Head-up display optical system based on turn-back type lens unit and vehicle

Abstract

The invention discloses a turn-back type lens unit-based head-up display optical system, which comprises an image generation unit (1), a first reflection unit (2), a turn-back type lens unit (3) and a front windshield (5), and is characterized in that the first reflection unit is arranged in front of the image generation unit, and an acute angle is formed between the first reflection unit and a light ray main axis, so that the first folding of a light path is realized; the turn-back type lens unit is installed in the emergent direction of the first reflection unit, the turn-back type lens unit and the first reflection unit are installed in an inclined mode, the turn-back type lens unit comprises at least two lenses, the rear surface of the tail end lens is plated with a high-reflection film (3a), light rays forwards penetrate through the lens set and then are reflected through the high-reflection film, the reflected light rays reversely penetrate through the lens set again and then are emitted, and second light path folding is completed; through twice folding, the overall volume of the system can be smaller than 5L. According to the invention, the size of the HUD system can be obviously reduced, the thermal drift is effectively inhibited, the cost is greatly reduced, the optical performance, the system integration and universality are improved, the optical energy efficiency is improved, and the reliability and durability are enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of automotive electronics, in particular to a head-up display optical system based on a folding lens unit and a vehicle. BACKGROUND

[0002] Head-up display (HUD) as an important automotive electronics technology has been widely used in the field of intelligent driving in recent years. Its core function is to project driving-related information (such as speed, navigation instructions, warning information, etc.) in the form of virtual images directly in front of the driver's field of view, so that the driver does not need to look down to check the instrument panel or central control screen, thereby improving driving safety and convenience.

[0003] Current vehicle-mounted HUD technology mainly includes the following types:

[0004] Basic HUD (WHUD): adopts off-axis reflective optical architecture, simple structure, low cost, suitable for most vehicle models. However, due to its limited field of view (FOV) and virtual image distance (VID), it can usually only display simple information.

[0005] Augmented reality HUD (AR-HUD): adopts a larger field of view (FOV) and a longer virtual image distance (VID), and realizes high-precision image projection through a complex optical system. It can display more rich information, such as lane-level navigation and front vehicle distance.

[0006] Optical waveguide HUD: uses laser or LED light source, and couples light into waveguide sheet through grating to form virtual image. Ultra-thin volume, large eyebox, suitable for limited space vehicle instrument table.

[0007] Holographic optical element HUD (HOE-HUD): uses holographic film to replace traditional lens group, and realizes light reflection and refraction through holographic optical element to form virtual image. Light weight, can be curved and attached, suitable for various vehicle models.

[0008] Although HUD technology has made significant progress, there are still some problems to be solved in the existing technology. Mainly including the following aspects:

[0009] 1. Large volume: existing HUD systems, especially traditional WHUD and AR-HUD, usually require a long optical path to achieve a large field of view (FOV) and virtual image distance (VID). This results in a large volume of HUD system, usually reaching 10-30 liters, which is difficult to adapt to the limited space of vehicle instrument table. For example, in order to achieve a larger magnification and aberration correction, a free-form mirror requires a longer optical path (250mm), which makes it difficult to further compress the overall size of the HUD system.

[0010] 2. Poor thermal stability: Changes in ambient temperature have a significant impact on the optical performance of the HUD system. Temperature changes can cause the lens to deform and displace, resulting in virtual image offset. The existing HUD system may have a virtual image offset of more than 0.8 mrad within a temperature range of -40℃ to 85℃. This thermal drift phenomenon not only affects the display effect, but also increases the visual fatigue of the driver.

[0011] 3. High cost: The cost of the existing HUD system is relatively high, especially the processing cost of the free-form mirror. The processing precision of the free-form mirror is extremely high (RMS < 10 nm), and its cost accounts for more than 60% of the entire HUD system. In addition, the interchangeability of the windshield is poor, and the optical system needs to be redesigned for each vehicle model, which further increases the development cost.

