Front vehicle body structure

Front vehicle body structure (10) includes a front sub frame (16) disposed under and fixedly connected to left and right side frames (11, 12), and a steering gear box (18) is mounted on the front sub frame to extend transversely along the width of the vehicle body. The body structure also has support portions (44, 45, 46) provided in left-right symmetrical arrangement on the front sub frame, and the steering gear box is mounted on the support portions via respective bushes.

TECHNICAL FIELD

The present invention relates to front vehicle body structures where a steering gear box is provided on a front sub frame disposed under left and right side frames.

BACKGROUND ART

Among the conventionally-known front vehicle body structures are ones where a front sub frame disposed under and fixedly connected to left and right side frames and front suspensions are attached to left and right end portions of the front sub frame. In such front vehicle body structures, a power source (engine) is disposed forwardly of the front sub frame, and the power source is connected, via a support member, to a substantial middle region of the front sub frame so that the power source is supported by the front sub frame (see, for example, Japanese Patent Application Laid-Open Publication No. 2000-238656). According to the front vehicle body structure disclosed in the 2000-238656 publication, when front wheels are braked during travel of the vehicle, loads are applied, in a width direction of the vehicle body, from the front suspensions to the front sub frame. Further, in order to bear the loads applied from the front suspensions and support the power source, a cross member is attached to the front sub frame to secure a sufficient rigidity of the front sub frame.

Further, in some of the conventionally-known front vehicle body structures, a steering gear box is mounted to the front sub frame by means of a combination of fastening bands and fixing bushes, or only by means of a plurality of fixing bushes.

With the conventionally-known front vehicle body structures, loads applied from the front suspensions to steering tie rods due to braking of left and right front wheels can be borne by steering-gear-box mounting members, such as the fixing bushes. However, because a steering gear pinion and electric assisting motor are provided on an end portion of one of left and right sides of the steering gear box, it is difficult to position the mounting members, such as the fixing bushes, in left-right symmetrical relation to one another. Thus, the left and right tie rods tend to move different amounts when loads are applied from the front suspensions to the steering tie rods. Therefore, it has been considered difficult to achieve same toe angle changes between left and right wheels caused by braking loads.

Further, with the front vehicle body structure disclosed in the 2000-238656 publication, it is necessary to provide a cross member on the front sub frame in order for the front sub frame to have a sufficient rigidity for bearing loads applied from the front suspensions and supporting the power source. The provision of the cross member on the front sub frame undesirably increases the number of necessary component parts, which would impede enhancement of productivity.

DISCLOSURE OF THE INVENTION

It is therefore a first object of the present invention to provide an improved front vehicle body structure which can minimize a difference in toe angle change between left and right wheels caused by braking loads, and which can secure a sufficient rigidity of the front sub frame without increasing the number of necessary component parts.

In order to accomplish the above-mentioned object, the present invention provides an improved front vehicle body structure, which comprises: a front sub frame disposed under and fixed to left and right side frames, a steering gear box being mounted on the front sub frame to extend in a vehicle width direction; and at least three support portions provided in left-right symmetrical arrangement on the front sub frame, the steering gear box being mounted on the support portions via bushes.

Because the steering gear box is mounted on the support portions provided in left-right symmetrical relation to each other, loads applied from left and right lower arms of left and right suspensions to the front sub frame can be borne uniformly by the steering gear box. Thus, when loads are applied from the left and right suspensions to left and right tie rods, the left and right tie rods can be caused to move the same amount. As a result, the present invention can minimize a difference in toe angle change between left and right wheels caused by braking loads. Further, because the loads applied from the left and right lower arms to the front sub frame can be borne uniformly by the steering gear box, the steering gear box can function also as a reinforcing member. Thus, there is no need to provide a cross member as a separate reinforcing member, so that the present invention can secure a sufficient rigidity of the front sub frame without increasing the number of necessary component parts.

Preferably, the support portions comprise left, right and middle support portions, the left and right support portions being provided in left-right symmetrical relation to each other with respect to the middle support portion.

In a preferred form, the left and right lower arms of the left and right suspensions are connected to left and right lower-arm mounting portions, respectively, of the front sub frame, the left and right lower-arm mounting portions being located near where the front sub frame is fixed to the left and right side frames. In this way, the left and right lower-arm mounting portions can be reinforced with the left and right side frames, so that a sufficient rigidity of the left and right lower-arm mounting portions can be secured.

