WO2009084009A1

WO2009084009A1 - Engine cradle assembly for a vehicle

Info

Publication number: WO2009084009A1
Application number: PCT/IN2008/000449
Authority: WO
Inventors: Soheb Ahmed; Abhay Deshpande; Umesh Abhyankar; Mandar Hazare
Original assignee: Tata Motors Limited
Priority date: 2008-01-01
Filing date: 2008-07-14
Publication date: 2009-07-09
Also published as: ZA201004681B

Abstract

This invention relates to an engine cradle assembly for a vehicle comprising a front cross member (2) and a rear cross member (5), said front and rear cross members (2, 5) being interconnected by a left side member (3) and a right side member (4); said front cross member (2) being provided with end mounting locations (13) and a center mounting location (14), said front cross member (2) is having provisions for mounting suspension and engine units; said front cross member (3) further comprises of elliptical sections at intermediate portions between the end mounting locations (13) and the center mounting location (14) which is oriented to have maximum stiffness for engine and suspension mounting; said engine cradle assembly is adapted to be attached to a vehicle body by fastening top surface of said end mountings (13) of said front cross member (2) with bottom surface of an reinforcement assembly of the vehicle body; and by fastening top end surfaces of said rear cross member (5) to bottom surfaces of the vehicle body by mounting means.

Description

ENGINE CRADLE ASSEMBLY FOR A VEHICLE

FIELD OF INVENTION

This invention relates in general to frame assemblies for vehicles. More particularly it relates to an improved structure for an engine cradle assembly for use in a vehicle.

BACKGROUND OF THE INVENTION

Engine cradle assembly is removable section of a vehicle frame that fastens under the bottom of the vehicle body. Engine cradle assembly is usually mounted at the bottom of a vehicle body at the front or the rear. For example in a front engine type vehicle, front suspension and an engine are mounted on a subframe at the front side of the vehicle body, and in a rear engine type vehicle rear suspension and an engine along with a differential gear unit are mounted on a subframe at the rear side of the vehicle body. US 6076625, US 5280957 & US 4263980 have demonstrated such engine cradle designs.

The primary requirement from the engine cradle assembly structure is to provide sufficient strength and stiffness. Strength of the structure is paramount since the cradle assembly is subjected to very large mechanical stresses due to the weight of the engine and load of the vehicle transferred to the cradle assembly from the suspension. Stiffness of the structure is required in order to have effective isolation of powertrain and road induced vibrations.

Conventionally the cradle assembly is typically made from a pair of spaced side frame members having front and rear ends, a front cross frame member connected across the front ends of the side frame members, and a rear cross frame member extending between the rear ends of the side frame members. The individual components are usually metallic pieces which are generally stamped then welded together to form the final engine cradle assembly. More recently the cradle assemblies have been formed from a single tubular component generally a U-shaped member using the process of expansion shaping, commonly referred to as hydroforming. Hydroforming is a process which uses pressurized fluid to deform a tubular member into a desired shape. To accomplish this, the tubular member is initially disposed between two die sections of a hydroforming apparatus which, when closed together, define a die cavity having a desired final shape. Thereafter, the tubular member is filled with a pressurized fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid is increased to a magnitude where the tubular member is expanded outwardly into conformance with the die cavity. As a result, the tubular member is deformed into the desired final shape. Hydroforming is an advantageous process for forming engine cradle and other structures because it can quickly deform a single component into a desired shape. US 5884722 describes one such U- shaped cradle following the hydroforming guidelines established in the prior art.

The engine cradle assembly is usually mounted to the vehicle frame with bolts. In order to prevent the collapse of the two spaced apart flanges when the bolt is tightened, a spacer is provided between the two flanges. The spacer is in the form of a tube sleeved on the bolt. The spaced flanges provide a stiff attachment which is very rigid and forms a strong joint to have least vibration and noise. US 6085856 describes one such arrangement. The spacers provide desirable strength and rigidity to the hollow ends of the engine cradle assembly, but also add undesirable expense.

