长期以来，推动高级驾驶员辅助系统（ADAS）和电气化发展的可能是乘用车领域，但如今，能够更快更广地应用这些技术的，却可能是非公路车辆领域。

 “尽管由于各种法规限制，（驾驶员辅助系统）在车辆中应用的难度非常大，但如今其发展仍主要集中在乘用车领域。”采埃孚公司负责工业技术高级工程的Manuel Götz博士表示，“因此，我相信未来大家将在非公路领域看到更多自动驾驶技术的应用，其发展速度甚至会超过乘用车领域。非公路设备领域是个相对封闭的环境，也没有道路车辆领域的种种法规限制，因此在应用这些自动驾驶技术方面应该会更简单。”

Götz博士补充道，“另外，这种高度自动化的趋势，还可能导致未来受过专业培训的驾驶员越来越少，从而缺乏训练有素的驾驶员来操作这些日益复杂的机器。因此，我们的“创新拖拉机”（Innovation Tractor）产品就开始向自动化操作方向发展。”

采埃孚公司正齐心协力，将其最初为乘用车开发的各种智能系统推广至重型卡车、大巴，及各种非公路设备。为了有效贯彻这个方针，去年采埃孚公司高级工程部门的工程师花费了一年时间，设计了一款装满摄像头和各种电子设备的Innovation Tractor展示设备，可实现自动转向与钩挂，更不用说进行行人监测了。采埃孚在德国亚琛展示了这款Innovation Tractor的性能：在一段坡度30％的水下路段行驶时，这款拖拉机在单轮驱动模式下，表现出优异的牵引力管理性能。

 “我们不仅能够完全控制设备的动力传动系统和发动机，还能控制转向和制动系统。”Götz博士表示，“对设备的完全控制非常必要，这样才能有效进行车辆的牵引控制和转向等操作。”

Götz博士表示，公司选择首先将自动驾驶技术应用至农业领域，而后还会向工程机械等其他领域推广。

 “这款Innovation Tractor测试原型机融合了所有我们认为在农机和工程机械中比较实用的功能，”采埃孚公司研发主管Harald Naunheimer博士表示，“重点是展示现有技术水平已经可以实现的功能，并为未来的技术创新设定基准。”

自动化操作和钩挂监测

采埃孚的Innovation Tractor共采用了10个摄像头，全面监测周边环境。凭借这些摄像头提供的数据，拖拉机才得以实现半自动驾驶，或可直接通过车外移动设备进行操控，这可以使机具的钩挂更加容易。

具体来说，6个摄像头安装在驾驶舱和发动机盖上。车载计算机可以分析摄像头传送过来的图像，并呈现一个360°的环视影像。驾驶员可以在平板上从各个角度查看这些图像，其中包括俯瞰视角。

Götz表示，正如汽车行业一样，这些摄像头可以实现互联，提供障碍监测预警功能，甚至在必要时还可以与制动系统进行连接。

另外2个摄像头安装在拖拉机后方，负责钩挂机具的监测。最后，还有2个摄像头也安装在拖拉机的后方，负责支持行人监测功能。值得注意的是，位于拖拉机后方的4个摄像头采用了独立数据处理单元。

Götz表示，未来在理想状态下，公司会将拖拉机上的摄像头数量从现有的10个整合至4个，均安装在车顶，通过协同作用，保证多种车辆功能的实现。

Innovation Tractor的SafeRange安全距离功能，允许驾驶员离开车辆，并在安全距离之外远程控制拖拉机和拖车。此时，驾驶员可以在平板上观察拖拉机与拖车的俯视图像。车辆的各种操作命令也已整合到这个操控界面，对于一些复杂环境下的倒车操作，用户可以直接指定希望拖车转向的方向，接着车辆系统将进行各种计算，并自动执行各种必要的转向动作。

驾驶员还可利用平板电脑调节车辆速度，拖拉机和拖车均可进行这样的调节。车辆的最高前进速度为4 km/h (2.5 mph)，而倒车速度为2 km/h (1.2 mph)。如果驾驶员停止在平板上的操作，或平板与牵引机之间的网络连接断开，车辆均会自动停止运转。值得注意的是，SafeRange安全距离功能在没有拖车的情况下也能操控拖拉机。

