Control system for chassis dynamometer for simulating road test of automotive vehicle

Abstract: A control system for a chassis dynamometer for bench testing vehicular performance, comprises at least one roller rotatably coupled with a vehicular wheel to be driven driving torque transmitted therefrom, at least one dynamometer coupled with the roller to be driven by the driving torque transmitted through the roller, first monitoring means for monitoring preselected control parameters for providing first chassis dynamometer control data, second monitoring means for monitoring equivalent inertia of rotary components in a system associated with the dynamometer including the dynamometer per se, for providing second chassis dynamometer control data, and control signal generator means for receiving the first and second chassis dynamometer control parameters for deriving a dynamometer control signal for providing resistance simulating predetermined vehicular driving condition.

Description: Field of the Invention The present invention relates generally to a chassis dynamometer for performing bench test of performance of an automotive vehicle. More specifically, the invention relates to a control system for chassis dynamometer which is particularly applicable for road test simulating bench test for a four wheel drive type automotive vehicle. Description of the Background Art Dynamometers for testing vehicles are known from UK-A-2 065 887, BE-A-754 189, US-A-4 656 576, JP-A-62-25233 and JP-A-62-198728. These documents primarily or exclusively deal with dynamometers for testing two-wheel drive vehicles. Insofar as such dynamometers can be used for testing four-wheel drive vehicles, they suffer from no, or inadequate account being taken of different torques being applied to the dynamometers associated with the front and rear wheels respectively. Considerable speed differences between the front and rear dynamometer rollers can arise. This is especially problematic for four-wheel drive vehicles having a torque distribution between front and rear axles which departs significantly from 50:50. Japanese Patent First (Unexamined) Publication (Tokkai) Showa 63-55433 discloses a chassis dynamometer for a four wheel drive type automotive vehicle. The disclosed chassis dynamometer employs rollers for respective of four vehicular wheels and power absorber device and a mechanical inertia device. Clutches are provided for connecting left and right rollers for synchronizing two front rollers and two rear rollers respectively by engagement of clutches. Namely, the chassis dynamometer disclosed in the above-identified publication is operable in two distinct modes. When the clutches are disconnected, the left and right wheels operates independently to each other for independent operation of respective four rollers. When the clutches are engaged for synchronous operation between respective left and right rollers. In such case, front and rear pairs of rollers are operative independently of the other. In the disclosed system, distribution of the driving torque for respective rollers is controlled as a function of acceleration of the overall unit of the chassis dynamometer. In derivation of a torque difference between between front and rear rollers, specific inertia, i.e. mechanical inertia, of front and rear wheels is not taken into consideration. Similar type of chassis dynamometer has been proposed in Japanese Patent First (Unexamined) Publication (Tokkai) shows 61-734 and Japanese Patent First (Unexamined) Publication (Tokkai) Heisei 2-46891. Even in the latter two publications, it can be predicted that a component of mechanical inertia is not taken into account. Since the vehicle is always subject to mechanical inertia, negligence of the mechanical inertia make cause degradation of accuracy of the results in test. In order words, the systems set forth above cannot precisely simulate road test because distribution of driving torque for respective rollers may be differentiated from actual road test data due to lack of the mechanical inertia factor. On the other hand, in order to simulate behavior of the four wheel vehicle, it becomes necessary to simulate load distribution between front and rear axles. That is, during actual driving of the vehicle, the vehicular attitude can be changed by shifting of gravity center affected by inertia moment. Typical attitude change are known as winding up or squat and nose dive, which are caused by axial shifting of the gravity center. Conventionally, such vehicular attitude changes have not been possible to be simulated. Aforementioned Japanese Patent First Publication Showa 63-55433 provides certain gain in simulating vehicular pitching motion by providing capability of operating the front rollers and rear rollers independently of each other. However, even by such chassis dynamometer, it has not yet been possible to successfully simulate nose dive caused by vehicular body inertia moment. On the other hand, in the modern automotive technologies, it has been becoming important to simulate vehicular body attitude change for testing performance of attitude control to be installed in the