The assembly of engine cradle also presents situation wherein a gap is disposed between two structures that are to be fastened together. The gap may be variably sized due to part to part manufacturing related variations. The gaps are undesirable as it may render the joint susceptible to flexure. One of the methods employed is to utilize the clamping force that is generated by a fastener to deform one or both of the structures to eliminate the gap. The drawback of this method is that the amount of clamping force that is absorbed by the deformation of one or both of the structures is not quantifiable and moreover the deformation in the structure due to clamping force will cause preloading which is not good from durability point of view.

Further requirement from cradle assemblies is that they should be dimensionally accurate in series production. This is evidently required from maintaining consistency of performance of suspension system as well as that of powertrain mounting system.

In addition to catering to the afore said diverse requirements the cradle assemblies are also required to have drain holes at desired locations in order to have efficient corrosion resistant coating at both outer as well as inner surfaces of the tubular structure.

OBJECTS OF INVENTION

The main object of this invention is to provide an engine cradle assembly for a vehicle with provisions for mounting engine assembly, gearbox assembly, suspension system and cooling system and exhaust system.

Another object of this invention is to provide engine cradle assembly for a vehicle with high dimensional accuracies for suspension and engine mounting hardpoints as well as other attachment points in series production.

Another object of this invention is to provide an engine cradle assembly for a vehicle with means for attaching an engine cradle assembly to a vehicle body capable of having stiffer joint, thereby reducing vibration and noise. Another object of the present invention is to provide an engine cradle assembly for a vehicle which can be accessed easily.

Yet another object of the present invention to provide an engine cradle assembly with a plurality of attaching points to provide additional stiffness

Yet another object of the present invention is to provide attachment bracket design which caters to manufacturing induced dimensional variations

Yet another object of the present invention to eliminate the requirement of drain holes for corrosion preventive coating on the engine cradle assembly

Another object of the present invention is to provide an engine cradle assembly for a vehicle which is simple in construction and cost effective.

BRIEF DESCRIPTION OF INVENTION

The engine cradle assembly for a vehicle in accordance with this invention basically comprises of at least four tubular members namely a pair of side members, a front cross member and a rear cross member. The front cross member is connected with front ends of the side members. The rear cross member extends between rear ends of the side members. The front cross member and the pair of side members are formed by using mechanical bending and hydroforming techniques. Said tubular members and attachment elements are provided such that they are improved structurally so that an improved engine cradle assembly for vehicles is obtained.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows an isometric rear view of an engine cradle assembly for a vehicle in accordance with this invention. Figure 2 shows an isometric front view of an engine cradle assembly for a vehicle in accordance with this invention.

Figure 3 shows an isometric rear view of front cross member used in this invention.

Figure 4 shows an isometric front view of front cross member used in this invention.

Figure 5 shows an isometric top view of right side member used in this invention.

Figure 6 shows an isometric bottom view of right side member used in this invention.

Figure 7 shows an isometric top view of left side member used in this invention.

Figure 8 shows an isometric bottom view of left side member used in this invention.

Figure 9 shows isometric view of reinforcements provided on front cross member and pair of side members

Figure 10 shows isometric view of reinforcement provided on rear cross member

Figure 11 shows sectional view at powertrain mounting location of left and right side members

Figure 12 shows isometric view of central connection bracket

Figure 13 shows isometric view of central connection bracket fastening arrangement to vehicle body

Figure 14 shows sectional view of central connection bracket fastening arrangement to vehicle body

Figure 15 shows sectional view of front cross member fastening arrangement to vehicle body

Figure 16 shows isometric view of rear cross member fastening arrangement to vehicle body

Figure 17 shows sectional view of rear cross member fastening arrangement to vehicle body DETAILED DESCRIPTION OF INVENTION

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same,

Referring to figs.l to 17 engine cradle assembly consists of front cross member (2), left side member (3), right side member (4), rear cross member (5), suspension inner pivot bracket (6), suspension outer pivot bracket (7), radiator mounting bracket (8), engine mount bracket (9), central connection bracket (10) wherein the end portions of left side member (3) and right side member (4) are joined to front cross member (2) and rear cross member thus forming a quadrilateral structure. Front cross member (2), left side member (3) and right side member (4) are manufactured by mechanical bending and hydroforming techniques.

