Hydraulic driving motor of tower crane equipment

Abstract

The utility model discloses a hydraulic drive motor for tower crane equipment, two ends of a motor sleeve shell are respectively and fixedly connected with a front end cover and a rear end cover, the inner wall of the motor sleeve shell is fixedly provided with a stator assembly, the interior of the stator assembly is rotatably connected with a rotor assembly, the rotor assembly is fixedly connected to a motor rotating shaft, and the motor rotating shaft is fixedly connected with the front end cover and the rear end cover. The two ends of the motor rotating shaft penetrate through and are rotationally connected to the middle of the front end cover and the middle of the rear end cover respectively, a fan cover is fixedly connected to the rear end cover, a brake is arranged on the rear end cover and the motor rotating shaft, and a fan is fixedly connected to the portion, on one side of the brake, of the motor rotating shaft. The tail end of a motor rotating shaft in the fan cover is rotationally connected to an encoder, the encoder is fixedly connected to a mounting plate, and the mounting plate is fixedly connected to the inner wall of the fan cover. The utility model aims to provide the hydraulic driving motor for the tower crane equipment, which is remarkably improved in the aspects of installation convenience, heat dissipation performance, electrical safety, braking performance and the like.

Description

Technical Field

[0001] This utility model relates to the field of motor equipment technology, specifically a hydraulic drive motor for tower crane equipment. Background Technology

[0002] With the rapid development of modern construction engineering, tower cranes, as important construction equipment, play an indispensable role in improving construction efficiency and safety. The hydraulic drive motor of a tower crane is one of its core components, responsible for driving various operations such as lifting, rotating, and tilting. Therefore, the performance of the hydraulic drive motor directly affects the working efficiency and safety of the tower crane.

[0003] Existing hydraulic drive motors have several design shortcomings. First, the installation process for many motors is complex, with inconvenient hoisting and securing, increasing the difficulty of installation and maintenance. Second, motors generate a significant amount of heat during operation; poor heat dissipation can lead to overheating, affecting their lifespan and performance. Furthermore, traditional motor wiring methods are cumbersome and susceptible to external environmental factors such as moisture and dust intrusion, which can compromise the safety and stability of electrical connections.

[0004] Meanwhile, the brake of the hydraulic drive motor of the tower crane is also a critical safety component. Existing braking systems may suffer from slow response and unstable braking effects during operation, especially under heavy loads and high-frequency operation. The performance of the brake directly affects the safety and stability of the tower crane. An inadequately designed brake may lead to brake failure or overheating, thereby causing safety accidents. Therefore, improving the performance and reliability of the brake is an important issue that urgently needs to be addressed in current technology.

[0005] Therefore, there is an urgent need for a new type of hydraulic drive motor for tower cranes, capable of a more user-friendly and convenient installation method in its structural design, while possessing excellent heat dissipation performance to ensure stable operation under high-intensity working environments. Furthermore, optimization of the wiring structure is also crucial to improve the motor's protection performance and enhance its reliability in harsh environments. Simultaneously, design and performance optimization of the brake improves its response speed and stability, thereby enhancing the overall safety and reliability of the tower crane equipment. This utility model addresses these issues by providing an improved hydraulic drive motor design to meet the high-performance requirements of modern engineering construction for tower crane equipment. Utility Model Content

[0006] In view of the above-mentioned shortcomings in the existing technology, the purpose of this utility model is to provide a hydraulic drive motor for tower crane equipment that has significant improvements in terms of installation convenience, heat dissipation performance, electrical safety, and braking performance.

