Camera module

A camera module is attached to an inside of a windshield of a vehicle to capture an image of an outside view. The camera module includes an imager, a lens set equipped with a first lens and a second lens, a lens barrel in which the lens set is disposed, and a main spacer fit in the lens barrel. The lens barrel retains the first lens using an axial force oriented along an optical axis of the lens set. The main spacer is disposed between the first and second lenses and transmits the axial force from one of the first and second lenses to the other. This structure enables the camera module to be reduced in size without sacrificing the optical performance thereof.

CROSS REFERENCE TO RELATED DOCUMENT

The present application claims the benefit of priority of Japanese Patent Application No. 2018-180279 filed on Sep. 26, 2018, the disclosure of which is incorporated herein by reference.

BACKGROUND

1 Technical Field

This disclosure relates generally to a camera module.

2 Background Art

There is known a lens holder in which a lens unit made up of a first lens and a second lens which are joined together and a third lens are retained. The lens holder includes a hollow outer cylinder and a cylindrical spacer disposed inside the outer cylinder. The spacer surrounds an outer periphery of the second lens. An annular lens retainer is fastened to a thread on the outer cylinder to exert an axial force on the first lens.

In recent years, automotive vehicles have been equipped with a camera module for use in an advanced driver-assistance system or an autonomous driving system. The camera module is required to have an optical performance to take a recognizable image of a wide-angle outside view. It is difficult for the structure in the above publication to have a decreased size without sacrificing the optical performance of a lens system when used as a camera module for vehicles.

SUMMARY

It is an object of this disclosure to provide a camera module which is enabled to have a decreased size without sacrificing an optical performance thereof.

According to one aspect of this disclosure, there is provided a camera module which is attached to an inner side of a windshield of a vehicle and works to capture an image of an outside view of the vehicle. The camera module comprises: (a) an imager which captures an image of an outside view; (b) a lens set which includes an outside view lens and a small-diameter lens located closer to the imager than the outside view lens is and through which light from the outside view passes to form an image in the imager; (c) a lens barrel in which the lens set is disposed; and (d) an inner lens barrel which is fit in the lens barrel and has the small-diameter lens disposed therein. The lens barrel includes a lens barrel axial force applying portion which retains the outside view lens using an axial force oriented along an optical axis (Al) of the lens set. The inner lens barrel is disposed between the small-diameter lens and the outside view lens and has an axial force-transmitting portion which transmits the axial force from one of the small-diameter lens and the outside view lens to the other.

The small-diameter lens is disposed inside the inner lens barrel and is smaller in diameter than the outside view lens. The axial force-transmitting portion is disposed between the outside view lens and the small-diameter lens and functions to achieve the transmission of the axial force between the outside view lens and the small-diameter lens. This ensures exertion of the axial force on the outside view lens and the small-diameter lens although the small-diameter lens and the outside view lens are different in diameter from each other, thereby enabling the small-diameter lens to be reduced in size without sacrificing the optical performance of the camera module.

According to the second aspect of this disclosure, there is provided a camera module which is attached to an inner side of a windshield of a vehicle and works to capture an image of an outside view of the vehicle. The camera module comprises: (a) an imager which captures an image of an outside view; (b) a lens set which includes an outside view lens through which light from the outside view passes to form an image in the imager; and (c) a lens barrel in which the lens set is disposed. The outside view lens has an optical surface facing the outside view and a step located outside the optical surface in a radial direction of the outside view lens. The lens barrel includes a lens barrel axial force applying portion which retains the step using an axial force oriented along an optical axis of the lens set.

The outside view lens has the step located outside the optical surface in the radial direction. The lens barrel is equipped with the lens barrel axial force applying portion to retain the step using the axial force oriented along the optical axis. The lens barrel axial force applying portion is disposed in a space defined by a recess of the step. This facilitates reduction in size of a front end portion of the lens barrel located close to the outside view lens, thereby enabling the front end portion of the lens barrel to be decreased in diameter without sacrificing a required outside diameter of the optical surface. This enables the size of the lens barrel to be reduced while ensuring a required level of the optical performance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments will be described below with reference to the drawings. Throughout the embodiments, the same reference numbers will refer to the same parts, and explanation thereof in detail will be omitted here. When only parts of components in one of the embodiments are referred to, the explanation of the other parts in the other embodiments is applied. Each of the embodiments may be designed to include all possible combinations or modifications of the components in the other embodiments

First Embodiment

The camera module1in the first embodiment is, as illustrated inFIGS.1and2, mounted in the vehicle2and works to capture an image of the outside view5. In the following discussion, a vertical direction of the vehicle2on a horizontal plane will also be referred to as a top-to-bottom direction. A length wise direction of the vehicle2will also be referred to as a longitudinal direction. A width-wise direction of the vehicle2will also be referred to as a lateral direction.

The camera module1is attached to an inside surface of the front windshield3of the vehicle2. The front windshield3is located in front of a driver's seat in the vehicle2. The front windshield3isolates the passenger compartment4of the vehicle2from the outside view5. The front windshield3is made of, for example, a transparent or translucent material, such as glass, through which light or optical image passes from the outside view5into the passenger compartment4.

The camera module1is mounted on a portion of the front windshield3which does not disturb or block the view of a driver sitting on a driver's seat in the passenger compartment4. Specifically, the camera module1is, as clearly illustrated inFIG.1, located in a vertical range Xv which occupies about 20% of an area of the window6adefined by the pillar6retaining a peripheral edge of the front windshield3from an upper edge of the window6a. The camera module1is also located in a horizontal range Xh of about 15 cm from the middle to the right and left of the window6a. In other words, the camera module1is, therefore, arranged in a wiping range Xr where a wiper moves on the front windshield3and on a portion of the front windshield3which is inclined about 22° to 90° in the longitudinal direction of the vehicle2.

The camera module1is, as illustrated inFIGS.2to4, equipped with the bracket assembly10, the camera casing20, the optical assembly30, the hood40, and the circuit unit50. The bracket assembly10is mainly made of the bracket body11. The bracket body11is made of an easy-to-machine hard material, such as resin, in a flat shape as a whole. The bracket body11is arranged along the inner surface3aof the front windshield3. The bracket body11has the flat upper surface11afirmly adhered to the inner surface3aof the front windshield3, so that the bracket assembly10is undetachably or permanently secured to the front windshield3of the vehicle2.

The camera casing20is, as clearly illustrated inFIGS.2to5, made of a pair of casing members21and22attached to each other. Each of the casing members21and22is made of hard material, such as aluminum, which has a relatively high degree of heat dissipation and shaped in a hollow form.

The upside-down cup shaped upper casing member21is arranged beneath the bracket assembly10to have an opening facing away from the bracket assembly10. The upper casing member21, as clearly illustrated inFIGS.3and5, has four fitting protrusions213two formed on each side thereof. The two fitting protrusions213on each side are separate from each other in the longitudinal direction of the vehicle2.