[0012] 4. Single aberration correction mechanism: The aberration correction mechanism of the existing HUD system is relatively single, and it is difficult to simultaneously consider aberration and thermal compensation. For example, the tilt and curved design of the windshield will cause complex aberrations such as Keystone Distortion and asymmetric astigmatism. The existing technology usually needs complex free-form optical elements to correct these aberrations, but the design, processing and detection cost of the free-form surface is extremely high.

[0013] 5. Difficulty in system integration: The integration of the HUD system needs to consider many factors, including the interior design of the vehicle, the instrument table space, the optical properties of the windshield, etc. The integration of the existing HUD system is difficult, and it needs to make great changes to the interior of the vehicle, which not only increases the development cost, but also may affect the overall design and aesthetics of the vehicle.

[0014] In summary, the existing HUD technology has played an important role in improving driving safety and convenience, but its large size, poor thermal stability, high cost, and complex aberration correction have limited its further development and widespread application. Therefore, it is of great practical significance to develop a small, low-cost, high-performance HUD optical system. SUMMARY

[0015] The present application provides a head-up display optical system based on a turn-around lens unit and a vehicle, the technical scheme is: a head-up display optical system based on a turn-around lens unit is provided, which includes an image generation unit, a first reflection unit, a turn-around lens unit and a front windshield arranged in sequence along the optical path;

[0016] The first reflection unit is arranged in front of the image generation unit and is installed at an acute angle with the main axis of the light emitted by the image generation unit, and reflects the light from the image generation unit to realize the first folding of the optical path;

[0017] The folding lens unit is installed in the light emitting direction of the first reflecting unit and is installed obliquely between the first reflecting unit; the folding lens unit includes at least two lenses, and the end lens located in the incident direction of the light has a rear surface coated with a high-reflection film. After the incident light passes through the lens group in the forward direction, it is reflected by the high-reflection film and passes through the lens group in the reverse direction to be emitted, thereby realizing a second folding of the light path;

[0018] The optical system can achieve an overall system volume of less than 5L by folding the optical path twice.

[0019] The image generation unit, also known as the image source, abbreviated as PGU, is usually a micro display, such as DLP, LCoS, TFT-LCD. It can also be a combination of a micro display and an illumination system. Its main function is to emit a divergent or collimated light beam carrying image information.

[0020] The first reflecting unit is installed at an acute angle to the main axis of the light emitted by the image generating unit, so that the light emitted by the image generating unit is obliquely incident when entering the first reflecting unit. After being reflected by the first reflecting unit, the light path of the image generating unit is changed, realizing the first folding of the light path, thereby effectively compressing the length of the light path.

[0021] Similarly, the folding lens unit is installed obliquely with respect to the first reflecting unit, so that the light beam emitted by the first reflecting unit is obliquely incident on the front surface of the first lens of the lens group. The effects of this structure on the light path can be divided into the following aspects:

[0022] Forward penetration: The oblique light beam from the first reflection unit passes through all lens sheets in sequence. During this process, the lens group refracts the light and performs preliminary aberration correction, such as spherical aberration and coma.

[0023] Reflection and refraction: When light passes through the last lens and reaches its rear surface, the light is reflected here instead of refracted because the rear surface of the last lens is coated with a highly reflective film.

[0024] Reverse Transmission: The light emitted by the highly reflective film passes through the lens units again, this time in the opposite direction to the forward transmission. During this reverse transmission process, the lens group continues to modulate the light and further correct aberrations. Ultimately, the light is emitted in the reverse direction from the front surface of the first lens of the folding lens unit, which is the incident surface.

[0025] Reducing system size is a key goal in HUD (head-up display) design. According to the principles of geometric optics, reducing the distance between the PGU (picture generation unit) image plane and the freeform reflector, or object distance u, is the most direct way to reduce HUD size.

