As is stated elsewhere in this volume, the engine and powertrain test cell structure has always been considered as, and designed to be, a hazard containment box. Any test cell built today may be considered as “machinery”
under the broad definition contained in the Machinery Directive 2006/42/EC.
In this sense the cell doors are essentially now the guard for the machine. Any internal guards, such as those for the drive shaft, are essentially supplementary, i.e. additional protection to personnel when controlled access to the test cell is required and the controller is in a “reduced speed mode”.
This role of the test cell as a complex programmable machine has to be kept in mind when considering all aspects of test cell design and its location within its immediate environment.
One of the early considerations in planning a new test facility will be the floor space required on one or more levels.
The interconnected areas to be considered are:
l The engine or powertrain test cell (the hazard containment space)
l The control room (whose role may differ widely between types of users and must be defined)
l The space required for cell services and support equipment
l The support workshop, UUT rig and de-rig areas
l The storage area required for rig items and consumables
l Office space for staff directly involved with the test cell(s).
Cell Sizing
A cramped cell in which there is no room to move around in safety and comfort is a permanent source of danger and inconvenience. The smaller the volume of the cell, the more difficult it is to control the ventilation system under conditions of varying load. However, unnecessarily large cells will lead to equipment, such as AC dynamometer drive cabinets, being installed in them that are not ideally suited to the highly variable conditions. Such cells also get used to house tool cabinets, leading to them being used as workshop spaces and to store occasionally used equipment, with the commensurate problems of housekeeping and the potential for damage.
As a rule of thumb, in automotive cells there should be an unobstructed walkway 1 m wide all round the rigged UUT and its connected dynamometer, but in most cases the exhaust tubes will form a barrier to a full 360of access.
This means that the access walkway is more often horseshoe shaped rather than an oval.
It is now often necessary, when testing automotive engines, to accommodate most of the exhaust system as used on the vehicle. The variation in engine and exhaust configurations to be used within a single cell may be the most signifi- cant factor in determining its size and internal configuration. Pre-planning activities need to include mock exhaust system layouts and should pay partic- ular attention to the possible need to run some exhausts under or very close to the dynamometer plinth.
It must be remembered that much of the plant in a test cell requires regular calibration so there must be adequate access for the calibration engineer, his instruments and, in some cases, such as a fuel-weigher, a ladder.
The calibration of the dynamometer requires accommodation of a torque arm and calibration weights, usually on both sides of the machine. A classic layout error is to install electrical boxes, trunking or service pipes that clash with the hanging position of the dynamometer calibration weights.
Cell height may be determined by the provision or not of a crane beam in the structure; in practice, most modern automotive cells are between 4 and 4.5 m internal height.
A Note Concerning Lifting Beams in Test Cells
While an in-cell crane is essential when working on large machines such as medium-speed diesels, and were often in automotive cells built before 1990, they come at a construction and insurance cost, particularly in containerized or panel-built cells (see below). This added cost comes about because the whole building frame has to be strengthened to allow it to support the crane built to the allowed bending limits required by the insurer’s overload capacity. Deep crane beams also lower effective cell height and can make airflow and lighting more difficult to optimize. Besides being one, albeit rather slow, method of engine mounting and de-mounting, a cell crane is certainly useful during initial installation of the cell. Subsequently crane beams can be used for, hopefully rare, major maintenance and tend to be used as a “sky-hook” for supporting various parts of the rigging looms and instrumentation. Where automotive engines are rigged on a removable pallet or trolley system, the cost/benefit calculation does not often justify a fixed crane installation.
Cells that are larger than the engine-transmission unit listed inTable 4.1 may be required for cells testing multiconfiguration transmission systems in which four-wheel dynamometers and one engine-simulating dynamometer have to be housed in various layouts. In the experience of many transmission test engineers their cells “are never big enough” and even the headroom can Chapter | 4 Powertrain Test Facility Design and Construction 53
become critical when a gear-change robot has to be rigged on a tall commercial vehicle gearbox.
Frequency of Change of Unit Under Test and Handling Systems
An important consideration in determining the size and layout of a test cell and its immediate environment is the frequency with which the UUT has to be changed.
At one extreme in the automotive sizes are “fuel and lube” cells, where the engine is virtually a permanent fixture, and at the other extreme are production hot test cells, where the engine’s test duration is a few minutes and the process of rig and de-rig is fully automated.
The system adopted for transporting, installing, and removing the UUT has to be considered together with the layout and content of the support workshop, the joining corridors, and the position of the control room. All operational specifications for new or modified test facilities should include the intended frequency of change of the UUT in their first draft.
Seeing and Hearing the Unit Under Test
Except in the case of large marine diesel engines, portable dynamometer stands, and some production test beds, it is almost universal practice to have a physical barrier to separate the control space from the UUT.