The bracket body11, as illustrated inFIG.3, has formed therein a plurality of fitting grooves112one for each of the fitting protrusions213. Each of the fitting grooves112is of an L-shape with the open end112aand the closed end112b. The camera casing20is detachably attached to the bracket assembly10by moving each of the fitting protrusions213is moved from the open end112auntil it reaches the closed end112bof one of the fitting grooves112. In other words, the camera casing20hands on the bracket assembly and is positioned relative to the front windshield3.

The upper casing member21, as illustrated inFIGS.2to5, has an upper wall including the windshield-facing wall portion210, the bent wall portion211, and the recessed wall portion212. The windshield-facing wall portion210is oriented to face the inner surface3aof the front windshield3through the bracket assembly10. The windshield-facing wall portion210is held in this condition close to the front windshield3.

The bent wall portion211is, as can be seen inFIGS.2and5, bent downward from the windshield-facing wall portion210. The bent wall portion211defines a ridge along with the windshield-facing wall portion210. The ridge extends over a substantially entire width of the upper casing member21in the lateral direction and is located close to the front windshield3.

The recessed wall portion212extends at a given angle (excluding zero) to the bent wall portion211. The recessed wall portion212is oriented to have an interval between itself and the front windshield3which decreases frontward from the bent wall portion211. In other words, the recessed wall portion212extends from the bent wall portion211so as to approach the windshield3. The recessed wall portion212defines the storage recess215(i.e., a chamber) between itself and the front windshield3in which the hood40is arranged.

The saucer-shaped lower casing member22is disposed beneath the upper casing member21with an upper opening facing the upper casing member21. The lower casing member22is attached to the upper casing member21using screws. The casing members21and22define therein the storage chamber25in which the optical assembly30and the circuit unit50are disposed.

The optical assembly30, as illustrated inFIGS.2to7, includes the assembly holder30a, the lens holder31, the lens set35, and the imager34. The assembly holder30ais made of an easy-to-machine hard material, such as resin, in a hollow block shape as a whole. The assembly holder30aand the lens holder31define the optical path chamber39through which an optical image is directed to the imager34.

The lens holder31is made of an easy-to-machine hard material, such as resin, in a hollow cylindrical form as a whole. The lens holder31, as can be seen inFIGS.2and5, may be joined to the upper casing member21of the camera casing20using adhesive. The lens holder31may alternatively be retained by the assembly holder30afastened to the upper casing member21using screws.

The lens holder31, as illustrated inFIG.2, has defined therein the optical path chamber39through which an optical image is directed using the lens set35disposed therein. The lens holder31has a front end exposed outside the camera casing20through the bent wall portion211. Specifically, the bent wall portion211, as illustrated inFIGS.2and5, has the lens window216through which the front end of the lens holder31passes. The lens window216is formed by a through-hole passing through a thickness of the lateral center of the lens holder31. The recessed wall portion212also has the recessed hole217formed in an upper surface thereof in the shape of a recess. The recessed hole217is located in the center of the recessed wall portion212in the width-wise direction thereof.

The lens set35shown inFIGS.2to7is made up of a plurality of lenses formed by a translucent material, such as glass. The lens set35is engineered to offer a relatively wide angle of view, for example, 75° to 150° to achieve an intended angle of view. The lens set35is also designed to have an f-number more than or equal to two in order to ensure given scene brightness and optical resolution. The lens set35is disposed in the lens holder31with each lens firmly retained by the lens holder31. The lens set35has the optical axis Al which is slightly inclined upward or downward in the forward direction or extends straight in the longitudinal direction of the vehicle2. The lens set35may alternatively be engineered to offer a wide angle of view larger than 150°.

The imager34shown inFIG.2is implemented by a color or back-and-white image sensor such as a CCD or a CMOS. The imager34may have an infrared cut-off filter (not shown) mounted in front of the image sensor. The imager34is of a rectangular plate shape as a whole. The imager34is mounted in the assembly holder30aso that it is arranged inside the rear optical path chamber39.

With the above arrangements of the optical assembly30, light from the outside view5passing through the front windshield3enters the lens set35to form an image in the imager34. Specifically, an optical image, as produced by light coming from an image capturing range in the outside view5, is formed as an inverted image in the imager34. The imager34takes the inverted image to output data, as derived by imaging the outside view5, in the form of an electrical signal.

The hood40is, as illustrated inFIGS.2to4, formed integrally with the bracket body11in resin molding. In other words, the hood40is made of a portion of the bracket assembly10. As viewed from above the hood40, an overall configuration thereof is of a disc shape symmetrical with respect to the optical axis Al of the lens set35in the lateral direction. The hood40includes the base wall41, the rear end wall42, and the side walls43.

The base wall41is arranged above the recessed wall portion212and below the optical axis Al in front of the bent wall portion211. The base wall41is disposed in the recessed storage chamber215between the recessed wall portion212and the front windshield3. The base wall41extends forward in front of the bent wall portion211so as to close the distance to the front windshield3. The base wall41is, therefore, shaped to have the bottom surface41a(i.e., an upper surface) which is of a substantially flat trapezoidal shape and faces the inner surface3aof the front windshield3through the imaging space410. An optical image in a given image capturing range where the imager34works to capture an image of the outside view5passes through the front windshield3and then is directed to the imaging space410.

The base wall41, as illustrated inFIG.2, has a plurality of optical block ribs411disposed thereon. The optical block ribs411protrude from the bottom surface41aof the base wall41toward the front windshield3, that is, the imaging space410. Each of the optical block ribs411extends straight in the form of a convexity or ridge. Specifically, the optical block ribs411extend in the lateral direction and are arranged at a given interval away from each other in the longitudinal direction. Every adjacent two of the optical block ribs411have walls facing each other and work to achieve multiple reflection of light traveling to the base wall41between those walls, thereby trapping it. The height of each of the optical block ribs411from the base wall41is selected to be a given value achieving such optical trapping.FIGS.3and4omit the optical block ribs411for the brevity of illustration.

The rear end wall42is so arranged as to have a width in the lateral direction whose center line coincides with the optical axis Al. The rear end wall42extends upward from a rear edge of the base wall41. The rear end wall42has the width broadening parallel to the bent wall portion211extending perpendicular to the optical axis Al. The rear end wall42has formed therein the lens window420which passes through a thickness thereof. The lens window420is located in the center of the width of the rear end wall42. The front end portion of the lens holder31passes through the lens window216and the lens window420and is exposed to the imaging space410above the base wall41. The optical axis Al is directed to the imaging space410corresponding to the image capturing range. The optical image of the outside view5in the image capturing range entering the imaging space410is, therefore, transmitted into the lens set35arranged on the optical axis Al.

The base wall41has the incident ray hole421formed in the center of the width of the bottom surface41ain the lateral direction. The incident ray hole421is located near the exposed front portion of the lens holder31to communicate with the lens window420. The recessed hole217formed in the recessed wall portion212is shaped to avoid physical interference with the incident ray hole421. The incident ray hole421is formed to have a depth large enough to permit the optical image of the outside view5within the whole of the image capturing range to enter the lens set35.

