| 1. | Method for manufacturing a chassis (1) of composite material for a kart, characterised in that said chassis (1) is manufactured by means of a resin transfer moulding (RTM) process. |
| 2. | Method according to claim 1, characterised in that stuffing material (3) is applied in the mould used in the RTM process to obtain one or more heights in the chassis (1). |
| 3. | Method according to claim 2, characterised in that said stuffing (3) material consists of one or more polyurethane sandwich foam centre blocks. |
| 4. | Method according to any one of claims 1 to 3, characterised in that one or more inserts (11) are fitted in said mould to provide a support for mounting other parts of the kart onto the chassis (1). |
| 5. | Method according to claim 4, characterised in that said inserts (11) are made of aluminium. |
| 6. | Method according to claims 4 or 5, characterised in that said inserts (11) are provided with one or more blind rivet nuts for mounting the other parts of the kart onto the chassis (1). |
| 7. | Method according any one of claims 1 to 6, characterised in that one or more blocks (10) are provided in said mould, in which said blocks (10) are provided to insert and fix a stub axle holder bush. |
| 8. | Method according to claim 7, characterised in that said blocks (10) are made of polyethylene terephtalate (PETP). |
| 9. | Method according to any one of the preceding claims, characterised in that in the RTM process a polyester resin is inserted in the mould to serve as glue. |
| 10. | Method according to claim 9, characterised in that in combination with said polyester resin a gelcoat is inserted in the mould in order to give a colour to the chassis (1). |
| 11. | Method according to any one of claims 1 to 10, characterised in that during the RTM process one or more conduit pipes (12) are provided for providing gas, brake and electricity cables of the kart. |
| 12. | Chassis of composite material for a kart, characterised in that the chassis (1) is manufactured by a method according to any one of claims 1 to 11. |
Nowadays, it is known to provide a metal framework as the base structure of a kart. This framework thereby serves as a base support for mounting other parts of the kart, including a seat for a driver, a bumper system, front and rear wheel axle assemblies, a steering mechanism, a braking mechanism, one or more engines and fuel tanks, transmission operable to drive the rear wheels, etc.
A disadvantage of karts made in this way is that the frame, which is a beam structure, tends to bend and is vulnerable to metal fatigue, this because of the changing bending and torsion forces when driving with a kart. The torsion forces on the chassis are high because of the fact that mostly a kart has no suspension. Metal fatigue has very disadvantageous consequences on the steering behaviour of the kart; the torsion of the chassis is performed in a different way while taking bends. Metal fatigue is the determining factor of the steel frame. Finally, the frame can even tear. Furthermore, when there is a damage of part of the vehicle, the whole frame has to be replaced, which is an expensive operation.
Another disadvantage of such a frame is that, when additionally parts have to be mounted on such a frame, one or more metal tubes have to be weld to the frame, which is not very aesthetic.
A solution to solve this problem is provided in PCT patent application PCT/GB00/00016, in which a structure of vehicles, more specifically a go-kart structure is described, which comprises a planar base which is fitted into the open underside of moulded bodywork to form a shell structure. The planar base makes face-to-face contact with the underside of
the moulded bodywork at certain locations where the two parts are bonded together. The planar base is a foam panel which is encased within a glass fibre reinforced, circumferentially continuous plastics skin. Inserts are fitted into the foam panel within the skin to provide an anchorage for vehicle components which require load bearing support.
Non-load bearing components including a bull-nose shaped nose cone and side fairings can be releasably fastened to the moulded bodywork.
In the method for manufacturing such a structure, two pairs of layers of glass cloth are laid up one on the other on either side of a core part, which has been cut out from an extruded sheet of closed cell foamed plastics material. After orienting the layers of glass cloth with respect to the core part, the glass cloth layers are folded around the edges to complete the circumferentially continuous four-ply glass fibre portion of the skin layer whereafter the core part with the glass cloth wrapped around it is placed in a suitable mould and the glass cloth is impregnated with a liquid thermo stating resin such as a polyester resin, which is subsequently cured by the application heat and pressure to complete the formation of the skin layer around the core part so that the former circumferentially continuously encases the latter to complete formation of the planar base support.
A first disadvantage of such a structure is that the chassis is formed out of two parts, i. e. a planar base and a moulded bodywork, in which the planar base fits into the open underside of the moulded bodywork. This structure is time consuming to manufacture.
