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基于单片机的电动助力系统的设计与实现

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摘要I

ABSTRACTII

第1章绪论1

1.1 转向助力系统的国内外研究现状与发展趋势1

1.2 选题的目的和意义3

1.3 本课题研究的内容和拟解决的主要问题4

1.3.1 本课题的主要内容4

1.3.2 拟解决的主要问题4

第2章 EPS系统的组成5

2.1 EPS工作原理与结构组成5

2.2 传统液压动力转向系统5

2.3 电动助力转向系统特点6

2.4 EPS的类型6

2.5 助力系统的关键部件7

2.5.1 助力电机7

2.5.2 转矩传感器7

2.5.3 车速传感器8

2.5.4 电子控制单元9

2.6 本章小结11

第3章 EPS系统的硬件设计12

3.1 EPS系统硬件电路结构12

3.2 单片机最小系统电路12

3.2.1 时钟电路12

3.2.2 复位13

3.3 电源电路14

3.4电动机的驱动15

3.5 三态缓冲器17

3.6 电动机的变频调速控制18

3.7 电动机H桥驱动方式18

3.8 本章小结19

第4章 EPS控制策略和软件设计20

4.1 EPS系统的控制要求20

4.1.1 回正控制20

4.1.2 阻尼控制20

4.2 转向助力特性曲线的选择21

4.2.1 助力特性的理论研究21

4.2.2 助力特性曲线的选择21

4.3 EPS的软件设计22

4.3.1 开发环境22

4.3.2 数字滤波程序设计24

4.3.3 AD模块25

4.3.4 电机助力子程序26

4.3.5 系统主程序27

4.4 本章小结27

第5章软件下载及系统的试验28

5.1 STC单片机程序下载器的使用28

5.2 系统的试验30

5.3 系统的调试30

5.4 本章小结30

结论32

参考文献33

致谢34

摘要

　　　汽车电动助力转向系统(EPS—Electric Powered Steering)是近年来发展起来的一种新型转向系统，该系统是由电子控制单元根据传感器采集到的信号来控制助力电机的运转，从而实现助力转向的功能，EPS除了具备液压动力转向器的转向轻便等优点之外，它还具有转向平稳、节能、环保等一系列特点，因此，EPS取代液压动力转向系统势在必然。当前国内在EPS的研究和产业化方面还比较落后，没有形成具有自主知识产权的EPS产品。因此，开展对EPS的研发上作具有重要的理论和实际意义。

　　　本文在分析、总结现有电动助力转向系统基础上，以提高系统运行可靠性与达到更好的助力效果为目标，开发了以STC89C52为微处理器的EPS控制器。硬件上结合单片机的资源，对电路进行了设计，包括外围电路以及单片机最小系统的改进。软件上并结合硬件电路，设计了相应的程序，提高了整个系统运行可靠性。

　　　最后,总结论文工作中涉及的一些问题,并给出对未来进行了讨论,形成了未来的研究方向和工作目标。　

关键词：汽车；电动助力转向；单片机

ABSTRACT

　　Electric power steering system(EPS) is a new developing direction of Power steering system in automotive．The principle of EPS is the assistant motor works according to the measured torque and vehicle signals．So that Dower steering can be realized．Besides EPS has the light steering torque like Hydraulic Power Steering (HPS)system，it has many other characteristics such as steering placidly，low energy consuming，environment protecting and so on．Therefore it is a certain tendency that EPS being instead of HPS，But at present．the R&D of the domestic EPS is behindhand．and a11 the EPS used in vehicles has no independent knowledge property right．Therefore it is very important in academic and practical significance in R&D of EPS．

　　　On basis of summary，analysis of the system，a EPS controller based on STC89C52 Was developed in order to improve the reliability and performance of system．With MCU hardware combined resources to circuit design, including peripheral circuit and single chip minimize system improvement. Software and hardware circuit, design with the corresponding program and improve the operation of the system reliability.

