Electric power steering device

An electric power steering device is provided which is excellent in the nature being mounted on a vehicle. The electric power steering device 1 comprises a rack shaft 20 constructed to be movable reciprocatively, a rack housing 10 receiving the rack shaft 20 therein, a sleeve 41 arranged coaxially around the rack shaft 20, a brushless motor 40 taking a generally cylindrical shape and constructed to rotate the sleeve 41, and a rotational angle sensor 50 constructed to detect the rotational angle of the brushless motor 40. The rack housing 10 has arranged thereon a power connecter 42 for supplying electric power to the brushless motor 40 and a sensor connecter 52 for outputting a detection signal of the rotational angle sensor 50. The power connecter 42 and the sensor connecter 52 are arranged to be shifted on the same side in the axial direction of the rack shaft 20 with respect to the brushless motor 40.

TECHNOLOGICAL FIELD

The present invention relates to an electric power steering device with a brushless motor arranged around a rack shaft in coaxial alignment.

BACKGROUND ART

Heretofore, for example, there has been an electric power steering device having a brushless motor which is arranged around a rack shaft in coaxial alignment.

Brushless motors are excellent in durability as well as in reliability because of being capable of eliminating mechanical electric contacts. On the other hand, for realization of smooth motor rotation, it is necessary to apply electricity to motor coils at respective timings each appropriate to the rotational angle.

Therefore, it is generally necessary for the aforementioned brushless motors to have a rotational angle sensor for detecting the rotational angle (refer to Japanese Unexamined, Published Patent Application No. 2003-158856 for example).

However, the prior art electric power steering device as aforementioned involves the following problem. That is, it is required to provide a sensor connecter containing output terminals for outputting a detection signal of the rotational angle sensor, in addition to a power connecter containing power terminals for supplying the brushless motor with drive power.

For example, where like the electric power steering device described in Japanese Unexamined, Published Patent Application No. 2003-158856, the power connecter and the sensor connecter are respectively arranged on the axial opposite sides of the brushless motor, it is required to secure in vehicle a mounting space which is axially long along the rack shaft.

Therefore, for those vehicles which cannot secure the axially long mounting space along the rack shaft, it was difficult to mount the electric power steering device as constructed above.

The present invention has been made to solve the problem involved in the prior art and is to provide an electric power steering device which is well-designed in the nature of being mounted onto vehicles.

DISCLOSURE OF THE INVENTION

The first invention resides in an electric power steering device having a rack shaft engaged with a steering pinion and constructed to be movable reciprocatively to follow rotational motion of the steering pinion; a rack housing receiving the rack shaft to be movable therein; a sleeve taking a generally cylindrical shape and arranged coaxially around the rack shaft through a ball screw mechanism formed externally of the rack shaft; a brushless motor taking a generally cylindrical shape, arranged almost coaxially between the rack housing and the sleeve and constructed to rotate the sleeve; and a rotational angle sensor received inside the rack housing and constructed to detect the rotational angle of the brushless motor, wherein the rack housing has arranged thereon a power connecter containing power terminals for supplying electric power to the brushless motor and a sensor connecter containing output terminals for outputting a detection signal of the rotational angle sensor and wherein the power connecter and the sensor connecter are arranged to be shifted on the same side in the axial direction of the rack shaft with respect to the brushless motor.

In the electric power steering device according to the present invention, the power connecter and the sensor connecter are arranged to be shifted on the same side in the axial direction of the rack shaft with respect to the brushless motor.

That is, in the electric power steering device, the foregoing two components which protrude relatively largely from the external surface of the rack housing are arranged to gather at almost the same places in the axial direction.

Thus, the electric power steering device can be mounted to the vehicle or the like which does not have any vacant space but only one place in the axial direction to face the external surface of the rack housing. Further, where the power connecter and the sensor connecter are arranged at similar places as aforementioned, it becomes possible for example to lay as a bundle vehicle-side harnesses to be connected to the respective connecters, so that the nature for such harness layout can be improved.

The second invention resides in the electric power steering device of the first invention, wherein the rack housing comprises a first rack housing receiving the brushless motor and the rotational angle sensor and having the power connecter and the sensor connecter secured thereto and a second rack housing connected to the first rack housing in the axial direction and wherein favorably, the rotational angle sensor, the power connecter and the sensor connecter which are secured to the first rack housing are arranged at respective places closer to the second rack housing than the brushless motor.

In this case, works for wirings between the brushless motor and the power connecter and between the rotational angle sensor and the sensor connecter can be done efficiently through the accesses from the side of an end of the first rack housing opening toward the second rack housing. Further, it becomes possible to obviate the necessity of carrying out the foregoing wiring works and the like from axial opposite end sides of the first rack housing as such would otherwise be required for example in the case where the power connecter and the sensor connecter are arranged with the brushless motor therebetween.

