advantages of providing cabin side-wall tapering inward to the rear of the car in that the full flow relevant to the analysis for a car includes the reflection in the ground, as in Figure 1. For this total flow, of car plus reflection, the plane of the ground becomes just a plane of symmetry. Consequently the relevant, fundamental, thickness aspect ratio for the flow may be related to twice the height of the car, divided by the width, rather than just the height to width ratio. That tends to make the width of the car become the "thickness" of the three-dimensional body being analysed and twice the height become the "span". Then, rather than tapering on the height, the width could be the more fundamental dimension aerodynamically for the application of boat-tailing. Figure 2 a, b shows according to a first aspect of the invention a car 2 having a roof 4 which is taller at the rear 3 than at the driver's seat 5. The car 2 of Figure 2 also shows a car having cabin side-walls 6 which taper towards the rear 3 of the car 2. Also shown in Figure 2b are the wings or fairings 9 which cover the wheels 11 (shown as a dotted line as they would be hidden in plan view). The passage between the wings, the cabin and the wheels is discussed in more detail in relation to Figures 6 and 7.

Figure 3 a, b shows according to the second aspect of the invention a car 2 having a roof 4 which is taller at the rear 3 than at the driver's seat 5. The car 2 of Figure 3 also has a driver's entrance port 8 disposed between the driver's seat 5 and the rear 3. Figure 3b also shows the wings or fairings 9 over the wheels 11 (shown as a dotted line as they would be hidden in plan view). The wings/fairings 9 provide a standing platform for ease of entrance into the car. This feature is discussed in more detail in relation to Figures 6 and 7.

Rear passenger seats in Figure 2 a, b, and 3 a, b are shown as 7.

Figure 4 shows according to the third aspect of the invention a car 2 having a tail-cone 10 at its fully extended configuration. The tail-cone surface starts at plane 12. Most of the reduction in the cross-sectional area of the cone 10 is provided by the upper surface. The under surface is smooth and rises only slowly. The sides of the tail-cone over the lower region are reasonably flat and parallel, so that the full span of the car is available at the rear, in particular for the rear lights. The sides in the upper region of the tail-cone follow as a continuation of the broadly rounded sweep of the car surfaces conventionally present from some distance upstream. The lower corners of the cone are also rounded, but less so than the upper corners.

When the car is being driven at low speed, or when it is parked or garaged, the tail- cone is in a retracted position and is stowed in the box-like space 14 between planes 12 and 16. Because of the nominally two-dimensional nature of the tail-cone described with reference to Figure 4, a more complex installation is accepted than for the axi-symmetric tail-cones described with reference to Figures 6 and 7 below. The structure of the tail-cone in Figure 4 is based on 2 circular cones. The cones are truncated, manufactured from high strength flexible plastic sheet, and pressurised. At their larger, forward end they are anchored to the car at plane 16, while at the rear they are fixed to the rear "base plate", with one circular cone fairly close to each end of the "plate". The "plate", while being nominally rigid, relies for its stiffness on the inflation of a mesh of tubes of the flexible plastic sheet. The physical surface and the required physical external shape of the tail-cone is obtained by building on to the base plate and on to the circular cones a structure formed from further high strength plastic sheeting, together with appropriate internal air pressures, positive or negative relative to ambient, to hold the whole structure reasonably firmly.

In order to make the system retractable each circular cone has 3 or more cables attached to an "anchorage", which is itself rigidly attached to the base plate and positioned a short distance upstream of it. These cables run to positions, at large diameter and equally spaced around the circumference, just inside their respective circular cone at its front face - or, at least, within the pressurised space associated with the circular cone so that there is no leakage when the cables move. The cables may now be supposed to pass over a pulley type system, and then the cables in each circular cone unite. The uniting of the cables, together with the symmetry of their layout, are critical to the simplicity and effectiveness of this particular mechanism for controlling a retractable tail-cone, as, given these features, if the united cables are now moved by some suitable means of actuation, all the cables move by accurately the same amount. It will now be seen that such actuation, given the symmetry of the actuation system, and accompanied by controlled bleed of the air pressurisation, causes the retractable tail-cone to retract, and to do so along an accurately and firmly controlled reversible and repeatable straight path, and with the correct orientation at all positions. Now under partial pressurisation the larger diameter regions of the circular cone, i.e. at the front, will remain open, while the smaller diameter as at the rear will collapse. Consequently the circular cones and the tail-cone as a whole will retract progressively, with the collapse starting from the rear base plate and moving forward. That arrangement should give greater stability compared with retraction working progressively in the opposite sense.

