Patent GB-1208053-A (GB)
Title: Stationary test-bench for automobile vehicles
IPC: G01L5/28
Filed: 1968-01-23
Abstract: 1,208,053. Dynamometers. SOC. ANON. FRANCAISE DU FERODO. Jan. 23, 1968 [Jan. 24, 1967; Dec.27, 1967], No.3448/68. Heading G1W. A stationary vehicle test bench comprises four rollers 1, 2, 3, 4 arranged each to support one wheel of the vehicle and all to be driven at the same speed by the vehicles driving wheels, the total inertia of the rollers about their axes of rotation being equivalent to the mass of the vehicle, an adjustable system acting at the centre of gravity of the vehicle to fix its longitudinal position on the test bench without limiting the vehicles other degrees of freedom of movement and means for measuring the forces acting between the vehicle wheels and the rollers. A transverse frame 10, Fig. 1, is clamped to the vehicle and two parts 12a, 12b of the frame are slidably adjusted and clamped on vertical columns 13a, 13b so that support points A, B lie on a horizontal line through the centre of gravity G of the vehicle and are symmetrically placed relative thereto. The columns 13a, 13b are parts of rigid structures pivoted about vertical arms 16a, 16b of other rigid structures. The arms 16a, 16b are slidable on horizontal guides 20a, 22a, 20b, 22b, in the vertical plane containing G which is normally transverse to the vehicle. Hydraulic jacks 29a, 29b between the two structures in each pair, are controlled by a hydraulic circuit, Fig. 4, including a measuring device 38 sensing changes in the position, of the points A, B to ensure that the deviations #X A , #X B  are equal and opposite in sense thus fixing the longitudinal position of G. To keep the resistance to movement low the pistons are allowed play and errors due to leakage are corrected by an automatic slide valve 35 controlling input and output conduits 37, 36. Springs 32a, 32b apply arestoring couple to compensate for a couple introduced when the vehicle turns about a vertical axis and the wheel contact areas with the rollers are displaced from the upper generator lines of the rollers. An alternative system is described with reference to Figs. 5, 6, 7 (not shown). The four metal rollers 1, 2, 3, 4 are of the same diameter which is at least twice that of the vehicle wheels and the length of each corresponds at least to the width of the vehicle. They may be of steel and to simulate road surfaces with different coefficients of friction provision may be made to vary their surfaces by changing rollers or changing their surfaces. Each roller is mounted on a shaft 5, 6, 7, 8 mounted in bearings on front or rear trolleys 9a, 9b longitudinally adjustable to adapt the bench to vehicles of different wheel base. Reaction forces between the rollers are measured through couplings C 1  and C 2  which transmit only torque. The inertia of the rollers may be suited to a single type of vehicle or made adjustable to suit different types. The adjustment may be made by adding or subtracting weights to or from the rotating parts or by applying a couple to the rollers proportional to the product of their acceleration and the deviation of the equivalent mass of the rollers from the mass of the vehicle. An electrical driving system with speed regulation may be used. To carry out a braking test on a vehicle on the test bench in conditions simulating particular road conditions, the bench is adjusted to the wheel base and mass of the vehicle and the reaction forces of its wheels on the rollers are measured while various effects are simulated. Provision for measuring the reaction forces is made by mounting the roller shafts on the trolleys by means of two dynamometer bearings or tables. Strain gauges measuring the deformation in three thin strips disposed in three mutually perpendicular directions and connecting a bearing to a trolley may be used. A horizontal strip disposed longitudinally would serve to measure the reaction force on each roller due to application of the vehicle wheel brakes. Air resistance is simulated by superimposing a braking force proportional to speed; ground slope and head or tail wind by adding or subtracting energy; side wind and centrifugal forces by a hydraulic circuit controlling jacks 39a, 39b, Fig. 4, and lift by jacks at the front and rear supported on air cushions. The number of revolutions and speed of rotation of the rollers provide a measure equivalent to road distance and speed and angular and lateral displacements of the vehicle may be measured through the system fixing the longitudinal position of the centre of gravity. The strain gauge resistances can be measured using a potentiometer circuit if temperature variation is negligible or using a Wheatstone bridge if temperature compensation is required.