　　　Finally，a summary of works involved in the thesis is given and some problems for the future are discussed，which forms the objectives for future research and works．

Key words: Automobile；Electric Power Steering；MCU

　　　转向系统是汽车的主要子系统之一，其性能直接关系到汽车的操纵稳定性和舒适性，对于确保行车安全、减少交通事故以及保护驾驶员的人身安全、改善驾驶员的工作条件起着重要的作用。而一个拥有性能可靠的控制系统则能使EPS实现以上效果，EPS具有节能、环保等优点，是未来转向系统的主流发展，是研究的重点项目。

1.3 本课题研究的内容和拟解决的主要问题

1.3.1 本课题的主要内容

　　　（1）设计一个小型电动转向助力系统，分析电动助力转向系统电子控制单元的功能。在充分考虑电动助力转向系统控制的可靠性、实时性的基础上，以单片机为核心的控制单元。

　　　（2）设计电子控制单元的硬件，采用P控制策略完成对直流电动机的控制、并对各种传感器信号进行采集和处理，通过单片机产生控制脉冲波来控制H桥驱动直流电动机正反转，满足EPS控制要求。

　　　（3）采用模块化设计的方法编写相应控制软件。控制软件中主要包含系统主程序、信号采集子程序，策略控制子程序等。

1.3.2 拟解决的主要问题

　　　（1）系统硬件电路的搭建，硬件电路需要单片机最小系统主要包括时钟电路、滤波电路、电源电路、复位电路等电路的设计。

　　　（2）传感器信号处理电路的设计，如转矩信号通过A/D转换输入处理器进行处理，再通过电机驱动电路控制电机转动方向。

　　　（3）将软件和硬件进行连接并进行测试，检查出现故障部分并思考出现故障的原因，再就相关知识努力将故障排除。第2章 EPS系统的组成

2.1 EPS工作原理与结构组成

　　　EPS的工作原理：当驾驶员操纵方向盘转向时，转向柱上的扭矩传感器检测到的信号与车速信号经过滤波处理后送入ECU，ECU对这些信号进行运算处理后输出PWM信号给电机驱动模块，从而实现对电动机的控制，电机经传动机构将助力转矩传递给牵引前轮转向的横拉杆，最终起到为驾驶员提供转向助力的目的。当车速超过一定值时，EPS系统退出助力工作模式。EPS可在不同车速的情况下提供不同的助力效果，保证汽车在低速行驶时的轻便性和高速行驶时的稳定可靠。EPS的主要组成有扭矩传感器、车速传感器、助力电机和电控单元。

2.2 传统液压动力转向系统

　　　液压动力转向系统（HPS）是在1928年就在汽车上首次应用的，到1940年左右HPS就已经实用化了，并在多种大型车辆上装备。在1951年在轿车上也得到了应用，获得了当时的好评，随后HPS在轿车上便迅速普及，到今天装备HPS的车辆已经超过了80%。

　　　HPS是在传统机械式转向器的基础上通过增加控制阀、动力缸、油泵、储油罐和进回油管等液压动力装置来提供转向助力。开始HPS的控制阀采用滑阀式，即控制阀以轴向一定来控制油路。滑阀式控制阀结构简单，生产工艺性好，操纵方便，但是滑阀灵敏度不够高。20世纪50年代出现了转阀式HPS，即控制阀中的阀芯以旋转运动来控制油路。与滑阀相比，转阀的灵敏度高、密封件少、结构比较先进。虽然由于转阀利用扭杆弹簧来使阀回位，结构较复杂，特别是对扭杆的材质和热处理工艺要求较高，但是其性能相对于滑阀有很大改进，而且在齿轮齿条式转向器中布置转阀比较容易。因此，目前在绝大部分轿车及部分货车上均采用的是转阀式HPS。　　　电动助力转向系统是未来汽车发展趋势的高新技术，本文在对EPS的原理和助力控制的基本过程进行了研究，通过硬件和软件的设计，主要工作如下：

　　　（1）通过对EPS的有关文献资料进行研究，对电动助力转向系统的关键部件进行研究和分析，选择合适的传感器信号模拟部件，电动机及其它部件。

　　　（2）以STC89C52为核心设计了电控单元，其中主要有电机驱动电路，信号采集电路，单片机最小电路，利用变频调制的方法对直流电机的电流大小进行控制，利用H桥实现对电机正反转的控制。

　　　（3）利用Keil软件编写了控制程序，软件的主要功能是对转矩和车速的信号进行采集和数字滤波，然后将经过处理的信号输入单片机，采用P控制策略完成对直流电动机的控制。

　　　（4）将程序下载到单片机中，将电路板通电试验，经过测试表明，控制器能有效对电机进行旋转方向和转速的调节。

　　　本次设计制作的电路板对转矩信号和车速信号用电位计进行了信号的模拟，并用TCL549模数转换芯片对信号采集并送入单片机，电机在单片机和L298电机控制芯片的调控下进行相应的旋转，从而实现在不同的情况下进行对助力的调节。总结以上的工作，有以下几点展望：