[0007] The technical solution adopted by this utility model to achieve the above-mentioned objectives is as follows: a hydraulic drive motor for tower crane equipment, comprising a motor housing, a front cover, a rear cover, a stator assembly, a rotor assembly, a motor shaft, a fan, and a fan cover. The front cover and rear cover are fixedly connected to both ends of the motor housing, respectively. The stator assembly is fixedly installed on the inner wall of the motor housing, and the rotor assembly is rotatably connected inside the stator assembly. The rotor assembly is fixedly connected to the motor shaft. The stator assembly inside the motor housing generates a magnetic field through current, driving the internal rotor assembly to rotate. The rotor assembly is fixed to the motor shaft, and its rotation generates mechanical energy. The two ends of the motor shaft pass through and are rotatably connected to the middle of the front cover and the rear cover, respectively, for supporting the rotation of the motor shaft and the rotor assembly. The motor shaft passes through the front cover and then... The tower crane equipment is connected to a hydraulic system. The mechanical energy of rotation is transmitted to the hydraulic system through a rotating shaft, driving the operation of the tower crane. A fan shroud is fixedly connected to the rear end cover. A brake is installed on the rear end cover and the motor shaft inside the fan shroud. When the motor is powered on, the brake releases the braking state on the motor shaft, and the motor runs normally. Conversely, the motor is in a braking state. A fan is fixedly connected to the motor shaft on one side of the brake to provide airflow for cooling the motor. The end of the motor shaft inside the fan shroud is rotatably connected to an encoder. The motor operating state is adjusted by changing the motor speed. The encoder is fixedly connected to a mounting plate. The outer periphery of the mounting plate is fixedly connected to the inner wall of the fan shroud. A ventilation mesh is opened on one side of the outer end of the fan shroud. Ventilation openings are provided on the mounting plate to ensure unidirectional airflow.

[0008] In the above technical solution, a bearing groove is provided on the front end cover located inside the motor. A first rolling bearing is installed in the bearing groove. The first rolling bearing is limited and connected to the motor shaft. A steel wave spring is provided in the bearing groove. The steel wave spring abuts against the first rolling bearing. A first skeleton oil seal is connected between the other side of the front end cover and the motor shaft.

[0009] In the above technical solution, an assembly groove is provided in the middle of the rear end cover located on one side inside the motor. A second rolling bearing is installed in the assembly groove. The second rolling bearing is limited and connected to the motor shaft. A first limiting retaining ring is fixedly connected to the motor shaft. The first limiting retaining ring abuts against one side of the second rolling bearing. A bearing inner cover is fixedly connected to the rear end cover on one side of the assembly groove by fasteners. The bearing inner cover abuts against the other side of the second rolling bearing. A second skeleton oil seal is connected between the rear end cover located on the outer end of the motor and the motor shaft.

[0010] In the above technical solution, the brake includes a brake stator, a brake rotor, friction pads, an excitation coil, a spring, a retaining ring, a bushing, a limiting ring, a second limiting retaining ring, and an adjusting bolt. The brake stator is fixedly connected to the rear end cover inside the wind shroud. An excitation coil is fixedly connected inside the brake stator. A retaining ring is provided in the inner ring of the brake stator and is fixedly connected to the motor shaft. A bushing is fixedly connected to one side of the retaining ring and is sleeved onto the motor shaft. A brake rotor is slidably connected to the bushing. The brake rotor and the bushing... A spline is provided between the components. A spring is sleeved on the brake rotor, with one end of the spring abutting against a fixed ring. A friction plate is fixedly connected to the brake rotor, with a gap between the friction plate and the brake stator. A limit ring is connected to a sliding sleeve on the motor shaft on one side of the bushing. One end of the limit ring abuts against the bushing, and the other end of the limit ring abuts against a second limit retaining ring. The second limit retaining ring is fixedly connected to the motor shaft. Several adjusting bolts are threaded onto the outer periphery of the limit ring, with one end of each adjusting bolt abutting against the brake rotor.

[0011] In the above technical solution, a lifting ring is fixedly connected to the upper middle part of the motor housing, and a junction box assembly is fastened to the motor housing on one side of the lifting ring. Several metal glands are fixedly connected to the junction box assembly, and the external power cord is connected to the junction box assembly through the metal glands.

[0012] In the above technical solution, a number of axially arranged heat sinks are fixedly connected to the outer wall of the motor housing, and gaps are left between the two sides of the motor housing and the edge of the fan cover, with one end of each heat sink set in the gap.

[0013] The beneficial effects of this utility model are:

[0014] Convenient installation and maintenance: The motor housing has a lifting ring at the top center, which significantly improves the convenience of motor installation and transportation. This design allows for easy lifting during installation, transportation or maintenance, reduces safety hazards caused by improper installation, and improves work efficiency.