Front cross member (2) is hydroformed such that it has rectangular sections (11, 12) at the end mounting location (13) and center mounting locations (14) as shown in fig. 3 and fig. 4. The rectangular sections (11, 12) provide flat resting/contact area (15) for bolting. Additionally the front cross member (2) has elliptical sections at the intermediate lengths between the end (13) and central (14) mounting areas. A depression (16) is also provided on the front cross member (2) to have improved clearances. Suspension outer pivot bracket (7), suspension inner pivot bracket (6) and engine mount bracket (9) are fitted to the front. The dimensional accuracy of suspension hard points is better achieved in this design since the hydro form pipe is straight and without any bends so no spring-back related issues are encountered. Additionally, the elliptical section in the intermediate lengths of suspension cross member is oriented such as to have maximum stiffness for engine mounting and suspension mounting. Holes (17, 18 & 19, 20) are mechanically drilled or hydro pierced at the end mounting location (13) and center mounting locations (14) as shown in fig. 3 and fig. 4 to receive sheet metal reinforcement (21). Holes (17, 19) are bigger in diameter as compared to holes (18, 20). Sheet metal reinforcement (21) is fitted such that the flange of sheet metal reinforcement is welded to suspension cross member (2) surface on the bigger hole (17, 19) side. The sheet metal reinforcement provides a low cost stiffening arrangement compared to machined collared sleeves which are conventionally used.

Left side member (3) is manufactured from tubular stock by mechanical bending and hydroforming such that it has rectangular cross section with bends as shown in fig. 7 and fig. 8. Holes (22, 23) are mechanically drilled or hydro pierced at the powertrain mounting locations (24) to receive sheet metal reinforcement (25). Hole (22) is bigger in diameter as compared to hole (23). Sheet metal reinforcement (25) are fitted such that the flange of sheet metal reinforcement is welded to left side member (3) surface on the bigger hole (22) side. An elliptical notch (28) at front end (26) of left side member (3) and rectangular notch (29) at rear end (27) of the left side member (3) is provided for fitting the left side member (3) to front cross member (2) and rear cross member (5) respectively. Right side member (4) is manufactured from tubular stock by mechanical bending and hydroforming such that it has rectangular cross section with bends as shown in side view shown in fig. 5 and fig. 6. Holes (30, 31) are mechanically drilled or hydropierced at the powertrain mounting locations (32) to receive sheet metal reinforcement (33). Hole (30) is bigger in diameter as compared to hole (31). Sheet metal reinforcements (33) are fitted such that the flange of sheet metal reinforcement is welded to right side member (4) surface on the bigger hole (30) side. An elliptical notch (36) at front end (34) of right side member (4) and rectangular notch (37) at rear end (35) of the right side member (4) is provided for fitting the right side member (4) to front cross member (2) and rear cross member (5) respectively. Rear cross member (5) is made by conventional tubular stock and is preferably having rectangular cross section. It has holes (39) drilled at the end mounting locations (38). Sheet metal reinforcement (40) is inserted from side openings and fitted at the mounting locations. Radiator mounting brackets (8) are fitted on one side of the rear cross member (5).

Referring to fig. 12 central connection bracket (10) comprises of horizontal surface (41), vertical surface (42) and side walls (43). Horizontal surface (41) and vertical surface (42) have a oblong holes (44, 45) with diameter bigger than bolting fastener diameter. Central connection bracket (10) is pre bolted to suspension cross member (2) using bolt (47) and nut (46).