The last part of the retraction process is to close the box 14 for security and for good appearance. Two plates are hinged to the car and effectively form part of the outer surface of the tail-cone when in its operating position. The later stages of the retraction of the tail-cone then actuates the plates to a partially closed position. Suitable link mechanisms, together with pneumatic or electromagnetic rams, inside box 14, can then complete the closure. Further operation of suitable pneumatic or electromagnetic bolts also inside box 14 then locks the whole arrangement into place. Box 14 itself is mounted on the door which gives access to the rear luggage space, with the door suitably strengthened and balanced.

The extension process is obtained by following the various stages of retraction in reverse, and in reverse order. Substantially full extension occurs when both of the circular cones are extended to substantially their full length by their internal air pressure. At that position the cables, nominally, all come on to their stops. The stiffness and strength of the whole assembly is then increased by increasing substantially the air pressure. The actual, final, adjustment of the cable stops is arranged such that at maximum pressure the loading is shared suitable between the cables and the high strength plastic sheeting.

Operation of the above retracting mechanism in either direction, i.e. as a retraction or as an extension, is thought of as being authorised specifically by the driver of the car and would be intended to be carried out and completed below some specified speed, perhaps 50 mph. A starting speed for the operation may then be limited to say 40 to 45 mph. If the car accelerated to above the 50 mph during the operation of the mechanism there could be a suitable over-ride, perhaps ensuring that the shorter route were taken to an end position, if that seemed appropriate.

When, as in Figure 4, the tail-cone 10 is not strongly truncated it is likely to be fairly slender in its general proportions. Consequently the operating cones could also then be fairly slender. On the other hand the loading on the tail-cone during operation for the extending and retracting mechanism could be considerable, unless the specified maximum car speed for the operation were rather low. Consequently it would probably be found very desirable for the operating circular cones to have as large a diameter as the tail-cone shape makes reasonably possible. One method for achieving some increase in diameter relative to the nominal maximum would be to compromise the optimised aerodynamics slightly by allowing the operating cones to bulge, slightly, through the aerodynamically specified surfaces. Some compensation aerodynamically could be obtained by sinking inwards the remainder of the span at the appropriate axial positions. Such a result could be obtained "automatically", on the upper surface of the tail-cone, by joining between the two operating cones by a single high strength plastic sheet, for the upper surface, and applying a suitable sub- ambient pressure under that upper surface.

The second example of the retractable tail-cone has essentially the same geometry as the first and air operation is used rather as before. However, the tail-cone is manufactured from woven sheets, woven from tough plastic thread, and sealed against the air pressure by plastic sprayed on to the surface. The woven plastic under pressure then provides all the stiffness, so that retraction is by a mesh of the very elastic and robust "bungee" cords fixed to the woven plastic at suitable positions.

The stability of the above described tail-cone arrangements would preferably require careful scrutiny, especially with regard to the two-dimensional tail-cone.

The third example of a retractable tail-cone is the axi-symmetric version which is described below in relation to Figures 5, 6 and 7, where the tail-cone is represented by the broken lines 10 in Figure 5 and by the chain dotted lines 10 in Figures 6 and 7. Figure 5 shows a fillet 40 which is omitted from Figures 6 and 7 for simplicity. Mechanically the fillet 40 is regarded as a fixed on extra, fixed to the main axi- symmetric tail-cone.

A fourth example is constructed of an artificial "rubber" "stretch" material, with extension and retraction by air inflation and deflation. Such an arrangement could be particularly suited to small tail-cones. A further such simplifying variant could have the size of the fully extended tail-cone determined by the air pressure.

Figure 5 shows that in some conventional cars 1 the cabin side-walls already have some curvature. 18 and 20 show the relevant curved cabin side-walls in the transverse vertical cross section taken at the fore and aft position of the driver. Consequently on a conventional cabin section, with some conventional curvature of the cabin side-walls, the addition of cabin side-wall tapering would allow an axi- symmetrical retractable tail-cone indicated by the broken lines 10 to be added at the rear of the car without undue distortion. In Figure 5 a fillet 40 is provided as an addon extra.

Figures 6 and 7 show a side and plan view of a car incorporating features of the first, second and third aspects of the invention. These features will now be described in some detail in relation to the car shown in Figures 6 and 7.