In an embodiment, the middle support portion is located at a substantial middle position, in a left-right direction, of the vehicle body, and the front vehicle body structure further includes a support member connected to the front sub frame to be located forwardly of the middle support portion for supporting a power source. Thus, a load applied from the support member to the front sub frame can be efficiently transmitted to the middle support portion. Because the steering gear box is mounted on the middle support portion, the load transmitted to the middle support portion can be efficiently borne by the steering gear box.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description, the terms “front”, “rear”, “left” and “right” are used to refer to directions as viewed from a human operator or driver.

FIG. 1is a plan view showing a front vehicle body structure10according to an embodiment of the present invention. The front vehicle body structure10includes: left and right side frames11and12; a left suspension13disposed laterally outwardly of the left side frame11; a right suspension14disposed laterally outwardly of the right side frame12; a front sub frame16disposed under and fixedly connected to the left and right side frames11and12; and a steering gear box18mounted on an upper portion16aof the front sub frame16.

Further, in the front vehicle body structure10, a left lower arm21of the left suspension13is connected to a left end portion of the front sub frame16, a right lower arm22of the right suspension14is connected to a right end portion of the front sub frame16, and a power source23is provided in front of the front sub frame16.

Left wheel25is mounted, via a hub (not shown), to a knuckle (not shown) of the left suspension13. Right wheel26is mounted, via a hub (not shown), to a knuckle27of the right suspension14.

The power source23is an engine/transmission unit transversely mounted between the left and right side frames11and12and comprising an engine28and a transmission29.

The power source23is mounted to the left side frame11via a left mounting bracket31and to the right side frame12via a right mounting bracket32, and it is connected to the front sub frame16via a support rod (support member)33.

FIG. 2is a perspective view of the front vehicle body structure10, andFIG. 3is an exploded perspective view of the front vehicle body structure10.

The front sub frame16, which has a substantially rectangular shape as viewed in plan, has a left front mounting portion36and left rear mounting portions37and47as portions connected to the left side frame11and a right front mounting portion38and right rear mounting portions39and49as portions connected to the right side frame12. The front sub frame16also has a left arm mounting portion (i.e., left-lower-arm mounting portion)41provided near the left front mounting portion36, and a right arm mounting portion (i.e., right-lower-arm mounting portion)42provided near the right front mounting portion36. The front sub frame16also has a support portion46, left and right support portions44and45and a connection section48that are all formed on the upper portion16a. The support portions44-46are disposed in left-right symmetrical arrangement with the left and right support portions44and45positioned in left-right symmetrical relation to each other with respect to the support portion46.

The left front mounting portion36extends toward the left side of the vehicle body with an upward slope, and the left rear mounting portion37extends toward the left side of the vehicle body. The left front mounting portion36and left rear mounting portion37are fixedly connected to the left side frame11by means of bolts51.

The right front mounting portion38extends toward the right side of the vehicle body with an upward slope, and the right rear mounting portion39extends toward the right side of the vehicle body. The right front mounting portion38and right rear mounting portion39are fixedly connected to the right side frame12by means of bolts52.

In the aforementioned manner, the front sub frame16is fixedly connected to the undersides of the left and right side frames11and12.

The left lower arm21, which constitutes part of the left front suspension13ofFIG. 1, is vertically pivotably connected at its proximal end portion21ato the left arm mounting portion41that is in turn mounted near the front side of the left front mounting portion36. The left knuckle (not shown) is pivotably mounted on a distal end portion of the left lower arm21, and the left wheel25ofFIG. 1is mounted, via the hub (not shown), to the left knuckle.

The right lower arm22, which constitutes part of the right front suspension14ofFIG. 1, is vertically pivotably connected at its proximal end portion22ato the right arm mounting portion42that is in turn mounted near the front side of the right front mounting portion38. The right knuckle27is pivotably mounted on a distal end portion22bof the right lower arm22, and the right wheel26ofFIG. 1is mounted, via the hub, to the right knuckle27.

In the aforementioned manner, the left lower arm21is connected to the left arm mounting portion41of the front sub frame16, and the right lower arm22is connected to the right arm mounting portion42. Thus, when the left and right front wheels25and26are braked during travel of the vehicle, loads acting in the width direction of the vehicle body are applied to the front sub frame16by way of the left and right lower arms21and22.

With the left arm mounting portion41mounted near the front side of the left front mounting portion36and the right arm mounting portion42mounted near the front side of the right front mounting portion38, the left and right arm mounting portions41and42can be reinforced with the left and right side frames11and12and thus can have a sufficient rigidity.