A second disadvantage is that with such a structure, there will be problems with the flex: - either the chassis will be too stiff, in which the handling of the kart doesn't fulfil the necessary requirements in the field of vibrations and flex; - either the chassis is too porous, in which through the flex the chassis can crack.
A further disadvantage of using a method for manufacturing such a structure is that problems can arise with surface of the chassis at one or the two sides.
Also in U. S. 6,026, 9023, a go-kart construction which uses a unibody construction wherein the body serves as a part of the suspension as well. The moulded body is made from a flexible yet resilient material such as fibreglass or a suitable plastic, such as ABS, such that it has sufficient flexion about a longitudinal axis to allow some twisting deformity without sagging when a passenger is supported in the vehicle. The unibody construction is generally moulded as a monolithic structure.
The disadvantage is that this kind of go-kart constructions only can drive at low speed.
When the kart is driven at high speed, the construction will tear because a monolithic structure is used in the body of the go-kart.
Furthermore, in such a construction it isn't possible to integrate different aspects, for example inserts, sandwich foam centre blocks, conduit pipes for electricity cables, etc.
The purpose of the invention is on the one hand to provide a method for manufacturing a chassis of composite material for a kart, in which the chassis has a composite shell structure in which there are different aspects integrated, for example inserts, stuffing material, this to improve assembly time. It's a further purpose to provide a method in which different layers within the chassis can be provided during the manufacturing process and in which reinforcements can be provided within the chassis.
On the other hand, the purpose of the invention is to provide a chassis of composite material for a kart which can bear very high bend and torsion forces and which is durable, safe, easy to assemble, is provided with the necessary reinforcements and which has furthermore an acceptable production speed and price.
This purpose is on the one hand achieved by providing a method for manufacturing a chassis of composite material for a kart, in which said chassis is manufactured by means of a resin transfer moulding (RTM) process.
A RTM process consists of injecting liquid resin into a closed mould containing glass reinforcements.
By using such a method, a chassis of composite material for a kart is obtained which comprises different layers, and in which different aspects can be integrated such as inserts, a sandwich foam centre, etc. , this to improve the assembly time.
To obtain one or more heights in the chassis, stuffing material is applied in the mould used in the RTM process.
In this way, a chassis is provided which has already a suitable form to mount other parts of the kart in a correct and easy way. In this way, even relief can be created in the chassis, through which other parts only can be mounted in the one and correct way onto the kart.
Said stuffing material consists preferably of one or more polyurethane sandwich foam centre blocks.
To provide a support for mounting other parts of the kart onto the chassis, one or more inserts are fitted in said mould.
Said inserts are preferably made of aluminium.
To easily mount other parts of the kart onto the chassis, said inserts are provided with one or more blind rivet nuts for mounting the other parts of the kart onto the chassis.
Blind rivet nuts are a one piece fastener installed blind from one side of the work piece.
They are clenched quickly and easily as a section of the shank collapses during installation.
The result is a precision high strength thread in thin walled sheets and hollow section.
In order to insert and fix a stub axle holder bush into the chassis, one or more blocks are provided in said mould.
Said blocks are preferably made of polyethylene terephtalate (PETP).
PETP is a thermoplastic polyester which has a great form stability and which accordingly is not sensitive for big reformations because of the movement of the front wheels. Another advantage is that the moisture admission is very low. Still another advantage is that these are very easy to glue together with the glass fibre mats.
In a preferred method according to any the invention, a polyester resin is inserted in the mould in the RTM process to serve as glue.
To give a colour to the chassis, in combination with said polyester resin a gelcoat is inserted in the mould.
In a preferred method according to the invention, during the RTM process one or more conduit pipes are provided for providing gas, brake and electricity cables of the kart.
On the other hand, the purpose of the invention is achieved by providing a chassis of composite material for a kart manufactured by a method as described above.
Through manufacturing a chassis of composite material by such a method, a chassis is obtained which can bear very high bend and torsion forces. Such a chassis is durable, save, easy to assemble, and is provided with the necessary reinforcements.
A chassis of composite material for a kart in which this invention is embodied and its manufacture is described now by way of example only with reference to the accompanying drawings, of which:
- figure 1 is a plan view of a chassis of composite material of a kart according to the invention; - figure 2 is a side view of a chassis as shown in figure 1; - figure 3 is a perspective view of a chassis as shown in figure 1, in which in one half the chassis is shown and in the other half the inserts which are provided in the chassis are shown.