The side walls43are arranged symmetrically with respect to the optical axis Al in the lateral direction, so that they are located on opposite sides of the imaging space410in the lateral direction. The side walls43extend upward from right and left side edges of the base wall41. Each of the side walls43is substantially perpendicular to the bottom surface41aof the base wall41, in other words, extends in the vertical direction. Each of the side walls43has the trapezoidal flat inner surface43a. The interval between the inner surfaces43aof the right and left side walls43in the lateral direction gradually increases toward the front of the base wall41. Each of the side walls43has a height from the base wall41which decreases toward the front of the base wall41, thereby creating, as clearly illustrated inFIG.2, the air gap430between each of the side walls43and the inner surface3aof the front windshield3. The air gaps430extend over the whole of the camera module1in the longitudinal direction.

The hood40which has the above described structure serves to block input of unwanted light from outside the image capturing range in the outside view5into the lens set35. For instance, the hood40blocks or minimizes the entry of light reflected by the inner surface3aof the front windshield3into the lens set35. The hood40also blocks light which is trapped by the optical block ribs411and then reflected on the base wall41into the lens set35.

The circuit unit50is, as illustrated inFIGS.2,6, and7, positioned inside the storage chamber25along with components of the optical assembly30. The circuit unit50is made of an assembly of the imaging substrate51, the flexible substrate (FPC), and the controller substrate54and includes the imaging circuit52and the control circuit55.

The imaging substrate51is, as illustrated inFIGS.2and7, made of a rigid board, such as a glass epoxy board, and of a substantially rectangular flat plate. The imaging substrate51is secured to the rear end of the assembly holder30aof the optical assembly30using adhesive, thereby closing the rear of the optical path chamber39. The imaging substrate51has the front mount surface510exposed to the optical path chamber39and the rear mount surface511which is opposed to the front mount surface510through a thickness thereof. The rear mount surface511is exposed to the storage chamber25. The front mount surface510has the imager34mounted thereon. The front and rear mount surfaces510and511have mounted thereon a plurality of circuit components which make up the imaging circuit52. The imaging circuit52achieves transmission of signals or data between itself and the imager34.

The FPC (i.e., flexible printed circuit)53is, as shown inFIGS.2,6, and7, is made of, for example, a resinous flexible base film and conductors mounted thereon and of a substantially rectangular shape. The FPC53is connected at an end thereof to a lower end of the imaging substrate51.

The control substrate54shown inFIGS.2and7is a rigid board, such as a glass epoxy board. The control substrate54is in the shape of a substantially rectangular plate. The control substrate54has an upper and a lower surface opposed to each other through a thickness thereof. The upper surface faces upward in the storage chamber25, while the lower surface faces downward in the storage chamber25. Specifically, the control substrate54has the upper mount surface540facing upward and the lower mount surface541facing downward. The control substrate54has an outer peripheral edge thereof and the upper mount surface540which are placed at a plurality of locations in contact with the upper casing member21. The lower mount surface541is placed at a plurality of locations in contact with the lower casing member22. This positions the control substrate54between the casing members21and22. The control substrate54has the connecting hole542passing through the center of the width thereof and opening at the upper and lower mount surfaces540and541. The connecting hole542is of a substantially rectangular shape and has the imaging substrate51and the lens holder31partially passing therethrough. In other words, the imaging substrate51and the lens holder31are arranged on both upper and lower sides of the control substrate54.

The mount surfaces540and541have a plurality of circuit components making up the control circuit55. The upper mount surface540has disposed thereon the external connector544exposed outside the camera casing20. The external connector544is connected to an external circuit arranged outside the camera casing20. For instance, the external connector544is connected to an ECU mounted outside the camera casing20. The lower mount surface541, as illustrated inFIG.2, has disposed thereon the internal connector543exposed to the storage chamber25. The internal connector543is connected to an end of the FPC53located below the control substrate54, so that the control substrate54is connected to the imaging substrate51through the FPC53to achieve transmission of signals or data between the control circuit55and the imaging circuit52.

The control circuit55has the microcomputer550mounted on the lower mount surface541as one of the circuit components. The microcomputer550includes a processor. The control circuit55works to process an image outputted from the imager34along with the imaging circuit52to produce the outside image551illustrated inFIG.8. The outside image551in which a structural object and/or an obstacle can be identified within the image capturing range is produced. The image capturing range is, as demonstrated inFIG.8, so selected that when the vehicle2has approached the traffic light5aas a structural object above a roof panel of the vehicle2, an image of the traffic light5acan be identified in the outside image551. The image capturing range is also so selected that when the front bumper of the vehicle2has approached the intersection5b, an image of the front obstacle5c, such as a pedestrian, a bicycle, or an automobile), entering the intersection5bcan be identified.

The control circuit55works along with the imaging circuit52to control imaging operations of the imager34including an exposure operation when the imager34takes an image. The control circuit55determines a range of effective pixels551b, as demonstrated inFIG.8, which is derived by removing from the outside image551produced by the image processing operations a range of the vehicle-image pixels551awhich is a lower portion of the outside image551and where a portion of the vehicle2(e.g., a bonnet or hood) appears in the outside image551. The control circuit55controls the exposure used to capture an image next time as a function of pixel values of the effective pixels551bin a given range. The pixel value used in such exposure control may be a gradation of only one or some of the effective pixels551b.

The control circuit55may be designed to perform an image recognition operation to identify a structural object or an obstacle appearing within the image capturing range on the outside image551in addition to the above described image processing operation and imaging control operation. Either of the control circuit55or the imaging circuit52may be engineered to perform only one of the image processing operation and the imaging control operation.

The structure of the lens set35and the lens holder31of the optical assembly30will be described below in detail.

The lens set35is, as illustrated inFIG.9, made as a 4-group 5-lens unit including the first lens36to the fifth lens38c. The first lens36to the fifth lens38care arranged in this order from outside the lens set35toward the imager34and have axes aligned with each other. The optical axis Al of the lens set35is oriented to pass through the principal point of the first lens36.

The first lens36, the fourth lens38b, and the fifth lens38cof the lens set35are each made of a spherical lens shaped to have a spherical optical surface. The first lens36and the fourth lens38bhave outer diameters identical with each other. The second lens37and the third lens38aare each made of an aspheric lens shaped to have an aspherical optical surface. The second lens37and the third lens38aare smaller in diameter than the spherical lenses. The first lens36, the second lens37, and the third lens38aare disposed in the first storage chamber31aof the lens holder31. The fourth lens38band the fifth lens38care disposed in the second storage chamber31bof the lens holder31.

The first lens36is shaped as a concave meniscus lens with the front convex surface360and the rear concave surface362. Specifically, the first lens36is designed as a wide-angle lens offering the above described wide angle of view. The first lens36is fit in a front end of the lens barrel321to close the front of the optical path chamber39. The front convex surface360is an optical surface which is located on the outermost side and exposed to the imaging space410through the lens opening326. The first lens36has the step361, the rear supporting surface363, and the outer peripheral supporting surface364formed thereon.