Of the three support portions44-46provided on the upper portion16aof the front sub frame16, the left support portion44is disposed in front of a box body19that forms of a casing of the steering gear box18. The left support portion44is an upwardly bulging portion located near the left front mounting portion36and left arm mounting portion41. Mounting hole44ais formed centrally through the left support portion44, and a nut (not shown) is welded to the underside surface of the left support portion44coaxially with the mounting hole44a.

The right support portion45is an upwardly bulging portion located near the right front mounting portion38and right arm mounting portion42. Mounting hole45ais formed centrally through the right support portion45, and a nut (not shown) is welded to the underside surface of the right support portion45coaxially with the mounting hole45a. Similarly to the left support portion44, the right support portion45is disposed in front of the box body19of the steering gear box18.

The middle support portion46is provided substantially on a longitudinal centerline of the vehicle body and thus is located in a substantial middle position, in the left-right direction, of the vehicle body. The middle support portion46has a mounting hole46aformed centrally through, and a nut (not shown) is welded to the underside surface of the middle support portion46coaxially with the mounting hole46a. The middle support portion46is disposed rearwardly of the box body19of the steering gear box18.

The steering gear box18is mounted to the left and right support portions44and45and the middle support portion46. The steering gear box18has: the box body19accommodating a steering gear17ofFIG. 2etc.; a left mounting piece56projecting toward the front of the vehicle body from a left end portion19aof the box body19; a right mounting piece57projecting toward the front of the vehicle body from a right end portion19bof the box body19; and a middle mounting piece58projecting toward the rear of the vehicle body from a middle portion19cof the box body19. The box body19is in the form of a cylindrical case.

Cylindrical bush56ais fitted in a mounting hole of the left mounting piece56. Bolt61is inserted through the cylindrical bush56aand mounting hole44aof the left support portion44and screwed into a nut (not shown) provide for the left support portion44.

Cylindrical bush57ais fitted in a mounting hole of the right mounting piece57. Bolt62is inserted through the cylindrical bush57aand mounting hole45aof the right support portion45and screwed into a nut (not shown) provide for the right support portion45.

Further, a cylindrical bush58ais fitted in a mounting hole of the middle mounting piece58. Bolt63is inserted through the cylindrical bush58aand mounting hole46aof the middle support portion46and screwed into a nut (not shown) provide for the middle support portion46.

The steering gear box18(box body19) is mounted transversely on the upper portion16aof the front sub frame16via the bushes56a,57aand58a. Steering wheel67is mounted on a steering shaft66extending from the steering gear box18(box body19).

As the steering wheel67is turned, the left and right tie rods68and69move in the width direction of the vehicle, so that the left and right knuckles (only the right knuckle27is shown) pivot to change the orientation of the left and right front wheels25and26(seeFIG. 1).

As noted above, the support portions44-46are disposed in left-right symmetrical arrangement on the front sub frame16with the left and right support portions44and45positioned in left-right symmetrical relation to each other with respect to the support portion46, and the steering gear box18is mounted on these support portions44-46. Thus, loads acting on the front sub frame16by way of the left and right lower arms21and22when the left and right front wheels25and26are braked can be borne uniformly by the steering gear box18.

Thus, when loads are applied from the left and right front suspensions13and14to the left and right tie rods68and69, the left and right tie rods68and69can be caused to move by the same amount, so that it is possible to minimize a difference in toe angle change between the left and right wheels caused by the braking loads.

Further, because loads acting on the front sub frame16by way of the left and right lower arms21and22can be borne uniformly by the steering gear box18, the steering gear box18can function also as a reinforcing member. Thus, there is no need to provide a cross member as a separate reinforcing member, so that the instant embodiment can secure a sufficient rigidity of the front sub frame16without increasing the number of necessary component parts.

The connection section48is formed on the upper portion16aof the front sub frame16and located forwardly of the middle support portion46. The support member33is connected to the front sub frame16to be located forwardly of the middle support portion46, so as to support the power source23. The connection section48has an upper mounting bracket71located forwardly of the middle support portion46, and has an accommodating space72formed between the mounting bracket71and the upper portion16a. Mounting holes71aand16bare formed coaxially in the upper mounting bracket71and upper portion16a, respectively, and a nut (not shown) is welded to the underside surface of the upper portion16acoaxially with the mounting hole16b.