对于自动钩挂功能，目前Innovation Tractor的拖车上还设置了3个目标位，以协助指导系统发挥作用。Götz博士表示，未来，公司将逐步移除这些辅助目标位，转而采用一些其他的技术支持。

Götz解释说，“你可以在不同的应用环境下将车辆算法调整至更佳，但这个过程将非常漫长。我认为，未来我们的系统将整合光学摄像头和激光系统。激光系统的功能非常强大，可以为车辆提供更加准确的监测信息，而且不但可以关注距离，还能关注环境的变化。因此，我认为自动驾驶操作势必会带来传感器的融合。”

Hitch Detection钩挂监测系统可以使用摄像头监测拖车的准确位置，以及拖车与拖拉机之间的相对角度，最大工作距离长达7米。在整个钩挂过程中，Hitch Detection系统将不断进行监测，并实时调整轮向车轮的角度。这款Innovation Tractor可以进行自动操作，直至达到最佳钩挂位置，而后将控制权交给驾驶员。系统误差为1.5厘米。

此外，当驾驶员通过平板电脑进行常规操作或机具钩挂时，车辆的摄像头将持续监测车辆周边7米之内的行人，并将相关信息显示在平板电脑上。当有行人位于危险位置时，如果操作牵引机的驾驶员未能及时作出反应，车辆将自动停止运行。此后，只有当行人远离危险区域后，刚刚已经中断的钩挂过程才会重新启动。

“农场经常会发生拖拉机碾人的事故，因此我们的系统带来了一项巨大的进步。”Götz博士表示，“目前，尚无任何法规强制要求车辆采用行人监测系统。不过，一旦此类技术真正进入市场，一定会有法规强制要求车辆采用这种解决方案。”

动力传动系统的电气化

采埃孚Innovation Tractor的动力传动系统电气化可以体现在多个方面，比如公司的TERRAMATIC变速器，用于为拖车与机具供电的电动单轮驱动TERRA+发电机模块，以及专门开发的牵引力管理系统。此外，这款拖拉机还将自动驾驶系统所必须的电动转向系统整合至车辆的控制网络。

动力传动系统可以持续提供功率为50千瓦的电力，并为拖车中的用电设备提供电源。车辆的电动磨轮头内整合了2个液冷三相异步马达，可以节省拖车车轴所占的空间；而对于拖车而言，该系统则安装在中轴上。系统额定电压为400V，此外还搭配了一个轮闸。

电机可为每个车轮提供6000 N·m (4425 lb·ft)的最大扭矩。

Götz博士表示，“虽然目前已经具备了相应的能力，但我们还没有进行制动系统的电气化，这将是我们的下一步工作。”制动系统可以帮助设备在下坡或转向时有效减速，从而防止车辆弯折与翻滚。Götz博士表示，“我们必须将制动系统整合在控制系统内，从而利用电动轴提供制动扭矩。这里的工作主要就是设置各种参数。”

Götz博士表示，车辆差速器中的扭矩矢量分配系统，可以为每个车轮分配不同的功率。目前，该系统并未安装到Innovation Tractor上，但未来可能有所应用。

 “我们可以提供70 kW，甚至100 kW的持续功率。”Götz博士表示，“现阶段，我们为Innovation Tractor展示机安装了一款50 kW的发电机系统。该系统已连接至车辆的动力电子元件，可以向拖车的各个车轮传输电流。但我们这样做并不是为了给这些电子元件供电，真正的目的在于实现有效控制。这样一来，我们才能真正优化拖拉机与拖车之间的牵引力控制。”

采埃孚拖拉机的全轮驱动AWD系统和拖车单轮驱动系统的电力推动功能可以协同工作，从而提供最佳的牵引力管理性能。Götz博士表示，在拖车电子辅助功能的帮助下，采埃孚的拖拉机可以爬上坡度高达30％的坡道，这是传统拖拉机做不到的。此外，这款拖拉机还可以应对空旷场地下的困难工况。

