Chassis dynamometer

0001This invention relates to a chassis dynamometer of the kind adapted to test motor vehicles under simulated road conditions.

0002It is common practice to subject a motor vehicle to test procedures utilizing a chassis dynamometer which is capable of simulating, to some extent, actual road conditions to which a vehicle is subjected in operation. Chassis dynamometers currently in use have energy absorbing rollers capable of being driven by the driving wheels of a vehicle to simulate the driving of the vehicle over a road. Some dynamometers also are capable of driving both the driving and non-driving wheels of a vehicle, thereby simulating a coasting vehicle.

0003Among the currently available chassis dynamometers are direct current and alternating current regenerative drive/absorbers. These kinds of dynamometers permit the widest range of actual conditions to be simulated and, in addition, are capable of converting mechanical energy into electrical energy for dissipation through a utility's power lines.

0004Conventional chassis dynamometers include a rotary drum for each driving wheel of a vehicle. For example, a dynamometer for testing two-wheel drive vehicles has a pair of drums, a four-wheel drive vehicle has two pairs of drums, and a six-wheel drive vehicle has three pairs of drums. Conventionally, the drums of each pair are coupled to one another for conjoint rotation so as to avoid excessive differential rotation between the wheels of a vehicle under test, inasmuch as such differential rotation could cause damage to the vehicle's driving axles or transmission.

0005One of the major problems associated with a chassis dynamometer wherein the wheel engaging drums are coupled together is that the torque associated with coupled drums is the same regardless of which drum is driven, thereby making it impossible to measure differences between the propulsion forces and the braking forces generated by individual wheels. Thus, chassis dynamometers currently in use cannot reproduce actual field conditions.

0006A chassis dynamometer constructed in accordance with the invention is capable of high fidelity simulation of actual conditions encountered by a ve- hide as it is driven over a road surface and comprises a plurality of rotary drums some of which are adapted for drive transmitting engagement with the ground-engageable, driving wheels of a vehicle and the remainder of which are adapted for drive transmitting engagement with the other wheels of the same vehicle. In some cases the driving wheels also will constitute the steerable wheels, whereas in other cases the driving wheels and the steerable wheels will be different. In some cases all of a vehicle's wheels will be driving wheels. In any event, a chassis dynamometer constructed in accordance with the invention has sufficient rotary drums to accommodate all of the driving wheels of a vehicle to be tested.

0007Each rotary drum of a chassis dynamometer according to the invention is constructed as an integral part of a synchronous electric motor and thus may be referred to as a motor/roller load testing unit. The rotary drum of each testing unit is journaled on a shaft and supports an inductive stator that is concentric with the drum and lies between the latter and the shaft. The shaft is journaled at its opposite ends on a rigid base, but is restrained against rotation by means of a reaction torque arm secured to the shaft and anchored to a fixed structure via a strut incorporating a bi-directional load cell or transducer which is operable to generate an electrical pulse in response to a change in its loading. Each of the motor/roller load testing units is independent of the others in the sense that none of the motor shafts is coupled to any other shaft.

0008Each of the load testing units is coupled electrically to a single control unit which is operable to vary the frequency of the AC energy supplied to each of the motor armatures in a manner to effect conjoint rotation of all drums at the same speed and in the same direction. Each load cell is electrically coupled to the frequency control unit and is capable of transmitting to the latter a signal proportional to the average of the torque changes sensed by the load cells so as to vary the frequency of the energy supplied to the motor armatures and thereby maintain the speed of rotation of all rollers uniform, even though there may be differences in the torque associated with each motor shaft. Each load cell also is coupled to an indicator which indicates the torque associated with each motor shaft, thereby enabling an operator of the dynamometer to detect variations in energy levels among the several wheels of the vehicle.

0009The ability of all drums of the dynamometer to rotate at the identical speed, at all times, not only enables the load testing units faithfully to simulate the surface of a road over which the vehicle under test is driven, but also precludes the imposition of unequal forces on any part of the vehicle via its wheels, thereby avoiding the possibility of damaging the vehicle's drive train. The continuously uniform rate of speed of the drums also enables the effectiveness of the brakes associated with each wheel to be tested individually.

0010Apparatus constructed in accordance with a preferred embodiment of the invention is disclosed in the following description and in the accompanying drawings, wherein: <ul id="ul0001" list-style="none"><li>Figure 1 is a diagrammatic, side elevational view of a chassis dynamometer adapted to test a two-wheel or four-wheel drive vehicle;</li><li>Figure 2 is an end elevational view of the apparatus shown in Figure 1;</li><li>Figure 3 is an enlarged sectional view through one of the load testing units; and</li><li>Figure 4 is a simplified, schematic diagram of the circuitry associated with the dynamometer.</li></ul>

0011A chassis dynamometer constructed in accordance with the preferred embodiment of the invention comprises a number of motor/roller load testing units 1 all of which are alike and each of which is mounted in a pit or chamber lying below a load supporting surface 2 over which a vehicle 3 may be driven. The vehicle shown has four ground engageable wheels comprising two steerable front wheels 4 and two rear wheels 5. For purposes of illustration either the front wheels or the rear wheels way be the driving or propulsion wheels, or all four wheels could he the driving wheels. For a typical four-wheel vehicle, regardless of whether it is equipped with a two- or four-wheel drive transmission, there should be one motor/roller unit for each wheel. The motor/roller units are so arranged as to correspond to the front-to-rear and the side-to-side spacing of the wheels 4 and 5, thereby enabling all four wheels to be in drive transmitting engagement with the respective units 1 simultaneously.