vehicle. For instance, capability of simulating nose dive will permit testing and evaluation of performance of anti-skid brake control system. In the current technology, nose dive may be simulated by providing load distribution control system for the vehicle per se or otherwise by utilizing special arrangement of the chassis dynamometer which is specifically designed for simulating nose dive. In the modern automotive technologies, there is two types of four wheel drive power train arrangements to be employed in the vehicle. One of those is full-time four wheel drive power train layout, in which driving torque generated by an automotive engine is always distributed to four wheels. The other is a part-time four wheel drive power train lay out, in which the power train normally operates as two wheel drive power train, and switches into four wheel drive at a predetermined condition, such as excessive wheel slippage at primary drive wheels. In case of the part-time four wheel power train layout, since the vehicle is normally drive by two wheel drive power train layout, simulation is substantially the same as that of the two wheel drive vehicle. Also, even when the part-time four wheel power train is switched into four wheel mode due to excessive wheel slippage at the primary driving wheels, since the wheel slippage may easily caused even in the four wheel drive mode power train layout both on the primary and auxiliary driving wheels, the simulation will not have significant difference with the conventional two wheel drive vehicle. However, on the other hand, in the modern full-time four wheel power train layout, distribution of driving torque is variable depending upon vehicular driving condition. Typically, torque distribution is adjusted in proportion to acceleration and deceleration. When bench test is to be performed on the chassis dynamometer for such vehicle having variable torque split full-time four wheel drive power train layout for simulating straight acceleration and deceleration on the smooth road, wheel speed at front and rear wheels will become different. At the same time, the rotation speed of the roller as imaginary road surface is required to be equal to all rollers. Particularly for performing 10 mode test or LA-4 mode test for testing fuel consumption and exhaust gas composition test, equality of the rollers becomes essentially for providing satisfactory accuracy of the test. Namely, in case of the four wheel drive vehicle having passive differential mechanism, such as center differential gear unit, wheel speed at the front and rear wheels should be different because ground speed at all wheels are equal to each other. Naturally, increasing of the wheel speed difference between the front and rear wheels may increase the internal loss of the driving torque in the center differential gear unit and may influence for exhaust gas composition and fuel consumption. On the chassis dynamometer, there is also exist wheel slippage characteristics similar to that occurring on the actual road surface. Therefore, it is considered that, by adjusting the peripheral speed of the rollers consistent with each other, torque distribution similar to that on the actual road can be simulated. In the actual road test, overall driving torque at four wheels can be expressed by the following equation: F = A + Bv 2 + Mg x (dv/dt) + Mgsin  wherein F: vehicular driving force; in case of four wheel drive vehicle, total driving force of driving forces at respective of four wheels; A: rolling resistance of the wheel; B: coefficient of air resistance; v: vehicular speed (m/sec.) M: vehicular inertia weight (kg) g: gravitical acceleration; and : inclination angle of the road surface in longitudinal direction. In the normal test is performed simulating flat road, the element (mgsin ) can be neglected. The the element (A) and element (Bv²) are absorbed by dynamometer or by power absorbing device. On the other hand, the element (mg(dv/dt)) is absorbed by mechanical inertia control device, such as flywheel or electrical inertia control means as disclosed on the above-identified publications. Especially, as illustrated in the aforementioned publication, the electrical inertia control means is frequently employed. This is because the mechanical inertia of the roller and power absorbing device becomes approximately double of that in the two wheel drive vehicle. For instance, in case of the chassis dynamometer having rollers of 1591 mm in diameter, the mechanical inertia of the roller and the power absorbing device will become in a range of 400 kg to 500 kg in case of the two wheel drive vehicle and in a range of 800 kg to 1000 kg in cause of the four wheel drive vehicle. Since the overall weight of general small size vehicle is in a range of 800 kg to 1300 kg, it almost equal to the mechanical inertia of the mechanical inertia absorbing device. Since the mechanical inertia in the electrical inertia absorbing means has much smaller mechanical inertia, the electric inertia absorbing means are advantageously employed. On the other hand, concerning composite ratio of travailing resistance, the elements (A) and (Bv² which are