Front cross member end mounting attachment to vehicle body is now explained. Referring to fig. 15 the front cross member end mounting attachment comprises of vehicle body long member (48), external reinforcement (49), internal reinforcement (50) and threaded spacer (51) such that external reinforcement (49) is fitted to vehicle body long member (48). Internal reinforcement (50) and threaded spacer (51) subassembly is fitted to interior surfaces of external reinforcement (49) to receive bolting fastener (52). The mounting is done such that the top flat surface () of suspension cross member (2) engages with bottom surface (53) of external reinforcement (49). When bolting fastener (52) is tightened the attachment is completed and a stiff and low cost arrangement is obtained.

Referring to fig. 13 and fig. 14 front cross member central mounting attachment to vehicle body comprises of central tunnel member (54), threaded sleeve (55) and internal reinforcement (56) such that internal reinforcement (56) and threaded sleeve (55) subassembly is fitted to internal surfaces of central tunnel member (54) to receive bolting fastener (57). The attachment is obtained by engaging central connection bracket (10) with central tunnel member (54) and fastening the bolt (57). The oblong holes (44, 45) on central connection bracket take care of dimensional variations in all three directions due to manufacturing process. This means that the connection is not preloaded and there is no flexure at the joint. Presence of central attachment between cradle assembly and vehicle body improves stiffness of engine mounting bracket. Additionally it helps in improving lateral stiffness of rear suspension resulting in better handling.

Fig. 16 and fig. 17 shows rear cross tube end mounting attachment. It comprises of vehicle body side bracket (58) having a bolting hole fitted to vehicle body long member. The attachment is accomplished by engaging bottom surface of bracket (59) with top surface of rear cross member and fastening the two using bolt (60) and nut (61).

All the vehicle body attachments are designed to have a stiff joint between cradle assembly and vehicle body. The reinforcement spacers for front and rear cross members is made by sheet metal stampings instead of machined collared sleeves conventionally used. This yields a low cost and stiff joint with predictable load path. Additionally, since all the vehicle body attachments are such that they have fasteners oriented in vertical direction providing ease of assembly in series production line as well as assembly/disassembly during service.

The stiff cradle assembly along with stiff attachment as explained in earlier paragraphs not only helps in better performance of suspension and engine mount but also helps to achieve improved torsional stability at the rear of vehicle body.

Rear suspension and wheel assembly is mounted on engine cradle assembly by bolting the suspension arms at suspension inner pivot bracket (6) and suspension outer pivot bracket (7). Powertrain assembly comprising of engine, gearbox and exhaust system is mounted on engine cradle assembly by bolting the engine mounts at engine mount bracket (9) present on suspension cross member (2), powertrain mounting holes (22,23) on left side member (3) and powertrain mounting holes (30,31) on right side member (4) respectively. The engine mounts directly seat on the left side member (3) and right side member (4) thus eliminating extra brackets which are seen in conventional designs. Moreover this design lends greater stiffness in vertical direction for the engine mounting hard points resulting in effective isolation. Additionally, the powertrain assembly is easily mountable on engine cradle as it has to be dropped down on the engine cradle assembly and fastening the engine mount bolts. Cooling module radiator is mounted on radiator mounting bracket (8) fitted in rear cross member using bolting fasteners. The engine cradle assembly thus serves to support the powertrain and exhaust assembly, cooling module, rear suspension assembly etc to provide a completely modular structure thus facilitating ease of assembly in series production of high volumes as well as assembly/disassembly during service.

One more advantage of the present invention is in ease of providing corrosion preventive coating without requiring drain holes which are present in conventional designs. The requirement of efficient corrosion preventive coating is that all interior and exterior surfaces of assembly are coated without creating any air pockets as well as paint accumulation. Usually drain and air holes are provided in prior art design to address this issue. In the present invention, the cradle assembly is dipped in the coating tank such that front cross member is at the bottom and rear cross member is at top with both left and right side members being vertical. As the assembly is dipped into the tank the coating fluid enters the front cross member from the end sides enabling complete interior and exterior coating of the member, on further dipping the fluid enters into the side members (3,4) from openings (70,71) respectively, the air inside the side members (3,4) escapes from openings (72,73). And finally the fluid enters the rear cross tube from the end sides. When the cradle assembly is pulled upwards all the fluid remaining inside cradle tubular members follows reverse path and is drained out. This ensures complete interior and exterior coating of the all the elements of cradle assembly.