车辆的牵引力管理主要由两个因素决定：其中耦合力决定拖拉机是正在推还是拉，另一个决定因素是拖车的负载监测。

此外，对于一些只是偶尔进行满载行驶的用户，拖车提供的额外功率，可以让这部分用户有机会选择较小的拖拉机。

采埃孚承认，目前CVT无级变速器的效率与全电动驱动系统相似，但成本更低，这的确阻碍了电气化进程的发展。然而，从操控性及牵引力控制优化方面来看，电力驱动系统仍表现出一定优势。此外，Götz博士预测，在未来可能5到20年内，非公路车辆领域也需要面对相应的二氧化碳排放规定，而这当然也会推动电力驱动的发展。

作者：Ryan Gehm
来源：SAE《非公路车辆》杂志
翻译：SAE 中国办公室

Automation, electrification focus of ZF’s Innovation Tractor prototype

The passenger-car industry may be driving development of advanced driver-assistance systems (ADAS) and electrification, but the off-highway segment may be best-positioned to utilize them more widely—and sooner.

“The main movement for [driver-assistance systems] is in passenger cars, although it’s much more difficult to get this on cars because of all the regulations,” said Dr. Manuel Götz, responsible for Advanced Engineering, Industrial Technology at ZF. “So I believe in the future, we’ll be seeing autonomous vehicles in off-highway more regularly and even earlier than on the highway. Due to the fact that we’re in an enclosed environment and don’t have the regulations of on-highway, this could make things easier to implement.”

“A higher degree of automation also addresses the trend of operators being less trained in the future and not being able to find highly trained people to operate more and more complex machinery. So this [Innovation Tractor] is a step toward autonomous operation,” he added.

ZF is making a concerted effort to transfer the intelligent systems it’s developed initially for passenger cars into heavy trucks and buses, as well as off-highway equipment. To effectively illustrate this point, engineers in the company’s Advanced Engineering department have spent the past year designing the Innovation Tractor, an advanced-technology demonstrator loaded with cameras and electronics to allow automated maneuvering and hitching, not to mention pedestrian detection. Electric single-wheel drive for trailers and implements helps to dramatically improve traction management, as demonstrated in Aachen, Germany, on a 30%-grade paved road that was thoroughly watered down.

“We have full control not only of the driveline and the engine on this vehicle but also the steering and the brakes,” he said. “This is necessary to have full control over the vehicle and to do things like trajectory control and steering the vehicle.”

Agricultural was selected as the first application for these automation technologies, but they are viable for construction and other off-highway segments, said Götz.

“The Innovation Tractor brings together in a test prototype all the new functions we believe are practical for agricultural and construction applications,” said Dr. Harald Naunheimer, Head of R&D at ZF Friedrichshafen AG. “The focus was on demonstrating what is already possible and technically feasible today, but sets a benchmark on future innovation.”

Automated operation and hitch detection

The Innovation Tractor is equipped with 10 environmental cameras to monitor its surroundings; the data from these cameras enables the vehicle to maneuver semi-autonomously or via mobile devices operated outside the driver's cab, making it easier to hitch implements, for example.

Six cameras are mounted on the driver’s cab and the hood. A computer analyzes the images and generates a 360° surround-view image of the tractor's environment. The operator can view this image on a tablet from various perspectives, including a bird’s-eye view.

These cameras could be linked to provide warnings for obstacle detection and to brake, if necessary, as is becoming more common in passenger cars, Götz said.

Two cameras located at the rear of the tractor are used for the Hitch Detection function. Two additional rear cameras, monitoring a 180° swath, have pedestrian-detection capabilities. These four rear-mounted cameras have a separate data-processing unit.

In future iterations, the tractor ideally will utilize just four cameras, all mounted on the roof, to handle all of these functions, said Götz.

The Innovation Tractor's SafeRange function allows the driver to leave the vehicle and remotely control the tractor/trailer combination from a safe distance. The Innovation Tractor and trailer are outlined as a bird's-eye view on a tablet display from which all the relevant driving and steering commands are managed. Dragging the tractor or trailer image with a finger to the right or left on the screen causes the actual tractor/trailer combination to maneuver in the chosen direction. For reversing in complicated situations, the user can specify the desired direction for the trailer and the system calculates and executes all the necessary steering movements.