The step361is formed in the front surface of the first lens36and located outside the front convex surface360in a radial direction of the first lens36. The step361is shaped to provide a difference in outer diameter of the first lens36. The step361includes the front supporting surface361a(i.e., a tread) and the lens side surface361b(i.e., a riser). Each of the front supporting surface361aand the lens side surface361bhas a black light-shielding layer formed thereon. The front supporting surface361ais of an annular shape with a flat face and oriented perpendicular to the optical axis Al. The lens side surface361bis of a hollow cylindrical shape and arranged coaxially with the optical axis Al. The lens side surface361bcontinuously leads to an inner edge of the front supporting surface361aand an outer edge of the front convex surface360. The lens side surface361bfaces an inner peripheral surface of the optical assembly30through an air gap in the radial direction of the optical assembly30.

The rear supporting surface363is formed by a portion of the rear surface of the first lens36and located outside the rear concave surface362in the radial direction of the first lens36. The rear supporting surface363is shaped as an annular flat surface which extends substantially perpendicular to the optical axis Al and faces the imager34. The rear supporting surface363has an inner edge located inside the inner edge of the front supporting surface361ain the radial direction of the first lens36. The outer peripheral supporting surface364is of a hollow cylindrical shape and arranged coaxially with the optical axis Al. The outer peripheral supporting surface364continuously leads to the front supporting surface361aand the rear supporting surface363.

The second lens37is located closer to the imager34than the first lens36is. The second lens37is shaped as a concave meniscus lens with the front concave surface371and the rear convex surface373. The second lens37is arranged away from the first lens36in the axial direction of the optical assembly30. In other words, the second lens37is a lens discrete from the first lens36and firmly retained by an axial force. The second lens37has the outer peripheral supporting surface370, the front supporting surface372, and the rear supporting surface374.

The outer peripheral supporting surface370is formed on an edge surface of the second lens37. The outer peripheral supporting surface370is shaped as a hollow cylindrical surface arranged coaxially with the optical axis Al. The outer peripheral supporting surface370continuously leads to outer edges of the front supporting surface372and the rear supporting surface374. The front supporting surface372is formed by a portion of the front surface of the second lens37and arranged outside the front concave surface371in the radial direction of the second lens37. The front supporting surface372is shaped as an annular flat surface extending perpendicular to the optical axis Al and faces the outside view. The rear supporting surface374is formed by a portion of the rear surface of the second lens37and arranged outside the rear convex surface373in the radial direction of the second lens37. The rear supporting surface374is formed as an annular surface which extends substantially perpendicular to the optical axis Al and faces the imager34.

The third lens38ais shaped to have major opposed convex surfaces: the front convex surface381and the rear convex surface383. The third lens38ahas the outer peripheral supporting surface380and the front supporting surface382formed thereon. The outer peripheral supporting surface380is formed on an edge surface of the third lens38a. The outer peripheral supporting surface380is shaped as a hollow cylindrical surface arranged coaxially with the optical axis Al. The outer peripheral supporting surface380continuously leads to an outer edge of the front supporting surface382. The front supporting surface382is formed by a portion of the front surface of the third lens38aand arranged outside the front convex surface381in the radial direction of the third lens38a. The front supporting surface382is shaped as an annular flat surface which extends substantially perpendicular to the optical axis Al and faces the outside view.

The fourth lens38band the fifth lens38care joined or adhered together in the form of a single lens. The fourth lens38bis shaped as a concave meniscus lens with the front convex surface386. The fifth lens38cis shaped to have major opposed convex surfaces one of which is the rear convex surface389. The fourth lens38bhas the rear supporting surface387and the outer peripheral supporting surface388formed thereon. The rear supporting surface387is formed by a portion of the rear surface of the fourth lens38band arranged outside a joined interface between the fourth lens38band the fifth lens38cin the radial direction of the fourth lens38b. The rear supporting surface387is shaped as an annular flat surface which extends substantially perpendicular to the optical axis Al and faces the imager34. The outer peripheral supporting surface388is formed on an edge surface of the fourth lens38b. The outer peripheral supporting surface388is shaped as a hollow cylindrical surface arranged coaxially with the optical axis Al. The outer peripheral supporting surface388continuously leads to outer edges of the front convex surface386and the rear supporting surface387.

The lens holder31, as illustrated inFIGS.9to13, includes the lens barrel32, the main spacer33a, and the sub-spacer33bwhich are made of the same hard material.

The lens barrel32is made of an assembly of the lens barrel body32a, the front cap32b, and the rear bracket32c. The front cap32band the rear bracket32care attached to the lens barrel body32a. The lens barrel32defines the first storage chamber31aand the second storage chamber31bin which the lens set35, the main spacer33a, and the sub-spacer33bare disposed. The first storage chamber31aand the second storage chamber31bconstitute a portion of the optical path chamber39.

The lens barrel body32ais shaped to be cylindrical as a whole and retains an outer periphery of the first lens36(seeFIG.10). The lens barrel body32ahas an inner peripheral wall (which will also be referred to as the lens barrel inner peripheral wall320) which defines the first storage chamber31a. The lens barrel inner peripheral wall320is equipped with a plurality of (six in this embodiment) lens barrel protrusions320a. Each of the lens barrel protrusions320ais shaped to protrude from the bases320dof the lens barrel inner peripheral wall320inwardly in the radial direction of the lens barrel inner peripheral wall320. The bases320dof the lens barrel inner peripheral wall320also serve as bases of the lens barrel protrusions320a. A bottom of a groove created between every adjacent two of the lens barrel protrusions320adefines the base320d. The lens barrel protrusions320aare arranged at equal angular intervals away from each other in the circumferential direction of the lens barrel body32a. The lens barrel protrusions320aextend from the rear end to the front end of the first storage chamber31ain the axial direction. Each of the lens barrel protrusions320ahas the inner cylindrical surface320bwhich is of a partially cylindrical shape. A cylinder, as defined by the six inner cylindrical surface320b, has an inner diameter substantially identical with an outer diameter of the main spacer33aand an outer diameter of the outer peripheral supporting surface364of the first lens36. The lens barrel protrusions320aretain the outer periphery of the main spacer33aon the inner cylindrical surfaces320b. The lens barrel protrusions320aalso retain the outer peripheral supporting surface364of the first lens36on front portions of the inner cylindrical surfaces320b.

The lens barrel body32aincludes the front fitting portion321, the rear fitting portion322, and the dividing wall323. The front fitting portion321is formed by an outer peripheral wall of a front portion of the lens barrel body32afacing the outside view. The front fitting portion321has, for example, an external thread engaging the front cap32b. The rear fitting portion322is formed by an inner peripheral wall of a base end portion of the lens barrel body32afacing the imager34. The rear fitting portion322has, for example, an internal thread engaging the rear bracket32c.

The dividing wall323is made of a cylindrical wall extending from the inner periphery of the lens barrel body32ainwardly in the radial direction of the lens barrel body32a. The dividing wall323defines or isolates the first storage chamber31aand the second storage chamber31bfrom each other within the lens barrel body32a. The dividing wall323has a front surface which faces the outside view and has an inner edge serving as the front support323a. The dividing wall323also has a rear surface which faces the imager34and has an inner edge serving as the rear support323b. The front support323ais placed in annular line-contact with an outer edge portion of the third lens38ato stop the third lens38afrom moving toward the imager34. The rear support323bis placed in annular line contact with an outer edge portion of the front convex surface386of the fourth lens38bto stop the fourth lens38bfrom moving toward the outside view.

