JPS593302B2 - Ball screw type steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ball screw type steering device, and particularly to a steering device that improves the feeling when an automobile is traveling straight at high speed.

Conventional ball screw type steering devices take into account manufacturing errors such as the shape of the ball screw groove of the ball screw shaft and pole nut, the screw lead, and the roundness of the screw groove to ensure smooth and light transfer of the ball. In addition, a certain amount of thread clearance is provided between the ball and each thread groove with which it makes rolling contact.

On the other hand, when a car is running at high speed, the reaction force from the tires is transmitted to the driver via the steering device and the bundle wheel. The vehicle starts to deviate from the desired direction of travel, giving a very uneasy feeling when driving.

This is because the threaded clearance causes the tire to meander, especially when traveling straight at high speed, resulting in a loss of steering stability.

In order to eliminate such drawbacks, for example,
As shown in Japanese Patent Application No. 33940, the diameter of the central part in the longitudinal direction of the ball screw shaft is made to be appropriately larger than the diameter of both ends of the ball screw shaft, so that the ball group and each thread groove with which it rolls in contact with each other when the automobile is traveling straight. A system was proposed in which the clearance between the ball screw shaft and the pole nut was increased to zero, thereby increasing the rigidity of the threaded connection between the ball screw shaft and the pole nut via the ball group.

That is, FIG. 1 and FIG. 2 (FIG. 2 is a conceptual diagram in which the difference in diameter is exaggerated for explanation.

), the diameter d at the center of the ball screw shaft 1.

is made larger than the diameter d2 at both ends over an appropriate width m in the length direction, and the change in diameter is linear.

On the other hand, in order to increase the stability of the operation of the pole nut, two rows of balls guided by at least two rows of circulators are provided in the thread groove between the pole nut and the ball screw shaft. The length of the line of balls is extremely long.

However, in this case, if the screw gap is set to zero when the vehicle is traveling straight, due only to a change in the diameter of the ball screw shaft 1, for example, when the vehicle is traveling straight and the steering wheel is turned to the right or left, In figure 3,
At least one row of three groups of balls interposed between the thread groove of the pole nut 2 and the ball screw shaft 1
Unless the ball nut 2 is allowed to travel a distance that is sufficient to completely exceed the area m of the large diameter portion d1 of the ball nut 2, a gap will occur between one of the balls and each thread groove in which it is in rolling contact. Therefore, until the rotation angle of the sector 5 that engages with the rack 4 of the pole nut 2 becomes considerably large, the clearance that allows the pole nut 2 to move easily is lost, and the handle becomes very difficult to operate. There is.

Furthermore, since the range of zero clearance becomes larger than necessary as shown in the travel distance of the pole nut 2, it affects the life of the ball screw and reduces its durability. This method has the disadvantage that it requires very strict checks on changes in the diameter of the thread groove, roundness of the thread groove, etc., resulting in extremely high costs.

The present invention provides a ball screw type steering device as described above, which uses a configuration as simple as possible to improve the feeling especially when the vehicle is running straight at high speed, and also eliminates the gap in the threaded portion of the ball screw (in reality). The object of the present invention is to set the range in which the steering wheel has a slight interference fit to the minimum necessary for straight-ahead driving, and to make the steering wheel handling during steering operation of the automobile easier.

To explain the embodiment, in FIGS. 4 and 5,
The axial length of the pole nut 2 is within the range of 0 or -, that is, either one of the two rows of ball groups is located between the ball screw shaft 1 and the thread groove of the pole nut 2 in the axial direction. Ball screw shaft 1 within the range corresponding to the length
The range m of the large diameter part d1 of the diameter of the thread groove (pitch diameter or bottom diameter of the thread groove) formed in the thread groove is determined, This is an exaggeration.

) The diameter d2 of both ends of the ball screw shaft 10 is formed to be a small diameter, and the change in diameter is formed linearly.

Two rows of circulators-6A provided on pole nut 2,
Two rows of balls 3A that circulate while being guided by 6B,
Group 3B is connected to the thread groove 2a of the pole nut 2 and the thread groove 1at1b of the ball screw shaft 1 (however, the thread groove 1a is the large diameter part d1).
In addition, the diameter portions 1b are formed in the small diameter portion d2, and are continuous with each other with a linear change in diameter so as to smooth the transfer of the ball.

), and the diameter of each ball of one of the ball groups (ball group 3A in the embodiment) is formed to be suitably larger than the diameter of each ball of the other ball group. When running straight, a group of large diameter balls hit the pole nut 2's net tJ2.
a and the thread groove 1a of the large diameter portion d1 of the ball screw shaft 10, and a group of small diameter balls (a group of balls 3B in the embodiment) are in contact with the thread groove 2a of the pole nut 2 and the small diameter groove 1a of the ball screw shaft 1. It is set so as to make rolling contact between the part d2 and the thread groove 1b.

In the embodiment, the diameter of each ball is determined so that there is virtually no gap between the thread grooves 2a, 1a and the large-diameter ball 3A when the car is traveling straight (actually, there is a slight tight fit). .

That is, FIG. 5 is a diagram conceptually showing the above configuration,
The figure shows the positional relationship of each member when the automobile is running straight ahead, and a group of large-diameter balls 3A guided by a circulator 6A are connected to the threaded groove 2a of the pole nut 2 and the large-diameter portion d of the ball screw shaft 1.

As shown in FIG. 6, there is no clearance between the screw groove 1a and the screw groove 1a.

When the steering wheel of the automobile is rotated to the right or left and the ball screw shaft 1 is rotated, the pole nut 2 is rotated through the respective screw grooves and the groups of balls 3A and 3B.
moves to the right or left.

