GB2504998A

GB2504998A - Sports car with rear facing seat and range of sports cars

Info

Publication number: GB2504998A
Application number: GB201214710A
Authority: GB
Inventors: Anthony George Shute; Paul Anthony Birch; Adriaan Lodewyk Gerber
Original assignee: CATERHAM TECHNOLOGY AND INNOVATION Ltd
Current assignee: CATERHAM TECHNOLOGY AND INNOVATION Ltd
Priority date: 2012-08-17
Filing date: 2012-08-17
Publication date: 2014-02-19
Also published as: GB201214710D0

Abstract

A sports car has two front wheels 106, 108 and two rear wheels 110, 112. The sports car has only two front-facing seats 102, 104, one of the front-facing seats being for a driver and the other for a front passenger. The sports car additionally has at least one rear facing seat 51, 53, located behind the front-facing seats. The sports car is preferably a 2+2 sports car, and may have only two side doors. The rear-facing seat preferably has restricted leg room compared with the front seats. The rear seat is preferably supported by a rear sub frame 55 attached to the chassis so that a model of the car without the rear seats can use the same chassis. Also claimed is a range of sports cars including at least two models, each model having a substantially identical tub chassis. The first model has only two seats which are both forward facing and the second model has the same wheelbase as the first model but also has two rear facing seats behind the forward facing seats.

Description

SPORTS CAR AND RANGE OF SPORTS CARS

BACKGROUND TO THE INVENTION

Field of the invention

The present invention relates to a sports car and to a range of sports cars. The invention also relates to a method of design of a range of sports cars. Of particular interest in the present application is an approach in which a range of sports cars share common features of structure and/or design in order to provide economies of scale, but which differ in other features of structure and/or design in order to provide, across the range, differentiation of characteristics that are of importance to the end user.

Related art Ranges of cars from individual car manufacturers are known, in which different car models are based on the same basic platform (e.g. chassis), the models having different characteristics. For example, some car manufacturers offer corresponding saloon, hatchback and estate models. However, these cars are generally manufactured in large volumes, the versions differing mainly in terms of luggage space and practicality.

Sports cars are typically manufactured in lower volumes than the cars discussed above.

These lower volumes mean that the amount of investment and development possible for each model is lower than for volume car manufacturers, or that the unit cost of each sports car is extremely high and therefore out of reach for most potential customers.

SUMMARY OF THE INVENTION

The present invention has been devised in order to allow manufacturers to provide sports cars having performance comparable to high performance sports cars, but at a fraction of the cost. The present invention therefore addresses the problem of efficiency of design and manufacture of a range of cars where only relatively low numbers of each model in the range are to be produced.

Accordingly, in a first aspect, the present invention provides a range of sports cars, including at least two models, wherein each model has a substantially identical tub chassis, the models having different configurations to each other in terms of at least one of the group of features selected from: front mid-engine layout, rear mid-engine layout, mid-engine layout; longitudinal driveline direction, transverse driveline direction; front subframe, rear subframe.

In a second aspect, the present invention provides a method of design and manufacture of a range of sports cars, the method including designing at least two sports car models, wherein each model has a substantially identical tub chassis, the models having different configurations to each other in terms of at least one of the group of features selected from: front mid-engine layout, rear mid-engine layout, mid-engine layout; longitudinal driveline direction, transverse driveline direction; front subframe, rear subframe, the method further including the step of manufacturing said at least two sports car models according to the designs.

Using the invention, it is therefore possible to provide a range of sports cars which are based on the same chassis, but which have different configurations in terms of engine layout and/or driveline directions and/or structures of front subframe or rear subframe.

These features can radically affect the driving characteristics of the car, but the research and development required for the chassis can be applied to all of the models in the range.

Preferred and/or optional features of the invention will now be set out. These are applicable singly or in any combination with any aspect of the invention, unless the context demands otherwise.

Recently, certain high performance sports cars have become available utilising a tub chassis of carbon fibre composite. A tub chassis is known for providing structural rigidity whilst being lightweight. Forming the tub chassis from carbon fibre composite material (in place of, for example, aluminium) allows further reduction of weight, and therefore improved performance and handling. However, these high performance sports cars are exceptionally expensive.