The front cap32bis of a flat cylindrical shape with a bottom as a whole. The front cap32bis retained by the lens barrel body32aand exerts the axial force Fax1(seeFIG.13) on the first lens36of the lens set35in a direction of the optical axis Al. The front cap32bhas the front fitting portion324, the lens opening326, and the lens barrel axial force applying portion325.

The front fitting portion324is formed by an inner periphery of a cylindrical wall of the front cap32band has, for example, an internal thread engaging the front fitting portion321. The lens opening326is of a true circle shape and formed in a radial center portion of a bottom wall of the front cap32bcoaxially with the front cap32b. The lens opening326serves as a transmissive window through which light reaches the lens set35. The lens barrel axial force applying portion325is of a flange shape and protrudes from the cylindrical wall of the front cap32binwardly in the radial direction of the front cap32b. The lens barrel axial force applying portion325has the annular front axial force-applying surface325afacing the imager34. The lens barrel axial force applying portion325threadedly engages the front fitting portion321of the front fitting portion324, thereby placing the front axial force-applying surface325ain contact with the first lens36.

The rear bracket32cis of a flat cylindrical shape as a whole. The rear bracket32cis retained by the lens barrel body32ato exert the axial force Fax2(seeFIG.13) on the fourth lens38bof the lens set35in the direction of the optical axis Al. The axial force Fax2, as produced by the rear bracket32c, is oriented in a direction opposite that in which the axial force Fax1produced by the front cap32bis oriented. The rear bracket32chas the rear fitting portion328and the rear axial force-applying surface329.

The rear fitting portion328is formed on an outer periphery of a cylindrical wall of the rear bracket32cand has, for example, an external thread engaging the rear fitting portion322. The rear axial force-applying surface329is formed by an annular front end surface of the rear bracket32cwhich faces the outside view. The rear axial force-applying surface329threadedly engages the rear fitting portion322of the rear fitting portion328, so that it contacts the rear supporting surface387of the fourth lens38b.

The main spacer33ais of a hollow cylindrical shape as a whole. The main spacer33ais disposed in the lens barrel32coaxially therewith. The main spacer33ahas the second lens37, the third lens38a, and the sub-spacer33bdisposed therein. The main spacer33ahas an inner wall (which will also be referred to below as the spacer inner peripheral wall330retaining be second lens37, the third lens38a, and the sub-spacer33b) which has a plurality of (three in this embodiment) inner convex portions330aand a plurality of (three in this embodiment) intermediate convex portions330cformed thereon (seeFIG.11).

The inner convex portions330aand the intermediate convex portions330care shaped to protrude from the bases330dof the spacer inner peripheral wall330inwardly in the radial direction of the main spacer33a. The bases330dof the spacer inner peripheral wall330serve as bases of the inner convex portions330aand the intermediate convex portions330c. A bottom of a groove created between an adjacent two of the inner convex portions330aand the intermediate convex portions330cdefines the base330d. The inner convex portions330aand the intermediate convex portions330care alternately arranged at equal interval away from each other in the circumferential direction of the main spacer33a. The inner convex portions330aand the intermediate convex portions330cextend from the rear edge to the front edge of the spacer inner peripheral wall330in the axial direction. The inner convex portions330ahave the inner peripheral cylindrical surfaces330bof a partially cylindrical shape. A cylinder, as defined by the three inner peripheral cylindrical surfaces330b, has an inner diameter identical with the outer diameters of the outer peripheral supporting surfaces370and380of the second lens37and the third lens38aand the outer diameter of the sub-spacer33b. The inner convex portions330aretain outer peripheries of the second lens37, the third lens38a, and the sub-spacer33bon the inner peripheral cylindrical surfaces330b. A cylinder, as defined by inner peripheral surfaces of the intermediate convex portions330c, has an inner diameter slightly larger than inner diameters of the inner convex portions330aand the outer diameters of the outer peripheral supporting surfaces370and380. The intermediate convex portions330care, therefore, placed in non-contact with the outer peripheral supporting surfaces370and380and the sub-spacer33b.

The main spacer33ahas an outer peripheral wall (which will also be referred to below as the spacer outer peripheral wall331) which has a plurality of (six in this embodiment) the outer convex portions331aformed thereon. The outer convex portions331aare shaped to protrude from the bases331dof the spacer outer peripheral wall331outward in the radial direction of the main spacer33a. The bases331dof the spacer outer peripheral wall331also serve as bases of the outer convex portions331a. A bottom of a groove between an adjacent two of the outer convex portions331adefines the base331d. The outer convex portions331aare arranged at equal intervals away from each other in the circumferential direction of the main spacer33a. The outer convex portions331aare shaped to extend from the rear edge to the front edges of the spacer outer peripheral wall331in the axial direction of main spacer33a. The outer convex portions331aeach have the outer peripheral cylindrical surface331bof a partial cylindrical shape. A cylinder, as defined by the six outer peripheral cylindrical surfaces331b, has an outer diameter substantially identical with the inner diameter of the inner cylindrical surface320bof the lens barrel body32a. When the main spacer33ais inserted into the lens barrel body32a, the outer convex portions331a, therefore, have the outer peripheral cylindrical surfaces331bplaced in close contact with inner cylindrical surface320bof the lens barrel inner peripheral wall320. The main spacer33ais, therefore, fit in the lens barrel body32aand retained by the lens barrel inner peripheral wall320.

The main spacer33aalso has the axial force-transmitting portion332. The axial force-transmitting portion332is formed in an inward-extending flange shape on an axial end of the main spacer33afacing the outside view. The axial force-transmitting portion332is placed in contact with the rear supporting surface363of the first lens36and protrudes inside the outer peripheral supporting surface370of the second lens37in the radial direction of the main spacer33a. The axial force-transmitting portion332is of an annular shape and arranged coaxially with the main spacer33aand includes the first axial force-applying surface332aand the second axial force-applying surface332b. The first axial force-applying surface332ais defined by an annular front end surface of the main spacer33awhich is oriented toward the outside view and faces the front axial force-applying surface325ain the axial direction of the main spacer33a. The first axial force-applying surface332ais placed in annular contact with the rear concave surface362of the first lens36. The second axial force-applying surface332bis defined by a rear end surface of the flange (i.e., the axial force-transmitting portion332) which faces the imager34and faces the end surface of the sub-spacer33bin the axial direction of the main spacer33a. The whole of the second axial force-applying surface332bis located inside the front axial force-applying surface325aand the front supporting surface361ain the radial direction of the main spacer33a. The second axial force-applying surface332bis placed in annular surface contact with the front supporting surface372of the second lens37. The axial force-transmitting portion332is arranged between the second lens37and the first lens36and works to transmit the axial force Fax1from one of the first lens36and the second lens37to the other.

The sub-spacer33bis of a cylindrical shape as a whole. The sub-spacer33bis arranged inside the main spacer33acoaxially therewith. The sub-spacer33bis located between the second lens37and the third lens38a. The sub-spacer33bhas the front axial force-applying end surface333and the rear axial force-applying end surface334.