[0015] Excellent heat dissipation performance: This motor design focuses on optimizing the heat dissipation structure, which can effectively dissipate the heat generated during operation and avoid overheating. This feature ensures stable operation of the motor under high-intensity work, extends the service life of the motor, and reduces the frequency of maintenance.

[0016] Enhanced electrical connection safety: By optimizing the wiring structure, this invention improves the protection performance of the motor, effectively preventing the influence of external environmental factors (such as moisture, dust, etc.) on the electrical connection, and ensuring the reliability and stability of the motor in harsh environments.

[0017] Improved brake performance: Compared with traditional designs, the improvements made to the brake in this invention enhance its response speed and braking effect, ensuring safety under heavy load and high-frequency operation conditions. This innovative design significantly reduces the risk of brake failure or overheating, and improves the overall safety of the tower crane equipment.

[0018] Overall performance optimization: By systematically designing and optimizing various key aspects of the hydraulic drive motor, this utility model achieves a comprehensive improvement in motor performance, which not only meets the needs of modern engineering construction for high efficiency and safety, but also lays a solid foundation for the widespread application of tower crane equipment.

[0019] In summary, the hydraulic drive motor for tower cranes of this invention has significantly improved in terms of installation convenience, heat dissipation performance, electrical safety, and braking performance, fully meeting the current construction industry's demand for high performance and high safety of tower crane equipment. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the cross-sectional connection structure of the motor of this utility model;

[0021] Figure 2 This is a front view schematic diagram of the motor connection structure of this utility model;

[0022] Figure 3 This is a schematic diagram of the brake connection structure of this utility model;

[0023] Figure 4 for Figure 3 Detailed structural diagram of part A1.

[0024] In the diagram: 1 Motor housing, 2 Front cover, 3 Rear cover, 4 Stator assembly, 5 Rotor assembly, 6 Brake, 7 Fan, 8 Encoder, 9 Fan cover, 10 Motor shaft, 101 First rolling bearing, 102 Steel wave spring, 103 First skeleton oil seal, 201 Second rolling bearing, 202 First limit retaining ring, 203 Bearing inner cover, 204 Second skeleton oil seal, 301 Brake stator, 302 Brake rotor, 303 Friction plate, 304 Excitation coil, 305 Spring, 306 Retaining ring, 307 Shaft sleeve, 308 Limiting ring, 309 Second limit retaining ring, 310 Adjusting bolt, 311 Spline, 401 Lifting ring, 402 Junction box assembly, 403 Metal gland, 404 Heat sink. Detailed Implementation

[0025] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0026] Please see Figure 1-4 A hydraulic drive motor for tower crane equipment includes a motor housing 1, a front cover 2, a rear cover 3, a stator assembly 4, a rotor assembly 5, a motor shaft 10, a fan 7, and a fan shroud 9. The front cover 2 and the rear cover 3 are fixedly connected to both ends of the motor housing 1, respectively. The stator assembly 4 is fixedly installed on the inner wall of the motor housing 1. The rotor assembly 5 is rotatably connected inside the stator assembly 4 and is fixedly connected to the motor shaft 10. The stator assembly 4 inside the motor housing 1 generates a magnetic field through current, driving the rotor assembly 5 to rotate. The rotor assembly 5 is fixed to the motor shaft 10, and its rotation generates mechanical energy. The two ends of the motor shaft 10 pass through and are rotatably connected to the middle of the front cover 2 and the rear cover 3, respectively, to provide rotational support for the motor shaft 10 and the rotor assembly 5. The motor shaft 10 passes through the front cover 2 and is connected to the tower crane... The equipment is connected to a hydraulic device, and the mechanical energy of rotation is transmitted to the hydraulic system through the rotating shaft to drive the operation of the tower crane. A fan shroud 9 is fixedly connected to the rear end cover 3. A brake 6 is set on the rear end cover 3 and the motor shaft 10 inside the fan shroud 9. When the motor is powered on, the brake 6 releases the braking state of the motor shaft 10, and the motor runs normally. Otherwise, the motor is in a braking state. A fan 7 is fixedly connected to the motor shaft 10 on one side of the brake 6 to provide airflow for cooling the motor. The end of the motor shaft 10 inside the fan shroud 9 is rotatably connected to an encoder 8. The motor operating state is adjusted by changing the motor speed. The encoder 8 is fixedly connected to the mounting plate. The outer periphery of the mounting plate is fixedly connected to the inner wall of the fan shroud 9. A ventilation mesh is opened on one side of the outer end of the fan shroud 9. A ventilation port is set on the mounting plate to ensure that the air flows in one direction.