Preferably, the tub chassis is a fibre-reinforced composite material tub chassis. Keeping the structure and shape of the chassis identical across the range of sports cars provides a very large efficiency saving in terms of the research and development needed for each model in the range.

Preferably, the range of sports cars includes at least three models. More preferably, the range of sports cars includes at least four, at least five, at least six, at least seven or at least eight models. These models have different configurations at in terms of the features identified above, i.e. engine layouts and/or driveline directions and/or structures of front subframe or rear subframe. To the knowledge of the inventors, no similar range of sports cars that has ever been marketed.

Preferably, the models' safety cells are substantially identical. The safety cell includes the chassis. Very significant research and development is needed in the safety cell, because it is the primary protection provided by the car to its occupants. It is important to note that the term "safety cell" does not include only the chassis. Significant additional components are included in the safety cell, some of which are specifically identified below.

Preferably, the models' body wiring harness systems are substantially identical.

Preferably, the models' steering columns are substantially identical. It should be noted that similar models may be manufactured with left hand drive and right hand drive, with corresponding minor changes to the structure used to accommodate the steering column made as necessary.

In some embodiments of the invention, the models' steering wheels are substantially identical. However, modification of the steering wheel between models may be possible in other embodiments, in order to meet customer requirements.

Preferably, the models' airbag systems are substantially identical. As will be understood, the system of airbags in the safety cell provides a great degree of protection to the occupants from collision with, for example, the steering wheel, the car pillars, the windscreen, etc. Thus, preferably, the number and location of the airbags is preferably substantially identical (at least in relation to the front seats).

Preferably, the models' windscreens are substantially identical. This relates to the glass itself of the windscreen and also to the structure supporting the windscreen. As will be understood, the windscreen and its supporting structure has an important role to play in sports car safety, especially for roadster models, in terms of providing protection to the occupants in the event of the car being inverted during an accident.

Preferably, the models' windscreen and side glass are substantially identical. However, in some embodiments the entire glasshouse systems are not substantially identical, because the glasshouse includes the rear quarter glass and the tailgate glass which typically differ between models.

In some embodiments of the invention, the models' roof system is substantially identical.

However, in other embodiments of the invention, different models may be provided as coupes, removable (or foldable) hard-top roadsters and soft-top roadsters.

Preferably, the models' front seat anchoring systems are substantially identical.

Similarly, the models' front seat layouts are preferably substantially identical (in terms of their location with respect to the safety cell).

In some embodiments of the invention, the models' seats are substantially identical.

However, in other embodiments of the invention, different seats may be offered for different models, according to the preference of the customer.

Preferably, the models' door hinges and/or door latches are substantially identical.

Furthermore, preferably the models' side impact beams (typically located within the door) are substantially identical. These features are important crash-protection features of the car.

Preferably, the models' interior trim and/or soft trim are substantially identical.

Preferably, the models' heating, ventilation and air conditioning (HVAC) systems are substantially identical.

Preferably, the models' instrumentation, control and electrical (ICE) systems are substantially identical.

Preferably, the models' handbrake systems are substantially identical.

The preferred features identified above explain the features that may be common to the different models in the range. Next we explain in more detail the preferred further differentiation between the different models.

The engine layout may be front mid-engine layout, rear mid-engine layout or mid-engine layout. The term mid-engine layout" relates to the location of the engine with respect to the wheelbase of the car. Typically, a front mid-engine layout has the engine located behind the front wheels but forward of the driver. A rear mid-engine layout has the engine located in front of the rear wheels but behind the driver. Such engine layouts provide advantages in terms of weight distribution and handling of the car. In the range, the front mid-engine layout model(s) typically are able to have a shorter wheelbase than the rear mid-engine layout model(s).

Preferably, the engine is an internal combustion engine. Suitable internal combustion engines are well known. For reasons of performance, it is preferred to use gasoline (rather than diesel) fuel.

Preferably, all of the models in the range have driven rear wheels. Some of the models in the range may additionally have driven front wheels, and thus are four-wheel drive (sometimes referred to as all-wheel drive).

The driveline direction may be referred to as a longitudinal driveline direction (or N-S driveline direction) or a transverse driveline direction (or E-W driveline direction). In order to drive the rear wheels, a front mid-engine layout model with a longitudinal driveline direction should have a driveshaft extending much of the distance along the wheelbase of the car. The chassis (common to all models) therefore preferably accommodates this.