As the pole nut 2 moves to the right or left, the large diameter balls 3A move to the right or left together with the pole nut 2 while rolling between the thread grooves 2a and 1a, and the large diameter portion d1 of the ball screw shaft 1 moves to the right or left. When the range m is exceeded, a gap is created between each thread groove and the large-diameter ball 3A, and the gap increases as the group of large-diameter balls 3A approaches the small-diameter portion d2 of the ball screw shaft 1, As shown in FIG. 7, the group of large diameter balls 3A reaches above the thread groove 1b of the small diameter portion d2.
, 2a and the large diameter ball 3A.

On the other hand, each ball of the group of small diameter balls 3B guided by the circulator 6B is inserted into the threaded groove 2 of the pole nut 2 in any case when the automobile is running straight or during steering operation.
a and the thread groove 1b or 1a of the ball screw shaft 1, the ball screw always rolls with a moderate clearance S4 (however, Sl changes on the small diameter part d2 and the large diameter part d1 of the ball screw shaft 1). , maintains the stability of the operation of the ball nut 2.

Therefore, the ball screw shaft has its thread groove 1a.

Any structure that is compatible with the above configuration, such as changing the pitch diameter of 1b or changing the bottom diameter, may be used.

Thus, according to the present invention, since a diameter difference is given between one ball group and the other ball group of the two rows of ball groups, the range in which the clearance becomes O while the automobile is traveling straight is set. The length of the row of large-diameter balls determined is at least 1/2 or less of the conventional length, and as shown in Figure 8, the rotation angle θ of the bundle is from 0 to θ1 (@Rotation angle very close to that during forward travel) range), the large diameter balls 3A group are connected to the thread groove 2a of the pole nut 2 and the large diameter portion d of the ball screw shaft 1.
Since the bundle is interposed with zero clearance between the bundle and the thread groove 1a of the bundle, the rigidity of the steering device necessary for straight-line running of the vehicle is maintained, and when the rotation angle θ of the bundle exceeds the above θ1, the large diameter ball 3A A gap is generated between the thread groove where the group contacts and the ball 3A, and until the maximum rotation angle θ2 is reached, the gap gradually increases in the range from 0 to ε1 and moves to the right or left of the pole nut 2. To facilitate the movement of a bundle and facilitate bundle operation.

・Thus, from the large diameter part d1 to the small diameter part d of the large diameter ball 3A group
Since the change in the diameter of the screw of the ball screw shaft 1 is set linearly, the transition to 2 is extremely smooth.

In other words, the present invention increases the rigidity of the steering device by eliminating the threading gap of the ball screw only when the automobile is traveling straight, and in particular, prevents the steering wheel (tire) from meandering when traveling straight at high speed, thereby improving its feeling. improve,
Moreover, in the range where the screw clearance is zero, one of the large diameter ball groups of the two rows of balls is connected to the ball screw shaft 1.
The length of the row of large-diameter balls is substantially 1/2 or less compared to the conventional one, and the length of the row of large-diameter balls is substantially 1/2 or less compared to the conventional one. The zero clearance range has been reduced to at least 1/2 of that of the conventional one, making steering operations of the car easier and improving the shape of the thread groove.
It eliminates the need to particularly strictly control machining accuracy such as thread groove lead error and thread groove roundness, and allows the ball screw to easily set the range of zero thread clearance, which is extremely advantageous in terms of production technology. At the same time, its structure is extremely simple and allows for a compact design.

In the illustrated embodiment, as shown in FIG. 5, each ball in the left ball group has a large diameter, and the large diameter portion of the ball screw shaft has
This is shown in the figure, which is set at a position corresponding to the group of large diameter balls when the car is traveling straight, but in this case, each ball in the group of balls on the right side is formed with a large diameter, and each ball in the group of balls on the left side is formed with a smaller diameter. It goes without saying that the large diameter portion of the ball screw shaft may be set at a position where the left group of balls rolls into contact when the vehicle is traveling straight.

The axial width (m) of the large diameter portion of the ball screw shaft 1 is determined to be an appropriate width, taking into account the number of turns of the large diameter balls that come into contact with this portion when the vehicle is running straight, and the feeling during bundle operation. Set to .

[Brief explanation of the drawing]

FIG. 1 is a front view of the ball screw shaft, FIG. 2 is an exaggerated view showing the change in diameter, FIG. 3 is a partially longitudinal front view of a conventional steering device, and FIG. 4 is a front view of an embodiment of the present invention. Plan view,
Figure 5 is a partially longitudinal front view conceptually showing its configuration;
7 are cross-sectional views showing the relationship between the balls and the ball screw when the bundle wheel is running straight and when the bundle wheel is turned to the right or left, and FIG. 8 is an explanatory diagram of the operation.

Claims (1)

[Claims] 1. When the vehicle is running straight, the diameter of the ball screw shaft portion corresponding to the position of the pole nut (the pitch diameter or bottom diameter of the screw) is different from the diameter of both ends of the ball screw shaft (the pitch diameter or bottom diameter of the screw) at that point. ), and in which two rows of balls guided by two rows of circulators are interposed between corresponding thread grooves of a ball screw shaft and a ball nut, A ball group in which the diameter of each ball in the ball group guided by one of the circulators is formed to be appropriately larger than the diameter of each ball in the ball group in the other row, and the large diameter balls are arranged. - When the bag moving vehicle runs straight, the large-diameter portion of the ball screw shaft rolls into contact with its thread groove, and the gap between the large-diameter balls and each thread groove with which it rolls becomes zero, and the other Sometimes, while forming an appropriate gap between the ball group and each thread groove,
1. A ball screw type steering device characterized in that a group of small diameter balls is constructed so as to have an appropriate clearance between each screw groove with which the small diameter balls come into rolling contact at any time.