Therefore, in the electric power steering device as constructed above, the other end opposite to the second rack housing of the first rack housing can be utilized as an end portion for the whole rack housing, so that it can be realized to constitute the rack housing as a two-dividable structure composed of the first rack housing and the second rack housing.

By taking the two-dividable structure of the rack housing, it can be realized to sufficiently enhance the assembling accuracy in the receiving structure receiving the rack shaft in the rack housing, particularly in the assembling accuracy in the axial direction of the rack shaft which accuracy largely influences the alignment accuracy and the like of steered wheels.

Further, by taking the two-dividable structure of the rack housing, the assembling accuracy in the axial direction of the rack shaft can be improved compared with the structure of the rack housing taking a three or more dividable structure, so that it becomes possible to suppress the variation of a preload which is exerted on the ball screw mechanism, shaft support bearings or the like.

Therefore, in the electric power steering device, it becomes possible to suppress the probability that chatter or the like occurs between the sleeve and the rack shaft, and it also becomes possible to make the efficiency in transmitting the force from the brushless motor through the ball screw mechanism to the rack shaft meet the design specifications determined beforehand therefor.

Accordingly, the electric power steering device becomes one which is of the character capable of operating to meet the design specifications and which is thus less in the variation of property and excellent in quality.

The third invention resides in the electric power steering device of the first invention, wherein favorably, the sensor connecter and the power connecter are arranged on the external surface of the rack housing with an interval of more than 0 and less than 180 degrees in the circumferential direction.

Where the sensor connecter and the power connecter are arranged within the aforementioned angular range, the sensor connecter and the power connecter can be arranged to be compact in the axial direction while suppressing the probability for them to interfere with each other, so that it can be realized to downsize the body structure in the axial direction of the whole of the electric power steering device.

The fourth invention resides in the electric power steering device of the second invention, wherein favorably, the sensor connecter and the power connecter are arranged on the external surface of the rack housing with an interval of more than 0 and less than 180 degrees in the circumferential direction.

Where the sensor connecter and the power connecter are arranged within the aforementioned angular range, the sensor connecter and the power connecter can be arranged to be compact in the axial direction while suppressing the probability for them to interfere with each other, so that it can be realized to downsize the body structure in the axial direction of the whole of the electric power steering device.

PREFERRED EMBODIMENT TO PRACTICE THE INVENTION

The present embodiment is an example regarding an electric power steering device1having a rack housing10taking a two-dividable structure. The details of the present embodiment will be described with reference toFIGS. 1 and 2.

The electric power steering device1in the present embodiment is provided with a rack shaft20having an axis “A” and engaged with a steering pinion25and constructed to be movable reciprocatively to follow rotational motion of the steering pinion25; a rack housing10receiving the rack shaft20to be movable therein; a sleeve41taking a generally cylindrical shape and arranged coaxially around the rack shaft20through a ball screw mechanism30formed externally of the rack shaft20; a brushless motor40taking a generally cylindrical shape, arranged almost coaxially between the rack housing10and the sleeve41and constructed to rotate the sleeve41; and a rotational angle sensor50received inside the rack housing10and constructed to detect the rotational angle of the brushless motor40.

Further, the rack housing10has arranged thereon a power connecter42containing power terminals421for supplying electric power to the brushless motor40and a sensor connecter52containing output terminals521for outputting a detection signal of the rotational angle sensor50. Here, the power connecter42and the sensor connecter52are arranged to be on the same side in the axial direction of the rack shaft20with respect to the brushless motor40.

Hereafter, the details of this will be described fully.

As shown inFIG. 1, the electric power steering device1in the present embodiment is constructed to be bolt-secured to brackets (not shown) on the side of a vehicle through mounting portions (not shown) formed on the rack housing10.

The rack housing10takes a two-dividable structure composed of a first rack housing11receiving the brushless motor40therein and a second rack housing12connected coaxially to an open end portion110in the axial direction of the first rack housing11.

The rack housing10in the present embodiment is constructed to mutually face and to bolt-joint flange portions119,129which are formed at axial end portions of the respective rack housings11,12.

As shown in the same figure, the first rack housing11and the second rack housing12takes a generally cylindrical shape as a whole in the state being assembled. Further, within the inside space, the rack shaft20is arranged in the state that it passes through the inside space and is movable reciprocatively in the axial direction. The rack shaft20is assembled in the rack housing10with itself being prevented from rotating about its axis. Further, opposite ends of the rack shaft20which passes through, and protrudes outside, the rack housing10are connected to left and right front wheels through tie rods (not shown).