In some embodiments, one or more models in the range may have at least one electric motor providing drive to at least one of the wheels. For example, at least one of the models may be all-electric, so that the drive provided to the wheels is exclusively electric.

In that case, the "engine" referred to above refers to the electric motor. At least one of the models may have an auxiliary electric drive, e.g. for driving the front wheels, in addition to an internal combustion engine providing the main drive.

In the case of an electric drive, a battery may be provided for powering the electric drive.

In that case, the battery may be wholly or partly located in order to improve the weight distribution of the car. Thus, if the electric motor has a front mid layout, the battery may have a rear mid location, and vice versa.

The subframes of the car are attached to the chassis. Typically, the suspension is attached to the subframes. This provides improvement in ride quality. The suspension systems of the models may be substantially identical. Again, this gives rise to significant economies of scale.

Different models may have different front and/or rear subframes in order to provide different external styling between the models.

Different models preferably have different shaped body panels. The body panels provide the car with the main features of external shape. It is envisaged that it would be possible for the entire car, except external body panels, to be assembled by a first party, and for a second party then to fit the external body panels to the car. This allows the overall external styling of the finished car to be under the control of the second party.

Different models may have different numbers of seats. For example, one model may have only two seats, both of these being forwards-facing. Another model may have two front seats and two rear seats. Such a model is typically designated a 2+2 model, particularly when the car has only two side doors.

In one preferred embodiment, the rear subframe of one of the models is adapted in order to provide space for two rearwards facing seats. Thus, this model is preferably a 2+2 model. The present inventors have realised that this represents a further aspect of the invention, as set out below, along with optional features that apply equally to the above aspects of the invention.

Many sports cars are considered to be impractical for daily use. Cars with only two seats can of course only carry a driver and one passenger. There is typically only very limited luggage space. It is known to provide sports cars in two models: a standard model having only two seats and a so-called 2+2 model having two rear seats. Typically, in a 2+2 model, the rear seats have restricted legroom and headroom compared with the front seats. Additionally, the 2+2 model may have a longer wheelbase than the standard model in order to accommodate the rear seats. The longerwheelbase typically means that the chassis of the two models are different. Furthermore, the requirement to have two rear seats means that the roofline of the two models must be different, in order to provide (even restricted) headroom for the rear passengers.

Accordingly, in a third aspect, the present invention provides a sports car having two front wheels and two rear wheels and only two front-facing seats, one of the front-facing seats being for a driver and the other for a front passenger, the sports car additionally having at least one rear facing seat, located behind the front-facing seats.

The use of rear-facing seats in the context of a sports car is, to the knowledge of the inventors, a feature not previously known in this field. There are various advantages associated with this seating layout. Of particular interest is safety. The passenger in a rear-facing seat is protected by the backrest (and headrest, where provided) of the seat when the car has a frontal impact. This passenger orientation is in fact safer than a forwards-facing seat. It is intended that the rear-facing seat is for only occasional use, but its incorporation into the car very significantly improves the practicality of the car.

Typically, there are two rear-facing seats provided. In this way, the sports car is preferably a 2+2 sports car. Preferably, the car has only two side doors.

The rear-facing seat typically has restricted legroom compared with the front seats. This balances the requirement for some legroom against the expected only occasional use of the seat. The rear-facing seat preferably has a headrest. This provides an important safety advantage, particularly in the event of the car having a frontal impact. The legroom and headroom provided by the rear-facing seat preferably is sufficient to accommodate at least a 5th percentile female (the 5th percentile female being an industry standard).

Preferably, the rear-facing seats are located at least partly behind an axis of rotation of the rear wheels. Thus, the base of the seat may be wholly rearwards of, or more preferably may overlie, the axis of rotation of the rear wheels.

Preferably, in use, the surface of the base of the front facing seats is at most 40 cm from the road surface. More preferably the surface of the base of the front facing seats is at most 30 cm from the road surface. Preferably, in use, the height of the top of the roof is at most 130 cm from the road surface.

Preferably, the car has a solid roof-i.e. it is preferably not a soft-top roadster, nor a removable hard-top roadster. Preferably, the car has a tailgate. The intention is that the passengers for the rear seats can access the seats via the tailgate. This is a significant different compared to 2+2 cars with forward-facing rear seats, in which the rear seats are accessed by the side doors. In the preferred embodiments of the present invention, therefore, the front seats do not (and need not) fold forwards, because there is no need for them to do so in order for the rear seats to be accessed.