Figure 7 shows a diagrammatic view looking downwards at a horizontal cross-section of the car taken at the height where the cabin width is greatest, i.e. slightly higher than the top of the wheel arches. In Figure 7 the tapering cabin side-walls are indicated by cabin side-walls 32 and 34 respectively. Rear wing fairings 25, 26 are provided to cover the wheels etc, which protrude outwards of the cabin when viewed in plan as in Figure 7. These fairings allow a passage for airflow, as indicated by the broken lines 27 to 30 of Figure 7 at a height mostly below the floor of the boot. The tapering side- walls preferably lead smoothly into the axi-symmetric tail-cone 10, which is extendible and retractable when the tail is moving. The rising line of the roof 4 in Figure 6 gives a good flow configuration with the tapering side-walls 32, 34 shown in Figure 7.

In Figures 6 and 7 the doorway 8 is towards the rear 3 of the car 2 at about the fore and aft position of the doors serving the rear seats 7 in a conventional four seat car, and at a threshold height slightly higher than a conventional doorway. Permanently fixed structural cabin side- walls are used up to the window line 22 - joining the lower edge of the windows - on the offside of the passenger cabin, and up to line 22 except for the cut-out for the doorway 8, which has a suitable reinforcement frame, on the near side. These fixed structural cabin side-walls are part of the main structure of the car and are joined integrally with that main structure, including with the floor of the cabin. They greatly reduce the maximum stress levels. The reinforcement for the doorway includes a rib (not shown) sloping downwards towards the rear.

Any windows provided in the cabin are fixed and are of a material of some significant structural ability, and are carefully bonded, or welded, into position, in order to provide secondary structure and so create a structural shell. The driver and passengers would be compensated for their inability to open the windows by their having an individual control for their air conditioning rather as on aircraft - with a rather more powerful flow and control for the driver.

With the above arrangements the main cut-outs in the structural shell are the main entry 8, the rear luggage access, probably circular or nearly so, a circular emergency exit above the driver (not shown), and a second emergency exit not yet determined. For such a shell the applied loading given by the use of the car is very light, especially after optimisation of the total car. Consequently a low weight construction and structure and a low weight car would be expected.

The fin 23, at the rear of the roofline, is primarily for aerodynamic purposes. Structurally it is a local feature external to the more smoothly rounded structural shell. However, as a prominent second skin it provides added support in a rollover.

The main structure of the car is constructed of a robust existing lightweight material, about the most robust, and tough, such material available, of reasonably low manufactured cost, in the form of single or double sheets, ribbed, with the ribs positioned along the most important lines of force, as well as elsewhere in some positions to prevent vibration. The more important ribs, including around the main cut-outs, are reinforced with galvanised steel. In the more important areas, which include all the areas with steel reinforcement, the sheets are double and are joined by electrothermal welding across the ribs, to form a deep girder double skin construction suitably enclosing the steel.

The use of the additional area of fixed structural cabin side-walls particularly at the front and lower region of the cabin, in comparison with conventional cars, and the consequent replacing of the stress concentration by direct compressive loading during front impact, should make the potential high strain of lightweight materials much more acceptable than it would be in a conventional type of design in that general area. The total load is limited to 400 kg, with any trailer limited to 100 kg out of the 400 kg, and additionally there is a trailer speed limit of 50 mph. Consequently the stressing is very low, so that very much more than usual of the car is in existing lightweight materials of reasonably low manufactured cost. Three roof lines 4 are shown in Figure 6. The lower broken line represents the roof for a conventional car. The upper broken line shows diagrammatically the roof which would have been used for the aerodynamic design according to the first aspect of the invention had there been no special structural requirement. The actual roof line 4 then shows the dome-like-shaped headroom space added to ease the single routine entry required structurally - and also to facilitate high level internal mirrors. A somewhat greater domed effect should be possible without undue compromise of the aerodynamics.

The rising line of the roof shown as 4 in Figure 6 is used mostly for its aerodynamic capabilities but it readily accommodates any dome shaped additional head-room required when the only entrance port is at the rear; that facilitates the cabin or the car being provided as a one piece shell.

The higher roof 4 discussed, as allowed by the aerodynamic design of the first aspect of the invention, provides a further structural advantage, in that the structural shell is brought significantly above the level of the top of the cut-out for the doorway 8. The floor level in the central region is as low as is mechanically acceptable, in order to achieve both maximum shell strength and maximum headroom.

And another advantage of the high aerodynamic roof is that a roll-bar type structure should fit in an ideal manner immediately to the rear of the single routine doorway: - the roll-bar type structure would occupy space and height not required for headroom, the aerodynamic change of roof section discussed according to the first aspect of the invention would fit the roll-bar structure, as would the rear reinforcing for the single main entry 8.