Then, the rack shaft20in the present embodiment is connected to a steering wheel (not shown) through the steering pinion25disposed in the second rack housing12. Further, an engaging section250of a well-known rack and pinion mechanism is formed between the rack shaft20and the steering pinion25.

As shown inFIG. 1, the first rack housing11is constructed to have the brushless motor40and the rotational angle sensor50(hereafter referred to as resolver50for convenience) arranged therein to be adjacent to each other in the axial direction. In the first rack housing11in the present embodiment, the resolver50is arranged to be close to the side of the second rack housing12.

The first rack housing11takes the shape of deflating or narrowing toward an end portion thereof opposite to the side of the second rack housing12, and a generally cylindrical shaft bush115which slidably supports the rack shaft20is arranged on an internal surface of the end portion. Further, the first rack housing11has formed a support surface116into which a first bearing61for rotatably supporting the sleeve41is to be inserted, at an internal surface thereof close to the side of the shaft bush115.

On the other hand, as shown inFIG. 1, the second rack housing12is constructed to receive the engaging section250between the steering pinion25and the rack shaft20in a portion close to its end portion opposite to the side of the first rack housing11.

Further, as shown inFIG. 2, the second rack housing12has a support surface126which fits on the external surface of a second bearing62rotatably carrying the sleeve41, at an internal surface of an end portion thereof on the side of the flange portion129.

As shown inFIG. 2, the brushless motor40is a motor having a drive stator43as motor stator with windings431arranged therearound and the sleeve41as motor rotor with permanent magnets arranged on its circumferential surface. In the present embodiment, the drive stator43is placed on the internal surface of the first rack housing11and then is fixedly fitted therein by a shrinkage fit process.

Furthermore, the first rack housing11has a connecter attaching hole114which is holed to secure the power connecter42containing electrode terminals421. The connecter attaching hole114is holed to pierce through the external wall of the first rack housing11. Then, terminal portions of the winding431wound on the drive stator43are welded to the power terminals421. That is, the brushless motor40in the present embodiment is constructed to be supplied with driving power from outside via the electrode terminals421contained in the power connecter42.

Further, as shown inFIG. 2, the resolver50is a sensor for detecting the rotational angle of the brushless motor40. The resolver50is composed of a generally cylindrical detection stator53constituting a detection stator and a generally cylindrical detection rotor54which is formed to constitute a detection rotor and to be smaller in diameter than the internal surface of the detection stator53.

Then, in the present embodiment, the detection stator53is fixedly fitted in the internal surface of the first rack housing11. And, the detection rotor54is fixedly fitted on the external surface of the sleeve41to face the internal surface of the detection stator53.

As shown inFIG. 2, the first rack housing11has a connecter attaching hole115holed therein for securing the sensor connecter52containing the output terminals521. Likewise the connecter attaching hole114, the connecter attaching hole115is holed to pierce through the external wall of the first rack housing11. Then, terminal portions of the windings arranged on the detection stator53is welded and electrically connected to the output terminals521.

On the first rack housing11in the present embodiment, as shown inFIG. 2, the connecter attaching hole114and the connecter attaching hole115are holed on the same side in the axial direction with respect to the layout position of the brushless motor40.

That is, in the electric power steering device1in the present embodiment, the power connecter42and the sensor connecter52are arranged to be shifted on the same side in the axial direction with respect to the layout position of the brushless motor40.

As shown inFIG. 2, the sleeve41is a member taking a cylindrical shape and is constructed to be arranged externally of the rack shaft20in coaxial alignment therewith. The sleeve41has a support portion421formed on the external surface at its end on the side of the steering pinion25(refer toFIG. 1). On the other hand, another support portion411larger in diameter than the support portion412is formed on the external surface of an end portion on the other side.

Then, the sleeve41is constructed to be rotatably supported inside the rack housing10through the first bearing61fitted on the support portion411and the second bearing62fitted on the support portion412.

Here, the permanent magnets415are arranged on an external surface portion facing the drive stator43of the external surface of the sleeve41, and the sleeve41is constructed to serve as the motor rotor of the brushless motor by itself. The sleeve41is constructed to generate a rotational torque about its axis when electricity is applied to the windings431of the drive stator43.

As shown inFIG. 2, the internal surface of the support portion411of the sleeve41is constructed to coaxially arrange a ball screw nut31therein. The ball screw nut31has a spiral ball screw groove310formed at its internal surface and is a member constituting the ball screw mechanism30which engages the sleeve41with the rack shaft20. On the other hand, a spiral ball screw groove200is provided on the external surface of the rack shaft20over a predetermined extent in the axial direction.