called as constant speed traveling resistance will not exceed 500N at the vehicle speed lower than or equal to 80 km/h. On the other hand, the traveling resistance of the element (Mg(dv/dt) at accelerating state in a magnitude of 0.1g and at 1000 kg of the overall vehicular weight, becomes approximately 980N and therefore greater than that of the constant speed traveling resistance. Accordingly, in the test including test for acceleration and deceleration, the technologies disclosed in the aforementioned publication is applicable only for 50:50 torque split ratio. In this reason, the speed difference control disclosed in the aforementioned Japanese Patent First Publication Showa 63-55433, becomes substantially low in response for the vehicle having torque split ratio far different from even distribution (50:50). SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a chassis dynamometer control system for a vehicle with four wheel drive which can provide enhanced road test simulating performance with satisfactorily high response characteristics. This object is achieved by the combination of features of the control device as specified in independent claim 1. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for explanation and understanding only. In the drawings: Fig. 1 is a plan view of the preferred embodiment of a chassis dynamometer, in accordance with the present invention; Fig. 2 is a block diagram of the preferred embodiment of a control system for controlling operation of the chassis dynamometer of Fig. 1; Fig. 3 is a block diagram of a braking force distribution calculating circuit employed in the preferred embodiment of the chassis dynamometer control system of Fig. 2; Fig. 4 is a block diagram of a roller speed control circuit employed in the preferred embodiment of the chassis dynamometer control system of Fig. 2; and Fig. 5 is a block diagram of a dynamometer control circuit employed in the preferred embodiment of the chassis dynamometer control system of Fig. 2. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, particularly to Fig. 1, the preferred embodiment of a chassis dynamometer includes four rollers 10FL, 10FR, 10RL and 10RR for respectively receiving front-left, front-right, rear-left and rear-right wheels (not shown) of the vehicle. Respective rollers 10 FL, 10FR, 10RL and 10RR will be occasionally referred as "front-left roller", "front-right roller", "rear-left roller" and "rear-right roller" and will be generally referred to as "rollers 10". The front-left and front right rollers 10FL and 10FR are rotatably supported on a common rotary shaft 12F. Similarly, the rear-left and rear-right rollers 10RL and 10RR are rotatably supported on a common rotary shaft 12R. The front rotary shaft 12F is connected to a dynamometer 14F which is designed for absorbing driving torque transmitted from front wheels of vehicle to the rotary shaft 12F via the front-left and front-right rollers 10FL and 10FR. Similarly, the rear rotary shaft 12R is connected to a dynamometer 14R which also absorbs driving torque transmitted from rear wheels of the vehicle to the rotary shaft 12R via the rear-left and rear-right rollers 10RL and 10RR. In order to simulate mechanical inertia, flywheels 16F and 16R may be provided in cooperation with the dynamometers 14F and 14R. The arrangement of flywheels may not be specified to the shown arrangement and can be of any desired arrangements. For example, although the shown embodiment employs front and rear flywheels 16F and 16R respectively for front and rear rotary shafts 12F and 12R, either one of or both of flywheels can be neglected if desirable. On the other hand, if necessary, a plurality of flywheels can be provided for each of the front and rear wheels. In addition, although it is not shown in the drawings, the preferred embodiment of the chassis dynamometer according to the invention may further employ a speed equalizer for mechanically coupling the front and rear rotary wheels for synchronously drive thereof. A clutch may also be employed between the speed equalizer and the roller for coupling and decoupling the speed equalized with the rollers. Fig. 2 shows the preferred embodiment of the chassis dynamometer according to the present invention in discrete manner. As can be easily appreciated, whole or part of the shown system may be implemented by a digital computer system. As can be seen from Fig. 2, the shown embodiment of the chassis dynamometer control system employs the front and rear dynamometers (DyF, DyR) 14F and 14R. Each of the dynamometers 14F and 14R incorporates load cells (LCF, LCR) 20F and 20R for detecting torque and speed detectors (PGF, PGR) 22F and 22R for monitoring speed. Typically, the speed detectors 22F and 22R are mounted on the rollers 10 for directly monitoring the rotation speed thereof. The dynamometers 14F and 14R are designed to be controlled independently of each other. In the principle of the invention, it should be clearly noted that the shown embodiment of the chassis dynamometer control system does not control the braking force to be generated by the dynamometer per se as that performed in the prior art