[0027] In one embodiment of this utility model, a bearing groove is provided on the front end cover 2 located inside the motor. The bearing groove provided inside the front end cover 2 provides space for installing and supporting the motor shaft 10. By installing a first rolling bearing 101 in the bearing groove, friction can be effectively reduced, ensuring the smooth rotation of the motor shaft 10. The first rolling bearing 101 is installed in the bearing groove and is limitedly connected to the motor shaft 10. The main function of the first rolling bearing 101 is to support the motor shaft 10, bear axial and radial loads, and ensure the stability of the motor during operation. A steel wave spring 102 is provided in the bearing groove. The steel wave spring 102 abuts against the first rolling bearing 101 to provide axial preload, prevent the first rolling bearing 101 from moving during operation, and improve the service life of the bearing. A first skeleton oil seal 103 is connected between the other side of the front end cover 2 and the motor shaft 10. Its main function is to prevent lubricating oil leakage, thereby maintaining the lubrication environment inside the motor, and at the same time preventing external dust and moisture from entering the motor, protecting the internal components of the motor.

[0028] In one embodiment of this utility model, an assembly groove is provided in the middle of the rear end cover 3 located inside the motor, providing space for installing the second rolling bearing 201 and ensuring stable support for the shaft. The second rolling bearing 201 is installed in the assembly groove and is connected to the motor shaft 10 for limiting. It is mainly responsible for supporting the other end of the shaft and bearing additional axial and radial loads, further improving the operating stability of the motor. A first limiting retaining ring 202 is fixedly connected to the motor shaft 10. The first limiting retaining ring 202 abuts against one side of the second rolling bearing 201, playing a limiting role and preventing... During operation, the second rolling bearing 201 experiences excessive displacement. A bearing inner cover 203 is fixedly connected to the rear end cover 3 on one side of the assembly slot by fasteners. The bearing inner cover 203 abuts against the other side of the second rolling bearing 201 and cooperates with the first limit ring 202 to prevent the second rolling bearing 201 from axially displacing on the motor shaft 10. A second skeleton oil seal 204 is connected between the rear end cover 3 on the outer end of the motor and the motor shaft 10. Its function is similar to that of the first skeleton oil seal 103, preventing lubricating oil leakage and preventing external contaminants from entering the motor, thus ensuring the normal operation of the motor.

[0029] In one embodiment of this utility model, the brake 6 includes a brake stator 301, a brake rotor 302, a friction plate 303, an excitation coil 304, a spring 305, a fixing ring 306, a bushing 307, a limiting ring 308, a second limiting retaining ring 309, and an adjusting bolt 310. The brake stator 301 is fixedly connected to the rear end cover 3 inside the fan cover 9. The excitation coil 304 is fixedly connected inside the brake stator 301. A fixing ring 306 is provided in the inner ring of the brake stator 301. The fixing ring 306 is fixedly connected to the motor shaft 10. A bushing 307 is fixedly connected to one side of the fixing ring 306. The bushing 307 is sleeved and connected to the motor shaft 10. The brake rotor 302 is slidably connected to the bushing 307. A spline 311 is provided between the brake rotor 302 and the bushing 307. A spring 305 is sleeved and connected to the brake rotor 302. One end of the spring 305 is connected to... The fixed ring 306 abuts against the brake rotor 302, and a friction plate 303 is fixedly connected to the brake rotor 302. There is a gap between the friction plate 303 and the brake stator 301. A limit ring 308 is connected to the motor shaft 10 on one side of the bushing 307. One end of the limit ring 308 abuts against the bushing 307, and the other end of the limit ring 308 abuts against the second limit retaining ring 309. The second limit retaining ring 309 is fixedly connected to the motor shaft 10. Several adjusting bolts 310 are threadedly connected to the outer periphery of the limit ring 308. One end of the adjusting bolts 310 abuts against the brake rotor 302. When the motor is powered on, the excitation coil 304 is de-energized. At this time, under the push of the spring force of the spring 305, the brake rotor 302 abuts against the adjusting bolts 310, that is, there is a gap between the friction plate 303 and the brake stator 301, and the brake rotor 302 rotates normally with the motor shaft 10.

