CVFA112HN-04 supervariator

Preliminary test result report, v.1.2.

Prepared by: Vitaly Davydov, Chief Engineer

Combarco engineering, Ltd.

Moscow

Jan, 31st, 2013

Supervariator

Supervariator is a multi-mode compound-split infinitely variable electromechanical transmission with deep power splitting. Supervariator consists of the differential unit, matching gearbox with range shifting mechanism, and two electric motor-generators with dual inverter. As a unit in a vehicle powertrain, supervariator performs multiple functions: - IVT mode (moving-off, crawling) - CVT driving modes - Fixed gears modes - Engine start function - Power supply function - EV traction mode

The supervariator may be applied in the following areas: - Land vehicles with conventional powertrain - Land vehicles with electric hybrid powertrain - Land vehicles with flywheel hybrid powertrain - Industrial variable transmissions

Supervariator kinematics example

CVFA112HN-04 supervariator prototype Prototype characteristics: The number of IVT/CVT modes: 4 “forward”, 1 “reverse” Rated input power: 90 kW Rated input torque: 270 Nm Rated input speed: 3200 rpm Peak output torque: 1100 Nm Torque spread: 8.6 Max kinematic gear ratio: infinite Min kinematic gear ratio: 0.58 Mean efficiency at rated power, for gear ratio 5..0.58: 95%

Supervariator prototype on the test bench

Hardware schematic at load tests

Prototype test plan

1. Supervariator running-in, control system adjustments. Input torque limitation: 135 Nm Input speed limitation: 800 rpm

Output torque limitation: 550 Nm Control system powering: self-powered

Testing duration: 30 hours Status: completed

2. Steady operation test, part 1 (with input speed limitation). Modes: R, I, I+II, II, II+III, III, III+IV, IV Input torque limitation: 270 Nm Input speed limitation: 1600 rpm

Output torque limitation: 1100 Nm Control system powering: self-powered

Test points number: 1000 Testing duration: 50 hours Status: completed

3. Engine start-up simulation

Input torque limitation: -300 Nm Input speed limitation: 800 rpm

Control system powering: from 12 V/75 Ah battery using 12/600 V 3 kW DC/DC converter. Test points number: 50 Testing duration: 3 hours Status: completed 4. Pure electric traction simulation

Mode: I Output torque limitation: 1100 Nm Output speed limitation: 1100 rpm

Control system powering: from 12 V/75 Ah battery using 12/600 V 3 kW DC/DC converter. Test points number: 100 Testing duration: 5 hours Status: processing 5. Simultaneous engine start-up and electric traction simulation

Mode: I Input torque limitation: -150 Nm Output torque limitation: 550 Nm Output speed limitation: 1100 rpm

Control system powering: from 12 V/75 Ah battery using 12/600 V 3 kW DC/DC converter. Test points number: 200 Testing duration: 10 hours

Prototype test plan

6. Steady operation test, part 12 (rated input speed). Modes: R, I, I+II, II, II+III, III, III+IV, IV Input torque limitation: 270 Nm Input speed limitation: 3200 rpm

Output torque limitation: 1100 Nm Control system powering: self-powered

Test points number: 700 Testing duration: 35 hours 7. Hybrid mode simulation (on mixed mechanical and electrical power). Tests with overload. Modes: R, I, I+II, II, II+III, III, III+IV, IV Input torque limitation: 540 Nm Input speed limitation: 3200 rpm

Output torque limitation: 1100 Nm Mechanical input limitation: 90 kW Electrical input limitation: 30 kW Control system powering: 600 V DC Test points number: 2000 Testing duration: 100 hours

Prototype test plan

Supervariator structure diagram

Mode I (IVT, i = ∞..2.93) Mode II (CVT, i = 2.93..1.71)

Mode III (CVT, i = 1.71..1) Mode IV (CVT, i = 1..0.4)

Legend: D1, D2, D3 – three-link differentials. 1 – sun gear, 2 – ring gear, 0 – carrier. RE2, R1, R2, R3, R4 – reducers. E1, E2 – electric motor-generators. Parameters: i12D1 = -1.92; i12D2 = -2.66; iR1 = 3.42; iR2 = 2.36; i12D3 = -2.14; iRE2 = 1.92; iR3 = 1.17; iR4 = 0.80.

Engineers can correlate experimental results with theoretical study. For this purpose, structure diagrams for all modes are shown.

Mode I+II (fixed gear, i = 2.93) Mode II+III (fixed gear, i = 1.71) Mode III+IV (fixed gear, i = 1)

Test results examples n1 = 800, 1600 rpm (25%, 50% of rated speed) T1max = 270 Nm (100% of rated torque) i = ∞...0.4

The experimentally gained efficiency charts show up the superiority of the power-split transmission over series electrical drivetrain. The efficiency of the small power series electric transmission, that forms electric path in the supervariator (red curves), doesn’t exceed 70%. At the same time, overall efficiency of Combarco power-split transmission (90..97% within whole ratio spread) is higher than that for most known continuously variable transmissions, despites this is a very first prototype. At fixed gears electrical drivetrain is deactivated. Electrical losses are eliminated, that’s why the efficiency raises by few percents. At straight fixed gear (III+IV) all the mechanical path is locked, and the efficiency of up to 99.5% was measured. A great potential for further efficiency improvement has been revealed during the research work. The final target efficiency is 94..98% within the main CVT ratio spread, what is typical for multispeed mechanical gearboxes.

