JP2007153141A - Rack-and-pinion type steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rack-and-pinion type steering device capable of preventing an increase in the weight of components, preventing steering feeling from being impaired for a long time, and enhancing the gear efficiency. <P>SOLUTION: The rack-and-pinion type steering device has a gear part with a pinion and a rack to be engaged therein with each other. A diamond-like carbon film F is deposited on gear teeth 3 of the pinion 1. The diamond-like carbon film F consists of a metal layer M on the inner side and a carbon layer C on the outer side. The wear resistance of the gear part with the rack and the pinion being engaged with each other therein is enhanced, an increase in adjust play affecting the steering feeling can be suppressed, and the gear efficiency can be enhanced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rack and pinion type steering device having a steering force assisting device for assisting a steering force of a steering wheel of a vehicle or the like.

  As a vehicle steering apparatus, a power steering apparatus for reducing a driver's steering load is known. Conventionally, hydraulic power steering devices have been used as power steering devices. However, in recent years, as the demand for higher efficiency of automobiles increases, the power steering apparatus is increasingly replaced with an electric power steering apparatus with higher efficiency.

  As is well known, the electric power steering device only needs to supply current to the motor when it needs steering assist force, whereas the hydraulic power steering device always drives the hydraulic pump with the power of the engine. As a result, the electric power steering apparatus has a great advantage in terms of efficiency. In general, it is said that the electric power steering device has a fuel efficiency improvement effect of about 3 to 5% in a practical area such as urban driving. From such a background, the column assist type or pinion assist type electric power steering device is not only a small car, Applications are expanding to medium and large vehicles.

  By the way, in rack and pinion type steering devices used for medium-sized vehicles and large vehicles, it is required to increase the output of rack thrust. For this reason, since the shaft torque input to the pinion shaft also increases, the strength and gear efficiency of each component become more problematic than ever. Further, it has been found that the main factor that increases the adjustment backlash which has a large influence on the steering feeling is the wear generated in the rack and the pinion, and it is essential to improve the wear resistance of both. Considering this point, we are trying to optimize gear specifications and developing low-friction grease, but that alone has its limitations.

  An object of the present invention is to provide a rack and pinion type steering device that does not increase the weight of components in order to achieve high output, does not impair steering feeling over a long period of time, and improves gear efficiency.

  A rack and pinion type steering device according to the present invention includes a pinion having gear teeth carved on a shaft, and a rack having rack teeth carved on a rack shaft, and the pinion gear teeth and the rack tooth of the rack, In a rack-and-pinion type steering device in which the steering force transmitted from the steering shaft to the pinion is transmitted to the rack, a diamond-like carbon film is formed on at least one of the gear teeth of the pinion and the rack teeth of the rack. It is characterized by being.

  By configuring in such a way, the wear resistance of the gear portion where the rack and the pinion mesh with each other is further improved. Therefore, the increase amount of the adjustment backlash that affects the steering feeling can be suppressed, and the low friction of the gear portion can be suppressed. The gear efficiency can be increased by making it easier.

  In the present invention, the diamond-like carbon film is preferably composed of a composite layer in which the first layer is an intermediate layer of chromium and the second layer is made of a carbon component.

  By comprising in this way, it becomes possible to greatly improve the adhesiveness of a diamond-like carbon film.

  In the present invention, it is desirable that the diamond-like carbon film has an internal composition of an inclined layer so as to eliminate the interface between the intermediate layer and the carbon constituting the diamond-like carbon.

  By comprising in this way, it becomes possible to further improve the adhesiveness of a diamond-like carbon film.

  In the present invention, it is preferable that a diamond-like carbon film is formed on the pinion tip support needle bearing raceway surface.

  By comprising in this way, abrasion of a bearing sliding part can be suppressed with a gear meshing part.

  In the present invention, the gear teeth of the pinion and the rack teeth of the rack, which are preferably meshed with each other, and the needle bearing raceway surface for supporting the pinion tip are lubricated with grease.

  By comprising in this way, it becomes possible to form a lubricating oil film reliably in a gear meshing part and a bearing sliding part, and wear can be further suppressed.

  An embodiment of a steering device according to the present invention will be described with reference to the drawings. FIG. 1 shows a main part of a rack and pinion type steering apparatus, and includes a pinion 1 connected to a steering shaft (not shown). This pinion 1 has a large number of gear teeth 3 engraved at one end of a shaft 2. In addition, the steering device includes a rack 4 disposed so as to cross the pinion 1 and the axis of each other. A large number of rack teeth 6 are formed on one surface of the rack shaft 5 in the rack 4. The gear teeth 3 of the pinion 1 and the rack teeth 6 of the rack 4 are engaged with each other so that in steering the vehicle, the steering force is transmitted from the pinion 1 to the rack 4 and further to the tie rods (not shown) connected to the left and right theories. It has become.

  The pinion 1 is supported by a bearing 7 at an intermediate portion of the shaft 2, and is supported by a needle bearing 8 at the farthest end of the shaft 2. The rack shaft 5 is in contact with a rack guide 9 that exerts a back pressure on the rack 4 on the side opposite to the rack teeth 6. The rack guide 9 is accommodated in a holder 10 that slides in a direction perpendicular to the rack axis. The holder 10 is in contact with a spring 11 that generates a compressive load in the axial direction. The pinion 1 and the rack 4 are accommodated in the housing 12 together with the elements that support them.

  In the figure, reference numeral 13 denotes an annular member that closes the pinion side opening of the housing 12, and reference numeral 14 denotes a sealing member that closes the holder side opening.