TABLE 4.1 Examples of Actual Test Cell Dimensions Found in UK Industry
Dimensions Cell Category
6.5 m long4 m wide4 m high QA test cell for small automotive diesels fitted with eddy-current dynamometer 7.8 m long6 m wide4.5 m high ECU development cell rated for 250 kW
engines, containing workbench and some emission equipment
6.7 m long6.4 m wide4.7 m high Gasoline engine development cell with AC dynamometer, special coolant, and inter-cooling conditioning
9.0 m long6 m wide4.2 m high (to suspended ceiling)
Engine and transmission development bed with two dynamometers in “tee”
configuration. Control room runs along 9 m wall
Thanks to modern instrumentation and closed circuit television, a window between control room and test cell is rarely absolutely necessary, although many users will continue to specify one. The cell window causes a number of design problems; it may compromise the fire rating and sound attenuation of the cell, and uses valuable wall space in the control room.
The choice to have a window or not is often made on quite subjective grounds. Cells in the motor-sport industry all tend to have large windows because they are visited by sponsors and press, whereas original equipment manufacturer (OEM) multi-cell research facilities increasingly rely on remote monitoring and CCTV. The use of multiscreen data displays means that many cell windows have become partially blanked out by these arrays.
The importance or otherwise of engine visibility from a window is linked to a fundamental question: Which way round are the key units in the cell to be arranged? A number of variants are covered later in this chapter.
The experienced operator will be concentrating attention on the indications of instruments and display screen, and will tend to use peripheral vision to watch events in the cell by whatever means provided. It is important to avoid unnecessary visual distractions, such as dangling labels or identity tags that can flutter in the ventilation wind.
Hearing has always been important to the experienced test engineer, who can often detect an incipient failure by ear before it manifests itself through an alarm.
Unfortunately modern test cells, with their generally excellent sound insulation, cut off this source of information and many cells need to have provision for in- cell microphones connected to external loudspeakers or earphones.
Containerized Test Cells
The nomenclature can be confusing since “containerized” cells have been built in several different forms, ranging from those using a modified ISO container, to a custom-designed suite of units constructed inside an existing building from prefabricated sections. Their advantage over conventional buildings is that of ease and speed of site construction rather than material cost. A further advantage, when the unit is constructed inside an already working factory, is that
“wet trades”1 are not required in their construction. The possibility of future relocation is often quoted as an advantage, but in reality it requires the unit to be specifically designed and expensively constructed for ease of later demounting.
The common feature of all true containerized cells is that they can be installed on a flat concrete base without any excavation for seismic blocks or service trenches. However, this flat-floor design feature requires a step or high sill between the floor of the cell and the concrete pad on which it sits, meaning
1. The wet trades referred to are those building tasks such as concrete pouring, block-laying, plastering, etc. None of this type of work is to be welcomed in a modern, working engineering production or test area.
Chapter | 4 Powertrain Test Facility Design and Construction 55
that loading the UUT, such as engines mounted on pallets, has to be carried out by a custom-built conveyor system, a fork-lift truck, or customized lift system.
Since internal space is often at a premium in these cells, service and subfloor areas tend to be very constricted, rather akin to marine engineering layouts, thus making any modification or even maintenance more difficult than in conven- tional buildings.
In most cases the weather-tight containerized test cells, installed outdoors, form a self-sufficient facility that requires only connections to cooling water (flow and return) and electrical power. Fuel supplies may be either part of the cell complex or plugged into an existing system. An advantage of this type of pre-packaged test cell is that the complete facility may be tested before delivery, thus giving the shortest possible installation and commissioning time at the customer’s site.
The common types of cell built under the heading of “containerized” are:
1. ISO shipping containerbased, using either the standard 20-foot or 40-foot unit. These base ISO units have an unlined internal height and width of only 2.352 m, and therefore are limited in the size of test bed that can be fitted. As they are externally durable and highly portable they have been used for military test facilities, typically made up of three containers: the test cell, the control module, and the services module. These are plugged together so as to be quickly taken apart, transported and reassembled.
However, this type of highly specialized and portable system has to be highly engine-range specific and is very expensive in terms of cost per volume of cell.
2. Standard “high” (4008080600) ISO Lloyd’s A1 specificationcold store containerthat has a stainless steel interior and is rated down to25C may be used, either as a cost-effective form of climatic cell or as a “cold soak”
facility in support of an exhaust emission test facility.
There is a range of non-ISO container-based cell types that differ from conventional concrete-built cells only by their construction materials but are still referred to as containerized cells, and they include the following variations:
3. All-weather, custom-built, panel-constructed cell and control room units are suitable for one-off or very occasional re-siting and are built for outside use.
Such a construction can offer the advantage of quickly extending an existing manufacture or test facility without disruption to the main building and the need for substantial excavations. In some locations the “temporary” nature of such a facility may offer advantages in fast-tracking planning and building permits. Experience has shown that the long-term external durability of such cells has been very variable and requires careful design and choice of enclo- sure materials when installed in corrosive environments (tropical, saline, etc.).
4. Custom-built, panel-constructed cell units (similar to type 3) that are constructed inside an existing shell building (Figure 4.1).