systems, but controls overall braking force including acceleration and deceleration acting on equivalent inertia weight of the mechanical rotary components. The speed detectors 22F and 22R typically comprise pulse generators, such as rotary encoders for generating pulse signal having frequency proportional to the rotation speed of the associated rollers. In case that the control system is frequency-to-volatge (F/V) converters (F/VF, F/VR) 24F and 24R are provided for performing F/V conversion to produce voltage signals having voltage level proportional to the frequency of the pulse signal output from the speed detectors 22F and 22R. As can be naturally appreciated, the F/V converters 24F and 24R are not necessary in case the control system is a digital system. Therefore, the F/V converters are not essential to be provided in the control system. In either case, front roller speed indicative signal VF and rear roller speed indicative signal VR are fed to an adder 26. The adder 26 sums the front roller speed indicative signal VF and the rear roller speed indicative signal VR and divides the sum value by 2 for obtaining an average speed data. This average speed data serves as an average vehicle speed indicative data Vm. The vehicle speed indicative data Vm are fed to a traveling resistance setting circuit (TRS) 28, a front mechanical power loss setting circuit (FMPLS) 30F and a rear mechanical power loss setting circuit (RMPLS) 30R. The traveling resistance setting circuit 28 derives a steady state traveling resistance RL. The front mechanical power loss setting circuit 30F derives a mechanical power loss on the front-left and front-right rollers 10FL and 10FR to provide a front mechanical power loss indicative data MLF. Similarly, the rear mechanical power loss setting circuit 30R derives a mechanical power loss at the rear-left and rear-right rollers 10RL and 10RR to provide a rear mechanical power loss indicative data MLR. Manner of deriving such steady state traveling resistance data RL and the front and rear mechanical power loss indicative data MLF and MLR have been known in the art, and there for not necessary to be discussed in further detail. The mechanical power loss represents power loss resistance on the roller, flywheel and other mechanical components and is preset as a function of speed forming a part of torque absorption in the dynamometers 14F and 14R. On the other hand, the traveling resistance indicative data RL serves as braking command. Therefore, in the practical control, the front and rear mechanical power loss indicative data MLF and MLR are added to the output of the load cells 20F and 20R to be used as feedback signal for the dynamometer control system. In the alternative, it is also possible to subtract the front and rear mechanical power loss indicative data MLF and MLR from the traveling resistance indicative data RL for forming braking command for the dynamometers 14F and 14R. The average vehicle speed indicative data Vm is also fed to an average acceleration calculation circuit (AAC)32. The average acceleration calculation circuit 32 differentiates the average vehicle speed indicative data Vm and thereby derives an average acceleration indicative data α. It should be noted that though the shown embodiment derives the average acceleration data based on the average vehicle speed indicative data Vm, it is also possible to initially derive the front wheel acceleration data by differentiating the front roller speed indicative data VF and the rear acceleration data by differentiating the rear roller speed indicative data VR. Both of the front and rear wheel acceleration data are added and divided by 2 in derive the average vehicle speed indicative data α. The average acceleration data α is then fed to an acceleration resistance deriving circuit (ARD) 34. The acceleration resistance deriving circuit 34 multiplied the average acceleration indicative data α with an equivalent inertia M as a vehicular testing condition indicative parameter, and which is set by an equivalent inertia setting circuit (EIS) 36 to derive an acceleration resistance indicative data Mα. The acceleration resistance indicative data Mα is fed to a braking force torque distribution deriving circuit (BFDD) 38. For the driving torque distribution deriving circuit 38 also receives the traveling resistance indicative data RL from the traveling resistance setting circuit 28. Therefore, the essentially the same parameters as that used in the foregoing equation (1) can be obtained at the driving torque distribution deriving means 38. Here, assuming that the mechanical inertia of the front wheel and rear wheels of the fourth wheel drive vehicle are respectively MMF and MMR, the electric inertia ME can be expressed by: ME = M - (MMF - MMR) can be set in the equivalent inertia setting circuit 36. In the alternative, the electric inertia resistance command value can be derived from the following equation: command value = {Me - (MMF + MFR)}α The braking force distribution deriving circuit 38 is also connected to a steady state braking force distribution setting switch 40 and a acceleration proportional braking force