To the connection section48located forwardly of the middle support portion46is fixedly connected a rear end portion33aof the support rod33supporting the power source23. Namely, a bolt75is inserted through a mounting hole71aof the upper mounting bracket71, mounting hole73of the rear end portion33aand mounting hole16bof the upper portion16aand screwed into a nut (not shown). Thus, the rear end portion33aof the support rod33connected to the connection section48is accommodated in the accommodating space72.

The support rod33is connected at its front end portion33bto the power source23via a mounting bracket77. Thus, the power source23can be supported by a middle region of a front portion16cof the front sub frame16via the support rod33.

Because the connection section48is located forwardly of the middle support portion46as noted above, loads transmitted to the middle region of the front portion16cof the front sub frame16can be delivered to the middle support portion46and efficiently borne by the steering gear box18(box body19).

With reference toFIGS. 4A and 4B, the following paragraphs describe how loads transmitted to the front sub frame16of the front vehicle body structure10are borne in the instant embodiment.

When the left and right front wheels25and26are braked, a load F1acts on (or is applied to) the left arm mounting portion41of the front sub frame16by way of the left lower arm21while a load F1acts on (or is applied to) the right arm mounting portion42of the front sub frame16by way of the right lower arm22, as shown inFIG. 4A.

With the left arm mounting portion41disposed near the front side of the left front mounting portion36, the left arm mounting portion41is reinforced with the left side frame11(seeFIG. 2). Thus, the load (reactive force) F1applied to the left arm mounting portion41can be transmitted as indicated by arrow A. Part of the load (reactive force) F1transmitted as indicated by arrow A is delivered to the steering gear box18by way of the left support portion44and borne by the steering gear box18.

Similarly, with the right arm mounting portion42disposed near the front side of the right front mounting portion38, the right arm mounting portion42is reinforced with the right side frame12. Thus, the load (reactive force) F1applied to the right arm mounting portion42can be transmitted as indicated by arrow B. Part of the load (reactive force) F1transmitted as indicated by arrow B is delivered to the steering gear box18by way of the right support portion45and borne by the steering gear box18.

Because the steering gear box18is mounted on the left and right support portions44and45and middle support portion46with the left and right support portions44and45positioned in left-right symmetrical relation to each other with respect to the support portion46as noted above, part of the loads (reactive force) F1acting on the front sub frame16by way of the left and right lower arms21and22can be transmitted uniformly from the left and right end portions19aand19b.

Thus, when the loads F1are applied from the left and right front suspensions13and14to the left and right tie rods68and69, the left and right tie rods68and69can be caused to move by the same amount, so that it is possible to minimize a difference in toe angle between the left and right wheels25and26caused by the braking loads.

Further, because part of the loads F1acting on the front sub frame16by way of the left and right lower arms21and22can be transmitted uniformly from the left and right end portions19aand19band borne by the steering gear box18. Consequently, the steering gear box18can function also as a reinforcing member. Thus, there is no need to provide a cross member as a separate reinforcing member, so that the instant embodiment can secure a sufficient rigidity of the front sub frame16without increasing the number of necessary component parts.

Further, when an impact load is applied to the front vehicle body structure in the front-to-rear direction of the vehicle body, part of the applied impact load is transmitted, as a load F2, to the support rod33by way of the power source23, as shown inFIG. 4B. The load F2transmitted to the support rod33is then transmitted to the middle region of the front portion16cof the front sub frame16via the connection section48.

Because the connection section48is located forwardly of the front side of the middle support portion46, the load transmitted to the middle region of the front portion16cis delivered to the middle support portion46. Further, because the middle support portion46is a porting mounting thereon the steering gear box18, the load transmitted to the middle region of the front portion16cof the front sub frame16via the connection section48can be borne efficiently by the steering gear box18. In this way, it is possible to secure a sufficient rigidity of the front sub frame16.

The shapes of the front sub frame16, steering gear box18, left and right lower arms21and22, support rod33, left, right and middle support portions44,45and46, etc. are not limited to those illustrated and described above and may be modified as necessary.

Further, whereas the preferred embodiment has been described as having three support portions44-46, the number of the support portions is not limited to three; for example, four such support portions may be provided as long as they are positioned in left-right symmetrical arrangement.

INDUSTRIAL APPLICABILITY

The front vehicle body structure of the present invention is well suited for use in automotive vehicles having a steering gear box provided on a front sub frame disposed under left and right side frames.