Both these “building within a building” type cells are made viable by the availability of industrial construction panels made of sound absorbent mate- rial sandwiched between metal sheets, of which the inner (cell) side is usually perforated. These 100-mm-thick panels are used with structural steel frames and, while not offering the same level of sound attenuation as dense block walls, give a quick and clean method of construction with a pleasing finished appearance.
It must be remembered that, when heavy equipment such as fuel condi- tioning units are to be fixed to the walls of such cells, precisely located
“hard-mounting” points must be built into the panel structure.
5. There have been successful variations of the “building within a building”
test cell construction where complete cell units have been built and pre- commissioned then craned and maneuvered into pre-prepared building compartments where pre-aligned service connections are made. However, such projects have to include multiples of identical units so that economies of scale can apply.
The Basic Minimum Engine Test Bed
There are some situations, such as in truck and bus fleet overhaul workshops, and occasionally in the specialist car after-market, in which there is a require- ment to run engines under load, but so infrequently that there is no economic justification for building a permanent test cell.
To provide controlled load in such cases, a “bolt-on” dynamometer can be used (see Chapter 10 for details). These require no independent foundation and
FIGURE 4.1 A “building within a building” test cell and control room, constructed on existing factory floor using acoustic panels within a steel frame. Note the raised door sill. All the services, including air blast cooler, are roof mounted.(Photo courtesy of Envirosound Ltd.)
Chapter | 4 Powertrain Test Facility Design and Construction 57
are bolted to the engine bell housing, using an adaptor plate, with a splined shaft connection engaging the clutch plate. Occasionally the dynamometer may be installed without removal of the engine from a truck chassis by dropping the propeller shaft and mounting the dynamometer on a hanger frame bolted to the chassis. This technique is useful for testing whole vehicle cooling systems without using a chassis dynamometer.
To support the needs of this sort of occasional test work all that is required is a suitable area provided with:
l Water supplies and drains with adequate flow capacity for the absorbed power (see Chapter 10)
l A portable fuel tank and supply pipe of the type sold for large marine outboard motor installations
l An adequately ventilated space, possibly out of doors
l Arrangements to take engine exhaust to exterior, if within a building
l Minimum necessary sound insulation or provision of personnel protection equipment (PPE)
l Adequate portable fire suppression and safety equipment.
Figure 4.2shows a typical installation, consisting of the following elements:
l Portable test stand for engine
l Dynamometer mounted directly to the engine flywheel housing using a multi-model fixing frame
l Control console
l Flexible water pipes and control cable.
For small installations and short-duration tests the dynamometer cooling water may be simply run from a mains supply, providing it has the capacity and
FIGURE 4.2 Portable dynamometer installed on a truck diesel mounted on a simple wheeled support frame fitted with a vehicle-type radiator.(Photo courtesy of Piper Test & Measurement Ltd.)
constancy of pressure, and the warm outflow run to waste. Much more suitable is a pumped system, including a cooling system, operating from a sump into which the dynamometer drains (see Figure 7.1).
The engine cooling water temperature and pressure can be maintained by a mobile cooling column of the type shown in Figure 7.2, or by a vehicle radiator and fan as shown inFigure 4.2.
The control console requires, as a minimum, indicators for dynamometer torque and speed. The adjustment of the dynamometer flow control valve and engine throttle may be by cable linkage or simple electrical actuators. The console should also house the engine stop control and an oil pressure gauge.
If required, a simple manually operated fuel consumption gauge of the
“burette” type is adequate for this type of installation.
Common Variations of Multi-Cell Layouts
Test cells are often built in side-by-side multiples, but it is the chosen method and route of loading engines into the cells that can most influence the detailed layout.
In the case of the layout shown in Figure 4.3, the cells have corridors running at both ends; the “front” of the cells is taken up by a common,
FIGURE 4.3 Cells arranged with a common control corridor at the front and with engine access at their rear.
Chapter | 4 Powertrain Test Facility Design and Construction 59
undivided, control room or corridor while the rear corridor is used for transport of rigged engines mounted on pallets or trolleys. This arrangement of building also determines that the position of the engine in the test cell will be at the opposite end from the control room and its window. It requires a larger footprint than that shown in Figure 4.4, but it keeps the control corridor clear of the disruption caused by periodic movement of engines through the space.
A third variant is shown inFigure 4.5, where the cells are positioned in a line with a common control room that is shared the by two cells on either side. In this arrangement engines enter the cell by way of a large door in the cell end wall while the operator may enter the cell by way of a door in the long wall to one side of the control desk. This arrangement finds some favor in facilities carrying out work for several different clients as it is easier to keep the work in each control room and pair of cells confidential. Avariation of this “back-to-back” arrangement uses the central room to house shared emission equipment and positions the control room in a corridor at the opposite end of the cell from the engine entry.
The cells shown in the layouts above are of similar size and general type; in large research facilities such clustering of cells having similar roles makes good operational sense. However, some types of work need to be kept physically remote from others to whom they may be poor neighbors.
FIGURE 4.4 Side-by-side cell arrangement where the engines are transported via trolleys through the control corridor, reducing space for the control desk over the arrangement shown in Figures 4.2and 4.4, but using a smaller footprint.