Speed is set by swiping the screen from the center to the edge, across the tractor model or the trailer. The maximum forward speed is 4 km/h (2.5 mph), with the top reversing speed limited to 2 km/h (1.2 mph). When contact with the screen is removed, or if radio contact is lost between the tablet and the tractor, the vehicle stops automatically. SafeRange also works when maneuvering the tractor without a trailer.

For the automatic hitching, currently there are three target shields mounted on the trailer to help guide the system. These shields will eventually go away, said Götz, but additional technology is required for that to happen.

“You have the opportunity to train your algorithm better on different implements, but this is a very lengthy [process]. I believe that in the future we might have a system that combines an optical camera and a laser system. With laser you have additional possibilities of detecting much more accurately, not only distances but also how the environment is changing. So I think we’ll see this sensor fusion for autonomous operation,” Götz explained.

The Hitch Detection system uses cameras to detect the exact position and angle of the trailer in relation to the tractor by using the targets. It works up to a distance of 7 m (23 ft). The position is continuously measured during the hitching process and the angle of the steered wheels corrected. The Innovation Tractor maneuvers automatically until it reaches the optimum position for hitching, which then is completed by hand. The system has a tolerance of 1.5 cm (0.6 in).

While using the tablet for maneuvering and hitching, cameras can detect pedestrians located between the vehicle and trailer up to 7 m away, with this information also displayed on the tablet. If the person controlling the tractor fails to respond, the system stops the vehicle. The interrupted hitching process can be restarted only once the pedestrian has moved out of the way.

“Many accidents happen on the farm with people getting run over, so this is a huge step,” said Götz. “Right now we don’t have the regulations demanding such a solution, but once the industry shows such technology I believe there will be regulations to have it implemented on the vehicles.”

Driveline electrification

Drivetrain electrification for the Innovation Tractor comes via ZF's TERRAMATIC transmission with the TERRA+ generator module, an electric single-wheel drive for trailers and implements, coupled with specially developed traction management. An electric steering system, required for automatic-driving functions, has been built into the control network.

This system generation can provide 50 kW of continuous electrical power and serves as the power source for the electrical consumers in the trailer. Two liquid-cooled, 3-phase asynchronous motors are integrated into the electrical wheel heads, saving space on the trailer axle; for the Innovation Tractor’s trailer, the system was installed on the middle axle. The nominal voltage is 400 V, and the system also can be fitted with a wheel brake.

The motors provide 6000 N·m (4425 lb·ft) maximum torque to each wheel.

“We have not yet implemented [the braking] but it is possible; it will be our next step,” said Götz. This function can help with deceleration when going downhill and making a turn, helping to prevent jackknifing and rollover. “We have to implement it in the control so we can use the electric axle to provide a braking torque. It is just a matter of applying the parameters.”

Torque vectoring—which is employed in automotive differentials and provides the ability to vary the power to each wheel—is another technology currently not available on the tractor but would be possible to implement, he said.

“From a space perspective we can go up to 70, even 100 kW continuous power,” said Götz. “In the vehicle at the moment we have installed a 50-kW generator system which is linked to our power electronics, from which we transfer the electric current to the wheels of the trailer. We’re not only powering them, we’re also controlling them; this way we are able to realize optimized traction control between the tractor and the trailer.”

The all-wheel-drive function of the ZF tractor and the electrical-boost function from the single-wheel drive on the trailer combine to deliver optimum traction management. With electrical assistance from the trailer, the tractor can climb uphill gradients of up to 30%, terrain normally off-limits for a conventional tractor/trailer setup, Götz noted. It also helps in difficult conditions in the open field.

A combination of two inputs determine traction management: the coupling force to determine if the trailer is pushing or pulling, and detection of load in the trailer.

The additional power from the trailer also allows a higher payload to be transported with a downsized tractor, ideal for users who only occasionally tow a fully-laden trailer.

ZF admits that its current CVTs are about as efficient as the full electric drive and less costly, so that hinders the move toward electrification. Other factors, however, such as improved controllability and the possibility for optimized traction control can help spur electric-drive adoption. As, of course, could CO2-emissions regulations, which “might not be that far off” for the off-highway sector, somewhere between five and 20 years down the road, Götz predicted.

Author: Ryan Rehm
Source: SAE Off-Highway Engineering Magazine