[0026] The virtual image distance VID (distance from the virtual image to the eyebox as perceived by the driver) is usually a design constraint. The basic formula for HUD virtual image formation is:

[0027] 1 / f = 1 / u - 1 / VID Formula 1 Where: f: system focal length;

[0028] u: object distance, distance from PGU to freeform mirror;

[0029] VID: virtual image distance;

[0030] As can be seen from Formula 1, with VID fixed, reducing the object distance u will inevitably lead to a significant shortening of the system focal length f. However, shortening f means that the radius of curvature R of the mirror needs to be reduced accordingly (R≈2f), leading to a sharp increase in the curvature of the mirror surface. In the application of HUD with large off-axis angles (large angle between the light ray and the principal axis), the growth of high-order optical aberrations such as astigmatism and coma is proportional to 1 / f. This dramatic increase in high-order aberrations makes it extremely difficult to effectively correct them under simple optical structures, becoming the main bottleneck restricting the miniaturization of traditional HUDs.

[0031] The present application breaks through the above limitations by introducing a carefully designed return lens unit, rather than a single mirror, to bear the total optical power required by the system Thus breaking through the above limitations:

[0032] Power sharing: total optical power Shared by multiple pieces of lens That is, (φ i : focal power of the i-th piece of lens). This allows the curvature of each lens surface to be designed more gently while achieving a short focal length f, greatly improving the imaging quality. The gentle curvature significantly reduces the requirement for lens surface accuracy, making manufacturing and processing more feasible.

[0033] Light path folding and equivalent focal length multiplication: the present optical system cleverly uses optical elements to fold the light path twice. The light rays propagate back and forth inside the lens group, effectively utilizing the actual physical propagation path length of the light rays. The same light propagation length can be achieved with a smaller physical envelope size, achieving the effect of light path multiplication.

[0034] Through the synergistic effect of the above two core design strategies of "multi-lens sharing optical power" and "folding light path multiplying light path", the overall volume of the system can be less than 5L.

[0035] Further, a correction lens unit is arranged between the return lens unit and the front windshield, which is used to compensate for the image distortion and asymmetric aberration caused by the front windshield.

[0036] The correction principle of the correction lens unit is that the correction lens unit is designed to introduce optical distortion opposite to the distortion of the front windshield in advance, and when the light is reflected after passing through the front windshield, the two distortions cancel each other out, and finally a clear virtual image without distortion is formed in the driver's eyes.

[0037] Further, the first reflection unit includes at least one lens, and the last lens in the light path incident direction has a first total reflection film coated on the back surface thereof.

[0038] Further, the second reflection unit includes a mirror substrate and a second total reflection film coated on the mirror substrate, and the second reflection unit is arranged on the light path between the front windshield and the user's field of view.

[0039] Further, the turn-back lens unit includes three lenses, and the optical surfaces of the three lenses are spherical or aspherical surfaces, and the temperature coefficient of the refractive index of the lens dn / dT is ≤-1.0×10 -4 / ℃.

[0040] Further, the high reflection film is one of an aluminum film, a silver film or a dielectric film, and the reflectivity is >90%, and the spectral range covers the visible light band.

[0041] Further, the first reflection unit is a mirror or a reflective lens.

[0042] Further, the first total reflection film is one of an aluminum film, a silver film or a dielectric film.

[0043] Further, a vehicle is provided, which comprises the head-up display optical system based on the turn-back lens unit.

[0044] The beneficial effects of the present application are as follows:

[0045] 1. Significantly reduce the system volume: the present application reduces the object distance of the optical system, compresses the focal length of the system, and reasonably allocates the optical power parameters of each lens to ensure excellent imaging quality. The turn-back lens unit introduced can make the light turn back inside the lens group, realize efficient folding of the light path, and greatly shorten the total length of the light path. For example, a design originally requiring a 300mm optical path can be compressed to about 200mm through the turn-back structure of the present application, greatly reducing the occupied space of the system in the vehicle, making it more suitable for the instrument table design of compact vehicles and new energy vehicles, and improving the adaptability and universality of the HUD system.