The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

Claims

CLAIMS:

1. An engine cradle assembly for a vehicle comprising: a front cross member and a rear cross member, said front and rear cross members being interconnected by a left side member and a right side member; said front cross member being provided with end mounting locations and a center mounting location, said front cross member is having provisions for mounting suspension and engine units; said front cross member further comprises of elliptical sections at intermediate portions between the end mounting locations and the center mounting location which is oriented to have maximum stiffness for engine and suspension mounting; said engine cradle assembly is adapted to be attached to a vehicle body by fastening top surface of said end mountings of said front cross member with bottom surface of an reinforcement assembly of the vehicle body; and by fastening top end surfaces of said rear cross member to bottom surfaces of the vehicle body mounting means.

2. The assembly as claimed in claim 1, wherein said rear cross member, left side member and right side member are having rectangular cross section.

3. The assembly as claimed in claims 1 and 2 , wherein the said front cross member and left and right side members are formed from tubular stock by mechanical bending and/or hydroforming.

4. The assembly as claimed in claims 1 to 3, wherein said front cross member is provided with rectangular sections at the end mounting locations and the center mounting location to assist fastening.

5. The assembly as claimed in claims 1 to 4, wherein a depression is provided on the front cross member to have improved clearances.

6. The assembly as claimed in claims 1 to 5, wherein sheet metal reinforcements are fitted onto the front cross member, and the left and right side members and rear cross member to have improved stiffness at fastening locations.

7. The assembly as claimed in claim 6, wherein said reinforcements fitted onto the rear cross member comprises of vertical depression along its length and plurality of angular depressions at its ends.

8. The assembly as claimed in claim 1 wherein said reinforcement assembly comprises of external reinforcement and internal reinforcement spaced apart by a threaded spacer to receive fastener.

9. The assembly as claimed in claim 1 to 6, wherein a plurality of holes are provided on opposite surfaces of the rectangular sections of the end mounting locations and center mounting location in the front cross member and on the top and bottom surfaces of the powertrain mounting locations in the left and right side members to receive the sheet metal reinforcements.

10. The assembly as claimed in claim 1, wherein a notch is provided at the front end of the left and right side member for fitting the left and right side member to the front cross member and a rectangular notch is provided at the rear end of the left and right side member for fitting said left and right side member to the rear cross member

11. The assembly as claimed in claim 1 to 10, wherein said center mounting location is provided with a central connection bracket comprising a horizontal surface, a vertical surface and sidewalls..

12. The assembly as claimed in claim 11, wherein the central connection bracket comprises oblong holes with diameter bigger than a bolting fastener diameter; said central connection bracket is engaged with a central tunnel member whose internal surface is fitted with an internal reinforcement and threaded sleeve to receive a fastener, said oblong holes capable of tolerating dimensional variations in all directions during manufacturing process to avoid flexure.

13. The assembly as claimed in any one of the preceding claims, wherein the said assembly is configured such that the powertrain assembly comprising at least of engine, gearbox and exhaust system are mounted thereon by fastening the engine mounts at engine mounting bracket on the front cross member and on the powertrain mounting holes on left and right side members, wherein the engine is mounted directly on the left and right side member thereby eliminating additional mounting brackets.

14. The assembly as claimed in any one of the preceding claims, wherein it further comprises openings on the front and rear ends of the left and right side members to facilitate in dip-coating of the said assembly, said openings are provided to allow coating fluid to enter the interior surfaces of the said left and right side members and to vent out air from inside the left and right side members.

15. An engine cradle assembly for a vehicle as hereinabove described with reference to the accompanying drawings.