The internal modifications for the single routine doorway include features previously discussed, as well as others: - various handholds, the back of the near side front seat tipping forward, a wider space between the central supports of the front seats, and the floor between those supports flat, clear and low. The last of these features means that the conventional deep stiffening along the floor centre-line is lost. That is justified by several items: - the smaller and lighter engine and gearbox, built as far forward as is reasonably possible, into the front of a full conventional-sized engine compartment under the bonnet, with a correspondingly modified bulkhead and crumple zone across the front of the cabin, in order to provide additional crumple space, and in order to control the crumple more effectively, between engine and cabin during front impact, and by the general shell structure of the cabin, with its double skinned girder construction and galvanised steel reinforcement where necessary.

The lower surface at entry to the passages defined by 27 to 30 in Figure 7 form the wings, on which one position is shown pinpointed at the dot and circles 24 in Figure 7 and, in Figure 6, at the dot 24 representing the same position, and immediately under the doorway 8. Consequently the near side the wing 25 in the vicinity of 24 is ideally placed for assisting routine external access to the doorway, especially when account is taken of the automatic inset of the upper edge of the doorway.

The tail-cone 10 may be manufactured in a material woven from robust plastic thread, of substantially non-stretch properties at ordinary stress levels, and sealed by spray. The tail-cone may be extended, while the car is moving, by applying internal air pressure. It may be retracted by tough, highly elastic, "bungee" type cords, when the pressure is released. Extension and retraction are both automatic once authorised by the driver provided there is no over-ride arrangement in operation. However, there could, for example, be an over-ride to prevent extension if the car were stationary. There could also be an over-ride in order to prevent either extension or retraction being started if the speed at authorisation exceeded say 45 mph.

Various warnings concerning the tail-cone apply both for the driver and for the following traffic. The tail-cone is mounted on the concave side of a light weight dished circular rear door, which is held, automatically, after closure, at several positions around the circumference, and which can be reversed, for security, by rotation at its spherical hinge.

The flow velocities in the rear bypass regions of the wing-to-cabin body junction, represented by the lines 27 to 30, are kept low, as far as is reasonably possible, by local diffusion just upstream. Re-acceleration occurs as sharply as possible at the exit from the rear bypass region, in order to keep a good flow on all surfaces. Such treatment needs a substantial flow area in the bypass. Consequently, the suspension linkages are set as low as is mechanically acceptable, in order to lower the floor of the bypass passages. Similarly all the relevant suspension elements are set as much as possible into the width of wheel. The arrows indicate the direction of airflow in Figure 7.

The tail-cone 10 preferably is also positioned as low as is mechanically acceptable and is given a slight downward inclination, again as much as is mechanically acceptable. That helps to keep a good streamlined flow on the undersurfaces in that region, probably as well as in the bypass channels for the rear wheels and suspension. It also allows as good a rear view as possible for the driver.

In order to secure the above low positions for the tail-cone 10 and bypass channels, one option with the present example of the car has its hydraulic rear damper adapted to contain a substantial active, quasi-steady, component of lift, for clearing urban, and other, bumps which occur at low speed. This option effectively converts the rear dampers to act additionally as lifting rams. It allows the prime low drag configuration to be designed as is required, for high speed, with low positions for the car and suspension, and with only small movements of the suspension. It could also give a low car position when stationary, for boarding and loading. The arrangement would probably be appropriate in all options.

In Figure 7 the rear wheels have been moved aft relative to the rear seats 7, in comparison with the conventional layout, in order to ease the geometry, but a moderate distance has been retained between the rear wheels and the rear of the car to give distance for that part of the streamlining. The conventional layout taken as a datum for the present example has been chosen as one of the longer "estate" cars for the European market, in order to obtain a generous spacing between the rear and the rear of the car. Additionally, the wheels and suspension have been taken to be slimmer than conventional; that has been justified on the basis of all the factors claimed to give a reduction in the total, all-up, weight of car plus maximum load.

The increased threshold sill level of the single routine doorway 8, relative to conventional, seems to give an aerodynamic advantage, in that loads from the rear can be taken more directly than is conventional. Consequently, the wall thickness can probably be decreased, to advantage, in the bypass passages between the cabin and the rear wheel fairings.

In the car of Figures 6 and 7 the above structural proposals are used in conjunction with proposals for very low aerodynamic drag as for Figures 3a and 3b, plus the retractable axi-symmetric rear tail-cone. The three sets of proposals complement each other. In particular,

(i) the aerodynamic features of Figures 3a and 3b make the critical, structural, single routine entry practicable, while

(ii) the mechanical features give low weight, and therefore slim wheels and suspension, so making the critical, rear, streamlining practicable, and

(iii) the features of Figures 3 a and 3b also make a simple retractable axi- symmetric tail-cone practicable, while the tail-cone eliminates most of the aerodynamic drag.