[0046] 2. Effective inhibition of thermal drift: The present application adopts a symmetric optical path design, making the light propagate forward and backward in the turnaround lens unit, partially offsetting the effects of refractive index changes and lens expansion / contraction on the optical path caused by temperature changes. Experiments show that the imaging offset of the HUD system of the present application can be controlled to be <0.3 mrad within the above temperature range, significantly improving the thermal stability of the system and ensuring the stability and reliability of the HUD display under extreme working conditions.

[0047] 3. Greatly reduce the cost: The present application optimizes the optical design, uses a large number of spherical and aspherical lenses to replace free-form mirrors, fully utilizes the advantages of aspherical lenses in aberration correction, and at the same time avoids the high design, processing and detection cost of free-form mirrors. In addition, the present application further reduces the development and production cost by simplifying the element type and optimizing the assembly process. For example, the unit price of aspherical lenses is only about 1 / 10 of that of free-form mirrors, and the processing period is shorter and the detection difficulty is lower. Through these measures, the cost of the HUD system of the present application can be reduced by more than 40%, greatly improving the market competitiveness and popularity of the HUD technology.

[0048] 4. Improve optical performance: The present application significantly improves the optical performance of the HUD system through multi-stage lens cooperative design. The turnaround lens unit is composed of multiple lenses, which not only realizes the light path multiplication, but also provides sufficient optical variables (such as curvature, thickness, material combination) to effectively correct aberrations such as field curvature, distortion and lateral chromatic aberration.

[0049] 5. Enhance system integration and versatility: The HUD optical system of the present application improves the integration and versatility of the system through innovative structural design. For example, the present application pre-compensates the complex aberrations introduced by the windshield through the correction lens unit, ensuring that the final user sees a clear and distortion-free image, making it easier to adapt to different windshield parameters of different vehicle models, reducing the cost of redesign and development caused by differences in vehicle models. In addition, the present application also provides an alternative solution for integrated architecture, further improving the independence and adaptability of the system, making it more flexible to be applied to different types of vehicles without major changes to the vehicle interior, reducing the difficulty and cost of system integration.

[0050] 6. Improve light energy efficiency: The present application optimizes the surface treatment of optical elements and the optical path design to improve the light energy efficiency of the system. For example, high-reflectivity dielectric films (reflectivity > 90%) and high-efficiency aspherical lenses are used to reduce light loss during transmission. Experiments show that the light energy efficiency of the HUD system of the present application can reach more than 80%, which not only improves the display brightness, but also reduces the system energy consumption, meeting the energy-saving requirements of new energy vehicles.

[0051] 7. System reliability and durability: The present application improves the reliability and durability of the HUD system by using optical materials with low thermal expansion coefficient and stable optical structure design. These materials and structures can maintain stable optical performance under extreme temperature and light conditions, reducing system failures and performance degradation caused by environmental changes, extending the service life of the HUD system, and reducing maintenance costs.

[0052] In summary, the present application realizes significant improvement of the HUD system in miniaturization, low cost, high performance, high stability and high integration through innovative optical design and structural optimization, effectively solves many problems existing in the prior art, provides a more advantageous HUD solution for the automotive electronics field, and has broad application prospects and important practical significance. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 Figure 1 is a structural schematic diagram of a simplified system of Embodiment One of the present application;

[0054] Figure 2 Figure 2 is an enlarged view of part A of Figure 1; Figure 1

[0055] Figure 3 Figure 3 is a structural schematic diagram with a virtual image formed; Figure 1

[0056] Figure 4 Figure 4 is a structural schematic diagram of a standard system of Embodiment Two of the present application;

[0057] Figure 5 Figure 5 is a structural schematic diagram of a three-level system of Embodiment Three of the present application;

[0058] Figure 6 Figure 6 is a structural schematic diagram of an integrated system of Embodiment Four of the present application;

