Motor vehicles – Steering gear – Each wheel steerable
Reexamination Certificate
2002-02-13
2004-07-20
Morris, Lesley D. (Department: 3611)
Motor vehicles
Steering gear
Each wheel steerable
C180S418000, C180S024010, C701S042000
Reexamination Certificate
active
06763906
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims priority of Japanese PCT Application No. PCT/JP00/04111 filed Jun. 22, 2000, the complete disclosure of which is hereby incorporated by reference.
TECHNICAL FIELD
The present invention relates to a vehicle rear wheel steering device, and in particular to a rear wheel steering device in a two rear axle type vehicle in which the rear part of the vehicle is supported by a rear-front axle and a rear-rear axle.
BACKGROUND ART
Conventionally, there has been widely used a truck with rear two axles as a truck having a high maximum carrying load since only a rear axle consisting of a single axle cannot bear a majority of a carrying load. In particular, with the use of a trunnion type suspension unit suspending rear two axles, no unbalance in load is present between a rear-front axle and a rear-rear axle, and accordingly, both axles can stably bear the carrying load.
In a truck having such a configuration that rear two axles are suspended by a trunnion type suspension unit, all load applied to the rear two axles are born at the middle point between the rear-front axle and the rear-rear axle, that is, at the attaching position of the trunnion bracket. Accordingly, the load is intensively applied to this single point in the longitudinal direction of the vehicle even with the configuration of the rear two axles, and accordingly, a high load has to be born at this position.
In such a truck having rear two axles, it may be considered that both rear two axles are shifted forward in order to reduce, in particular, the load exerted to front wheels having a single tire. That is, the load exerted to the front axle can be reduced by biasing the attaching position of the trunnion bracket forward. However, when both rear two axles are shifted forward, the overhanging part of the vehicle, afterward from the rear-rear axle becomes longer, and accordingly, there is raised such a problem that the rear end of the vehicle swings right and left during turning of the vehicle.
In order to allow the length of the overhanging part to fall in a predetermined range, and as well to reduce the load exerted to the front wheels, the rear front axle is shifted forward and to set the distance between the rear-front axle and the rear-rear axle to be longer. However, should the unsteerable rear-front axle largely biased forward from the rear-rear axle, rear-front wheels (tires) attached to both ends of the rear-front axle would eccentrically be worn during turning of the vehicle. As a result, there has been raised such a problem that the use life of the rear-front wheels (tires) is shortened.
In order to prevent eccentric abrasion of the rear-front wheels (tires), it may be consider to steer the rear-front wheels in response to steering of the front wheels. However, the rear-front wheels bear a high load in comparison with the front wheels, and accordingly, each of the rear-front wheels is usually composed of double wheels having two tires. Thus, a steering unit having a large-sized actuator which can exhibit a large steering force is required for steering the rear-front wheels. As a result, the steering unit becomes large-scale, and accordingly, there has been raised such a problem that the manufacturing cost for the vehicle is increased.
Further, when the rear-front wheels are steered sensitively in response to fine steering of the front wheels, the steering mechanism for the rear-front wheels is operated frequently, causing abrasion of the steering mechanism for the rear-front, as a result, the durability of the steering mechanisms deteriorates, thereby the reliability of the vehicle becomes lower.
Further, when the rear-front wheels are steered sensitively in response to fine steering of the front wheels, the rectilinear running ability of the vehicle is deteriorated during high speed running, and accordingly, the running stability of the vehicle is lowered during high speed running.
A first object of the present invention is to provide a rear-wheel steering device in which a substantial part of a carrying load is born by rear two axles so as to reduce the burden to front wheels, and further, the rear-front wheels can be steered so as to prevent eccentric abrasion of the rear- front wheel tires.
A second object of the present invention is to provide a rear wheel steering device which can steer the rear-front wheels with a relatively small-sized actuator so as to prevent deterioration of the durability of the rear-front wheels, which is caused by unnecessary steering, and further, which can enhance the rectilinear running ability during high speed running, thereby it is possible to improve the running stability.
DISCLOSURE OF INVENTION
The invention relating to claim
1
, as shown in
FIGS. 1
to
3
and
FIG. 8
, is an improvement in a rear wheel steering device in a vehicle in which a rear part of a vehicle body is supported by a rear-front axle
18
and a rear-rear axle
20
.
The characteristic configuration of this invention comprises a rear-front wheel steering mechanism for steering right and left rear-front wheels
17
,
17
which are rotatably mounted at opposite ends of a rear-front axle
18
, an actuator
51
for driving the rear-front wheel steering mechanism so as to steer the rear-front wheels
17
, and control means
69
for controlling the actuator
51
, wherein the control means
69
stops the steering for the rear-front wheels
17
when a vehicle speed is approximately zero, but the control means
69
operates the actuator
51
when a difference between a theoretical steering angle of the rear-front wheels
17
, relative to a steering angle of the front wheel
15
, and an actual steering angle exceeds a predetermined value even though the vehicle speed is approximately zero.
It is noted that the control means
69
may be constituted so as to cause the actuator
51
to be inoperative when a transmission
25
is set at a neutral position. Further, the control means
69
may be constituted so as to cause the actuator
51
to be inoperative when a clutch is disengaged.
The invention relating to claim 4, as shown in
FIGS. 1
to
3
and
8
, is an improvement in a rear wheel steering device in a vehicle in which a rear part of a vehicle body is supported by a rear-front axle
18
and a rear-rear axle
20
.
The characteristic configuration of this invention comprises a rear-front wheel steering mechanism for steering right and left rear-front wheels
17
,
17
which are rotatably mounted at opposite ends of a rear-front axle
18
, an actuator
51
for driving the rear-front wheel steering mechanism so as to steer the rear-front wheels
17
, and control means
69
for controlling the actuator
51
, wherein the control means
69
operates the actuator
51
in accordance with a steering angle of front wheels
15
so as to steer the front-rear wheels
17
, and the control means
69
causes the actuator
51
to be inoperative so as to prevent the rear-front wheels
17
from being steered when the steering angle of the front wheels
15
is not more than a predetermined value.
In this arrangement, a ratio of the steering angle of the rear-front wheels
17
with respect to that of the front wheels
15
may be changed in accordance with a vehicle speed, the higher the vehicle speed, the smaller the ratio of the steering angle of the rear-front wheels
17
. Further, the critical values in the range of the steering angel of the front wheels
15
, in which the rear-front wheels
17
are prevented from being steered, may be changed in accordance with a vehicle speed.
The invention relating to claim
7
, as shown in
FIGS. 1
to
3
and
8
, is an improvement in a rear wheel steering device in a vehicle having three axles, in which a front part of a vehicle body is supported by a front axle
16
while a rear part of the vehicle body is supported by a rear-front axle
18
and a rear-rear axle
20
.
In the characteristic configuration of this invention, an inter-axle distance, B, between the rear-front axle
18
and the rear-rear axle
20
is set to be not
Enomoto Mitsuru
Momiyama Fujio
Hino Motors Ltd.
Morris Lesley D.
Winner Tony
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