The front axial force-applying end surface333is defined by a front annular end of the sub-spacer33bwhich faces the outside view. The front axial force-applying end surface333faces the second axial force-applying surface332bin the axial direction of the sub-spacer33b. The front axial force-applying end surface333is placed in annular contact with the rear supporting surface374of the second lens37. The rear axial force-applying end surface334is defined by a rear annular end of the sub-spacer33bwhich faces the imager34. The rear axial force-applying end surface334faces the front support323aof the dividing wall323in the axial direction. The rear axial force-applying end surface334is placed in annular contact with the front supporting surface382of the third lens38a. The sub-spacer33bis disposed between the second lens37and the third lens38aand works to supply the axial force Fax1from one of the second lens37and the third lens38ato the other.

How to install the lens set35in the lens holder31and the axial forces Fax1and Fax2resulting from the installation of the lens set35will be described below in detail with reference toFIGS.12and13.

First, the second lens37, the sub-spacer33b, and the third lens38aare fitted into the main spacer33ain this order. The second lens37and the third lens38aare, therefore, retained at the outer peripheral supporting surfaces370and380thereof by the inner peripheral cylindrical surfaces330b.

The main spacer33ain which the second lens37and the third lens38aare disposed is fit in the first storage chamber31aof the lens barrel body32awith the rear convex surface383of the third lens38aoriented to face the imager34. The main spacer33ais, therefore, retained at the outer peripheral cylindrical surfaces331bthereof by the inner cylindrical surface320bof the lens barrel32.

After the installation of the main spacer33a, the first lens36is fit in the lens barrel body32a. The first lens36is retained at the outer peripheral supporting surface364thereof by a front portion of the inner cylindrical surface320b. After the main spacer33aand the first lens36are fitted into the first storage chamber31ain this order, the front cap32bis attached to the lens barrel body32a. The first cap32bretained by the lens barrel body32abrings the front axial force-applying surface325aof the lens barrel axial force applying portion325into close contact with the front supporting surface361aof the first lens36, thereby exerting the axial force Fax1on the front supporting surface361a.

The axial force Fax1works to urge the rear supporting surface363of the first lens36into annular contact with the first axial force-applying surface332aof the main spacer33a, thereby causing the axial force Fax1, as produced by the front cap32b, to be applied to the axial force-transmitting portion332. The first lens36is, therefore, firmly held or nipped between the lens barrel axial force applying portion325and the first axial force-applying surface332a, in other words, retained by the lens barrel32using the axial force Fax1.

The application of the axial force Fax1to the axial force-transmitting portion332also urges the second axial force-applying surface332bof the axial force-transmitting portion332into annular contact with the front supporting surface372of the second lens37, thereby exerting the axial force Fax1, as transmitted from the first lens36, on the front supporting surface372. This causes the axial force Fax1to be applied from the rear supporting surface374of the second lens37to the front axial force-applying end surface333of the sub-spacer33band also from the rear axial force-applying end surface334of the sub-spacer33bto the front supporting surface382of the third lens38a. This presses the third lens38aat the rear convex surface383thereof against the front support323a.

As apparent from the above discussion, the second lens37and the third lens38ahold the sub-spacer33btherebetween and are firmly retained between the axial force-transmitting portion332and the front support323a, so that it is supported by the lens barrel32using the axial force Fax1. In this way, the first lens36, the second lens37, and the third lens38aare firmly fixed or positioned relative to each other along the optical axis Al.

The fourth lens38band the fifth lens38cattached to each other as a lens unit is fitted into the second storage chamber31bof the lens barrel body32awith the front convex surface386oriented to face the outside view. The fourth lens38bis, therefore, retained at the outer peripheral supporting surface388thereof by the inner periphery of the lens barrel body32a. The fitting of the rear bracket32cinto the lens barrel body32aurges the rear axial force-applying surface329of the rear bracket32cinto contact with the rear supporting surface387of the fourth lens38b, thereby exerting the axial force Fax2on the rear supporting surface387.

The application of the axial force Fax2to the rear supporting surface387causes the front convex surface386of the fourth lens38bto be pressed against the rear support323bof the dividing wall323, thereby firmly holding the fourth lens38bbetween the rear bracket32cand the dividing wall323. In other words, the fourth lens38bis firmly retained by the lens barrel32using the axial force Fax2. In this way, the fourth lens38band the fifth lens38care firmly fixed or positioned relative to the lenses36,37, and38aalong the optical axis Al.

As apparent from the above discussion, the second lens37in the first embodiment is disposed within the main spacer33aand is smaller in diameter than the first lens36. The axial force-transmitting portion332which is arranged between the first lens36and the second lens37functions to achieve transmission of the axial force Fax1between the first lens36and the second lens37. This achieves application of axial force Fax1both to the first lens36and to the second lens37although they are different in diameter from each other. The above described structure of the optical assembly30, therefore, ensures the stability in firmly holding or retaining the first lens36and the second lens37in the lens barrel32at design locations with high accuracy regardless of conditions of installation thereof in the vehicle2and also enables the second lens37to be reduced in size without sacrificing required optical ability thereof.

The first lens36in the first embodiment, as described above, has the step61formed outside the front convex surface360in the radial direction of the first lens36. The lens barrel32is shaped to have the lens barrel axial force applying portion325which retains the step361using the axial force Fax1. In other words, such a structure of the lens barrel32creates a chamber which is defined by a recessed shape of the step361and in which the lens barrel axial force applying portion325is disposed. This enables a front end portion of the lens barrel32near the first lens36to be reduced in size, thereby enabling the front convex surface360of the first lens36(seeFIGS.14(a) and14(b)) to have a diameter large enough to offer a required wide angle of view and also enabling the front end diameter d1of the lens barrel32to be minimized. This results in a decrease in size of the lens barrel32without sacrificing a required level of optical ability of the optical assembly30.

The decrease in size of the front end portion of the lens barrel32, as can be seen inFIG.14(a), enables the hood40to be reduced in size. Specifically, the camera module1is designed to have the hood40oriented at a given angle to the horizontal plane (e.g., the road surface) in order to obtain a lower angle of view to capture an image of an object at a specific position on the road surface relative to the vehicle2. If the large-sized lens barrel132is used, it will result in an increased interval between the front windshield3and the hood140due to the large diameter d2of the lens barrel132(d2>d1), thereby leading to the need for increasing the length or size of the hood140.

In contrast, the small-sized lens barrel32in the first embodiment is enabled to have the hood40arranged close to the front windshield3, thereby enabling the length of the hood40in the longitudinal direction to be decreased by more than a decrease in size or diameter of the lens barrel32. The decrease in diameter of the lens barrel32, therefore, enables the hood40, i.e., the camera module1to be reduced in size thereof.

The whole of the step361is located outside the front supporting surface372of the second lens37in the radial direction, thus resulting in a large deviation of a location where the axial force Fax1acts on the step361from the lenses36and37in the radial direction. In order to alleviate such a problem, the axial force-transmitting portion332of the main spacer33ais shaped to extend inside the outer peripheral supporting surface370in the radial direction in contact with the first lens36and thus functions to transmit the axial force Fax1from radially outside the second lens37to the front supporting surface372. Accordingly, the axial force-transmitting portion332shaped to have the inwardly extending flange is capable of transmitting the axial force Fax1both to the first lens36and to the second lens37which are different in diameter from each other.