setting switch 42. The braking force distribution setting switch 40 provides a constant K1 according to set braking force distribution. Also, the acceleration proportional braking force setting switch 42 provides a constant K2 representative of the braking force distribution depending upon acceleration. The braking force distribution deriving circuit 38 may operates the following three ways: a) deriving a steady state distribution ratio; b) deriving the steady state distribution ratio and a variation of the distribution ratio proportional to acceleration; and c) deriving the steady state distribution ratio, a variation of the distribution ratio proportional to overall braking force, and the variation of the distribution ratio proportional to the acceleration. Among the aforementioned three ways, a) derives the braking force distribution with taking the load distribution between the front and rear wheels or a driving torque distribution during steady state. In this case, because the four wheel drive vehicle can take much different driving torque distribution from the load distribution between the front and rear wheels, response characteristics and precision level of control when speed difference control for differentiating and synchronizing the rotation speed of the front and rear rollers. b) concerns only acceleration resistance and ignores variation of braking force distribution during steady state. At low speed range, the traveling resistance is relatively small and variation of braking force distribution is not significant. Therefore, by introducing variation of the braking force distribution depending upon acceleration, response characteristics in speed difference control for the front and rear rollers can be improved. However, when vehicular driving torque distribution is to be simulated, the detected torque distribution can be differentiated from that on the actual road. Especially, at relatively high speed range, i.e. over 100 km/h, the steady state traveling resistance becomes substantial to cause unacceptably large difference between the simulated driving torque distribution and actual one. In case of c), most desirable and precise results can be obtained even in testing the driving torque distribution. On the other, however, this way c) may requires extra number of characteristic setting means to make the circuit of the control system more complicated. Fig. 3 shows the preferred construction of the braking force distribution deriving circuit 38 employed in the preferred embodiment of the chassis dynamometer control system of Fig. 2. As seen, the traveling resistance indicative data RL and the acceleration resistance indicative data Mα are supplied to an adder 381. The adder 381 thus derives a sum value (RL + Mα) of the traveling resistance indicative data RL and the acceleration resistance indicative data Mα and output the sum value to a multiplier 382 to which the set inertia representative constant K1 is supplied. The multiplier 382 is so designed to perform calculation to output -(x·y)/10 in response to inputs at x input terminal to which the sum value (RL + Mα) is supplied and y input terminal to which the set inertia representative constant K1 is supplied. The output (-K1(RL + Mα)) of the multiplier 382 is then supplied to an inverting amplifier 383. The inverting amplifier 383 inverts the input from the multiplier 282 and supplies the inverted value to an adder 384. On the other hand, the sum value (RL + Mα) of the adder 381 is also supplied to an adder 385, to which the output of the multiplier 382 is also supplied. The adder 385 sums these inputs to supply the sum value (1 - K1)(RL + Mα) is supplied to another adder 386. The acceleration resistance indicative data Mα is also input to another multiplier 387 which performs the identical function to that performed by the multiplier 382. The acceleration indicative data Mα is supplied to the x input terminal of the multiplier 387. To the y input terminal of the multiplier, the acceleration dependent constant value -K2α is supplied from the acceleration proportional braking force setting switch 42 via a gain amplifier 388. The gain amplifier 388 is set the amplifier gain at H/L (wherein H is road clearance of the vehicular body and L is wheel base of the vehicle). The output of the multiplier 387 is supplied to the adder 384 via an inverter 389. In turn, the output of the mutiplier 387 is directly supplied to the adder 386. Returning to Fig. 2, the front and rear roller speed representative data VF and VR are supplied to a speed difference control circuit (SDC) 44. The speed difference control circuit 44 also receives a speed difference setting command from a speed difference setting switch 46. The speed difference control circuit 44 is per se known in the prior art and utilized to selectively equalize the peripheral speed of the front and rear rollers or, in the alternative to, adjust the peripheral speed difference between the front and rear wheel (ΔV = VF - VR) to a predetermined value corresponding to a commanded value input from the speed difference setting switch 46. One embodiment of the speed difference control circuit 