Preferably, the car has a fibre-reinforced composite material tub chassis, as explained with respect to the first and second aspects.

The rear seats may be supported by a rear subframe. The rear subframe is preferably attached to the chassis so that a model of the car without the rear seats can use the same chassis. This feature of the invention leads back to the concept of a range of sports cars in which the chassis is common, for the purposes of economies of scale.

Thus, in a fourth preferred aspect, the present invention provides a range of sports cars, including at least two models, wherein each model has a substantially identical tub chassis: (i) a first model having only two seats, each of the seats being forward-facing; and (ii) a second model having the same wheelbase as the first model but additionally having two rear facing seats located behind the forward-facing seats.

Preferably, the first and second models differ at least in terms of a rear subframe, which supports the rear-facing seats in the second model, the rear subframe being attached to the chassis.

Features of the first, second, third and/or fourth aspects may be combined with each other.

Optional features set out with respect to the first, second and/or third aspects of the invention are applicable singly or in any combination to any aspect (including the fourth aspect) of the invention.

Further optional features of the invention are set out below.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be set out by way of example with reference to the drawings.

Figs. 1-8 show schematic plan views of the layout of a range of models of sports car according to a preferred embodiment of the invention.

Fig. 1 shows a Front Mid-Engine (N-S) Rear Drive 2 Seat model, provided as LHD or RHD and Roadster or Coupe.

Fig. 2 shows a Rear Mid-Engine (E-W) Rear Drive 2 Seat model, provided as LHD or RHD and Roadster or Coupe.

Fig. 3 shows a Rear Mid-Electric (E-W) Rear Drive 2 Seat model provided as LHD or RHD and Roadster or Coupe.

Fig. 4 shows a Front Mid-Engine (N-S) and Front Electric Four Wheel Drive model, provided as LHD or RHD and Roadster or Coupe.

Fig. 5 shows a Front Mid-Engine (N-S) Rear Drive 2+2 Seat model, provided as LHD or RHD and Coupe.

Fig. 6 shows a Front Mid-Engine (N-S) Front Electric Four Wheel Drive 2+2 Seat model, provided as LHD or RHD and Coupe.

Fig. 7 shows a Rear Mid-Engine (N-S) Rear Drive 2 Seat model provided as LHD or RHD and Roadster or Coupe.

Fig. 8 shows a Rear Mid-Engine (N-S) Front Electric Four Wheel Drive 2 Seat model, provided as LHD or RHD and Roadster or Coupe.

Fig. 9 shows a schematic plan view of another embodiment of the invention, in the form of a 2+2 model.

Fig. 10 shows a schematic side sectional view of the model of Fig. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS! FURTHER

OPTIONAL FEATURES OF THE INVENTION

In the preferred embodiments of the present invention, a range of sports cars is provided, in which each model in the range uses the same safety cell. This means that the overall investment required over the range of sports cars is greatly reduced compared to a similar number of models not sharing the same safety cell. It is important to note that in the preferred embodiments, the safety cell is not just a structure in which the occupants sit and are protected, but also contains the interior trim, body wiring harness, steering column and wheel, airbag system, seats, windscreen, HVAC system, door hinges, latches and side impact beam, instrumentation and ICE systems, soft trim and handbrake.

Making these parts common in each model of the range significantly reduces investment around the vehicle systems, which is always an issue on low volume niche vehicles, and increases the number required for each of the common parts as they are used across all models.

This applies not just to a range of sports cars provided by a single manufacturer, but allows the basic structure of the range of cars to be manufactured by a first party and then for the basic structure to be clothed in a specific design of body panels by a second party (or by several second parties).

The differentiation between each model is preferably in terms of: the powertrain and driveline; the body system (i.e. the shape of the parts for the exterior of the car at the front, rear, bodysides, roof outer and door outers); the wheels, the lights and the subrames (front and rear).

The common parts between each model are preferably: the safety cell (including the chassis); the windscreen and side windows; the roof system; the front seats; the suspension; the brakes and ABS/ESP systems; the steering system (EPAS); the airbag system I SRS; the HVAC, the fuel system (gasoline); at least 50% of the electrical / electronic systems; the displays; the ICE systems; the seals; the tyres.