The three inner convex portions330aof the spacer inner peripheral wall330serve to position the second lens37in the radial direction thereof on the inner peripheral cylindrical surfaces330b. Usually, it is easier to ensure the circularity of the inner peripheral cylindrical surfaces330bthan that of the whole of the spacer inner peripheral wall330. The use of the inner peripheral cylindrical surfaces330bof the inner convex portions330ato hold the second lens37, therefore, facilitates the achievement of concentricity of the main spacer33aand the second lens37as compared with use of the whole of the spacer inner peripheral wall330. This easily achieves the alignment of the axes of the first lens36and the second lens37.

The outer peripheral cylindrical surfaces331bof the six outer convex portions331aof the spacer outer peripheral wall331are retained by the lens barrel inner peripheral wall320, thereby positioning the main spacer33ain the radial direction thereof within the optical assembly30. It is, like the spacer inner peripheral wall330, easier to ensure the circularity of the outer peripheral cylindrical surfaces331bthan that of the whole of the spacer outer peripheral wall331. The use of the lens barrel inner peripheral wall320to hold the outer peripheral cylindrical surfaces331bof the outer convex portions331a, therefore, facilitates the achievement of concentricity of the lens barrel32and the main spacer33a. This ensures the stability in alignment of the axis of the second lens37with that of the first lens36.

The six lens barrel protrusions320aof the lens barrel inner peripheral wall320serve to position the main spacer33ain the radial direction thereof on the inner cylindrical surface320b. It is, like the main spacer33a, easier to ensure the circularity of the inner cylindrical surfaces320bof the lens barrel body32athan that of the whole of the lens barrel inner peripheral wall320. The use of the inner cylindrical surfaces320bengaging the outer convex portions331ato retain the main spacer33a, therefore, facilitates the achievement of concentricity of the lens barrel32and the main spacer33a. This ensures the stability in alignment of the axis of the second lens37with that of the first lens36.

The lens barrel32in the first embodiment is, as described above, made by an assembly of the front cap32bwith the lens barrel axial force applying portion325and the lens barrel body32a. Such a structure enables the axial force Fax1to be exerted on the lenses of the lens set35both from the side of the imager34and from the side of the outside view. It is, thus, possible to minimize the magnitude of the axial force Fax1acting on the first lens36and the second lens37of the lens set35in the optical assembly30. This ensures the stability in retaining the first lens36and the second lens37using the axial force Fax1regardless of a difference in diameter therebetween.

In this disclosure, the front windshield is also referred to as a windshield. The lens barrel body32ais also referred to as a retainer body. The lens barrel inner peripheral wall320is also referred to as an inner peripheral wall of a lens barrel. The inner cylindrical surfaces320bare also referred to as partial cylindrical surfaces. The front cap32bis also referred to as an axial force-applying retainer. The main spacer33ais also referred to as an inner lens barrel. The spacer inner peripheral wall330is also referred to as an inner peripheral wall of the inner lens barrel. The spacer outer peripheral wall331is also referred to as an outer peripheral wall of the inner lens barrel. The first lens36is also referred to as an outside view lens. The front convex surface360is also referred to as an optical surface. The second lens37is also referred to as a small-diameter lens. The outer peripheral supporting surface370is also referred to as an outer peripheral surface. The front supporting surface372is also referred to as a small-diameter contact surface.

Second Embodiment

The second embodiment is, as can be seen inFIGS.15to17, a modification of the first embodiment. The lens holder231in the second embodiment includes the intermediate spacer33cand the lens barrel232in addition to the main spacer33aand the sub-spacer33bwhich are identical with those in the first embodiment.

The intermediate spacer33cis of a hollow cylindrical shape as a whole. The intermediate spacer33cis identical in outer diameter with the main spacer33aand fit in the lens barrel inner peripheral wall320. The intermediate spacer33cis arranged in alignment with the main spacer33ain the axial direction of the lens barrel inner peripheral wall320. The intermediate spacer33cis disposed between the third lens38aand the fourth lens38bto set an interval between the third lens38aand the fourth lens38bto a given value. The intermediate spacer33cincludes the front support323aand the rear support323b.

The lens barrel232is made of the rear bracket32cfit in the lens barrel body232a. The lens barrel232has the storage chamber231awhich is defined as a portion of the optical path chamber39and corresponds to the chambers31aand31bshown inFIG.9in the first embodiment.

The lens barrel body232ais of a hollow cylindrical shape as a whole. The lens barrel inner peripheral wall320of the lens barrel body232ahas an inner diameter kept constant from a portion of the lens barrel body232aretaining the outer peripheral supporting surface388of the fourth lens38bto a portion of the lens barrel body232aretaining the outer peripheral supporting surface364of the first lens36. The lens barrel inner peripheral wall320has the lens barrel protrusions320aformed thereon.

The lens barrel protrusions320ahas the inner cylindrical surfaces320bfit on or around the first lens36, the main spacer33a, the intermediate spacer33c, and the fourth lens38b. The lens barrel body232ahas the lens barrel axial force applying portion325formed thereon in addition to the rear fitting portion322retaining the rear bracket32c. The lens barrel axial force applying portion325is formed in the shape of a protrusion or flange which protrudes radially inwardly from the lens barrel inner peripheral wall320. The lens barrel axial force applying portion325has the front axial force-applying surface325aplaced in contact with the front supporting surface361ato hold the first lens36from moving toward the outside view.

How to install the lens set35in the lens holder231and the axial force Fax resulting from such installation will be described below.

The first lens36, the main spacer33a, the intermediate spacer33c, and joined lenses (i.e. a lens unit) are, as illustrated inFIG.16, fitted in the lens barrel body232ain this order. Specifically, the first lens36is first inserted into the storage chamber231afrom the rear opening of the lens barrel body232awith the front convex surface360facing the outside view until the front supporting surface361aof the first lens36contacts the front axial force-applying surface325a, thereby closing the lens opening326. In this way, the first lens36is retained at the outer peripheral supporting surface364by the front end portion of the inner cylindrical surface320b.

Next, the main spacer33ain which the second lens37, the sub-spacer33b, and the third lens38aare disposed is inserted into the storage chamber231aof the lens barrel body232awith the first axial force-applying surface332afacing the outside view. The main spacer33ais inserted into the storage chamber231auntil the first axial force-applying surface332acontacts the rear supporting surface363, so that it is stopped by the first lens36from moving toward the outside view. In this way, the main spacer33ais retained at the outer peripheral cylindrical surfaces331bby the lens barrel protrusions320a.

The intermediate spacer33cis then inserted into the storage chamber231aof the lens barrel body232awith the front support323afacing the outside view. The intermediate spacer33cis inserted into the storage chamber231auntil the front support323acontacts the rear convex surface383of the third lens38a, so that it is stopped from moving toward the outside view. In this way, the intermediate spacer33cis radially retained by the lens barrel protrusions320a.