44 is illustrated in Fig. 4. In Fig. 4, the front roller speed indicative data VF representative of the peripheral speed of the front rollers 10FL and 10FR is supplied to an adder 441. On the other hand, the rear roller speed indicative data VR representative of the peripheral speed of the rear rollers 10RL and 10RR is supplied to the adder 441 via an inverter 442. Therefore, the adder 441 outputs a roller peripheral speed difference indicative data ΔV. The roller peripheral speed difference indicative data Δv is supplied to an adder 444 via an inverter 443. The adder 444 also receives the speed difference setting command ΔVc from the speed difference setting switch 46 via a equalization and differentiation switch 445. The adder 444 then derives an error signal Ev representative of a difference between the speed difference indicative data ΔV and the speed difference setting command ΔVc. The error signal Ev is fed to a servo amplifier 446. The servo amplifier 446 derives a braking force correction data ΔF for adjusting the difference of the peripheral speeds of the front and rear rollers toward the value of the speed difference setting command ΔVc. When equal peripheral speeds of the front and rear rollers are desired, the equliazation and differentiation switch 445 is switched from the shown position to the position connected to the other grounding terminal. Then the input to the adder 444 from the switch 445 becomes zero. Therefore, the error signal value Ev becomes equal to the peripheral speed difference indicative data ΔV. The braking force correction data ΔF thus generated serves for equalization of the peripheral speeds of the front and rear rollers. It should be appreciated that the speed difference control circuit 44 is often composed of a digital circuit to perform functions discussed in the words of the analog circuit hereabove, may be taken care of by software executed by the digital circuit system. Such control performed by the digital circuit is typically called as synchronization control. Also, is possible to additionally employ a roller phase detectors for respective of the front and rear rollers, and perform roller phase control for synchronizing the rotational phases of the front and rear rollers. The braking force correction data ΔF thus output from the speed difference control circuit 44 is fed to an adder 48 via an inverting amplifier 50 and a mode switch 52 which is designed to be turned ON when relative roller speed control, i.e. equalization or adjustment to the desired peripheral speed difference, is to be performed. On the other hand the braking force correction data ΔF is also fed to an adder 54 via the mode switch 52. To the adders 54 and 48, a front braking force control data FCF and a rear brake force control data FCR as output data of the braking force distribution deriving circuit 38 are respectively supplied. The adder 54 thus sums the braking force correction data ΔF to the front braking force control data FCF to derive a modified front braking force control data FCF'. Similarly, the adder 48 sums the inverted braking force correction data -ΔF as inverted by the inverting amplifier 50, and the rear braking force control data FCR for deriving a modified rear braking force control data FCR'. The modified front braking force control data FCF' is then fed from the adder 54 to a front chassis dynamometer control device (FCDC) 56. To the front chassis dynamometer control device 56, a front mechanical inertial dependent acceleration deriving circuit (FMIDAD) 58 is connected. The front mechanical inertia dependent acceleration deriving circuit 58 is connected to a front roller acceleration deriving circuit (FRAD) 60 which derives front roller acceleration data αF based on the front roller speed indicative data VF. In practice, the front roller acceleration deriving circuit 60 differentiates the front roller speed indicative data VF to derive the front roller acceleration data αF. Similarly, the modified rear braking force control data FCR' is then fed from the adder 48 to a rear chassis dynamometer control device (RCDC) 62. To the rear chassis dynamometer control device 62, a rear mechanical inertial dependent acceleration deriving circuit (RMIDAD) 64 is connected. The rear mechanical inertia dependent acceleration deriving circuit 64 is, in turn, connected to a rear roller acceleration deriving circuit (RRAD) 66 which derives rear roller acceleration data αR based on the rear roller speed indicative data VR. In practice, the rear roller acceleration deriving circuit 66 differentiates the rear roller speed indicative data VR to derive the rear roller acceleration data αR. Each of the front and rear mechanical inertia dependent acceleration deriving circuits 58 and 64 derives acceleration exerted on the mechanical equivalent inertia MMF or MMR of the rotary components, such as roller, dynamometer, flywheel and so forth. When the chassis dynamometers are full electric inertia control type, the mechanical equivalent inertia MMF and MMR will become a fixed value. However, in case that the chassis dynamometer is provided with a flywheel disconnectable with the chassis