[0030] When the motor is powered off, the excitation coil 304 is energized and generates an electromagnetic field. Under the action of the magnetic force, the brake rotor 302 slides along the bushing 307 toward the brake stator 301, so that the friction plate 303 contacts and rubs against the brake stator 301, thereby generating braking force. Since the brake rotor 302 and the bushing 307 are connected by the spline 311, the braking effect can be applied to the motor shaft 10, thereby quickly stopping the rotation of the motor shaft 10. After the encoder 8 detects that the motor shaft 10 has stopped rotating, it automatically disconnects the energization of the excitation coil 304. At this time, under the action of the spring 305, the brake rotor 302 automatically returns to its original position.

[0031] During prolonged use, the wear of the friction pads 303 in the brake 6 will cause the gap to increase, thus affecting the normal engagement and braking of the brake 6. Therefore, it is necessary to adjust the gap. The adjustment method is to rotate the adjusting bolt 310. The adjusting bolt 310 pushes the brake rotor 302 towards the brake stator 301 through the threaded connection, thereby reducing the gap and ensuring that the brake 6 can engage and brake normally.

[0032] In one embodiment of this utility model, a lifting ring 401 is fixedly connected to the upper middle part of the motor housing 1, mainly for facilitating the hoisting and installation of the motor, providing a reliable hanging point, so that the motor can be easily suspended or fixed in the required position during installation, transportation or maintenance. A junction box assembly 402 is fastened to the motor housing 1 on one side of the lifting ring 401. Several metal glands 403 are fixedly connected to the junction box assembly 402. The external power cord is connected to the junction box assembly 402 through the metal glands 403. The metal glands 403 are used as cable inlets, providing mechanical support and sealing functions to prevent external factors such as moisture and dust from entering the junction box and protecting the safety of the internal electrical connections. In use, the power cord is led out from the stator assembly 4, passes through the junction box assembly 402 and the metal glands 403, and then the power is turned on to provide power to the motor.

[0033] In one embodiment of this utility model, a plurality of axially arranged heat sinks 404 are fixedly connected to the outer wall of the motor housing 1. There are gaps between the two sides of the motor housing 1 and the edge of the fan cover 9. One end of each heat sink 404 is set in the gap. When the motor is working, the motor shaft 10 drives the fan 7 to rotate. The fan 7 draws in air through the ventilation mesh in the middle and blows the air out through the gap between the motor housing 1 and the edge of the fan cover 9. At this time, the air will flow along the groove formed between the adjacent heat sinks 404, thereby carrying away the heat on the motor housing 1 and the heat sinks 404, and increasing the heat dissipation effect when the motor is working.

[0034] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0035] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A tower crane equipment hydraulic drive motor, comprising a motor casing (1), a front end cover (2), a rear end cover (3), a stator assembly (4), a rotor assembly (5), a motor rotating shaft (10), a fan (7), a fan cover (9), characterized in that: The motor housing (1) is respectively fixedly connected with a front end cover (2) and a rear end cover (3), the inner wall of the motor housing (1) is fixedly installed with a stator assembly (4), the stator assembly (4) is rotatably connected with a rotor assembly (5) inside, the rotor assembly (5) is fixedly connected on a motor rotating shaft (10), the both ends of the motor rotating shaft (10) are respectively penetrated and rotatably connected in the middle of the front end cover (2) and the rear end cover (3), the motor rotating shaft (10) is connected with a tower crane equipment hydraulic device after penetrating the front end cover (2), the rear end cover (3) is fixedly connected with a fan cover (9), the rear end cover (3) inside the fan cover (9) is provided with a brake (6) on the motor rotating shaft (10), the motor rotating shaft (10) on one side of the brake (6) is fixedly connected with a fan (7), the motor rotating shaft (10) inside the fan cover (9) is rotatably connected with an encoder (8) at the end, the encoder (8) is fixedly connected on a mounting plate, and the outer peripheral edge of the mounting plate is fixedly connected with the inner wall of the fan cover (9).