[0059] Figure 7 Figure 7 is a structural schematic diagram with a virtual image formed; Figure 6

[0060] REFERENCE NUMERALS:

[0061] 1 - image generating unit, 2 - first reflecting unit, 21 - first reflecting lens, 22 - second reflecting lens, 2a - first total reflection film, 3 - turn-back lens unit, 31 - first lens sheet, 32 - second lens sheet, 33 - third lens sheet, 3a - high reflection film, 4 - correction lens unit, 5 - front windshield, 6 - second reflecting unit, 6a - second total reflection film, 7 - eyebox, 8 - virtual image. DETAILED DESCRIPTION

[0062] ​​​The specific embodiments of the present invention are described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention.

[0063] Example 1

[0064] like Figures 1-3 As shown, a simplified HUD optical system is provided, comprising an image generation unit 1, a first reflection unit 2, a folding lens unit 3, and a front windshield 5, arranged sequentially along an optical path. The image generation unit 1 is a microdisplay or a combination of a microdisplay and an illumination system, capable of emitting either a divergent or collimated light beam. The first reflection unit 2 is a reflector, arranged obliquely in front of the image generation unit 1, and is used to reflect the light beam emitted by the image generation unit 1, thereby achieving a first folding of the light beam. The folding lens unit 3 is mounted diagonally below the first reflection unit 2 and comprises three aspheric lenses: a first lens 31, a second lens 32, and a third lens 33, from top to bottom. A highly reflective film 3a is provided on the rear surface of the third lens 33. The light beam reflected by the first reflection unit 2 passes through the first lens 31, the second lens 32, and the third lens 33 in the forward direction, is reflected by the highly reflective film 3a on the rear surface of the third lens 33, and then exits through the lens group in the reverse direction, achieving a second folding of the optical path. The folding lens unit 3 is also located obliquely below the front windshield 5. After the light beam passes through the folding lens unit 3, it is reflected by the front windshield 5 and enters the user's eyes, that is, the eye box 7. At this time, a virtual image 8 is formed not far in front of the user's eyes (see Figure 3 ), the virtual image 8 is used to present vehicle driving related information, such as vehicle speed, navigation instructions, warning information, etc.

[0065] The folding principle of the light beam in the folding lens unit 3 composed of the first lens 31, the second lens 32 and the third lens 33 is as follows:

[0066] Forward penetration: the oblique light beam from the first reflection unit 2 passes through the first lens 31, the second lens 32 and the third lens 33 in sequence. During this process, the lens group refracts the light and performs preliminary aberration correction.

[0067] Reflection: Light passes through the third lens 33 and is reflected by the high-reflection film 3a on the rear surface of the third lens 33. The high-reflection film 3a is a dielectric film with a reflectivity greater than 90%. The spectrum range covers the visible light band.

[0068] Reverse penetration: the light emitted by the high-reflection film 3 a passes through the third lens 33 , the second lens 32 and the first lens 31 in sequence and enters the front windshield 5 .

[0069] In the above structure, the first lens 31, the second lens 32 and the third lens 33 have been designed to compensate for the distortion of the front windshield, so a clear and visible virtual image 8 can be formed at the user's viewing angle.

[0070] Example 2

[0071] like Figure 4 As shown, a standard HUD optical system is provided. The main difference between Example 2 and Example 1 is that Example 2 adds a correction lens unit 4. Correction lens unit 4 is arranged in the optical path between the reflex lens unit 3 and the front windshield 5. When the reflex lens unit 3 itself cannot compensate for the distortion of the front windshield, correction lens unit 4 corrects the light reflected by the reflex lens unit 3. Correction lens unit 4 is pre-designed to have an optical distortion opposite to that of the front windshield 5. As a result, when the light beam passes through correction lens unit 4 and the front windshield 5, the distortion of the two cancels each other, forming a clear and distortion-free virtual image 8 in the user's field of view.