Turning now to the specific models shown in Figs. 1-8, these drawings are illustrated so that common features are given the same reference numbers.

Fig. 1 illustrates a front mid-engine model with N-S (longitudinal) driveline. The model is a rear wheel drive model. There are only two seats -a driver's seat 102 (indicated on the right in this drawing) and a front passenger seat (104). As will be clear, a left hand drive model can be provided with the driver's seat on the left hand side of the car. The model can be a roadster (i.e. a convertible -with a soft roof or a hard roof) or a coupe (with a hard, non-removable roof). The safety cell is indicated by 100. Front wheels are indicated by 106, 108 and rear wheels by 110, 112. The engine 10(gasoline-fuelled)is located towards the front of the car, in front of the driver, but rearwards of the axis of rotation of the front wheels. The transmission 12 and drive shaft 14 extend longitudinally along the car to a differential 16 for driving the rear wheels. The overall body shape is provided by an array of body panels, indicated generally by 18.

Fig. 2 illustrates a rear mid-engine model with E-W (transverse) driveline. The safety cell is identical to that shown in Fig. 1. The model can be a roadster or a coupe. The engine 20 is located towards the rear of the car, behind the driver, but forwards of the axis of rotation of the rear wheels 110, 112. The transmission 22 extends transversely along the car for driving the rear wheels. The overall body shape is provided by an array of body panels, indicated generally by 28.

Fig. 3 illustrates a rear mid-engine model with E-W (transverse) driveline. In these respects, this model is similar to the model shown in Fig. 2. However, the engine 30 is an electric motor. This is located towards the rear of the car, behind the driver, but forwards of the axis of rotation of the rear wheels 110, 112. The transmission 32 extends transversely along the car for driving the rear wheels. The overall body shape is provided by an array of body panels, indicated generally by 38. A battery 39 is provided forwards of the driver but rearwards of the axis of rotation of the front wheels 106, 108.

The location of the battery here assists in providing suitable weight distribution for good handling characteristics for the car.

Fig. 4 illustrates a front mid-engine model with N-S (longitudinal) driveline. In many respects, this model is similar to the model illustrated in Fig. 1. Safety cell 100 is identical to the other models previously described. Engine 40 (gasoline-fuelled) is located towards the front of the car, in front of the driver, but rearwards of the axis of rotation of the front wheels 106, 108. The transmission 42 and drive shaft 44 extend longitudinally along the car to a differential 46 for driving rear wheels 110, 112. The overall body shape is provided by an array of body panels, indicated generally by 48. A feature of differentiation of the model shown in Fig. 4 compared with that shown in Fig. 1 relates to the driving of the front wheels 106, 108. In Fig. 4, the model is a four-wheel drive model. Electric motor 47 is provided to drive front wheels 106, 108. The car's main drive comes from engine 40, but electric motor 47 operates as an auxiliary drive to drive the front wheels when needed.

Fig. 5 illustrates a front mid-engine model with N-S (longitudinal) driveline. The model is a rear wheel drive model. This model is identical in many respects to the model illustrated in Fig. 1. However, the model shown in Fig. 5 is provided only as a coupe.

This is because, in a feature of differentiation compared with the model shown in Fig. 1, the model shown in Fig. 5 has two rearwards-facing seats 51, 53. These are located immediately behind the front seats 102, 104. The rear seats 51, 53 are supported on rear subframe 55, which is attached directly to safety cell 100. Engine 50 (gasoline-fuelled), transmission 52, drive shaft 54 and differential 56 are located as for the model shown in Fig. 1. This model shown in Fig. 5 has a tailgate (not shown) through which passengers for the rear seats can access those rear seats. The overall body shape is provided by an array of body panels, indicated generally by 58.

Fig. 6 illustrates a front mid-engine model with N-S (longitudinal) driveline. This model is similar in many respects to the model shown in Fig. 5 with the exception that this is a four-wheel drive model, the front wheels 106, 108 being powered by electric motor 67.

The engine 60 (gasoline-fuelled), transmission 62, drive shaft 64 and differential 66 are located as for the model shown in Fig. 5.