The chassis (1) of the kart according to the invention, as shown in figures 1 and 2, is made of a composite material and has a composite shell structure. To manufacture such a chassis (1), a resin moulding transfer (RTM) process is used. A RTM process consists of injecting liquid resin into a closed mould containing glass reinforcements.
In this process, a mould is used which consists of an upper and a lower part. In these two parts, first of all one or more layers of glass fibre mats are provided. The layers of glass fibre mats can have a different quality, can be laid in different directions, and a different number of glass fibre mats can be laid upon each other, this depending on local requirements such as strength, flexibility, durability, etc. For instance, on the place (2) where the seat is located, few glass fibre is provided.
In a first part of the mould, different layers are provided. First of all, in order to obtain one or more heights in the chassis (1), stuffing material (3), preferably one or more polyurethane sandwich foam centre blocks, is provided. For instance to provide - a first height (3a) for mounting the rear bumper; - a second height (3b) for mounting the side bumpers; - a third height (3c) for mounting the front bumper; - etc.
As shown in figure 3, second of all, one or more blocks (10) are provided. In said blocks (10), a hole is bored, in which a steal stub axle holder bush is inserted and glued. In this stub axle holder bush, a stub axle holder can be inserted, which forms part of the
connection between a front wheel and the chassis (1). These blocks (10) are preferably made of polyethylene terephtalate (PETP).
PETP is a thermoplastic polyester which has following advantages: - a great form stability, and accordingly not sensitive for big reformations because of the movement of the front wheels; - very low moisture admission; - very easy to pass with the glass fibre mats.
Third of all, one or more inserts (11), preferably made of aluminium (for instance with a thickness of 3 mm), are fitted in the upper part of the mould to provide a support for mounting other parts of the kart onto the chassis (1). Accordingly, the inserts (11) are provided in the chassis (1).
As shown in figure 3, following inserts (11) are putted into the chassis (1) : - a first insert (1 la) for mounting a pump for a braking mechanism and a support for a steering column (also called nasapanel); - a second insert (1 lb) for mounting pedals; - a third insert (1 lc) for mounting a support of the steering column; - a fourth insert (1 d) for mounting a plate which vouches for locking of a seat; - fifth (11 e) and seventh (1 g) inserts for mounting of an adjustable seat; - a sixth insert (1 If) for mounting a support for an engine, one or more fuel tanks and axle bearing holders. The engine is placed on said support and the axle bearing holders serve for keeping the rear axle into a correct position.
These other parts are mounted on the chassis (1) by means of a bolt-nut system throughout the chassis (1). In stead of a bolt-nut system, also plates with one or more blind rivet nuts (not shown on the figures), can be used to mount said other parts of the kart onto the chassis (1).
Furthermore, also one or more conduit pipes (12) are provided in said first part of the mould for providing gas, brake and electricity cables of the kart.
In the second part of the mould, only a layer of one or more glass fibre mats is provided.
The first and second part of the mould are then closed and clamped together by bolds at the edges. The first part of the mould is provided with a number of threaded holes, that can be used for both injection gate as well as overflow gate. The polyester resin is injected into one of the holes and the other holes are checked upon overflow. If an overflow gate releases resin, it is closed with a bolt. After all overflow gates show resin, the injection is ready and all holes are closed with bolts. After that, the mould is placed in an oven for a few hours (depending on the resin type) in order to cure the resin.
In combination with this polyester resin, gelcoat can be inserted into the mould. This gelcoat serves for the necessary colour of the chassis (1). A good surface finish is guaranteed on the lower as well as the upper side of the chassis (1).
The lower side of the chassis (1) is flat, this in order to avoid hooking of the chassis (1) on obstacles in the driving surface, and is provided with apertures to provide for instance countersink head bolts.
By using the RTM process for manufacturing a chassis (1) with a composite shell structure, first of all a chassis (1) which is built up out of different layers can be manufactured. Furthermore, a chassis (1) is obtained which can bear very high bend and torsion forces. Such a chassis (1) is durable, save, easy to assemble, and provides the necessary reinforcements. Such a process has an acceptable production speed and price.