[0072] Example 3

[0073] like Figure 5 As shown, a HUD optical system with a cascade architecture is provided. The main difference between Example 3 and Example 2 is that the first reflection unit 2 of Example 3 is composed of two reflection lenses, namely a first reflection lens 21 and a second reflection lens 22. The rear surface of the second reflection lens 22 is coated with a first total reflection film 2a, and the first total reflection film 2a is any one of an aluminum film, a silver film or a dielectric film.

[0074] In the cascaded architecture, since the first reflective unit 2 is composed of two reflective lenses and the rear surface of the second reflective lens 22 is coated with the first total reflection film 2a, the first reflective unit 2 itself effectively becomes a "reflective lens unit." This structure not only folds the optical path, but also achieves internal folding of the optical path by passing through the two reflective lenses in the forward direction and then again in the reverse direction. This structure offers improved spatial compression, greater optical path symmetry, and enhanced thermal stability.

[0075] Example 4

[0076] like Figure 6 and Figure 7 As shown, an integrated HUD optical system is provided. The main difference between the fourth embodiment and the first embodiment is the addition of a second reflective unit 6. The second reflective unit 6 comprises a mirror substrate and a second total reflection film 6a coated on the surface of the mirror substrate. The second reflective unit 6 is positioned in the optical path between the front windshield 5 and the user's field of view. The light beam reflected by the folding lens unit 3 is directly reflected by the second reflective unit 6 into the eye box 7 without passing through the front windshield 5. This prevents the virtual image 8 from being unclear or distorted due to distortion of the front windshield 5.

[0077] Further provided is a vehicle comprising the simplified architecture HUD optical system of embodiment one, or the standard architecture HUD optical system of embodiment two, or the cascade architecture HUD optical system of embodiment three, or the integrated architecture HUD optical system of embodiment four.

[0078] The following table shows the performance comparison between the HUD optical systems of embodiments one to four and a conventional HUD optical system.

[0079]

[0080] As shown in the above table, under the premise of keeping the light energy efficiency and MTF@20lp / mm parameters almost the same as those of the conventional HUD, the system volume of the present application is greatly reduced from 10-30L of the conventional HUD to 3.2-5L, effectively saving the vehicle space and reducing the limitation on the vehicle modeling; the system FOV is increased, enabling the driver to observe a wider range of information; the virtual image distance (VID) is increased, projecting the display information to a farther place, and the focus change of the driver when switching between the line of sight and the information is smaller, thereby reducing the visual fatigue during driving; the thermal drift is reduced, making the image display stability of the system higher under different environmental temperatures, effectively inhibiting image jitter or deviation; the residual distortion compensation is greatly reduced, making the final presented image more accurate and straight, significantly reducing the deformation, improving the image quality and visual fidelity, and further enhancing the user's trust in the display information.

[0081] The present application is applicable to different application scenarios:

[0082] The volume of embodiment one (simplified system) is 4.8L, the physical installation depth is 96mm, the system FOV is 8°x3°, the virtual image distance is 5m, the light energy efficiency is 79.2%, the MTF@20lp / mm is 0.41, the thermal drift is 0.12mrad, and the residual distortion compensation is 2.5%. The comprehensive performance is relatively balanced, and the cost and imaging effect are in a good balance. The residual distortion is relatively large, and the present application is suitable for general vehicle models with a windshield curvature radius >3500mm or a FOV <5° and general performance requirements.

[0083] Embodiment two (standard system) is characterized by low cost and small volume. The physical installation depth is only 60mm, and the mechanical envelope size is thin, which is suitable for installation environments with limited space. The system FOV is 8°x3°, the MTF@20lp / mm is 0.46, the thermal drift is 0.09mrad, the residual distortion compensation is 1.8%, and the imaging quality is good. The present application is suitable for medium vehicle models with moderate requirements on cost and imaging effect.