Subsequently, the fourth lens38band the fifth lens38cthat are lenses joined together in the form of a lens unit are disposed inside the storage chamber231aof the lens barrel body232awith the front convex surface386facing the outside view. Specifically, the fourth lens38bis inserted into the storage chamber231auntil the front convex surface360contacts the rear support323b, so that it is radially retained by the lens barrel protrusions320a. The rear bracket32cis then attached to the lens barrel body232a. The rear bracket32chas the rear axial force-applying surface329placed in direct contact with the rear supporting surface387of the fourth lens38b, thereby applying the axial force Fax to the rear supporting surface387. The axial force Fax is larger than each of the axial forces Fax1and Fax2illustrated inFIG.13in the first embodiment.

The axial force Fax exerts on the fourth lens38bto press the front convex surface386of the fourth lens38bagainst the rear support323bof the intermediate spacer33c, so that the fourth lens38bis held between the rear bracket32cand the intermediate spacer33cand firmly retained by the lens barrel232using the axial force Fax.

The axial force Fax, as produced by the rear bracket32c, is transmitted to the third lens38athrough the intermediate spacer33cand then to the sub-spacer33bthrough the third lens38a. The axial force Fax is further transmitted to the second lens37through the sub-spacer33band then to the axial force-transmitting portion332through the second lens37. In this way, the axial force Fax is exerted on the rear convex surface383, the rear axial force-applying end surface334, the rear supporting surface374, and the second axial force-applying surface332b. This causes the second lens37and the third lens38ato hold the sub-spacer33btherebetween and be firmly nipped between the axial force-transmitting portion332and the intermediate spacer33c, so that they are fixed by the lens barrel232using the axial force Fax.

The transmission of the axial force Fax to the axial force-transmitting portion332causes the first axial force-applying surface332aof the axial force-transmitting portion332to be firmly attached to the rear supporting surface363of the first lens36in an annular form, thereby applying the axial force Fax, as transmitted from the second lens37, to the rear supporting surface363. The front supporting surface361aof the first lens36is, thus, pressed against the front axial force-applying surface325a. The first lens36is, therefore, held between the lens barrel axial force applying portion325and the axial force-transmitting portion332and firmly fixed by the lens barrel232using the axial force Fax. In the above way, the lenses of the lens set35are positioned relative to each other along the optical axis Al.

The second embodiment offers substantially the same beneficial advantages as in the first embodiment. The structure of the lens holder231continues to apply the axial force Fax to the first lens36and the second lens37and enables the second lens37to be reduced in size without sacrificing the optical performance of the optical assembly30.

The lens barrel232in the second embodiment has the lens barrel axial force applying portion325disposed in a recess or chamber defined by the step361formed in the first lens36. This offers the same beneficial advantage as in the first embodiment that the diameter of the front end of the lens barrel232may be reduced to decrease the size of the camera module1.

The optical assembly30in the second embodiment is designed to have the smaller-diameter second lens37and the smaller-diameter third lens38aretained in the main spacer33a. The whole of the lens barrel inner peripheral wall320of the lens barrel body232amay, therefore, be shaped to have an inner diameter matching the outer diameter of the larger-diameter first lens36, thereby enabling all the lenses36to38cto be inserted in sequence into the lens barrel body232afrom the side of the imager34. The structure of the optical assembly30in the second embodiment omits the front cap32b, thereby enabling the front end portion of the lens barrel232near the first lens36to be reduced in diameter, which also enables the hood40or the camera module1to be reduced in size without sacrificing the optical performance of the camera module1.

Modifications

The lens barrel32or232has the lens barrel axial force applying portion325placed in contact with the front convex surface360or the edge of the first lens36to exert the axial force on the first lens36. This structure eliminates the need for the step361formed in the first lens36.

The second lens37and the third lens38aare shaped to have the same outer diameter as that of the first lens36. The second lens37and the third lens38aare, like the first lens36, fit in the lens barrel inner peripheral wall320with outer peripheries thereof placed in direct contact with the inner surface of the lens barrel inner peripheral wall320. This structurer eliminates the main spacer33a.

The main spacer33ais designed to have only the second lens37disposed therein. At least one of the third lens38ato the fifth lens38cdisposed behind the second lens37has the outer peripheral surface retained by the lens barrel inner peripheral wall320. The number, the layout, or the size of the lenses of the lens set35may be changed as needed. Over half of the lenses of the lens set35may be shaped to have aspheric surfaces. Alternatively, all of the lenses of the lens set35may be designed to have spherical surfaces.

The number, layout, or size of the inner convex portions330aor the outer convex portions331aof the main spacer33amay be changed as needed. It is preferable that the main spacer33ahas three or more inner convex portions330aor three or more outer convex portions331a. The main spacer33amay alternatively be designed to omit the intermediate convex portions330cand have the six inner convex portions330aformed on the spacer inner peripheral wall330. The spacer inner peripheral wall330may also be formed to have ribs connecting the inner convex portions330atogether. Additionally, the spacer outer peripheral wall331may also have ribs connecting the outer convex portions331atogether. The number, layout, or size of the lens barrel protrusions320aof the lens barrel32or232may be, like the inner convex portions330a, change as needed. The lens barrel32or232is preferably shaped to have three or more lens barrel protrusions320a. As long as the concentricity of the lens barrel32or232, the second lens37, and the main spacer33ais ensured, the inner convex portions330a, the outer convex portions331a, and/or the lens barrel protrusions320amay be omitted as needed.

The front cap32bor the rear bracket32cthreadedly fastened to the lens barrel body32ain the above embodiments may alternatively be secured to the lens barrel body32ain another way, such as crimping or bonding. All the lenses36to38c, unlike the second embodiment, may be inserted in sequence into the storage chamber231aof the lens barrel body232afrom the outside view. This structure eliminates the need for the rear bracket32c. The axial force, as produced by the front cap32b, will be exerted on all the lenses36to38c.

At least a portion of the control circuit55working to control the operation of the imager34may be realized by an external circuit, such as an ECU, arranged outside the camera casing20. The control circuit55may control the exposure of the camera module1for use at a subsequent time to take an image using pixel values of a given range including pixels capturing a vehicle existing in the outside view. The control substrate54may omit the connecting hole542. In this case, the imaging substrate51may be connected to the internal connector543arranged on an upper mounting surface of the control substrate54through or not through an FPC. The imaging substrate51may alternatively be connected to the internal connector543arranged on a lower mounting surface of the control substrate54using an FPC bypassing the outer periphery of the control substrate54.

The camera casing20may be designed not to have at least one of the windshield-facing wall portion210or the recessed wall portion212. An attachment pad may be secured to the front windshield3to directly retain the camera casing20without use of the bracket body11. The hood40may be designed to be discrete from the bracket body11. In this case, the hood40may have side walls whose inner surfaces are bent or curved. The optical block ribs411of the hood40may be shaped to have the same height. The hood40may alternatively shaped not to have the optical block ribs411.

The camera module1may be designed to have a plurality of imagers or a plurality of lens holders. The camera module1may be attached to an inner surface of a rear windshield of the vehicle2. In this case, the camera module1is oriented in a direction reversed to that in the above embodiments with the imager34facing the front of the vehicle2.