　　　（1）电控单元的进一步设计和开发。如电路中抗干扰及保护措施的完善。故障诊断功能的完善等。

　　　（2）EPS控制策略的研究。如何采用更加先进的控制策略，增强对EPS系统控制的效果，以及对EPS数学模型的建立和助力特性曲线的建立。

　　　（3）对助力系统的控制不够准确，需要大量的试验，从而使EPS系统更加完善。

　　　虽然做出了一定的成果，但由于个人能力和时间限制，系统仅仅是在电动助力方面的一个验证性实验，离最后的实用化、产品化还有一定的距离，未来进一步的研究方向主要是在程序上设计的更加贴近实用性，以达到更加合理的助力目标。

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内容简介：: 附录BHistoryThe earliest known patent related to power steering was that by Frederick W. Lanchester in the UK,in February 1902. His invention was to cause the steering mechanism to be actuated by hydraulic power. The next design was filed as recorded by the US Patent Office on August 30, 1932, by Klara Gailis, from Belmont, Massachusetts. There is another inventor credited with the invention of power steering by the name of Charles F. Hammond an American, born in Detroit, who filed similar patents, the first of which was filed as recorded by the Canadian Intellectual Property Office.Chrysler Corporation introduced the first commercially available power steering system on the 1951 Chrysler Imperial under the name Hydraguide. Most new vehicles now have power steering, owing to the trends toward front wheel drive, greater vehicle mass, and wider tires, which all increase the required steering effort. Heavier vehicles as common in some countries would be extremely difficult to maneuver at low speeds, while vehicles of lighter weight may not need power assisted steering at allHydraulic systemsA power steering fluid reservoir and pulley driven pumpMost power steering systems work by using a hydraulic system to turn the vehicles wheels. The hydraulic pressure is usually provided by a gerotor or rotary vane pump driven by the vehicles engine. A double-acting hydraulic cylinder applies a force to the steering gear, which in turn applies a torque to the steering axis of the roadwheels. The flow to the cylinder is controlled by valves operated by the steering wheel; the more torque the driver applies to the steering wheel and the shaft it is attached to, the more fluid the valves allow through to the cylinder, and so the more force is applied to steer the wheels in the appropriate direction.One design for measuring the torque applied to the steering wheel is to fix a torsion bar to the end of the steering shaft. As the steering wheel rotates, so does the attached steering shaft, and so does the top end of the attached torsion bar. Since the torsion bar is relatively thin and flexible and the bottom end is not completely free to rotate, the bar will soak up some of the torque; the bottom end will not rotate as far as the top end. The difference in rotation between the top and bottom ends of the torsion bar can be used to control the valve that allows fluid to flow to the cylinder which provides steering assistance; the greater the twist of the torsion bar, the more steering assistance will be provided.Since the pumps employed are of the positive displacement type, the flow rate they deliver is directly proportional to the speed of the engine. This means that at high engine speeds the steering would naturally operate faster than at low engine speeds. Because this would be undesirable, a restricting orifice and flow control valve are used to direct some of the pumps output back to the hydraulic reservoir at high engine speeds. A pressure relief valve is also used to prevent a dangerous build-up of pressure when the hydraulic cylinders piston reaches the end of the cylinder.Some modern implementations also include an electronic pressure relief valve which can reduce the hydraulic pressure in the power steering lines as the vehicles speed increases (this is known as variable assist power steering).DIRAVIIn the DIRAVI system invented by Citron, the force turning the wheels comes from the cars high pressure hydraulic system and is always the same no matter what the road speed is. As the steering wheel is turned, the wheels are turned simultaneously to a corresponding angle by a hydraulic piston. In order to give some artificial steering feel, there is a separate