Then, a plurality of rolling balls32are arranged to be rolled in a space of approximately round in cross-section which is made by combining the ball screw groove200on the external surface of the rack shaft20with the ball screw groove310on the internal surface of the ball screw nut31.

In this manner, as shown in the same figure, the ball screw mechanism30is formed between the rack shaft20and the sleeve41. And, the ball screw mechanism30is constructed to translate the rotational torque of the sleeve41in the positive and negative-going directions into the driving force in the reciprocative movement of the rack shaft20.

Further, the electric power steering device1in the present embodiment is constructed to utilize the driving force for the reciprocative movement translated as described above as an assist force for lightening the steering force on a steering wheel (not shown) connected to the steering pinion25(refer toFIG. 1).

As described above, the rack housing11in the present embodiment is constructed to dispose the resolver50in the neighborhood of the open end portion110side with respect to the brushless motor40. Furthermore, the power connecter42for supplying drive power to the brushless motor40and the sensor connecter52for outputting the measured signal of the resolver50are attached closer to the open end position110side than the brushless motor40.

With this construction, in the electric power steering device1in the present embodiment, the mountings of the brushless motor40and the resolver50inside the first rack housing11and the inside wiring works for the power connecter421and the sensor connecter521can all be efficiently carried out from the side of the open end portion110of the first rack housing11.

Therefore, in the electric power steering device1in the present embodiment, the end portion opposite to the open end portion110of the first rack housing11can be formed to take a narrowing shape as an end portion of the whole rack housing10. And therefore, it can be realized to constitute the rack housing10as one taking the two-dividable structure composed of the first rack housing11and the second rack housing12.

Where the rack housing10takes the two-dividable structure like the electric power steering device1, sufficient enhancement can be realized in the assembling accuracy of the structure which receives the rack shaft20in the rack housing10, particularly in the assembling accuracy of the rack shaft20in the axial direction which accuracy largely influences the alignment of the steered wheels.

Further, where the rack housing10takes the two-dividable structure, the assembling accuracy of the rack shaft20in the axial direction can be enhanced as aforementioned, so that it is possible to suppress the variation of an axial preload which is exerted on the ball screw mechanism30, the bearings61,62and the like.

Therefore, in the electric power steering device1in the present embodiment, it is possible to suppress the probability that chatter or the like occurs between the sleeve41and the rack shaft20and to make the efficiency in transmitting the force from the brushless motor40through the ball screw mechanism30to the rack shaft20meet the design specifications determined beforehand.

Accordingly, the electric power steering device1becomes one which is capable of operating to meet the design specifications and which is less in the variation of property and excellent in quality.

Furthermore, where the two components like the power connecter42and the sensor connecter52which relatively largely protrude from the external of the rack housing10are disposed at almost the same places, the mounting can be realized onto, e.g., the vehicle or the like which does not have any vacant space but only one place in the axial direction to face the external surface of the rack housing10. In addition, where the power connecter42and the sensor connecter52are disposed at similar places, it becomes possible for example to layout as a bundle vehicle-side harnesses to be connected to the respective connecters42,52, so that the nature for such harnesses layout can be improved.

COMPARED EXAMPLE 1

This example is an example showing a prior art electric power steering device9wherein a sensor connecter952and a power connecter942are arranged at opposite sides in the axial direction of a brushless motor940. The details of this example will be described with reference toFIG. 3.

A rack housing910in the example takes a three-dividable structure made by combining first to third rack housings911to913. Then, the brushless motor940and a resolver950are received in the second rack housing912which is arranged at an intermediate portion between the first rack housing911and the third rack housing913.

Further, in a similar manner to the foregoing first embodiment, a detection signal of the resolver950is outputted through output terminals contained in the sensor connecter952, while electric power is supplied to the brushless motor940through power terminals contained in the power connecter942.

In the electric power steering device in this example, the sensor connecter952and the power connecter942are arranged on the second rack housing912to have the brushless motor940therebetween in the axial direction.

With this construction, prior to welding the power terminals to the winding ends of the brushless motor940and prior to welding the output terminals to the winding ends of the resolver950, wiring works have to be done from opposite sides of the second housing912containing the brushless motor940therein. Thus, in the second rack housing912of the present example, it is required to form open portions to which other rack housings911,913are to be jointed, at opposite ends thereof in the axial direction.

Other constructions are the same as those in the embodiment 1.

INDUSTRIAL APPLICABILITY

The electric power steering device according to the present invention is suitable to be applied to a steering system for transmitting the rotation of a handle of a motor car to wheels.