Fig. 7 illustrates a rear mid-engine model with N-S (longitudinal) driveline. The model is a rear wheel drive model. Again, the safety cell 100 is identical to the safety cell used in the other models in the range. However, it will be noted that the wheelbase of this model shown in Fig. 7 is longer than in the models shown in Figs. 1-6. This is due to the location and drive line direction of the engine. Engine 70 (gasoline-fuelled) is located towards the rear of the car, behind the driver but forwards of the axis of rotation of rear wheels 110, 112. Transmission 72 extends longitudinally along the car and incorporates a differential for driving the rear wheels. The overall body shape is provided by an array of body panels, indicated generally by 78. This model can be a roadster or a coupe.

Fig. 8 illustrates a rear mid-engine model with N-S (longitudinal) drive line. The model is similar to the model shown in Fig. 6 with the exception that the model is four-wheel drive model. The front wheels 106, 108 are drive by electric motor 87.

Figs. 9 and 10 show schematic views of another embodiment of the invention, in the form of a 2+2 model. This model is intended to be similar in overall layout to the model shown in Fig. 5. Note that this model as illustrated in Fig. 9 is a left-hand drive model. Safety cell/chassis 200 is as described previously, providing two front seats for driver 204 and front passenger 202. Steering column 205 extends from the driver to the steering actuation system (not shown in Fig. 9). Front wheels 206, 208 are supported via suspension (not shown) on front subframe 209. This model is a rear wheel drive front mid-engine (N-S) model. The engine is not shown in Fig. 9.

At the rear of the car is provided rear subframe 214. This supports two rearwards-facing seats for occasional passengers 216, 218. In this embodiment, the location of these rearwards-facing seats is such that the seats are located behind the axis of rotation of rear wheels 210, 212.

As shown more clearly in Fig. 10, the use of rearwards4acing seats behind the front seats means that the head of the driver and the head of the rear passenger are located relatively close together. Thus, the rear passenger can have the benefit of headroom that is already provided for the driver. This allows the roofline of the car (in this case a coupe) to flow more naturally downwards towards the rear of the car without unnecessarily restricting the headroom for the rear passenger. If the rear passenger was forwards-facing, then additional headroom would need to be provided further back in the car. The result of this would be a non-aerodynamic roof shape and/or the need for an elongated wheel base for the car. These would be disadvantageous in terms of handling characteristics of the car.

The embodiments set out above have been described by way of example. On reading this disclosure, modifications of these embodiments, further embodiments and modifications thereof will be apparent to the skilled person and as such are within the scope of the present invention.

Claims

CLAIMS1. A sports car having two front wheels and two rear wheels and only two front-facing seats, one of the front-facing seats being for a driver and the other for a front passenger, the sports car additionally having at least one rear facing seat, located behind the front-facing seats.
2. A sports car according to claim 1, wherein there are two rear-facing seats provided.
3. A sports car according to claim 1 or claim 2, wherein the sports car is a 2÷2 sports car, the car having only two side doors.
4. A sports car according to any one of claims 1 to 3, wherein the rear-facing seat has restricted legroom compared with the front seats.
5. A sports car according to any one of claims 1 to 4, wherein the legroom and headroom provided by the rear-facing seat is sufficient to accommodate at least a 5th percentile female.
6. A sports car according to any one of claims 1 to 5, wherein the rear-facing seat has a headrest.
7. A sports car according to any one of claims 1 to 6, wherein the rear-facing seat is located at least partly behind an axis of rotation of the rear wheels.
8. A sports car according to any one of claims 1 to 7, wherein the car has a solid roof and a tailgate, a passenger for the rear seat being able to access the seat via the tailgate.
9. A sports car according to any one of claims 1 to 8, having a fibre-reinforced composite material tub chassis.
10. A sports car according to any one of claims 1 to 9, wherein the rear seat is supported by a rear subframe attached to the chassis so that a model of the car without the rear seats can use the same chassis.
11. A range of sports cars, including at least two models, wherein each model has a substantially identical tub chassis: (i) a first model having only two seats, each of the seats being forward-facing: and (ii) a second model having the same wheelbase as the first model but additionally having two rear facing seats located behind the forward-facing seats.
12. A range of sports cars according to claim 11, wherein the first and second models differ at least in terms of a rear subframe, which supports the rear-facing seats in the second model, the rear subframe being attached to the chassis.