Optimisation gives a virtuous circle with very low drag, low total weight, small size components, easier streamlining (particularly of the fairings at the rear wheels and suspension), low first costs, low maintenance costs, and a very low fuel consumption, as well as low external noise and improved crashworthiness, all in comparison with conventional cars.

Figure 8 shows an alternative arrangement for the four-seat car shown in Figure 3b. In this alternative arrangement a reduction in the span of the rear wheels 36, 38 allows the wheels 36, 38 to be inset, largely into the cabin volume, so that the bypass passages (shown in Figure 7 as lines 27 to 30) may be eliminated. Such an arrangement might be found acceptable as a suitable compromise for a four-seat car, but probably less likely for the two seats or occasional 4-seat arrangements described herein. A single rear wheel, centrally placed at the rear of the car, could be acceptable for a car of very low power, but it is envisaged that such an arrangement would not be suitable for a "high performance" vehicle due to the reduction in stability as compared to a car with a rectangular plan form.

Claims

1. A car comprising a roof, a rear, a cabin and cabin side-walls and containing a driver's seat, in which the cabin side-walls taper inwardly towards the rear and the roof of the car is taller at the rear than at the driver's seat.

2. A car as claimed in claim 1 in which the cabin of the car is substantially narrower, over its full height, at the rear of the car than at the driver's seat.

3. A car as claimed in claim 1 or claim 2 in which the centre-line of the roof rises, overall, when going rearwards, from the top of a windscreen to the top of a fin-like shape at the rear of the car proper.

4. A car as claimed in any preceding claim further comprising a driver's entrance port disposed at the rear or between the driver's seat and the rear.

5. A car as claimed in claim 4 in which the driver's entrance port leads to a path from behind the driver's seat to the driver's seat and any adjacent seats at the front of the car.

6. A car as claimed in claim 5, in which the path to the driver's seat is provided with suitable headroom, by forming a suitable dome-like space on or near the centre-line of the roof of the car.

7. A car according to any one of claims 4 to 6 in which the only passenger access is through the driver's entrance port.

8. A car according to any one of claims 4 to 7 in which the driver's entrance port is on the near side of the vehicle.

9. A car according to any preceding claim in which any windows are non- opening and are a fixed part of the structure.

10. A car according to any preceding claim further comprising a retractable tail- cone.

1 1. A car according to claim 10 in which the tail-cone is extendible and retractable whilst the car is in motion

12. A car according to claim 10 in which the retractable tail-cone is basically axi- symmetric but may include small non-axi-symmetric attachments.

13. A car comprising a roof, a rear and containing a driver's seat and having a driver's entrance port disposed at the rear or between the driver's seat and the rear, and the roof of the car is taller at the rear than at the driver's seat.

14. A car according to claim 13 further comprising cabin side-walls which taper inwardly towards the rear.

15. A car according to claim 13 or claim 14 in which in which the car is substantially narrower, over its full height, at the rear of the car than at the driver's seat.

16. A car as claimed in any one of claims 13 to 15 in which the centre-line of the roof rises, overall, when going rearwards, from the top of a windscreen to the top of a fin-like shape at the rear of the car proper.

17. A car as claimed in any one of claims 13 to 16 in which the driver's entrance port leads to a path from behind the driver's seat to the driver's seat and any adjacent seats at the front of the car.

18. A car as claimed in claim 17, in which the path to the driver's seat is provided with suitable headroom, by forming a suitable dome-like space on or near the centre-line of the roof of the car.

19. A car according to any one of claims 13 to 18 in which the only passenger access is through the driver's entrance port.

20. A car according to any one of claims 13 to 19 in which the driver's entrance port is on the near side of the vehicle.

21. A car according to any one of claims 13 to 20 in which any windows are non- opening and are a fixed part of the structure.

22. A car according to any one of claims 13 to 21 further comprising a retractable tail-cone.

23. A car comprising a retractable tail-cone at its rear.

24. A car according to claim 23 in which the tail-cone is extendible and retractable whilst the car is in motion

25. A car according to claim 23 further comprising a roof, a rear and cabin side- walls and containing a driver's seat, in which the cabin side- walls taper inwardly towards the rear and the roof of the car is taller at the rear than at the driver's seat.

26. A car according to claim 23 further comprising a roof, a rear and containing a driver's seat and having a driver's entrance port disposed at the rear or between the driver's seat and the rear, and the roof of the car is taller at the rear than at the driver's seat.

27. A car substantially as described herein, particularly with reference to Figures 2 to 8 of the accompanying drawings.