  In the present embodiment, at least one of the gear teeth 3 engraved on the pinion 1 and the rack teeth 6 engraved on the rack 4 is coated, and this coating treatment has a coefficient of friction higher than that of the base material. Is formed of a low diamond-like carbon film. Here, diamond-like carbon is a generic name for carbon films having high hardness similar to diamond synthesized by a gas phase synthesis method using ions. The structure of the diamond-like carbon film is usually a smooth amorphous structure containing some hydrogen, and has diamond bonds and graphite bonds.

  A diamond-like carbon film is characterized by high hardness, low friction, and low lubricity compared to a conventional ceramic film. The characteristics of a diamond-like carbon film vary greatly depending on the treatment method, and the hardness and adhesion of the film differ depending on the presence or absence of hydrogen in the film, and it is desirable to select the film quality depending on the conditions used. This diamond-like carbon film is formed by physical vapor deposition (PVD), chemical vapor deposition (CVD), sputtering, or the like. A typical film forming material is pure carbon. In addition to this, many materials such as materials containing metals such as Cr, Ti, and W containing hydrogen can be used. The hardness is as high as 1000 to 8000 Hv, the surface is smooth, and it has excellent wear resistance.

  On the gear teeth 3 of the pinion 1 of the present embodiment, as shown in FIG. 2A, a film F having a uniform thickness is formed by diamond-like carbon. As shown in FIG. 2B, the film F is composed of two layers, that is, an inner metal layer M and an outer carbon layer C. The metal layer M is made of a metal such as Cr or Ti. The carbon layer C is made of carbon, and the film F is formed by a sputtering method. As shown in FIG. 3, the film formation range of the film F of the present embodiment is limited to the range where the film teeth mesh with the rack teeth 6 of the rack 4, not the entire gear teeth.

  On the other hand, as shown in FIG. 4A, a film F having a uniform thickness of diamond-like carbon is formed on the rack teeth 6 of the rack 4 of the present embodiment. As shown in FIG. 4B, the film F is composed of two layers, that is, an inner metal layer M and an outer carbon layer C. The metal layer M is made of a metal such as Cr or Ti. The carbon layer C is made of carbon, and the film F is formed by a sputtering method. Although not shown, the film F is formed over the entire rack tooth.

  According to the film F made of diamond-like carbon, since the metal layer M as an intermediate layer is interposed, the adhesion of the film F can be further increased, and the film F is peeled even when repeated stress is applied. Can be reliably prevented. In addition, the diamond-like carbon film has an internal composition of an inclined layer, so that the interface between the intermediate layer and the carbon constituting the diamond-like carbon can be eliminated, and the adhesion can be further improved.

  Since the film F made of diamond-like carbon has lubricity, for example, even if the lubricating oil film such as running out of oil is lost, the gear teeth 3 of the pinion 1 and Wear of the rack teeth 6 of the rack 4 can be prevented.

  The film F may be formed only on one of the pinion 1 and the rack 4.

  Further, a film F may be formed on the gear teeth 3 of the pinion 1, and a film made of diamond-like carbon may be formed on the shaft 2 following the raceway surface of the needle bearing 8, as shown in FIG. Desirably, such a steering apparatus supplies a lubricant such as grease to the pinion 1 and the rack 4 so as to always hold the lubricating oil film.

  FIG. 6 shows the results of a durability test with and without a diamond-like carbon film. In the graph, the vertical axis represents the ratio between the amount of increase in the adjustment back when not treated with diamond-like carbon and the amount of increase in the adjustment back when treated with diamond-like carbon, and the horizontal axis represents the durability. According to the comparison of the number of durability times X, it can be seen that the amount of increase in the adjustment backlash is reduced by about 76% when treated with diamond-like carbon.

  In addition, this invention is not limited to embodiment mentioned above, It can implement by changing variously.

It is sectional drawing which shows one Embodiment of the steering device by this invention. The pinion by this invention is shown, (a) is a front view of a pinion, (b) is an enlarged view of the film | membrane formed in the gear tooth of a pinion. It is a figure which shows the film-forming range on the gear tooth of the pinion by this invention. 1 shows a rack according to the present invention, in which (a) is a front view of the rack, and (b) is an enlarged view of a film formed on the rack teeth of the rack. It is a figure which shows the film-forming range on the shaft of the pinion by this invention. It is a graph which shows the result of the durability test of the member processed with the diamond-like carbon by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pinion 2 ... Shaft 3 ... Gear tooth 4 ... Rack 5 ... Rack shaft 6 ... Rack tooth F ... Membrane M ... Metal layer
C ... Carbon layer

Claims (5)

  A pinion having gear teeth engraved on the shaft and a rack having rack teeth engraved on the rack shaft, and the gear teeth of the pinion and the rack teeth of the rack are engaged with each other from the steering shaft to the pinion. In the rack-and-pinion type steering apparatus configured to transmit a transmitted steering force to the rack, a diamond-like carbon film is formed on at least one of the gear teeth of the pinion and the rack teeth of the rack. Rack and pinion type steering device.   The rack-and-pinion type steering apparatus according to claim 1, wherein the diamond-like carbon film comprises a composite layer in which the first layer is an intermediate layer of chromium and the second layer is made of a carbon component.   The rack-and-pinion type steering device according to claim 2, wherein the diamond-like carbon film has an internal composition of an inclined layer to eliminate an interface between the intermediate layer and carbon constituting the diamond-like carbon.   4. A rack and pinion type steering apparatus according to claim 1, wherein a diamond-like carbon film is formed on a needle bearing raceway surface for supporting the tip of the pinion. 5. The rack and pinion according to claim 1, wherein the gear teeth of the pinion and the rack teeth of the rack, which are engaged with each other, and the needle bearing raceway surface for supporting the pinion tip are lubricated with grease. Steering device.

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