2. The tower crane apparatus hydraulic drive motor of claim 1, wherein: The front end cover (2) inside the motor is provided with a bearing groove, the first rolling bearing (101) is installed in the bearing groove, the first rolling bearing (101) is limitingly connected on the motor rotating shaft (10), the steel wave spring (102) is arranged in the bearing groove, the steel wave spring (102) abuts against the first rolling bearing (101), and the first skeleton oil seal (103) is connected between the other side of the front end cover (2) and the motor rotating shaft (10).

3. The hydraulic drive motor of a tower crane device according to claim 1, characterized in that: The middle of the rear end cover (3) on one side of the motor is provided with an assembly groove, the second rolling bearing (201) is installed in the assembly groove, the second rolling bearing (201) is limitingly connected on the motor rotating shaft (10), the first limiting baffle (202) is fixedly connected on the motor rotating shaft (10), the first limiting baffle (202) abuts against one side of the second rolling bearing (201), the bearing inner cover (203) is fixedly connected on the rear end cover (3) on one side of the assembly groove through fasteners, the bearing inner cover (203) abuts against the other side of the second rolling bearing (201), and the second skeleton oil seal (204) is connected between the rear end cover (3) on the other side of the motor and the motor rotating shaft (10).

4. The tower crane apparatus hydraulic drive motor of claim 1, wherein: The brake (6) includes brake stator (301), brake rotor (302), friction plate (303), excitation coil (304), spring (305), fixed ring (306), shaft sleeve (307), limit ring (308), second limit check ring (309), adjusting bolt (310), the rear end cover (3) inside the fan cover (9) is fixedly connected with brake stator (301), the brake stator (301) is fixedly connected with excitation coil (304) in, the inner ring of brake stator (301) is provided with fixed ring (306), the fixed ring (306) is fixedly connected on motor shaft (10), one side of the fixed ring (306) is fixedly connected with shaft sleeve (307), the shaft sleeve (307) is connected on motor shaft (10), the brake rotor (302) is connected in the sleeve of the shaft sleeve (307), the brake rotor (302) and shaft sleeve (307) are provided with spline (311), the brake rotor (302) is connected in the sleeve of spring (305), one end of the spring (305) is in contact with fixed ring (306), the brake rotor (302) is fixedly connected with friction plate (303), the friction plate (303) and brake stator (301) are left with gap, the motor shaft (10) on one side of the shaft sleeve (307) is connected in the sleeve of limit ring (308), one end of the limit ring (308) is in contact with shaft sleeve (307), the other side of the limit ring (308) is in contact with second limit check ring (309), the second limit check ring (309) is fixedly connected on motor shaft (10), the outer periphery of the limit ring (308) is respectively connected with a plurality of adjusting bolts (310), one end of the adjusting bolt (310) is respectively in contact with brake rotor (302).

5. The tower crane apparatus hydraulic drive motor of claim 1, wherein: The upper end of the motor shell (1) is fixedly connected with a lifting ring (401), and the motor shell (1) on one side of the lifting ring (401) is connected with a terminal box assembly (402) through fastening, a plurality of metal gland heads (403) are fixedly connected on the terminal box assembly (402), and external power supply lines are connected to the terminal box assembly (402) through the metal gland heads (403).

6. The tower crane apparatus hydraulic drive motor of claim 1, wherein: The outer wall of the motor shell (1) is fixedly connected with a plurality of axially arranged cooling fins (404), and the two sides of the motor shell (1) and the edges of the fan cover (9) are left with gaps, and one end of the cooling fin (404) is arranged in the gap.

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