0012Preferably, the surface 2 has openings therein through which the motor/roller units project, and suitable stabilizing rolls of the like (not shown) are provided to ensure stability of the vehicle on the motor/roller units, as is conventional.

0013As is best shown in Figure 3, each unit 1 comprises a hollow armature shaft 6 independent of all the other shafts and journaled at its opposite ends in stationary supports 7 by means of bearings 8. The supports 7 extend upwardly from a base 9 which is fixed to a suitable floor 10 below the surface 2. Encircling each shaft 6 is an annular drum 11 having end walls 12 provided with bearings 13 for journaling the drum on the shaft 6. A stationary armature 14 is fixed on the shaft 6 and has its winding connected to a suitable AC power source by electrically conductive lines 15 which extend through an opening 16 in the shaft 6. On the inner surface of each drum 11, and between the latter and the armature 14, is an inductive stator 17 which is fixed to the drum so as to be rotatable therewith. The armature 14 and the stator 17 form a synchronous motor.

0014Each shaft 6 is in communication at one end thereof with a blower 18 which delivers cooling air to the interior of the hollow shaft 6. A baffle 19 in the shaft diverts the cooling air via the opening 16 into a chamber 20 formed by the drum 11 and its end walls. A second opening 21 is provided in the shaft 6 on the downstream side of the baffle 19 and through which air from the chamber 20 may be discharged toward the opposite end of the shaft.

0015In the disclosed embodiment of the invention each shaft 6 is freely rotatable relatively to its supports 7 and each drum 11 is freely rotatable relatively to the associated shaft 6. To limit or restrict rotation of each shaft 6 there is fixed to the latter a torque arm 22 which projects radially and is pivoted to one end of a strut 23, the opposite end of which is pivoted to an anchor 24 fixed on the base 9. Each strut incorporates a pair of relatively movable links 25 and 26 having corresponding ends connected to a bi-directional torque sensing load cell 27 of known construction which is operable to generate an electrical signal in response to a change in torque associated with the shaft 6.

0016The circuitry of a dynamometer constructed in accordance with the invention is regenerative and is disclosed in Figure 4 as being adapted for use with a 3-phase, 230/460 volt, 60 Hz alternating current energy, source S. The armature 14 of each motor/roller unit 1 is connected to the source via a variable output frequency control unit 28 and a manually or computer controlled variable input frequency selector 29 of known construction. The variable output frequency control unit 28 may be any one of a number of thyristor drive control systems, one of which is manufactured by Westinghouse Electric Corporation under the trademark VARICHRON. The control unit 28 includes an AC to DC converter 30 coupled to the frequency selector 29. The converter 30 converts the alternating current to direct current. The converter 30 is connected to a DC to AC inverter 31 having a variable frequency output in circuit with the armatures of all of the motor/roller assemblies.

0017A microprocessor 32 forming part of the control unit 28 interconnects the latter with a conventional summing circuit regulating unit 33 which is connected to each of the load cells 27. The unit 33 thus is capable of receiving from each of the load cells 27 signals generated in response to changes in torque imposed on the shaft 6 of the associated motor/roller unit 1. The unit 33 averages such signals and transmits a signal proportional to the average to the microprocessor 32 which, in turn, acts on the converter 30 and the inverter 31 to vary the frequency output of the inverter so that all of the drums 11 of the motor/roller units 1 rotate at a uniform speed, regardless of the torque associated therewith. Each of the load cells 27 also is connected to an indicator 34 which is operable to indicate the torque applied on the respective torque arms 22.

0018Each indicator 34 may be a visually readable device, or it may be one that is coupled to a recorder or other mechanism that is operable to indicate the torque applied to the associated load cell.

0019Inasmuch as the drums of the several motor/roller units 1 always rotate at a uniform speed, the wheels of a vehicle under test will rotate at a uniform speed, thereby faithfully duplicating the effect of driving the vehicle along a road. However, should there be any differences between the torque associated with any shaft 6, such difference will be indicated by the associated indicator 34, thereby alerting the dynamometer operator to the existence of an actual or potential defect in the vehicle under test.

0020A chassis dynamometer constructed according to the invention not only can be used to absorb energy developed by driving of the vehicle's propulsion units, but it also can be used to drive the vehicle's wheels. The dynamometer therefore can be used to simulate coasting of a vehicle, and it also can be used to test simultaneously the brakes associated with all of the wheels that are in driving relationship with the load testing units.

0021When any drum of the units 1 is driven by the vehicle's propulsion system, the energy is dissipated to the non-driven drums and/or to the power supply system to ensure that all of the drums are driven at the same speed.