hydraulically operated system that tries to turn the steering wheel back to centre position. The amount of pressure applied is proportional to road speed, so that at low speeds the steering is very light, and at high speeds it is very difficult to move more than a small amount from the centre position.As long as there is pressure in the cars hydraulic system, there is no mechanical connection between the steering wheel and the roadwheels. This system was first introduced in the Citron SM in 1970, and was known as VariPower in the UK and SpeedFeel in the U.S.While DIRAVI is not the mechanical template for all modern power steering arrangements, it did innovate the now common benefit of speed adjustable steering. The force of the centering device increases as the cars road speed increases.Electro-hydraulic systemsElectro-hydraulic power steering systems, sometimes abbreviated EHPS, and also sometimes called hybrid systems, use the same hydraulic assist technology as standard systems, but the hydraulic pressure is provided by a pump driven by an electric motor instead of being belt-driven by the engine.In 1965, Ford experimented with a fleet of wrist-twist instant steering equipped Mercury Park Lanes that replaced the conventional large steering wheel with two 5-inch (127mm) rings, a fast 15:1 gear ratio, and an electric hydraulic pump in case the engine stalled.In 1994 Volkswagen produced the Mark 3 Golf Ecomatic, which utilized an electric pump so that the power steering could operate while the engine had been turned off by the computer to save fuel.Electro-hydraulic systems can be found in some cars by Ford, Volkswagen, Audi, Peugeot, Citroen, SEAT, Skoda, Suzuki, Opel, MINI, Toyota, Honda, and Mazda.ServotronicServotronic offers true speed-dependent power steering, in which the amount of servo assist depends on road speed, and thus provides even more comfort for the driver. The amount of power assist is greatest at low speeds, for example when parking the car. The greater assist makes it easier to maneuver the car. At higher speeds, an electronic sensing system gradually reduces the level of power assist. In this way, the driver can control the car even more precisely than with conventional power steering. Servotronic is used by a number of automakers, including Audi, BMW, Volkswagen, Volvo, and Porsche. Servotronic is a trademark of AM General Corp. 附录C历史已知最早的专利有关的动力转向系统是由弗雷德里克兰彻斯特在英国，在1902年2月。 His invention was to cause the steering mechanism to be actuated by hydraulic power.他的发明是“导致转向驱动机制，由液压动力”。 The next design was filed as recorded by the US Patent Office on August 30, 1932, by Klara Gailis, from Belmont, Massachusetts.接下来的设计提出由美国专利局记录1932年8月30日在克拉拉盖利斯，从贝尔蒙，马萨诸塞州。 There is another inventor credited with the invention of power steering by the name of Charles F. Hammond an American, born in Detroit, who filed similar patents, the first of which was filed as recorded by the Canadian Intellectual Property Office.有与动力转向由查尔斯F哈蒙德在底特律的美国，谁提出了类似的专利，其中被提交由加拿大知识产权局录得的第一个出生的，名字记入另一位发明家发明。 Chrysler Corporation introduced the first commercially available power steering system on the 1951 Chrysler Imperial under the name Hydraguide. 克莱斯勒公司推出了第一款商业化的动力转向在1951年克莱斯勒帝国的名义Hydraguide系统。 Most new vehicles now have power steering, owing to the trends toward front wheel drive, greater vehicle mass, and wider tires , which all increase the required steering effort.现在大部分新车的动力转向，由于对前轮驱动的趋势，更多的车辆质量，和更广泛的轮胎，所有增加必要的指导工作。 Heavier vehicles as common in some countries would be extremely difficult to maneuver at low speeds, while vehicles of lighter weight may not need power assisted steering at all.在一些国家，共同将很难在低速行驶机动车辆较重，而重量轻的车辆可能不需要辅助转向的一切权力。液压助力转向大多数动力转向系统工作，通过使用液压系统把车辆的车轮。 The hydraulic pressure is usually provided by a gerotor or rotary vane pump driven by the vehicles engine.液压通常由一gerotor或旋片泵的汽车引擎驱动。 A double-acting hydraulic cylinder applies a force to the steering gear, which in turn applies a torque to the steering axis of the roadwheels.双作用液压缸适用于一队的舵机，从而适用于一扭矩对负重轮转向轴。 