dynamometer by means of the clutch, the mechanical equivalent inertia may be differentiated by connecting and disconnecting the clutch. Therefore, in such case, the values of the mechanical equivalent inertia MMF and MMR may be switched between predetermined values by detecting operational state of the clutch. It should be noted that the signal representative of connecting and disconnecting state of the clutch is also utilized in the front and rear chassis dynamometer control devices 56 and 62. The front and rear chassis dynamometer control devices 56 and 62 have essentially the identical construction to each other and differentiated from that employed in the prior art. Because of the identical constructions between the front and rear chassis dynamometer control devices 56 and 62, only front chassis dynamometer control device 56 will be discussed herebelow with reference to Fig. 5. As shown in Fig. 5, the front chassis dynamometer control device 56 has an adder 561 to which the front mechanical power loss indicative data MLF is input from the front mechanical power loss setting circuit 30F. Also, the front mechanical inertia dependent acceleration indicative output (MMFα) of the front mechanical inertia dependent acceleration deriving circuit 58 is input to the adder 561. Furthermore, the output of the load cell 20F is input via a signal conditioning circuit 21. The adder 561 thus derives a sum value. The sum valve is then fed to an adder 562 via an inverting amplifier 563. The adder 562 also receives the modified front braking force control data FCF' from the adder 54. The adder 562 thus derives a sum value to be fed to a servo amplifier 564 via a switch 565. The sum value derived by the adder 562 represents a difference between the commanded braking force as represented by the modified braking force control data FCF' and the actual braking force represented by the output of the adder 561 as the sum value of the front mechanical power loss indicative data MLF, the front mechanical inertia dependent acceleration indicative value MMFα and the conditioned load cell output. Therefore, the output of the adder 562 serves as an error signal. The servo amplifier 564 performs PID calculation based on the error signal to derive a current control signal. The current control signal is fed to a current control device (CC) 566. The current control device 566 is associated with a thyrister unit (THY) 567 via a phase control device (PC) 568 for cooperating therewith to control the primary power supply for the dynamometer 14F. With the construction set forth above, since the present invention controls the chassis dynamometer with taking the mechanical inertia exerted on the overall rotary elements in the system, precisition level of control and response characteristics can be maintained at satisfactorily high level even when driving torque distribution between the front and rear wheels are far differentiated from even distribution. Furthermore, in the shown system, the accuracy of control and response characteristics will not be degraded even when the set inertia value is close to the mechanical inertia of the chassis dynamometer. Furthermore, with taking the mechanical inertia into consideration, error in measurement during acceleration or deceleration transition from the steady state can be minimized. In addition, for control constant in the speed difference control circuit may not be required to frequency adapted for the vehicle to be tested. Furthermore, the chassis dynamometer according to the present invention can perform equivalent speed equalization of front and rear rollers in a level equivalent to the chassis dynamometers which are mechanically and rigidly coupled to each other. Therefore, the present invention can fulfills all of the objects and advantages sought therefor. While the present invention has been discussed in detail in terms of the preferred embodiment of the invention, the present invention can be embodied in various fashion. Therefore, it should be appreciated that the invention includes all possible embodiments and modification thereof which can be embodied without depart from the principle of the invention, which is defined in the appended claims. For instance, though the foregoing embodiment employs the direct current type dynamometer, it can be easily replaced with alternating current type dynamometer. In such case, the current control device, the phase control device and the thyrister may be replaced with a a power regeneration type inverter and a current control device for the inverter. Also, the braking force may be electrically or arithmetically derived based on the voltage, current or velocity of the primary circuit, in place of the load cell. In such case, the load cell is replaced with an electric arithmetic circuit. Furthermore, if desired, the load cell can also be replaced with an axial torque meter. In addition, in the foregoing embodiment, the pair of front rollers and the pair of rear rollers are coupled rigidly by means of common rotary shaft. However, by providing four mutually independent chassis dynamometer, all for rollers can be made independent to each other.