Test results: high efficiency of the supervariator

Test results: high efficiency of the supervariator

Test results: high efficiency of the supervariator

The outstanding efficiency of the supervariator is caused by extra deep power splitting. The electric power flow doesn’t exceed 14% of the total transmitted power within the whole ratio spread. This is the best result among all known power-split transmissions. Due to low installed power of the electric torque converter, the supervariator combines high efficiency with small package and weight. In commercial vehicles applications a final target specific weight of the supervariator is 0.5..1 kg/kW. The electric power flow of the 90 kW supervariator doesn’t exceed 11 kW at highest load. Low installed power of electric torque converter gives high potential for cost and weight reduction. Two low-cost industrial AC induction motors are used in the supervariator prototype. Custom AC motors are going to be used in commercial products to reduce weight by 60% while their efficiency keeps at the same level. Taking overload capacity into consideration, two 15 kW inverters are enough for a 90 kW supervariator. Comparing to single-mode power-split transmission (for example, Toyota Prius eCVT), the installed power of the electric components can be reduced by 3..4 times.

Test results: low power flow via the electrical path

Test results: low power flow via the electrical path

Test results: low power flow via the electrical path

Phase voltage

Phase current

Test results: low power flow via the electrical path

In 4-mode design, torque spread of the supervariator is 7..9. These values are usually enough for passenger cars, LCVs and agricultural machinery. Higher number of modes (5..6) assures torque spread of 13..20 and even more, thus meeting the requirements for heavy duty vehicles.

Test results: large torque spread

Test results: large torque spread

Test results: large torque spread

All engaging parts are synchronized before shifting the modes (“soft shifting”). The shifting process is shock-free, that’s why compact and reliable dog-type clutches are used instead of multi-plate wet clutches. Unlike wet friction clutches, dog-type clutches do not reduce overall transmission efficiency.

Test results: synchronous shifting of the modes

a) at n1 = 800 rpm

Test results: efficiency maps

At low input rpm, the infinitely highest kinematic ratio can be reached for moving-off the vehicle. Comparing to mechanical gearboxes, energy losses during moving-off are reduced by 50%. The lowest ratio at n1=800 rpm may reach 0.4, thus making possible keeping low rpm of the engine at high vehicle speeds. At higher crankshaft speeds kinematic and torque spread are reduced within the range of 5.05..0.58.

b) at n1 = 1131 rpm

Test results: efficiency maps

At shifting points between the modes (i = 2.93, 1.71 and 1) fixed gears can be engaged. In these modes the electrical drivetrain may be deactivated, thus increasing the efficiency of the supervariator by 1..5%. At i = 1 straight connection is engaged between input and output shafts and all the gearings get locked. In this mode, the efficiency reaches 99.5%

The efficiency of the supervariator prototype exceeds the efficiency of most known CVTs. It remains high at wide spread of load and speed. Highest efficiency values (up to 96%) have been gained at CVT modes III and IV, the most demanded for automotive transport (about 80% of total operation time). The efficiency tends to grow at higher loads and speeds.

c) at n1 = 1600 rpm

Test results: efficiency maps

Test results: engine start-up and power supply emulation

Due to compound split structure, loads and speeds of the electric motors are equalized during engine start-up operation of the stopped vehicle. Thanks to that, the efficiency of the electric drive reaches 58..60% at crankshaft speeds of 100 rpm and crankshaft power of 3 kW. Electronic control eliminates inrush battery overload. At zero crankshaft speed the measured current was about 100 A. At speeds over 100 rpm the measured current was 480 A. If high-power high-voltage battery of a hybrid powertrain is used for start-up function, the efficiency of the system may be improved up to 80%. Peak shaft power at engine start-up mode may be raised up to 22 kW. During the tests, shaft power was limited by 14 kW. Power supply function was also tested. Electrical power of up to 12 kW was taken off at engine speed of 800 rpm. Measured electrical efficiency was up to 71%.

Test results: engine start-up emulation Electric drive efficiency map

Test results: engine start-up emulation 12 V/480 Amps start-up system steady-state operation charts

Conclusions

1. Supervariator prototype was operable in all modes. 2. Control system was stable in all tested modes (with input shaft speed of up to

1600 rpm) 3. Experimental results correlate theoretical study well. 4. Average CVT mode efficiency at high loads was 94%. At fixed gear modes the

efficiency reached 93..99.5%. 5. The area of highest efficiency was estimated at higher loads and speeds. These

modes should be probed during further tests. 6. Heat dissipation of the supervariator was moderate. Steady-state value of

temperature rise was 40..50 centigrade at input torque of 190..270 Nm and input speed of 1600 rpm.

7. Starter function works well. The parameters of starter modes were improved comparing to conventional starter system.

8. Alternator function also works well. Higher efficiency and capacity were also verified comparing to conventional belt-driven alternator.