The flow to the cylinder is controlled by valves operated by the steering wheel; the more torque the driver applies to the steering wheel and the shaft it is attached to, the more fluid the valves allow through to the cylinder, and so the more force is applied to steer the wheels in the appropriate direction.到汽缸流控制的方向盘操作阀，扭矩更适用于驾驶方向盘，它是连接轴，更流体阀允许通过在气缸，所以更多的力量适用于在适当的引导方向的车轮。 One design for measuring the torque applied to the steering wheel is to fix a torsion bar to the end of the steering shaft.衡量一个适用于方向盘上的扭矩设计用于修复扭杆的督导轴端。 As the steering wheel rotates, so does the attached steering shaft, and so does the top end of the attached torsion bar.随着方向盘转动，因此没有附加的转向轴，所以也所附扭杆高端。 Since the torsion bar is relatively thin and flexible and the bottom end is not completely free to rotate, the bar will soak up some of the torque; the bottom end will not rotate as far as the top end.由于扭杆比较薄，灵活，低端不完全自由旋转，酒吧将吸收一些的扭矩;底部的结束将不会旋转尽可能的最高端。 The difference in rotation between the top and bottom ends of the torsion bar can be used to control the valve that allows fluid to flow to the cylinder which provides steering assistance; the greater the twist of the torsion bar, the more steering assistance will be provided.在之间扭杆的顶部和底部旋转的差异，可以用来控制阀，使流体流向汽缸提供指导帮助，在更大的“扭曲的扭力杆”，更将转向援助提供。 Since the pumps employed are of the positive displacement type, the flow rate they deliver is directly proportional to the speed of the engine.由于该泵采用容积式类型，流速它们提供成正比的发动机转速。 This means that at high engine speeds the steering would naturally operate faster than at low engine speeds.这意味着，在发动机转速高，督导工作自然会比在低转速更快。 Because this would be undesirable, a restricting orifice and flow control valve are used to direct some of the pumps output back to the hydraulic reservoir at high engine speeds.因为这将是不好的，限制口和流量控制阀是用来直接泵的输出部分回到高发动机转速液压水库。 A pressure relief valve is also used to prevent a dangerous build-up of pressure when the hydraulic cylinders piston reaches the end of the cylinder.阿泄压阀也可以用来防止危险的累积压力，液压缸的活塞到达气缸结束。 Some modern implementations also include an electronic pressure relief valve which can reduce the hydraulic pressure in the power steering lines as the vehicles speed increases (this is known as variable assist power steering).一些现代的实现还包括一个电子泄压阀，可以减少在舵机作为车辆的速度增加线路功率液压（这是可变动力转向协助已知）。 DIRAVI在DIRAVI制度雪铁龙发明，部队把车轮来自汽车的高压液压系统及始终是相同的，不管什么道路速度。 As the steering wheel is turned, the wheels are turned simultaneously to a corresponding angle by a hydraulic piston .由于方向盘被打开，车轮转向同时向相应角度的液压活塞。 In order to give some artificial steering feel, there is a separate hydraulically operated system that tries to turn the steering wheel back to centre position.为了让一些人为的转向感觉，有一个独立的液压系统，试图扭转方向盘回中心的地位。 The amount of pressure applied is proportional to road speed, so that at low speeds the steering is very light, and at high speeds it is very difficult to move more than a small amount from the centre position.施加压力的量成正比，车速，以便在转向很轻低速和高速很难比移动中心的地位，从少量的。 As long as there is pressure in the cars hydraulic system, there is no mechanical connection between the steering wheel and the roadwheels.只要有在汽车上的液压系统的压力，两者之间没有方向盘和负重轮的机械连接。 This system was first introduced in the Citron SM in 1970, and was known as VariPower in the UK and SpeedFeel in the US该系统首次引入雪铁龙钐于1970年，被称为VariPower在英国和SpeedFeel在美国 While DIRAVI is not the mechanical template for all modern power steering arrangements, it did innovate the now common benefit of speed adjustable steering .虽然DIRAVI不是机械模板所有现代动力转向器的安排，它创新的速度现在的共同利益调整的转向。 The force of the centering device increases as the cars road speed increases.作为汽车的道路速度增加定心装置增加力量电液压系统电动液压助力转向系统，有时缩写液压助力转向，以及有时也被称为“混合型”系统，使用标准系统相同的液压辅助技术，但水压由一而不是带电动马达驱动的水泵提供的驱动由发动机。 In 1965, Ford experimented with a fleet of wrist-twist instant steering equipped Mercury Park Lanes that replaced the conventional large steering wheel with two 5-inch (127mm) rings, a fast 15:1 gear ratio, and an electric hydraulic pump in case the engine stalled. 1 2 1965年，福特试行了“腕扭即时指导舰队”装备水星公园车道的两个5取代传统的大方向盘英寸（127毫米）戒指，快速15:1齿轮比，和一个电动液压泵的情况下，引擎突然熄火。In 1994 Volkswagen pro

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