Claims: A control device for a chassis dynamometer for in place testing of a four-wheel drive vehicle, said chassis dynamometer including a front axle roller (10FR, 10FL, 12F) operatively associated with a first dynamometer (14F) and a rear axle roller (10RR, 10RL, 12R) operatively connected with a second dynamometer (14R), said first and second dynamometers being mechanically unconnected, said control device comprising: means (22, 24) for detecting peripheral speeds of each of said front and rear axle rollers individually and converting them to respective signals (VF, VR); means (26) for computing the average value (Vm) of said front and rear roller peripheral speed signals; running resistance setting means (28) outputting a steady state running resistance speed (RL) of said vehicle based on said average speed signal (Vm); mechanical power loss setting means (30) outputting in response to said average value (Vm) respective front and rear mechanical power loss signals (MLF, MLR) indicative of mechanical power loss due to resistance on said front and rear rollers, any flywheel and any other mechanical components ; acceleration calculating means (32) determining an average acceleration speed (α) by differentiation of said average speed signal (Vm); acceleration resistance processing means (34) outputting an electrical inertial resistance command (M·α) controlled in dependence on said average acceleration speed (α) and on an inertia value (M) from an inertia setting device (36); first adding means (381) continuously adding said running resistance speed (RL) and said electrical inertial resistance command (Mα) ; braking force ratio calculating means (382-389) active to divide an output power represented by said signal output from said first adding means (381) according to a ratio obtained from multiplying a set stationary ratio (K1) and a value (K2·α) set as a factor of the average acceleration speed and outputting respective braking force control data (FCF, FCR) to each of said front and rear axle rollers, said braking force control data calculated in accordance with operation of proportional setting means (42); first comparing means (441, 442) calculating a difference in peripheral speeds (ΔV) of said front and rear axle rollers; second comparing means (443, 444) calculating and outputting a speed difference deviation (Ev), based on a speed difference command signal (ΔVc) generated by speed difference setting means (46) and said difference in peripheral speeds (ΔV) calculated by said first comparing means (441, 442); a servo amplifier (446) outputting braking force correction date (ΔF) for adjusting the speed difference between said front and rear axle rollers to a preset value in response to said speed difference deviation signal (Ev) input from said second comparing means (444); second adding means (54) outputting modified front axle roller braking control data (FCF') based on said front axle braking force control data (FCF), output from said braking force ratio calculating means (382-389), and said braking force correction data (ΔF); third adding means (48) outputting modified rear axle roller braking control data (FCR'), based on said rear axle braking force control data (FCR) output from said braking force ratio calculating means (382-389), and the inverted value of said braking force correction data (-ΔF); first dynamometer control means (56) for controlling said first dynamometer in response to the sum of said modified front axle braking force control data (FCF') and said front mechanical power loss signal (MLF); and second dynamometer control means (62) for controlling said second dynamometer in response to the sum of said modified rear axle braking force control data (FCR') and said rear mechanical power loss signal (MLR). A control device as set forth in claim 1, further including a synchronizing controller operable in place of said speed difference setting means in accordance with a synchronization command, said sychronizing controller operable according to a speed pulse having a fequency proportional to a speed detected by said speed detecting means of said front and rear axle rollers generated by said device, said speed pulses being input to an up-down counter which counts front speed pulses as. an up-count and rear speed pulses as a down count the obtained signal detected from roller speed differences being converted to an anaogue signal by a D/A converter and said analogue signal being input to said servo amplifier for effecting synchronization of front and rear roller speeds. A control device as set forth in claim 1, further including at least one clutchable flywheel engageable with one or both of said front and rear axle rollers when mechanical inertial of said front and rear axle rollers differs, said control device operable to obtain a front axle roller acceleration signal by differentiation of a front axle roller speed and to obtain a rear axle roller acceleration signal by differentiation of a rear axle roller speed, said control device thus operable to obtain an average acceleration speed according to a summation of said front and rear axle roller speeds according to a ratio of front and rear mechanical inertia inclusive of front and rear axle rollers, front and rear dynomometers and said flywheel. A control device as set forth in claim 2, further including at least one clutchable flywheel engageable with one or both of said front and rear axle rollers when mechanical inertial of said front and rear axle rollers differs, said control device operable to obtain a front axle roller acceleration signal by differentiation of a front axle roller speed and to obtain a rear axle roller acceleration signal by differentiation of a rear axle roller speed, said control device thus operable to obtain an average acceleration speed according to a summation of said front and rear axle roller speeds according to a ratio of front and rear mechanical inertia inclusive of front and rear axle rollers, front and rear dynomometers and said flywheel. A control system as set forth in claim 2, further including switch means operable in a first mode in which speeds of said first and second dynamometers are controlled independently, and a second mode in which said synchronization command is generated.

Inventors: SUZUKI YORIKATSU, SUZUKI, YORIKATSU
Applicants: MEIDENSHA ELECTRIC MFG CO LTD, KABUSHIKI KAISHA MEIDENSHA
Application year: 1991
Main classification: G01M17
IPC codes: G01M17