[0084] The embodiment three (level association system) is excellent in field of view angle and imaging quality. The system FOV thereof is 12°*5°, which can provide wider field of view and is suitable for high-end imaging application, especially ARHUD. The MTF@20lp / mm is 0.52, the thermal drift is 0.08 mrad, and the distortion compensation residual error is 1.4%. Moreover, the volume thereof is small, which is suitable for installation environment with limited space. It can be applied to high-end vehicle of ARHUD with high requirements on imaging quality and installation space.

[0085] The embodiment four (integrated system) has the highest system independence and compatibility. The MTF@20lp / mm is 0.50, the thermal drift is 0.07 mrad, the distortion compensation residual error is 1.2%, and the imaging quality is good. It does not need to rely on windshield surface type and has excellent distortion control ability, which can be compatible with various vehicle models and platforms.

[0086] In summary, the four embodiments have advantages respectively and are suitable for different application scenarios. The embodiment one is suitable for ordinary vehicle model, the embodiment two is suitable for medium vehicle model, the embodiment three is suitable for high-end vehicle model, and the embodiment four is suitable for scenario with high requirements on system independence and compatibility.

[0087] The above is only a feasible implementation example of the present application, and does not limit the scope of the present application. Any equivalent structural change made by using the content of the present application and the drawings is included in the present application.

Claims

1. A head-up display optical system based on a folding lens unit, characterized in that: It comprises an image generation unit (1), a first reflection unit (2), a folding lens unit (3) and a front windshield (5) which are sequentially arranged along an optical path; The first reflection unit (2) is arranged in front of the image generation unit (1) and is installed at an acute angle to the main axis of the light emitted by the image generation unit (1), reflecting the light from the image generation unit (1) to achieve the first folding of the light path; The folding lens unit (3) is installed in the light emitting direction of the first reflecting unit (2) and is installed obliquely between the first reflecting unit (2); the folding lens unit (3) comprises at least two lenses, the end lens located in the light incident direction has a high reflective film (3a) coated on its rear surface, and the incident light passes through the lens group in the forward direction, is reflected by the high reflective film (3a), and passes through the lens group in the reverse direction to be emitted, thereby realizing a second folding of the light path; The optical system can achieve an overall system volume of less than 5L by folding the optical path twice.

2. The head-up display optical system based on a folding lens unit according to claim 1, characterized in that: A correction lens unit (4) is provided between the folding lens unit (3) and the front windshield (5), and the correction lens unit (4) is used to compensate for image distortion and asymmetric aberration caused by the front windshield (5).

3. The head-up display optical system based on a folding lens unit according to claim 2, characterized in that: The first reflection unit (2) comprises at least one lens, which is located at the end lens in the incident direction of the light path and has a rear surface coated with a first total reflection film (2a).

4. The head-up display optical system based on a folding lens unit according to claim 1, characterized in that: The invention also includes a second reflection unit (6), which includes a mirror substrate and a second total reflection film (6a) coated on the mirror substrate. The second reflection unit (6) is arranged on the optical path between the front windshield (5) and the user's field of view.

5. The head-up display optical system based on a folding lens unit according to claim 1, characterized in that: The folding lens unit (3) comprises three lenses, the optical surfaces of the three lenses are all spherical or aspherical, and the refractive index temperature coefficient of the lens is dn / dT≤-1.0×10 -4 / ℃.

6. The head-up display optical system based on a folding lens unit according to claim 1, characterized in that: The high-reflection film (3a) is one of an aluminum film, a silver film or a dielectric film, has a reflectivity greater than 90%, and a spectral range covering the visible light band.

7. A head-up display optical system based on a folding lens unit according to claim 1, characterized in that: The first reflecting unit is a reflecting mirror or a reflecting lens.

8. The head-up display optical system based on a folding lens unit according to claim 3, wherein: The first total reflection film (2a) is one of an aluminum film, a silver film or a dielectric film.

9. A vehicle, characterized in that: A head-up display optical system based on a folding lens unit comprising any one of claims 1 to 8.

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